A method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip

Abstract

The present invention discloses an integrated Fabry-Perot MEMS acceleration sensitive chip processing method, comprising the following steps: firstly, wet etching is used to make a cavity depth reference groove, the cavity is etched on a silicon wafer with the groove as a reference, and silicon oxide and silicon nitride films are repeatedly and alternately deposited on the cavity surface to make an optical anti-reflection film; then silicon oxide and silicon nitride films are repeatedly and alternately deposited on the surface of a glass wafer, and an optical anti-reflection film is formed by patterning; then silicon and glass wafers are anodically bonded, and the silicon wafer is thinned to a target thickness; finally, deep reactive ion etching technology is used to release the spring mass structure. The present invention can avoid the problem of residual stress in the prior art of etching first and then bonding, which causes deformation or damage of the sensitive chip, and has the advantages of simple process and high yield rate; in addition, thanks to the cavity depth reference groove step, it can ensure that the manufactured sensitive chip works in a high sensitivity state.

Description

Technical Field

[0001] The invention relates to the technical field of micro-electromechanical systems, and in particular to a method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip. Background Art

[0002] MEMS accelerometers are widely used in the fields of robots, drones, smart cars, and consumer electronics due to their high precision, small size, low power consumption, low cost, and ease of mass production. At present, common MEMS accelerometers can be divided into capacitive, resonant, piezoresistive, and optical types according to their detection methods. Among them, MEMS accelerometers based on the principle of optical interference combine the ultra-high displacement resolution of optical detection with the small size and low power consumption of MEMS technology, and have broad application prospects.

[0003] The processing technology of the MEMS acceleration sensor sensitive chip based on the Fabry-Perot cavity is a major difficulty in the development of integrated optical MEMS acceleration sensors. Its process flow usually includes key steps such as optical coating, functional structure production, and cavity formation. In the above process steps, there are three points that need special attention: 1. Optical coating generally requires alternating and repeated production of multiple layers of thin films. The thickness of a single layer of thin film is generally at the level of hundreds of nanometers. The thickness of the film directly determines the reflectivity of the Fabry-Perot cavity, which in turn affects the sensitivity of the acceleration sensor. Therefore, during the coating process, it is necessary to accurately control the film growth rate to control its thickness; 2. In order to ensure the improvement of the sensitivity of the acceleration sensor, its spring mass structure is generally designed with a low main frequency. The specific structure is reflected in the "long and thin" support beam and the "large and thick" inertial mass block. This structure is generally fragile and easy to damage during the process; 3. The Fabry-Perot cavity formed by the final bonding requires a high degree of parallelism between the movable mirror and the fixed mirror, otherwise it will affect the output consistency of the acceleration sensor. It is usually necessary to optimize the design of the spring mass structure and the bonding process to ensure the parallelism of the cavity.

[0004] The currently reported technologies, for example, the Fabry-Perot optical MEMS acceleration sensitive chip processing technology disclosed in Chinese patents CN201911213113.9 and CN202011125893.4, have the following processing flow: first, an optical anti-reflection film or an anti-reflection film is made on the surface of the wafer by magnetron sputtering, electron beam evaporation or vapor deposition to adjust the reflectivity of the Fabry-Perot cavity; then, according to the specific characteristics of the spring mass structure, the functional structure is processed on another wafer in sequence through steps such as photolithography, development, and etching; finally, the released spring mass structure and the wafer with the optical anti-reflection or anti-reflection film are fixed together by silicon-silicon direct bonding, silicon-glass anodic bonding or gluing technology to form a Fabry-Perot cavity, thereby completing the preparation of the Fabry-Perot MEMS acceleration sensor sensitive chip. Although the processing of the Fabry-Perot MEMS acceleration sensitive chip can be completed according to the above process steps, the spring mass structure has been released during the final bonding process. The high temperature and mechanical pressure applied during the bonding process will cause stress in the spring mass structure, resulting in structural deformation or even damage. In addition, the process operation is difficult and the spring mass structure is easily damaged. In addition, the neutral plane of the support beam and the mass block of the spring mass structure processed by the above process is usually not in the same plane, resulting in the poor parallelism of the cavity of the final sensitive chip when it is subjected to lateral acceleration, thereby affecting the sensor output. Summary of the invention

[0005] The purpose of the present invention is to provide an integrated Fabry-Perot MEMS acceleration sensitive chip processing method to overcome the problem of residual stress in the prior art of etching first and then bonding, which leads to deformation or damage of the sensitive chip. The method has the advantages of simple process and high yield. In addition, the present invention can ensure the consistency of the cavity length of the final Fabry-Perot cavity with the design value, thereby ensuring that the sensor is in a highly sensitive working state.

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

[0007] A method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip comprises the following steps:

[0008] (1) Silicon wafer cleaning to remove oxide film and surface impurities;

[0009] (2) etching the silicon wafer cleaned in step (1) using anisotropic silicon wet etching technology to produce a cavity depth reference groove;

[0010] (3) depositing a silicon nitride film on the surface of the depth reference groove produced in step (2) by a low pressure chemical vapor deposition method, and patterning the silicon nitride film by a reactive ion etching technique;

[0011] (4) using the silicon nitride film patterned in step (3) as a mask, etching the silicon cavity using deep reactive ion etching technology, and stopping the etching when the etching depth reaches the bottom of the depth reference groove to achieve precise control of the cavity etching depth;

[0012] (5) depositing a multilayer anti-reflection film on the surface of the silicon cavity produced in step (4) by a low-pressure chemical vapor deposition method;

[0013] (6) using reactive ion etching technology and wet etching technology to pattern the multi-layer anti-reflection film deposited in step (5) step by step;

[0014] (7) Glass wafer cleaning to remove surface impurities;

[0015] (8) depositing a multilayer anti-reflection film on the surface of the glass wafer cleaned in step (7) by a low pressure chemical vapor deposition method;

[0016] (9) patterning the multilayer anti-reflection film deposited in step (8) using reactive ion etching technology;

[0017] (10) bonding the silicon cavity produced in steps (1) to (6) and the glass wafer produced in steps (7) to (9) together using silicon-glass anodic bonding technology to form a Fabry-Perot interferometer cavity;

[0018] (11) thinning the silicon wafer bonded in step (10) to a target thickness using a thinning process;

[0019] (12) The silicon wafer thinned in step (11) is etched using deep reactive ion etching technology to pattern the spring mass structure, thereby completing the integrated processing of the Fabry-Perot MEMS acceleration sensor chip.

[0020] Furthermore, the etching depth reference groove produced by the silicon anisotropic wet etching technology in step (2) utilizes the etching angle of 54.74° caused by the different etching rates of silicon in different crystal directions during the wet etching process. By designing the size of the etching mask window, the etching can be automatically stopped after the etching depth reaches a preset value, thereby providing a depth reference for subsequent cavity etching.

[0021] Furthermore, in step (3), the thickness of the silicon nitride film deposited on the surface of the depth reference groove is 200 nm.

[0022] Furthermore, in the steps (5) and (8), the multilayer anti-reflection film is a dielectric film or a metal film. When a dielectric film is used, the deposition process adopts an alternating and repeated deposition method to ensure that the manufactured multilayer film has an optical anti-reflection effect.

[0023] Furthermore, the dielectric film is made of two of silicon dioxide, silicon nitride, silicon monoxide and magnesium fluoride.

[0024] Furthermore, the metal film is made of aluminum or germanium.

[0025] Furthermore, the multilayer anti-reflection film deposition process in step (5) and step (8) is specifically as follows: alternately and repeatedly depositing silicon dioxide film and silicon nitride film, step (5) deposits 4 layers, step (8) deposits 6 layers, and each layer of silicon dioxide film has a thickness of 162 nm, and each layer of silicon nitride film has a thickness of 117 nm.

[0026] Furthermore, the patterning process of the multi-layer anti-reflection film in step (6) is as follows: the first three layers of silicon nitride / silicon dioxide / silicon nitride from top to bottom are etched using reactive ion etching technology, while the last layer of silicon dioxide is etched using wet etching technology.

[0027] Furthermore, in the step (11), a thinning process is used to thin the silicon wafer bonded in the step (10) to 80 μm-100 μm.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] The present invention adopts a process sequence of first bonding and then etching to release the spring mass structure, which can avoid the problem of deformation or damage of the sensitive chip caused by various stresses existing in the prior art of first etching to release the spring mass structure and then bonding, and has the advantages of simple process and low operation difficulty. In addition, since bonding is performed before etching, the surface morphology and characteristic dimensions of silicon and glass wafers are relatively good, so the parallelism of the manufactured cavity is high; in addition, the support beam of the spring mass structure processed by the present invention and the neutral plane of the mass block are in the same plane, which can ensure that the cavity of the sensitive chip still maintains high parallelism when subjected to lateral acceleration, so that the cross sensitivity of the sensor is low. At the same time, the etching depth reference groove made by silicon anisotropic wet etching technology in this process flow can provide a depth reference for the subsequent dry etching step of the cavity, thereby ensuring the consistency of the cavity length of the final Fabry-Perot cavity with the design value, thereby ensuring that the sensor is in a highly sensitive working state. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1The present invention is a flowchart of a method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip. DETAILED DESCRIPTION

[0032] 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.

[0033] The following is combined with specific Figure 1 The technical solution of the present invention is described in detail.

[0034] (1) Prepare the silicon 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.

[0035] (2) etching the silicon wafer cleaned in step (1) using anisotropic silicon wet etching technology to produce a cavity depth reference groove;

[0036] (3) using a low pressure chemical vapor deposition (LPCVD) system to deposit a silicon nitride film with a thickness of 200 nm on the surface of the depth reference groove produced in step (2), and using reactive ion etching (RIE) technology to pattern the silicon nitride film to produce a mask for dry etching;

[0037] (4) Using the silicon nitride film patterned in step (3) as a mask, the cavity is etched using deep reactive ion etching technology; the etching process adopts a staged etching method, that is, firstly, the etching rate of the current parameters is determined by etching for a short period of time, and then the etching is carried out for a long time at the same rate until it is about 10 μm away from the target depth, and finally, when etching, it is necessary to compare with the depth reference groove, and the etching is stopped when the etching depth reaches the bottom of the depth reference groove, so as to achieve accurate control of the cavity etching depth;

[0038] (5) Using a low pressure chemical vapor deposition (LPCVD) system, a multilayer film (four layers in total) of silicon dioxide (162 nm) and silicon nitride (117 nm) is alternately and repeatedly deposited on the surface of the cavity formed by etching in step (4) to produce an anti-reflection film for the movable reflective mirror (spring mass structure surface). The above combined film can make the reflectivity of the Fabry-Perot cavity to lasers in the 700-1000 nm band reach about 70%;

[0039] (6) Using reactive ion etching (RIE) and wet etching technology to pattern the multilayer anti-reflection film deposited in step (5) step by step; wherein the first three layers (i.e., silicon nitride / silicon oxide / silicon nitride) are patterned using reactive ion etching technology, and the last layer of silicon dioxide is wet etched using a BOE solution; the use of this combination of dry and wet processes can ensure that the silicon of the device layer will not be damaged during the patterning of the anti-reflection film, and after the etching is completed, only the anti-reflection film on the surface area of ​​the inertial mass block structure is retained.

[0040] (7) Prepare 4-inch BF33 anodic bonding glass, and then immerse it in acetone and alcohol solution for cleaning;

[0041] (8) Using a low pressure chemical vapor deposition (LPCVD) system, a multilayer film of silicon dioxide (162 nm) and silicon nitride (117 nm) (six layers in total) is alternately deposited on the glass surface cleaned in step (7) to produce a fixed reflective mirror. The above combined film can make the reflectivity of the Fabry-Perot cavity to the laser in the 700-1000 nm band reach about 70%;

[0042] (9) patterning the multilayer anti-reflection film deposited in step (8) by using reactive ion etching (RIE) technology, and after etching, only the multilayer film in the same area as the glass surface and the mass block is retained;

[0043] (10) Using silicon-glass anodic bonding technology, the silicon cavity manufactured through steps (1) to (6) and the glass wafer manufactured through steps (7) to (9) are bonded together to form a Fabry-Perot interferometer cavity; during bonding, attention should be paid to the alignment of the glass cavity wafer and the silicon cavity.

[0044] (11) The silicon wafer bonded in step (10) is thinned to 80 μm-100 μm using a thinning process.

[0045] (12) The silicon wafer thinned in step (11) is etched using deep reactive ion etching (DRIE) technology to pattern the spring mass structure, and the inertial mass block is released after the etching is completed.

[0046] In step (12), a pressure sensitive film can be patterned to form a MEMS micromirror, or an optical filter can be patterned to form a pressure sensitive film.

[0047] The process flow of the present invention adopts a process sequence of bonding first and then etching to release the spring mass structure, which can avoid the problem of deformation or damage of the sensitive chip caused by various stresses existing in the prior art of first etching to release the spring mass structure and then bonding, and has the advantages of simple process and low operation difficulty. In addition, since bonding is performed before etching, the surface morphology and characteristic dimensions of the silicon and glass wafers are relatively good, so the parallelism of the manufactured cavity is high; in addition, the support beam of the spring mass structure processed by the technical solution and the neutral plane of the mass block are in the same plane, which can ensure that the cavity of the sensitive chip still maintains high parallelism when subjected to lateral acceleration, so that the cross sensitivity of the sensor is low. At the same time, the etching depth reference groove made by silicon anisotropic wet etching technology in the process flow can provide a depth reference for the subsequent dry etching step of the cavity, thereby ensuring the consistency of the cavity length of the final Fabry-Perot cavity with the design value, thereby ensuring that the sensor is in a highly sensitive working state.

[0048] 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 an integrated Fabry-Perot MEMS acceleration sensitive chip, characterized in that: The following steps are involved: (1) Silicon wafer cleaning to remove oxide film and surface impurities; (2) etching the silicon wafer cleaned in step (1) using anisotropic silicon wet etching technology to produce a cavity depth reference groove; (3) depositing a silicon nitride film on the surface of the depth reference groove produced in step (2) by a low pressure chemical vapor deposition method, and patterning the silicon nitride film by a reactive ion etching technique; (4) using the silicon nitride film patterned in step (3) as a mask, etching the silicon cavity using deep reactive ion etching technology, and stopping etching when the etching depth reaches the bottom of the depth reference groove; (5) depositing a multilayer anti-reflection film on the surface of the silicon cavity produced in step (4) by a low-pressure chemical vapor deposition method; (6) using reactive ion etching technology and wet etching technology to pattern the multi-layer anti-reflection film deposited in step (5) step by step; (7) Glass wafer cleaning to remove surface impurities; (8) depositing a multilayer anti-reflection film on the surface of the glass wafer cleaned in step (7) by a low pressure chemical vapor deposition method; (9) patterning the multilayer anti-reflection film deposited in step (8) using reactive ion etching technology; (10) bonding the silicon cavity produced in steps (1) to (6) and the glass wafer produced in steps (7) to (9) together using silicon-glass anodic bonding technology to form a Fabry-Perot interferometer cavity; (11) thinning the silicon wafer bonded in step (10) to a target thickness using a thinning process; (12) The silicon wafer thinned in step (11) is etched using deep reactive ion etching technology to pattern the spring mass structure, thereby completing the integrated processing of the Fabry-Perot MEMS acceleration sensor chip.

2. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 1, characterized in that: In the step (3), the thickness of the silicon nitride film deposited on the surface of the depth reference groove is 200 nm.

3. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 1, characterized in that: In the steps (5) and (8), the multilayer anti-reflection film is made of a dielectric film or a metal film. When a dielectric film is used, the deposition process is carried out in an alternating and repeated deposition manner.

4. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 3, characterized in that: The dielectric film uses two of silicon dioxide, silicon nitride, silicon monoxide and magnesium fluoride.

5. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 3, characterized in that: The metal film is made of aluminum or germanium.

6. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 1, characterized in that: The multilayer anti-reflection film deposition process in step (5) and step (8) is specifically as follows: silicon dioxide film and silicon nitride film are deposited alternately and repeatedly, four layers are deposited in step (5), and six layers are deposited in step (8), and the thickness of each silicon dioxide film layer is 162 nm, and the thickness of each silicon nitride film layer is 117 nm.

7. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 6, characterized in that: The patterning process of the multi-layer anti-reflection film in step (6) is as follows: the first three layers of silicon nitride / silicon dioxide / silicon nitride from top to bottom are etched using reactive ion etching technology, while the last layer of silicon dioxide is etched using wet etching technology.

8. The method for processing an integrated Fabry-Perot MEMS acceleration sensitive chip according to claim 1, characterized in that: In the step (11), the silicon wafer bonded in the step (10) is thinned to 80 μm-100 μm by a thinning process.

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