WO2016103342A1 - Inertial sensor and method for manufacturing same - Google Patents

Inertial sensor and method for manufacturing same Download PDF

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Publication number
WO2016103342A1
WO2016103342A1 PCT/JP2014/084058 JP2014084058W WO2016103342A1 WO 2016103342 A1 WO2016103342 A1 WO 2016103342A1 JP 2014084058 W JP2014084058 W JP 2014084058W WO 2016103342 A1 WO2016103342 A1 WO 2016103342A1
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Prior art keywords
inertial sensor
electrode
layer
fixed electrode
mass body
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Application number
PCT/JP2014/084058
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French (fr)
Japanese (ja)
Inventor
貴支 塩田
佐久間　憲之
礒部　敦
千咲紀 田窪
雄大 鎌田
Original Assignee
株式会社日立製作所
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Priority to PCT/JP2014/084058 priority Critical patent/WO2016103342A1/en
Publication of WO2016103342A1 publication Critical patent/WO2016103342A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/13—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by measuring the force required to restore a proofmass subjected to inertial forces to a null position

Definitions

  • the present invention relates to an inertial sensor, for example, an acceleration sensor that detects minute acceleration smaller than gravity.
  • Patent Document 1 describes a technology relating to a MEMS (Micro Electrical Mechanical Systems) sensor in which both an upper electrode and a lower electrode are patterned and both the upper electrode and the lower electrode vibrate. Yes.
  • the convex portion of the upper electrode functions as a stopper that prevents adhesion with the lower electrode
  • the convex portion on the silicon substrate functions as a stopper that prevents adhesion with the lower electrode.
  • Reflection seismic exploration is a geophone that generates a shock wave or continuous wave on the ground surface, and reflects the reflected waves that return from the ground reflecting surface (boundary surface where the acoustic impedance changes) back to the ground.
  • This is a method for exploring the depth distribution and underground structure of the subsurface reflecting surface by measuring and analyzing the above.
  • this reflection seismic exploration is widely used as the main exploration method for oil and natural gas.
  • an acceleration sensor that detects vibration acceleration far smaller than gravitational acceleration has attracted attention. In order to put such an acceleration sensor into practical use, it is desired to develop an acceleration sensor with low noise and very high sensitivity.
  • the acceleration sensor connects the mass body to the fixed portion via a resiliently deformable beam in the cavity, and detects the change in physical quantity due to the displacement of the mass body when acceleration is applied. Is detected.
  • the mass body functions as a movable electrode
  • the fixed electrode is disposed at a position facing the mass body.
  • the objective of this invention is providing the technique which can suppress the etching damage in the sticking of an inertial sensor, or the manufacturing process of an inertial sensor.
  • An inertial sensor includes a first movable electrode that is displaceable in a first direction, a plurality of first openings that pass through the first movable electrode, and a first movable electrode that is spaced apart from the first movable electrode in the first direction.
  • a plurality of first protections formed on opposing surfaces of the first fixed electrode disposed opposite to the first fixed electrode facing the first movable electrode and provided corresponding to each of the plurality of first openings.
  • each of the plurality of first protection portions includes a first opening corresponding to each of the plurality of first protection portions.
  • the inertial sensor manufacturing method includes (a) a step of forming a fixed electrode inside the groove of the base layer having the groove, (b) a step of forming a plurality of protective portions on the fixed electrode, (C) After the step (b), a step of bonding the MEMS layer on the base layer is provided. Then, (d) by patterning the MEMS layer, a fixed portion fixed to the base layer, a beam connected to the fixed portion, a mass that is suspended by the beam and functions as a movable electrode that can be displaced in the first direction. And a step of forming a plurality of openings penetrating the mass portion.
  • a cap layer connected to the fixing portion formed on the MEMS layer is formed on the MEMS layer, so that the mass portion formed on the MEMS layer is changed between the base layer and the cap layer.
  • the plurality of openings are formed so that each of the plurality of protection portions includes an opening corresponding to each of the plurality of protection portions in a plan view as viewed from the first direction. To do.
  • the reliability of the inertial sensor can be improved. Specifically, according to the inertial sensor in one embodiment, sticking can be suppressed. Moreover, according to the manufacturing method of the inertial sensor in one embodiment, etching damage can be suppressed.
  • FIG. 3 is a cross-sectional view showing a cross section of the acceleration sensor in the first embodiment.
  • 3 is a plan view showing a planar layout configuration of a base layer in Embodiment 1.
  • FIG. 3 is a plan view showing a planar layout configuration of a MEMS layer in the first embodiment.
  • FIG. 10 is a plan view showing an example of a planar layout configuration of a base layer in a second embodiment. It is a top view which shows the plane layout structural example (modification) of a base layer.
  • FIG. 10 is a plan view showing a planar layout configuration of a MEMS layer in a second embodiment. It is a top view which shows the example of a plane layout structure (modification) of a MEMS layer. It is a graph which shows the relationship between sealing pressure and mechanical noise.
  • FIG. 9 is a diagram showing a cross-sectional configuration of an acceleration sensor in a third embodiment.
  • FIG. 10 is a cross-sectional view showing a cross section of an acceleration sensor in a fourth embodiment.
  • FIG. 10 is a plan view showing a planar layout configuration of a base layer that constitutes a part of an acceleration sensor according to a fourth embodiment.
  • FIG. 10 is a plan view showing a planar layout configuration of a MEMS layer that constitutes a part of the acceleration sensor in the fourth embodiment. It is sectional drawing which shows the manufacturing process of the acceleration sensor in Embodiment 4.
  • FIG. 18 is a cross-sectional view showing a manufacturing process of the acceleration sensor following FIG. 17. It is sectional drawing which shows the manufacturing process of the acceleration sensor following FIG.
  • FIG. 20 is a cross-sectional view showing a manufacturing step of the acceleration sensor following FIG. 19.
  • the constituent elements are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.
  • Acceleration sensors are used in a wide range of fields such as automobile attitude control, smartphones, and game machines.
  • the acceleration sensor used in these fields is small and can detect acceleration several times as large as gravity in a low frequency band of several hundred Hz or less.
  • the field of use of the acceleration sensor is not limited to the above-mentioned field, but has been expanded to a field for exploring underground resources.
  • reflection seismic wave exploration which is a kind of geophysical exploration, artificially generates a seismic wave and then receives a geophone (acceleration sensor) installed on the ground surface.
  • the reflected waves that bounce off the ground are captured and the results are analyzed to reveal the underground structure.
  • Fig. 1 is a schematic cross-sectional view of the earth's surface showing an outline of the reflection elastic wave exploration.
  • the excitation source VB installed on the ground surface GND to the ground
  • the elastic waves reflected by the boundary BUD1 and the boundary BUD2 of the plurality of formations are grounded.
  • Sensing is performed by an acceleration sensor (vibrator) AS installed in the vehicle. Since a general excitation source VB oscillates in a direction perpendicular to the ground surface, a P wave is efficiently excited in a direction close to the vertical direction. For this reason, the P wave is used in the reflection elastic wave exploration.
  • the acceleration sensor AS needs to detect the elastic vibration in the vertical direction.
  • the elastic wave excited in various directions propagates in the ground with large attenuation, reflects at the boundary BUD1 and boundary BUD2 of a plurality of formations, and propagates again in the ground with large attenuation. It spreads over a wide area and returns to the ground surface GND.
  • the acceleration sensor AS in order to detect weak elastic vibration, the acceleration sensor AS needs to be highly sensitive in the vertical direction. Specifically, since the acceleration of weak elastic vibration is smaller than the gravitational acceleration, the acceleration sensor used in the reflection elastic wave exploration is required to detect acceleration smaller than the gravitational acceleration with high sensitivity. .
  • the mass of the mass body that is a component of the acceleration sensor is increased, And the structure which makes a spring constant small and the structure which provides a some opening part in a mass body and reduces air resistance are employ
  • side effects occur as described in the section “Problems to be Solved by the Invention”. Therefore, in the first embodiment, a device that can suppress this side effect is taken. Below, the technical idea in this Embodiment 1 which gave this device is demonstrated.
  • FIG. 2 is a sectional view showing one section of the acceleration sensor AS1 in the first embodiment.
  • the acceleration sensor AS1 in the first embodiment has a base layer BL made of, for example, silicon (Si), and a fixed electrode FE made of, for example, a polysilicon film is formed on the base layer BL. ing.
  • a plurality of protection parts PU are formed on the surface of the fixed electrode FE so as to be separated from each other.
  • the plurality of protection units PU1 are formed of an insulating film typified by a silicon oxide film, for example.
  • a MEMS layer ML made of, for example, silicon is disposed above the base layer BL, and the MEMS layer ML is formed by processing the MEMS layer ML.
  • Part FU is formed.
  • the mass body MS is formed on the MEMS layer ML, and the mass body MS is disposed at a position facing the fixed electrode FE formed on the base layer BL.
  • the mass body MS is connected to the fixed portion FU via a beam (not shown). That is, the mass body MS is suspended by a beam and can be displaced in the z direction of FIG. For example, the mass body MS is displaced in the z direction when acceleration is applied in the z direction from the outside.
  • a plurality of openings OP penetrating the mass body MS are formed in the mass body MS.
  • the plurality of openings OP are provided so as to correspond to the plurality of protection units PU formed on the fixed electrode FE. That is, the protection part PU is provided so as to correspond to each of the plurality of openings OP.
  • the mass body MS is made of conductive silicon and can be displaced in the z direction, it also functions as the movable electrode VE. Therefore, in the acceleration sensor AS1 in the first embodiment, a capacitance is formed by the fixed electrode FE formed on the base layer BL and the mass body MS (movable electrode VE) formed on the MEMS layer ML. Will be.
  • a cap layer CL made of silicon is disposed on the MEMS layer ML.
  • the MEMS layer ML is sandwiched between the base layer BL and the cap layer CL in a cross-sectional view, and the mass body MS formed in the MEMS layer ML includes the base layer BL, the fixing unit FU, and the cap layer CL. It will be arrange
  • the acceleration sensor AS1 includes the movable electrode VE (mass body MS) that can be displaced in the z direction, the plurality of openings OP that penetrate the movable electrode VE, and the movable electrode in the z direction.
  • a plurality of protection portions formed on the opposing surfaces of the fixed electrode FE spaced apart from the VE and the fixed electrode FE facing the movable electrode VE, and provided corresponding to each of the plurality of openings OP.
  • Each of the PUs are the movable electrode VE (mass body MS) that can be displaced in the z direction, the plurality of openings OP that penetrate the movable electrode VE, and the movable electrode in the z direction.
  • the acceleration sensor AS1 includes a base layer BL, a cap layer CL disposed above the base layer BL, a cavity CAV sandwiched between the base layer BL and the cap layer CL, a cavity And a MEMS layer ML disposed in the part CAV.
  • the fixed electrode FE is formed on the base layer BL in the cavity CAV1.
  • the MEMS layer ML has a fixed portion FU fixed to the base layer BL and the cap layer CL, a beam connected to the fixed portion FU, and is suspended in the cavity CAV by the beam and functions as the movable electrode VE. Mass body MS to be formed.
  • FIG. 3 is a plan view showing a planar layout configuration of the base layer BL in the first embodiment.
  • a cross section taken along line AA in FIG. 3 corresponds to the base layer BL in FIG.
  • a cavity CAV is formed inside the base layer BL, and a fixed electrode FE is formed inside the cavity CAV.
  • a plurality of protection units PU are formed on the fixed electrode FE.
  • a plurality of protection parts PU spaced apart from each other are provided on the surface of the fixed electrode FE, and an uneven shape is formed on the surface of the fixed electrode FE.
  • FIG. 4 is a plan view showing a planar layout configuration of the MEMS layer ML in the first embodiment.
  • a cross section taken along line AA in FIG. 4 corresponds to the MEMS layer ML in FIG.
  • a cavity CAV is formed inside the MEMS layer ML.
  • a fixed part FU Inside the cavity CAV, a fixed part FU, a beam BM connected to the fixed part FU, and the beam BM
  • a mass body MS to be connected is formed. That is, in the MEMS layer ML, the mass body MS is connected to the fixed portion FU via the beam BM, and the mass portion MS is suspended by the beam BM.
  • a plurality of openings OP are formed in the mass body MS.
  • each planar size of the plurality of protection units PU corresponds to each of the plurality of protection units PU.
  • the opening size OP is larger than the planar size.
  • each of the plurality of protection units PU is formed so as to include the opening OP corresponding to each of the plurality of protection units PU.
  • the acceleration sensor AS1 is an acceleration sensor that captures acceleration applied in the z direction as a change in capacitance of a variable capacitor including the movable electrode VE and the fixed electrode FE.
  • the acceleration sensor AS1 is an acceleration sensor that captures acceleration applied in the z direction as a change in capacitance of a variable capacitor including the movable electrode VE and the fixed electrode FE.
  • it is possible to detect acceleration by detecting a change in capacitance due to acceleration due to acceleration without applying a modulation signal.
  • the detection signal based on the capacitance change in the variable capacitance corresponding to the acceleration is a low-frequency signal, it is easily affected by 1 / f noise.
  • a modulation signal is used.
  • the detection signal based on the capacitance change in the variable capacitor corresponding to the acceleration is modulated by the modulation signal to become a high frequency signal, it is difficult to receive 1 / f noise. That is, since the 1 / f noise is smaller in the high-frequency signal than in the low-frequency signal, the S / N ratio can be improved. As a result, the detection sensitivity of the acceleration sensor AS1 can be improved. For this reason, in the first embodiment, first, a modulation signal is applied to a variable capacitor composed of the movable electrode VE and the fixed electrode FE.
  • the mass body MS is displaced in the z direction.
  • a change in the capacitance of the variable capacitor including the movable electrode VE (mass body MS) and the fixed electrode FE occurs.
  • This capacitance change is added to the modulation signal and output to the signal processing circuit.
  • a modulation signal to which a capacitance change due to acceleration is added is input to the CV conversion unit, and the capacitance change is converted into an analog voltage signal.
  • the converted analog voltage signal is converted into a digital voltage signal by the AD converter.
  • the demodulated signal is extracted by the synchronous detector.
  • the demodulated signal demodulated by the synchronous detection section passes through an LPF (low frequency band pass filter), and finally an acceleration signal (detection signal) corresponding to the acceleration is output from the output terminal.
  • LPF low frequency band pass filter
  • FIG. 5 is an enlarged view of a part of FIG.
  • the feature point in the first embodiment is that each of the plurality of protection units PU corresponds to each of the plurality of protection units PU in a plan view viewed from the z direction.
  • the point is to include the opening OP (see FIGS. 3 and 4). Reflecting this feature point, in FIG.
  • the width L1 in the x direction of the protection part PU is larger than the opening dimension L3 in the x direction of the opening OP, and the protection part PU
  • the non-overlapping region NOR that does not overlap with the opening OP is formed.
  • the first advantage in the first embodiment is that the mass body MS can be prevented from sticking to the fixed electrode FE.
  • the acceleration sensor AS1 in the first embodiment has a configuration in which the mass of the mass body MS is increased and the spring constant of the beam is decreased in order to realize a highly sensitive acceleration sensor.
  • the mass body MS is greatly displaced and comes into contact with the fixed electrode FE, sticking is likely to occur.
  • the surface of the fixed electrode FE is flat, when the mass body MS comes into contact with the fixed electrode FE, the contact area increases, and thus sticking is likely to occur.
  • the mass body MS does not return to the original position, and the acceleration sensor AS1 does not operate normally. That is, since sticking causes a decrease in the reliability of the acceleration sensor AS1, it is necessary to suppress the sticking from the viewpoint of improving the reliability of the acceleration sensor AS1.
  • the surface of the fixed electrode FE has an uneven shape. It is formed. Therefore, even when the mass body MS is in contact with the fixed electrode FE due to excessive displacement of the mass body MS, since the uneven shape is formed on the surface of the fixed electrode FE, the protection unit PU and the mass body MS The contact area becomes smaller and sticking is less likely to occur. This means that a reduction in reliability of the acceleration sensor AS1 due to sticking can be suppressed.
  • the reliability of acceleration sensor AS1 can be improved.
  • each of the plurality of protection units PU is provided corresponding to the opening OP1. Therefore, even if the mass body MS is displaced in the z direction so as to contact the fixed electrode FE, the mass body MS does not contact the entire width L3 of the protection portion PU, but instead of the protection portion PU and the opening OP. The contact is made within the range of the width L2 of the non-overlapping region NOR. This means that the contact area between the mass body MS and the protection part PU can be reduced.
  • the plurality of protection portions PU are provided on the surface of the fixed electrode FE so as to be separated from each other, and as a result, an uneven shape is formed on the surface of the fixed electrode FE.
  • Each of the plurality of protection units PU is provided so as to include the corresponding opening OP. As a result, the contact area between the mass body MS and the protection part PU is reduced due to the formation of an uneven shape on the surface of the fixed electrode FE, and each of the protection parts PU has a corresponding opening.
  • the length L2 in the x direction of the non-overlapping region NOR between each of the plurality of protection units PU and the opening OP corresponding to each of the plurality of protection units PU is equal to the plurality of protection units PU.
  • the protection part PU and the opening OP provided corresponding to the protection part PU when attention is paid to the protection part PU and the opening OP provided corresponding to the protection part PU, one end of the protection part PU from one end of the opening OP in the x direction in a plan view seen from the z direction.
  • the distance (L2) to the portion can be made smaller than the opening dimension L3 of the opening OP in the x direction.
  • the second advantage of the feature point in the first embodiment is an advantage in the manufacturing process.
  • the mass body MS and the opening OP penetrating the mass body MS are formed by patterning the MEMS layer ML, and this patterning step includes a step of dry etching the MEMS layer ML.
  • the fixed portion FU, the beam, the mass body MS, and the plurality of openings OP are formed by etching the MEMS layer ML.
  • these components are included in the MEMS layer ML.
  • regions having different opening areas are etched at the same time.
  • the etching time is determined in accordance with the opening OP having the smallest opening area. Furthermore, even in the wafer plane, the etching rate is different between the central portion and the peripheral portion of the wafer, so the etching time is set to be longer than the etching time necessary for the penetration of the MEMS layer ML. Therefore, overetching is performed. However, if over-etching is performed, the fixed electrode FE disposed below the MEMS layer ML is etched, and the fixed electrode FE may be damaged.
  • each of the plurality of protection units PU includes an opening OP corresponding to each of the plurality of protection units PU.
  • the protection unit PU covers the region. Therefore, the fixed electrode FE can be protected from over-etching within a necessary and sufficient range. This is the second advantage brought about by the feature points in the first embodiment. As described above, according to the first embodiment, it is possible to protect the fixed electrode FE from etching damage, thereby improving the reliability of the acceleration sensor AS1.
  • the width L2 of the non-overlapping region NOR shown in FIG. 5 becomes larger, the fixed electrode FE can be protected from side etching. From the viewpoint of reducing etching damage to the fixed electrode FE, the non-overlapping region is as much as possible. It would be desirable to increase the NOR width L2. Therefore, the requirement for the width L2 of the non-overlapping region NOR is contradictory between the case where attention is paid to the viewpoint of suppressing sticking and the case where attention is paid to the viewpoint of suppressing etching damage. As a realistic response in this regard, it is within a well-balanced range so that it is within a reasonable range from the viewpoint of suppressing sticking and within a reasonable range from the viewpoint of suppressing etching damage. It is desirable to set the width L2 of the non-overlapping area NOR.
  • the mass of the mass body MS of the acceleration sensor AS1 is increased in order to detect an acceleration smaller than the gravitational acceleration with high sensitivity without considering side effects.
  • the mass body MS can be provided with a plurality of openings OP. That is, according to the feature point in the first embodiment, the detection sensitivity of the acceleration sensor AS1 can be improved while effectively suppressing the side effect of the mass body MS sticking and the etching damage to the fixed electrode FE. An excellent effect can be obtained.
  • FIG. 6 is a plan view showing a planar layout configuration example of the base layer BL in the second embodiment.
  • a fixed electrode FE, a servo electrode SE1, and a servo electrode SE2 are formed in the base layer BL.
  • the servo electrode SE1, the fixed electrode FE, and the servo electrode SE2 are arranged so as to be aligned in the y direction, and the fixed electrode is sandwiched between the servo electrode SE1 and the servo electrode SE2 in plan view.
  • FE is arranged.
  • a plurality of protection parts PU are formed on the fixed electrode FE, and a plurality of protection parts PU are also formed on the servo electrodes SE1 and SE2.
  • the feature point that the plurality of protection parts PU spaced apart from each other is provided on the surface of the fixed electrode FE and the uneven shape is provided on the surface of the fixed electrode FE is realized.
  • not only the fixed electrode FE but also the servo electrode SE1 and the servo electrode SE2 are provided with a plurality of protective portions PU spaced from each other on the surfaces of the servo electrode SE1 and the servo electrode SE2, and the servo electrode Concave and convex shapes are provided on the surfaces of SE1 and servo electrode SE2. For this reason, the above-described feature points are also realized in the servo electrode SE1 and the servo electrode SE2.
  • the servo electrode SE1 and the servo electrode SE2 are formed on the base layer BL shown in FIG.
  • the base layer BL shown in FIG. 6 is formed of the same layer as the fixed electrode FE, and is disposed above the base layer BL in the z direction (upward direction in FIG. 6) (illustrated).
  • the servo electrode SE1 and the servo electrode SE2 that are arranged opposite to each other and generate an electrostatic force that cancels the displacement of the mass body in the z direction are formed.
  • a servo voltage is applied to the servo electrode SE1 and the servo electrode SE2, and the acceleration is caused by the Coulomb force (electrostatic force) generated by applying the servo voltage to the servo electrode SE1 and the servo electrode SE2.
  • the displacement in the z direction of the mass body based thereon is cancelled.
  • the mass body is hardly displaced in the z direction, but the servo electrode SE1 and the servo electrode SE2 have a servo voltage proportional to the magnitude of the acceleration.
  • this servo voltage it is possible to detect the acceleration applied to the acceleration sensor according to the second embodiment.
  • the advantage of providing the servo electrode SE1 and the servo electrode SE2 is that acceleration can be detected without displacing the mass body in the z direction. That is, by providing a servo mechanism, when a large acceleration is applied to the acceleration sensor, it is possible to prevent the mass body from contacting the fixed electrode FE due to an unexpected displacement of the mass body.
  • the mass body and the fixed electrode FE can be prevented by the servo mechanism as well as the anti-sticking effect due to the feature point in the first embodiment described above.
  • an anti-sticking effect can be obtained.
  • the configuration in which the servo electrode SE1 and the servo electrode SE2 are provided in the acceleration sensor has an effect of enhancing the effect of preventing sticking, and is a useful configuration from the viewpoint of suppressing the sticking and improving the reliability of the acceleration sensor. Recognize.
  • the servo mechanism works in the operating state of the acceleration sensor, it is possible to obtain the anti-sticking effect caused by the feature points in the first embodiment and the anti-sticking effect caused by the servo mechanism.
  • the servo mechanism does not work, so that it is not possible to obtain an anti-sticking effect caused by the servo mechanism.
  • the mass body will be displaced.
  • the servo mechanism Since it does not work, sticking may occur.
  • the effect of preventing sticking caused by the feature point in the first embodiment described above can be obtained. That is, the configuration in which the concavo-convex shape is provided by the plurality of protection units PU exists regardless of the operation state or non-operation state of the acceleration sensor. Therefore, even in the acceleration sensor according to the second embodiment, an effect of preventing sticking can be obtained not only when the acceleration sensor is in the operating state but also when the acceleration sensor is in the non-operating state. That is, unlike the servo mechanism, the feature point in the first embodiment described above is excellent in that an effect of preventing sticking can be obtained regardless of whether the acceleration sensor is in an operating state or a non-operating state. It can be said that
  • the wiring WL is drawn from the fixed electrode FE.
  • the wiring WL1 is drawn from the servo electrode SE1
  • the wiring WL2 is drawn from the servo electrode SE2.
  • a wiring protection unit WPU that covers a part of the wiring WL and a part of the wiring WL1 is formed.
  • a wiring protection part WPU that covers a part of the wiring WL and a part of the wiring WL2 is formed.
  • the wiring protection unit WPU is formed in the same layer as the plurality of protection units PU, and has a function of protecting the wiring WL, the wiring WL1, and the wiring WL2 from etching damage when the MEMS layer is etched. .
  • a through-hole penetrating the MEMS layer ML is also formed. Therefore, a part of the wiring may be arranged on the base layer BL below the MEMS layer ML so as to overlap the through hole in a plan view. In this case, a portion of the wiring that overlaps with the through hole in a plane is damaged by etching when the through hole is formed.
  • the wiring protection portion WPU is formed across a part of the wiring WL and the part of the wiring WL1 that overlaps the through-hole in a plan view
  • a wiring protection part WPU is formed across a part of the wiring WL and a part of the wiring WL2 overlapping each other.
  • the wiring protection part WPU is formed so as to include the through hole in a plan view.
  • FIG. 7 is a plan view showing a planar layout configuration example of the base layer BL.
  • a rectangular fixed electrode FE is formed on the base layer BL, and this fixed electrode FE also functions as a servo electrode SE. That is, in the planar layout configuration example of the base layer BL shown in FIG. 7, a configuration in which the fixed electrode FE also serves as the servo electrode SE is shown. In this case, the detection operation by the fixed electrode FE and the servo operation by the servo electrode SE are performed in a time division manner.
  • the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIG. 6 but also the planar layout configuration shown in FIG.
  • FIG. 8 is a plan view showing a planar layout configuration example of the base layer BL.
  • the fixed electrode FE and the servo electrode SE1 are separately formed on the base layer BL.
  • the fixed electrode FE and the servo electrode SE1 are arranged so as to be aligned in the x direction.
  • the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIGS. 6 and 7, but also the planar layout configuration shown in FIG.
  • FIG. 9 is a plan view illustrating a planar layout configuration example of the base layer BL.
  • the fixed electrode FE and the servo electrode SE1 are separately formed on the base layer BL.
  • the fixed electrode FE and the servo electrode SE1 are arranged so as to be aligned in the y direction.
  • the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIGS. 6 to 8, but also the planar layout configuration shown in FIG.
  • FIG. 10 is a plan view showing a planar layout configuration of the MEMS layer ML in the second embodiment.
  • the MEMS layer ML has a rectangular shape.
  • a fixed portion FU Inside the MEMS layer ML, a fixed portion FU, a beam BM connected to the fixed portion FU, and a mass body MS connected to the beam BM. And are formed. That is, in the MEMS layer ML, the mass body MS is connected to the fixed portion FU via the beam BM, and the mass portion MS is suspended by the beam BM.
  • a plurality of openings OP are formed.
  • the planar shape of each of the plurality of openings OP is a slit shape SL.
  • each of the plurality of protection units PU is formed so as to include an opening OP corresponding to each of the plurality of protection units PU. It can be seen that the feature points in 1 are realized.
  • FIG. 11 is a plan view illustrating a planar layout configuration example of the MEMS layer ML.
  • the mass body MS connected to the fixed portion FU via the beam BM is formed in the MEMS layer ML, and a plurality of openings are formed in the mass body MS so as to penetrate the mass body MS.
  • OP is formed.
  • the planar shape of each of the plurality of openings OP is a hole shape HL.
  • the planar layout configuration of the MEMS layer ML can adopt not only the planar layout configuration shown in FIG. 10 but also the planar layout configuration shown in FIG.
  • the mass body MS is provided with a plurality of openings OP to reduce the air resistance, and the mass body MS is sufficiently more than the atmospheric pressure. Sealed with low pressure. Thereby, mechanical noise can also be reduced in the second embodiment.
  • FIG. 12 is a graph showing the relationship between sealing pressure and mechanical noise.
  • the horizontal axis represents the sealing pressure (Pa)
  • the vertical axis represents the mechanical noise (ng / ⁇ Hz).
  • FIG. 12 corresponds to a graph corresponding to a configuration in which no opening is provided in the mass body ((a) no hole) and a configuration in which a rough slit-like opening is provided in the mass ((b) rough slit).
  • the configuration corresponding to the configuration in which the mass body is provided with a dense slit-shaped opening ((c) slit dense), and the configuration in which the mass body is provided with a hole-shaped opening ((d) hole) The graph is shown. As shown in FIG.
  • the mechanical noise decreases as the sealing pressure decreases. It can also be seen that the mechanical noise varies depending on the shape of the opening provided in the mass body. For example, when there is no opening, the mechanical noise is about 200 (ng / ⁇ Hz) when the sealing pressure is 1 (Pa), while when the opening is present, the sealing pressure is 1 (Pa). It can be seen that the mechanical noise is about 20 (ng / ⁇ Hz). Therefore, not only in the first embodiment but also in the second embodiment, the mass body MS is provided with a plurality of openings OP, and the mass body MS is sealed at a pressure sufficiently lower than the atmospheric pressure.
  • the acceleration detection sensitivity can be improved not only in the first embodiment but also in the second embodiment. That is, also in the second embodiment, the acceleration detection sensitivity can be improved without incurring the side effect of sticking the mass body MS and etching damage to the fixed electrode FE.
  • FIG. 13 is a diagram illustrating a cross-sectional configuration of the acceleration sensor AS1 according to the third embodiment, and corresponds to FIG. 2 illustrating the first embodiment.
  • a fixed electrode FE1 is formed on the base layer BL, and a plurality of protective portions PU1 are formed on the fixed electrode FE1.
  • each of the plurality of protection parts PU1 is formed so as to include the opening OP corresponding to each of the plurality of protection parts PU1.
  • the fixed electrode FE3 is formed on the lower surface of the cap layer CL, and the fixed surface of the fixed electrode FE3 facing the mass body MS is formed on the opposite surface.
  • Each of the plurality of protection units PU3 corresponding to each of the plurality of openings OP is formed. And in the planar view seen from z direction, each of several protection part PU3 is formed so that the opening part OP corresponding to each of several protection part PU3 may be included.
  • the contact area between the mass body MS and the protection unit PU3 is reduced due to the formation of the uneven shape on the surface of the fixed electrode FE3, and a plurality of protections.
  • Each of the parts PU3 is provided so as to include the corresponding opening OP.
  • the fixed electrode FE1 provided in the base layer BL not only suppression of sticking but also etching damage in the step of dry etching the MEMS layer ML disposed above the base layer BL may be received. It is necessary to design a plurality of protection units PU1 in consideration.
  • the fixed electrode FE3 provided in the cap layer CL is joined to the MEMS layer ML together with the cap layer CL after forming the MEMS layer ML. Therefore, it is not necessary to consider etching damage in the fixed electrode FE3. That is, the plurality of protection portions PU3 formed on the fixed electrode FE3 provided in the cap layer CL can be designed from the viewpoint of suppressing sticking without considering etching damage.
  • each of the plurality of protection units PU3 is formed so as to include an opening OP corresponding to each of the plurality of protection units PU3 in a plan view viewed from the z direction. It is only necessary to reduce the planar size of the plurality of protection units PU3 as much as possible within the range of this condition. This is because, according to this configuration, even if an unexpected large displacement occurs in the mass body MS, the contact area between the fixed electrode FE3 (specifically, the protection unit PU3) provided in the cap layer CL and the mass body MS. This is because sticking can be effectively suppressed as a result.
  • the acceleration sensor AS1 according to the third embodiment includes a first variable capacitor including a fixed electrode FE1 and a mass body MS, and a second variable capacitor including a fixed electrode FE3 and the mass body MS. Yes.
  • the capacitance change of the first variable capacitor and the capacitance change of the second variable capacitor when the acceleration in the z direction is applied have opposite characteristics. That is, when the capacitance of the first variable capacitor increases, the capacitance of the second variable capacitor decreases, while when the capacitance of the first variable capacitor decreases, the capacitance of the second variable capacitor decreases. To increase.
  • the acceleration sensor AS1 in the third embodiment the following advantages can be obtained.
  • a first variable capacitor and a second variable capacitor are connected in series between a first input terminal and a second input terminal, and CV conversion is performed at a connection portion (connection node) between the first variable capacitor and the second variable capacitor.
  • connection portion connection node
  • opposite-phase modulation signals having a phase difference of 180 ° are applied to the first input terminal and the second input terminal, respectively.
  • the capacitance of the first variable capacitance when no acceleration is applied is “C”
  • the capacitance of the second variable capacitance when no acceleration is applied is “C”. C ".
  • the mass body MS is common to the first variable capacitor and the second variable capacitor, and the distance between the mass body MS and the fixed electrode FE1 and the mass body MS are fixed. This is because the distance from the electrode FE3 can be made equal, and the plane size of the fixed electrode FE1 and the plane size of the fixed electrode FE3 can be designed to be equal.
  • the capacitance of the first variable capacitance increases to “C + ⁇ C”, while the capacitance of the second variable capacitance decreases to “C ⁇ C”.
  • the capacitance “C” of the first variable capacitor and the capacitance of the second variable capacitor are set to “ “C” is canceled, and the charge transfer amount includes only the component of the capacitance change 2 ⁇ C caused by the acceleration.
  • the signal includes only the component of capacitance change (2 ⁇ C) caused by acceleration.
  • FIG. 14 is a cross-sectional view showing one cross section of the acceleration sensor AS2 in the fourth embodiment.
  • the fixed electrode FE1 and the fixed electrode FE2 are disposed on the base layer BL so as to be spaced apart from each other.
  • a plurality of protection portions PU1 are formed on the surface of the fixed electrode FE1 so as to be separated from each other, and a plurality of protection portions PU2 are also formed on the surface of the fixed electrode FE2 so as to be separated from each other.
  • the MEMS layer ML is disposed above the base layer BL.
  • the MEMS layer ML has a fixed portion FU formed by processing the MEMS layer ML, and the MEMS layer ML is located above the base layer BL by bonding the fixed portion FU and the base layer BL. Will be placed.
  • the mass body MS1 is formed in the MEMS layer ML, and the mass body MS1 is disposed at a position facing the fixed electrode FE1 formed in the base layer BL.
  • the mass body MS2 is formed in the MEMS layer ML, and the mass body MS2 is disposed at a position facing the fixed electrode FE2 formed in the base layer BL.
  • the mass body MS1 and the mass body MS2 are connected to the fixed portion FU via a beam (not shown). That is, each of mass body MS1 and mass body MS2 is suspended by the beam.
  • a plurality of openings OP1 penetrating the mass body MS1 are formed in the mass body MS1.
  • the plurality of openings OP1 are provided so as to correspond to the plurality of protection units PU1 formed on the fixed electrode FE1. That is, the protection part PU1 is provided so as to correspond to each of the plurality of openings OP1.
  • a plurality of openings OP2 penetrating the mass body MS2 are formed in the mass body MS2, as shown in FIG.
  • the plurality of openings OP2 are provided so as to correspond to the plurality of protection units PU2 formed on the fixed electrode FE2. That is, the protection part PU2 is provided so as to correspond to each of the plurality of openings OP2.
  • the mass body MS1 also functions as the movable electrode VE1. That is, in the acceleration sensor AS2 in the fourth embodiment, a capacitance is formed by the fixed electrode FE1 formed on the base layer BL and the mass body MS1 (movable electrode VE1) formed on the MEMS layer ML. Will be. Similarly, the mass body MS2 also functions as the movable electrode VE2. That is, in the acceleration sensor AS2 in the fourth embodiment, a capacitance is formed by the fixed electrode FE2 formed on the base layer BL and the mass body MS2 (movable electrode VE2) formed on the MEMS layer ML. Will be.
  • the cap layer CL is disposed on the MEMS layer ML.
  • the MEMS layer ML is sandwiched between the base layer BL and the cap layer CL in a cross-sectional view, and the mass body MS1 formed in the MEMS layer ML includes the base layer BL, the fixed portion FU, and the cap layer CL. It is arrange
  • the mass body MS2 formed in the MEMS layer ML is disposed inside the cavity CAV2 surrounded by the base layer BL, the fixing part FU, and the cap layer CL.
  • the inside of the cavity CAV1 and the cavity CAV2 is filled with gas, and the pressure inside the cavity CAV1 and the cavity CAV2 is, for example, a pressure sufficiently lower than the atmospheric pressure.
  • each plane size of the plurality of openings OP1 is smaller than each plane size of the plurality of openings OP2, and each plane size of the plurality of protection units PU1 is equal to the plurality of protection units PU2. It is smaller than each plane size.
  • a mass difference is generated between the mass body MS1 and the mass body MS2.
  • the acceleration sensor AS2 in the fourth embodiment performs a “seesaw operation”.
  • each of the plurality of protection units PU1 includes an opening OP corresponding to each of the plurality of protection units PU in a plan view viewed from the z direction
  • Each of the protection parts PU2 includes an opening OP2 corresponding to each of the plurality of protection parts PU2.
  • the mass of the mass body MS1 and the mass of the mass body MS2 of the acceleration sensor AS2 are detected with high sensitivity in order to detect an acceleration smaller than the gravitational acceleration without considering side effects. And the spring constant of the beam can be reduced. Furthermore, in order to reduce mechanical noise, the mass body MS1 can be provided with a plurality of openings OP1, and the mass body MS2 can be provided with a plurality of openings OP2. That is, also in the fourth embodiment, it is possible to obtain an excellent effect that the detection sensitivity of the acceleration sensor AS2 can be improved while effectively suppressing the side effects of sticking and etching damage.
  • the acceleration sensor AS2 in the fourth embodiment includes a first variable capacitor composed of a fixed electrode FE1 and a mass body MS1, and a second variable capacitor composed of a fixed electrode FE2 and a mass body MS2. Yes.
  • the acceleration sensor AS2 in the fourth embodiment has a “seesaw structure”, and the capacitance change of the first variable capacitor and the capacitance change of the second variable capacitor when the acceleration in the z direction is applied are reversed. It becomes a characteristic. That is, when the capacitance of the first variable capacitor increases, the capacitance of the second variable capacitor decreases, while when the capacitance of the first variable capacitor decreases, the capacitance of the second variable capacitor decreases. To increase. As a result, according to the acceleration sensor AS2 in the fourth embodiment, the following advantages can be obtained.
  • a first variable capacitor and a second variable capacitor are connected in series between a first input terminal and a second input terminal, and CV conversion is performed at a connection portion (connection node) between the first variable capacitor and the second variable capacitor.
  • connection portion connection node
  • opposite-phase modulation signals having a phase difference of 180 ° are applied to the first input terminal and the second input terminal, respectively.
  • the capacitance of the first variable capacitor when no acceleration is applied is “C1”
  • the capacitance of the second variable capacitor when no acceleration is applied is “C2”.
  • the capacitance of the first variable capacitor increases to “C1 + ⁇ C1,” while the capacitance of the second variable capacitor decreases to “C2 ⁇ C2.”
  • the capacitance “C1” of the first variable capacitor and the capacitance of the second variable capacitor are expressed as “
  • the ratio of the component of the capacitance change ( ⁇ C1 + ⁇ C2) caused by the acceleration is increased in the charge transfer amount.
  • the influence of the capacitance “C1” and the capacitance “C2” unrelated to the capacitance change ( ⁇ C1 + ⁇ C2) due to acceleration is reduced in the amount of charge transfer (becomes C1-C2).
  • the component of capacitance change ( ⁇ C1 + ⁇ C2) caused by the acceleration included in the signal can be increased.
  • FIG. 15 is a plan view showing a planar layout configuration of the base layer BL constituting a part of the acceleration sensor according to the fourth embodiment.
  • a section taken along line AA in FIG. 15 corresponds to the base layer BL in FIG.
  • the base layer BL has a rectangular shape, and a fixed portion FU is formed at the center of the base layer BL.
  • a fixed electrode FE1, a servo electrode SE1A, and a servo electrode SE2A are formed in the left region from the center of the base layer BL. Specifically, as shown in FIG.
  • the servo electrode SE1A, the fixed electrode FE1, and the servo electrode SE2A are arranged so as to be aligned in the y direction, and are arranged on the servo electrode SE1A and the servo electrode SE2A in a plan view.
  • the fixed electrode FE1 is disposed so as to be sandwiched.
  • a plurality of protection portions PU1 are formed on the fixed electrode FE1, and a plurality of protection portions PU1 are also formed on the servo electrode SE1A and the servo electrode SE2A.
  • a plurality of protection portions PU1 that are spaced apart from each other are provided on the surfaces of the servo electrode SE1A and the servo electrode SE2A.
  • Concave and convex shapes are provided on the surfaces of SE1A and servo electrode SE2A. For this reason, the above-described feature points are also realized in the servo electrode SE1A and the servo electrode SE2A.
  • a fixed electrode FE2, a servo electrode SE1B, and a servo electrode SE2B are formed in a region on the right side from the center of the base layer BL. Specifically, as shown in FIG. 15, the servo electrode SE1B, the fixed electrode FE2, and the servo electrode SE2B are arranged so as to be aligned in the y direction, and the servo electrode SE1B and the servo electrode SE2B are arranged in a plan view.
  • the fixed electrode FE2 is disposed so as to be sandwiched.
  • a plurality of protection portions PU2 are formed on the fixed electrode FE2, and a plurality of protection portions PU2 are also formed on the servo electrode SE1B and the servo electrode SE2B.
  • the feature point that the plurality of protection parts PU2 spaced apart from each other is provided on the surface of the fixed electrode FE2, and the uneven shape is provided on the surface of the fixed electrode FE2.
  • a plurality of protection portions PU2 that are spaced apart from each other are provided on the surfaces of the servo electrode SE1B and the servo electrode SE2B. Concave and convex shapes are provided on the surfaces of SE1B and servo electrode SE2B. For this reason, the above-described feature points are also realized in the servo electrode SE1B and the servo electrode SE2B.
  • the respective planar sizes of the plurality of protection units PU1 are smaller than the respective plane sizes of the plurality of protection units PU2.
  • the base layer BL in the fourth embodiment has a planar layout configuration.
  • FIG. 16 is a plan view showing a planar layout configuration of the MEMS layer ML that constitutes a part of the acceleration sensor according to the fourth embodiment.
  • a section taken along line AA in FIG. 16 corresponds to the MEMS layer ML in FIG.
  • the MEMS layer ML has a rectangular shape, and a fixed portion FU and a beam BM are formed at the center of the MEMS layer ML.
  • a mass body MS1 suspended from the beam BM is formed in the left area of the central portion, and a mass body MS2 suspended from the beam BM is formed in the right area of the central portion.
  • each planar size of the plurality of openings OP1 is smaller than each planar size of the plurality of openings OP2.
  • each of the plurality of protection units PU1 corresponds to each of the plurality of protection units PU1. It is larger than the planar size of the opening OP1.
  • each of the plurality of protection units PU1 is formed so as to include an opening OP1 corresponding to each of the plurality of protection units PU1.
  • each of the plurality of protection units PU2 is larger than the plane size of the opening OP2 corresponding to each of the plurality of protection units PU2.
  • each of the plurality of protection units PU2 is formed so as to include an opening OP2 corresponding to each of the plurality of protection units PU2.
  • the MEMS layer ML according to the fourth embodiment has a planar layout configuration.
  • the acceleration sensor according to the fourth embodiment is configured as described above, and the manufacturing method thereof will be described below with reference to the drawings.
  • a base layer BL made of a silicon wafer (semiconductor substrate) is prepared. Then, a pair of grooves DIT is formed on the surface of the base layer BL by using a photolithography technique and an etching technique. Subsequently, after a polysilicon film is formed on each bottom surface of the pair of grooves DIT, the fixed electrode FE1 is formed on the bottom surface of one groove DIT by using a photolithography technique and an etching technique, and the other groove A fixed electrode FE2 is formed on the bottom surface of the DIT.
  • an insulating film made of, for example, a silicon oxide film is formed on the surface of the fixed electrode FE1 and the surface of the fixed electrode FE2.
  • a plurality of island-shaped protective portions PU1 are formed on the surface of the fixed electrode FE1
  • a plurality of island-shaped protective portions PU2 are formed on the surface of the fixed electrode FE2 by using a photolithography technique and an etching technique.
  • a plurality of protection parts PU1 spaced apart from each other are formed on the surface of the fixed electrode FE1
  • a plurality of protection parts PU2 spaced apart from each other are formed on the surface of the fixed electrode FE2.
  • the protection unit PU1 and the protection unit PU2 are formed so that the respective planar sizes of the plurality of protection units PU1 are smaller than the respective plane sizes of the plurality of protection units PU2.
  • the MEMS layer (MEMS substrate) ML made of, for example, silicon is disposed on the surface of the base layer BL, and the base layer BL and the MEMS layer ML are formed by using a wafer bonding technique. And join. Thereafter, the surface of the MEMS layer ML is polished. Specifically, for example, polishing is performed so that the thickness of the MEMS layer ML is about 250 ⁇ m.
  • the MEMS layer ML is patterned by using a photolithography technique and a dry etching technique. Accordingly, a fixed portion FU fixed to the base layer BL, a beam (not shown) connected to the fixed portion FU, a mass portion MS1 that functions as a movable electrode that is suspended by the beam and is displaceable in the z-direction. A mass body MS2 is formed. In particular, the mass body MS1 is formed to face the fixed electrode FE1 formed on the base layer BL, and the mass body MS2 is formed to face the fixed electrode FE2 formed on the base layer BL. .
  • a plurality of openings OP1 penetrating the mass body MS1 and a plurality of openings OP2 penetrating the mass body MS2 are formed.
  • the planar size of the opening OP1 is smaller than the planar size of the opening OP2.
  • the mass of mass body MS1 can be made larger than the mass of mass body MS2.
  • the etching rate of the opening OP1 and the etching rate of the opening OP2 are different. Specifically, the etching rate of the opening OP1 having a small planar size is slower than the etching rate of the opening OP2 having a large planar size. Furthermore, since there is a distribution in the etching rate even within the wafer surface, over-etching is performed so as not to cause insufficient etching.
  • each of the plurality of protection units PU1 includes an opening OP1 corresponding to each of the plurality of protection units PU1, and each of the plurality of protection units PU2 includes a plurality of protection units PU2.
  • An opening OP2 corresponding to each of the protective parts PU2 is included.
  • the fixing unit FU formed on the MEMS layer ML and the cap layer CL are joined on the MEMS layer ML. Accordingly, the mass body MS1 formed in the MEMS layer ML is sealed in the cavity CAV1 sandwiched between the base layer BL and the cap layer CL, and the mass body MS2 formed in the MEMS layer ML is sealed with the base layer BL. It can be sealed in the cavity CAV2 sandwiched between the cap layers CL. At this time, the inside of the cavity part CAV1 and the inside of the cavity part CAV2 are sealed with a pressure sufficiently lower than the atmospheric pressure, for example. As described above, the acceleration sensor according to the fourth embodiment can be manufactured.
  • the method for manufacturing the acceleration sensor AS1 is not described.
  • the method for manufacturing the acceleration sensor AS2 is described.
  • the acceleration sensor AS1 in the first embodiment can be manufactured through substantially the same process as the manufacturing process described in the fourth embodiment.
  • an acceleration sensor has been described as an example of the inertial sensor.
  • the technical idea in the above-described embodiment is that the mass body is restrained from sticking between the fixed body and the mass body, and there are a plurality of mass sensors. This is made from the viewpoint of suppressing etching damage to the fixed electrode when the openings are provided. Therefore, any inertial sensor having a mass body and a fixed electrode and having a configuration in which a plurality of openings are formed in the mass body can be widely applied.
  • a configuration in which a mass body and a fixed electrode are provided and a plurality of openings are formed in the mass body may be employed. In addition, it can be widely applied to angular velocity sensors.

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Abstract

Provided is a technology whereby sticking of an inertial sensor and an etching damage of the inertial sensor in manufacturing steps can be suppressed. Specifically, in a plan view from the z direction, each of a plurality of protection units PU includes an opening OP corresponding to each of the protection units PU. Reflecting the configuration, for instance, the width L1 of the protection units PU, said width being in the x direction, is set larger than the opening dimension L3 of the opening OP, said opening dimension being in the x direction, and a non-overlapping region NOR not overlapping the opening OP is formed in each of the protection units PU.

Description

慣性センサおよびその製造方法Inertial sensor and manufacturing method thereof
　本発明は、慣性センサに関し、例えば、重力よりも小さい微小加速度を検出する加速度センサに関する。 The present invention relates to an inertial sensor, for example, an acceleration sensor that detects minute acceleration smaller than gravity.
　特開２００９－２８８０６号公報（特許文献１）には、上部電極と下部電極のいずれもがパターニングされ、上部電極と下部電極がともに振動するＭＥＭＳ（Micro Electrical Mechanical Systems）センサに関する技術が記載されている。この技術では、上部電極の凸部が、下部電極との密着を防止するストッパとして機能し、シリコン基板上の凸部が、下部電極との密着を防止するストッパとして機能するとしている。 Japanese Unexamined Patent Application Publication No. 2009-28806 (Patent Document 1) describes a technology relating to a MEMS (Micro Electrical Mechanical Systems) sensor in which both an upper electrode and a lower electrode are patterned and both the upper electrode and the lower electrode vibrate. Yes. In this technique, the convex portion of the upper electrode functions as a stopper that prevents adhesion with the lower electrode, and the convex portion on the silicon substrate functions as a stopper that prevents adhesion with the lower electrode.
特開２００９－２８８０６号公報JP 2009-28806 A
　反射法地震探査は、地表で衝撃波または連続波を発生させることにより、地下の反射面（音響インピーダンスの変化する境界面）から反射して地上に戻ってくる反射波を、地表に展開した受振器で測定し、解析して地下反射面の深度分布や地下構造を探査する方法である。例えば、この反射法地震探査は、石油や天然ガスの主な探査方法として広く利用されている。特に、次世代の反射法地震探査用センサとして、重力加速度よりも遥かに微小な振動加速度を検知する加速度センサが注目されている。このような加速度センサを実用化するために、低ノイズで非常に高感度な加速度センサの開発が望まれている。 Reflection seismic exploration is a geophone that generates a shock wave or continuous wave on the ground surface, and reflects the reflected waves that return from the ground reflecting surface (boundary surface where the acoustic impedance changes) back to the ground. This is a method for exploring the depth distribution and underground structure of the subsurface reflecting surface by measuring and analyzing the above. For example, this reflection seismic exploration is widely used as the main exploration method for oil and natural gas. In particular, as a next-generation reflection seismic exploration sensor, an acceleration sensor that detects vibration acceleration far smaller than gravitational acceleration has attracted attention. In order to put such an acceleration sensor into practical use, it is desired to develop an acceleration sensor with low noise and very high sensitivity.
　加速度センサは、例えば、空洞部内において、質量体を弾性変形可能な梁を介して固定部に接続し、加速度が印加されたときの質量体の変位に起因する物理量の変化を検出することにより加速度を検出する。具体的には、質量体を可動電極として機能させ、かつ、この質量体と対向する位置に固定電極を配置する。これにより、加速度が印加された際の質量体の変位によって、質量体と固定電極からなる静電容量の容量変化が生じ、この容量変化に基づいて、加速度を検出することができる。 The acceleration sensor, for example, connects the mass body to the fixed portion via a resiliently deformable beam in the cavity, and detects the change in physical quantity due to the displacement of the mass body when acceleration is applied. Is detected. Specifically, the mass body functions as a movable electrode, and the fixed electrode is disposed at a position facing the mass body. As a result, the displacement of the mass body when the acceleration is applied causes a capacitance change of the capacitance composed of the mass body and the fixed electrode, and the acceleration can be detected based on the capacitance change.
　このような加速度センサの高感度化（Ｓ／Ｎ比の向上）を実現する観点からは、質量体の質量体を大きくし、かつ、梁のバネ定数を小さくすることが望ましい。また、機械雑音を低減するために、質量体に複数の開口部を設けて、空気抵抗を低減することが望ましい。 From the viewpoint of realizing such high sensitivity (improvement of S / N ratio) of the acceleration sensor, it is desirable to increase the mass body of the mass body and reduce the spring constant of the beam. In order to reduce mechanical noise, it is desirable to reduce the air resistance by providing a plurality of openings in the mass body.
　ところが、質量体の質量を大きくし、かつ、梁のバネ定数を小さくすると、質量体の変位によって、質量体が固定電極に接触したまま張り付くステッキングが発生しやすくなる。また、固定電極を形成した後、例えば、ドライエッチングを使用することにより、質量体に複数の開口部を形成するが、開口部を形成した後のオーバエッチングにより、固定電極がダメージを受けるおそれがある。つまり、加速度センサの高感度化を実現する構成に伴って、ステッキングやエッチングダメージが問題点として顕在化する。このため、ステッキングやエッチングダメージを抑制する観点から改善の余地が存在する。 However, when the mass of the mass body is increased and the spring constant of the beam is decreased, sticking in which the mass body sticks to the fixed electrode easily occurs due to the displacement of the mass body. In addition, after forming the fixed electrode, a plurality of openings are formed in the mass body by using, for example, dry etching, but the fixed electrode may be damaged by over-etching after the opening is formed. is there. In other words, sticking or etching damage becomes a problem as the acceleration sensor is configured to achieve high sensitivity. For this reason, there is room for improvement from the viewpoint of suppressing sticking and etching damage.
　本発明の目的は、慣性センサのステッキングや慣性センサの製造工程におけるエッチングダメージを抑制することができる技術を提供することにある。
　その他の課題と新規な特徴は、本明細書の記述および添付図面から明らかになるであろう。 The objective of this invention is providing the technique which can suppress the etching damage in the sticking of an inertial sensor, or the manufacturing process of an inertial sensor.
Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.
　一実施の形態における慣性センサは、第１方向に変位可能な第１可動電極と、第１可動電極を貫通する複数の第１開口部と、第１方向において、第１可動電極と離間して対向配置された第１固定電極と、第１可動電極と対向する第１固定電極の対向面に形成され、かつ、複数の第１開口部のそれぞれに対応して設けられた複数の第１保護部のそれぞれと、を備える。ここで、第１方向から見た平面視において、複数の第１保護部のそれぞれは、複数の第１保護部のそれぞれに対応した第１開口部を内包する。 An inertial sensor according to an embodiment includes a first movable electrode that is displaceable in a first direction, a plurality of first openings that pass through the first movable electrode, and a first movable electrode that is spaced apart from the first movable electrode in the first direction. A plurality of first protections formed on opposing surfaces of the first fixed electrode disposed opposite to the first fixed electrode facing the first movable electrode and provided corresponding to each of the plurality of first openings. Each of the sections. Here, in a plan view as viewed from the first direction, each of the plurality of first protection portions includes a first opening corresponding to each of the plurality of first protection portions.
　また、一実施の形態における慣性センサの製造方法は、（ａ）溝を有するベース層の溝の内部に固定電極を形成する工程、（ｂ）固定電極上に複数の保護部を形成する工程、（ｃ）（ｂ）工程後、ベース層上にＭＥＭＳ層を接合する工程を備える。そして、（ｄ）ＭＥＭＳ層をパターニングすることにより、ベース層に固定された固定部と、固定部と接続される梁と、梁で懸架され、第１方向に変位可能な可動電極として機能する質量部と、質量部を貫通する複数の開口部とを形成する工程を備える。さらに、（ｅ）（ｄ）工程後、ＭＥＭＳ層上に、ＭＥＭＳ層に形成された固定部と接続するキャップ層を形成することにより、ＭＥＭＳ層に形成された質量部をベース層とキャップ層で挟まれる空洞部内に封止する工程を備える。ここで、（ｄ）工程は、第１方向から見た平面視において、複数の保護部のそれぞれが、複数の保護部のそれぞれに対応した開口部を内包するように、複数の開口部を形成する。 The inertial sensor manufacturing method according to the embodiment includes (a) a step of forming a fixed electrode inside the groove of the base layer having the groove, (b) a step of forming a plurality of protective portions on the fixed electrode, (C) After the step (b), a step of bonding the MEMS layer on the base layer is provided. Then, (d) by patterning the MEMS layer, a fixed portion fixed to the base layer, a beam connected to the fixed portion, a mass that is suspended by the beam and functions as a movable electrode that can be displaced in the first direction. And a step of forming a plurality of openings penetrating the mass portion. Further, after the steps (e) and (d), a cap layer connected to the fixing portion formed on the MEMS layer is formed on the MEMS layer, so that the mass portion formed on the MEMS layer is changed between the base layer and the cap layer. A step of sealing in the hollow portion to be sandwiched. Here, in the step (d), the plurality of openings are formed so that each of the plurality of protection portions includes an opening corresponding to each of the plurality of protection portions in a plan view as viewed from the first direction. To do.
　一実施の形態によれば、慣性センサの信頼性を向上することができる。具体的に、一実施の形態における慣性センサによれば、ステッキングを抑制することができる。また、一実施の形態における慣性センサの製造方法によれば、エッチングダメージを抑制することができる。 According to one embodiment, the reliability of the inertial sensor can be improved. Specifically, according to the inertial sensor in one embodiment, sticking can be suppressed. Moreover, according to the manufacturing method of the inertial sensor in one embodiment, etching damage can be suppressed.
反射法弾性波探査の概要を示した地表の断面模式図である。It is the cross-sectional schematic diagram of the ground surface which showed the outline | summary of the reflection method elastic wave exploration. 実施の形態１における加速度センサの一断面を示す断面図である。FIG. 3 is a cross-sectional view showing a cross section of the acceleration sensor in the first embodiment. 実施の形態１におけるベース層の平面レイアウト構成を示す平面図である。3 is a plan view showing a planar layout configuration of a base layer in Embodiment 1. FIG. 実施の形態１におけるＭＥＭＳ層の平面レイアウト構成を示す平面図である。3 is a plan view showing a planar layout configuration of a MEMS layer in the first embodiment. FIG. 図２の一部を拡大して示す図である。It is a figure which expands and shows a part of FIG. 実施の形態２におけるベース層の平面レイアウト構成例を示す平面図である。FIG. 10 is a plan view showing an example of a planar layout configuration of a base layer in a second embodiment. ベース層の平面レイアウト構成例（変形例）を示す平面図である。It is a top view which shows the plane layout structural example (modification) of a base layer. ベース層の平面レイアウト構成例（変形例）を示す平面図である。It is a top view which shows the plane layout structural example (modification) of a base layer. ベース層の平面レイアウト構成例（変形例）を示す平面図である。It is a top view which shows the plane layout structural example (modification) of a base layer. 実施の形態２におけるＭＥＭＳ層の平面レイアウト構成を示す平面図である。FIG. 10 is a plan view showing a planar layout configuration of a MEMS layer in a second embodiment. ＭＥＭＳ層の平面レイアウト構成例（変形例）を示す平面図である。It is a top view which shows the example of a plane layout structure (modification) of a MEMS layer. 封止圧力と機械雑音との関係を示すグラフである。It is a graph which shows the relationship between sealing pressure and mechanical noise. 実施の形態３における加速度センサの断面構成を示す図である。FIG. 9 is a diagram showing a cross-sectional configuration of an acceleration sensor in a third embodiment. 実施の形態４における加速度センサの一断面を示す断面図である。FIG. 10 is a cross-sectional view showing a cross section of an acceleration sensor in a fourth embodiment. 実施の形態４における加速度センサの一部を構成するベース層の平面レイアウト構成を示す平面図である。FIG. 10 is a plan view showing a planar layout configuration of a base layer that constitutes a part of an acceleration sensor according to a fourth embodiment. 実施の形態４における加速度センサの一部を構成するＭＥＭＳ層の平面レイアウト構成を示す平面図である。FIG. 10 is a plan view showing a planar layout configuration of a MEMS layer that constitutes a part of the acceleration sensor in the fourth embodiment. 実施の形態４における加速度センサの製造工程を示す断面図である。It is sectional drawing which shows the manufacturing process of the acceleration sensor in Embodiment 4. 図１７に続く加速度センサの製造工程を示す断面図である。FIG. 18 is a cross-sectional view showing a manufacturing process of the acceleration sensor following FIG. 17. 図１８に続く加速度センサの製造工程を示す断面図である。It is sectional drawing which shows the manufacturing process of the acceleration sensor following FIG. 図１９に続く加速度センサの製造工程を示す断面図である。FIG. 20 is a cross-sectional view showing a manufacturing step of the acceleration sensor following FIG. 19.
　以下の実施の形態においては便宜上その必要があるときは、複数のセクションまたは実施の形態に分割して説明するが、特に明示した場合を除き、それらはお互いに無関係なものではなく、一方は他方の一部または全部の変形例、詳細、補足説明等の関係にある。 In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.
　また、以下の実施の形態において、要素の数等（個数、数値、量、範囲等を含む）に言及する場合、特に明示した場合および原理的に明らかに特定の数に限定される場合等を除き、その特定の数に限定されるものではなく、特定の数以上でも以下でもよい。 Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.
　さらに、以下の実施の形態において、その構成要素（要素ステップ等も含む）は、特に明示した場合および原理的に明らかに必須であると考えられる場合等を除き、必ずしも必須のものではないことは言うまでもない。 Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.
　同様に、以下の実施の形態において、構成要素等の形状、位置関係等に言及するときは、特に明示した場合および原理的に明らかにそうではないと考えられる場合等を除き、実質的にその形状等に近似または類似するもの等を含むものとする。このことは、上記数値および範囲についても同様である。 Similarly, in the following embodiments, when referring to the shape, positional relationship, etc., of components, etc., unless otherwise specified, and in principle, it is considered that this is not clearly the case, it is substantially the same. Including those that are approximate or similar to the shape. The same applies to the above numerical values and ranges.
　また、実施の形態を説明するための全図において、同一の部材には原則として同一の符号を付し、その繰り返しの説明は省略する。なお、図面をわかりやすくするために平面図であってもハッチングを付す場合がある。 In all the drawings for explaining the embodiments, the same members are, in principle, given the same reference numerals, and the repeated explanation thereof is omitted. In order to make the drawings easy to understand, even a plan view may be hatched.
　（実施の形態１）
　＜加速度センサの適用分野例＞
　加速度センサは、自動車の姿勢制御、スマートフォン、あるいは、ゲーム機等の幅広い分野で利用される。これらの分野で使用される加速度センサは、小型で数百Ｈｚ以下という低周波数帯域で、重力の数倍の大きさの加速度を検出することができる。 (Embodiment 1)
<Examples of application fields of acceleration sensors>
Acceleration sensors are used in a wide range of fields such as automobile attitude control, smartphones, and game machines. The acceleration sensor used in these fields is small and can detect acceleration several times as large as gravity in a low frequency band of several hundred Hz or less.
　一方、近年において、加速度センサの利用分野は、上述した分野に限らず、地中の資源探査を目的とする分野にも拡大している。このような地中の資源探査分野において、物理探査の一種である反射法弾性波探査（反射法地震探査）は、人工的に地震波を発生させた後、地表に設置した受振器（加速度センサ）で地下から跳ね返ってくる反射波を捉えることにより、その結果を解析して地下構造を解明する技術である。 On the other hand, in recent years, the field of use of the acceleration sensor is not limited to the above-mentioned field, but has been expanded to a field for exploring underground resources. In such subsurface resource exploration field, reflection seismic wave exploration (reflection seismic exploration), which is a kind of geophysical exploration, artificially generates a seismic wave and then receives a geophone (acceleration sensor) installed on the ground surface. In this technology, the reflected waves that bounce off the ground are captured and the results are analyzed to reveal the underground structure.
　図１は、反射法弾性波探査の概要を示した地表の断面模式図である。図１において、地表ＧＮＤに設置された起振源ＶＢから地中に弾性波（図中の矢印）を伝播させた後、複数の地層の境界ＢＵＤ１や境界ＢＵＤ２で反射した弾性波を、地表ＧＮＤに設置された加速度センサ（受振器）ＡＳでセンシングする。一般的な起振源ＶＢは、地表に対して垂直方向に発振するため、鉛直方向に近い方向にＰ波が効率よく励振される。このため、反射法弾性波探査では、Ｐ波が用いられる。また、再び地表ＧＮＤに戻ってくる弾性波は、鉛直方向に近い方向から伝播してくるＰ波であるため、加速度センサＡＳは、鉛直方向の弾性振動を検知する必要がある。図１に示すように、様々な方向に励振された弾性波は、減衰の大きい地中を伝播し、複数の地層の境界ＢＵＤ１や境界ＢＵＤ２で反射し、再び減衰の大きい地中を伝搬して、広い領域に拡散して地表ＧＮＤに戻ってくる。 Fig. 1 is a schematic cross-sectional view of the earth's surface showing an outline of the reflection elastic wave exploration. In FIG. 1, after elastic waves (arrows in the figure) are propagated from the excitation source VB installed on the ground surface GND to the ground, the elastic waves reflected by the boundary BUD1 and the boundary BUD2 of the plurality of formations are grounded. Sensing is performed by an acceleration sensor (vibrator) AS installed in the vehicle. Since a general excitation source VB oscillates in a direction perpendicular to the ground surface, a P wave is efficiently excited in a direction close to the vertical direction. For this reason, the P wave is used in the reflection elastic wave exploration. Further, since the elastic wave returning to the ground surface GND is a P wave propagating from a direction close to the vertical direction, the acceleration sensor AS needs to detect the elastic vibration in the vertical direction. As shown in FIG. 1, the elastic wave excited in various directions propagates in the ground with large attenuation, reflects at the boundary BUD1 and boundary BUD2 of a plurality of formations, and propagates again in the ground with large attenuation. It spreads over a wide area and returns to the ground surface GND.
　このように、反射法弾性波探査では、微弱な弾性振動を検知するため、加速度センサＡＳには、鉛直方向に高感度である必要がある。具体的に、微弱な弾性振動の加速度は、重力加速度よりも小さいため、反射法弾性波探査で使用される加速度センサには、重力加速度よりも小さな加速度を高感度に検出することが要求される。 As described above, in the reflection elastic wave exploration, in order to detect weak elastic vibration, the acceleration sensor AS needs to be highly sensitive in the vertical direction. Specifically, since the acceleration of weak elastic vibration is smaller than the gravitational acceleration, the acceleration sensor used in the reflection elastic wave exploration is required to detect acceleration smaller than the gravitational acceleration with high sensitivity. .
　このことから、本実施の形態１では、重力加速度よりも小さな加速度を高感度に検出する（Ｓ／Ｎ比を向上する）観点から、加速度センサの構成要素である質量体の質量を大きくし、かつ、バネ定数を小さくする構成と、機械雑音を低減するために、質量体に複数の開口部を設けて空気抵抗を減らす構成とを採用している。ところが、本発明者が検討したところ、これらの構成を採用する場合、「発明が解決しようとする課題」の欄で説明したように副作用が生じる。そこで、本実施の形態１では、この副作用を抑制することができる工夫を施している。以下では、この工夫を施した本実施の形態１における技術的思想について説明することにする。 For this reason, in the first embodiment, from the viewpoint of detecting an acceleration smaller than the gravitational acceleration with high sensitivity (improving the S / N ratio), the mass of the mass body that is a component of the acceleration sensor is increased, And the structure which makes a spring constant small and the structure which provides a some opening part in a mass body and reduces air resistance are employ | adopted in order to reduce mechanical noise. However, as a result of studies by the present inventor, when these configurations are adopted, side effects occur as described in the section “Problems to be Solved by the Invention”. Therefore, in the first embodiment, a device that can suppress this side effect is taken. Below, the technical idea in this Embodiment 1 which gave this device is demonstrated.
　＜加速度センサの断面構成＞（片持ち構造）
　図２は、本実施の形態１における加速度センサＡＳ１の一断面を示す断面図である。図２において、本実施の形態１における加速度センサＡＳ１は、例えば、シリコン（Ｓｉ）からなるベース層ＢＬを有し、このベース層ＢＬ上に、例えば、ポリシリコン膜からなる固定電極ＦＥが形成されている。そして、固定電極ＦＥの表面に複数の保護部ＰＵが互いに離間するように形成されている。この複数の保護部ＰＵ１は、例えば、酸化シリコン膜に代表される絶縁膜から形成されている。 <Cross-sectional configuration of acceleration sensor> (cantilever structure)
FIG. 2 is a sectional view showing one section of the acceleration sensor AS1 in the first embodiment. In FIG. 2, the acceleration sensor AS1 in the first embodiment has a base layer BL made of, for example, silicon (Si), and a fixed electrode FE made of, for example, a polysilicon film is formed on the base layer BL. ing. A plurality of protection parts PU are formed on the surface of the fixed electrode FE so as to be separated from each other. The plurality of protection units PU1 are formed of an insulating film typified by a silicon oxide film, for example.
　続いて、図２に示すように、ベース層ＢＬの上方には、例えば、シリコンからなるＭＥＭＳ層ＭＬが配置されており、このＭＥＭＳ層ＭＬは、ＭＥＭＳ層ＭＬを加工することにより形成された固定部ＦＵが形成されている。この固定部ＦＵとベース層ＢＬとを接合することにより、ＭＥＭＳ層ＭＬがベース層ＢＬの上方に配置されることになる。そして、このＭＥＭＳ層ＭＬには、質量体ＭＳが形成され、質量体ＭＳは、ベース層ＢＬに形成された固定電極ＦＥと対向する位置に配置される。この質量体ＭＳは、梁（図示せず）を介して、固定部ＦＵと接続されている。すなわち、質量体ＭＳは、梁によって懸架されており、図２のｚ方向に変位可能となっている。例えば、質量体ＭＳは、外部からｚ方向に加速度が印加されると、ｚ方向に変位することになる。 Subsequently, as shown in FIG. 2, a MEMS layer ML made of, for example, silicon is disposed above the base layer BL, and the MEMS layer ML is formed by processing the MEMS layer ML. Part FU is formed. By joining the fixing portion FU and the base layer BL, the MEMS layer ML is disposed above the base layer BL. The mass body MS is formed on the MEMS layer ML, and the mass body MS is disposed at a position facing the fixed electrode FE formed on the base layer BL. The mass body MS is connected to the fixed portion FU via a beam (not shown). That is, the mass body MS is suspended by a beam and can be displaced in the z direction of FIG. For example, the mass body MS is displaced in the z direction when acceleration is applied in the z direction from the outside.
　さらに、質量体ＭＳには、図２に示すように、質量体ＭＳを貫通する複数の開口部ＯＰが形成されている。これらの複数の開口部ＯＰは、固定電極ＦＥ上に形成された複数の保護部ＰＵに対応するように設けられている。すなわち、複数の開口部ＯＰのそれぞれに対応するように保護部ＰＵが設けられている。 Furthermore, as shown in FIG. 2, a plurality of openings OP penetrating the mass body MS are formed in the mass body MS. The plurality of openings OP are provided so as to correspond to the plurality of protection units PU formed on the fixed electrode FE. That is, the protection part PU is provided so as to correspond to each of the plurality of openings OP.
　また、質量体ＭＳは、導電性を有するシリコンから形成され、かつ、ｚ方向に変位可能であることから、可動電極ＶＥとしても機能する。したがって、本実施の形態１における加速度センサＡＳ１では、ベース層ＢＬ上に形成された固定電極ＦＥと、ＭＥＭＳ層ＭＬに形成された質量体ＭＳ（可動電極ＶＥ）とによって、静電容量が形成されることになる。 Further, since the mass body MS is made of conductive silicon and can be displaced in the z direction, it also functions as the movable electrode VE. Therefore, in the acceleration sensor AS1 in the first embodiment, a capacitance is formed by the fixed electrode FE formed on the base layer BL and the mass body MS (movable electrode VE) formed on the MEMS layer ML. Will be.
　次に、図２に示すように、ＭＥＭＳ層ＭＬ上には、例えば、シリコンからなるキャップ層ＣＬが配置されている。この結果、ＭＥＭＳ層ＭＬは、断面視において、ベース層ＢＬとキャップ層ＣＬで挟まれることになり、ＭＥＭＳ層ＭＬに形成されている質量体ＭＳは、ベース層ＢＬと固定部ＦＵとキャップ層ＣＬとで囲まれる空洞部ＣＡＶの内部に配置されることになる。このとき、空洞部ＣＡＶの内部には気体が充填されており、空洞部ＣＡＶの内部の圧力は、例えば、大気圧よりも充分に低い圧力となっている。 Next, as shown in FIG. 2, for example, a cap layer CL made of silicon is disposed on the MEMS layer ML. As a result, the MEMS layer ML is sandwiched between the base layer BL and the cap layer CL in a cross-sectional view, and the mass body MS formed in the MEMS layer ML includes the base layer BL, the fixing unit FU, and the cap layer CL. It will be arrange | positioned inside the cavity part CAV enclosed by these. At this time, the cavity CAV is filled with gas, and the pressure inside the cavity CAV is, for example, a pressure sufficiently lower than the atmospheric pressure.
　このように、本実施の形態１における加速度センサＡＳ１は、ｚ方向に変位可能な可動電極ＶＥ（質量体ＭＳ）と、可動電極ＶＥを貫通する複数の開口部ＯＰと、ｚ方向において、可動電極ＶＥと離間して対向配置された固定電極ＦＥと、可動電極ＶＥと対向する固定電極ＦＥの対向面に形成され、かつ、複数の開口部ＯＰのそれぞれに対応して設けられた複数の保護部ＰＵのそれぞれとを備える。 As described above, the acceleration sensor AS1 according to the first embodiment includes the movable electrode VE (mass body MS) that can be displaced in the z direction, the plurality of openings OP that penetrate the movable electrode VE, and the movable electrode in the z direction. A plurality of protection portions formed on the opposing surfaces of the fixed electrode FE spaced apart from the VE and the fixed electrode FE facing the movable electrode VE, and provided corresponding to each of the plurality of openings OP. Each of the PUs.
　そして、本実施の形態１における加速度センサＡＳ１は、ベース層ＢＬと、ベース層ＢＬの上方に配置されたキャップ層ＣＬと、ベース層ＢＬとキャップ層ＣＬとで挟まれた空洞部ＣＡＶと、空洞部ＣＡＶ内に配置されたＭＥＭＳ層ＭＬとを有する。このとき、空洞部ＣＡＶ１内において、ベース層ＢＬ上に固定電極ＦＥが形成されている。また、ＭＥＭＳ層ＭＬに、ベース層ＢＬとキャップ層ＣＬとに固定された固定部ＦＵと、固定部ＦＵに接続された梁と、この梁によって空洞部ＣＡＶ内に懸架され、可動電極ＶＥとして機能する質量体ＭＳとが形成されている。 The acceleration sensor AS1 according to the first embodiment includes a base layer BL, a cap layer CL disposed above the base layer BL, a cavity CAV sandwiched between the base layer BL and the cap layer CL, a cavity And a MEMS layer ML disposed in the part CAV. At this time, the fixed electrode FE is formed on the base layer BL in the cavity CAV1. The MEMS layer ML has a fixed portion FU fixed to the base layer BL and the cap layer CL, a beam connected to the fixed portion FU, and is suspended in the cavity CAV by the beam and functions as the movable electrode VE. Mass body MS to be formed.
　＜加速度センサの平面構成＞
　続いて、本実施の形態１における加速度センサの平面構成について説明する。以下では、まず、ベース層ＢＬの平面構成について説明し、その後、ＭＥＭＳ層ＭＬの平面構成について説明することにする。 <Planar configuration of acceleration sensor>
Next, the planar configuration of the acceleration sensor according to the first embodiment will be described. Hereinafter, the planar configuration of the base layer BL will be described first, and then the planar configuration of the MEMS layer ML will be described.
　＜＜ベース層の平面構成＞＞
　図３は、本実施の形態１におけるベース層ＢＬの平面レイアウト構成を示す平面図である。図３のＡ－Ａ線での断面が図２のベース層ＢＬに対応する。図３において、ベース層ＢＬの内部には、空洞部ＣＡＶが形成されており、この空洞部ＣＡＶの内部に固定電極ＦＥが形成されている。そして、固定電極ＦＥ上には、複数の保護部ＰＵが形成されている。これにより、互いに離間した複数の保護部ＰＵを固定電極ＦＥの表面に設けて、固定電極ＦＥの表面に凹凸形状が形成されることになる。 << Planar structure of base layer >>
FIG. 3 is a plan view showing a planar layout configuration of the base layer BL in the first embodiment. A cross section taken along line AA in FIG. 3 corresponds to the base layer BL in FIG. In FIG. 3, a cavity CAV is formed inside the base layer BL, and a fixed electrode FE is formed inside the cavity CAV. A plurality of protection units PU are formed on the fixed electrode FE. As a result, a plurality of protection parts PU spaced apart from each other are provided on the surface of the fixed electrode FE, and an uneven shape is formed on the surface of the fixed electrode FE.
　＜＜ＭＥＭＳ層の平面構成＞＞
　図４は、本実施の形態１におけるＭＥＭＳ層ＭＬの平面レイアウト構成を示す平面図である。図４のＡ－Ａ線での断面が図２のＭＥＭＳ層ＭＬに対応する。図４において、ＭＥＭＳ層ＭＬの内部には、空洞部ＣＡＶが形成されており、この空洞部ＣＡＶの内部に、固定部ＦＵと、この固定部ＦＵと接続される梁ＢＭと、この梁ＢＭと接続される質量体ＭＳとが形成されている。つまり、ＭＥＭＳ層ＭＬには、質量体ＭＳが梁ＢＭを介して固定部ＦＵに接続されており、質量部ＭＳは、梁ＢＭによって懸架されていることになる。そして、質量体ＭＳには、複数の開口部ＯＰが形成されている。ここで、図３に示すベース層ＢＬと図４に示すＭＥＭＳ層ＭＬとを平面的に重ねるとわかるように、複数の保護部ＰＵのそれぞれの平面サイズは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰの平面サイズよりも大きくなっている。言い換えれば、平面視において、複数の保護部ＰＵのそれぞれは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰを内包するように形成されることになる。 << Planar structure of MEMS layer >>
FIG. 4 is a plan view showing a planar layout configuration of the MEMS layer ML in the first embodiment. A cross section taken along line AA in FIG. 4 corresponds to the MEMS layer ML in FIG. In FIG. 4, a cavity CAV is formed inside the MEMS layer ML. Inside the cavity CAV, a fixed part FU, a beam BM connected to the fixed part FU, and the beam BM A mass body MS to be connected is formed. That is, in the MEMS layer ML, the mass body MS is connected to the fixed portion FU via the beam BM, and the mass portion MS is suspended by the beam BM. A plurality of openings OP are formed in the mass body MS. Here, as can be seen when the base layer BL shown in FIG. 3 and the MEMS layer ML shown in FIG. 4 are overlapped in a plane, each planar size of the plurality of protection units PU corresponds to each of the plurality of protection units PU. The opening size OP is larger than the planar size. In other words, in the plan view, each of the plurality of protection units PU is formed so as to include the opening OP corresponding to each of the plurality of protection units PU.
　＜加速度センサの動作＞
　次に、本実施の形態１における加速度センサＡＳ１の動作について説明する。本実施の形態１における加速度センサＡＳ１は、ｚ方向に印加される加速度を、可動電極ＶＥと固定電極ＦＥからなる可変容量の容量変化として捉える加速度センサである。例えば、原理的には、変調信号を印加しなくても加速度に起因する可変容量での容量変化を検出することにより、加速度を検出することは可能である。ただし、加速度に対応した可変容量での容量変化に基づく検出信号は、低周波信号であるため、１／ｆノイズの影響を受けやすくなる。すなわち、加速度に対応した可変容量での容量変化に基づく検出信号をそのまま使用する構成では、１／ｆノイズが大きくなる結果、Ｓ／Ｎ比が劣化して、加速度センサの検出感度が低下することになる。そこで、本実施の形態１では、変調信号を使用している。この場合、加速度に対応した可変容量での容量変化に基づく検出信号が変調信号で変調されて高周波信号となるため、１／ｆノイズを受けにくくなるのである。つまり、高周波信号では、低周波信号よりも１／ｆノイズが小さくなることから、Ｓ／Ｎ比を向上できる結果、加速度センサＡＳ１の検出感度を向上することができるのである。このような理由から、本実施の形態１では、まず、可動電極ＶＥと固定電極ＦＥからなる可変容量に変調信号を印加する。 <Operation of acceleration sensor>
Next, the operation of the acceleration sensor AS1 in the first embodiment will be described. The acceleration sensor AS1 according to the first embodiment is an acceleration sensor that captures acceleration applied in the z direction as a change in capacitance of a variable capacitor including the movable electrode VE and the fixed electrode FE. For example, in principle, it is possible to detect acceleration by detecting a change in capacitance due to acceleration due to acceleration without applying a modulation signal. However, since the detection signal based on the capacitance change in the variable capacitance corresponding to the acceleration is a low-frequency signal, it is easily affected by 1 / f noise. In other words, in the configuration in which the detection signal based on the capacitance change in the variable capacitor corresponding to the acceleration is used as it is, the 1 / f noise increases, resulting in the deterioration of the S / N ratio and the detection sensitivity of the acceleration sensor. become. Therefore, in the first embodiment, a modulation signal is used. In this case, since the detection signal based on the capacitance change in the variable capacitor corresponding to the acceleration is modulated by the modulation signal to become a high frequency signal, it is difficult to receive 1 / f noise. That is, since the 1 / f noise is smaller in the high-frequency signal than in the low-frequency signal, the S / N ratio can be improved. As a result, the detection sensitivity of the acceleration sensor AS1 can be improved. For this reason, in the first embodiment, first, a modulation signal is applied to a variable capacitor composed of the movable electrode VE and the fixed electrode FE.
　ここで、例えば、ｚ方向に加速度が印加されたとする。この場合、質量体ＭＳは、ｚ方向に変位する。この結果、可動電極ＶＥ（質量体ＭＳ）と固定電極ＦＥからなる可変容量の容量変化が生じる。この容量変化は、変調信号に加わって信号処理回路へ出力される。具体的に、信号処理回路では、加速度に起因する容量変化が加わった変調信号がＣＶ変換部に入力されて、容量変化がアナログ電圧信号に変換される。そして、変換されたアナログ電圧信号は、ＡＤ変換部でデジタル電圧信号に変換される。その後、同期検波部で復調信号が抽出される。続いて、同期検波部で復調された復調信号は、ＬＰＦ（低周波数帯域通過フィルタ）を通過することにより、最終的に、加速度に対応した加速度信号（検出信号）が出力端子から出力される。以上のようにして、本実施の形態１における加速度センサＡＳ１によれば、ｚ方向の加速度を検出することができる。 Here, for example, it is assumed that acceleration is applied in the z direction. In this case, the mass body MS is displaced in the z direction. As a result, a change in the capacitance of the variable capacitor including the movable electrode VE (mass body MS) and the fixed electrode FE occurs. This capacitance change is added to the modulation signal and output to the signal processing circuit. Specifically, in the signal processing circuit, a modulation signal to which a capacitance change due to acceleration is added is input to the CV conversion unit, and the capacitance change is converted into an analog voltage signal. The converted analog voltage signal is converted into a digital voltage signal by the AD converter. Thereafter, the demodulated signal is extracted by the synchronous detector. Subsequently, the demodulated signal demodulated by the synchronous detection section passes through an LPF (low frequency band pass filter), and finally an acceleration signal (detection signal) corresponding to the acceleration is output from the output terminal. As described above, according to the acceleration sensor AS1 in the first embodiment, the acceleration in the z direction can be detected.
　＜実施の形態１における特徴＞
　次に、本実施の形態１における特徴点について説明する。図５は、図２の一部を拡大して示す図である。断面図である図５には示されないが、本実施の形態１における特徴点は、ｚ方向から見た平面視において、複数の保護部ＰＵのそれぞれは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰを内包する点にある（図３および図４参照）。この特徴点を反映して、断面図である図５では、例えば、保護部ＰＵのｘ方向の幅Ｌ１が、開口部ＯＰのｘ方向の開口寸法Ｌ３よりも大きくなり、かつ、保護部ＰＵには、開口部ＯＰと重ならない非重複領域ＮＯＲが形成されることになる。 <Characteristics in Embodiment 1>
Next, feature points in the first embodiment will be described. FIG. 5 is an enlarged view of a part of FIG. Although not shown in FIG. 5 which is a cross-sectional view, the feature point in the first embodiment is that each of the plurality of protection units PU corresponds to each of the plurality of protection units PU in a plan view viewed from the z direction. The point is to include the opening OP (see FIGS. 3 and 4). Reflecting this feature point, in FIG. 5 which is a cross-sectional view, for example, the width L1 in the x direction of the protection part PU is larger than the opening dimension L3 in the x direction of the opening OP, and the protection part PU The non-overlapping region NOR that does not overlap with the opening OP is formed.
　これにより、本実施の形態１によれば、以下に示すような利点を得ることができる。まず、本実施の形態１における第１利点は、質量体ＭＳが固定電極ＦＥに張り付くステッキングを防止できることである。例えば、本実施の形態１における加速度センサＡＳ１では、高感度な加速度センサを実現するために、質量体ＭＳの質量を大きくし、かつ、梁のバネ定数を小さくする構成が取られている。この場合、質量体ＭＳが大きく変位して、固定電極ＦＥに接触するとステッキングが起こりやすくなる。特に、固定電極ＦＥの表面が平坦であると、質量体ＭＳが固定電極ＦＥに接触した際、接触面積が大きくなるため、ステッキングが生じやすい。このようなステッキングが生じると、質量体ＭＳが元の位置に戻らなくなるため、加速度センサＡＳ１が正常に動作しなくなる。つまり、ステッキングは、加速度センサＡＳ１の信頼性の低下を招く要因となるので、加速度センサＡＳ１の信頼性を向上する観点から、ステッキングを抑制する必要がある。 Thereby, according to the first embodiment, the following advantages can be obtained. First, the first advantage in the first embodiment is that the mass body MS can be prevented from sticking to the fixed electrode FE. For example, the acceleration sensor AS1 in the first embodiment has a configuration in which the mass of the mass body MS is increased and the spring constant of the beam is decreased in order to realize a highly sensitive acceleration sensor. In this case, if the mass body MS is greatly displaced and comes into contact with the fixed electrode FE, sticking is likely to occur. In particular, if the surface of the fixed electrode FE is flat, when the mass body MS comes into contact with the fixed electrode FE, the contact area increases, and thus sticking is likely to occur. When such sticking occurs, the mass body MS does not return to the original position, and the acceleration sensor AS1 does not operate normally. That is, since sticking causes a decrease in the reliability of the acceleration sensor AS1, it is necessary to suppress the sticking from the viewpoint of improving the reliability of the acceleration sensor AS1.
　この点に関し、本実施の形態１における特徴点によれば、固定電極ＦＥの表面に複数の保護部ＰＵが設けられている結果、図５に示すように、固定電極ＦＥの表面に凹凸形状が形成される。したがって、質量体ＭＳの過剰な変位によって、質量体ＭＳが固定電極ＦＥに接触する場合であっても、固定電極ＦＥの表面に凹凸形状が形成されているため、保護部ＰＵと質量体ＭＳとの接触面積が小さくなり、ステッキングが起きにくくなる。このことは、ステッキングに起因する加速度センサＡＳ１の信頼性低下を抑制できることを意味する。つまり、本実施の形態１によれば、固定電極ＦＥの表面に互いに離間する複数の保護部ＰＵを設けることにより、固定電極ＦＥの表面に凹凸形状を形成することができ、この凹凸形状によって、質量体ＭＳと固定電極ＦＥとのステッキングを効果的に抑制することができるのである。これにより、本実施の形態１によれば、加速度センサＡＳ１の信頼性を向上することができる。 In this regard, according to the feature point of the first embodiment, as a result of the provision of the plurality of protective portions PU on the surface of the fixed electrode FE, as shown in FIG. 5, the surface of the fixed electrode FE has an uneven shape. It is formed. Therefore, even when the mass body MS is in contact with the fixed electrode FE due to excessive displacement of the mass body MS, since the uneven shape is formed on the surface of the fixed electrode FE, the protection unit PU and the mass body MS The contact area becomes smaller and sticking is less likely to occur. This means that a reduction in reliability of the acceleration sensor AS1 due to sticking can be suppressed. That is, according to the first embodiment, by providing a plurality of protective portions PU that are spaced apart from each other on the surface of the fixed electrode FE, it is possible to form an uneven shape on the surface of the fixed electrode FE. The sticking between the mass body MS and the fixed electrode FE can be effectively suppressed. Thereby, according to this Embodiment 1, the reliability of acceleration sensor AS1 can be improved.
　さらに、本実施の形態１では、図５に示すように、複数の保護部ＰＵのそれぞれが、開口部ＯＰ１に対応して設けられている。したがって、質量体ＭＳが固定電極ＦＥに接触する程度に大きくｚ方向に変位したとしても、質量体ＭＳは保護部ＰＵの幅Ｌ３全体に接触するのではなく、保護部ＰＵと開口部ＯＰとの非重複領域ＮＯＲの幅Ｌ２の範囲で接触することになる。このことは、質量体ＭＳと保護部ＰＵとの接触面積を低減することができることを意味する。すなわち、本実施の形態１における加速度センサＡＳ１では、複数の保護部ＰＵが互いに離間して固定電極ＦＥの表面上に設けられている結果、固定電極ＦＥの表面に凹凸形状が形成される点と、複数の保護部ＰＵのそれぞれが、対応する開口部ＯＰを内包するように設けられている点とが実現されている。これにより、固定電極ＦＥの表面に凹凸形状が形成される点に起因して質量体ＭＳと保護部ＰＵとの接触面積が低減される点と、複数の保護部ＰＵのそれぞれが、対応する開口部ＯＰを内包するように設けられていることにより、保護部ＰＵの表面全体で接触するのではなく、非重複領域ＮＯＲでのみ接触する点との相乗効果を得ることができる。この結果、本実施の形態１によれば、上述した構成の相乗効果によって、加速度センサＡＳ１におけるステッキングを効果的に抑制することができるという優れた効果を奏する。 Furthermore, in the first embodiment, as shown in FIG. 5, each of the plurality of protection units PU is provided corresponding to the opening OP1. Therefore, even if the mass body MS is displaced in the z direction so as to contact the fixed electrode FE, the mass body MS does not contact the entire width L3 of the protection portion PU, but instead of the protection portion PU and the opening OP. The contact is made within the range of the width L2 of the non-overlapping region NOR. This means that the contact area between the mass body MS and the protection part PU can be reduced. That is, in the acceleration sensor AS1 according to the first embodiment, the plurality of protection portions PU are provided on the surface of the fixed electrode FE so as to be separated from each other, and as a result, an uneven shape is formed on the surface of the fixed electrode FE. Each of the plurality of protection units PU is provided so as to include the corresponding opening OP. As a result, the contact area between the mass body MS and the protection part PU is reduced due to the formation of an uneven shape on the surface of the fixed electrode FE, and each of the protection parts PU has a corresponding opening. By being provided so as to include the portion OP, it is possible to obtain a synergistic effect with the point of contact only in the non-overlapping region NOR, not in contact with the entire surface of the protection portion PU. As a result, according to the first embodiment, there is an excellent effect that the sticking in the acceleration sensor AS1 can be effectively suppressed by the synergistic effect of the configuration described above.
　特に、図５に示す非重複領域ＮＯＲの幅Ｌ２が小さくなればなるほど、質量体ＭＳと保護部ＰＵとの接触面積が小さくなることから、ステッキングを抑制する観点からは、なるべく、非重複領域ＮＯＲの幅Ｌ２を小さくすることが望ましいことになる。例えば、図５に示すように、複数の保護部ＰＵのそれぞれと複数の保護部ＰＵのそれぞれに対応した開口部ＯＰとの非重複領域ＮＯＲのｘ方向の長さＬ２は、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰのｘ方向の開口寸法Ｌ３よりも小さくすることができる。言い換えれば、保護部ＰＵと保護部ＰＵに対応して設けられた開口部ＯＰとに着目した場合、ｚ方向から見た平面視において、ｘ方向における開口部ＯＰの一端部から保護部ＰＵの一端部までの距離（Ｌ２）は、ｘ方向における開口部ＯＰの開口寸法Ｌ３よりも小さくすることができる。 In particular, the smaller the width L2 of the non-overlapping region NOR shown in FIG. 5, the smaller the contact area between the mass body MS and the protection part PU. From the viewpoint of suppressing sticking, the non-overlapping region is as much as possible. It would be desirable to reduce the NOR width L2. For example, as illustrated in FIG. 5, the length L2 in the x direction of the non-overlapping region NOR between each of the plurality of protection units PU and the opening OP corresponding to each of the plurality of protection units PU is equal to the plurality of protection units PU. Can be made smaller than the opening dimension L3 in the x direction of the opening OP corresponding to each of the above. In other words, when attention is paid to the protection part PU and the opening OP provided corresponding to the protection part PU, one end of the protection part PU from one end of the opening OP in the x direction in a plan view seen from the z direction. The distance (L2) to the portion can be made smaller than the opening dimension L3 of the opening OP in the x direction.
　続いて、本実施の形態１における特徴点の第２利点は、製造工程中での利点である。具体的に、質量体ＭＳおよびこの質量体ＭＳを貫通する開口部ＯＰは、ＭＥＭＳ層ＭＬをパターニングすることにより形成され、このパターニング工程には、ＭＥＭＳ層ＭＬをドライエッチングする工程が含まれる。ここで、実際には、ＭＥＭＳ層ＭＬをエッチングすることにより、固定部ＦＵ、梁、質量体ＭＳ、および、複数の開口部ＯＰを形成することになるが、ＭＥＭＳ層ＭＬに、これらの構成要素を形成する際には、開口面積の異なる領域を同時にエッチングすることになる。特に、開口面積の小さな領域ほどエッチングに要する時間が長くなるため、開口面積の最も小さな開口部ＯＰに合わせてエッチング時間が決められる。さらには、ウェハ面内においても、ウェハの中心部と周辺部とでは、エッチング速度が異なるため、ＭＥＭＳ層ＭＬの貫通に必要なエッチング時間以上にエッチング時間を設定している。これらのことから、オーバエッチングが行なわれることになる。ところが、オーバエッチングを実施すると、ＭＥＭＳ層ＭＬの下方に配置されている固定電極ＦＥまでエッチングされて、固定電極ＦＥがダメージを受けるおそれがある。 Subsequently, the second advantage of the feature point in the first embodiment is an advantage in the manufacturing process. Specifically, the mass body MS and the opening OP penetrating the mass body MS are formed by patterning the MEMS layer ML, and this patterning step includes a step of dry etching the MEMS layer ML. Here, in practice, the fixed portion FU, the beam, the mass body MS, and the plurality of openings OP are formed by etching the MEMS layer ML. However, these components are included in the MEMS layer ML. When forming the film, regions having different opening areas are etched at the same time. In particular, since the time required for etching becomes longer in a region having a smaller opening area, the etching time is determined in accordance with the opening OP having the smallest opening area. Furthermore, even in the wafer plane, the etching rate is different between the central portion and the peripheral portion of the wafer, so the etching time is set to be longer than the etching time necessary for the penetration of the MEMS layer ML. Therefore, overetching is performed. However, if over-etching is performed, the fixed electrode FE disposed below the MEMS layer ML is etched, and the fixed electrode FE may be damaged.
　この点に関し、本実施の形態１によれば、複数の保護部ＰＵのそれぞれは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰを内包している。この結果、本実施の形態１によれば、開口部ＯＰを形成後、オーバエッチングが実施されても、開口部ＯＰを内包する保護部ＰＵによって、固定電極ＦＥをオーバエッチングから保護することができるのである。つまり、固定電極ＦＥの表面領域のうち、開口部ＯＰ１と平面的に重なる領域がオーバエッチングによるダメージを受けることになりやすいが、本実施の形態１では、この領域を覆うように保護部ＰＵが形成されているため、必要十分な範囲で、固定電極ＦＥをオーバエッチングから保護することができるのである。この点が本実施の形態１における特徴点によってもたらされる第２利点である。このように、本実施の形態１によれば、固定電極ＦＥをエッチングダメージから保護することができ、これによって、加速度センサＡＳ１の信頼性を向上することができるのである。 In this regard, according to the first embodiment, each of the plurality of protection units PU includes an opening OP corresponding to each of the plurality of protection units PU. As a result, according to the first embodiment, even if the overetching is performed after the opening OP is formed, the fixed electrode FE can be protected from the overetching by the protection unit PU that includes the opening OP. It is. That is, of the surface region of the fixed electrode FE, a region that overlaps the opening OP1 in a plan view is likely to be damaged by overetching. In the first embodiment, the protection unit PU covers the region. Therefore, the fixed electrode FE can be protected from over-etching within a necessary and sufficient range. This is the second advantage brought about by the feature points in the first embodiment. As described above, according to the first embodiment, it is possible to protect the fixed electrode FE from etching damage, thereby improving the reliability of the acceleration sensor AS1.
　ここで、図５に示す非重複領域ＮＯＲの幅Ｌ２が大きくなればなるほど、サイドエッチングから固定電極ＦＥを保護できることから、固定電極ＦＥへのエッチングダメージを低減する観点からは、なるべく、非重複領域ＮＯＲの幅Ｌ２を大きくすることが望ましいことになる。したがって、ステッキングを抑制する観点に着目した場合とエッチングダメージを抑制する観点に着目した場合とでは、非重複領域ＮＯＲの幅Ｌ２に対する要求が相反することになる。この点に関しての現実的な対応としては、ステッキングを抑制する観点からも妥当な範囲に収まり、かつ、エッチングダメージを抑制する観点からも妥当な範囲に収まるように、バランスの取れた範囲内に非重複領域ＮＯＲの幅Ｌ２を設定することが望ましい。 Here, as the width L2 of the non-overlapping region NOR shown in FIG. 5 becomes larger, the fixed electrode FE can be protected from side etching. From the viewpoint of reducing etching damage to the fixed electrode FE, the non-overlapping region is as much as possible. It would be desirable to increase the NOR width L2. Therefore, the requirement for the width L2 of the non-overlapping region NOR is contradictory between the case where attention is paid to the viewpoint of suppressing sticking and the case where attention is paid to the viewpoint of suppressing etching damage. As a realistic response in this regard, it is within a well-balanced range so that it is within a reasonable range from the viewpoint of suppressing sticking and within a reasonable range from the viewpoint of suppressing etching damage. It is desirable to set the width L2 of the non-overlapping area NOR.
　以上のことから、本実施の形態１における特徴点によれば、副作用を考慮することなく、重力加速度よりも小さな加速度を高感度に検出するために、加速度センサＡＳ１の質量体ＭＳの質量を大きくし、かつ、梁のバネ定数を小さくし、かつ、機械雑音を低減するために、質量体ＭＳに複数の開口部ＯＰを設けることができる。すなわち、本実施の形態１における特徴点によれば、質量体ＭＳのステッキングおよび固定電極ＦＥへのエッチングダメージという副作用を効果的に抑制しながら、加速度センサＡＳ１の検出感度を向上することができるという優れた効果を得ることができる。 From the above, according to the feature point in the first embodiment, the mass of the mass body MS of the acceleration sensor AS1 is increased in order to detect an acceleration smaller than the gravitational acceleration with high sensitivity without considering side effects. In order to reduce the spring constant of the beam and reduce mechanical noise, the mass body MS can be provided with a plurality of openings OP. That is, according to the feature point in the first embodiment, the detection sensitivity of the acceleration sensor AS1 can be improved while effectively suppressing the side effect of the mass body MS sticking and the etching damage to the fixed electrode FE. An excellent effect can be obtained.
　（実施の形態２）
　本実施の形態２では、前記実施の形態１とは別のレイアウト構成例（ベース層ＢＬの平面レイアウト構成例およびＭＥＭＳ層ＭＬの平面レイアウト構成例）について説明する。 (Embodiment 2)
In the second embodiment, another layout configuration example (planar layout configuration example of the base layer BL and planar layout configuration example of the MEMS layer ML) different from the first embodiment will be described.
　＜ベース層の平面構成例＞
　（１）図６は、本実施の形態２におけるベース層ＢＬの平面レイアウト構成例を示す平面図である。図６において、ベース層ＢＬの内部に固定電極ＦＥとサーボ電極ＳＥ１とサーボ電極ＳＥ２とが形成されている。具体的には、ｙ方向に並ぶように、サーボ電極ＳＥ１と固定電極ＦＥとサーボ電極ＳＥ２とが配置され、かつ、平面視において、サーボ電極ＳＥ１とサーボ電極ＳＥ２とに挟まれるように、固定電極ＦＥが配置されている。 <Example of planar configuration of base layer>
(1) FIG. 6 is a plan view showing a planar layout configuration example of the base layer BL in the second embodiment. In FIG. 6, a fixed electrode FE, a servo electrode SE1, and a servo electrode SE2 are formed in the base layer BL. Specifically, the servo electrode SE1, the fixed electrode FE, and the servo electrode SE2 are arranged so as to be aligned in the y direction, and the fixed electrode is sandwiched between the servo electrode SE1 and the servo electrode SE2 in plan view. FE is arranged.
　そして、固定電極ＦＥ上には、複数の保護部ＰＵが形成されているとともに、サーボ電極ＳＥ１およびサーボ電極ＳＥ２上にも、複数の保護部ＰＵが形成されている。これにより、互いに離間した複数の保護部ＰＵを固定電極ＦＥの表面に設けて、固定電極ＦＥの表面に凹凸形状を設けるという特徴点が実現されることになる。さらに、本実施の形態２では、固定電極ＦＥだけでなく、サーボ電極ＳＥ１およびサーボ電極ＳＥ２においても、互いに離間した複数の保護部ＰＵをサーボ電極ＳＥ１およびサーボ電極ＳＥ２の表面に設けて、サーボ電極ＳＥ１およびサーボ電極ＳＥ２の表面に凹凸形状を設けている。このため、サーボ電極ＳＥ１およびサーボ電極ＳＥ２においても、上述した特徴点が実現される。 A plurality of protection parts PU are formed on the fixed electrode FE, and a plurality of protection parts PU are also formed on the servo electrodes SE1 and SE2. Thereby, the feature point that the plurality of protection parts PU spaced apart from each other is provided on the surface of the fixed electrode FE and the uneven shape is provided on the surface of the fixed electrode FE is realized. Further, in the second embodiment, not only the fixed electrode FE but also the servo electrode SE1 and the servo electrode SE2 are provided with a plurality of protective portions PU spaced from each other on the surfaces of the servo electrode SE1 and the servo electrode SE2, and the servo electrode Concave and convex shapes are provided on the surfaces of SE1 and servo electrode SE2. For this reason, the above-described feature points are also realized in the servo electrode SE1 and the servo electrode SE2.
　このように、図６に示すベース層ＢＬには、固定電極ＦＥの他に、サーボ電極ＳＥ１およびサーボ電極ＳＥ２が形成されている。つまり、図６に示すベース層ＢＬには、固定電極ＦＥと同層で形成され、かつ、ｚ方向（図６の紙面上側方向）において、ベース層ＢＬの上方に配置される質量体（図示されず）と離間して対向配置され、かつ、ｚ方向への質量体の変位を打ち消す静電気力を発生させるサーボ電極ＳＥ１およびサーボ電極ＳＥ２が形成されている。このサーボ電極ＳＥ１およびサーボ電極ＳＥ２には、サーボ電圧が印加されるようになっており、サーボ電極ＳＥ１およびサーボ電極ＳＥ２にサーボ電圧を印加することにより発生するクーロン力（静電気力）によって、加速度に基づく質量体のｚ方向の変位が打ち消されるようになっている。これにより、本実施の形態２における加速度センサに加速度が印加されても、質量体はｚ方向にほとんど変位しないが、サーボ電極ＳＥ１およびサーボ電極ＳＥ２には、加速度の大きさに比例したサーボ電圧が印加されることになるから、このサーボ電圧を出力することにより、結果的に、本実施の形態２における加速度センサに印加された加速度を検出することができる。 Thus, in addition to the fixed electrode FE, the servo electrode SE1 and the servo electrode SE2 are formed on the base layer BL shown in FIG. In other words, the base layer BL shown in FIG. 6 is formed of the same layer as the fixed electrode FE, and is disposed above the base layer BL in the z direction (upward direction in FIG. 6) (illustrated). The servo electrode SE1 and the servo electrode SE2 that are arranged opposite to each other and generate an electrostatic force that cancels the displacement of the mass body in the z direction are formed. A servo voltage is applied to the servo electrode SE1 and the servo electrode SE2, and the acceleration is caused by the Coulomb force (electrostatic force) generated by applying the servo voltage to the servo electrode SE1 and the servo electrode SE2. The displacement in the z direction of the mass body based thereon is cancelled. As a result, even if acceleration is applied to the acceleration sensor in the second embodiment, the mass body is hardly displaced in the z direction, but the servo electrode SE1 and the servo electrode SE2 have a servo voltage proportional to the magnitude of the acceleration. As a result, by outputting this servo voltage, it is possible to detect the acceleration applied to the acceleration sensor according to the second embodiment.
　このサーボ電極ＳＥ１およびサーボ電極ＳＥ２を設ける利点は、質量体をｚ方向に変位させることなく、加速度を検出することができる点にある。すなわち、サーボ機構を設けることにより、加速度センサに大きな加速度が印加された場合、質量体の想定外の変位によって、質量体と固定電極ＦＥとが接触することを防止することができる。 The advantage of providing the servo electrode SE1 and the servo electrode SE2 is that acceleration can be detected without displacing the mass body in the z direction. That is, by providing a servo mechanism, when a large acceleration is applied to the acceleration sensor, it is possible to prevent the mass body from contacting the fixed electrode FE due to an unexpected displacement of the mass body.
　このことから、加速度センサにサーボ電極ＳＥ１およびサーボ電極ＳＥ２を設ける構成では、上述した前記実施の形態１における特徴点に起因するステッキング防止効果とともに、サーボ機構によっても、質量体と固定電極ＦＥの接触が抑制される結果、ステッキング防止効果を得ることができる。すなわち、加速度センサにサーボ電極ＳＥ１およびサーボ電極ＳＥ２を設ける構成は、ステッキング防止効果を高める効果があり、ステッキングを抑制して加速度センサの信頼性を向上する観点から有用な構成であることがわかる。 Accordingly, in the configuration in which the servo electrode SE1 and the servo electrode SE2 are provided in the acceleration sensor, the mass body and the fixed electrode FE can be prevented by the servo mechanism as well as the anti-sticking effect due to the feature point in the first embodiment described above. As a result of the contact being suppressed, an anti-sticking effect can be obtained. In other words, the configuration in which the servo electrode SE1 and the servo electrode SE2 are provided in the acceleration sensor has an effect of enhancing the effect of preventing sticking, and is a useful configuration from the viewpoint of suppressing the sticking and improving the reliability of the acceleration sensor. Recognize.
　ここで、加速度センサの動作状態では、サーボ機構が働くため、前記実施の形態１における特徴点に起因するステッキング防止効果と、サーボ機構に起因するステッキング防止効果を得ることができる。一方、加速度センサの非動作状態では、サーボ機構も働かないため、サーボ機構に起因するステッキング防止効果を得ることはできない。つまり、加速度センサの非動作状態でも、梁によって懸架されている質量体に外力が加わると、質量体が変位することになるが、この場合、加速度センサが非動作状態にあると、サーボ機構が働かないため、ステッキングが生じる可能性がある。この点に関し、本実施の形態２によれば、加速度センサの非動作状態であっても、上述した前記実施の形態１における特徴点に起因するステッキング防止効果を得ることができる。すなわち、複数の保護部ＰＵによって凹凸形状を設けるという構成は、加速度センサの動作状態あるいは非動作状態に関わらず存在する。このことから、本実施の形態２における加速度センサでも、加速度センサが動作状態にある場合だけでなく、非動作状態にある場合であっても、ステッキング防止効果を得ることができる。すなわち、サーボ機構とは異なり、上述した前記実施の形態１における特徴点は、加速度センサの動作状態と非動作状態のいずれの状態であっても、ステッキング防止効果を得ることができる点で優れているということができる。 Here, since the servo mechanism works in the operating state of the acceleration sensor, it is possible to obtain the anti-sticking effect caused by the feature points in the first embodiment and the anti-sticking effect caused by the servo mechanism. On the other hand, in the non-operating state of the acceleration sensor, the servo mechanism does not work, so that it is not possible to obtain an anti-sticking effect caused by the servo mechanism. In other words, even when the acceleration sensor is not in operation, if an external force is applied to the mass body suspended by the beam, the mass body will be displaced. In this case, if the acceleration sensor is in the non-operation state, the servo mechanism Since it does not work, sticking may occur. In this regard, according to the second embodiment, even if the acceleration sensor is in a non-operating state, the effect of preventing sticking caused by the feature point in the first embodiment described above can be obtained. That is, the configuration in which the concavo-convex shape is provided by the plurality of protection units PU exists regardless of the operation state or non-operation state of the acceleration sensor. Therefore, even in the acceleration sensor according to the second embodiment, an effect of preventing sticking can be obtained not only when the acceleration sensor is in the operating state but also when the acceleration sensor is in the non-operating state. That is, unlike the servo mechanism, the feature point in the first embodiment described above is excellent in that an effect of preventing sticking can be obtained regardless of whether the acceleration sensor is in an operating state or a non-operating state. It can be said that
　なお、図６では、固定電極ＦＥとサーボ電極ＳＥ１とサーボ電極ＳＥ２とが別々の構成要素として設けられていることから、加速度の検出動作と質量体の変位を打ち消すサーボ動作とを同時に行なうことができる利点が得られる。 In FIG. 6, since the fixed electrode FE, the servo electrode SE1, and the servo electrode SE2 are provided as separate components, the acceleration detecting operation and the servo operation for canceling the displacement of the mass body can be performed simultaneously. Benefits that can be obtained.
　続いて、本実施の形態２では、図６に示すように、固定電極ＦＥから配線ＷＬが引き出されている。同様に、サーボ電極ＳＥ１から配線ＷＬ１が引き出され、サーボ電極ＳＥ２から配線ＷＬ２が引き出されている。このとき、例えば、図６に示すように、配線ＷＬの一部分および配線ＷＬ１の一部分を覆う配線保護部ＷＰＵが形成されている。同様に、図６において、配線ＷＬの一部分および配線ＷＬ２の一部分を覆う配線保護部ＷＰＵが形成されている。この配線保護部ＷＰＵは、複数の保護部ＰＵと同層で形成されており、ＭＥＭＳ層をエッチング加工する際のエッチングダメージから、配線ＷＬ、配線ＷＬ１および配線ＷＬ２を保護する機能を有している。 Subsequently, in the second embodiment, as shown in FIG. 6, the wiring WL is drawn from the fixed electrode FE. Similarly, the wiring WL1 is drawn from the servo electrode SE1, and the wiring WL2 is drawn from the servo electrode SE2. At this time, for example, as illustrated in FIG. 6, a wiring protection unit WPU that covers a part of the wiring WL and a part of the wiring WL1 is formed. Similarly, in FIG. 6, a wiring protection part WPU that covers a part of the wiring WL and a part of the wiring WL2 is formed. The wiring protection unit WPU is formed in the same layer as the plurality of protection units PU, and has a function of protecting the wiring WL, the wiring WL1, and the wiring WL2 from etching damage when the MEMS layer is etched. .
　すなわち、例えば、ＭＥＭＳ層ＭＬをエッチング加工する際、質量体ＭＳに形成される開口部ＯＰの他に、ＭＥＭＳ層ＭＬを貫通する貫通孔も形成される。したがって、この貫通孔と平面的に重なるように、ＭＥＭＳ層ＭＬの下層のベース層ＢＬに配線の一部分が配置されることがある。この場合、貫通孔を形成する際のエッチングによって、貫通孔と平面的に重なる配線の一部分がエッチングダメージを受けることになる。 That is, for example, when etching the MEMS layer ML, in addition to the opening OP formed in the mass body MS, a through-hole penetrating the MEMS layer ML is also formed. Therefore, a part of the wiring may be arranged on the base layer BL below the MEMS layer ML so as to overlap the through hole in a plan view. In this case, a portion of the wiring that overlaps with the through hole in a plane is damaged by etching when the through hole is formed.
　そこで、本実施の形態１では、例えば、図６において、貫通孔と平面的に重なる配線ＷＬの一部分と配線ＷＬ１の一部分とに跨って配線保護部ＷＰＵを形成し、かつ、貫通孔と平面的に重なる配線ＷＬの一部分と配線ＷＬ２の一部分とに跨って配線保護部ＷＰＵを形成している。そして、図６では示されないが、平面視において、配線保護部ＷＰＵは、貫通孔を内包するように形成される。これにより、本実施の形態２によれば、保護部ＰＵで固定電極ＦＥをエッチングダメージから保護できるだけでなく、配線保護部ＷＰＵで、貫通孔と平面的に重なる配線ＷＬの一部分、配線ＷＬ１の一部分、および、配線ＷＬ２の一部分をエッチングダメージから保護することができる。この結果、本実施の形態２によれば、加速度センサの信頼性向上を図ることができる。以上のようにして、本実施の形態２におけるベース層ＢＬが平面レイアウト構成されていることになる。 Therefore, in the first embodiment, for example, in FIG. 6, the wiring protection portion WPU is formed across a part of the wiring WL and the part of the wiring WL1 that overlaps the through-hole in a plan view, and A wiring protection part WPU is formed across a part of the wiring WL and a part of the wiring WL2 overlapping each other. Although not shown in FIG. 6, the wiring protection part WPU is formed so as to include the through hole in a plan view. Thereby, according to the second embodiment, not only can the protective electrode PU protect the fixed electrode FE from etching damage, but also the wiring protection unit WPU includes a part of the wiring WL and a part of the wiring WL1 that overlaps the through hole in a plane. In addition, a part of the wiring WL2 can be protected from etching damage. As a result, according to the second embodiment, the reliability of the acceleration sensor can be improved. As described above, the base layer BL in the second embodiment has a planar layout configuration.
　（２）次に、ベース層ＢＬの平面レイアウト構成の変形例について説明する。図７は、ベース層ＢＬの平面レイアウト構成例を示す平面図である。図７において、ベース層ＢＬには、矩形形状の固定電極ＦＥが形成されており、この固定電極ＦＥは、サーボ電極ＳＥとしても機能する。すなわち、図７に示すベース層ＢＬの平面レイアウト構成例では、固定電極ＦＥがサーボ電極ＳＥを兼ねている構成が示されている。この場合、固定電極ＦＥによる検出動作とサーボ電極ＳＥによるサーボ動作とは時分割で行なわれることになる。このようにベース層ＢＬの平面レイアウト構成は、図６に示す平面レイアウト構成だけでなく、図７に示す平面レイアウト構成を採用することもできる。 (2) Next, a modified example of the planar layout configuration of the base layer BL will be described. FIG. 7 is a plan view showing a planar layout configuration example of the base layer BL. In FIG. 7, a rectangular fixed electrode FE is formed on the base layer BL, and this fixed electrode FE also functions as a servo electrode SE. That is, in the planar layout configuration example of the base layer BL shown in FIG. 7, a configuration in which the fixed electrode FE also serves as the servo electrode SE is shown. In this case, the detection operation by the fixed electrode FE and the servo operation by the servo electrode SE are performed in a time division manner. As described above, the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIG. 6 but also the planar layout configuration shown in FIG.
　（３）続いて、ベース層ＢＬの平面レイアウト構成の別の変形例について説明する。図８は、ベース層ＢＬの平面レイアウト構成例を示す平面図である。図８において、ベース層ＢＬには、固定電極ＦＥとサーボ電極ＳＥ１とが別体として形成されており、特に、図８において、固定電極ＦＥとサーボ電極ＳＥ１とは、ｘ方向に並ぶように配置されている。このようにベース層ＢＬの平面レイアウト構成は、図６や図７に示す平面レイアウト構成だけでなく、図８に示す平面レイアウト構成を採用することもできる。 (3) Next, another modified example of the planar layout configuration of the base layer BL will be described. FIG. 8 is a plan view showing a planar layout configuration example of the base layer BL. In FIG. 8, the fixed electrode FE and the servo electrode SE1 are separately formed on the base layer BL. In particular, in FIG. 8, the fixed electrode FE and the servo electrode SE1 are arranged so as to be aligned in the x direction. Has been. As described above, the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIGS. 6 and 7, but also the planar layout configuration shown in FIG.
　（４）さらに、ベース層ＢＬの平面レイアウト構成の別の変形例について説明する。図９は、ベース層ＢＬの平面レイアウト構成例を示す平面図である。図９において、ベース層ＢＬには、固定電極ＦＥとサーボ電極ＳＥ１とが別体として形成されており、特に、図９において、固定電極ＦＥとサーボ電極ＳＥ１とは、ｙ方向に並ぶように配置されている。このようにベース層ＢＬの平面レイアウト構成は、図６～図８に示す平面レイアウト構成だけでなく、図９に示す平面レイアウト構成を採用することもできる。 (4) Further, another modified example of the planar layout configuration of the base layer BL will be described. FIG. 9 is a plan view illustrating a planar layout configuration example of the base layer BL. In FIG. 9, the fixed electrode FE and the servo electrode SE1 are separately formed on the base layer BL. In particular, in FIG. 9, the fixed electrode FE and the servo electrode SE1 are arranged so as to be aligned in the y direction. Has been. As described above, the planar layout configuration of the base layer BL can employ not only the planar layout configuration shown in FIGS. 6 to 8, but also the planar layout configuration shown in FIG.
　＜ＭＥＭＳ層の平面構成＞
　（１）図１０は、本実施の形態２におけるＭＥＭＳ層ＭＬの平面レイアウト構成を示す平面図である。図１０において、ＭＥＭＳ層ＭＬは、矩形形状をしており、ＭＥＭＳ層ＭＬの内部に、固定部ＦＵと、この固定部ＦＵと接続される梁ＢＭと、この梁ＢＭと接続される質量体ＭＳとが形成されている。つまり、ＭＥＭＳ層ＭＬには、質量体ＭＳが梁ＢＭを介して固定部ＦＵに接続されており、質量部ＭＳは、梁ＢＭによって懸架されていることになる。そして、質量体ＭＳには、複数の開口部ＯＰが形成されており、例えば、図１０では、複数の開口部ＯＰのそれぞれの平面形状は、スリット形状ＳＬとなっている。そして、図６に示すベース層ＢＬと図１０に示すＭＥＭＳ層ＭＬとを平面的に重ねるとわかるように、複数の保護部ＰＵのそれぞれの平面サイズは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰの平面サイズよりも大きくなっている。言い換えれば、平面視において、複数の保護部ＰＵのそれぞれは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰを内包するように形成されており、本実施の形態２でも、前記実施の形態１における特徴点が実現されていることがわかる。 <Planar configuration of MEMS layer>
(1) FIG. 10 is a plan view showing a planar layout configuration of the MEMS layer ML in the second embodiment. In FIG. 10, the MEMS layer ML has a rectangular shape. Inside the MEMS layer ML, a fixed portion FU, a beam BM connected to the fixed portion FU, and a mass body MS connected to the beam BM. And are formed. That is, in the MEMS layer ML, the mass body MS is connected to the fixed portion FU via the beam BM, and the mass portion MS is suspended by the beam BM. In the mass body MS, a plurality of openings OP are formed. For example, in FIG. 10, the planar shape of each of the plurality of openings OP is a slit shape SL. Then, as can be seen when the base layer BL shown in FIG. 6 and the MEMS layer ML shown in FIG. 10 are planarly overlapped, the respective planar sizes of the plurality of protection units PU correspond to the plurality of protection units PU, respectively. It is larger than the planar size of the opening OP. In other words, in plan view, each of the plurality of protection units PU is formed so as to include an opening OP corresponding to each of the plurality of protection units PU. It can be seen that the feature points in 1 are realized.
　（２）次に、ＭＥＭＳ層ＭＬの平面レイアウト構成の変形例について説明する。図１１は、ＭＥＭＳ層ＭＬの平面レイアウト構成例を示す平面図である。図１１において、ＭＥＭＳ層ＭＬには、梁ＢＭを介して固定部ＦＵに接続された質量体ＭＳが形成されており、この質量体ＭＳには、質量体ＭＳを貫通するように複数の開口部ＯＰが形成されている。特に、図１１では、複数の開口部ＯＰのそれぞれの平面形状は、ホール形状ＨＬとなっている。このようにＭＥＭＳ層ＭＬの平面レイアウト構成は、図１０に示す平面レイアウト構成だけでなく、図１１に示す平面レイアウト構成を採用することもできる。 (2) Next, a modification of the planar layout configuration of the MEMS layer ML will be described. FIG. 11 is a plan view illustrating a planar layout configuration example of the MEMS layer ML. In FIG. 11, the mass body MS connected to the fixed portion FU via the beam BM is formed in the MEMS layer ML, and a plurality of openings are formed in the mass body MS so as to penetrate the mass body MS. OP is formed. In particular, in FIG. 11, the planar shape of each of the plurality of openings OP is a hole shape HL. As described above, the planar layout configuration of the MEMS layer ML can adopt not only the planar layout configuration shown in FIG. 10 but also the planar layout configuration shown in FIG.
　ここで、前記実施の形態１だけでなく、本実施の形態２でも、質量体ＭＳに複数の開口部ＯＰを設けて、空気抵抗を低減し、かつ、質量体ＭＳを大気圧よりも充分に低い圧力で封止している。これにより、本実施の形態２でも、機械雑音を低減することができる。 Here, not only in the first embodiment but also in the second embodiment, the mass body MS is provided with a plurality of openings OP to reduce the air resistance, and the mass body MS is sufficiently more than the atmospheric pressure. Sealed with low pressure. Thereby, mechanical noise can also be reduced in the second embodiment.
　具体的に、図１２は、封止圧力と機械雑音との関係を示すグラフである。図１２において、横軸は封止圧力（Ｐａ）を示しており、縦軸は機械雑音（ｎｇ／√Ｈｚ）を示している。図１２には、質量体に開口部を設けない構成（（ａ）穴なし）に対応したグラフと、質量体に粗いスリット状の開口部を設けた構成（（ｂ）スリット粗）に対応したグラフと、質量体に密なスリット状の開口部を設けた構成（（ｃ）スリット密）に対応したグラフと、質量体にホール状の開口部を設けた構成（（ｄ）ホール）に対応したグラフとが示されている。図１２に示すように、封止圧力を小さくするほど、機械雑音が小さくなることがわかる。また、質量体に設けられる開口部の形状によっても機械雑音が変化することがわかる。例えば、開口部が存在しない場合、封止圧力が１（Ｐａ）のとき、機械雑音は約２００（ｎｇ／√Ｈｚ）となる一方、開口部が存在する場合、封止圧力が１（Ｐａ）のとき、機械雑音は約２０（ｎｇ／√Ｈｚ）となることがわかる。したがって、前記実施の形態１だけでなく、本実施の形態２でも、質量体ＭＳに複数の開口部ＯＰを設けるとともに、質量体ＭＳを大気圧よりも充分に低い圧力で封止している。 Specifically, FIG. 12 is a graph showing the relationship between sealing pressure and mechanical noise. In FIG. 12, the horizontal axis represents the sealing pressure (Pa), and the vertical axis represents the mechanical noise (ng / √Hz). FIG. 12 corresponds to a graph corresponding to a configuration in which no opening is provided in the mass body ((a) no hole) and a configuration in which a rough slit-like opening is provided in the mass ((b) rough slit). Corresponding to the graph, the configuration corresponding to the configuration in which the mass body is provided with a dense slit-shaped opening ((c) slit dense), and the configuration in which the mass body is provided with a hole-shaped opening ((d) hole) The graph is shown. As shown in FIG. 12, it can be seen that the mechanical noise decreases as the sealing pressure decreases. It can also be seen that the mechanical noise varies depending on the shape of the opening provided in the mass body. For example, when there is no opening, the mechanical noise is about 200 (ng / √Hz) when the sealing pressure is 1 (Pa), while when the opening is present, the sealing pressure is 1 (Pa). It can be seen that the mechanical noise is about 20 (ng / √Hz). Therefore, not only in the first embodiment but also in the second embodiment, the mass body MS is provided with a plurality of openings OP, and the mass body MS is sealed at a pressure sufficiently lower than the atmospheric pressure.
　これにより、前記実施の形態１および本実施の形態２において、機械雑音を低減することができ、この結果、Ｓ／Ｎ比を向上することができる。すなわち、前記実施の形態１だけでなく本実施の形態２においても、加速度の検出感度を向上させることができる。つまり、本実施の形態２においても、質量体ＭＳのステッキングおよび固定電極ＦＥへのエッチングダメージという副作用を招くことなく、加速度の検出感度を向上できる。 Thereby, in the first embodiment and the second embodiment, mechanical noise can be reduced, and as a result, the S / N ratio can be improved. That is, the acceleration detection sensitivity can be improved not only in the first embodiment but also in the second embodiment. That is, also in the second embodiment, the acceleration detection sensitivity can be improved without incurring the side effect of sticking the mass body MS and etching damage to the fixed electrode FE.
　（実施の形態３）
　＜加速度センサの断面構成＞
　本実施の形態３では、前記実施の形態１における加速度センサＡＳ１の変形例について説明する。図１３は、本実施の形態３における加速度センサＡＳ１の断面構成を示す図であり、前記実施の形態１を示す図２に対応した図である。図１３において、本実施の形態３における加速度センサＡＳ１でも、ベース層ＢＬ上に固定電極ＦＥ１が形成され、この固定電極ＦＥ１上に複数の保護部ＰＵ１が形成されている。そして、ｚ方向から見た平面視において、複数の保護部ＰＵ１のそれぞれは、複数の保護部ＰＵ１のそれぞれに対応した開口部ＯＰを内包するように形成されている。さらに、本実施の形態３における加速度センサＡＳ１では、図１３に示すように、キャップ層ＣＬの下面に、固定電極ＦＥ３が形成され、かつ、質量体ＭＳと対向する固定電極ＦＥ３の対向面には、複数の開口部ＯＰのそれぞれに対応した複数の保護部ＰＵ３のそれぞれが形成されている。そして、ｚ方向から見た平面視において、複数の保護部ＰＵ３のそれぞれは、複数の保護部ＰＵ３のそれぞれに対応した開口部ＯＰを内包するように形成されている。 (Embodiment 3)
<Cross-sectional configuration of acceleration sensor>
In the third embodiment, a modification of the acceleration sensor AS1 in the first embodiment will be described. FIG. 13 is a diagram illustrating a cross-sectional configuration of the acceleration sensor AS1 according to the third embodiment, and corresponds to FIG. 2 illustrating the first embodiment. In FIG. 13, also in the acceleration sensor AS1 according to the third embodiment, a fixed electrode FE1 is formed on the base layer BL, and a plurality of protective portions PU1 are formed on the fixed electrode FE1. And in the planar view seen from the z direction, each of the plurality of protection parts PU1 is formed so as to include the opening OP corresponding to each of the plurality of protection parts PU1. Furthermore, in the acceleration sensor AS1 according to the third embodiment, as shown in FIG. 13, the fixed electrode FE3 is formed on the lower surface of the cap layer CL, and the fixed surface of the fixed electrode FE3 facing the mass body MS is formed on the opposite surface. Each of the plurality of protection units PU3 corresponding to each of the plurality of openings OP is formed. And in the planar view seen from z direction, each of several protection part PU3 is formed so that the opening part OP corresponding to each of several protection part PU3 may be included.
　これにより、本実施の形態３によれば、固定電極ＦＥ３の表面に凹凸形状が形成される点に起因して質量体ＭＳと保護部ＰＵ３との接触面積が低減される点と、複数の保護部ＰＵ３のそれぞれが、対応する開口部ＯＰを内包するように設けられていることになる。この結果、本実施の形態３によれば、ベース層ＢＬに設けられている固定電極ＦＥ１へのステッキングを抑制できるだけでなく、キャップ層ＣＬに設けられている固定電極ＦＥ３へのステッキングも抑制することができる。 Thus, according to the third embodiment, the contact area between the mass body MS and the protection unit PU3 is reduced due to the formation of the uneven shape on the surface of the fixed electrode FE3, and a plurality of protections. Each of the parts PU3 is provided so as to include the corresponding opening OP. As a result, according to the third embodiment, not only can the sticking to the fixed electrode FE1 provided in the base layer BL be suppressed, but also the sticking to the fixed electrode FE3 provided in the cap layer CL can be suppressed. can do.
　ここで、ベース層ＢＬに設けられている固定電極ＦＥ１においては、ステッキングの抑制だけでなく、ベース層ＢＬの上方に配置されるＭＥＭＳ層ＭＬをドライエッチングする工程でのエッチングダメージを受けることも考慮して、複数の保護部ＰＵ１を設計する必要がある。これに対し、キャップ層ＣＬに設けられている固定電極ＦＥ３は、ＭＥＭＳ層ＭＬを形成した後に、キャップ層ＣＬとともにＭＥＭＳ層ＭＬに接合される。したがって、固定電極ＦＥ３においては、エッチングダメージを考慮する必要はなくなる。つまり、キャップ層ＣＬに設けられる固定電極ＦＥ３上に形成される複数の保護部ＰＵ３は、エッチングダメージを考慮することなく、ステッキングを抑制する観点から設計することができる。例えば、ステッキングを抑制する観点からは、ｚ方向から見た平面視において、複数の保護部ＰＵ３のそれぞれが、複数の保護部ＰＵ３のそれぞれに対応した開口部ＯＰを内包するように形成されていればよく、この条件の範囲内で、なるべく、複数の保護部ＰＵ３の平面サイズを小さくすることが望ましい。なぜなら、この構成によれば、質量体ＭＳに想定外の大きな変位が生じても、キャップ層ＣＬに設けられている固定電極ＦＥ３（詳細には、保護部ＰＵ３）と質量体ＭＳとの接触面積が低減される結果、ステッキングを効果的に抑制することができるからである。 Here, in the fixed electrode FE1 provided in the base layer BL, not only suppression of sticking but also etching damage in the step of dry etching the MEMS layer ML disposed above the base layer BL may be received. It is necessary to design a plurality of protection units PU1 in consideration. On the other hand, the fixed electrode FE3 provided in the cap layer CL is joined to the MEMS layer ML together with the cap layer CL after forming the MEMS layer ML. Therefore, it is not necessary to consider etching damage in the fixed electrode FE3. That is, the plurality of protection portions PU3 formed on the fixed electrode FE3 provided in the cap layer CL can be designed from the viewpoint of suppressing sticking without considering etching damage. For example, from the viewpoint of suppressing sticking, each of the plurality of protection units PU3 is formed so as to include an opening OP corresponding to each of the plurality of protection units PU3 in a plan view viewed from the z direction. It is only necessary to reduce the planar size of the plurality of protection units PU3 as much as possible within the range of this condition. This is because, according to this configuration, even if an unexpected large displacement occurs in the mass body MS, the contact area between the fixed electrode FE3 (specifically, the protection unit PU3) provided in the cap layer CL and the mass body MS. This is because sticking can be effectively suppressed as a result.
　＜実施の形態３における加速度センサのさらなる利点＞
　本実施の形態３における加速度センサＡＳ１は、図１３に示すように、固定電極ＦＥ１と質量体ＭＳからなる第１可変容量と、固定電極ＦＥ３と質量体ＭＳからなる第２可変容量とを備えている。このとき、本実施の形態３における加速度センサＡＳ１では、ｚ方向の加速度が印加された場合の第１可変容量の容量変化と第２可変容量の容量変化とが逆特性となる。すなわち、第１可変容量の静電容量が増加する場合、第２可変容量の静電容量が減少する一方、第１可変容量の静電容量が減少する場合、第２可変容量の静電容量が増加する。この結果、本実施の形態３における加速度センサＡＳ１によれば、以下に示す利点を得ることができる。 <Additional Advantage of Acceleration Sensor in Embodiment 3>
As shown in FIG. 13, the acceleration sensor AS1 according to the third embodiment includes a first variable capacitor including a fixed electrode FE1 and a mass body MS, and a second variable capacitor including a fixed electrode FE3 and the mass body MS. Yes. At this time, in the acceleration sensor AS1 according to the third embodiment, the capacitance change of the first variable capacitor and the capacitance change of the second variable capacitor when the acceleration in the z direction is applied have opposite characteristics. That is, when the capacitance of the first variable capacitor increases, the capacitance of the second variable capacitor decreases, while when the capacitance of the first variable capacitor decreases, the capacitance of the second variable capacitor decreases. To increase. As a result, according to the acceleration sensor AS1 in the third embodiment, the following advantages can be obtained.
　例えば、第１入力端子と第２入力端子との間に第１可変容量と第２可変容量とを直列接続し、第１可変容量と第２可変容量との接続部分（接続ノード）にＣＶ変換部を接続する構成を考える。まず、第１入力端子と第２入力端子に、それぞれ１８０°位相の異なる逆位相の変調信号を印加する。ここで、本実施の形態３では、加速度が印加されていない場合の第１可変容量の静電容量を「Ｃ」とし、加速度が印加されていない場合の第２可変容量の静電容量を「Ｃ」とすることができる。なぜなら、本実施の形態３によれば、第１可変容量と第２可変容量とにおいて、質量体ＭＳが共通しており、かつ、質量体ＭＳと固定電極ＦＥ１との距離と質量体ＭＳと固定電極ＦＥ３との距離を等しくでき、かつ、固定電極ＦＥ１の平面サイズと固定電極ＦＥ３の平面サイズとを等しく設計することができるからである。そして、加速度が印加された場合、第１可変容量の静電容量が「Ｃ＋ΔＣ」に増加する一方、第２可変容量の静電容量が「Ｃ－ΔＣ」に減少するとする。この場合、第１入力端子と第２入力端子とに互いに逆位相の変調信号（Ｖ）が印加されているため、第１可変容量には、Ｑ１＝（Ｃ＋ΔＣ）Ｖの電荷が蓄積される一方、第２可変容量には、Ｑ２＝－（Ｃ－ΔＣ）Ｖの電荷が蓄積される。したがって、第１可変容量と第２可変容量全体での電荷移動量は、（Ｃ＋ΔＣ）Ｖ－（Ｃ－ΔＣ）Ｖ＝２ΔＣＶとなる。つまり、第１入力端子と第２入力端子とに互いに逆位相の変調信号が印加されている場合には、第１可変容量の静電容量「Ｃ」と第２可変容量の静電容量を「Ｃ」とがキャンセルされて、電荷移動量には、加速度に起因する容量変化２ΔＣの成分だけが含まれることになる。この結果、電荷移動量において、加速度に起因する容量変化（２ΔＣ）とは無関係な静電容量「Ｃ」の影響を排除することができる。この結果、信号には、加速度に起因する容量変化（２ΔＣ）の成分だけが含まれることになる。これにより、本実施の形態３における加速度センサＡＳ１によれば、加速度の検出感度を向上することができる。 For example, a first variable capacitor and a second variable capacitor are connected in series between a first input terminal and a second input terminal, and CV conversion is performed at a connection portion (connection node) between the first variable capacitor and the second variable capacitor. Consider a configuration that connects the parts. First, opposite-phase modulation signals having a phase difference of 180 ° are applied to the first input terminal and the second input terminal, respectively. Here, in the third embodiment, the capacitance of the first variable capacitance when no acceleration is applied is “C”, and the capacitance of the second variable capacitance when no acceleration is applied is “C”. C ". This is because, according to the third embodiment, the mass body MS is common to the first variable capacitor and the second variable capacitor, and the distance between the mass body MS and the fixed electrode FE1 and the mass body MS are fixed. This is because the distance from the electrode FE3 can be made equal, and the plane size of the fixed electrode FE1 and the plane size of the fixed electrode FE3 can be designed to be equal. When acceleration is applied, the capacitance of the first variable capacitance increases to “C + ΔC”, while the capacitance of the second variable capacitance decreases to “C−ΔC”. In this case, since the modulation signals (V) having opposite phases to each other are applied to the first input terminal and the second input terminal, the charge of Q1 = (C + ΔC) V is stored in the first variable capacitor. In the second variable capacitor, a charge of Q2 = − (C−ΔC) V is accumulated. Therefore, the amount of charge transfer in the entire first variable capacitor and second variable capacitor is (C + ΔC) V− (C−ΔC) V = 2ΔCV. That is, when modulation signals having opposite phases are applied to the first input terminal and the second input terminal, the capacitance “C” of the first variable capacitor and the capacitance of the second variable capacitor are set to “ “C” is canceled, and the charge transfer amount includes only the component of the capacitance change 2ΔC caused by the acceleration. As a result, it is possible to eliminate the influence of the capacitance “C” that is unrelated to the capacitance change (2ΔC) caused by the acceleration in the amount of charge transfer. As a result, the signal includes only the component of capacitance change (2ΔC) caused by acceleration. Thereby, according to acceleration sensor AS1 in this Embodiment 3, the detection sensitivity of an acceleration can be improved.
　（実施の形態４）（シーソ構造）
　＜加速度センサの断面構成＞
　次に、本実施の形態４における加速度センサＡＳ２について説明する。図１４は、本実施の形態４における加速度センサＡＳ２の一断面を示す断面図である。図１４において、ベース層ＢＬ上には、互いに離間して固定電極ＦＥ１および固定電極ＦＥ２が配置されている。そして、固定電極ＦＥ１の表面に互いに離間して複数の保護部ＰＵ１が形成され、かつ、固定電極ＦＥ２の表面にも互いに離間して複数の保護部ＰＵ２が形成されている。 (Embodiment 4) (Seesaw structure)
<Cross-sectional configuration of acceleration sensor>
Next, the acceleration sensor AS2 in the fourth embodiment will be described. FIG. 14 is a cross-sectional view showing one cross section of the acceleration sensor AS2 in the fourth embodiment. In FIG. 14, the fixed electrode FE1 and the fixed electrode FE2 are disposed on the base layer BL so as to be spaced apart from each other. A plurality of protection portions PU1 are formed on the surface of the fixed electrode FE1 so as to be separated from each other, and a plurality of protection portions PU2 are also formed on the surface of the fixed electrode FE2 so as to be separated from each other.
　続いて、図１４に示すように、ベース層ＢＬの上方には、ＭＥＭＳ層ＭＬが配置されている。このＭＥＭＳ層ＭＬは、ＭＥＭＳ層ＭＬを加工することにより形成された固定部ＦＵが形成されており、この固定部ＦＵとベース層ＢＬとを接合することにより、ＭＥＭＳ層ＭＬがベース層ＢＬの上方に配置されることになる。そして、このＭＥＭＳ層ＭＬには、質量体ＭＳ１が形成され、質量体ＭＳ１は、ベース層ＢＬに形成された固定電極ＦＥ１と対向する位置に配置される。同様に、本実施の形態４では、ＭＥＭＳ層ＭＬに質量体ＭＳ２が形成され、質量体ＭＳ２は、ベース層ＢＬに形成された固定電極ＦＥ２と対向する位置に配置される。これらの質量体ＭＳ１および質量体ＭＳ２は、梁（図示せず）を介して、固定部ＦＵと接続されている。すなわち、質量体ＭＳ１および質量体ＭＳ２のそれぞれは、梁によって懸架されている。 Subsequently, as shown in FIG. 14, the MEMS layer ML is disposed above the base layer BL. The MEMS layer ML has a fixed portion FU formed by processing the MEMS layer ML, and the MEMS layer ML is located above the base layer BL by bonding the fixed portion FU and the base layer BL. Will be placed. The mass body MS1 is formed in the MEMS layer ML, and the mass body MS1 is disposed at a position facing the fixed electrode FE1 formed in the base layer BL. Similarly, in the fourth embodiment, the mass body MS2 is formed in the MEMS layer ML, and the mass body MS2 is disposed at a position facing the fixed electrode FE2 formed in the base layer BL. The mass body MS1 and the mass body MS2 are connected to the fixed portion FU via a beam (not shown). That is, each of mass body MS1 and mass body MS2 is suspended by the beam.
　さらに、質量体ＭＳ１には、図１４に示すように、質量体ＭＳ１を貫通する複数の開口部ＯＰ１が形成されている。これらの複数の開口部ＯＰ１は、固定電極ＦＥ１上に形成された複数の保護部ＰＵ１に対応するように設けられている。すなわち、複数の開口部ＯＰ１のそれぞれに対応するように保護部ＰＵ１が設けられている。 Furthermore, as shown in FIG. 14, a plurality of openings OP1 penetrating the mass body MS1 are formed in the mass body MS1. The plurality of openings OP1 are provided so as to correspond to the plurality of protection units PU1 formed on the fixed electrode FE1. That is, the protection part PU1 is provided so as to correspond to each of the plurality of openings OP1.
　同様に、質量体ＭＳ２には、図１４に示すように、質量体ＭＳ２を貫通する複数の開口部ＯＰ２が形成されている。これらの複数の開口部ＯＰ２は、固定電極ＦＥ２上に形成された複数の保護部ＰＵ２に対応するように設けられている。すなわち、複数の開口部ＯＰ２のそれぞれに対応するように保護部ＰＵ２が設けられている。 Similarly, a plurality of openings OP2 penetrating the mass body MS2 are formed in the mass body MS2, as shown in FIG. The plurality of openings OP2 are provided so as to correspond to the plurality of protection units PU2 formed on the fixed electrode FE2. That is, the protection part PU2 is provided so as to correspond to each of the plurality of openings OP2.
　そして、質量体ＭＳ１は、可動電極ＶＥ１としても機能する。すなわち、本実施の形態４における加速度センサＡＳ２では、ベース層ＢＬ上に形成された固定電極ＦＥ１と、ＭＥＭＳ層ＭＬに形成された質量体ＭＳ１（可動電極ＶＥ１）とによって、静電容量が形成されることになる。同様に、質量体ＭＳ２は、可動電極ＶＥ２としても機能する。すなわち、本実施の形態４における加速度センサＡＳ２では、ベース層ＢＬ上に形成された固定電極ＦＥ２と、ＭＥＭＳ層ＭＬに形成された質量体ＭＳ２（可動電極ＶＥ２）とによって、静電容量が形成されることになる。 The mass body MS1 also functions as the movable electrode VE1. That is, in the acceleration sensor AS2 in the fourth embodiment, a capacitance is formed by the fixed electrode FE1 formed on the base layer BL and the mass body MS1 (movable electrode VE1) formed on the MEMS layer ML. Will be. Similarly, the mass body MS2 also functions as the movable electrode VE2. That is, in the acceleration sensor AS2 in the fourth embodiment, a capacitance is formed by the fixed electrode FE2 formed on the base layer BL and the mass body MS2 (movable electrode VE2) formed on the MEMS layer ML. Will be.
　次に、図１４に示すように、ＭＥＭＳ層ＭＬ上には、キャップ層ＣＬが配置されている。この結果、ＭＥＭＳ層ＭＬは、断面視において、ベース層ＢＬとキャップ層ＣＬで挟まれることになり、ＭＥＭＳ層ＭＬに形成されている質量体ＭＳ１は、ベース層ＢＬと固定部ＦＵとキャップ層ＣＬとで囲まれる空洞部ＣＡＶ１の内部に配置されることになる。同様に、ＭＥＭＳ層ＭＬに形成されている質量体ＭＳ２は、ベース層ＢＬと固定部ＦＵとキャップ層ＣＬとで囲まれる空洞部ＣＡＶ２の内部に配置されることになる。このとき、空洞部ＣＡＶ１および空洞部ＣＡＶ２の内部には気体が充填されており、空洞部ＣＡＶ１および空洞部ＣＡＶ２の内部の圧力は、例えば、大気圧よりも充分に低い圧力となっている。 Next, as shown in FIG. 14, the cap layer CL is disposed on the MEMS layer ML. As a result, the MEMS layer ML is sandwiched between the base layer BL and the cap layer CL in a cross-sectional view, and the mass body MS1 formed in the MEMS layer ML includes the base layer BL, the fixed portion FU, and the cap layer CL. It is arrange | positioned inside the cavity part CAV1 enclosed by these. Similarly, the mass body MS2 formed in the MEMS layer ML is disposed inside the cavity CAV2 surrounded by the base layer BL, the fixing part FU, and the cap layer CL. At this time, the inside of the cavity CAV1 and the cavity CAV2 is filled with gas, and the pressure inside the cavity CAV1 and the cavity CAV2 is, for example, a pressure sufficiently lower than the atmospheric pressure.
　そして、質量体ＭＳ１の質量は、質量体ＭＳ２の質量よりも重くなっている。具体的には、複数の開口部ＯＰ１のそれぞれの平面サイズは、複数の開口部ＯＰ２のそれぞれの平面サイズよりも小さく、かつ、複数の保護部ＰＵ１のそれぞれの平面サイズは、複数の保護部ＰＵ２のそれぞれの平面サイズよりも小さくなっている。これにより、質量体ＭＳ１と質量体ＭＳ２との間に質量差が生じる結果、例えば、＋ｚ方向に加速度が印加されると、重い質量体ＭＳ１が－ｚ方向に変位する一方、軽い質量体ＭＳ２が＋ｚ方向に変位して、本実施の形態４における加速度センサＡＳ２は、「シーソ動作」をすることになる。 And the mass of the mass body MS1 is heavier than the mass of the mass body MS2. Specifically, each plane size of the plurality of openings OP1 is smaller than each plane size of the plurality of openings OP2, and each plane size of the plurality of protection units PU1 is equal to the plurality of protection units PU2. It is smaller than each plane size. As a result, a mass difference is generated between the mass body MS1 and the mass body MS2. As a result, for example, when acceleration is applied in the + z direction, the heavy mass body MS1 is displaced in the −z direction, while the light mass body MS2 is displaced. By displacing in the + z direction, the acceleration sensor AS2 in the fourth embodiment performs a “seesaw operation”.
　ここで、本実施の形態４においても、ｚ方向から見た平面視において、複数の保護部ＰＵ１のそれぞれは、複数の保護部ＰＵのそれぞれに対応した開口部ＯＰを内包し、かつ、複数の保護部ＰＵ２のそれぞれは、複数の保護部ＰＵ２のそれぞれに対応した開口部ＯＰ２を内包している。これにより、本実施の形態４によれば、前記実施の形態１と同様のメカニズムによって、質量体ＭＳ１および質量体ＭＳ２のステッキング並びに固定電極ＦＥ１および固定電極ＦＥ２へのエッチングダメージを抑制することができる。 Here, also in the fourth embodiment, each of the plurality of protection units PU1 includes an opening OP corresponding to each of the plurality of protection units PU in a plan view viewed from the z direction, and Each of the protection parts PU2 includes an opening OP2 corresponding to each of the plurality of protection parts PU2. Thereby, according to the fourth embodiment, the same mechanism as in the first embodiment can suppress the sticking of the mass body MS1 and the mass body MS2 and the etching damage to the fixed electrode FE1 and the fixed electrode FE2. it can.
　以上のことから、本実施の形態４においても、副作用を考慮することなく、重力加速度よりも小さな加速度を高感度に検出するために、加速度センサＡＳ２の質量体ＭＳ１の質量および質量体ＭＳ２の質量を大きくし、かつ、梁のバネ定数を小さくすることができる。さらに、機械雑音を低減するために、質量体ＭＳ１に複数の開口部ＯＰ１を設けることができるとともに、質量体ＭＳ２に複数の開口部ＯＰ２を設けることができる。すなわち、本実施の形態４においても、ステッキングおよびエッチングダメージという副作用を効果的に抑制しながら、加速度センサＡＳ２の検出感度を向上することができるという優れた効果を得ることができる。 From the above, also in the fourth embodiment, the mass of the mass body MS1 and the mass of the mass body MS2 of the acceleration sensor AS2 are detected with high sensitivity in order to detect an acceleration smaller than the gravitational acceleration without considering side effects. And the spring constant of the beam can be reduced. Furthermore, in order to reduce mechanical noise, the mass body MS1 can be provided with a plurality of openings OP1, and the mass body MS2 can be provided with a plurality of openings OP2. That is, also in the fourth embodiment, it is possible to obtain an excellent effect that the detection sensitivity of the acceleration sensor AS2 can be improved while effectively suppressing the side effects of sticking and etching damage.
　＜実施の形態４における加速度センサの利点＞
　本実施の形態４における加速度センサＡＳ２は、図１４に示すように、固定電極ＦＥ１と質量体ＭＳ１からなる第１可変容量と、固定電極ＦＥ２と質量体ＭＳ２からなる第２可変容量とを備えている。このとき、本実施の形態４における加速度センサＡＳ２が「シーソ構造」をしており、ｚ方向の加速度が印加された場合の第１可変容量の容量変化と第２可変容量の容量変化とが逆特性となる。すなわち、第１可変容量の静電容量が増加する場合、第２可変容量の静電容量が減少する一方、第１可変容量の静電容量が減少する場合、第２可変容量の静電容量が増加する。この結果、本実施の形態４における加速度センサＡＳ２によれば、以下に示す利点を得ることができる。 <Advantages of the acceleration sensor in the fourth embodiment>
As shown in FIG. 14, the acceleration sensor AS2 in the fourth embodiment includes a first variable capacitor composed of a fixed electrode FE1 and a mass body MS1, and a second variable capacitor composed of a fixed electrode FE2 and a mass body MS2. Yes. At this time, the acceleration sensor AS2 in the fourth embodiment has a “seesaw structure”, and the capacitance change of the first variable capacitor and the capacitance change of the second variable capacitor when the acceleration in the z direction is applied are reversed. It becomes a characteristic. That is, when the capacitance of the first variable capacitor increases, the capacitance of the second variable capacitor decreases, while when the capacitance of the first variable capacitor decreases, the capacitance of the second variable capacitor decreases. To increase. As a result, according to the acceleration sensor AS2 in the fourth embodiment, the following advantages can be obtained.
　例えば、第１入力端子と第２入力端子との間に第１可変容量と第２可変容量とを直列接続し、第１可変容量と第２可変容量との接続部分（接続ノード）にＣＶ変換部を接続する構成を考える。まず、第１入力端子と第２入力端子に、それぞれ１８０°位相の異なる逆位相の変調信号を印加する。ここで、加速度が印加されていない場合の第１可変容量の静電容量を「Ｃ１」とし、加速度が印加されていない場合の第２可変容量の静電容量を「Ｃ２」とする。そして、加速度が印加された場合、第１可変容量の静電容量が「Ｃ１＋ΔＣ１」に増加する一方、第２可変容量の静電容量が「Ｃ２－ΔＣ２」に減少するとする。この場合、第１入力端子と第２入力端子とに互いに逆位相の変調信号（Ｖ）が印加されているため、第１可変容量には、Ｑ１＝（Ｃ１＋ΔＣ１）Ｖの電荷が蓄積される一方、第２可変容量には、Ｑ２＝－（Ｃ２－ΔＣ２）Ｖの電荷が蓄積される。したがって、第１可変容量と第２可変容量全体での電荷移動量は、（Ｃ１＋ΔＣ１）Ｖ－（Ｃ２－ΔＣ２）Ｖ＝（Ｃ１－Ｃ２）Ｖ＋（ΔＣ１＋ΔＣ２）Ｖとなる。つまり、第１入力端子と第２入力端子とに互いに逆位相の変調信号が印加されている場合には、第１可変容量の静電容量「Ｃ１」と第２可変容量の静電容量を「Ｃ２」とが差分されて、電荷移動量には、加速度に起因する容量変化（ΔＣ１＋ΔＣ２）の成分の割合が大きくなる。この結果、電荷移動量において、加速度に起因する容量変化（ΔＣ１＋ΔＣ２）とは無関係な静電容量「Ｃ１」や静電容量「Ｃ２」の影響が低減される（Ｃ１－Ｃ２となる）。この結果、信号に含まれる加速度に起因する容量変化（ΔＣ１＋ΔＣ２）の成分を大きくすることができる。これにより、本実施の形態４における加速度センサＡＳ２によれば、加速度の検出感度を向上することができるのである。 For example, a first variable capacitor and a second variable capacitor are connected in series between a first input terminal and a second input terminal, and CV conversion is performed at a connection portion (connection node) between the first variable capacitor and the second variable capacitor. Consider a configuration that connects the parts. First, opposite-phase modulation signals having a phase difference of 180 ° are applied to the first input terminal and the second input terminal, respectively. Here, the capacitance of the first variable capacitor when no acceleration is applied is “C1”, and the capacitance of the second variable capacitor when no acceleration is applied is “C2”. When acceleration is applied, the capacitance of the first variable capacitor increases to “C1 + ΔC1,” while the capacitance of the second variable capacitor decreases to “C2−ΔC2.” In this case, since the modulation signals (V) having opposite phases to each other are applied to the first input terminal and the second input terminal, the charge of Q1 = (C1 + ΔC1) V is accumulated in the first variable capacitor. In the second variable capacitor, a charge of Q2 = − (C2−ΔC2) V is accumulated. Accordingly, the amount of charge transfer in the first variable capacitor and the second variable capacitor as a whole is (C1 + ΔC1) V− (C2−ΔC2) V = (C1−C2) V + (ΔC1 + ΔC2) V. That is, when modulation signals having opposite phases are applied to the first input terminal and the second input terminal, the capacitance “C1” of the first variable capacitor and the capacitance of the second variable capacitor are expressed as “ As a result, the ratio of the component of the capacitance change (ΔC1 + ΔC2) caused by the acceleration is increased in the charge transfer amount. As a result, the influence of the capacitance “C1” and the capacitance “C2” unrelated to the capacitance change (ΔC1 + ΔC2) due to acceleration is reduced in the amount of charge transfer (becomes C1-C2). As a result, the component of capacitance change (ΔC1 + ΔC2) caused by the acceleration included in the signal can be increased. Thereby, according to acceleration sensor AS2 in this Embodiment 4, the detection sensitivity of an acceleration can be improved.
　＜加速度センサの平面構成＞
　＜＜ベース層の平面構成＞＞
　図１５は、本実施の形態４における加速度センサの一部を構成するベース層ＢＬの平面レイアウト構成を示す平面図である。図１５のＡ－Ａ線での断面が図１４のベース層ＢＬに対応する。図１５において、ベース層ＢＬは、矩形形状をしており、ベース層ＢＬの中央部に固定部ＦＵが形成されている。そして、ベース層ＢＬの中央部から左側の領域に固定電極ＦＥ１とサーボ電極ＳＥ１Ａとサーボ電極ＳＥ２Ａとが形成されている。具体的には、図１５に示すように、ｙ方向に並ぶように、サーボ電極ＳＥ１Ａと固定電極ＦＥ１とサーボ電極ＳＥ２Ａとが配置され、かつ、平面視において、サーボ電極ＳＥ１Ａとサーボ電極ＳＥ２Ａとに挟まれるように、固定電極ＦＥ１が配置されている。そして、固定電極ＦＥ１上には、複数の保護部ＰＵ１が形成されているとともに、サーボ電極ＳＥ１Ａおよびサーボ電極ＳＥ２Ａ上にも、複数の保護部ＰＵ１が形成されている。これにより、互いに離間した複数の保護部ＰＵ１を固定電極ＦＥ１の表面に設けて、固定電極ＦＥ１の表面に凹凸形状を設けるという特徴点が実現されることになる。さらに、本実施の形態４でも、固定電極ＦＥ１だけでなく、サーボ電極ＳＥ１Ａおよびサーボ電極ＳＥ２Ａにおいても、互いに離間した複数の保護部ＰＵ１をサーボ電極ＳＥ１Ａおよびサーボ電極ＳＥ２Ａの表面に設けて、サーボ電極ＳＥ１Ａおよびサーボ電極ＳＥ２Ａの表面に凹凸形状を設けている。このため、サーボ電極ＳＥ１Ａおよびサーボ電極ＳＥ２Ａにおいても、上述した特徴点が実現される。 <Planar configuration of acceleration sensor>
<< Planar structure of base layer >>
FIG. 15 is a plan view showing a planar layout configuration of the base layer BL constituting a part of the acceleration sensor according to the fourth embodiment. A section taken along line AA in FIG. 15 corresponds to the base layer BL in FIG. In FIG. 15, the base layer BL has a rectangular shape, and a fixed portion FU is formed at the center of the base layer BL. A fixed electrode FE1, a servo electrode SE1A, and a servo electrode SE2A are formed in the left region from the center of the base layer BL. Specifically, as shown in FIG. 15, the servo electrode SE1A, the fixed electrode FE1, and the servo electrode SE2A are arranged so as to be aligned in the y direction, and are arranged on the servo electrode SE1A and the servo electrode SE2A in a plan view. The fixed electrode FE1 is disposed so as to be sandwiched. A plurality of protection portions PU1 are formed on the fixed electrode FE1, and a plurality of protection portions PU1 are also formed on the servo electrode SE1A and the servo electrode SE2A. Thereby, the feature point that the plurality of protection parts PU1 spaced apart from each other is provided on the surface of the fixed electrode FE1 and the uneven shape is provided on the surface of the fixed electrode FE1 is realized. Further, also in the fourth embodiment, not only the fixed electrode FE1, but also the servo electrode SE1A and the servo electrode SE2A, a plurality of protection portions PU1 that are spaced apart from each other are provided on the surfaces of the servo electrode SE1A and the servo electrode SE2A. Concave and convex shapes are provided on the surfaces of SE1A and servo electrode SE2A. For this reason, the above-described feature points are also realized in the servo electrode SE1A and the servo electrode SE2A.
　一方、ベース層ＢＬの中央部から右側の領域に固定電極ＦＥ２とサーボ電極ＳＥ１Ｂとサーボ電極ＳＥ２Ｂとが形成されている。具体的には、図１５に示すように、ｙ方向に並ぶように、サーボ電極ＳＥ１Ｂと固定電極ＦＥ２とサーボ電極ＳＥ２Ｂとが配置され、かつ、平面視において、サーボ電極ＳＥ１Ｂとサーボ電極ＳＥ２Ｂとに挟まれるように、固定電極ＦＥ２が配置されている。そして、固定電極ＦＥ２上には、複数の保護部ＰＵ２が形成されているとともに、サーボ電極ＳＥ１Ｂおよびサーボ電極ＳＥ２Ｂ上にも、複数の保護部ＰＵ２が形成されている。これにより、互いに離間した複数の保護部ＰＵ２を固定電極ＦＥ２の表面に設けて、固定電極ＦＥ２の表面に凹凸形状を設けるという特徴点が実現されることになる。さらに、本実施の形態４でも、固定電極ＦＥ２だけでなく、サーボ電極ＳＥ１Ｂおよびサーボ電極ＳＥ２Ｂにおいても、互いに離間した複数の保護部ＰＵ２をサーボ電極ＳＥ１Ｂおよびサーボ電極ＳＥ２Ｂの表面に設けて、サーボ電極ＳＥ１Ｂおよびサーボ電極ＳＥ２Ｂの表面に凹凸形状を設けている。このため、サーボ電極ＳＥ１Ｂおよびサーボ電極ＳＥ２Ｂにおいても、上述した特徴点が実現される。 On the other hand, a fixed electrode FE2, a servo electrode SE1B, and a servo electrode SE2B are formed in a region on the right side from the center of the base layer BL. Specifically, as shown in FIG. 15, the servo electrode SE1B, the fixed electrode FE2, and the servo electrode SE2B are arranged so as to be aligned in the y direction, and the servo electrode SE1B and the servo electrode SE2B are arranged in a plan view. The fixed electrode FE2 is disposed so as to be sandwiched. A plurality of protection portions PU2 are formed on the fixed electrode FE2, and a plurality of protection portions PU2 are also formed on the servo electrode SE1B and the servo electrode SE2B. Thereby, the feature point that the plurality of protection parts PU2 spaced apart from each other is provided on the surface of the fixed electrode FE2, and the uneven shape is provided on the surface of the fixed electrode FE2. Further, also in the fourth embodiment, not only the fixed electrode FE2, but also the servo electrode SE1B and the servo electrode SE2B, a plurality of protection portions PU2 that are spaced apart from each other are provided on the surfaces of the servo electrode SE1B and the servo electrode SE2B. Concave and convex shapes are provided on the surfaces of SE1B and servo electrode SE2B. For this reason, the above-described feature points are also realized in the servo electrode SE1B and the servo electrode SE2B.
　ここで、図１５に示すように、本実施の形態４におけるベース層ＢＬでは、複数の保護部ＰＵ１のそれぞれの平面サイズは、複数の保護部ＰＵ２のそれぞれの平面サイズよりも小さくなっている。以上のようにして、本実施の形態４におけるベース層ＢＬが平面レイアウト構成されていることになる。 Here, as shown in FIG. 15, in the base layer BL according to the fourth embodiment, the respective planar sizes of the plurality of protection units PU1 are smaller than the respective plane sizes of the plurality of protection units PU2. As described above, the base layer BL in the fourth embodiment has a planar layout configuration.
　＜＜ＭＥＭＳ層の平面構成＞＞
　図１６は、本実施の形態４における加速度センサの一部を構成するＭＥＭＳ層ＭＬの平面レイアウト構成を示す平面図である。図１６のＡ－Ａ線での断面が図１４のＭＥＭＳ層ＭＬに対応する。図１６において、ＭＥＭＳ層ＭＬは、矩形形状をしており、ＭＥＭＳ層ＭＬの中央部に固定部ＦＵおよび梁ＢＭが形成されている。そして、中央部の左側の領域に梁ＢＭに懸架された質量体ＭＳ１が形成され、かつ、中央部の右側の領域に梁ＢＭに懸架された質量体ＭＳ２が形成されている。 << Planar structure of MEMS layer >>
FIG. 16 is a plan view showing a planar layout configuration of the MEMS layer ML that constitutes a part of the acceleration sensor according to the fourth embodiment. A section taken along line AA in FIG. 16 corresponds to the MEMS layer ML in FIG. In FIG. 16, the MEMS layer ML has a rectangular shape, and a fixed portion FU and a beam BM are formed at the center of the MEMS layer ML. A mass body MS1 suspended from the beam BM is formed in the left area of the central portion, and a mass body MS2 suspended from the beam BM is formed in the right area of the central portion.
　さらに、質量体ＭＳ１には、複数の開口部ＯＰ１が形成されており、質量体ＭＳ２には、複数の開口部ＯＰ２が形成されている。このとき、複数の開口部ＯＰ１のそれぞれの平面サイズは、複数の開口部ＯＰ２のそれぞれの平面サイズよりも小さくなっている。 Furthermore, a plurality of openings OP1 are formed in the mass body MS1, and a plurality of openings OP2 are formed in the mass body MS2. At this time, each planar size of the plurality of openings OP1 is smaller than each planar size of the plurality of openings OP2.
　ここで、図１５に示すベース層ＢＬと図１６に示すＭＥＭＳ層ＭＬとを平面的に重ねるとわかるように、複数の保護部ＰＵ１のそれぞれの平面サイズは、複数の保護部ＰＵ１のそれぞれに対応した開口部ＯＰ１の平面サイズよりも大きくなっている。言い換えれば、平面視において、複数の保護部ＰＵ１のそれぞれは、複数の保護部ＰＵ１のそれぞれに対応した開口部ＯＰ１を内包するように形成されている。 Here, as seen when the base layer BL shown in FIG. 15 and the MEMS layer ML shown in FIG. 16 are planarly overlapped, the planar size of each of the plurality of protection units PU1 corresponds to each of the plurality of protection units PU1. It is larger than the planar size of the opening OP1. In other words, in plan view, each of the plurality of protection units PU1 is formed so as to include an opening OP1 corresponding to each of the plurality of protection units PU1.
　同様に、複数の保護部ＰＵ２のそれぞれの平面サイズは、複数の保護部ＰＵ２のそれぞれに対応した開口部ＯＰ２の平面サイズよりも大きくなっている。言い換えれば、平面視において、複数の保護部ＰＵ２のそれぞれは、複数の保護部ＰＵ２のそれぞれに対応した開口部ＯＰ２を内包するように形成されている。以上のようにして、本実施の形態４におけるＭＥＭＳ層ＭＬが平面レイアウト構成されていることになる。 Similarly, the plane size of each of the plurality of protection units PU2 is larger than the plane size of the opening OP2 corresponding to each of the plurality of protection units PU2. In other words, in plan view, each of the plurality of protection units PU2 is formed so as to include an opening OP2 corresponding to each of the plurality of protection units PU2. As described above, the MEMS layer ML according to the fourth embodiment has a planar layout configuration.
　＜加速度センサの製造方法＞
　本実施の形態４における加速度センサは、上記のように構成されており、以下に、その製造方法について図面を参照しながら説明する。 <Method for manufacturing acceleration sensor>
The acceleration sensor according to the fourth embodiment is configured as described above, and the manufacturing method thereof will be described below with reference to the drawings.
　まず、図１７に示すように、例えば、シリコンウェハ（半導体基板）からなるベース層ＢＬを用意する。そして、フォトリソグラフィ技術およびエッチング技術を使用することにより、ベース層ＢＬの表面に一対の溝ＤＩＴを形成する。続いて、一対の溝ＤＩＴのそれぞれの底面にポリシリコン膜を成膜した後、フォトリソグラフィ技術およびエッチング技術を使用することにより、一方の溝ＤＩＴの底面に固定電極ＦＥ１を形成し、他方の溝ＤＩＴの底面に固定電極ＦＥ２を形成する。 First, as shown in FIG. 17, for example, a base layer BL made of a silicon wafer (semiconductor substrate) is prepared. Then, a pair of grooves DIT is formed on the surface of the base layer BL by using a photolithography technique and an etching technique. Subsequently, after a polysilicon film is formed on each bottom surface of the pair of grooves DIT, the fixed electrode FE1 is formed on the bottom surface of one groove DIT by using a photolithography technique and an etching technique, and the other groove A fixed electrode FE2 is formed on the bottom surface of the DIT.
　次に、図１８に示すように、固定電極ＦＥ１の表面および固定電極ＦＥ２の表面に、例えば、酸化シリコン膜からなる絶縁膜を形成する。その後、フォトリソグラフィ技術およびエッチング技術を使用することにより、固定電極ＦＥ１の表面に複数の島状の保護部ＰＵ１を形成し、かつ、固定電極ＦＥ２の表面に複数の島状の保護部ＰＵ２を形成する。すなわち、固定電極ＦＥ１の表面には、互いに離間した複数の保護部ＰＵ１が形成され、固定電極ＦＥ２の表面には、互いに離間した複数の保護部ＰＵ２が形成される。このとき、複数の保護部ＰＵ１のそれぞれの平面サイズは、複数の保護部ＰＵ２のそれぞれの平面サイズよりも小さくなるように、保護部ＰＵ１および保護部ＰＵ２が形成される。 Next, as shown in FIG. 18, an insulating film made of, for example, a silicon oxide film is formed on the surface of the fixed electrode FE1 and the surface of the fixed electrode FE2. Thereafter, a plurality of island-shaped protective portions PU1 are formed on the surface of the fixed electrode FE1, and a plurality of island-shaped protective portions PU2 are formed on the surface of the fixed electrode FE2 by using a photolithography technique and an etching technique. To do. That is, a plurality of protection parts PU1 spaced apart from each other are formed on the surface of the fixed electrode FE1, and a plurality of protection parts PU2 spaced apart from each other are formed on the surface of the fixed electrode FE2. At this time, the protection unit PU1 and the protection unit PU2 are formed so that the respective planar sizes of the plurality of protection units PU1 are smaller than the respective plane sizes of the plurality of protection units PU2.
　続いて、図１９に示すように、ベース層ＢＬの表面上に、例えば、シリコンからなるＭＥＭＳ層（ＭＥＭＳ基板）ＭＬを配置し、ウェハ接合技術を使用することにより、ベース層ＢＬとＭＥＭＳ層ＭＬとを接合する。その後、ＭＥＭＳ層ＭＬの表面を研磨する。具体的には、例えば、ＭＥＭＳ層ＭＬの厚さが、約２５０μｍとなるように研磨する。 Subsequently, as shown in FIG. 19, the MEMS layer (MEMS substrate) ML made of, for example, silicon is disposed on the surface of the base layer BL, and the base layer BL and the MEMS layer ML are formed by using a wafer bonding technique. And join. Thereafter, the surface of the MEMS layer ML is polished. Specifically, for example, polishing is performed so that the thickness of the MEMS layer ML is about 250 μm.
　次に、図２０に示すように、フォトリソグラフィ技術およびドライエッチング技術を使用することにより、ＭＥＭＳ層ＭＬをパターニングする。これにより、ベース層ＢＬに固定された固定部ＦＵと、固定部ＦＵと接続される梁（図示せず）と、梁で懸架され、ｚ方向に変位可能な可動電極として機能する質量部ＭＳ１および質量体ＭＳ２を形成する。特に、質量体ＭＳ１は、ベース層ＢＬに形成された固定電極ＦＥ１に対向するように形成され、かつ、質量体ＭＳ２は、ベース層ＢＬに形成された固定電極ＦＥ２に対向するように形成される。さらに、この加工工程においては、質量体ＭＳ１を貫通する複数の開口部ＯＰ１と、質量体ＭＳ２を貫通する複数の開口部ＯＰ２とが形成される。このとき、質量体ＭＳ１と質量体ＭＳ２との間に質量差を設けるため、開口部ＯＰ１の平面サイズは、開口部ＯＰ２の平面サイズよりも小さくなっている。これにより、質量体ＭＳ１の質量を質量体ＭＳ２の質量よりも大きくすることができる。 Next, as shown in FIG. 20, the MEMS layer ML is patterned by using a photolithography technique and a dry etching technique. Accordingly, a fixed portion FU fixed to the base layer BL, a beam (not shown) connected to the fixed portion FU, a mass portion MS1 that functions as a movable electrode that is suspended by the beam and is displaceable in the z-direction. A mass body MS2 is formed. In particular, the mass body MS1 is formed to face the fixed electrode FE1 formed on the base layer BL, and the mass body MS2 is formed to face the fixed electrode FE2 formed on the base layer BL. . Further, in this processing step, a plurality of openings OP1 penetrating the mass body MS1 and a plurality of openings OP2 penetrating the mass body MS2 are formed. At this time, since a mass difference is provided between the mass body MS1 and the mass body MS2, the planar size of the opening OP1 is smaller than the planar size of the opening OP2. Thereby, the mass of mass body MS1 can be made larger than the mass of mass body MS2.
　ここで、開口部ＯＰ１の平面サイズと開口部ＯＰ２の平面サイズとが相違する結果、開口部ＯＰ１のエッチング速度と開口部ＯＰ２のエッチング速度が異なることになる。具体的には、平面サイズの小さな開口部ＯＰ１のエッチング速度が、平面サイズの大きな開口部ＯＰ２のエッチング速度よりも遅くなる。さらには、ウェハ面内でもエッチング速度に分布が存在するため、エッチング不足が発生しなうように、オーバエッチングが実施される。この点に関し、本実施の形態４においても、複数の保護部ＰＵ１のそれぞれは、複数の保護部ＰＵ１のそれぞれに対応した開口部ＯＰ１を内包し、かつ、複数の保護部ＰＵ２のそれぞれは、複数の保護部ＰＵ２のそれぞれに対応した開口部ＯＰ２を内包している。この結果、本実施の形態４によれば、開口部ＯＰ１および開口部ＯＰ２を形成後、オーバエッチングが実施されても、開口部ＯＰ１を内包する保護部ＰＵ１と開口部ＯＰ２を内包する保護部ＰＵ２によって、固定電極ＦＥ１および固定電極ＦＥ２をオーバエッチングから保護することができる。このように、本実施の形態４における加速度センサの製造方法によれば、固定電極ＦＥ１および固定電極ＦＥ２をエッチングダメージから保護することができ、これによって、加速度センサの信頼性を向上することができる。 Here, as a result of the difference between the planar size of the opening OP1 and the planar size of the opening OP2, the etching rate of the opening OP1 and the etching rate of the opening OP2 are different. Specifically, the etching rate of the opening OP1 having a small planar size is slower than the etching rate of the opening OP2 having a large planar size. Furthermore, since there is a distribution in the etching rate even within the wafer surface, over-etching is performed so as not to cause insufficient etching. In this regard, also in the fourth embodiment, each of the plurality of protection units PU1 includes an opening OP1 corresponding to each of the plurality of protection units PU1, and each of the plurality of protection units PU2 includes a plurality of protection units PU2. An opening OP2 corresponding to each of the protective parts PU2 is included. As a result, according to the fourth embodiment, even if overetching is performed after forming the opening OP1 and the opening OP2, the protection part PU1 that includes the opening OP1 and the protection part PU2 that includes the opening OP2 Thus, the fixed electrode FE1 and the fixed electrode FE2 can be protected from over-etching. Thus, according to the method for manufacturing the acceleration sensor in the fourth embodiment, it is possible to protect the fixed electrode FE1 and the fixed electrode FE2 from etching damage, thereby improving the reliability of the acceleration sensor. .
　その後、図１４に示すように、ＭＥＭＳ層ＭＬ上に、ＭＥＭＳ層ＭＬに形成された固定部ＦＵとキャップ層ＣＬとを接合する。これにより、ＭＥＭＳ層ＭＬに形成された質量体ＭＳ１をベース層ＢＬとキャップ層ＣＬで挟まれる空洞部ＣＡＶ１内に封止し、かつ、ＭＥＭＳ層ＭＬに形成された質量体ＭＳ２をベース層ＢＬとキャップ層ＣＬで挟まれる空洞部ＣＡＶ２内に封止することができる。このとき、空洞部ＣＡＶ１の内部および空洞部ＣＡＶ２の内部は、例えば、大気圧よりも充分に低い圧力で封止される。以上のようにして、本実施の形態４における加速度センサを製造することができる。 Thereafter, as shown in FIG. 14, the fixing unit FU formed on the MEMS layer ML and the cap layer CL are joined on the MEMS layer ML. Accordingly, the mass body MS1 formed in the MEMS layer ML is sealed in the cavity CAV1 sandwiched between the base layer BL and the cap layer CL, and the mass body MS2 formed in the MEMS layer ML is sealed with the base layer BL. It can be sealed in the cavity CAV2 sandwiched between the cap layers CL. At this time, the inside of the cavity part CAV1 and the inside of the cavity part CAV2 are sealed with a pressure sufficiently lower than the atmospheric pressure, for example. As described above, the acceleration sensor according to the fourth embodiment can be manufactured.
　なお、前記実施の形態１では、加速度センサＡＳ１の製造方法について説明していない一方、本実施の形態４では、加速度センサＡＳ２の製造方法について説明している。そして、本実施の形態４で説明した製造工程とほぼ同様の工程を経ることにより、前記実施の形態１における加速度センサＡＳ１を製造することができる。 In the first embodiment, the method for manufacturing the acceleration sensor AS1 is not described. On the other hand, in the fourth embodiment, the method for manufacturing the acceleration sensor AS2 is described. The acceleration sensor AS1 in the first embodiment can be manufactured through substantially the same process as the manufacturing process described in the fourth embodiment.
　以上、本発明者によってなされた発明をその実施の形態に基づき具体的に説明したが、本発明は前記実施の形態に限定されるものではなく、その要旨を逸脱しない範囲で種々変更可能であることは言うまでもない。 As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.
　前記実施の形態では、慣性センサの一例として、加速度センサを例に挙げて説明したが、前記実施の形態における技術的思想は、質量体と固定電極とのステッキングの抑制と、質量体に複数の開口部を設ける際の固定電極へのエッチングダメージを抑制する観点からなされたものである。したがって、質量体と固定電極を有し、かつ、質量体に複数の開口部を形成する構成を有する慣性センサであれば、幅広く適用することができる。例えば、角速度センサにおいても、質量体と固定電極を有し、かつ、質量体に複数の開口部を形成する構成が採用される場合があるため、前記実施の形態における技術的思想は、加速度センサだけでなく、角速度センサにも幅広く適用することができる。 In the above-described embodiment, an acceleration sensor has been described as an example of the inertial sensor. However, the technical idea in the above-described embodiment is that the mass body is restrained from sticking between the fixed body and the mass body, and there are a plurality of mass sensors. This is made from the viewpoint of suppressing etching damage to the fixed electrode when the openings are provided. Therefore, any inertial sensor having a mass body and a fixed electrode and having a configuration in which a plurality of openings are formed in the mass body can be widely applied. For example, even in an angular velocity sensor, a configuration in which a mass body and a fixed electrode are provided and a plurality of openings are formed in the mass body may be employed. In addition, it can be widely applied to angular velocity sensors.
　ＦＥ　固定電極
　ＯＰ　開口部
　ＰＵ　保護部
　ＶＥ　可動電極 FE fixed electrode OP opening PU protection part VE movable electrode

Claims (15)

  1. 　第１方向に変位可能な第１可動電極と、
    　前記第１可動電極を貫通する複数の第１開口部と、
    　前記第１方向において、前記第１可動電極と離間して対向配置された第１固定電極と、
    　前記第１可動電極と対向する前記第１固定電極の対向面に形成された複数の第１保護部と、
    　を備え、
    　前記第１方向から見た平面視において、前記複数の第１保護部のそれぞれは、前記複数の第１保護部のそれぞれに対応して設けられた第１開口部を内包する、慣性センサ。     A first movable electrode displaceable in a first direction;
    A plurality of first openings penetrating the first movable electrode;
    A first fixed electrode disposed opposite to the first movable electrode in the first direction;
    A plurality of first protection portions formed on a facing surface of the first fixed electrode facing the first movable electrode;
    With
    In the planar view seen from the first direction, each of the plurality of first protection portions includes a first opening provided corresponding to each of the plurality of first protection portions.
  2. 　請求項１に記載の慣性センサにおいて、
    　前記複数の第１保護部のそれぞれの平面サイズは、前記複数の第１保護部のそれぞれに対応して設けられた第１開口部の平面サイズよりも大きい、慣性センサ。     The inertial sensor according to claim 1,
    Each of the plurality of first protection portions has a planar size larger than a planar size of a first opening provided corresponding to each of the plurality of first protection portions.
  3. 　請求項２に記載の慣性センサにおいて、
    　前記複数の第１保護部のうちの所定の第１保護部と、前記所定の第１保護部に対応して設けられた第１開口部とに着目した場合、前記第１方向から見た平面視において、前記第１方向と交差する第２方向における前記第１開口部の一端部から前記所定の第１保護部の一端部までの距離は、前記第２方向における前記第１開口部の開口寸法よりも小さい、慣性センサ。     The inertial sensor according to claim 2,
    When attention is paid to a predetermined first protective portion of the plurality of first protective portions and a first opening provided corresponding to the predetermined first protective portion, a plane viewed from the first direction. In view, the distance from one end of the first opening in the second direction intersecting the first direction to the one end of the predetermined first protection part is the opening of the first opening in the second direction. Inertial sensor, smaller than dimensions.
  4. 　請求項１に記載の慣性センサにおいて、
    　前記慣性センサは、さらに、
    　前記第１固定電極と同層で形成され、かつ、前記第１方向において、前記第１可動電極と離間して対向配置され、かつ、前記第１方向への前記第１可動電極の変位を打ち消す静電気力を発生させるサーボ電極を有する、慣性センサ。     The inertial sensor according to claim 1,
    The inertial sensor further includes:
    It is formed in the same layer as the first fixed electrode, and is disposed opposite to the first movable electrode in the first direction, and cancels the displacement of the first movable electrode in the first direction. An inertial sensor having servo electrodes that generate electrostatic force.
  5. 　請求項１に記載の慣性センサにおいて、
    　前記複数の第１保護部は、前記第１可動電極が前記第１固定電極に張り付くステッキングを抑制する機能を有する、慣性センサ。     The inertial sensor according to claim 1,
    The plurality of first protection parts are inertial sensors having a function of suppressing sticking of the first movable electrode sticking to the first fixed electrode.
  6. 　請求項１に記載の慣性センサにおいて、
    　前記複数の第１開口部のそれぞれの平面形状は、ホール形状、または、スリット形状のいずれかである、慣性センサ。     The inertial sensor according to claim 1,
    The inertial sensor, wherein each of the plurality of first openings has a planar shape that is either a hole shape or a slit shape.
  7. 　請求項１に記載の慣性センサにおいて、
    　前記複数の第１保護部のそれぞれは、絶縁膜から形成される、慣性センサ。     The inertial sensor according to claim 1,
    Each of the plurality of first protection parts is an inertial sensor formed of an insulating film.
  8. 　請求項１に記載の慣性センサにおいて、
    　前記慣性センサは、
    　ベース層と、
    　前記ベース層の上方に配置されたキャップ層と、
    　前記ベース層と前記キャップ層とで挟まれた第１空洞部と、
    　前記第１空洞部内に配置されたＭＥＭＳ層と、
    　を有し、
    　前記第１空洞部内において、前記ベース層上に前記第１固定電極が形成され、
    　前記ＭＥＭＳ層に、前記ベース層と前記キャップ層とに固定された固定部と、前記固定部に接続された第１梁と、前記第１梁によって前記第１空洞部内に懸架され、前記第１可動電極として機能する第１質量体とが形成される、慣性センサ。     The inertial sensor according to claim 1,
    The inertial sensor is
    The base layer,
    A cap layer disposed above the base layer;
    A first cavity sandwiched between the base layer and the cap layer;
    A MEMS layer disposed in the first cavity,
    Have
    In the first cavity, the first fixed electrode is formed on the base layer,
    The MEMS layer is suspended in the first cavity by the first beam connected to the base layer and the cap layer, the first beam connected to the fixed unit, and the first beam. An inertial sensor in which a first mass body that functions as a movable electrode is formed.
  9. 　請求項８に記載の慣性センサにおいて、
    　前記慣性センサは、さらに、
    　前記第１固定電極と接続される配線の一部分であって、前記ＭＥＭＳ層を貫通する貫通孔と平面的に重なる前記配線の一部分上に、前記複数の第１保護部と同層で形成された配線保護部が形成され、
    　前記第１方向から見た平面視において、前記配線保護部は、前記貫通孔を内包する、慣性センサ。     The inertial sensor according to claim 8.
    The inertial sensor further includes:
    A portion of the wiring connected to the first fixed electrode and formed in the same layer as the plurality of first protection portions on a portion of the wiring that overlaps the through hole penetrating the MEMS layer in a plane. A wiring protection part is formed,
    In the plan view seen from the first direction, the wiring protection part includes the through hole.
  10. 　請求項８に記載の慣性センサにおいて、
    　前記慣性センサは、さらに、
    　前記ベース層と前記キャップ層とで挟まれ、前記第１空洞部と離間した第２空洞部と、
    　前記第２空洞部内に配置された前記ＭＥＭＳ層と、
    　を有し、
    　前記第２空洞部内において、前記ベース層上に第２固定電極が形成され、
    　前記ＭＥＭＳ層に、前記ベース層と前記キャップ層とに固定された前記固定部と、前記固定部に接続された第２梁と、前記第２梁によって前記第２空洞部内に懸架され、第２可動電極として機能する第２質量体とが形成され、
    　前記第２可動電極は、前記第１方向に変位可能であり、
    　前記第２可動電極には、前記第２可動電極を貫通する複数の第２開口部が形成され、
    　前記第２可動電極と対向する前記第２固定電極の対向面には、複数の第２保護部が形成され、
    　前記第１方向から見た平面視において、前記複数の第２保護部のそれぞれは、前記複数の第２保護部のそれぞれに対応して設けられた第２開口部を内包する、慣性センサ。     The inertial sensor according to claim 8.
    The inertial sensor further includes:
    A second cavity sandwiched between the base layer and the cap layer and spaced apart from the first cavity,
    The MEMS layer disposed in the second cavity;
    Have
    A second fixed electrode is formed on the base layer in the second cavity,
    The MEMS layer is suspended in the second cavity by the second beam connected to the fixing portion, the second beam connected to the fixing portion, the second beam fixed to the base layer and the cap layer, A second mass that functions as a movable electrode is formed,
    The second movable electrode is displaceable in the first direction;
    The second movable electrode is formed with a plurality of second openings penetrating the second movable electrode,
    A plurality of second protective portions are formed on the facing surface of the second fixed electrode facing the second movable electrode,
    In the planar view seen from the first direction, each of the plurality of second protection portions includes a second opening provided corresponding to each of the plurality of second protection portions.
  11. 　請求項１０に記載の慣性センサにおいて、
    　前記第１質量体の質量は、前記第２質量体の質量よりも重く、
    　前記複数の第１開口部のそれぞれの平面サイズは、前記複数の第２開口部のそれぞれの平面サイズよりも小さく、
    　前記複数の第１保護部のそれぞれの平面サイズは、前記複数の第２保護部のそれぞれの平面サイズよりも小さい、慣性センサ。     The inertial sensor according to claim 10,
    The mass of the first mass body is heavier than the mass of the second mass body,
    Each plane size of the plurality of first openings is smaller than each plane size of the plurality of second openings,
    Each of the plurality of first protection parts has an inertial size that is smaller than each of the plurality of second protection parts.
  12. 　請求項８に記載の慣性センサにおいて、
    　前記キャップ層の下面には、第３固定電極が形成され、
    　前記第１可動電極と対向する前記第３固定電極の対向面には、複数の第３保護部が形成され、
    　前記第１方向から見た平面視において、前記複数の第３保護部のそれぞれは、前記複数の第３保護部のそれぞれに対応して設けられた第１開口部を内包する、慣性センサ。     The inertial sensor according to claim 8.
    A third fixed electrode is formed on the lower surface of the cap layer,
    A plurality of third protective portions are formed on the facing surface of the third fixed electrode facing the first movable electrode,
    In the planar view seen from the first direction, each of the plurality of third protection portions includes a first opening provided corresponding to each of the plurality of third protection portions.
  13. 　請求項１に記載の慣性センサにおいて、
    　前記慣性センサは、前記第１方向に印加される加速度を、前記第１可動電極と前記第１固定電極からなる静電容量の容量変化として捉える加速度センサである、慣性センサ。     The inertial sensor according to claim 1,
    The inertial sensor, wherein the inertial sensor is an acceleration sensor that captures acceleration applied in the first direction as a capacitance change of an electrostatic capacitance composed of the first movable electrode and the first fixed electrode.
  14. 　（ａ）溝を有するベース層の前記溝の内部に固定電極を形成する工程、
    　（ｂ）前記固定電極上に複数の保護部を形成する工程、
    　（ｃ）前記（ｂ）工程後、前記ベース層上にＭＥＭＳ層を接合する工程、
    　（ｄ）前記ＭＥＭＳ層をパターニングすることにより、前記ベース層に固定された固定部と、前記固定部と接続される梁と、前記梁で懸架され、第１方向に変位可能な可動電極として機能する質量体と、前記質量体を貫通する複数の開口部とを形成する工程、
    　（ｅ）前記（ｄ）工程後、前記ＭＥＭＳ層上に、前記ＭＥＭＳ層に形成された前記固定部と接続するキャップ層を形成することにより、前記ＭＥＭＳ層に形成された前記質量体を前記ベース層と前記キャップ層で挟まれる空洞部内に封止する工程、
    　を備え、
    　前記（ｄ）工程は、前記第１方向から見た平面視において、前記複数の保護部のそれぞれが、前記複数の保護部のそれぞれに対応した開口部を内包するように、前記複数の開口部を形成する、慣性センサの製造方法。     (A) forming a fixed electrode inside the groove of the base layer having the groove;
    (B) forming a plurality of protective portions on the fixed electrode;
    (C) a step of bonding a MEMS layer on the base layer after the step (b),
    (D) By patterning the MEMS layer, it functions as a fixed portion fixed to the base layer, a beam connected to the fixed portion, a movable electrode suspended by the beam and displaceable in the first direction. Forming a mass body and a plurality of openings penetrating the mass body,
    (E) After the step (d), by forming a cap layer connected to the fixing portion formed on the MEMS layer on the MEMS layer, the mass body formed on the MEMS layer is formed on the base. Sealing in a cavity sandwiched between a layer and the cap layer,
    With
    In the step (d), the plurality of openings are arranged so that each of the plurality of protection parts includes an opening corresponding to each of the plurality of protection parts in a plan view as viewed from the first direction. The manufacturing method of the inertial sensor which forms.
  15. 　請求項１４に記載の慣性センサの製造方法において、
    　前記（ｄ）工程は、ドライエッチングを使用し、
    　前記複数の保護膜は、前記ドライエッチングから前記固定電極を保護する機能を有する、慣性センサの製造方法。     In the manufacturing method of the inertial sensor according to claim 14,
    The step (d) uses dry etching,
    The method for manufacturing an inertial sensor, wherein the plurality of protective films have a function of protecting the fixed electrode from the dry etching.
PCT/JP2014/084058 2014-12-24 2014-12-24 Inertial sensor and method for manufacturing same WO2016103342A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11186566A (en) * 1997-12-25 1999-07-09 Nissan Motor Co Ltd Manufacture of fine device
WO2000042666A1 (en) * 1999-01-13 2000-07-20 Mitsubishi Denki Kabushiki Kaisha Inertia force sensor and method for producing inertia force sensor
JP2002521695A (en) * 1998-07-31 2002-07-16 リットン システムズ インコーポレイテッド Micromechanical semiconductor accelerometer
WO2002103368A1 (en) * 2001-06-13 2002-12-27 Mitsubishi Denki Kabushiki Kaisha Silicon device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11186566A (en) * 1997-12-25 1999-07-09 Nissan Motor Co Ltd Manufacture of fine device
JP2002521695A (en) * 1998-07-31 2002-07-16 リットン システムズ インコーポレイテッド Micromechanical semiconductor accelerometer
WO2000042666A1 (en) * 1999-01-13 2000-07-20 Mitsubishi Denki Kabushiki Kaisha Inertia force sensor and method for producing inertia force sensor
WO2002103368A1 (en) * 2001-06-13 2002-12-27 Mitsubishi Denki Kabushiki Kaisha Silicon device

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