阅读说明：本技术 一种mems绝压式压力传感器及其加工方法 (MEMS absolute pressure type pressure sensor and processing method thereof ) 是由 郭伟龙 焦海龙 陈家林 杨挺 王晓宇 张晓永 张洪涛 张皓 王健 于 2021-01-19 设计创作，主要内容包括：本发明提供了一种MEMS绝压式压力传感器及其加工方法,该传感器包括玻璃盖板、硅感压膜和玻璃衬底；硅感压膜一面与玻璃衬底阳极键合,形成两个连通的真空参考腔,另一面与玻璃盖板阳极键合,形成两个独立的开放式气体感压结构,两个连通的真空参考腔与两个独立的开放式气体感压结构上下对应,并与硅感压膜构成串联互感双电容结构,硅感压膜上加工有引线电极,用于引出气压检测信号。外部气压通过开放式气体感压结构施加在硅感压膜上,与真空参考腔形成压差使硅感压膜变形,继而改变了硅感压膜与玻璃衬底之间电容极板间距,使电容值发生变化而反应外界气压大小；基于上述传感器的加工工艺步骤少,合格率极高,产品长期稳定性好,便于大规模批量生产。(The invention provides an MEMS absolute pressure type pressure sensor and a processing method thereof, wherein the sensor comprises a glass cover plate, a silicon pressure sensing film and a glass substrate; one side of the silicon pressure sensing film is anodically bonded with the glass substrate to form two communicated vacuum reference cavities, the other side of the silicon pressure sensing film is anodically bonded with the glass cover plate to form two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities vertically correspond to the two independent open type gas pressure sensing structures and form a series mutual inductance double-capacitor structure with the silicon pressure sensing film, and lead electrodes are processed on the silicon pressure sensing film and used for leading out gas pressure detection signals. External air pressure is applied to the silicon pressure sensing film through the open type gas pressure sensing structure, and pressure difference is formed between the external air pressure and the vacuum reference cavity to enable the silicon pressure sensing film to deform, so that the distance between a capacitor plate and a glass substrate between the silicon pressure sensing film and the glass substrate is changed, and the capacitance value is changed to reflect the external air pressure; the processing technology based on the sensor has the advantages of few steps, extremely high qualification rate, good long-term stability of products and convenience for large-scale batch production.)

1. An MEMS absolute pressure type pressure sensor is characterized by comprising a glass cover plate (100), a silicon pressure sensing film (200) and a glass substrate (300); one side of the silicon pressure sensing film (200) is in anodic bonding with the glass substrate (300) to form two communicated vacuum reference cavities, the other side of the silicon pressure sensing film (200) is in anodic bonding with the glass cover plate (100) to form two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities correspond to the two independent open type gas pressure sensing structures up and down, the two communicated vacuum reference cavities and the silicon pressure sensing film (200) form a series mutual inductance double-capacitance structure, and lead electrodes (202) are processed on the silicon pressure sensing film (200) and used for leading out air pressure detection signals.

2. The MEMS pressure-insulated sensor of claim 1, wherein the glass cover plate (100) is formed with two pressure-guiding through holes (101) and two electrode through holes (102) respectively adjacent to the pressure-guiding through holes (101), the pressure-guiding through holes (101) are used for forming two independent open gas pressure-sensitive structures with the silicon pressure-sensitive film (200) after the silicon pressure-sensitive film (200) is anodically bonded with the glass cover plate (100), and the electrode through holes (102) are used for forming lead electrodes (202) on the silicon pressure-sensitive film (200) so that electrode leads are led out from the upper part of the sensor.

3. The MEMS absolute pressure type pressure sensor is characterized in that holes of the two pressure leading through holes (101) close to the silicon pressure sensing film (200) are circular in shape and the hole diameters are the same.

4. The MEMS absolute pressure sensor according to claim 2, wherein the base material of the silicon pressure sensing film (200) is wafer-grade N-type single crystal silicon with a resistivity <0.001 Ω -cm.

5. The MEMS pressure-insulated sensor according to claim 4, wherein two separate silicon electrode plates (201) are etched on the back of the bonding surface of the silicon pressure-sensitive film (200) and the glass cover plate (100), the coverage area of the silicon electrode plates (201) after the silicon pressure-sensitive film (200) and the glass cover plate (100) are anodically bonded comprises corresponding areas of the pressure-induced through holes (101) and the electrode through holes (102), and lead electrodes (202) are respectively processed on the silicon electrode plates (201) surrounded by the bottom surfaces of the two electrode through holes (102).

6. The MEMS pressure-insulated pressure sensor is characterized in that two pits (301) are processed in the central area of the glass substrate (300), after the silicon pressure sensing film (200) is anodically bonded with the glass cover plate (100) and the glass substrate (300), the pits (301) are consistent with the hole shape of the pressure guiding through hole (101) close to the side of the silicon pressure sensing film (200), are positioned in the area of the silicon electrode plate (201), and form a vacuum reference cavity with the silicon electrode plate (201); the middle of each pit groove (301) is communicated with a long-strip-shaped groove, the whole structure is similar to a dumbbell, and electrode films (302) smaller than the bottom area of the pit grooves (301) are sputtered on the bottom surfaces of the two pit grooves (301).

7. The MEMS pressure-insulated sensor of claim 6, wherein the depth of the pits (301) is 5 μm to 100 μm, and the depths of the two pits (301) are the same; and/or

The electrode film (302) is made of getter metal.

8. The MEMS pressure-insulated sensor of one of claims 2 to 7, wherein the thickness of the silicon pressure-sensitive film (200) is 0.5 ± 0.1 μm to 2000 ± 0.3 μm, the aperture of the pressure-guiding through hole (101) near the silicon pressure-sensitive film (200) is 0.5 to 5mm, and the pressure-measuring range of the sensor is 1kpa to 50 Mpa.

9. The MEMS absolute pressure type pressure sensor according to claim 6 or 7, wherein the depth of the pit (301) is 5 μm to 100 μm, the thickness of the electrode film (302) is 100nm to 1 μm, and the intrinsic value of the sensor capacitance is 1pF to 15 pF.

10. A processing method of an MEMS absolute pressure type pressure sensor is characterized by comprising the following steps:

step 1, sputtering metal thin film layers on two sides of a glass wafer and coating photoresist to be used as mask layers for resisting dry etching or wet corrosion, completing mask patterning of a pressure leading through hole (101) and an electrode through hole (102) on the glass wafer by utilizing photoetching and metal corrosion, and completing preparation of the pressure leading through hole (101) and the electrode through hole (102) by utilizing wet corrosion;

step 2, carrying out anodic bonding on the glass cover plate (100) subjected to wet cleaning and dry activation and the silicon pressure sensing film (200), wherein the bonding surface of the glass cover plate (100) is the surface with smaller aperture of the tapered hole of the pressure guiding through hole (101), and the surface of the silicon pressure sensing film (200) wafer is selected;

step 3, etching the unbonded surface of the silicon pressure sensing film (200) bonded with the glass cover plate (100) to form a discrete silicon electrode plate (201) by utilizing photoetching and patterning combined with dry etching;

step 4, sputtering a metal film layer and coating photoresist on the glass wafer to be used as a mask layer which resists dry etching or wet etching, exposing and developing, and etching the mask layer metal to be patterned, and then etching the glass substrate (300) by using the wet etching or dry etching to obtain two pit slots (301) with the same size, wherein the diameter of each pit slot (301) is the same as the small diameter of the tapered hole of the pressure guiding through hole (101) and is smaller than that of the silicon electrode plate (201); preparing an electrode film (302) on the bottom surface of each pit groove (301) by photoresist coating, exposure, development, getter metal sputtering and lift-off processes;

step 5, bonding the silicon surface of the silicon pressure sensing film (200) subjected to wet cleaning and dry activation with the anode of the surface of the glass substrate (300) on which the silicon electrode plate (201) is processed, and then annealing the activated electrode film (302) at high temperature in an inert atmosphere to obtain a vacuum reference cavity;

and 6, coating photoresist on the non-bonding surface of the glass cover plate (100), exposing, developing, depositing a metal material by adopting a plasma sputtering method, removing the photoresist and redundant metal on the photoresist by a lift-off process, leaving a lead electrode (202) in the electrode through hole (102), and annealing to form ohmic contact with the silicon pressure sensing film (200).

Technical Field

The invention belongs to the field of MEMS (micro-electromechanical systems) micro-machining and manufacturing, and particularly relates to an MEMS absolute pressure type pressure sensor and a machining method thereof.

Background

Different from the traditional Mechanical pressure sensor, a Micro-Electro-Mechanical System (abbreviated as MEMS) pressure sensor has the advantages of small volume, light weight, low power consumption, integration capability and the like, and is widely applied to the fields of aerospace, vacuum instruments and meters, industrial field control and detection, land-based and oceanographic weather, health monitoring, intelligent medical treatment and the like. How to achieve low cost, small volume packaging and reliable electrical lead-out technology is a key factor in determining the stability and commercialization of MEMS pressure sensors.

Compared with MEMS pressure sensors based on other principles, the MEMS capacitive pressure sensor has many advantages such as simple structure, high yield, high output impedance, good dynamic performance and the like, and the sensitive mechanism is as follows: the electrode plates of the parallel plate capacitor deform when being pressed, and the gap between the two electrode plates changes to cause the change of capacitance value. The difficulty of the sensitive chip of the sensor is the sealing of the vacuum reference cavity and the leading-out of the electrode lead. The mainstream packaging method of the vacuum reference cavity of the MEMS capacitive pressure sensor at present mainly comprises the following steps: wafer level direct bonding techniques (e.g., silicon-silicon direct bonding, silicon-glass anodic bonding), transition layer assisted bonding techniques (e.g., metal thermocompression bonding, organic BCB bonding, glass paste bonding), and the like. The electrode leading-out mode mainly comprises the following steps: and (3) directly penetrating the bonding layer by a thin metal electrode lead pattern, preparing an electrode by adopting a TSV (through silicon via) technology and the like.

However, in the packaging mode of the vacuum reference cavity of the MEMS capacitive pressure sensor, silicon-silicon direct bonding needs high temperature annealing at more than 800 ℃, metal thermocompression bonding needs expensive TSV technology to complete electrode preparation, BCB and glass paste bonding are favorable for airtightness of an electrode passing through a bonding region, but the working temperature of the sensor is limited, and the vacuum degree of the vacuum reference cavity is not good enough; in the electrode leading-out mode, the metal electrode lead penetrating through the bonding layer easily causes air leakage, which is not favorable for the long-term stability of the sensor, and the TSV electrode preparation technology is expensive and has poor commercialization degree, and meanwhile, the long-term stability is to be examined.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the MEMS absolute pressure type pressure sensor based on the capacitor series principle overcomes at least one defect in the conventional technology, and is small in corresponding processing steps, simple in process, high in qualified rate, low in cost and convenient for large-scale batch production based on the structure of the pressure sensor.

The technical scheme provided by the invention is as follows:

in a first aspect, a MEMS absolute pressure sensor includes a glass cover plate, a silicon pressure sensing film, and a glass substrate; one side of the silicon pressure sensing film is in anodic bonding with the glass substrate to form two communicated vacuum reference cavities, the other side of the silicon pressure sensing film is in anodic bonding with the glass cover plate to form two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities are in up-and-down correspondence with the two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities and the silicon pressure sensing film form a series mutual inductance double-capacitance structure, and lead electrodes are processed on the silicon pressure sensing film and used for leading out air pressure detection signals.

In a second aspect, a method for processing an MEMS absolute pressure sensor includes the following steps:

step 1, sputtering metal film layers on two sides of a glass wafer and coating photoresist to be used as mask layers for resisting dry etching or wet corrosion, completing mask imaging of a pressure-leading through hole and an electrode through hole on the glass wafer by utilizing photoetching and metal corrosion, and completing preparation of the pressure-leading through hole and the electrode through hole by utilizing wet corrosion;

step 2, carrying out anodic bonding on the glass cover plate subjected to wet cleaning and dry activation and a silicon pressure sensing film, wherein the bonding surface of the glass cover plate is the surface with smaller aperture of the tapered hole of the pressure inducing through hole, and the surface of the silicon pressure sensing film wafer is selected;

step 3, etching the non-bonding surface of the silicon pressure sensing film bonded with the glass cover plate to form a discrete silicon electrode plate by utilizing photoetching and patterning combined with dry etching;

step 4, sputtering a metal thin film layer and coating photoresist on the glass wafer to be used as a mask layer which resists dry etching or wet etching, exposing and developing, and etching the glass substrate by using the wet etching or dry etching to obtain two pit grooves with the same size after the mask layer is subjected to metal etching patterning, wherein the diameter of each pit groove is the same as the small diameter of the tapered hole of the pressure-leading through hole and is smaller than that of the silicon electrode plate; preparing an electrode film on the bottom surface of each pit groove by processes of coating photoresist, exposing, developing, sputtering getter metal and lift-off;

step 5, the silicon surface of the silicon pressure sensing film which is cleaned by the wet method and activated by the dry method is anodically bonded with the surface of the glass substrate, which is provided with the silicon electrode plate, and then the electrode film is activated by high-temperature annealing in an inert atmosphere to obtain a vacuum reference cavity;

and 6, coating photoresist on the non-bonded surface of the glass cover plate, exposing and developing, depositing a metal material by adopting a plasma sputtering method, removing the photoresist and redundant metal on the photoresist by a lift-off process, leaving a lead electrode in the electrode through hole, and forming ohmic contact with the silicon pressure sensing film after annealing.

According to the MEMS absolute pressure type pressure sensor and the processing method thereof provided by the invention, the beneficial effects are as follows:

(1) compared with the technology (such as a product of a related capacitance pressure sensor of the Vaisala company), which is used for forming a vacuum cavity by a silicon-silicon bonding process in the prior art, the MEMS voltage insulation type pressure sensor provided by the invention adopts a glass-silicon-glass three-layer anodic bonding mode, does not need high-temperature annealing, has lower requirements on equipment, does not need complex standard cleaning and activating processes, greatly simplifies the process flow and has high economic benefit;

(2) in the MEMS voltage-isolating pressure sensor provided by the invention, a monocrystalline silicon wafer with ultralow resistivity (<0.001 omega-cm) is used as a device layer, after the device layer is bonded with a glass wafer and is thinned and physically and chemically polished, the device layer can be extremely accurately controlled to be as thin as 0.5 mu m +/-0.1 mu m or as thick as 2000 mu m +/-0.3 mu m, the pressure in the range of 1kPa to 50MPa can be correspondingly detected, and the problem that the detection pressure is limited due to the limited ion implantation depth of the monocrystalline silicon wafer is solved;

(3) in the MEMS voltage-insulating pressure sensor provided by the invention, the silicon pressure sensing film is etched to obtain two independent N-type silicon electrode plates, the anode bonding process and the electrode film of the glass substrate are combined to form a series mutual inductance double capacitor, and the condition of vacuum failure or long-term micro-air leakage possibly caused by the fact that an electrode lead passes through a bonding region is avoided through the design of the lead electrode independent of the voltage sensing region, so that the long-term stability and the good environmental adaptability of the sensor are ensured;

(4) in the MEMS pressure-insulated pressure sensor provided by the invention, the two sides of the pressure-sensitive film are connected with the glass cover plate and the glass substrate through anodic bonding, and the anodic bonding areas of the pressure-sensitive parts have the same size, so that stress matching is realized, the pressure-sensitive film stress balance of the sensor at different temperatures is ensured, and the pressure-sensitive film pressure sensor has the advantages of stability, reliability and small thermal mismatch;

(5) in the MEMS voltage-insulated pressure sensor provided by the invention, the glass substrate obtains the micro-gap of the silicon electrode plate by accurately controlling the depth of the corrosion pit groove, and different capacitance electrode plate distance variation can be obtained by matching different silicon pressure-sensitive film thicknesses with the pit groove depth, so that different sensitivities are obtained;

(6) in the MEMS pressure-insulated pressure sensor provided by the invention, the electrode film of the getter is prepared on the bottom surface of the pit groove of the glass substrate, and the electrode film can absorb bonding residual gas of the vacuum reference cavity after being activated at high temperature, so that very high vacuum degree (better than 0.1Pa) is obtained, and the long-term vacuum maintenance capability is excellent;

(7) the MEMS absolute pressure type pressure sensor provided by the invention has the advantages of few processing steps, extremely high qualification rate, good long-term stability and low cost, can be developed into capacitive pressure sensors with various measuring range ranges (micro-pressure, normal pressure and ultrahigh pressure), is easy to realize micro-nano processing, can reduce the volume of a finished chip to 6mm multiplied by 4mm multiplied by 0.7mm, and can be integrated on a PCB board as an air pressure measuring unit.

Drawings

Fig. 1 is a three-dimensional anatomical schematic view of an MEMS pressure-insulated pressure sensor according to the present invention;

FIG. 2 is a schematic view of a glass cover plate structure used in the present invention;

FIG. 3 is a schematic view of a silicon pressure-sensitive film used in the present invention;

FIG. 4 is a schematic view of the structure of a glass substrate used in the present invention;

FIG. 5 is a schematic diagram of an equivalent capacitor circuit according to the present invention;

FIG. 6 is a schematic view of a step of processing a glass cover plate according to the present invention;

FIG. 7 is a schematic diagram of the anodic bonding step between the glass cover plate and the silicon pressure-sensing film according to the present invention;

FIG. 8 is a schematic diagram of the etching step of the silicon pressure-sensitive film according to the present invention;

FIG. 9 is a schematic view of a step of processing a glass substrate according to the present invention;

FIG. 10 is a schematic view showing an anodic bonding step of a glass substrate and a silicon pressure-sensitive film according to the present invention;

FIG. 11 is a schematic diagram of a step of sputtering a lead electrode according to the present invention.

Description of the reference numerals

100-glass cover plate, 101-pressure guiding through hole, 102-electrode through hole; 200-silicon pressure sensing film, 201-silicon electrode plate, 202-lead electrode; 300-glass substrate, 301-pit-trench, 302-electrode film.

Detailed Description

The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.

According to a first aspect of the present invention, as shown in fig. 1, there is provided a MEMS pressure-insulated pressure sensor, comprising a glass cover plate 100, a silicon pressure-sensitive film 200, and a glass substrate 300; one side of the silicon pressure sensing film 200 is anodically bonded with the glass substrate 300 to form two communicated vacuum reference cavities, the other side of the silicon pressure sensing film 200 is anodically bonded with the glass cover plate 100 to form two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities are vertically corresponding to the two independent open type gas pressure sensing structures, the two communicated vacuum reference cavities and the silicon pressure sensing film 200 form a series mutual inductance double-capacitance structure, and lead electrodes 202 are processed on the silicon pressure sensing film 200 and used for leading out gas pressure detection signals. External air pressure is applied to the silicon pressure sensing film 200 through the open type gas pressure sensing structure, and forms a pressure difference with the vacuum reference cavity to deform the silicon pressure sensing film 200, so that the distance between the capacitance plates between the silicon pressure sensing film 200 and the glass substrate 300 is changed, and the capacitance value is changed to reflect the external air pressure.

In the invention, the MEMS absolute pressure type pressure sensor is a glass-silicon-glass three-layer anodic bonding mode, and compared with the technology (such as a product of a capacitance pressure sensor related to Vaisala company) for forming a vacuum cavity by a silicon-silicon bonding process in the prior art, the MEMS absolute pressure type pressure sensor does not need high-temperature annealing, has lower requirements on equipment, does not need complex standard cleaning and activating processes, greatly simplifies the process flow and has high economic benefit. And the design of the series mutual inductance double-capacitor structure ensures that the lead electrode is only needed to be prepared on the contact surface of the silicon pressure sensing film communicated with the pressure sensing area, so that the lead-out of a capacitance-air pressure detection signal can be realized, the condition of vacuum failure or long-term micro air leakage possibly caused by the electrode lead passing through a bonding area is avoided, and the long-term stability and good environmental adaptability of the sensor are ensured.

In a preferred embodiment, the glass cover plate 100 is formed with two pressure guiding through holes 101 and two electrode through holes 102 respectively adjacent to the pressure guiding through holes 101, the pressure guiding through holes 101 are used for forming two independent open gas pressure sensing structures with the silicon pressure sensing film 200 after the silicon pressure sensing film 200 is anodically bonded with the glass cover plate 100, and the electrode through holes 102 are used for forming lead electrodes 202 on the silicon pressure sensing film 200 so that the electrode leads are led out from the upper part of the sensor. As an example, fig. 2 shows a schematic structural view of the glass cover plate 100 of the present invention. A metal film layer is sputtered on the double sides of a BF33 glass wafer and coated with photoresist to serve as a mask layer for resisting dry etching or wet etching, mask patterning of a pressure leading through hole 101 and a pressure leading through hole 102 is completed on a glass cover plate 100 through photoetching and metal etching, and preparation of the pressure leading through hole 101 and the pressure leading through hole 102 is completed through HF wet etching.

Further, the holes of the two pressure guiding through holes 101 on the side close to the silicon pressure sensing film 200 are circular and have the same diameter. The anode bonding areas at the edge of the open type gas pressure sensing structure are the same in size, stress matching is achieved, pressure sensing films of the sensor at different temperatures are guaranteed to be balanced in stress, and the open type gas pressure sensing structure has the advantages of being stable, reliable and small in thermal mismatch.

In a preferred embodiment, the base material of the silicon pressure sensing film 200 is wafer-level N-type ultra-low resistivity (<0.001 Ω · cm) monocrystalline silicon, and is anodically bonded with the glass cover plate 100, wherein the bonding surface of the glass cover plate 100 is a surface with a smaller diameter of the tapered hole of the pressure guiding through hole 101, which is subjected to HF wet etching to form the tapered hole, and the silicon pressure sensing film 200 is optionally one surface of the wafer, and then the unbonded surface of the silicon pressure sensing film 200 bonded with the glass cover plate 100 is etched to form the discrete silicon electrode plate 201 by using photolithography patterning and ICP dry etching. After photoresist is coated on the non-bonding surface of the glass cover plate 100, exposure and development are carried out, a metal material is deposited by adopting a plasma sputtering method, then the photoresist and redundant metal on the photoresist are removed by a lift-off process (metal stripping process), a lead electrode 202 is left in the electrode through hole 102, and ohmic contact is formed with the silicon pressure sensing film 200 after annealing.

In a preferred embodiment, two pits 301 are processed in the central area of the glass substrate 300, after the silicon pressure sensing film 200 is anodically bonded with the glass cover plate 100, and the pits 301 are consistent with the hole shape of the pressure guiding through hole 101 close to the silicon pressure sensing film 200 side and are positioned in the area of the silicon electrode plate 201, and form a vacuum reference cavity with the silicon electrode plate 201; the middle of each pit 301 is communicated with a long-strip-shaped groove, the whole structure is similar to a dumbbell, and electrode films 302 smaller than the bottom area of the pits 301 are sputtered on the bottom surfaces of the two pits 301. As an example, fig. 4 shows a schematic structural view of a glass substrate 300 of the present invention. Sputtering a metal film layer and coating photoresist on a BF33 glass wafer to be used as a mask layer which resists dry etching or wet etching, exposing and developing, and etching and patterning mask layer metal, and etching the glass wafer by using an HF wet etching method or an ICP dry etching method to obtain two pit slots 301 with the same size, wherein the diameter of each pit slot 301 is the same as the small diameter of the tapered hole of the pressure leading through hole 101 and is smaller than that of the silicon electrode plate 201 by one circle; and completing the preparation of the electrode film 302 with the function of a getter on the bottom surface of each pit 301 through processes of coating photoresist, exposing, developing, sputtering Ti or Zr and lift-off. The silicon surface of the silicon pressure sensing film 200 which is activated by wet cleaning and RIE dry cleaning is bonded with the surface of the glass substrate 300 with the etched pattern through an anode, and then the electrode film 302 is activated by high-temperature annealing under the protection of nitrogen atmosphere to obtain the high-vacuum environment of the reference cavity.

Further, the depth of the pit 301 is 5 μm to 100 μm, and the depths of the two pits 301 are the same.

Further, the electrode film 302 is made of a getter metal (such as Ti or Zr), and long-term vacuum degree of the vacuum reference cavity can be guaranteed after bonding annealing.

Further, the width of the elongated groove in the middle of the pit 301 is not more than 20 μm.

According to the MEMS absolute pressure type pressure sensor, external air pressure is applied to the silicon pressure sensing film 200 through the pressure guiding through hole 101, pressure difference is formed between the external air pressure and a vacuum reference cavity formed by the pit groove 301 and the silicon electrode plate 201, so that the pressure sensing area of the silicon pressure sensing film 200 is deformed, the distance between the capacitor electrode plates is changed, the capacitance value is changed to reflect the size of the external air pressure, and a lead is welded on the lead electrode 202 through the electrode through hole 102 to achieve signal guiding. The silicon pressure sensing film region corresponding to the pressure leading through hole forms a double-capacitor series connection form through mutual inductance between capacitor plates, and the specific principle refers to fig. 5.

In the invention, the thickness of the silicon pressure sensing film 200, the aperture of the pressure leading through hole 101 close to the silicon pressure sensing film 200 side and the pressure measuring range are designed in a matching way. Specifically, the thickness of the silicon pressure sensing film 200 is 0.5 +/-0.1 microns to 2000 +/-0.3 microns, the aperture of the pressure leading through hole 101 close to the silicon pressure sensing film 200 is 0.5-5 mm, and the pressure measuring range of the sensor is 1 Kpa-50 Mpa. For example, when the thickness of the silicon pressure sensing film 200 is 32um and the hole diameters of the two pressure guiding through holes 101 close to the silicon pressure sensing film 200 are 3mm, the pressure measuring range of the sensor is 0-1 MPa.

In the present invention, the depth of the pit 301 and the thickness control of the electrode film 302 are designed to match the intrinsic value of the sensor capacitance. Specifically, the depth of the pit 301 is 5 μm to 100 μm, the thickness of the electrode film 302 is 100nm to 1 μm, and the intrinsic value of the sensor capacitor is 1pF to 15 pF. For example, when the electrode plate pitch is 5 μm and the thickness of the electrode film 302 is 0.5 μm, the intrinsic value of the sensor capacitance is about 4 pF.

According to a second aspect of the present invention, there is provided a method for processing a MEMS absolute pressure sensor, comprising the steps of:

step 1: as shown in fig. 6, the glass cover plate 100 adopts a BF33 glass wafer, metal film layers are sputtered and photoresist is coated on both sides of the BF33 glass wafer to serve as mask layers for dry etching or wet etching resistance, mask patterning of the pressure-inducing via 101 and the electrode via 102 is completed on the glass wafer by using photolithography and metal etching, and preparation of the pressure-inducing via 101 and the electrode via 102 is completed by using HF wet etching;

step 2: as shown in fig. 7, anodic bonding is performed on a wafer-level glass cover plate 100 subjected to wet cleaning by concentrated sulfuric acid and dry activation by RIE and a wafer-level N-type ultra-low resistivity (<0.001 Ω · cm) double-sided polished monocrystalline silicon pressure-sensitive film 200, wherein the bonding surface of the glass cover plate 100 is a surface with a smaller aperture of a tapered hole of a pressure-inducing through hole 101, and the silicon pressure-sensitive film 200 is an optional surface of a wafer;

and step 3: as shown in fig. 8, a discrete silicon electrode plate 201 is etched on the non-bonded surface of the silicon pressure sensing film 200 bonded to the glass cover plate 100 by using photolithography patterning in combination with ICP dry etching (for complete representation of the relationship of the layers, the cross-sectional illustration is developed by a cutting line shown by a dotted line a-a in fig. 3);

and 4, step 4: as shown in fig. 9, a BF33 glass wafer is adopted as the glass substrate 300, a metal film layer is sputtered and a photoresist is coated on the BF33 glass wafer to serve as a mask layer which is resistant to dry etching or wet etching, after exposure and development and patterning of mask layer metal etching, the glass substrate 300 is etched by using an HF wet etching method or an ICP dry etching method to obtain two pit slots 301 with the same size, wherein the diameter of each pit slot 301 is the same as the small diameter of the tapered hole of the pressure introduction through hole 101, and the pit slots are both smaller than the silicon electrode plate 201; preparing an electrode film 302 with the function of a getter on the bottom surface of each pit groove 301 through processes of coating photoresist, exposing, developing, sputtering getter metal and lift-off;

and 5: as shown in fig. 10, the silicon surface of the silicon pressure sensing film 200 which is cleaned by the concentrated sulfuric acid wet method and activated by the RIE dry method is anodically bonded with the surface of the glass substrate 300 on which the silicon electrode plate 201 is processed, and then the electrode film 302 is activated by high-temperature annealing in an inert atmosphere to obtain a vacuum reference cavity;

step 6: as shown in fig. 11, a photoresist is coated on the non-bonding side of the glass cover plate 100, exposed, developed, and then a metal material is deposited by a plasma sputtering method, and then the photoresist and the excess metal thereon are removed by a lift-off process, leaving a lead electrode 202 in the electrode via hole 102, and after annealing, forming an ohmic contact with the silicon pressure-sensitive film 200 (for complete representation of the relationship of the layers, the cross-sectional illustration is developed by a cross-sectional line shown by a dotted line a-a in fig. 3).

In the invention, in step 2, after the glass cover plate 100 is anodically bonded with the silicon pressure sensing film 200, the wafer of the silicon pressure sensing film 200 is thinned to the required thickness by adopting chemical mechanical grinding; the wafer of the silicon pressure-sensitive film 200 is polished by chemical mechanical polishing until the roughness Rq is less than or equal to 10 nm.

In the present invention, in step 6, the volume of the prepared sensor finished product can reach 6mm × 4mm × 0.7 mm.

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.