A MEMS multifunctional sensor and a preparation method thereof

Abstract

The application provides a MEMS multifunctional sensor and a preparation method thereof. The MEMS multifunctional sensor comprises a first substrate, a second substrate and a sensor component. The first substrate comprises a sensor area and an annular bonding area. The annular bonding area is connected to the sensor area along the circumference of the sensor area. A circumferential cavity is formed between the annular bonding area and the sensor area. The circumferential cavity is an annular cavity structure. The annular bonding area is bonded to the second substrate. The end of the annular bonding area in contact with the second substrate has an annular groove. The second substrate covers the annular groove of the annular bonding area and forms an annular bonding cavity. The sensor component is arranged in the sensor area and is used for sensing external pressure. The circumferential cavity and the thin layer of medium around the bonding cavity can offset part of the thermal stress transmitted from the bonding interface, effectively reduce the bonding thermal stress at the position of the pressure-sensitive resistor, avoid the sensor zero-point output drift caused by stress concentration, and improve the output accuracy of the sensor.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application belong to the technical field of micro-electro-mechanical system (MEMS), and particularly relate to a MEMS multifunctional sensor and a preparation method thereof. BACKGROUND

[0002] MEMS sensors can be classified into piezoresistive, capacitive, resonant and piezoelectric types. Among them, MEMS piezoresistive sensors have an important position in this field due to their high sensitivity, fast response, miniaturization and low power consumption. Generally, MEMS piezoresistive sensors work based on the piezoresistive effect. When external physical quantities act on the sensitive film, the film deforms, causing the resistance of the piezoresistive resistor to change, and the change is converted into an electrical signal output through a Wheatstone bridge.

[0003] Traditional MEMS piezoresistive sensors generally adopt a square prism sealed cavity structure, and use a "back" shaped bonding area to connect different substrates during the process of wafer processing. However, due to the difference in the thermal expansion coefficient between the silicon substrate and the glass substrate, and the temperature required by the anodic bonding process is significantly higher than the working temperature, thermal stress will be generated at the bonding interface, which is transmitted to the film surface and the piezoresistive resistor through the silicon substrate medium above the bonding interface, thereby causing zero drift problem and affecting the measurement accuracy of the sensor. To solve this problem, low-temperature bonding process is usually used in the prior art, but this will reduce the bonding strength and affect the service life of the sensor. SUMMARY

[0004] Embodiments of the present application aim to at least solve one of the technical problems existing in the prior art, and provide a MEMS multifunctional sensor and a preparation method thereof.

[0005] The first aspect of the present application provides a MEMS multifunctional sensor, which comprises:

[0006] A first substrate, the first substrate comprises a sensor area and an annular bonding area, the annular bonding area is connected to the sensor area along the circumference of the sensor area, a circumferential cavity is formed between the annular bonding area and the sensor area, and the circumferential cavity is an annular cavity structure;

[0007] A second substrate, the annular bonding area is bonded to the second substrate, one end of the annular bonding area in contact with the second substrate has an annular groove, and the second substrate covers the annular groove of the annular bonding area and forms an annular bonding cavity;

[0008] A sensor assembly, the sensor assembly is arranged in the sensor area, and the sensor assembly is used for sensing external pressure.

[0009] In some embodiments of the present application, the circumferential cavity comprises a first annular cavity and a second annular cavity along a direction from the first substrate to the second substrate, the first annular cavity is in communication with the second annular cavity, and a radial thickness of the first annular cavity is greater than a radial thickness of the second annular cavity.

[0010] In some embodiments of the present application, the second annular cavity is in communication with the first annular cavity near an inner ring of the sensor region.

[0011] In some embodiments of the present application, a cross section of the annular groove is trapezoidal.

[0012] In some embodiments of the present application, an end cavity is formed between the sensor region and the second substrate, the end cavity is in communication with the circumferential cavity.

[0013] In some embodiments of the present application, the sensor region has a thin film cavity, the thin film cavity is a cuboid cavity, a cross section of the cuboid cavity is square in a thickness direction perpendicular to the first substrate, a portion of the sensor region corresponding to a side of the thin film cavity away from the second substrate is a sensitive thin film, and the sensor assembly comprises:

[0014] four first piezoresistors, the four first piezoresistors are arranged on a side of the sensitive thin film away from the second substrate, the four first piezoresistors are respectively arranged at centers of four sides of the thin film cavity, and the four first piezoresistors constitute a first Wheatstone bridge;

[0015] four pairs of first ohmic contacts, each pair of the first ohmic contacts is arranged at two ends of a corresponding one of the first piezoresistors.

[0016] In some embodiments of the present application, the sensor region has four block cavities, the four block cavities correspond to four corners of the thin film cavity, each of the block cavities is in communication with the thin film cavity and the end cavity, a portion of the sensor region between two adjacent block cavities forms a bridge, a portion of the sensor region between the four block cavities forms a mass block, the mass block is arranged at a center of the thin film cavity, and the sensor assembly comprises:

[0017] four second piezoresistors, the four second piezoresistors are respectively arranged on a side of each of the four bridges away from the thin film cavity, and the four second piezoresistors constitute a second Wheatstone bridge.

[0018] four pairs of second ohmic contacts, each pair of the second ohmic contacts is arranged at two ends of a corresponding one of the second piezoresistors.

[0019] In some embodiments of the present application, each of the second piezoresistors is arranged at an end of the bridge close to the mass block.

[0020] In some embodiments of the present application, the MEMS multifunctional sensor further comprises an insulating layer covering the surface of the first substrate away from the second substrate.

[0021] The second aspect of the present application provides a preparation method of a MEMS multifunctional sensor, which is used for preparing the MEMS multifunctional sensor of any of the above embodiments, and the method comprises:

[0022] Step one: select an N-type single crystal silicon wafer with a 100 crystal face as the first substrate;

[0023] Step two: prepare a silicon dioxide thin layer at the shallow layer on the upper surface of the first substrate by oxygen injection isolation technology, to prepare for the subsequent preparation of a thin film cavity and a circumferential cavity;

[0024] Step three: form a ring cavity shape required for the bonding cavity by wet etching on the outside of the bottom of the first substrate;

[0025] Step four: form a cylindrical end cavity by photolithography and deep reactive ion etching on the inner side area of the bottom of the first substrate;

[0026] Step five: again prepare a cavity and a ring-shaped narrow slot on the central and peripheral areas of the bottom of the first substrate by photolithography and deep reactive ion etching, so as to expose the mass block and the lower half of the bridge structure, and ensure that the silicon dioxide thin layer on the shallow layer of the upper surface of the silicon wafer is in communication;

[0027] Step six: remove the silicon dioxide thin layer by wet etching on the shallow layer of the upper surface of the first substrate through the cavity and the ring-shaped narrow slot, to form a thin film cavity, a sensitive thin film, a circumferential cavity, a mass block and a bridge; the thin film cavity is in communication with the four block cavities around the mass block;

[0028] Step seven: form a first piezoresistor and a second piezoresistor by P-type doping on the surface and back of the silicon wafer;

[0029] Step eight: form a first ohmic contact and a second ohmic contact by P-type heavy doping on both ends of the first piezoresistor and the second piezoresistor;

[0030] Step nine: form an insulating layer by depositing a silicon dioxide layer on the surface of the silicon wafer;

[0031] Step ten: select a glass wafer, and realize the sealing of the cavity and form a second substrate by anodically bonding the ring-shaped bonding area on the back of the silicon wafer with the surface of the glass substrate, so as to complete the preparation of the sensor.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] 1. The MEMS multifunctional sensor of the present invention, by adopting a special structure of annular bonding region and end cavity, can transmit bonding thermal stress upward in a uniform and rapidly decreasing manner, and utilize the deformation of the circumferential cavity and the thin layer of dielectric around the bonding cavity to offset part of the thermal stress transmitted from the bonding interface, effectively reducing the bonding thermal stress at the location of the varistor, avoiding zero-point output drift of the sensor caused by stress concentration, and improving the sensor output accuracy.

[0034] 2. The MEMS multifunctional sensor of the present invention utilizes the medium beneath the pressure sensor's sensitive film to fabricate the accelerometer mass block and bridge through a stacking method, thereby achieving device integration, improving space utilization, and simplifying the processing flow by optimizing the cavity release process, achieving compatibility between floor space and fabrication process optimization, and reducing production costs.

[0035] 3. The MEMS multifunctional sensor of the present invention increases the bonding strength at the bonding interface by using single-crystal silicon dielectrics on both sides of the bonding cavity, and maintains the internal vacuum environment by utilizing the double-layer cavity structure of the end cavity and the bonding cavity, ensuring long-term airtightness, extending the device life, and reducing the damping coefficient of the accelerometer, thereby improving the quality factor and sensitivity of the sensor. Attached Figure Description

[0036] Figure 1 This is a top view schematic diagram of the arrangement of pressure sensor piezoresistors in the MEMS multifunctional sensor of the present invention;

[0037] Figure 2 This is a top view schematic diagram of the arrangement of accelerometer piezoresistors in the MEMS multifunctional sensor of the present invention;

[0038] Figure 3 The MEMS multifunctional sensor of the present invention is along Figure 1 Cross-sectional view along the A-A' direction;

[0039] Figure 4 This is a cross-sectional view of the structure corresponding to step one in the embodiments of the present invention;

[0040] Figure 5 This is a cross-sectional view of the structure corresponding to step two in this embodiment of the invention;

[0041] Figure 6 for Figure 5 The diagram shows the B-B' cross-section of the structure corresponding to step two of the preparation process.

[0042] Figure 7 This is a cross-sectional view of the structure corresponding to step three in this embodiment of the invention;

[0043] Figure 8 for Figure 7The diagram shows the bottom view of the structure corresponding to step three of the preparation process.

[0044] Figure 9 This is a cross-sectional view of the structure corresponding to step four in this embodiment of the invention;

[0045] Figure 10 for Figure 9 The bottom view of the structure corresponding to preparation step four is shown;

[0046] Figure 11 This is a cross-sectional view of the structure corresponding to step five in this embodiment of the invention;

[0047] Figure 12 for Figure 11 The bottom view of the structure corresponding to preparation step five is shown;

[0048] Figure 13 This is a cross-sectional view of the structure corresponding to step six in this embodiment of the invention;

[0049] Figure 14 for Figure 13 The diagram shows the B-B' cross-sectional view of the structure corresponding to preparation step six;

[0050] Figure 15 for Figure 13 The bottom view of the structure corresponding to preparation step six is ​​shown;

[0051] Figure 16 This is a cross-sectional view of the structure corresponding to step seven in this embodiment of the invention;

[0052] Figure 17 for Figure 16 The top view of the structure corresponding to preparation step seven is shown;

[0053] Figure 18 for Figure 16 The bottom view of the structure corresponding to preparation step seven is shown;

[0054] Figure 19 This is a cross-sectional view of the structure corresponding to step eight in this embodiment of the invention;

[0055] Figure 20 for Figure 19 The top view of the structure corresponding to preparation step eight is shown;

[0056] Figure 21 for Figure 19 The bottom view of the structure corresponding to preparation step eight is shown.

[0057] Figure 22 This is a cross-sectional view of the structure corresponding to step nine in this embodiment of the invention;

[0058] Figure 23This is a cross-sectional view of the structure corresponding to step nine in this embodiment of the invention.

[0059] The labels in the attached diagram are as follows:

[0060] 1. Insulating layer; 2. First substrate; 3. First varistor; 4. First ohmic contact; 5. Thin film cavity; 6. Sensitive thin film; 7. Circumferential cavity; 8. Mass block; 9. Second varistor; 10. Second ohmic contact; 11. Bridge; 12. Second substrate; 13. End cavity; 14. Bonding cavity; 15. Annular bonding region; 16. Sensor region. Detailed Implementation

[0061] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit disclosure. The described embodiments are some, but not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0062] like Figures 1 to 3 As shown, a first aspect embodiment of the present invention provides a MEMS multifunctional sensor, which includes: a first substrate 2, a second substrate 12, and a sensor assembly, wherein the sensor assembly is disposed in the sensor region 16 of the first substrate 2 (e.g., Figure 3 As shown, the sensor assembly is used to sense external pressure. Specifically, the first substrate 2 includes a sensor region 16 and an annular bonding region 15. The annular bonding region 15 is connected to the sensor region 16 circumferentially, and a circumferential cavity 7 is formed between the annular bonding region 15 and the sensor region 16. The circumferential cavity 7 is an annular cavity structure. The annular bonding region 15 is bonded to the second substrate 12. One end of the annular bonding region 15 that contacts the second substrate 12 has an annular groove. The second substrate 12 covers the annular groove of the annular bonding region 15 and forms an annular bonding cavity 14.

[0063] According to an embodiment of the present invention, a MEMS multifunctional sensor includes a first substrate 2, a second substrate 12, and a sensor assembly. The first substrate 2 includes a sensor region 16 and an annular bonding region 15 connected to the sensor region 16 circumferentially. The sensor region 16 is provided with a sensor assembly for sensing external pressure. The sensor region 16 is not in contact with the second substrate 12. The annular bonding region 15 is bonded to the second substrate 12 to realize the connection between the first substrate 2 and the second substrate 12. The closed annular bonding cavity 14 formed by the annular bonding region 15 and the second substrate 12 reduces the contact area between the annular bonding region 15 and the second substrate 12, thereby reducing the thermal stress generated by the bonding between the annular bonding region 15 and the second substrate 12, and thus reducing the thermal stress transmitted from the annular bonding region 15 to the sensor region 16. The thermal stress generated by the bonding connection between the annular bonding region 15 and the second substrate 12 is transmitted along the thickness direction of the first substrate 2 from the end of the annular bonding region 15 near the second substrate 12 to the end of the annular bonding region 15 away from the second substrate 12. The circumferential cavity 7 between the annular bonding region 15 and the sensor region 16 blocks the transmission of the thermal stress of the annular bonding region 15 to the sensor region 16. Through the dual action of the annular bonding cavity 14 and the axial cavity, the influence of bonding thermal stress on the sensor region 16, i.e., the sensor assembly located in the sensor region 16, can be reduced, avoiding zero-point output drift of the sensor due to stress concentration in the sensor region 16 and the sensor assembly, thereby improving the accuracy of the sensor output and ensuring the service life of the sensor.

[0064] In some embodiments of the present invention, the MEMS multifunctional sensor further includes an insulating layer 1, which covers the surface of the first substrate 2 on the side opposite to the second substrate 12. Specifically, the insulating layer 1 completely covers the upper surface of the first substrate 2 to achieve isolation and protection of the varistor of the sensor region 16. The material of the insulating layer 1 is at least one of silicon dioxide or silicon nitride, and the thickness of the insulating layer 1 is 100-500 nm.

[0065] In some embodiments of the present invention, the first substrate 2 includes a sensor region 16 and an annular bonding region 15 connected circumferentially along the sensor region 16. The sensor region 16 is not in contact with the second substrate 12 and forms a cavity along the thickness direction of the first substrate 2. The annular bonding region 15 is bonded to the second substrate 12 at one end near the second substrate 12. Specifically, the sensor region 16 is generally cylindrical, the inner ring of the annular bonding region 15 is circular, and the outer ring of the annular bonding region 15 is a positive ring. That is, the circular inner ring of the annular bonding region 15 is connected to the outer wall of the cylindrical sensor region 16 along the circumference of the cylindrical sensor region 16, and the end of the annular bonding region 15 facing away from the second substrate 12 is connected to the sensor region 16. The annular groove of the annular bonding region 15 is an annular groove, and the annular bonding cavity 14 formed by the annular groove is an annular cavity structure. The sensor region 16 and the annular bonding region 15 are integrally formed, and the sensor region 16 and the annular bonding region 15 are made of the same material. The material of the first substrate 2 is single-crystal silicon, that is, the sensor region 16 and the ring bonding region 15 are both made of single-crystal silicon, and the thickness of the first substrate 2 is 300-500μm.

[0066] Specifically, the annular bonding region 15 has a first end and a second end that are disposed opposite to each other. The first end is bonded to the second substrate 12 and has an annular groove. The second end is connected to the sensor region 16 along the circumference of the sensor region 16.

[0067] In some embodiments of the present invention, along the direction from the first substrate 2 to the second substrate 12, the circumferential cavity 7 includes a first annular cavity and a second annular cavity, the first annular cavity and the second annular cavity are in communication, and the radial thickness of the first annular cavity is greater than the radial thickness of the second annular cavity. By setting the radial thickness of the first annular cavity to be greater than the radial thickness of the second annular cavity, the distance between the second end of the annular bonding region 15 and the sensor region 16 is greater than the distance between other locations of the annular bonding region 15 and the sensor region 16, thereby further reducing the transmission of thermal stress.

[0068] In some embodiments of the present invention, the second annular cavity is connected to the inner ring of the first annular cavity near the sensor region 16. Specifically, the circumferential cavity extends radially from the outer wall of the cylindrical sensor region 16 to the inner wall of the annular bonding region 15. That is, both the first and second annular cavities are formed by extending from the outer wall of the cylindrical sensor region 16 to the inner wall of the annular spacer region. Therefore, the wall thickness of the annular bonding region 15 corresponding to the first annular cavity is smaller than the wall thickness of the annular bonding region 15 corresponding to the second annular cavity. By reducing the wall thickness of the second end where the annular bonding region 15 connects to the sensor region 16, the heat dissipation of the second end of the annular bonding region 15 can be improved, thereby reducing the thermal stress transmitted from the annular bonding region 15 to the sensor region 16.

[0069] In some embodiments of the present invention, the cross-section of the annular groove is trapezoidal. The single-crystal silicon dielectric inside the bonding cavity 14 deforms under the action of bonding thermal stress, thereby releasing the bonding thermal stress and reducing the stress transmitted to the sensitive thin film 6. Furthermore, the area of ​​contact between the second end of the trapezoidal cross-section annular bonding region 15 and the second substrate 12 is small. Simultaneously, the cross-section of the annular groove gradually decreases along the direction away from the second substrate 12, which can give the annular bonding region 15 sufficient rigidity. The single-crystal silicon dielectric on both sides of the bonding cavity 14 serves to increase the anodic bonding strength and the vacuum level inside the cavity.

[0070] In some embodiments of the present invention, the sensor region 16 and the second substrate 12 are in a non-contact state, and an end cavity 13 is formed between the sensor region 16 and the second substrate 12. The end face of the sensor region 16 near the second substrate 12, the end face of the second substrate 12 near the first substrate 2, and the circular inner wall of the annular bonding region 15 together form a cylindrical end cavity 13. The end cavity 13 is connected to the circumferential cavity 7 and the thin film cavity 5, respectively, and is located at the center of the surface of the first substrate 2 near the second substrate 12. The bonding thermal stress generated can be uniformly transferred to the sensor surface through the end cavity 13.

[0071] In some embodiments of the present invention, the sensor region 16 has a thin-film cavity 5, which is a cuboid cavity perpendicular to the thickness direction of the first substrate 2. The cross-section of the cuboid cavity is square. The portion of the sensor region 16 corresponding to the side of the thin-film cavity 5 facing away from the second substrate 12 is the sensitive thin film 6. Further, the circumferential cavity 7 is located on the outer periphery of the thin-film cavity 5 at the same height, that is, the minimum distance between the circumferential cavity and the insulating layer 1 is the same as the minimum distance between the thin-film cavity 5 and the insulating layer 1. The cross-section of the circumferential cavity 7 along the thickness direction of the first substrate 2 is a rectangular ring. The thin film connected to the sensor region 16 by the annular bonding region 15 above the circumferential cavity 7 deforms under the action of bonding thermal stress, thereby releasing the bonding thermal stress and reducing the stress transmitted to the sensitive thin film 6.

[0072] The sensor assembly includes four first varistors 3, which are disposed on the side of the sensitive film 6 facing away from the second substrate 12. The four first varistors 3 correspond to the centers of the four sides of the thin film cavity 5, and form a first Wheatstone bridge. Specifically, the four first varistors 3 are located on the lower surface of the insulating layer 1. The first varistors 3 can be disposed within grooves on the surface of the sensitive film 6. The four first varistors 3 are arranged parallel to each other at the centers of the four sides of the sensitive film 6 and directly opposite the center of the edge of the thin film cavity, thus placing the varistors at the location of maximum stress in the sensitive film 6, forming a first Wheatstone bridge. The material of the first varistors 3 is P-type doped single-crystal silicon, and the thickness of the first varistor 3 is 0.1-3 μm, while the length and width are determined according to design specifications.

[0073] The sensor assembly includes four pairs of first ohmic contacts 4, each pair of first ohmic contacts 4 being disposed at both ends of a corresponding first varistor 3. Specifically, the first ohmic contacts 4 are located at both ends of the first varistor 3 to achieve good electrical interconnection between the first varistor 3 and the leads. The material of the first ohmic contacts 4 is p-type heavily doped single-crystal silicon, the thickness of the first ohmic contacts 4 is the same as the thickness of the first varistor 3, and their shape is determined by the specific layout and wiring.

[0074] In some embodiments of the present invention, the sensor region 16 has four block cavities, which correspond to the four corners of the thin-film cavity 5. Each block cavity connects the thin-film cavity 5 and the end cavity 13. The portion of the sensor region 16 between two adjacent block cavities forms a bridge 11, and the portion of the sensor region 16 between the four block cavities forms a mass block 8, which is located at the center of the thin-film cavity 5. Specifically, the mass block 8 and the four bridges 11 are composed of a single-crystal silicon dielectric directly below the thin-film cavity. The mass block 8 is located at the center of the first substrate 2, and its thickness is 100-200 μm. The four bridges 11 are symmetrically arranged on the center lines of the four sides of the mass block 8 to connect the mass block 8 with the surrounding single-crystal silicon dielectric. The width and height of the bridges 11 are both smaller than the mass block 8.

[0075] The sensor assembly includes four second varistors 9, which are respectively disposed on the side of the four bridges 11 opposite to the thin film cavity 5, forming a second Wheatstone bridge. Specifically, the four second varistors 9 are arranged in parallel on the lower surface of the bridge 11 near the mass block 8, thereby placing the varistors at the point of maximum stress on the sensitive thin film 6, forming a second Wheatstone bridge. The material of the second varistors 9 is P-type doped single-crystal silicon, and the thickness of the second varistor 9 is 0.1-3 μm, while its length and width are determined according to the design specifications.

[0076] The sensor assembly includes four pairs of second ohmic contacts 10, each pair of which is disposed across the two ends of a corresponding second varistor 9. Specifically, the second ohmic contacts 10 are located across the two ends of the second varistor 9 to achieve good electrical interconnection between the second varistor 9 and the leads. The material of the second ohmic contacts 10 is p-type heavily doped single-crystal silicon, and the thickness of the second ohmic contacts 10 is the same as the thickness of the second varistor 9. Their shape is determined by the specific layout and wiring.

[0077] Furthermore, the second substrate 12 is located directly below the first substrate 2, and its surface is sealed together with the annular bonding region 15 on the outer side of the back of the first substrate 2, thereby achieving environmental sealing of the annular bonding cavity 14. Specifically, the material of the second substrate 12 is at least one of single-crystal silicon or glass, and the thickness of the second substrate 12 is 400-1000 μm. The function of the annular bonding region 15 is to reduce the bonding thermal stress on the sensor surface.

[0078] The working principle of the MEMS multifunctional sensor of the present invention is as follows:

[0079] When the sensor is subjected to external pressure, the sensitive film 6 deforms, causing stress and strain at the first piezoresistive resistor 3. Based on the piezoresistive effect, the resistance of the piezoresistive resistor changes accordingly, generating an output voltage through the first Wheatstone bridge. When the sensor is subjected to external vertical acceleration, the bridge 11 deforms, causing stress and strain at the second piezoresistive resistor 9. Based on the piezoresistive effect, the resistance of the piezoresistive resistor changes accordingly, generating an output voltage through the second Wheatstone bridge. Because the annular bonding region 15 is used for anodic bonding, and the thermal stress is transferred through the monocrystalline silicon dielectric surrounding the lower cylindrical cavity of the end cavity 13, compared to the traditional "U"-shaped bonding region and square truncated pyramidal sealed cavity structure, the thermal stress is evenly distributed and rapidly reduced upwards to the sensor surface, effectively reducing the bonding thermal stress at the location of the piezoresistive resistor. During this process, the single-crystal silicon dielectric inside the bonding cavity 14 and the thin-layer dielectric above the circumferential cavity 7 both offset part of the thermal stress transmitted from the bonding interface through deformation, further reducing the bonding thermal stress transmitted to the first varistor 3 and the second varistor 9, thereby reducing the influence of bonding thermal stress on the zero-point drift of the sensor and improving the measurement accuracy.

[0080] A second aspect of the present invention provides a method for fabricating a MEMS multifunctional sensor, a method for fabricating the MEMS multifunctional sensor described in any of the above embodiments, the method comprising:

[0081] Step 1: Select an N-type single-crystal silicon wafer with a thickness of 500μm and a crystal plane of (100) as the first substrate 2, such as... Figure 4 As shown;

[0082] Step 2: A thin silicon dioxide layer is prepared on the shallow surface of the first substrate 2 using SIMOX (Separation by Implanted Oxygen) technology. This silicon dioxide thin film corresponds to the positions of the thin film cavity 5 and the circumferential cavity 7, preparing for the subsequent fabrication of the first annular cavity of the thin film cavity 5 and the circumferential cavity 7. Figure 5 and Figure 6 As shown;

[0083] Step 3: Wet etching is performed around the bottom outer perimeter of the first substrate 2 to form the required annular cavity shape for the bonding cavity 14, i.e., an annular groove with a trapezoidal cross-section, as shown below. Figure 7 and Figure 8 As shown;

[0084] Step 4: By photolithography and DRIE (Deep Reactive Ion Etching) on ​​the inner bottom region of the first substrate 2, a cylindrical end cavity 13 is formed at one end of the sensor region 16 near the annular groove, as shown below. Figure 9 and Figure 10 As shown;

[0085] Step 5: Using photolithography and DRIE, four block cavities and annular narrow grooves are fabricated again in the central and surrounding areas of the bottom of the first substrate 2. The annular narrow grooves are the second annular cavities of the circumferential cavity, exposing the mass block 8 and the lower half of the bridge 11 structure, ensuring communication with the silicon dioxide thin layer on the shallow surface of the silicon wafer. That is, the four block cavities extend to the silicon dioxide thin film layer corresponding to the thin film cavity, and the second annular cavity extends to the silicon dioxide thin film layer corresponding to the first annular cavity of the circumferential cavity. Figure 11 and Figure 12 As shown;

[0086] Step Six: Wet etching is performed on the shallow layer of the upper surface of the first substrate 2 through the cavity and the annular narrow groove to remove the silicon dioxide thin layer, forming the first annular cavity, the thin film cavity 5, the sensitive thin film 6, the circumferential cavity 7, the mass block 8, and the bridge 11. The thin film cavity 5 is connected to the four block cavities surrounding the mass block 8, as shown below. Figure 13 , Figure 14 and Figure 15 As shown;

[0087] Step 7: A first varistor 3 and a second varistor 9 are formed by P-type doping of the surface and back of the silicon substrate. Both varistors have a thickness of 2 μm. Figure 16 , Figure 17 and Figure 18 As shown;

[0088] Step 8: Form the first ohmic contact 4 and the second ohmic contact 10 by performing P-type heavy doping across the first varistor 3 and the second varistor 9, as follows: Figure 19 , Figure 20 and Figure 21 As shown;

[0089] Step 9: An insulating layer 1 is formed by depositing a silicon dioxide layer on the surface of the first silicon substrate. The insulating layer 1 has a thickness of 100 nm. Figure 22 As shown;

[0090] Step 10: Select a 500μm thick BF33 glass sheet. Anodicly bond the annular bonding region 15 on the back of the silicon wafer to the surface of the glass substrate to seal the cavity and form a second substrate 12, thus completing the sensor fabrication. Figure 23 As shown.

[0091] The MEMS multifunctional sensor fabricated by the method of the present invention utilizes the deformation of the thin dielectric layer around the circumferential cavity 7 and the bonding cavity 14 to offset part of the thermal stress transmitted from the bonding interface, effectively reducing the bonding thermal stress at the location of the varistor, avoiding zero-point output drift of the sensor due to stress concentration, and improving the output accuracy of the sensor.

[0092] Compared with the prior art, the present invention has the following advantages:

[0093] 1. The MEMS multifunctional sensor of the present invention, by adopting a special structure of annular bonding region 15 and end cavity 13, can transmit bonding thermal stress upward in a uniform and rapidly decreasing manner, and utilize the deformation of the thin dielectric layer around the circumferential cavity 7 and bonding cavity 14 to offset part of the thermal stress transmitted from the bonding interface, effectively reducing the bonding thermal stress at the location of the varistor, avoiding sensor zero-point output drift caused by stress concentration, and improving sensor output accuracy.

[0094] 2. The MEMS multifunctional sensor of the present invention uses a stacking method to fabricate the accelerometer mass block 8 and the bridge 11 by utilizing the medium under the pressure sensor sensitive film 6, thereby achieving device integration, improving space utilization, and simplifying the processing flow by optimizing the cavity release process, achieving compatibility between floor space and fabrication process integration and optimization, and reducing production costs.

[0095] 3. The MEMS multifunctional sensor of the present invention increases the bonding strength at the bonding interface by using single-crystal silicon dielectrics on both sides of the bonding cavity 14, and maintains the internal vacuum environment by utilizing the double-layer cavity structure of the end cavity 13 and the bonding cavity 14, ensuring long-term airtightness, extending the device life, and reducing the damping coefficient of the accelerometer, thereby improving the quality factor and sensitivity of the sensor.

[0096] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A MEMS multi-function sensor, characterized by, The MEMS multifunctional sensor comprises: a first substrate comprising a sensor region and an annular bonding region connected to the sensor region along the circumference of the sensor region, a circumferential cavity being formed between the annular bonding region and the sensor region, the circumferential cavity being an annular cavity structure; a second substrate, an end cavity being formed between the sensor region and the second substrate, the end cavity being in communication with the circumferential cavity, the annular bonding region being bonded to the second substrate, one end of the annular bonding region in contact with the second substrate having an annular groove, the second substrate covering the annular groove of the annular bonding region and forming an annular bonding cavity; a sensor assembly provided in the sensor region, the sensor assembly being used for sensing external pressure; the sensor region having a thin film cavity, the thin film cavity being a cuboid cavity, the cross section of the cuboid cavity being square in the direction perpendicular to the thickness of the first substrate, the portion of the sensor region corresponding to the side of the thin film cavity away from the second substrate being a sensitive thin film; the sensor region having four block cavities, the four block cavities corresponding to the four corners of the thin film cavity, each of the block cavities being in communication with the thin film cavity and the end cavity, the portion of the sensor region between two adjacent block cavities forming a bridge, the portion of the sensor region between the four block cavities forming a mass block, the mass block corresponding to the center of the thin film cavity.

2. The MEMS multi-functional sensor of claim 1, wherein, In the direction from the first substrate to the second substrate, the circumferential cavity comprises a first annular cavity and a second annular cavity, the first annular cavity being in communication with the second annular cavity, and the radial thickness of the first annular cavity being greater than the radial thickness of the second annular cavity.

3. The MEMS multi-functional sensor of claim 2, wherein, The second annular cavity is in communication with the inner ring of the first annular cavity close to the sensor region.

4. The MEMS multi-functional sensor of claim 1, wherein, The cross section of the annular groove is trapezoidal.

5. The MEMS multi-functional sensor of claim 1, wherein, The sensor assembly comprises: four first piezoresistors, the four first piezoresistors being provided on the side of the sensitive thin film away from the second substrate, the four first piezoresistors respectively corresponding to the center of the four sides of the thin film cavity, the four first piezoresistors constituting a first Wheatstone bridge; four pairs of first ohmic contacts, each pair of the first ohmic contacts being provided at the two ends of a corresponding first piezoresistor.

6. The MEMS multi-functional sensor of claim 5, wherein, The sensor assembly comprises: four second piezoresistors, the four second piezoresistors respectively corresponding to the side of the four bridges away from the thin film cavity, the four second piezoresistors constituting a second Wheatstone bridge; four pairs of second ohmic contacts, each pair of the second ohmic contacts being provided at the two ends of a corresponding second piezoresistor.

7. The MEMS multi-functional sensor of claim 6, wherein, Each of the second piezoresistors is provided at one end of the bridge close to the mass block.

8. The MEMS multi-functional sensor of claim 1, wherein, The MEMS multifunctional sensor further comprises an insulating layer covering the surface of the side of the first substrate away from the second substrate.

9. A method for manufacturing a MEMS multifunction sensor according to any one of claims 1 to 8, characterized by, The method comprises: Step 1: selecting an N-type single crystal silicon wafer with a 100 crystal face as a first substrate; Step two: a thin layer of silicon dioxide is prepared on the shallow surface of the first substrate by oxygen isolation technology, which is used for the preparation of the thin film cavity and the circumferential cavity; Step three: the required ring cavity shape for the bonding cavity is formed by wet etching on the outside of the bottom of the first substrate; Step four: the end cavity in the shape of a cylinder is formed by photolithography and deep reactive ion etching on the inside of the bottom of the first substrate; Step five: the cavity and the annular narrow slot are prepared again by photolithography and deep reactive ion etching on the central and peripheral areas of the bottom of the first substrate, which exposes the mass block and the lower half of the bridge structure and ensures the communication with the thin layer of silicon dioxide on the shallow surface of the first substrate; Step six: the thin layer of silicon dioxide is removed by wet etching on the shallow surface of the first substrate through the cavity and the annular narrow slot, forming the thin film cavity, the sensitive thin film, the circumferential cavity, the mass block and the bridge; the thin film cavity is in communication with the four block cavities around the mass block; Step seven: the first and second piezoresistors are formed by P-type doping on the surface and the back of the silicon wafer; Step eight: the first and second ohmic contacts are formed by P-type heavy doping on both ends of the first and second piezoresistors; Step nine: the insulating layer is formed by depositing a layer of silicon dioxide on the surface of the silicon wafer; Step ten: the sensor is prepared by selecting a glass substrate and anodically bonding the annular bonding area on the back of the silicon wafer with the surface of the glass substrate to seal the cavity and form the second substrate.

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