WO2022217402A1 - Mems扬声器及其制造方法以及电子设备 - Google Patents

Mems扬声器及其制造方法以及电子设备 Download PDF

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WO2022217402A1
WO2022217402A1 PCT/CN2021/086449 CN2021086449W WO2022217402A1 WO 2022217402 A1 WO2022217402 A1 WO 2022217402A1 CN 2021086449 W CN2021086449 W CN 2021086449W WO 2022217402 A1 WO2022217402 A1 WO 2022217402A1
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silicon
strip
mask
based skeleton
actuator
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PCT/CN2021/086449
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English (en)
French (fr)
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张孟伦
孙晨
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诺思(天津)微***有限责任公司
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Priority to PCT/CN2021/086449 priority Critical patent/WO2022217402A1/zh
Publication of WO2022217402A1 publication Critical patent/WO2022217402A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/02—Loudspeakers

Definitions

  • the present invention relates to a MEMS speaker, a manufacturing method thereof, and an electronic device.
  • Micro-speakers are currently widely used in various miniaturized and miniaturized acoustic devices and electronic equipment, and are used in multimedia and electronic entertainment equipment.
  • MEMS speakers based on MEMS (Micro-Electro-Mechanical System) actuators are a new and important means of realizing micro-speakers.
  • the miniaturization/miniaturization of speakers is one of the concerns in the industry. Due to the small size, the improvement of speaker performance (such as output sound pressure) is restricted to a certain extent. How to optimize the internal structure of the loudspeaker in a small size/small space is a key factor affecting the performance of the miniature loudspeaker.
  • the present invention proposes a MEMS speaker, a manufacturing method thereof, and an electronic device.
  • the method proposes that in order to achieve the goal of miniaturization and high sound pressure of the MEMS speaker, a MEMS piezoelectric actuator with vertical and smooth sides is required.
  • the present invention provides the following technical solutions:
  • the actuator of the speaker has a plurality of strip-shaped branches arranged in parallel in the vibration direction, and the angle between the side surface of the silicon-based skeleton with the laminated structure and the adjacent side surface of the strip-shaped branches is 70° to 110° or between 80° to 100°; and/or, the side surface of the silicon-based framework having the layered structure has a roughness of less than 100 nm or less than 10 nm.
  • the silicon-based skeleton of the strip-shaped branch is ⁇ 110> type silicon, and the plane of the silicon-based skeleton perpendicular to the vibration direction is the ⁇ 111> crystal plane.
  • the inner wall of the speaker between the ends of the adjacent silicon-based frameworks has a pentagonal inclined surface.
  • the two sides or one side of the silicon-based skeleton are followed by a piezoelectric layer and a top electrode from the inside to the outside; or, the two sides or one side of the silicon-based skeleton are the bottom electrode, the piezoelectric layer, and the top electrode from the inside to the outside. ; Or, the two sides or one side of the silicon-based skeleton are followed by a seed layer, a bottom electrode, a piezoelectric layer, and a top electrode.
  • the material of the silicon-based framework is N-type or P-type doped silicon.
  • the resistivity of the doped silicon is lower than 2000 ohm cm.
  • an included angle between the strip portion and an intersection of the ⁇ 110> crystal plane and the ⁇ 111> crystal plane is within 2°, and the ⁇ 111> crystal plane is perpendicular to the ⁇ 110> crystal plane.
  • the silicon wafer is an SOI type wafer
  • the silicon dioxide layer of the SOI type wafer serves as an etch stop layer
  • the method further includes: removing a middle portion of the silicon dioxide layer in a horizontal direction to form a circle of silicon dioxide protrusions.
  • each functional layer is formed on the silicon-based skeleton.
  • the step of forming each functional layer on the silicon-based skeleton includes: sequentially fabricating a piezoelectric layer and a top electrode on both sides or one side of the silicon-based skeleton; the step of forming each functional layer on the silicon-based skeleton includes: The bottom electrode, the piezoelectric layer, and the top electrode are sequentially made on both sides or one side of the base skeleton; or, the step of forming each functional layer on the silicon-based skeleton includes: sequentially making a seed layer, a bottom electrode on both sides or one side of the silicon-based skeleton Electrode, piezoelectric layer, top electrode.
  • the mask window is a plurality of parallel strip-shaped windows; after each functional layer is formed on the silicon-based skeleton, a cutter is used to cut the strip-shaped branches obtained by the etching to form strips with free ends shaped branch.
  • the mask window is a plurality of parallel strip windows; after each functional layer is formed on the silicon-based skeleton, a mask is covered on the actuator branch, and the position of the mask window corresponds to the needs of the actuator branch.
  • the disconnected position is processed by a deep silicon etching process.
  • the mask window is a plurality of polyline-shaped windows arranged in parallel, and the polyline-shaped window includes a first straight line portion, a turning portion, and a second straight line portion connected in sequence, wherein the first straight line portion and the second straight line portion are connected in sequence.
  • the two straight lines are parallel, and the free ends of the two are respectively located on a set of opposite sides of the mask window; after each functional layer is formed on the silicon-based skeleton, a cutter is used to cut off the turning part in the zigzag branch obtained by the etching to Form strips with free ends.
  • the mask window is a plurality of polyline-shaped windows arranged in parallel, and the polyline-shaped window includes a first straight line portion, a turning portion, and a second straight line portion connected in sequence, wherein the first straight line portion and the second straight line portion are connected in sequence.
  • the two straight lines are parallel, and the free ends of the two are respectively located on a set of opposite sides of the mask window; after each functional layer is formed on the silicon-based skeleton, a mask is covered on the actuator branch, and the position of the mask window corresponds to the actuator
  • the turning part of the branch is processed by deep silicon etching process.
  • An electronic device includes the MEMS speaker of the present invention.
  • the present invention proposes to improve the performance of the actuator of a MEMS loudspeaker from its shape and surface properties.
  • MEMS piezoelectric actuators fins
  • the verticality of the fin should be greater than 70 degrees, and the side roughness of the silicon skeleton should be less than 100 nm; further, the verticality of the fin should be greater than 80 degrees, and the side surface of the silicon skeleton should The roughness should be less than 10nm.
  • the ⁇ 110> type silicon wafer is etched by wet method, and the strip portion of the mask window has a specific direction, so as to form the strip branch of the actuator with good verticality and excellent surface roughness .
  • FIG. 1A is a schematic diagram of an external three-dimensional structure of a MEMS speaker according to an embodiment of the present invention
  • FIG. 1B is a schematic diagram of an exploded structure of a MEMS speaker according to an embodiment of the present invention.
  • FIG. 1C is a schematic diagram of a structure of an actuator of a MEMS speaker according to an embodiment of the present invention.
  • 1D is a schematic diagram of the overall structure of a speaker actuator according to an embodiment of the present invention.
  • FIGS. 1E and 1F are schematic diagrams of lateral and longitudinal expansion of a functional substrate, respectively, according to an embodiment of the present invention.
  • FIG. 2A is a schematic diagram of a cross-section of a MEMS speaker according to an embodiment of the present invention.
  • 2B is a schematic diagram of a structure of a material layer of an actuator of a MEMS speaker according to an embodiment of the present invention
  • 2C is a schematic diagram of another structure of a material layer of an actuator of a MEMS speaker according to an embodiment of the present invention.
  • 2D is a schematic diagram of vibration modes of an actuator of a MEMS speaker according to an embodiment of the present invention.
  • FIG. 2E and 2F are schematic views of the air flow direction when the actuator in the structure shown in FIG. 2A vibrates;
  • Fig. 2G is a part taken from Fig. 2E;
  • 2H is a schematic diagram of the air flow between the ends of the actuator branches of the MEMS speaker and the inner wall of the speaker according to an embodiment of the present invention
  • 3A-3E are schematic diagrams of internal gaps of a MEMS speaker according to an embodiment of the present invention.
  • FIGS. 4A to 4C are schematic diagrams of a manner of forming a longitudinal gap of a MEMS speaker according to an embodiment of the present invention.
  • 4D is a schematic diagram of the structure of the SOI wafer according to an embodiment of the present invention.
  • 5A and 5B are schematic diagrams of intermediate states of etching on SOI-type wafers to form actuator branches according to embodiments of the present invention
  • 6A to 6E are schematic diagrams of crystal orientations involved in an embodiment of the present invention.
  • 6F is a schematic diagram of the intersection of the ⁇ 110> crystal plane and the ⁇ 111> crystal plane on the wafer;
  • FIG. 7A is a schematic diagram of a mask according to an embodiment of the present invention.
  • FIG. 7B is a schematic diagram of the effect of wet etching using the mask of FIG. 7A;
  • FIG. 8 is a schematic diagram of an etching process according to an embodiment of the present invention.
  • 9A is a scanning electron microscope image of a silicon material obtained by etching in the prior art.
  • 9B is a scanning electron microscope image of a silicon material obtained by etching according to an embodiment of the present invention.
  • 10A and 10B are schematic diagrams illustrating changes in the distance between the actuator branch and the inner wall of the speaker formed during wet etching according to an embodiment of the present invention
  • 11A and 11B are schematic diagrams of forming an end gap of an actuator branch according to an embodiment of the present invention.
  • FIG. 1A is a schematic diagram of an external three-dimensional structure of a MEMS speaker according to an embodiment of the present invention.
  • this MEMS speaker is in the shape of a rectangular box, with upper and lower bottom surfaces parallel to each other and four side walls between them.
  • the speaker includes a first packaging substrate C1 forming a lower bottom surface, a functional substrate D1 forming side walls and an actuator, and a second packaging substrate C2 forming an upper bottom surface.
  • M3 is an imaginary section.
  • the coordinate systems indicated in each figure in this document are consistent coordinate systems.
  • FIG. 1B is a schematic diagram of an exploded structure of a MEMS speaker according to an embodiment of the present invention, wherein a row of through holes is distributed on C1, and a certain through hole is Vj; similarly, a certain through hole in a row of through holes distributed on C2 is Uk
  • a plurality of parallel plate-shaped actuator branches can be seen in its interior, and the overall structure of each branch constitutes the actuator of the speaker, which vibrates under the piezoelectric effect to output sound pressure.
  • the vibration direction of the actuator of the speaker is in the XY plane, which can be visually understood as the left and right swing similar to the fins, so this kind of speaker can also be called a fin-type speaker.
  • One branch of the actuator is equivalent to a fin, and the actuator as a whole A fin array structure.
  • 1C is a schematic diagram of the structure of an actuator of a MEMS speaker according to an embodiment of the present invention, which shows a state in which a part of the peripheral frame of D1 is cut away, and the structure of each fin such as a certain fin Fn can be seen, which is long Plate-shaped, one end is connected to the inner wall of D1, and the other end is a free end. Other possible configurations of fins can also be seen later.
  • FIG. 1D is a schematic diagram of the overall structure of the speaker actuator according to an embodiment of the present invention, wherein the area F is the area where the fins are located. It can also be noted from FIG. 1D that one end of each fin (upper end from the perspective of the figure) is connected to the peripheral frame while the other end (the lower end from the perspective of the figure) is suspended and maintains a small gap with the inner wall of the frame.
  • FIGS. 1E and 1F are schematic diagrams of lateral and longitudinal expansion, respectively, of a functional substrate according to an embodiment of the present invention.
  • the functional substrate D1 can be copied to obtain D2 and then spliced in the horizontal direction as shown in FIG. 1E , or spliced in the vertical direction as shown in FIG. 1F .
  • FIG. 2A is a schematic diagram of a cross-section of a MEMS speaker according to an embodiment of the present invention.
  • FIG. 2A if FIG. 1A is cut according to the section M3, the cross-sectional view of the structure shown in FIG. 2A can be obtained: here, for the sake of clarity, as a schematic illustration, the number of fins and through holes is reduced, and only the Fins F1 to F7, and vias V1 to V4 above and U1 to U4 below. It can be seen from FIG. 2A that the upper and lower end surfaces of each fin in the cross-sectional view maintain a small gap with the inner wall of C1 or C2.
  • FIG. 2B is a schematic diagram of a structure of a material layer of an actuator of a MEMS speaker according to an embodiment of the present invention.
  • a branch of the actuator such as Fn, is as follows from the inside to the outside:
  • F00 silicon-based framework, the material is monocrystalline silicon or polycrystalline silicon
  • F01 Seed layer, containing AlN or other thin film materials to assist the growth of the piezoelectric layer;
  • the material can be selected from common electrode materials such as Mo and Pt;
  • Piezoelectric layer commonly used piezoelectric thin film materials such as AlN, doped AlN, PZT;
  • the material can be selected from common electrode materials such as Mo, Pt, Au, Al, etc.
  • the material layers F02, F03, and F04 on each side of the skeleton F00 form a piezoelectric sandwich structure.
  • the piezoelectric layer F03 will vibrate under the action of the piezoelectric effect.
  • the sandwich structures on both sides can drive the skeleton F00 to move in the same direction, thereby realizing the vibration of the fins.
  • adjacent fins can move in opposite directions, as shown in FIG. 2D , which is the vibration state of the actuator of the MEMS speaker according to the embodiment of the present invention. , in which a certain fin Fn and its two adjacent fins Fn-1 and Fn+1 move in opposite directions.
  • FIG. 2C is a schematic diagram of another structure of the material layer of the actuator of the MEMS speaker according to the embodiment of the present invention.
  • the difference between the structure and the structure shown in FIG. 2B is that in FIG. 2C , the piezoelectric layer F03 is directly grown on the side of F00 instead of including the seed layer F01 and the electrode layer F02 .
  • F00 is realized by patterning low-resistance silicon, and uses the conductive properties of low-resistance silicon to use F00 as an electrode.
  • FIG. 2C is a schematic diagram of a vibration mode of an actuator of a MEMS speaker according to an embodiment of the present invention.
  • this structural design can not only greatly reduce the cost by directly using low-resistance silicon, but also save the fabrication of some metal electrodes, but also reduce the electrical loss formed on the silicon-based F00, thereby improving the electrical-mechanical energy conversion efficiency.
  • the resistivity of low-resistance silicon is less than 2000 ohm cm.
  • FIG. 2E and FIG. 2F are schematic views of the air flow direction when the actuator in the structure shown in FIG. 2A vibrates.
  • the distribution rules of the through holes and the actuator branches are: U1-F1-V1-F2, U2-F3-V2- F4, .
  • the fins F1-F3 are still taken as an example, in which F2 and F3 move towards each other, while F1 and F2 move away from each other, resulting in the space between F2 and F3 being compressed. , and the space between F1 and F2 is stretched.
  • a part of the air originally between F2 and F3 is bound to be displaced into the atmospheric environment through the through hole on C2 and between F2 and F3 (such as As shown by the downward arrow in C1 in the figure), and part of the gas in the atmospheric environment will also be sucked into the space between F1 and F2 through the through hole on C2 and between F1 and F2 (C2 in the figure) shown by the down arrow in ).
  • Fig. 2G is a part taken from Fig. 2E.
  • F1-F3 the distance between the upper and lower end surfaces of the fins and the inner surface of the package substrate C1C2 is too large, there will be a considerable amount of The air molecules enter the "next door" space from the space between F1 and F2 in the direction of the arrow in the figure, resulting in a decrease in the amount of air exhausted by the V1 hole.
  • the air molecules entering between F2 and F3 in the direction of the arrow will also lead to the U2 hole.
  • FIG. 2H is a schematic diagram of the air flow between the end of the actuator branch of the MEMS speaker and the inner wall of the speaker according to an embodiment of the present invention, wherein the gap between the free end of the fin and the side wall of the frame is also There will be air passing through, and the airflow direction is similar to that shown by the arrow in the figure, so the size of the gap will also have the same effect on the sound pressure output.
  • This type of gap is called a lateral gap or an XY gap.
  • FIG. 3A to FIG. 3E it is a schematic diagram of the internal gap of the MEMS speaker according to the embodiments of the present invention.
  • the gap widths d1 and d2 between the upper and lower top surfaces of each fin and the inner surfaces of the upper and lower packaging substrates respectively are not more than 20um, preferably not more than 5um.
  • the gap width d3 ( As shown in Fig. 3B) no more than 20um, preferably no more than 5um.
  • the lateral gap d4 is defined as the distance from the end face of each fin to the inner wall of the frame.
  • the middle lateral gap d5 is defined as the distance from the end face of each fin to the end face of the opposite short fin, and in Figure 3E the lateral gap d6 is defined as the distance between the side wall of each fin and the side wall of the opposite short fin. distance.
  • the values of d4, d5, and d6 are not more than 50um, preferably not more than 20um.
  • SOI type wafers can be used.
  • 4A to 4C are schematic diagrams of how the longitudinal gap of the MEMS speaker is formed according to an embodiment of the present invention.
  • 4D is a schematic diagram of the structure of the SOI wafer according to the embodiment of the present invention, wherein TS is the top silicon, OX is the silicon dioxide layer, and BS is the bottom silicon.
  • CR2 made of silicon dioxide on the edge of the upper surface of C2, and the height of CR2 is d2.
  • D1 and CR2 do not actually have a separation state, and the figure is only for illustration.
  • C2 instead of using an SOI type wafer, C2 may be formed on a silicon substrate, and D1 may be formed by etching on the silicon substrate, or material may be deposited on the silicon substrate to form D1.
  • C1 is formed from a single piece of silicon substrate, referring to FIG. 4B, it can be flipped over to cover D1 after processing is complete.
  • One of C1 and C2 uses SOI wafers, and the other can be fabricated with a single silicon substrate.
  • a circle of protrusions DR1 can be formed on the edge of one layer, such as D1, and then turned over to cover D2. Similar to the above d1 and d2, the SOI wafer can be used to make D1, and the DR1 is formed by a silicon dioxide layer at this time; D1 can also be made of a silicon substrate, and the DR1 can be formed by etching on the silicon substrate at this time, Or deposit material on the silicon substrate to form the DR1.
  • the lateral gap deep silicon etching Bosch process combined with a patterned mask can be used to realize the gap size is determined by the size of the mask window.
  • the lateral gap can also be realized by mechanical processing. It is more common to use a disc silicon wafer dicing knife to cut the end of the fin structure through high-speed rotation. At this time, the gap size is determined by the thickness of the blade, the speed of the blade and the feed It is determined by parameters such as speed.
  • a patterned mask can be used to make an actuator branch that does not include d4 and d5, that is, the two ends of the actuator branch are connected to the side walls, and then the knife is cut at the places marked d4 and d5 in the figure. .
  • a patterned mask can be used to form a state without the gap d6, that is, a polyline-shaped silicon-based skeleton is formed at this time, and then the connection between the upper and lower actuator branches in Fig. 3E is marked
  • the knife is cut at d6; or directly obtained by deep silicon dry etching or wet etching after patterning the mask.
  • FIGS. 5A and 5B are schematic diagrams of intermediate states of performing etching on an SOI-type wafer to form actuator branches according to an embodiment of the present invention.
  • 5A is a three-dimensional state diagram
  • FIG. 5B is a corresponding line diagram of FIG. 5A .
  • multiple parallel grooves are formed on the top silicon of SOI wafers, and the walls of the grooves are used as actuator branches; the bottom of the grooves is a SiO2 layer, which needs to be removed as a sacrificial layer or only the surrounding one is left.
  • circle refer to CR2 in Figure 4A.
  • the actuator branches are suspended up and down so that they can swing.
  • FIGS. 6A to 6E are schematic diagrams of the crystal orientation involved in the embodiment of the present invention.
  • each cube is a lattice cell
  • the shaded plane in FIG. 6A is the ⁇ 110> crystal plane
  • the shaded plane in FIGS. 6B to 6E is the ⁇ 111> crystal plane, in which FIG.
  • FIG. 6C It is parallel to the shaded plane in Figure 6D, and its intersection with the ⁇ 110> crystal plane is Q1; the shaded plane in Figures 6B and 6E is parallel, and its intersection with the ⁇ 110> crystal plane is Q2, where Q1 is and Q2 are shown in FIG. 6F, which is a schematic diagram of the intersection of the ⁇ 110> crystal plane and the ⁇ 111> crystal plane on the wafer.
  • the wafer W1 is parallel to the ⁇ 110> crystal plane, and the plane perpendicular to the wafer W1 (represented as a straight line in the figure) can be divided into two groups, one group is parallel to Q1, the other group Parallel to Q2. The angle between these two groups is about 70.53°.
  • a chamfer B1 of the wafer which is substantially parallel to Q1 .
  • the ⁇ 110> type silicon crystal can be treated with alkaline solution (20%-60% mass concentration potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution or other alkaline solution) at high temperature (80-120 degrees Celsius).
  • alkaline solution (20%-60% mass concentration potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution or other alkaline solution) at high temperature (80-120 degrees Celsius).
  • KOH potassium hydroxide
  • NaOH sodium hydroxide
  • FIG. 7B is a schematic diagram of the effect of wet etching using the mask of FIG. 7A .
  • the outer contour of the mask in the embodiment of the present invention is a rectangle, and other shapes can also be used in implementation, but the mask window needs to correspond to the shape of the actuator branch.
  • FIG. 7A on the upper surface of the TS layer of the SOI-type wafer in FIG. 4D, and the L direction is roughly parallel to the above-mentioned Q1 or Q2 direction, and the deviation angle is within 2°, otherwise the etching cannot be formed.
  • FIGS. 5A and 5B show a part of the wafer.
  • pentagonal inclined planes P4 and ⁇ 111> crystal planes P5 are formed at the left and right ends of the strip-shaped mask window.
  • the loudspeaker here has thicker side walls, thereby increasing its mechanical strength.
  • the P1 and P0 planes are the ⁇ 110> crystal planes, and the P2 and P3 planes are parallel to the ⁇ 111> crystal planes.
  • FIG. 8 is a schematic diagram of the etching process according to an embodiment of the present invention, which corresponds to FIG. 5A or The XZ plane of Figure 5B.
  • the P1 surface continuously descends in the top silicon to form a trench
  • the sidewall of the trench is a ⁇ 111> crystal plane with good verticality
  • a crystal orientation is also generated at the intersection of the trench bottom and the sidewall. It is the slight slope of ⁇ 112>. Since this ⁇ 112> surface will adversely affect subsequent processes, it needs to be removed.
  • the ⁇ 112> crystal plane is extremely unstable in the wet environment, and is quickly decomposed in the etching solution after being formed and replaced by the new ⁇ 112> crystal plane under it.
  • the single crystal silicon material below the plane P1 where the bottom surface of the middle trench is located is replaced by the etching stop material (the stop etching material refers to a material that is highly resistant to etching compared with single crystal silicon.
  • the stop etching material can be Silicon dioxide, silicon nitride, etc.), and appropriately prolonging the etching time can remove the ⁇ 112> crystal face, while the sidewall ⁇ 111> face remains stable, thus forming P1 and ⁇ 111> at the bottom of the trench
  • other methods can also be used, such as silicon material with a silicon dioxide layer.
  • FIG. 9A is a scanning electron microscope image of a silicon material obtained by etching according to the prior art
  • FIG. 9B is a scanning electron microscope image of a silicon material obtained by etching according to an embodiment of the present invention.
  • the silicon material in FIG. 9A is a scanning electron microscope image of a silicon material obtained by etching according to the prior art
  • FIG. 9B is a scanning electron microscope image of a silicon material obtained by etching according to an embodiment of the present invention.
  • DRIE deep silicon etch
  • Bosch system in the prior art, which actually consists of several isotropic etching cycles, so that usually leaves on the sidewalls
  • the surface state of the silicon-based framework will have a very adverse effect on the lattice state of the sandwich film layer grown on it, especially the crystal orientation disorder of the aluminum nitride piezoelectric layer and the deterioration of the flatness of the film layer.
  • High temperature annealing in a hydrogen atmosphere can greatly reduce the roughness of the silicon substrate after the Bosch process.
  • the Bosch process etching machine and hydrogen annealing furnace are often expensive, and hydrogen is a high-risk gas, which requires strict surrounding safety protection measures. Therefore, the Bosch process combined with hydrogen annealing solution has high manufacturing costs.
  • the verticality of the fins formed by etching the silicon-based skeleton by the Bosch process is not good, and it is usually difficult to ensure that the verticality of most of the fins between and within the wafer is greater than 80 degrees. rate is lower.
  • Using the above-mentioned method in the embodiment of the present invention can not only generate a fin side with better steepness (close to 90 degrees), but also the side surface finish is significantly better than the processing result of the Bosch process (as shown in FIG. 9B , by After high-temperature KOH solution etching, the roughness of most areas is less than 10nm), which can meet the requirements of subsequent film growth without hydrogen annealing process, and the market price of strong bases such as potassium hydroxide with electronic grade purity is low, so it can be used. The manufacturing cost is greatly reduced, and the manufacturing yield is high.
  • FIGS. 10A and 10B are schematic diagrams illustrating changes in the distance between the actuator branch and the inner wall of the speaker formed during wet etching according to an embodiment of the present invention.
  • the fin mask of the patterned mask M3 as shown in FIG. 10A has a length L1 and a free end E1, and there is a gap between E1 and the other side E2 of the mask.
  • FIG. 11A and FIG. 11B it is a schematic diagram of forming an end gap of an actuator branch according to an embodiment of the present invention.
  • the structure shown in FIG. 7B can be first processed by using the mask of FIG. 7A and each functional layer can be deposited, and then a mask can be added to process the gap X1 shown in FIG. 11A and FIG. 11B on each fin by using the Bosch process.
  • the Bosch process can achieve good control accuracy for the slit width d5 and the distance t1 between the slit and the vertex of the ⁇ 111> crystal plane P4 at the bottom of the trench.
  • the local roughness brought by the Bosch process does not have any impact on device performance.
  • wet method and Bosch etching process on the one hand, the main surface with ideal smoothness and steepness can be obtained, and the precise control of the local process surface can also be achieved; at the same time, the selection of ⁇ 110> type silicon wafer can be compatible with the above-mentioned Two processes.
  • the through holes and the actuators of the MEMS speaker have specific arrangements, and each internal gap has size requirements, which helps to improve the output sound pressure of the speaker.
  • the MEMS speaker When the MEMS speaker is applied to an electronic device, it occupies a small space and has a large volume.
  • the ⁇ 110> type silicon wafer is etched by wet method, and the strip-shaped portion of the mask window has a specific direction, thereby forming the strip-shaped branch of the actuator.
  • the Bosch process the air tightness of the speaker can be further improved.
  • the embodiment of the present invention improves its performance from the shape and surface properties of the actuator of the MEMS speaker: the MEMS piezoelectric actuator fins have vertical sides, so the vertical longitudinal space of the speaker can be fully utilized, and a larger space can be achieved in a small space. Sound pressure and volume; the vertical sides of the MEMS piezoelectric actuator are very smooth at the same time, so the piezoelectric film on it is of good quality and the piezoelectric coefficient is high, so the actuator can achieve a large amount of displacement and a larger amount in a small space. Sound pressure and volume.

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Abstract

本发明提出一种MEMS扬声器及其制造方法以及电子设备，该MEMS扬声器具有较好的性能。该扬声器的执行器具有多个按振动方向平行排布的条形分支，所述条形分支的硅基骨架的具有层叠结构的侧面与相邻侧面的夹角在70°至110°之间或者在80°至100°之间；并且/或者，所述硅基骨架的具有层叠结构的侧面的粗糙度小于100nm或小于10nm。

Description

MEMS扬声器及其制造方法以及电子设备 技术领域
本发明涉及一种MEMS扬声器及其制造方法以及电子设备。
背景技术
微型扬声器目前被广泛的应用于各类小型化微型化的声学器件、电子设备，用于多媒体及电子娱乐设备之中。基于MEMS(微机电***)执行器的MEMS扬声器是实现微型扬声器的一种新的重要手段，其核心工作原理是利用压电材料实现声能(机械能)-电能的耦合和相互转化。
目前，扬声器的小型/微型化是业内的关注点之一。由于尺寸小，扬声器的性能(如输出声压)提升受到一定的制约。如何在小尺寸/小空间下进行扬声器的内部结构优化设计是影响微型扬声器性能的关键要素。
发明内容
有鉴于此，本发明提出一种MEMS扬声器及其制造方法以及电子设备，该方法提出，为了实现MEMS扬声器实现小型化、高声压的目标，需要有垂直、光滑侧面的MEMS压电执行器。本发明提供如下技术方案：
一种MEMS扬声器，所述扬声器的执行器具有多个按振动方向平行排布的条形分支，所述条形分支的硅基骨架的具有层叠结构的侧面与相邻侧面的夹角在70°至110°之间或者在80°至100°之间；并且/或者，所述硅基骨架的具有层叠结构的侧面的粗糙度小于100nm或小于10nm。
可选地，所述条形分支的硅基骨架为<110>型硅，该硅基骨架的垂直于振动方向的面为<111>晶面。
可选地，相邻所述硅基骨架的端部之间的扬声器内壁具有五边形倾斜面。
可选地，在硅基骨架两侧面或一侧面由内向外依次为压电层、顶电极；或者，在硅基骨架两侧面或一侧面由内向外依次为底电极、压电层、顶电极；或者，在硅基骨架两侧面或一侧面依次为晶种层、底电极、压电层、顶电极。
可选地，所述硅基骨架的材料为N型或P型掺杂硅。
可选地，所述掺杂硅的电阻率低于2000欧姆厘米。
一种制造MEMS扬声器的方法，所述扬声器的执行器具有多个平行设置的条形分支，该方法包括：在<110>硅晶圆上覆盖掩膜，然后使用湿法进行刻蚀以得到所述条形分支的硅基骨架，该掩膜的掩膜窗口具有条形部；或者，在硅晶圆上覆盖掩膜，使用深硅刻蚀工艺得到所述条形分支的硅基骨架，然后将硅基骨架在氢气氛围内高温退火，该掩膜的掩膜窗口具有条形部。
可选地，该条形部与<110>晶面和<111>晶面的一条交线的夹角在2°以内，该<111>晶面垂直于该<110>晶面。
可选地，所述硅晶圆为SOI型晶圆，该SOI型晶圆的二氧化硅层作为止刻层。
可选地，还包括：在水平方向上去除所述二氧化硅层的中间部分，以形成一圈二氧化硅凸起。
可选地，得到所述条形分支的硅基骨架之后，在硅基骨架上形成各功能层。
可选地，在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作压电层、顶电极；在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作底电极、压电层、顶电极；或者，在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作晶种层、底电极、压电层、顶电极。
可选地，所述掩膜窗口为多个平行的条形窗口；在硅基骨架上形成各功能层之后，采用刀具对所述刻蚀所得到的条形分支进行切割以形成具有自由端的条形分支。
可选地，所述掩膜窗口为多个平行的条形窗口；在硅基骨架上形成各功能层之后，在执行器分支上覆盖掩膜，掩膜窗口的位置对应于执行器分支的需要断开的位置，采用深硅刻蚀工艺进行加工。
可选地，所述掩膜窗口为多个并行设置的折线形窗口，所述折线形窗口包含依次连接的第一直线部、转折部、第二直线部，其中第一直线部与第二直线部平行，二者的自由端分别位于掩膜窗口的一组对边；在硅基骨架上形成各功能层之后，采用刀具切除所述刻蚀所得到的折线形分支中的转折部以形成具有自由端的条形分支。
可选地，所述掩膜窗口为多个并行设置的折线形窗口，所述折线形窗口包含依次连接的第一直线部、转折部、第二直线部，其中第一直线部与第二直线部平行，二者的自由端分别位于掩膜窗口的一组对边；在硅基骨架上形成各功能层之后，在执行器分支上覆盖掩膜，掩膜窗口的位置对应于执行器分支的转折部，采用深硅刻蚀工艺进行加工。
一种电子设备，包含本发明所述的MEMS扬声器。
本发明提出从MEMS扬声器的执行器的形状和表面性质来提高其性 能。MEMS压电执行器(鳍片)具有垂直的侧面，因此可以充分利用扬声器的垂直纵向空间，在小空间下实现更大的声压和音量；MEMS压电执行器的垂直侧面同时非常光滑，因此其上的压电薄膜质量好，压电系数高，因此执行器可以实现大的位移量，在小空间下实现更大的声压和音量。一般情况下，要实现小尺寸、大声压的MEMS扬声器，鳍片的垂直度应大于70度，硅骨架侧面粗糙度应小于100nm；进一步地，鳍片的垂直度应大于80度，硅骨架侧面粗糙度应小于10nm。为实现上述目的，采用湿法对<110>型硅晶圆进行刻蚀，掩膜窗口条形部具有特定方向，从而形成执行器的垂直度良好的条形分支，并且具有优良的表面粗糙度。
附图说明
为了说明而非限制的目的，现在将根据本发明的优选实施例、特别是参考附图来描述本发明，其中：
图1A是根据本发明实施方式的MEMS扬声器的外形立体结构的示意图；
图1B是根据本发明实施方式的MEMS扬声器的分解结构的示意图；
图1C是根据本发明实施方式的MEMS扬声器的执行器的结构的示意图；
图1D是根据本发明实施方式的扬声器执行器的整体结构的示意图；
图1E和图1F分别是根据本发明实施方式的功能基底横向和纵向扩展的示意图；
图2A是根据本发明实施方式的MEMS扬声器的剖面的示意图；
图2B是根据本发明实施方式的MEMS扬声器的执行器的材料层的一种结构的示意图；
图2C是根据本发明实施方式的MEMS扬声器的执行器的材料层的另一种结构的示意图；
图2D是根据本发明实施方式的MEMS扬声器的执行器的振动模式的示意图；
图2E和图2F是图2A所示结构中的执行器振动时空气流动方向的示意图；
图2G为从图2E中截取的局部；
图2H为根据本发明实施方式的MEMS扬声器的执行器分支的端部与扬声器内壁之间空气流动的示意图；
图3A至图3E是根据本发明实施方式的MEMS扬声器的内部间隙的示意图；
图4A至图4C是根据本发明实施方式的MEMS扬声器的纵向间隙的形成方式的示意图；
图4D是本发明实施方式涉及的SOI型晶圆的结构的示意图；
图5A和图5B是根据本发明实施方式的在SOI型晶圆上进行刻蚀以形成执行器分支的中间状态的示意图；
图6A至图6E是本发明实施例涉及的晶向的示意图；
图6F是<110>晶面和<111>晶面在晶圆上的交线的示意图；
图7A是根据本发明实施方式的掩膜的示意图；
图7B是使用图7A的掩膜进行湿法刻蚀的效果的示意图；
图8是根据本发明实施方式的刻蚀过程的示意图；
图9A是根据现有技术中刻蚀方式得到的硅材料的扫描电镜成像；
图9B是根据本发明实施方式的刻蚀方式得到的硅材料的扫描电镜成像；
图10A和图10B是根据本发明实施方式的湿法刻蚀时形成的执行器分支与扬声器内壁距离变化的示意图；
图11A和图11B是根据本发明实施方式的形成执行器分支端部间隙的示意图。
具体实施方式
在本发明实施方式中，对于本发明的MEMS扬声器的结构和制作方法加以举例说明。图1A是根据本发明实施方式的MEMS扬声器的外形立体结构的示意图。如图1A所示，这种MEMS扬声器外形呈长方盒状，具有互相平行的上下底面和二者之间的四个侧壁。当然也可以是多边形底面从而有多个侧壁。在基本结构方面，该扬声器包含形成下底面的第一封装基底C1，和形成侧壁以及执行器的功能基底D1，以及形成上底面的第二 封装基底C2。其中M3为一假想的剖面。为了便于理解，本文的各图所标示出的坐标系为一致化的坐标系。
若将图1A中的结构沿Z方向拆解，可得到图1B所示的分解图。图1B是根据本发明实施方式的MEMS扬声器的分解结构的示意图，其中C1上分布着一列通孔，其中某一个通孔为Vj；同样，分布于C2上的一列通孔中的某一个为Uk；此外D1除了周边框架结构，在其内部还可见多个平行的板状的执行器分支，各分支的总体构成扬声器的执行器，在压电效应下振动从而输出声压。
扬声器的执行器的振动方向在XY平面，可以形象地理解为类似于鱼鳍的左右摆动，所以这种扬声器也可以叫做鳍片型扬声器，执行器的一个分支相当于一个鳍片，执行器整体呈鳍片阵列结构。图1C是根据本发明实施方式的MEMS扬声器的执行器的结构的示意图，其中示出了将D1周边框架切除一部分的状态，可以看到各鳍片例如某一个鳍片Fn的结构，其呈长板状，一端连接于D1内壁，另一端为自由端。在后文中还可以看到鳍片的其他可行结构。
D1的俯视状态如图1D所示，图1D是根据本发明实施方式的扬声器执行器的整体结构的示意图，其中区域F为鳍片所在区域。从图1D中还可注意到每个鳍片一端(按图中视角为上端)与周边框架相连接而另一端(按图中视角为下端)悬空并与框架内壁保持微小的间隙。
图1E和图1F分别是根据本发明实施方式的功能基底横向和纵向扩展的示意图。如图1E所示，可将功能基底D1复制得到D2然后如图1E所示进行水平方向拼接，或如图1F所示进行竖直方向拼接。
以下对于本发明实施方式中的MEMS扬声器的进一步结构细节进行说明，并结合说明执行器的运行方式。
图2A是根据本发明实施方式的MEMS扬声器的剖面的示意图。如图2A所示，若将图1A按照剖面M3剖开，可获得图2A所示的结构剖面图：此处为了展示清晰，作为示意，减少了鳍片和通孔的数量，仅示出了鳍片F1至F7，以及上方的通孔V1至V4和下方的通孔U1至U4。由图2A可知，每个鳍片在剖视图中的上下端面均与C1或C2的内壁保持微小间隙。
图2B是根据本发明实施方式的MEMS扬声器的执行器的材料层的一种结构的示意图。如图2B所示，执行器的一个分支例如Fn由内向外依次如下：
F00：硅基骨架，材料为单晶硅或多晶硅；
F01：晶种层，包含AlN或其他辅助压电层生长的薄膜材料；
F02：底电极，材料可选Mo、Pt等常用电极材料；
F03：压电层，AlN、掺杂AlN、PZT等常用压电薄膜材料；
F04：顶电极，材料可选Mo、Pt、Au、Al等常用电极材料。
骨架F00每一侧的材料层F02、F03、F04均构成一个压电三明治结构，当在电极F02和F04之间施加交变电压时，压电层F03便会在压电效应的作用下发生振动，适当调整每个骨架F00两侧三明治结构的电压相位差，就可以实现两侧三明治结构向同一方向带动骨架F00运动，从而实现鳍片振动。同理，适当调整相邻鳍片的电压相位关系，可实现相邻的鳍片朝着相反的方向运动，例如图2D所示，图2D是根据本发明实施方式的MEMS扬声器的执行器振动状态的示意图，其中某一鳍片Fn与其相邻的两个鳍片Fn-1和Fn+1运动方向均相反。
此外，位于硅基骨架F00侧面上的电极和压电层还可以按照图2C的方式分布，图2C是根据本发明实施方式的MEMS扬声器的执行器的材料层的另一种结构的示意图，该结构与图2B所示结构的区别在于：图2C中压电层F03直接生长于F00侧面而不在包含晶种层F01和电极层F02。F00通过图形化低阻硅实现，并利用低阻硅的导电特性将F00作为电极。 在2C所示的结构中，通过在硅基骨架F00上施加参考电位，并在两侧电极层F04上施加与参考电位不同的电位；当两侧F04的电位相位相反时，即可实现与图2B结构相同的振动模式，该振动模式如图2D所示，图2D是根据本发明实施方式的MEMS扬声器的执行器的振动模式的示意图。并且这种结构设计不仅可以通过直接使用低阻硅大幅降低成本，省去了一部分金属电极的制作，还可以减少在硅基F00上形成的电学损耗，从而提电能-机械能转换效率。低阻硅的电阻率低于2000欧姆厘米。
基于上述运动规则，当图2A所示的静态结构开始工作时，便会出现图2E和2F所示的情形。图2E和图2F是图2A所示结构中的执行器振动时空气流动方向的示意图。图2A、图2E、图2F中，按照执行器分支的分布方向，即图中的x方向，通孔和执行器分支的分布规律是：U1-F1-V1-F2、U2-F3-V2-F4、……。即相邻分支之间有且只有一个通孔，该通孔为上方通孔或下方通孔。按照这种分布的特点，对于图2E所示的鳍片运动状态，以鳍片F1-F3为例，其中F1与F2相向运动，而F2与F3相离运动，从而导致F1与F2之间的空间被压缩，而F2与F3之间的空间则被拉伸，根据气体平衡法则，原本处于F1与F2之间一部分空气势必被通过C1上且处于F1和F2之间的通孔排挤到大气环境中(如图中的C1中的向上箭头所示)，而大气环境中的一部分气体也会通过C2上且处于F2和F3之间的通孔被吸入F2和F3之间的空间(如图中的C2中的向上箭头所示)。
同理，对于图2F所示的鳍片运动状态，仍以鳍片F1-F3为例，其中F2与F3相向运动，而F1与F2相离运动，从而导致F2与F3之间的空间被压缩，而F1与F2之间的空间则被拉伸，根据气体平衡法则，原本处于F2与F3之间一部分空气势必被通过C2上且处于F2和F3之间的通孔排挤到大气环境中(如图中的C1中的向下箭头所示)，而大气环境中的一部分气体也会通过C2上且处于F1和F2之间的通孔被吸入F1和F2之间的空间(如图中的C2中的向下箭头所示)。
这样，图2E和2F中的运动组合在一起便在每一个通孔出口处形成了 一次完整周期的空气振动，周而复始的空气振动便形成声波传播到大气环境中。单位时间内通孔内的气体通量越大，则扬声器输出的声压就越高(声音越响亮)。在上述过程中，假设鳍片运动频率一定且C1、C2和D1之间密封状态良好，直接影响通孔单位时间内与外界大气交换气体量的因素主要有以下两个：
(1)鳍片的振幅
鳍片振幅越大，对相邻鳍片之间的空间挤压/拉伸幅度就越大，单位时间排出/吸入的空气量也就越多。
(2)每两个鳍片间空间与相邻鳍片间空间的连通性
鳍片间空间的连通性越差，该空间对空气的密闭性就越好，当两侧鳍片对空间中空气进行挤压时，可确保不会发生“漏气”。
以下通过图2G和图2H对因素(2)中的“连通性”对声压的影响进行说明。图2G为从图2E中截取的局部，以F1-F3为例，当鳍片F1和F2相向运动，若鳍片的上下端面与封装基底C1C2的内表面距离过大时，就会有可观数量的空气分子沿图中箭头方向从F1F2之间的空间进入“隔壁”空间，从而导致由V1孔排出的空气量减少，此外由箭头方向进入F2和F3之间的空气分子还会导致由U2孔吸入的空气量减少，从而导致扬声器输出声压下降，该类间隙称为纵向间隙或Z向间隙。同理，对于如图1G所示的纵向拓展结构，上述纵向间隙还存在于相邻层的鳍片之间。此外，如图2H所示，图2H为根据本发明实施方式的MEMS扬声器的执行器分支的端部与扬声器内壁之间空气流动的示意图，其中鳍片自由端与框架侧壁间的间隙中也会有空气通过，气流方向类似如图中箭头所示，因此该间隙的大小也会对声压输出造成同样的影响，该类间隙称为横向间隙或XY向间隙。
因此本发明实施方式给出这种MEMS扬声器的一些尺寸的可选及优选值，参见图3A至图3E，是根据本发明实施方式的MEMS扬声器的内部间隙的示意图。
对于纵向间隙，每个鳍片上、下顶面分别与上、下封装基底的内表面的间隙宽度d1和d2(如图3A)不超过20um，优选的不超过5um。对于纵向层叠拓展结构，要求某一层中的某个鳍片的上/下顶面和邻层中位于所述鳍片正上/正下方的鳍片的下/上顶面的间隙宽度d3(如图3B所示)不超过20um，优选的不超过5um。
对于横向间隙，根据使用的工艺不同，可有为图3C至图3E所示的几种变化，在图3C中横向间隙d4被定义为每个鳍片的端面到框架内壁的距离，在图3D中横向间隙d5被定义为每个鳍片的端面到对侧短鳍片端面的距离，在图3E中横向间隙d6被定义为每个鳍片的侧壁与对侧短鳍片的侧壁的距离。d4、d5、d6的值不超过50um，优选的不超过20um。
纵向间隙的形成方式可参考图4A至图4C，其中可以用到SOI型晶圆。图4A至图4C是根据本发明实施方式的MEMS扬声器的纵向间隙的形成方式的示意图。图4D是本发明实施方式涉及的SOI型晶圆的结构的示意图，其中TS为顶硅，OX为二氧化硅层，BS为底硅。
对于d2的形成，可参考图4A，在C2的上表面边缘具有二氧化硅材质的一圈凸起CR2，CR2的高度即为d2。可以利用SOI型晶圆的二氧化硅层来实现。即用SOI型晶圆的顶硅加工形成D1，中间的二氧化硅层形成CR2，底硅形成C2。这种情况下D1和CR2实际上不存在分离状态，图中仅为示意。另外，也可以不采用SOI型晶圆，而是在一块硅基底上形成C2，以及在该硅基底上刻蚀形成D1，或者在该硅基底上沉积材料从而形成D1。
对于d1的形成，可以是C1下表面边缘的凸起的高度，其形成方式可参考d2的形成。如果C1是用单独一块硅基底形成，参考图4B，可在加工完成之后翻转覆盖到D1上。在C1和C2中的一者采用SOI型晶圆，那么另一者即可单独采用一块硅基底进行制作。
对于d3的形成，可参考图4C，如果执行器为D1和D2两层，可以在其中一层例如D1的边缘形成一圈凸起DR1，然后翻转覆盖到D2上。类似于上述d1和d2，可以采用SOI型晶圆制作D1，此时该DR1即为二氧化硅层形成；也可以采用硅基底制作D1，此时在该硅基底上刻蚀可形成该DR1，或者在该硅基底上沉积材料形成该DR1。
对于横向间隙，可以采用深硅刻蚀Bosch工艺结合图形化掩模的方式来实现，间隙尺寸由掩模窗口尺寸决定。此外，横向间隙还可以采用机械加工方式实现，较为常见的是采用圆盘硅晶圆划片刀，通过高速旋转对鳍片结构末端进行切割得到，此时间隙尺寸由刀片厚度，刀片转速以及进给速度等参数决定。对于图3C和图3D，可以先用图形化掩模制作出不包含d4和d5的执行器分支，即执行器分支两端连接侧壁，然后再在图中标示d4和d5之处进刀切割。
对于图3E，可以先用图形化掩模的方式形成不存在间隙d6的状态，即此时形成折线形的硅基骨架，然后再在图3E的上、下方执行器分支的连接处例如标示的d6之处进刀切割；或者通过图形化掩膜后进行深硅干法刻蚀或湿法刻蚀直接得到。
以下再对于本发明实施方式中的MEMS扬声器的执行器加工方式作进一步说明。
本发明实施方式中，如前文提及的，采用图4D所示的SOI型晶圆来加工执行器。可参考图5A和图5B，图5A和图5B是根据本发明实施方式的在SOI型晶圆上进行刻蚀以形成执行器分支的中间状态的示意图。其中图5A为立体状态图，图5B是图5A相应的线条图。加工时，总体而言，在SOI型晶圆的顶硅上形成多个平行的槽，槽的壁即作为执行器分支；槽底为SiO2层，需要全部作为牺牲层去除或者只留周围的一圈，可参考图4A中的CR2。这个各执行器分支即上下悬空从而可以摆动。
在进行刻蚀时，本发明实施方式提出选取<110>型硅晶圆进行刻蚀并且掩膜窗口具有特定的方向，以形成条状的执行器分支。关于晶向可参考图6A至图6E，图6A至图6E是本发明实施例涉及的晶向的示意图。图6A至图6E中，每个立方体都是一个晶格元胞，图6A中的阴影平面为<110>晶面，图6B至图6E中的阴影平面为<111>晶面，其中图6C和图6D中的阴影平面平行，其与<110>晶面的交线为Q1；图6B和图6E中的阴影平面平行，其与<110>晶面的交线为Q2，此处的Q1和Q2示于图6F中，图6F是<110>晶面和<111>晶面在晶圆上的交线的示意图。如图6F所示，晶圆W1与<110>晶面平行，则与晶圆W1垂直的平面(在图中即体现为一条直线)可以分为两组，一组与Q1平行，另一组与Q2平行。这两组之间夹角约为70.53°。另外图6F中示出了晶圆的倒角B1，其基本上平行于Q1。
操作时可在高温(80-120摄氏度)碱性溶液(20％-60％质量浓度的氢氧化钾(KOH)或氢氧化钠(NaOH)溶液或其它碱性溶液)对<110>型硅晶圆进行湿法刻蚀。其中所用的掩膜如图7A和图7B所示，图7A是根据本发明实施方式的掩膜的示意图，图7B是使用图7A的掩膜进行湿法刻蚀的效果的示意图。本发明实施方式中的掩膜外轮廓为矩形，在实现中也可以采用其他形状，但掩膜窗口需要相应于执行器分支的形状。将图7A中的掩膜M2铺在图4D的SOI型晶圆的TS层上表面，并且L方向与上述的Q1或Q2方向大致平行，偏离角度在2°之内，否则刻蚀无法形成呈条形的刻蚀槽，从而无法得到条形的执行器分支。刻蚀之后得到图7B的状态，该状态的立体图即为图5A和图5B(图5A和图5B示出了晶圆的一部分)。从图中可以看出，在条形掩膜窗口的左右两端形成了五边形倾斜面P4，以及<111>晶面P5。此处的扬声器的侧壁较厚，由此可提高其机械强度。P1面和P0面为<110>晶面，P2面和P3面平行，为<111>晶面，即如果P2面和P3面沿Y轴延伸的方向为Q1方向，则P5为Q2方向。
P2面和P3面与P1面形成了理想的直角，但在刻蚀过程中并非如此，可参考图8，图8是根据本发明实施方式的刻蚀过程的示意图，该图对应 于图5A或图5B的XZ平面。在刻蚀过程中，P1面在顶硅中不断地下降从而形成沟槽，沟槽侧壁为垂直度良好的<111>晶面，而沟槽底部与侧壁的相交处还生成了晶向为<112>的微小倾斜面。由于此<112>面会对后续工艺造成不利影响，所以需将其除去。实验结果表明，<112>晶面在湿法环境中极不稳定，形成后便很快在刻蚀液中分解掉并被位于其下的新<112>晶面所替代，因此若将图8中沟槽底面所在的平面P1以下的单晶硅材料替换为止刻材料(止刻材料指某种与单晶硅相比高度耐刻蚀的材料，如对于KOH刻蚀环境，止刻材料可以是二氧化硅，氮化硅等)，并适度延长刻蚀时间便可以将此<112>晶面除去，而侧壁<111>面仍保持稳定，从而形成了沟槽底部的P1与<111>晶面所成的理想的直角。因此，可以采用SOI型晶圆进行上述加工，利用其中间的SiQ2层作为止刻层。当然也可以采用其他方式，例如带有二氧化硅层的硅材料等。
采用上述方式不仅沟槽侧壁的垂直度良好，还能够获得光滑的表面。而沟槽侧壁即为执行器分支的侧面。参考图9A和图9B，图9A是根据现有技术中刻蚀方式得到的硅材料的扫描电镜成像，图9B是根据本发明实施方式的刻蚀方式得到的硅材料的扫描电镜成像。图9A中的硅材料通常由现有技术中的Bosch体系的深度硅刻蚀(DRIE)来实现，该工艺实际上是由若干次各向同性刻蚀循环构成，因此通常会在侧壁上留下许多鳞片或波浪状起伏，如图9A所示，这些起伏不仅密集而且起伏顶点到谷点的距离通常为几十个甚至上百个纳米。这种硅基骨架的表面状态会对后续生长于其上的三明治膜层的晶格状态产生非常不利的影响，尤其会导致氮化铝压电层的晶向混乱及膜层平整度恶化，从而大幅度降低压电层的机电耦合系数和对输入电能的利用效率，最终导致鳍片振幅低而无法输出足够声压。而采用本发明实施方式，可以避免这些不利情况的产生。
利用氢气氛围高温退火(如在100％的氢气氛围内1100摄氏度下热处理20分钟以上)可以大幅降低Bosch工艺后硅基的粗糙度。但是Bosch工艺刻蚀机和氢气退火炉往往价格昂贵，且氢气属于高危气体，对周边配套的安全防护措施要求严苛，因此Bosch工艺结合氢气退火的方案制造成 本高。另一方面，Bosch工艺刻蚀硅基骨架形成的鳍片垂直度不佳，通常难以保证片间和片内的绝大部分鳍片垂直度大于80度，因此Bosch工艺结合氢气退火的方案制造良率较低。
而采用本发明实施方式中上述的方不仅可以生成陡直度更好的鳍片侧面(接近90度)，且侧面的光洁度也要显著优于Bosch工艺的加工结果(如图9B所示，通过高温KOH溶液刻蚀后，大部分区域的粗糙度低于10nm)，无需氢气退火工艺就已可满足后续膜层生长的要求，并且电子级纯度的氢氧化钾等强碱市场价格低廉，因此可大幅降低制造成本，且制造良率很高。
湿法刻蚀<110>型硅晶圆的不足之处在于对某些型面的操控性差，除了生成可利用的陡直的<111>晶面之外还会不可避免地会生成额外的型面。参考图10A和图10B，图10A和图10B是根据本发明实施方式的湿法刻蚀时形成的执行器分支与扬声器内壁距离变化的示意图。如图10A所示的图形化掩模M3的鳍片掩模具有长度L1和自由端E1，且E1与掩膜的另一边E2之间有间隙。实验表明，在掩模M3覆盖下经湿法刻蚀所生成的鳍片结构的自由端并不能在刻蚀液中形成稳定的<111>晶面，导致自由端E1会不断在湿法环境下被分解掉，从而使鳍片真实长度L2按左边4个箭头的方向缩短，从而短于设计长度L1；同时边缘E2也会在刻蚀液的作用下向右移动(如图中右边箭头方向所示)，从而使鳍片末端与边界之间的间隙大于设计尺寸，如图10B所示，导致扬声器的气密性变差。
为解决上述问题，参考图11A和图11B，是根据本发明实施方式的形成执行器分支端部间隙的示意图。可先采用图7A的掩模加工出图7B中的结构并沉积各功能层，然后附加掩模，利用Bosch工艺在每个鳍片上加工出图11A和图11B所示的间隙X1。在此过程中，Bosch工艺对缝隙宽度d5以及缝隙与<111>晶面P4位于沟槽底部的顶点的距离t1可实现良好的控制精度。由于X1的两个侧壁并不需要沉积任何膜层，因此Bosch工艺带来的局部粗糙度并不会对器件性能带来任何影响。通过湿法和Bosch 刻蚀工艺结合，一方面可以得到光洁度和陡直度理想的主型面，还可实现对局部工艺面的精确控制；同时选用<110>型的硅晶圆可以同时兼容上述两种工艺。
根据本发明实施方式的技术方案，MEMS扬声器的通孔和执行器有特定的排布，并且内部各间隙有尺寸要求，有助于提高扬声器的输出声压。该MEMS扬声器应用于电子设备时，占用空间小，并且音量大。采用湿法对<110>型硅晶圆进行刻蚀，掩膜窗口条形部具有特定方向，从而形成执行器的条形分支。在此基础上，再结合Bosch工艺，可以进一步提高扬声器的气密性。本发明实施方式从MEMS扬声器的执行器的形状和表面性质来提高其性能：MEMS压电执行器鳍片具有垂直的侧面，因此可以充分利用扬声器的垂直纵向空间，在小空间下实现更大的声压和音量；MEMS压电执行器的垂直侧面同时非常光滑，因此其上的压电薄膜质量好，压电系数高，因此执行器可以实现大的位移量，在小空间下实现更大的声压和音量。
上述具体实施方式，并不构成对本发明保护范围的限制。本领域技术人员应该明白的是，取决于设计要求和其他因素，可以发生各种各样的修改、组合、子组合和替代。任何在本发明的精神和原则之内所作的修改、等同替换和改进等，均应包含在本发明保护范围之内。

Claims (17)

  1. 一种MEMS扬声器，所述扬声器的执行器具有多个按振动方向平行排布的条形分支，其特征在于，
    所述条形分支的硅基骨架的具有层叠结构的侧面与相邻侧面的夹角在70°至110°之间或者在80°至100°之间；
    并且/或者，所述硅基骨架的具有层叠结构的侧面的粗糙度小于100nm或小于10nm。
  2. 根据权利要求1所述的MEMS扬声器，其特征在于，
    所述条形分支的硅基骨架为<110>型硅，该硅基骨架的垂直于振动方向的面为<111>晶面。
  3. 根据权利要求2所述的MEMS扬声器，其特征在于，
    相邻所述硅基骨架的端部之间的扬声器内壁具有五边形倾斜面。
  4. 根据权利要求1、2或3所述的MEMS扬声器，其特征在于，
    在硅基骨架两侧面或一侧面由内向外依次为压电层、顶电极；
    或者，在硅基骨架两侧面或一侧面由内向外依次为底电极、压电层、顶电极；
    或者，在硅基骨架两侧面或一侧面依次为晶种层、底电极、压电层、顶电极。
  5. 根据权利要求1、2或3所述的MEMS扬声器，其特征在于，所述硅基骨架的材料为N型或P型掺杂硅。
  6. 根据权利要求4所述的MEMS扬声器，其特征在于，所述掺杂硅的电阻率低于2000欧姆厘米。
  7. 一种制造MEMS扬声器的方法，所述扬声器的执行器具有多个平 行设置的条形分支，其特征在于，该方法包括：
    在<110>硅晶圆上覆盖掩膜，然后使用湿法进行刻蚀以得到所述条形分支的硅基骨架，该掩膜的掩膜窗口具有条形部；
    或者，在硅晶圆上覆盖掩膜，使用深硅刻蚀工艺得到所述条形分支的硅基骨架，然后将硅基骨架在氢气氛围内高温退火，该掩膜的掩膜窗口具有条形部。
  8. 根据权利要求7所述的方法，其特征在于，
    该条形部与<110>晶面和<111>晶面的一条交线的夹角在2°以内，该<111>晶面垂直于该<110>晶面。
  9. 根据权利要求7所述的方法，其特征在于，
    所述硅晶圆为SOI型晶圆，该SOI型晶圆的二氧化硅层作为止刻层。
  10. 根据权利要求9所述的方法，其特征在于，还包括：在水平方向上去除所述二氧化硅层的中间部分，以形成一圈二氧化硅凸起。
  11. 根据权利要求7所述的方法，其特征在于，得到所述条形分支的硅基骨架之后，在硅基骨架上形成各功能层。
  12. 根据权利要求11所述的方法，其特征在于，
    在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作压电层、顶电极；
    在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作底电极、压电层、顶电极；
    或者，在硅基骨架上形成各功能层的步骤包括：在硅基骨架两侧面或一侧面依次制作晶种层、底电极、压电层、顶电极。
  13. 根据权利要求11或12所述的方法，其特征在于，
    所述掩膜窗口为多个平行的条形窗口；
    在硅基骨架上形成各功能层之后，采用刀具对所述刻蚀所得到的条形分支进行切割以形成具有自由端的条形分支。
  14. 根据权利要求11或12所述的方法，其特征在于，
    所述掩膜窗口为多个平行的条形窗口；
    在硅基骨架上形成各功能层之后，在执行器分支上覆盖掩膜，掩膜窗口的位置对应于执行器分支的需要断开的位置，采用深硅刻蚀工艺进行加工。
  15. 根据权利要求11或12所述的方法，其特征在于，
    所述掩膜窗口为多个并行设置的折线形窗口，所述折线形窗口包含依次连接的第一直线部、转折部、第二直线部，其中第一直线部与第二直线部平行，二者的自由端分别位于掩膜窗口的一组对边；
    在硅基骨架上形成各功能层之后，采用刀具切除所述刻蚀所得到的折线形分支中的转折部以形成具有自由端的条形分支。
  16. 根据权利要求11或12所述的方法，其特征在于，
    所述掩膜窗口为多个并行设置的折线形窗口，所述折线形窗口包含依次连接的第一直线部、转折部、第二直线部，其中第一直线部与第二直线部平行，二者的自由端分别位于掩膜窗口的一组对边；
    在硅基骨架上形成各功能层之后，在执行器分支上覆盖掩膜，掩膜窗口的位置对应于执行器分支的转折部，采用深硅刻蚀工艺进行加工。
  17. 一种电子设备，其特征在于，包含权利要求1至6中任一项所述的MEMS扬声器。
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Citations (4)

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Publication number Priority date Publication date Assignee Title
US20170125660A1 (en) * 2011-11-29 2017-05-04 Qualcomm Mems Technologies, Inc. Transducer with piezoelectric, conductive and dielectric membrane
CN109879238A (zh) * 2019-01-15 2019-06-14 江苏大学 内嵌通道式的微悬臂梁装置、加工方法及一种检测方法
CN111182428A (zh) * 2019-12-31 2020-05-19 瑞声科技（南京）有限公司 Mems扬声器及其制造方法
CN111885469A (zh) * 2020-07-09 2020-11-03 诺思(天津)微***有限责任公司 Mems扬声器及其制造方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170125660A1 (en) * 2011-11-29 2017-05-04 Qualcomm Mems Technologies, Inc. Transducer with piezoelectric, conductive and dielectric membrane
CN109879238A (zh) * 2019-01-15 2019-06-14 江苏大学 内嵌通道式的微悬臂梁装置、加工方法及一种检测方法
CN111182428A (zh) * 2019-12-31 2020-05-19 瑞声科技（南京）有限公司 Mems扬声器及其制造方法
CN111885469A (zh) * 2020-07-09 2020-11-03 诺思(天津)微***有限责任公司 Mems扬声器及其制造方法

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