CN216559443U - MEMS substrate and MEMS pressure sensor - Google Patents
MEMS substrate and MEMS pressure sensor Download PDFInfo
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- CN216559443U CN216559443U CN202123448244.0U CN202123448244U CN216559443U CN 216559443 U CN216559443 U CN 216559443U CN 202123448244 U CN202123448244 U CN 202123448244U CN 216559443 U CN216559443 U CN 216559443U
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Abstract
The utility model provides an MEMS substrate and an MEMS pressure sensor, wherein the MEMS substrate comprises an inner cavity local thinning structure, the inner cavity local thinning structure is arranged in a cavity and is positioned in the substrate, so that the structure still keeps the smoothness of the surface of the substrate after the preparation of a strain film structure is finished, and the manufacturing of the integration of a sensor and a circuit is easy.
Description
Technical Field
The utility model belongs to the field of micro-electro-mechanical system (MEMS) sensor design, and relates to an MEMS substrate and an MEMS pressure sensor.
Background
An MEMS (micro Electro Mechanical system), namely a micro Electro Mechanical system, is a novel interdisciplinary high and new technical field, integrates a plurality of micro processing technologies, and can realize acquisition, processing and conversion of a plurality of information quantities. When some sensor devices are manufactured by using the MEMS technology, a thin film structure is used, in which a cavity is formed on the surface or back of a silicon wafer by using a semiconductor processing process, and a sealed cavity is formed by bonding with a substrate or filling a material, so as to form a structure of the thin film and the cavity. Firstly, using a dry method or a wet method to carry out anisotropic corrosion on the back of a silicon wafer to form a strain film structure with the thickness of several microns to dozens of microns on a local substrate, and then carrying out anodic bonding on the corroded silicon wafer and glass to form a sealed cavity; secondly, forming a vacuum cavity on the surface of the silicon wafer by adopting an MEMS sacrificial layer technology, specifically, depositing a sacrificial layer material on the surface of the substrate, depositing a layer of stress film material on the sacrificial layer, manufacturing holes on two sides by utilizing photoetching to release the sacrificial layer, and finally sealing the through hole to form a sealed cavity; thirdly, using two silicon wafers, wherein one silicon wafer is used as a device layer, the other silicon wafer is used as a substrate, thermally oxidizing the substrate to form a layer of silicon dioxide, manufacturing a cavity on the substrate, etching to manufacture the cavity, bonding the silicon wafer used as the device layer with the substrate with the cavity, and thinning the thickness of the device layer to a required strain film to form a structure similar to an SOI silicon wafer and a sealed cavity; fourthly, monocrystalline silicon or polycrystalline silicon is used as a substrate, shallow grooves are etched on the silicon substrate through anisotropic etching, then, after the side walls of the shallow grooves are protected, isotropic etching is carried out to generate communicated cavities, then, a sealed cavity is formed on the substrate through an epitaxial monocrystalline silicon or polycrystalline silicon mode, and finally, the surface of the silicon substrate is flat through mechanical polishing.
The piezoresistor is manufactured on the surface of the wafer by the methods of ion implantation and the like on the basis of the structure of the sealed cavity and the strain film, the resistance value change of the piezoresistor caused by the deformation of the film due to factors such as external pressure and the like is converted into the change of output voltage by applying voltage to the piezoresistor, and various types of sensors can be manufactured on the basis of the structure and the principle. When manufacturing such a high-sensitivity sensor device having a thin film structure, in addition to reducing the thickness of the strained film, the strained film structure is usually locally thinned to form a cross beam structure, so as to further improve the sensitivity of the device. The cross beam structure has the advantages that stress concentration is realized, the sensitivity of a device is improved, the integral rigidity of the structure is increased, and the linearity and the dynamic response characteristic of the sensor are improved.
However, the structures have disadvantages, the cavity and the strain film are manufactured by utilizing anisotropic etching, the consistency and the repeatability of the device are difficult to ensure due to harsh process conditions, the thickness of the strain film is difficult to accurately control, and meanwhile, the required size of the bottom of the cavity is far larger than that of the silicon strain film due to the inclination angle between the side surface of the formed cavity and the silicon strain film, which is not beneficial to the miniaturization design of the pressure sensor; in the cavity structure manufactured by using the MEMS sacrificial layer technology, a strain film of the cavity structure usually has residual stress and stress gradient, which causes the problems of low sensitivity, large hysteresis error and the like of a sensor; meanwhile, in order to improve the sensitivity, when the cross beam structure is prepared, corrosion or etching needs to be carried out on the surface of the device layer of the silicon wafer, so that the surface is uneven, and the integration of a sensor and a circuit is difficult to follow.
SUMMERY OF THE UTILITY MODEL
The utility model aims to solve the problems and provides an MEMS substrate and an MEMS pressure sensor, wherein an inner cavity local thinning structure is arranged in a substrate cavity and is positioned in the substrate, so that the structure has the advantages of the traditional cross beam structure, the flatness of the surface of the substrate is still kept after the preparation of a strain film structure is finished, and the sensor and a circuit are easy to integrate and manufacture.
Specifically, the technical scheme of the utility model is as follows:
a MEMS substrate comprising:
the device comprises a first substrate, a second substrate and a cavity, wherein the first substrate and the second substrate are overlapped, and the cavity is sealed between the first substrate and the second substrate;
wherein the first substrate comprises a first surface and a second surface which are opposite;
the first surface of the first substrate comprises a first groove;
the second substrate comprises a third surface and a fourth surface which are opposite;
a third surface of the second substrate comprises a local thinning structure;
the first groove and the local thinning joint are oppositely arranged to form the inner cavity.
Optionally, the second substrate comprises monocrystalline silicon or an SOI substrate.
Optionally, the locally thinned structure is disposed on a top silicon layer of the SOI substrate.
Optionally, the local thinning structure includes a cross beam structure or a peninsula beam structure formed on the third surface of the second substrate.
Optionally, the cavity top surface includes a partially exposed SOI buried oxide layer.
Optionally, a projection of the local thinning structure in the first groove is located in the first groove.
The utility model also provides a MEMS pressure sensor which comprises the MEMS substrate.
Optionally, the display device further comprises a piezoresistor arranged on the fourth surface of the second substrate.
Optionally, the piezoresistors constitute a wheatstone bridge.
Optionally, the fourth surface is a thinned layer of a bottom silicon layer of the SOI substrate or a top silicon layer with a buried oxide layer of the SOI removed.
Compared with the prior art, the technical scheme provided by the utility model at least has the following beneficial effects:
(1) compared with the traditional piezoresistive pressure sensor with a flat membrane structure, the piezoresistive pressure sensor with the local thinning process of the MEMS inner cavity has the advantages of high sensitivity and large measuring range, and the stress is concentrated to a local thinning area by arranging the local thinning structure and utilizing the stress concentration principle, so that the sensitivity of the sensor is improved;
(2) by arranging the raised mass block, the overall rigidity of the structure is increased, large deformation of the silicon strain film is restrained, the linearity and the dynamic response characteristic of the sensor are improved, and the measuring range of the sensor is improved, so that high sensitivity, high linearity and wide measuring range are realized.
(3) Compared with the traditional piezoresistive pressure sensor with the front cross beam structure, the locally thinned structure controls the size of the cavity to be equal to that of the strain film by arranging the cavity on the first substrate, so that the problem that the bottom surface area of the cavity is larger than that of the strain film due to anisotropic corrosion is solved, and the area of a chip is reduced;
(4) the surface of the second substrate with the local thinning structure is bonded with the first substrate with the cavity to form a base with an inner cavity local thinning structure, the thickness of the strain film can be controlled by thinning the non-bonding surface of the base, so that the thickness of the strain film is not limited by the thickness of the top silicon of the SOI sheet, and compared with the traditional wet etching method for forming the cavity, the precision is higher, and the consistency is better; in addition, no corrosion process is adopted in the subsequent process after bonding, the surface of the substrate is kept flat, and the integration of a circuit and a sensor is facilitated.
Drawings
One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.
FIG. 1 is a schematic top view of a piezoresistive pressure sensor manufactured by the local thinning process of the MEMS inner cavity of the present invention;
FIGS. 2-13 are schematic cross-sectional views of the local thinning process of the MEMS inner cavity along the A-A 'direction and the B-B' direction in FIG. 1;
FIGS. 14-19 are schematic cross-sectional views of a process flow along the direction B-B' in FIG. 1 for fabricating a piezoresistive pressure sensor from a MEMS substrate according to the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not constitute any limitation to the specific implementation manner of the present invention, and the embodiments may be mutually incorporated and referred to without contradiction.
Fig. 1 is a schematic top view of a piezoresistive pressure sensor manufactured by the local thinning process of the MEMS inner cavity of the present invention.
Wherein, in FIGS. 2-10 and 13, (a) is a schematic sectional view along A-A 'direction, and (B) is a schematic sectional view corresponding to B-B' direction; fig. 14-19 correspond to a schematic sectional view in the direction B-B'.
Example 1
The embodiment provides a MEMS substrate with a local thinning structure of an inner cavity, as shown in fig. 2 to 6, including the following steps:
selecting a first substrate 1, the first substrate 1 comprising a first surface 101 and a second surface 102 opposite;
selecting a second substrate 2, the second substrate 2 comprising a third surface 201 and a fourth surface 202 opposite to each other, as shown in fig. 2;
the first substrate in this embodiment may be, for example, a silicon wafer, glass, or ceramic, and has a thickness of, for example, 50 to 800 μm; the second substrate of this embodiment may be selected from an N-type monocrystalline silicon wafer, a P-type monocrystalline silicon wafer, or an soi (silicon on insulator) wafer.
In this embodiment, the first substrate 1 is exemplified by a silicon wafer, and the second substrate 2 is exemplified by a single crystal silicon wafer of an N-type (100) crystal plane.
Etching the first surface 101 of the first substrate 1 to form a first groove 103;
specifically, in order to etch the first groove 103, first, the first substrate 1 is subjected to surface thermal oxidation, and a layer of silicon oxide 3 is grown on each of the front and back sides of the first substrate 1, as shown in fig. 3;
the first surface 101 of the first substrate 1 is patterned and a first recess 103 is etched by a bulk silicon etching process, as shown in fig. 4.
Etching the third surface of the second substrate to form a local thinning structure;
specifically, the third surface 201 of the second substrate 2 is patterned and lithographically patterned to form a local thinning structure 203, as shown in fig. 4;
the local thinning structure 203 may be a cross beam structure or a silicon island structure.
Bonding the first surface 101 of the first substrate 1 and the third surface 201 of the second substrate 2, of course, the first surface 101 of the first substrate 1 further includes an oxide layer 3 thereon, forming an inner cavity 4 including a local thinning structure 203, as shown in fig. 5.
Further, the fourth surface 202 of the second substrate 2 may be further thinned to form a strained film, thereby completely forming a base with a locally thinned inner cavity structure for subsequent sensor applications, as shown in fig. 6.
Example 2
With respect to embodiment 1, the second substrate 2 of the present embodiment employs an SOI substrate, in which the second substrate SOI includes: a bulk silicon layer 204, a buried oxide layer 205, and a top silicon layer 206, as shown in fig. 7.
Wherein the thickness of the bulk silicon layer 204 is, for example, 50-800 μm, the thickness of the buried oxide layer 205 is 1-50 μm, the thickness of the top silicon layer 206 is 1-50 μm,
the second substrate SOI top silicon layer is lithographically and patterned to etch a local region of the SOI top silicon layer 206 to form a top silicon layer local thinning structure 203, as shown in fig. 8.
The steps and processes for etching the first substrate 1 to form the first groove 103 and bonding the first substrate 1 and the second substrate 2 to form the base with the cavity 4 are the same as those of embodiment 1, and are not described again here.
Further, the fourth surface 202 of the second substrate 2 may be further thinned to form a strained film, and in this embodiment, the thinning may be started from the bulk silicon layer 204 of the SOI substrate to the buried oxide layer 205, so as to completely form a base with a locally thinned inner cavity structure for subsequent device applications such as sensors, as shown in fig. 9 to 10.
Example 3
With respect to embodiment 1, the second substrate 2 of the present embodiment employs an SOI substrate, in which the second substrate SOI includes: a bulk silicon layer 204, a buried oxide layer 205, and a top silicon layer 206.
Compared with embodiment 2, in this embodiment, when the top silicon layer local thinning structure 203 is prepared, the top silicon layer 206 is etched to reach the buried oxide layer 205.
The steps and processes for etching the first substrate 1 to form the first groove 103 and bonding the first substrate 1 and the second substrate 2 to form the base with the cavity 4 are the same as those of embodiment 1, and are not described again here.
Wherein the projection of the top silicon layer local thinning structure 203 in the first recess 103 is smaller than in the area of the first recess 103, i.e. the local thinning structure 203 is located in the area of the first recess 103, as shown in fig. 11.
Further, the fourth surface 202 of the second substrate 2 may be further thinned to form a strained film, and in this embodiment, the thinning may be started from the bulk silicon layer 204 of the SOI substrate to the buried oxide layer 205, so as to completely form a base with a locally thinned inner cavity structure for subsequent device applications such as sensors, as shown in fig. 12.
Example 4
With respect to embodiment 1, the second substrate 2 of the present embodiment employs an SOI substrate, in which the second substrate SOI includes: a bulk silicon layer 204, a buried oxide layer 205, and a top silicon layer 206.
Compared with embodiment 2, in this embodiment, when the top silicon layer local thinning structure 203 is prepared, the top silicon layer is etched to the buried oxide layer.
The steps and processes of etching the first substrate 1 to form the first groove 103, and bonding the first substrate 1 and the second substrate 2 to form the base with the cavity 4 are the same as those of embodiment 1, and are not repeated herein.
Wherein the projection of the top silicon layer local thinning structure 203 in the first recess 103 is smaller than in the area of the first recess 103, i.e. the local thinning structure 203 is located in the area of the first recess 103. This is the same as in example 3 and will not be described again.
Further, the fourth surface 202 of the second substrate 2 may be further thinned to form a strained film, and in this embodiment, the thinning may be started from the bulk silicon layer 204 of the SOI substrate until the remaining thickness of the bulk silicon layer 204 is 0.1-50 μm, so as to completely form a base with a locally thinned inner cavity structure for subsequent device applications such as sensors, as shown in fig. 13.
Example 5
The present implementation provides a MEMS pressure sensor and a method of manufacturing the same, the MEMS pressure sensor using the MEMS substrate provided in embodiments 1 to 4 as a substrate, comprising the steps of:
on the substrate obtained in embodiments 1 to 4, the periphery of the strained film 10 is sequentially subjected to photolithography and ion implantation, so as to fabricate a lightly doped varistor 5 and a heavily doped ohmic contact region 6, where the ohmic contact region 6 is mainly used for interconnecting the varistor 5 with a subsequent metal lead 7 and interconnecting the varistors 5, as shown in fig. 14;
depositing an oxide layer with a thickness of 0.01-1 μm and a nitride layer with a thickness of 0.03-3 μm by APCVD, PECVD or LPCVD, etc., thereby forming an insulating dielectric layer 8, as shown in FIG. 15;
the insulating dielectric layer 8 above the ohmic contact region 6 is etched and etched away to form a lead hole 12, as shown in fig. 16;
sputtering one or more layers of metal material such as Au, Al, Ti, etc. to a thickness of 0.1-4 μm and photolithography to form metal leads 7 and metal pads 15, as shown in fig. 17;
forming a protective layer 11 by depositing an oxide layer having a thickness of 0.01 to 1 μm and a nitride layer having a thickness of 0.03 to 3 μm by APCVD, PECVD, LPCVD, or the like, as shown in fig. 18;
the resist 11 over the metal pad 15 is photo-etched and removed, so that the metal pad 15 is exposed as a metal pad 15 for testing, as shown in fig. 19.
In this example, the substrate obtained in example 1 was used as a substrate to prepare a MEMS pressure sensor, and the substrates obtained in other examples were used to prepare MEMS pressure sensors in the same manner, and the description thereof will not be repeated.
Has the advantages that:
(1) compared with the traditional piezoresistive pressure sensor with a flat membrane structure, the piezoresistive pressure sensor with the local thinning process of the MEMS inner cavity has the advantages of high sensitivity and large measuring range, and the stress is concentrated to a local thinning area by arranging the local thinning structure and utilizing the stress concentration principle, so that the sensitivity of the sensor is improved;
(2) by arranging the raised mass block, the overall rigidity of the structure is increased, large deformation of the silicon strain film is restrained, the linearity and the dynamic response characteristic of the sensor are improved, and the measuring range of the sensor is improved, so that high sensitivity, high linearity and wide measuring range are realized.
(3) Compared with the traditional piezoresistive pressure sensor with the front cross beam structure, the locally thinned structure controls the size of the cavity to be equal to that of the strain film by arranging the cavity on the first substrate, so that the problem that the bottom surface area of the cavity is larger than that of the strain film due to anisotropic corrosion is solved, and the area of a chip is reduced;
(4) the surface of the second substrate with the local thinning structure is bonded with the first substrate with the cavity to form a base with an inner cavity local thinning structure, the thickness of the strain film can be controlled by thinning the non-bonding surface of the base, so that the thickness of the strain film is not limited by the thickness of the top silicon of the SOI sheet, and compared with the traditional wet etching method for forming the cavity, the precision is higher, and the consistency is better; in addition, no corrosion process is adopted in the subsequent process after bonding, the surface of the substrate is kept flat, and the integration of a circuit and a sensor is facilitated.
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the utility model, and that various changes in form and details may be made therein without departing from the spirit and scope of the utility model in practice.
Claims (10)
1. A MEMS substrate, comprising:
the device comprises a first substrate, a second substrate and a cavity, wherein the first substrate and the second substrate are overlapped, and the cavity is sealed between the first substrate and the second substrate;
wherein the first substrate comprises a first surface and a second surface which are opposite;
the first surface of the first substrate comprises a first groove;
the second substrate comprises a third surface and a fourth surface which are opposite;
a third surface of the second substrate comprises a local thinning structure;
the first groove and the local thinning joint are oppositely arranged to form the inner cavity.
2. A MEMS substrate according to claim 1 wherein: the second substrate includes a single crystal silicon or an SOI substrate.
3. A MEMS substrate according to claim 2 wherein: the local thinning structure is arranged on the top silicon layer of the SOI substrate.
4. A MEMS substrate according to claim 1 wherein: the local thinning structure comprises a cross beam structure or a peninsula beam film structure formed on the third surface of the second substrate.
5. A MEMS substrate according to claim 2 wherein: the top surface of the inner cavity comprises a partially exposed SOI buried oxide layer.
6. A MEMS substrate according to claim 2 wherein: the projection of the local thinning structure in the first groove is positioned in the first groove.
7. A MEMS pressure sensor comprising the MEMS substrate of any one of claims 1-6.
8. The MEMS pressure sensor of claim 7, further comprising a piezo-resistor disposed on a fourth surface of the second substrate.
9. The MEMS pressure sensor of claim 8, wherein the piezoresistors form a wheatstone bridge.
10. The MEMS pressure sensor of claim 8, wherein the fourth surface is a thinned layer of a bulk silicon layer of the SOI substrate or a top silicon layer with a buried oxide layer of the SOI removed.
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| CN202123448244.0U CN216559443U (en) | 2021-12-31 | 2021-12-31 | MEMS substrate and MEMS pressure sensor |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114964599A (en) * | 2022-06-14 | 2022-08-30 | 南京高华科技股份有限公司 | Micromechanical pressure sensor and method for producing the same |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114964599A (en) * | 2022-06-14 | 2022-08-30 | 南京高华科技股份有限公司 | Micromechanical pressure sensor and method for producing the same |
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