Fabrication method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever-beam - center dual-mass structure

Abstract

The present invention discloses a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure, belonging to the field of MEMS. Based on the diaphragm structure design of traditional MEMS piezoresistive pressure sensors, the present invention ingeniously combines a cantilever beam-center double-mass block structure, and symmetric center mass block structures are designed on the front and back sides of the cantilever beam respectively. This innovative cantilever beam-center double-mass block structure design can generate greater deformation at the beam end under the same pressure, improving the sensitivity and signal strength of the sensor; through symmetric design, the stress changes caused by temperature are balanced, reducing the influence of temperature changes on the performance of the sensor, greatly reducing temperature drift, and enhancing its stability in high-temperature environments, enabling the sensor to exhibit excellent mechanical and electrical properties at high temperatures; the introduction of the center double-mass block not only increases the mass of the structure but also improves the dynamic response characteristics of the sensor, making it perform better in dynamic pressure measurement.

Description

Technical Field

[0001] The present invention relates to the field of MEMS technology, and particularly to a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure. Background Art

[0002] Microelectromechanical system (MEMS) pressure sensors have been widely used in modern industries, aerospace, automotive manufacturing and other fields. However, traditional MEMS piezoresistive pressure sensors have problems such as decreased sensitivity, zero drift and poor long-term stability in high-temperature environments. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure, so as to solve the problems of decreased sensitivity, zero drift and poor long-term stability of traditional MEMS piezoresistive pressure sensors in high-temperature environments.

[0004] To solve the above technical problems, the present invention provides a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure, including:

[0005] The first step: Provide an N<100>, top silicon layer thickness of 1.5 µm to 100 µm, intermediate oxide layer thickness of 0.2 µm to 1.2 µm, substrate silicon layer thickness of 350 µm to 420 µm, double-polished SOI substrate material wafer. Through a thermal oxidation process in a furnace tube, silicon dioxide layers are grown on the front and back of the SOI substrate material wafer respectively;

[0006] The second step: Perform N-type isolation barrier structure lithography process, injection with glue, and removal of the photoresist;

[0007] The third step: Perform P-type piezoresistor strip structure lithography process, injection with glue, and removal of the photoresist;

[0008] The fourth step: Perform P-type interconnection structure lithography process, injection with glue, and removal of the photoresist;

[0009] The fifth step: Through a low-pressure chemical vapor deposition process in a furnace tube, silicon dioxide layers and silicon nitride layers are deposited on the front and back of the device in sequence, and an annealing process is performed; Perform contact hole structure lithography, dry-etch the silicon dioxide layer and silicon nitride layer on the front, and remove the photoresist;

[0010] The sixth step: Perform a photoresist coating process, evaporate a high-temperature metal material layer for coating, strip the photoresist, and form a metal interconnection structure; or, perform a high-temperature metal material layer sputtering process, a photoresist lithography process, a metal interconnection structure etching process, and remove the photoresist;

[0011] Step 7: Deposit a passivation protection layer on the front side of the device through a plasma-enhanced chemical vapor deposition process, perform a photolithography process for the passivation protection layer, a dry etching process for the passivation protection layer structure, and remove the photoresist; perform an alloying process;

[0012] Step 8: Perform a photolithography process for the front cantilever-beam - center dual-mass block structure and a dry etching process for the dielectric layer; perform wet etching of the top silicon of the SOI with KOH, the etching temperature is 70°C to 80°C, and the remaining film thickness of the top silicon after wet etching depends on the pressure range requirements of the MEMS pressure sensor product; remove the photoresist;

[0013] Step 9: Coat a protective glue on the front side; perform a photolithography process for the back dielectric layer, a dry etching process for the back dielectric layer, and remove the photoresist; perform a photolithography process for the back cavity deep groove structure, and perform the first dry etching for the back cavity deep groove structure to etch out the height difference of the back center mass block structure, the height difference is 5 µm to 200 µm, and the dry etching process uses deep reactive ion etching with a high selectivity of Si to SiO2 of 150:1 to 220:1, and the etching gas is sulfur hexafluoride; remove the photoresist;

[0014] Step 10: Perform the second dry etching for the back cavity deep groove structure, the dry etching process uses deep reactive ion etching with a high selectivity of Si to SiO2 of 150:1 to 220:1, and the etching gas is sulfur hexafluoride; perform a wet etching process for the intermediate oxide layer of the SOI, the BOE etching rate is 100 nm / min to 1000 nm / min, check that the dehydration state appears on the etched surface of the back cavity, indicating that the silicon dioxide layer has been removed cleanly; remove the photoresist; remove the protective glue on the front side; complete the preparation of the SOI high-temperature MEMS piezoresistive pressure sensor based on the cantilever-beam - center dual-mass block structure.

[0015] In one embodiment, in the second step, the implanted ion type is phosphorus, the implantation energy is 80 - 100 keV, the implantation dose is 4E15 - 9E15, and the implantation angle is 7° - 10°; in the third step, the implanted ion type is boron, the implantation energy is 25 - 80 keV, the implantation dose is 1.0E14 - 9E14, and the implantation angle is 7° - 10°; in the fourth step, the implanted ion type is boron, the implantation energy is 25 - 80 keV, the implantation dose is 4E15 - 9E15, and the implantation angle is 7° - 10°.

[0016] In one embodiment, in the fifth step, the thickness of the newly deposited silicon dioxide layer is 0.2 µm - 0.5 µm, and the thickness of the silicon nitride layer is 0.1 µm - 0.2 µm; the annealing temperature is 950°C - 1200°C, the annealing time is 30 min - 150 min; the contact hole size is 5 µm - 20 µm.

[0017] In one embodiment, the thickness of the high-temperature metal material layer is 1 µm to 2 µm, and the high-temperature metal material is selected from platinum, a titanium / platinum / gold multi-layer structure, or nickel-chromium alloy aluminum / copper alloy.

[0018] In one embodiment, in the seventh step, the passivation protection layer material is a single-layer silicon nitride layer or a stack of silicon dioxide and silicon nitride. The stack of silicon dioxide and silicon nitride is a silicon dioxide layer and a silicon nitride layer sequentially deposited on the front side of the substrate material wafer after the sixth-step process. The overall thickness of the passivation protection layer is 0.2 µm to 1.2 µm; the alloying temperature is 400 °C to 500 °C, and the alloying time is 30 min to 200 min.

[0019] The preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure provided by the present invention has the following beneficial effects:

[0020] (1) Based on the diaphragm structure design of the traditional MEMS piezoresistive pressure sensor, the present invention ingeniously combines a cantilever beam-center double-mass block structure, and symmetric center mass block structures are designed on the front and back sides of the cantilever beam respectively. Compared with the traditional diaphragm structure, the cantilever beam-center double-mass block symmetric structure design can balance the forces on the front and back sides and better control the deformation area, optimize the stress distribution, avoid the stress concentration problem of the large-area diaphragm at high temperature, make the deformation of the cantilever beam under the action of pressure more uniform, effectively reduce the non-linear error caused by asymmetric stress, and effectively improve the reliability and service life of the sensor in a high-temperature environment. Compared with the traditional diaphragm structure and the cantilever beam-center single-mass block structure, this innovative cantilever beam-center double-mass block structure design can generate a larger beam-end deformation under the same pressure, improve the sensitivity and signal strength of the sensor; this structure balances the stress change caused by temperature through symmetric design, reduces the influence of temperature change on the sensor performance, greatly reduces the temperature drift, and improves its stability in a high-temperature environment, making the sensor exhibit excellent mechanical and electrical properties at high temperature; the introduction of the center double-mass block not only increases the mass of the structure, but also improves the dynamic response characteristics of the sensor, making it perform better in dynamic pressure measurement. In addition, the pressure range of the sensor can be adjusted by changing the etching depth of the front cantilever beam and the front center mass block, realizing a variety of pressure ranges for products, making the adjustment of the product structure design more flexible, the product variety coverage wider, supporting faster product iteration and upgrade, and thus being able to quickly respond to market demands.

[0021] (2) The SOI substrate material sheet used in the present invention has excellent high-temperature performance and can maintain stable mechanical and electrical characteristics under high-temperature conditions. The present invention prepares a cantilever beam structure and a piezoresistive element on the top single-crystalline silicon of the SOI substrate material sheet. The SOI substrate material sheet further enhances the electrical insulation performance and thermal isolation performance of the sensor, reduces the influence of temperature on the electrical performance of the pressure sensor, especially in a high-temperature environment, its zero drift is significantly reduced, ensuring the stable operation of the pressure sensor.

[0022] (3) The present invention realizes a SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam - center double-mass block structure and its manufacturing method through high-precision double-sided lithography alignment process technology, N-type isolation barrier structure process technology, P-type piezoresistive strip structure process technology, high-temperature metal material layer interconnection structure process technology, front-side cantilever beam - center double-mass block structure etching technology, back cavity deep groove structure dry etching process technology, etc. An innovative processing method for the cantilever beam - center double-mass block structure is designed. This processing method can improve the product linearity and change the product sensitivity by flexibly adjusting the thickness of the back island; this processing method can flexibly adjust the etching depth of the top single-crystalline silicon of the front-side SOI substrate material sheet, realizing a process processing mode of completing multiple pressure range chips with a single set of lithography layout structure, accelerating the R & D cycle and reducing the R & D cost. Brief Description of the Drawings

[0023] Figure 1 It is a cross-sectional structure schematic diagram of the preparation process of the silicon dioxide layer structure deposited in the furnace tube on the SOI double-polished wafer.

[0024] Figure 2 It is a cross-sectional structure schematic diagram of the preparation process of the N-type isolation barrier structure.

[0025] Figure 3 It is a cross-sectional structure schematic diagram of the preparation process of the P-type piezoresistive strip structure.

[0026] Figure 4 It is a cross-sectional structure schematic diagram of the preparation process of the P-type interconnection structure.

[0027] Figure 5 It is a cross-sectional structure schematic diagram of the preparation process of the contact hole structure.

[0028] Figure 6 It is a cross-sectional structure schematic diagram of the preparation process of the metal interconnection structure.

[0029] Figure 7 It is a cross-sectional structure schematic diagram of the preparation process of the passivation protection layer structure.

[0030] Figure 8 It is a cross-sectional structure schematic diagram of the preparation process of the front-side cantilever beam - center double-mass block structure.

[0031] Figure 9 It is a schematic cross-sectional structure diagram of the preparation process of the first dry-etched back cavity deep groove structure.

[0032] Figure 10 It is a schematic cross-sectional structure diagram of the preparation process of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure.

[0033] Figure 11 It is Figure 1 、 2 、3, 4, 5, 6, 7, 9, 10 schematic diagram of the cross-sectional positions of the cross-sectional structure diagrams.

[0034] Figure 12 It is Figure 8 schematic diagram of the cross-sectional position of the cross-sectional structure diagram. Detailed implementation manners

[0035] The following further details a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure according to the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0036] The present invention provides a preparation method of an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever beam-center double-mass block structure. The specific process flow of the preparation method includes the following steps:

[0037] First step: Provide an N<100>, double-polished SOI substrate material sheet with a top silicon thickness of 1.5 µm to 100 µm, an intermediate oxide layer thickness of 0.2 µm to 1.2 µm, a substrate silicon thickness of 350 µm to 420 µm; through a thermal oxidation process in a furnace tube, grow silicon dioxide layers on the front and back of the SOI substrate material sheet respectively, and the thickness of the silicon dioxide layer is 0.1 µm to 0.2 µm, as Figure 1 shown.

[0038] Second step: Perform an N-type isolation blocking structure lithography process, inject with glue, the injected ion type is phosphorus (P), the injection energy is 80 to 100 keV, the injection dose is 4E15 to 9E15, and the injection angle is 7° to 10°; remove the photoresist, as Figure 2 shown.

[0039] Step 3: Perform the photolithography process for the P-type varistor strip structure, inject with glue, the ion species for injection is boron (B), the injection energy is 25 - 80 keV, the injection dose is 1.0E14 - 9E14, and the injection angle is 7° - 10°; remove the photoresist, as Figure 3 shown.

[0040] Step 4: Perform the photolithography process for the P-type interconnection structure, inject with glue, the ion species for injection is boron (B), the injection energy is 25 - 80 keV, the injection dose is 4E15 - 9E15, and the injection angle is 7° - 10°; remove the photoresist, as Figure 4 shown.

[0041] Step 5: Through the LPCVD (Low Pressure Chemical Vapor Deposition) process in the furnace tube, deposit a silicon dioxide layer and a silicon nitride layer on the front and back of the substrate material wafer that has completed the fourth step process in sequence. The thickness of the newly deposited silicon dioxide layer is 0.2 µm - 0.5 µm, and the thickness of the silicon nitride layer is 0.1 µm - 0.2 µm; perform the annealing process, the annealing temperature is 950°C - 1200°C, and the annealing time is 30 min - 150 min; perform the photolithography for the contact hole structure, the contact hole size is 5 µm - 20 µm, and remove the photoresist by dry etching the silicon dioxide layer and the silicon nitride layer on the front, as Figure 5 shown.

[0042] Step 6: Perform the photoresist coating process, evaporate the high-temperature metal material layer for coating, and strip the photoresist (Lift-Off) to form the metal interconnection structure. Or, through the sputtering process of the high-temperature metal material layer, the photolithography process of the photoresist, and the etching process of the metal interconnection structure, remove the photoresist. The thickness of the high-temperature metal material layer is 1 µm - 2 µm, and the high-temperature metal material can be selected from platinum (Platinum, Pt), titanium / platinum / gold (Ti / Pt / Au) multi-layer structure, nickel-chromium alloy (Nickel-Chromium Alloy, NiCr), aluminum / copper alloy (Al / Cu), etc., as Figure 6 shown.

[0043] Step 7: Deposit a passivation protection layer on the front of the substrate material wafer that has completed the sixth step process through the PECVD (Plasma Enhanced Chemical Vapor Deposition) process. The passivation protection layer material can be a single-layer silicon nitride layer or a stack of silicon dioxide and silicon nitride. The stack of silicon dioxide and silicon nitride is to deposit a silicon dioxide layer and a silicon nitride layer on the front of the substrate material wafer that has completed the sixth step process in sequence. The overall thickness of the passivation protection layer is 0.2 µm - 1.2 µm; perform the photolithography process for the passivation protection layer, the dry etching process for the passivation protection layer structure, and remove the photoresist; perform the alloying process, the alloying temperature is 400°C - 500°C, and the alloying time is 30 min - 200 min, as Figure 7 shown.

[0044] Step 8: Perform lithography process for the front cantilever - center dual - mass - block structure and dry etching process for the dielectric layer; wet etching of the top silicon of SOI with KOH, the etching temperature is 70°C - 80°C, and the remaining film thickness of the top silicon after wet etching depends on the pressure range requirements of the MEMS pressure sensor product; remove the photoresist, as Figure 8 shown.

[0045] Step 9: Coat protective glue on the front; perform lithography process for the back dielectric layer, dry etching process for the back dielectric layer, and remove the photoresist; perform lithography process for the back - cavity deep - groove structure, first dry etching for the back - cavity deep - groove structure to etch out the height difference of the back - center mass - block structure, the height difference is 5 µm - 200 µm, and the dry etching process uses deep reactive ion etching (DRIE) with a high selectivity of Si to SiO2 of 150:1 - 220:1, and the etching gas is sulfur hexafluoride (SF6); remove the photoresist; as Figure 9 shown.

[0046] Step 10: Second dry etching for the back - cavity deep - groove structure, the dry etching process uses deep reactive ion etching (DRIE) with a high selectivity of Si to SiO2 of 150:1 - 220:1, and the etching gas is sulfur hexafluoride (SF6); wet etching process for the middle oxide layer of SOI, the BOE etching rate is 100 nm / min - 1000 nm / min, check that the dehydration state appears on the etched surface of the back - cavity chamber, indicating that the silicon dioxide layer has been removed completely; remove the photoresist; remove the protective glue on the front; complete the preparation of the SOI high - temperature MEMS piezoresistive pressure sensor based on the cantilever - center dual - mass - block structure, as Figure 10 shown.

[0047] Figure 11 is Figure 1 、 2 、3、4、5、6、7、9、10 schematic diagrams of the cross - section positions; Figure 12 is Figure 8 schematic diagram of the cross - section position.

[0048] The application of traditional MEMS piezoresistive pressure sensors at high temperatures is restricted by structural design and material properties. The present invention provides a preparation method for an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever-beam - central double-mass structure. Based on the diaphragm structure design of traditional MEMS piezoresistive pressure sensors, advanced SOI substrate wafers are used, and the innovative cantilever-beam - central double-mass structure is ingeniously combined. Symmetrical central mass blocks are designed on both the front and back sides of the cantilever beam, successfully breaking through these limitations and expanding the application scope of the sensor. The present invention realizes an SOI high-temperature MEMS piezoresistive pressure sensor based on a cantilever-beam - central double-mass structure and its preparation method through high-precision double-sided lithography alignment technology, N-type isolation barrier structure technology, P-type piezoresistive resistor strip structure technology, high-temperature metal material layer interconnection structure technology, front-side cantilever-beam - central double-mass structure etching technology, back cavity deep groove structure dry etching technology, etc. An innovative processing method for the cantilever-beam - central double-mass structure is designed. This processing method can improve the product linearity and change the product sensitivity by flexibly adjusting the thickness of the back island; this processing method can flexibly adjust the etching depth of the top single-crystalline silicon of the front-side SOI substrate wafer, realizing a process processing mode in which multiple pressure range chips are completed with a single set of lithography layout structures, accelerating the R & D cycle and reducing the R & D cost.

[0049] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the field of the present invention based on the above disclosure fall within the protection scope of the claims.

Claims

1. A method for preparing a SOI high temperature MEMS piezoresistive pressure sensor based on a cantilever beam-central double mass block structure, characterized in that: include: Step 1: Provide N <100> , the top silicon thickness is 1.5µm~100µm, the middle oxide layer thickness is 0.2µm~1.2µm, the substrate silicon thickness is 350µm~420µm, and the double-polished SOI substrate material sheet is subjected to a thermal oxidation process in a furnace tube to grow silicon dioxide layers on the front and back of the SOI substrate material sheet respectively; Step 2: Perform N-type isolation barrier structure photolithography process, inject glue, and remove photoresist; Step 3: Perform the photolithography process of the P-type varistor strip structure, inject the tape, and remove the photoresist; Step 4: Perform P-type interconnect structure photolithography process, inject glue, and remove photoresist; Step 5: Using a low-pressure chemical vapor deposition process in the furnace tube, a silicon dioxide layer and a silicon nitride layer are sequentially deposited on the front and back of the device, and an annealing process is performed; contact hole structure photolithography is performed, and the silicon dioxide layer and silicon nitride layer on the front are dry-etched to remove the photoresist; Step 6: Perform a photoresist coating process, a high-temperature metal material layer evaporation process, and a film coating process, and then strip the photoresist to form a metal interconnection structure; or, perform a high-temperature metal material layer sputtering process, a photoresist lithography process, and a metal interconnection structure etching process to remove the photoresist; Step 7: Deposit a passivation protection layer on the front of the device by plasma enhanced chemical vapor deposition process, perform passivation protection layer photolithography process, and perform passivation protection layer structure dry etching process to remove the photoresist; Carry out alloying process; Step 8: Perform photolithography of the front cantilever beam-center double-mass block structure and dry etching of the dielectric layer; wet etching of the top silicon of SOI by KOH at a temperature of 70°C to 80°C. The thickness of the top silicon film after wet etching depends on the pressure range requirements of the MEMS pressure sensor product; remove the photoresist; Step 9: Apply protective glue on the front; Back dielectric layer photolithography process, back dielectric layer dry etching process, removal of photoresist; Back cavity deep groove structure photolithography process, the first dry etching of the back cavity deep groove structure, etching out the height difference of the back center mass block structure, the height difference is 5µm~200µm, the dry etching process adopts deep reactive ion etching with a high selectivity of Si to SiO2 of 150:1~220:1, and the etching gas is sulfur hexafluoride; Removing photoresist; Step 10: The back cavity deep groove structure is dry-etched for the second time. The dry-etching process uses deep reactive ion etching with a high selectivity of 150:1~220:1 for Si to SiO2, and sulfur hexafluoride is used as the etching gas. The SOI intermediate oxide layer is wet-etched with a BOE etching rate of 100nm / min~1000nm / min. Check that the corrosion surface of the back cavity is dehydrated, indicating that the silicon dioxide layer has been removed completely. Removing photoresist; Remove the front protective glue; The preparation of SOI high-temperature MEMS piezoresistive pressure sensor based on cantilever beam-central double mass block structure has been completed.

2. The method for preparing the SOI high temperature MEMS piezoresistive pressure sensor based on the cantilever beam-central dual mass block structure according to claim 1, characterized in that: In the second step, the implanted ion type is phosphorus, the implantation energy is 80~100keV, the implantation dose is 4E15~9E15, and the implantation angle is 7°~10°; in the third step, the implanted ion type is boron, the implantation energy is 25~80keV, the implantation dose is 1.0E14~9E14, and the implantation angle is 7°~10°; in the fourth step, the implanted ion type is boron, the implantation energy is 25~80keV, the implantation dose is 4E15~9E15, and the implantation angle is 7°~10°.

3. The method for preparing the SOI high temperature MEMS piezoresistive pressure sensor based on the cantilever beam-central dual mass block structure according to claim 1, characterized in that: In the fifth step, the thickness of the newly deposited silicon dioxide layer is 0.2µm~0.5µm, and the thickness of the silicon nitride layer is 0.1µm~0.2µm; the annealing temperature is 950℃~1200℃, and the annealing time is 30min~150min; the contact hole size is 5µm~20µm.

4. The method for preparing the SOI high temperature MEMS piezoresistive pressure sensor based on the cantilever beam-central dual mass block structure according to claim 1, characterized in that: The thickness of the high temperature metal material layer is 1µm-2µm, and the high temperature metal material is selected from platinum, titanium / platinum / gold multilayer structure or nickel-chromium alloy aluminum / copper alloy.

5. The method for preparing the SOI high temperature MEMS piezoresistive pressure sensor based on the cantilever beam-central dual mass block structure according to claim 1, characterized in that: In the seventh step, the passivation protective layer material is a single-layer silicon nitride layer or a stack of silicon dioxide and silicon nitride, wherein the stack of silicon dioxide and silicon nitride is a silicon dioxide layer and a silicon nitride layer deposited in sequence on the front side of the substrate material sheet that has completed the sixth step process, and the overall thickness of the passivation protective layer is 0.2µm~1.2µm; the alloy temperature is 400℃~500℃, and the alloy time is 30min~200min.

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