Processing method of Fabry-Perot acceleration sensitive chip suitable for double-layer beam structure

Abstract

The present invention discloses a method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure, comprising the following steps: firstly, etching a bonding positioning groove on the device layer of an SOI wafer, after which silicon oxide and silicon nitride films are alternately deposited, and a reflection enhancement film is formed by patterning; then, an aluminum mask is made by a stripping process, and a back cavity of a spring support beam is etched and released by deep reactive ion etching technology; then, two SOI wafers processed by the above steps are bonded, and etching is used to release the mass block structure; then, a glass wafer is wet-etched to make a cavity of the Fabry-Perot cavity, and after completion, silicon oxide and silicon nitride multilayer reflection enhancement films are deposited on the cavity surface; finally, the spring mass structure is bonded to the glass cavity by small pieces. The method provided by the present invention can complete the processing of a Fabry-Perot MEMS acceleration sensitive chip based on a double-layer fully symmetrical spring mass structure, and has the advantages of high processing accuracy, simple process, and high yield rate.

Description

Technical Field

[0001] The invention relates to the technical field of micro-electromechanical systems, and in particular to a method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure. Background Art

[0002] MEMS accelerometer is a typical MEMS device. In recent years, driven by the market demand for robots, drones, smart cars, electronic consumer products, etc., MEMS accelerometers have formed different types such as capacitance, resonance, piezoresistive, and optical, with different characteristics such as high precision, low power consumption, and a large range, and a complete product series for different purposes such as military, industrial, and consumer products. Among them, the MEMS accelerometer based on the principle of optical interference combines the ultra-high displacement resolution of optical detection with the small size and low power consumption of MEMS technology, showing great application prospects in the upcoming era of the Internet of Everything.

[0003] Fabry-Perot interferometry is a detection method often used in optical MEMS accelerometers. Its core structure usually includes a spring-mass structure, a fixed substrate, and a Fabry-Perot cavity composed of the two. The Fabry-Perot cavity is composed of two plane mirrors with a specific reflectivity at a certain distance from each other. For Fabry-Perot MEMS accelerometers, one of the mirrors is usually combined with an inertial mass block to form a movable mirror, while the other is combined with the substrate to form a fixed mirror. When the accelerometer is subjected to external acceleration, the cavity length of the Fabry-Perot cavity composed of the movable mirror and the fixed mirror will change, which will lead to changes in the intensity of the interference light. Acceleration measurement is achieved by demodulating the light intensity. For the above-mentioned Fabry-Perot acceleration sensitive chip, the parallelism of the interference cavity formed by the movable mirror and the fixed mirror is an important factor to ensure the consistency of sensor output and low cross sensitivity. However, for the existing Fabry-Perot MEMS acceleration sensitive chip, due to process limitations, the neutral planes of its spring support beam and mass block are located in different planes, which causes the mass block to rotate when the sensitive chip is subjected to lateral force, making the cavity non-parallel, thereby affecting the sensor output. In order to solve this problem, it is necessary to develop a special process to make a double-layer spring mass structure in which the neutral planes of the support beam and the mass block are located in the same plane.

[0004] Researchers from Huazhong University of Science and Technology used a customized five-layer SOI wafer to prepare an acceleration-sensitive chip with a double-layer spring mass block structure. The process of this method is simple, but due to the etching masking problem, the upper and lower layers of springs must be arranged in a staggered manner, otherwise the etching of the upper and lower spring mass structures cannot be completed at the same time. At the same time, since the dry etching needs to be repeated once in the last step of the preparation process, the process difficulty and risk increase. Researchers from the Institute of Geology and Geophysics, Chinese Academy of Sciences, combined the wet etching process and the bonding process to produce a double-layer spring mass block acceleration-sensitive chip. The specific process flow is to first produce a single-layer spring mass structure through a wet etching process, and then bond the produced single-layer spring mass structure back to back through a silicon-silicon bonding process to form a double-layer spring mass structure. However, the mass block of this structure is made through a wet etching process, so its mass block structure itself has a 54.74° inclined sidewall, which sacrifices the mass of the mass block to a certain extent and reduces the sensitivity of the acceleration sensor. At the same time, due to the problem of precision control of the wet etching process, the characteristic size error of the processed structure is large, which in turn affects the performance of the acceleration sensor. Summary of the invention

[0005] The purpose of the present invention is to provide a method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure to overcome the defects of the prior art. The present invention can ensure that the acceleration sensor has high sensitivity under lower requirements for supporting photoelectric components, and has the advantages of high processing accuracy, simple process and high yield.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure comprises the following steps:

[0008] (1) Clean the SOI wafer to remove the oxide film and surface impurities;

[0009] (2) using deep reactive ion etching technology to etch the device layer of the SOI wafer cleaned in step (1) to form a bonding positioning groove;

[0010] (3) using a low pressure chemical vapor deposition method to alternately and repeatedly deposit a silicon dioxide film and a silicon nitride film on the SOI wafer device layer after etching in step (2) to form an optical anti-reflection film;

[0011] (4) etching and patterning the optical anti-reflection film deposited in step (3) in steps by using reactive ion etching technology and wet etching;

[0012] (5) combining electron beam evaporation coating technology and stripping technology to form an etched aluminum mask for subsequent release of the spring mass structure on the surface of the SOI wafer device layer patterned in step (4);

[0013] (6) etching the base layer of the SOI wafer after aluminum masking in step (5) by deep reactive ion etching technology, and stopping the etching when the buried oxide layer is reached;

[0014] (7) bonding the two SOI wafers etched in step (6) together using silicon-silicon direct bonding technology to form a dual device layer structure;

[0015] (8) etching the device layer of the double device layer structure bonded in step (7) by deep reactive ion etching technology to pattern the spring support beam;

[0016] (9) removing the aluminum mask by wet etching of aluminum and releasing the spring mass structure by HF, and then dividing the SOI wafer into a single spring mass structure;

[0017] (10) Glass wafer cleaning to remove surface impurities;

[0018] (11) etching the glass wafer cleaned in step (10) using a wet etching technique to produce a Fabry-Perot cavity;

[0019] (12) using a low pressure chemical vapor deposition method to alternately and repeatedly deposit a silicon dioxide film and a silicon nitride film on the cavity surface etched by step (11) to form an optical anti-reflection film;

[0020] (13) patterning the optical anti-reflection film deposited in step (12) using reactive ion etching technology, and after completion, using a dicing machine to cut the glass wafer into a single glass cavity;

[0021] (14) Using the bonding positioning groove processed in step (2) as an assembly and alignment reference, two glass cavities and a spring mass structure are bonded together, and the edges are sealed and glued to form a double-layer beam structure Fabry-Perot acceleration sensitive chip.

[0022] Furthermore, in the step (3), the thicknesses of the silicon dioxide film and the silicon nitride film deposited in a single time are 162 nm and 117 nm respectively, and the deposition is repeated twice.

[0023] Furthermore, the patterning process of the optical anti-reflection film in step (4) is as follows: the first three layers of silicon nitride / silicon dioxide / silicon nitride from top to bottom are patterned using reactive ion etching technology, and the last layer of silicon dioxide is patterned using wet etching technology.

[0024] Furthermore, the reason why step (5) is placed before step (6) in the process sequence is that it can avoid the need to perform photolithography and other steps to mask the spring mass structure of the etched device layer after etching the SOI substrate layer, which may cause structural damage.

[0025] The step (6) has a real-time detection function for the deep reactive ion etching process of the SOI wafer, so as to ensure that the etching stops in time when the buried oxide layer is reached.

[0026] Furthermore, the spring mass structure formed in steps (7)-(9) has a double-layer spring support beam, and the double-layer spring support beam is symmetrical in the upper and lower directions about the neutral plane of the mass block.

[0027] Furthermore, the depth of wet etching in step (11) is 40-60 μm. If the depth is less than 40 μm, the silicon movable mass block may fit into the glass cavity. If the depth is greater than 60 μm, the optical properties of Fabry-Perot interference may be affected.

[0028] Furthermore, the thicknesses of the silicon dioxide film and silicon nitride film deposited in step (12) are 162 nm and 117 nm respectively, and the deposition is repeated three times. This process combination can ensure that the reflectivity of the Fabry-Perot cavity to the laser in the 700-1000 nm band reaches about 70%.

[0029] Furthermore, the bonding technology used in step (14) is epoxy resin bonding, and the bonding process is small-chip bonding, which can avoid the high requirements of silicon glass anodic bonding on the cleanliness and roughness of the wafer surface and the problem of structural deformation or damage caused by residual stress caused by mechanical pressure and high temperature during the bonding process; the key to this step is the bonding positioning groove made in step (2), which can ensure accurate positioning and assembly during single-chip bonding, and the process is simple, and the bonding process can be completed without special equipment.

[0030] Furthermore, the step (14) uses epoxy resin edge sealing and gluing.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects:

[0032] Firstly, the processing method disclosed in the present invention can complete the processing of the Fabry-Perot MEMS acceleration sensitive chip based on the double-layer fully symmetrical spring mass structure, and has the advantages of high processing precision, simple process and high yield rate; secondly, thanks to the steps of small piece gluing and etching bonding positioning grooves adopted in the process flow, the present invention avoids the problems of high requirements on the cleanliness and roughness of the wafer surface in the existing silicon glass anode bonding and the residual stress caused by the mechanical pressure and high temperature during the bonding process, which leads to structural deformation or damage. At the same time, the processed bonding positioning groove can also be used as a chip assembly positioning structure when the sensor is packaged as a whole; finally, the process parameters of the low pressure chemical vapor deposition (LPCVD) system provided by the present invention for making the optical anti-reflection film can ensure that the reflectivity of the Fabry-Perot cavity is at the optimal value of about 70%, thereby ensuring that the acceleration sensor has high sensitivity under lower requirements for supporting photoelectric components. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 It is a specific process flow chart of the method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure disclosed in the present invention. DETAILED DESCRIPTION

[0035] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0036] The following is combined with specific Figure 1 The technical solution of the present invention is described in detail.

[0037] (1) Prepare the SOI wafer by first immersing it in an acetone and alcohol solution for cleaning, and then immersing it in a solution of sulfuric acid / hydrogen peroxide for cleaning to remove the oxide film, metal ions and other impurities;

[0038] (2) using deep reactive ion etching (DRIE) technology to etch the device layer of the SOI wafer cleaned in step (1) to form a bonding positioning groove for subsequent assembly and alignment. The characteristic size of the positioning groove is the same as the size of the glass cavity, so that the glass cavity can be exactly embedded in the groove;

[0039] (3) using a low pressure chemical vapor deposition (LPCVD) system to alternately and repeatedly deposit silicon dioxide (162 nm) and silicon nitride (117 nm) multilayer films (four layers in total) on the SOI wafer device layer after etching in step (3) to produce an anti-reflection film for the movable reflective mirror (spring mass structure surface). The above combined films can make the reflectivity of the Fabry-Perot cavity to the laser in the 700-1000 nm band reach about 70%;

[0040] (4) The multilayer anti-reflection film deposited in step (3) is patterned using reactive ion etching (RIE) and wet etching techniques. The patterning process is that the first three layers (i.e., silicon nitride / silicon dioxide / silicon nitride) are patterned using reactive ion etching technology, while the last layer of silicon dioxide is wet etched using BOE solution. This dry and wet step-by-step combination process can ensure that the silicon of the device layer will not be damaged during the patterning of the anti-reflection film. After the etching is completed, only the anti-reflection film on the surface area of ​​the inertial mass block structure is retained.

[0041] (5) Using an electron beam evaporation coating machine, a 4 μm thick aluminum film is evaporated on the SOI device layer patterned in step (4), and then patterned by a lift-off process to form an etching mask for the subsequent release spring mass structure.

[0042] (6) Using deep reactive ion etching (DRIE) technology to etch the base layer of the SOI wafer after aluminum masking in step (5), the etching stops when the buried oxide layer is formed. The deep reactive ion etching process has a real-time detection function of the etching depth to ensure that the etching stops in time when the buried oxide layer is formed, thereby ensuring the uniformity of the spring support beam.

[0043] (7) using silicon-silicon direct bonding technology to bond two SOI wafers etched in step (6) together to form a dual device layer structure. Before bonding, the cross alignment marks on the surface of each SOI wafer are used for alignment to ensure that the mass blocks formed by etching in step (6) are completely overlapped.

[0044] (8) Using deep reactive ion etching (DRIE) technology to etch the device layer of the double device layer structure bonded in step (7) to pattern the spring support beam and achieve the purpose of releasing the inertial mass block; the double-layer spring support beam formed after etching is symmetrical in the upper and lower directions with respect to the neutral plane of the mass block.

[0045] (9) Using aluminum wet etching technology to remove the aluminum mask, and using gaseous HF to etch the oxide layer of the SOI wafer, thereby releasing the spring mass structure, and then using a laser scriber to cut the SOI wafer into small pieces;

[0046] (10) Prepare 4-inch BF33 anodic bonding glass, and then immerse it in acetone and alcohol solution for cleaning;

[0047] (11) preparing a glass etching solution (HF:H2O=1:5), and using a wet etching technique to etch the glass wafer cleaned in step (10) to produce a Fabry-Perot cavity. Note that during the etching process, the etching depth should be regularly checked with a step profiler to prevent over-etching.

[0048] (12) using a low pressure chemical vapor deposition (LPCVD) system to alternately and repeatedly deposit silicon dioxide (162 nm) and silicon nitride (117 nm) multilayer films (a total of six layers) on the cavity surface that has been etched in step (11) to produce a fixed reflective mirror. The above combined films can make the reflectivity of the Fabry-Perot cavity to lasers in the 700-1000 nm band reach about 70%;

[0049] (13) patterning the multilayer anti-reflection film deposited in step (12) by using reactive ion etching (RIE) technology, and after etching, only the multilayer film in the area with the same area as the mass block in the glass cavity is retained;

[0050] (14) Using the bonding positioning groove processed in step (2) as an assembly and alignment reference, assemble the two glass cavities and the spring mass structure together, and seal the edges with epoxy resin.

[0051] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure, characterized in that: The following steps are involved: (1) Clean the SOI wafer to remove the oxide film and surface impurities; (2) using deep reactive ion etching technology to etch the device layer of the SOI wafer cleaned in step (1) to form a bonding positioning groove; (3) using a low pressure chemical vapor deposition method to alternately and repeatedly deposit a silicon dioxide film and a silicon nitride film on the SOI wafer device layer after etching in step (2) to form an optical anti-reflection film; (4) etching and patterning the optical anti-reflection film deposited in step (3) in steps by using reactive ion etching technology and wet etching; (5) combining electron beam evaporation coating technology and stripping technology to form an etched aluminum mask for subsequent release of the spring mass structure on the surface of the SOI wafer device layer patterned in step (4); (6) etching the base layer of the SOI wafer after aluminum masking in step (5) by deep reactive ion etching technology, and stopping the etching when the buried oxide layer is reached; (7) bonding the two SOI wafers etched in step (6) together using silicon-silicon direct bonding technology to form a dual device layer structure; (8) etching the device layer of the double device layer structure bonded in step (7) by deep reactive ion etching technology to pattern the spring support beam; (9) removing the aluminum mask by wet etching of aluminum and releasing the spring mass structure by HF, and then dividing the SOI wafer into a single spring mass structure; (10) Glass wafer cleaning to remove surface impurities; (11) etching the glass wafer cleaned in step (10) using a wet etching technique to produce a Fabry-Perot cavity; (12) using a low pressure chemical vapor deposition method to alternately and repeatedly deposit a silicon dioxide film and a silicon nitride film on the cavity surface etched by step (11) to form an optical anti-reflection film; (13) patterning the optical anti-reflection film deposited in step (12) using reactive ion etching technology, and after completion, using a dicing machine to cut the glass wafer into a single glass cavity; (14) Using the bonding positioning groove processed in step (2) as an assembly and alignment reference, two glass cavities and a spring mass structure are bonded together, and the edges are sealed and glued to form a double-layer beam structure Fabry-Perot acceleration sensitive chip.

2. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The thicknesses of the silicon dioxide film and silicon nitride film deposited in a single step (3) are 162 nm and 117 nm respectively, and the deposition is repeated twice.

3. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 2, characterized in that: The patterning process of the optical anti-reflection film in step (4) is as follows: the first three layers of silicon nitride / silicon dioxide / silicon nitride from top to bottom are patterned using reactive ion etching technology, and the last layer of silicon dioxide is patterned using wet etching technology.

4. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The spring mass structure formed by steps (7)-(9) has a double-layer spring support beam, and the double-layer spring support beam is symmetrical in the upper and lower directions with respect to the neutral plane of the mass block.

5. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The depth of the wet etching in step (11) is 40-60 μm.

6. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The thicknesses of the silicon dioxide film and silicon nitride film deposited in a single step (12) are 162 nm and 117 nm respectively, and the deposition is repeated three times.

7. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The bonding technology used in step (14) is epoxy resin bonding, and the bonding process is small piece bonding.

8. The method for processing a Fabry-Perot acceleration sensitive chip suitable for a double-layer beam structure according to claim 1, characterized in that: The step (14) uses epoxy resin edge sealing and gluing.

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