A method for preparing a MEMS core mold

Abstract

The present invention belongs to the field of semiconductor device technology and relates to a method for preparing a MEMS core mold, comprising the following steps: first, bonding the oxide layer side of a silicon wafer to a wafer substrate via a pyrolytic film, simultaneously forming a desired pattern on the surface of the silicon wafer using deep reactive ion etching, and depositing a metal film on the surface; then, bonding the metal film side of the silicon wafer to the wafer substrate via the pyrolytic film, further etching to form the desired pattern, heating and separating, peeling off the metal film, and removing the oxide layer to obtain a MEMS core mold; wherein the pyrolytic film described in S1 and S2 is composed of a polyethylene terephthalate base film and an acrylic adhesive layer coated on both sides of the base film. The present invention utilizes the pyrolytic film in combination with the oxide layer and metal film of the silicon wafer to effectively avoid contact between the silicon wafer and the pyrolytic film during the lamination and release processes, thereby reducing contamination and damage to the MEMS core mold during or after etching, and can also achieve rapid release.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and more particularly, to a method for preparing a MEMS core die. Background Art

[0002] With the rapid development of the integrated circuit industry, traditional integrated circuits are no longer able to meet the ever-changing needs of end-use applications. The convergence of microelectronics, micromechanics, and other natural science disciplines has led to the development of new chip technologies called MEMS, based on integrated circuit processes and combined with bulk micromachining technology. However, MEMS devices are small and extremely complex, typically requiring multiple etching steps to form the required complex structures. Furthermore, their small size makes direct etching difficult, often requiring a lamination process where they are bonded to a wafer substrate or other carrier using adhesives before etching. Currently, commonly used adhesives are silicone grease, rosin oil, or photoresist. The release of silicone grease and rosin oil after etching can cause significant contamination of MEMS core mold components, making it difficult to completely remove contaminants from the tiny structures even with prolonged cleaning. While photoresist is less contaminating than silicone grease or rosin oil, its release time is significantly longer, typically requiring prolonged immersion in a debonding solution to remove the MEMS core mold. Therefore, there is a continued need to develop a method that can reduce contamination of MEMS core mold devices and enable fast release. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects or shortcomings of the MEMS core mold device preparation process that is prone to cause serious contamination and has a long release time, and to provide a method for preparing a MEMS core mold.

[0004] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0005] The present invention provides a method for preparing a MEMS core die, comprising the following steps:

[0006] S1. Take a silicon wafer A having an oxide layer on at least one side, bond the oxide layer side to the wafer substrate via a pyrolytic film; use deep reactive ion etching (DRIE etching) to etch the desired pattern on the side of silicon wafer A away from the wafer substrate to obtain silicon wafer B, and then heat and separate silicon wafer B from the wafer substrate;

[0007] S2. Depositing a metal film on the patterned side of silicon wafer B in S1 and bonding the metal film side to the wafer substrate via a pyrolysis film; using deep reactive ion etching to form the desired pattern on the side of silicon wafer B away from the metal film to obtain silicon wafer C; then, thermally separating silicon wafer C from the wafer substrate, peeling off the metal film and removing the oxide layer to obtain the MEMS core die;

[0008] The pyrolysis films in S1 and S2 are composed of a polyethylene terephthalate (PET) base film and acrylic adhesive layers coated on both sides of the base film.

[0009] It should be noted that the oxide layer is located on the surface of the silicon wafer. Its main function is to prevent direct contact between the silicon wafer and the pyrolytic film, thereby reducing contamination of the pyrolytic film on the MEMS core. Even if a small amount of pyrolytic film remains on the surface of the oxide layer after thermal separation, the oxide layer can be removed to further protect the MEMS core.

[0010] In a specific embodiment, the average thickness of the pyrolysis films in steps S1 and S2 is 100-300 μm.

[0011] The thickness of the pyrolytic film primarily affects the heat dissipation during silicon wafer etching, which in turn affects the etching rate and etching selectivity. Studies have found that an average pyrolytic film thickness of 100 to 300 μm provides better heat dissipation and adhesion. Preferably, the pyrolytic film is 200 μm thick, with the PET layer at 100 μm and the acrylic adhesive layer at 50 μm.

[0012] Optionally, in step S1 , both sides of the silicon wafer A have an oxide layer.

[0013] Compared with single-sided oxide layer silicon wafers, double-sided oxide layer silicon wafers can not only better protect the silicon wafers from contamination during deep reactive ion etching, but also are more convenient to operate, which is conducive to improving production efficiency.

[0014] Specifically, in step S1, the oxide layer of silicon wafer A is first etched to form a desired pattern, and then the oxide layer side is bonded to the wafer substrate via a pyrolytic film. Optionally, the thickness of the oxide layer in step S1 is 1 μm to 2 μm.

[0015] The thickness of the oxide layer mainly affects the composite mask etching effect, and its thickness can be selected according to the actual situation of the etching pattern and etching selectivity.

[0016] Generally, the thickness of the metal film Preferably, the thickness of the metal film is

[0017] In actual production, it is found that when the metal film is too thin, it is not only easy to fall off, but also leads to poor uniformity of the actual film thickness in the etched deep hole. In order to protect the device surface from side etching and drilling while ensuring metal deposition in the deep hole, the thickness of the metal film needs to be In addition to serving as a stop layer, the metal film can also effectively protect the process device from drilling and side etching, thereby improving the etching accuracy of the device.

[0018] In a specific embodiment, the metal film is any one of an aluminum film (Al), a chromium film (Cr), and a gold film (Au).

[0019] In the preparation method of the present invention, a metal film is used as an etching stop layer. The selection of the metal film needs to take into account the difficulty of its removal in subsequent processes; for example, it is necessary to consider the destructive effect of the metal corrosive liquid on silicon-based devices. Compared with other metal films, the above-mentioned aluminum film, chromium film and gold film not only have the function of a stop layer, but are also easier to remove, have less impact on silicon-based devices, and have better effects.

[0020] Specifically, the temperature for heating and separating is 90-160°C, preferably, the temperature for heating and separating is 130-150°C.

[0021] The pyrolytic film used in the present invention has a decomposition temperature of 90°C to 160°C. It begins to dissolve at temperatures above 160°C and decomposes at 270°C. Taking into account the residual amount of the pyrolytic film on the oxide layer and metal film surface and the duration of release, it was found that a heating separation temperature of 130°C to 150°C has the best effect.

[0022] The present invention has the following beneficial effects:

[0023] The present invention adopts pyrolytic film instead of conventional adhesive, and utilizes the adhesive layer of the pyrolytic film to cover the specific structure on both sides of the base film, so that it will not flow freely like conventional adhesive during the lamination process. At the same time, combined with the oxide layer and metal film of the silicon wafer, it effectively avoids the contact between the silicon wafer and the adhesive during the lamination and release process, thereby reducing the contamination and damage to the MEMS core mold during or after the etching process. The characteristics of the pyrolytic film can also be utilized to achieve rapid release through simple heating treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process of preparing the MEMS core mold.

[0025] Figure 2 Schematic diagram of the double-sided pattern opening process of the double-polished oxide silicon wafer in Example 1.

[0026] Figure 3 Schematic diagram of the single-sided pattern etching process of the core mold in Example 1.

[0027] Figure 4 Schematic diagram of the core mold growth stop layer and backside pattern etching process in Example 1.

[0028] Figure 5 This is a schematic diagram of the post-processing process after the core mold etching is completed in Example 1.

[0029] Figure 6 This is a physical picture of the core mold in Example 1.

[0030] Figure 7 This is a physical picture of the core mold in Comparative Example 1.

[0031] Figure 8 This is a physical picture of the core mold in Comparative Example 2. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0033] Unless otherwise specified, all reagents and materials used in the following examples were commercially available. The pyrolytic film used in Examples 1-3 was manufactured by Suzhou Hechang Electronic Materials Co., Ltd., with the brand name HBL-100M279. The surface material (PET) was 100 μm thick, and the adhesive layers (acrylic adhesive) applied to both sides of the surface material were each 50 μm thick.

[0034] Example 1

[0035] A method for preparing a MEMS core mold comprises the following steps (eg Figure 1 shown):

[0036] S1. Use automatic rotary coating to apply 3μm of glue on one side of a 4-inch double-sided oxidized polished silicon wafer (positive photoresist process), then use a photolithography machine to perform patterning exposure, then perform drying treatment, and then perform development treatment; then place the patterned 4-inch silicon wafer in a RIE etcher for etching (etching parameters are CHF3:Ar=1:1sccm, pressure 32mTorr, etching time is 24min three cycles). Use NMP as a degumming agent to clean the silicon wafer after etching, then rinse with pure water and dry; repeat the above operation and perform patterning on the other side of the 4-inch silicon wafer (such as Figure 2 As shown, 1 is the oxide layer, 2 is the silicon wafer, and 3 is the photoresist).

[0037] S2. Use the automatic rotary coating method to apply 3μm of glue to one side of the double-sided patterned 4-inch silicon wafer in S1 (positive photoresist process), use the photolithography machine to expose the secondary overlay pattern, and then develop it. After development, observe the integrity of the surface pattern. Take the 6-inch wafer as the stacking substrate and stick the pyrolytic film on the surface of the 6-inch wafer. The surface must be flat and free of bubbles. The double-sided patterned 4-inch silicon wafer is bonded to the 6-inch wafer and etched using the DRIE-Bosch process to etch the secondary overlay pattern to the required depth. Heat at 130℃ to separate the 4-inch silicon wafer from the 6-inch wafer, and then remove the glue, clean it, and dry it (as shown in the figure). Figure 3 As shown, 4 is a pyrolysis film and 5 is a wafer substrate).

[0038] S3. Bond the 4-inch silicon wafer etched in S2 to the 6-inch wafer, and continue to use the DRIE-Bosch process to etch the exposed silicon surface for a second time, using the surface oxide layer as a secondary barrier layer (composite mask process). After the etching is completed, heat at 130°C to separate the 4-inch silicon wafer from the 6-inch wafer (as shown in the figure). Figure 3 shown).

[0039] S4. After the etching in S3 is completed, the thickness of the deposited pattern side of the 4-inch silicon wafer is Aluminum film as a stop layer (such as Figure 4 As shown, 6 is the stop layer).

[0040] S5. Perform a smear process on the back of the 4-inch wafer (smear thickness is 3μm), pattern it using a photolithography machine, and observe the integrity of the pattern after development; bond the metal film side of the 4-inch silicon wafer to the 6-inch wafer through a pyrolytic film, and use the DRIE-Bosch process to etch the back pattern to form the MEMS core mold body (such as Figure 4 shown).

[0041] S6. Heat at 130℃ to separate the MEMS core mold body from the 6-inch wafer, clean the MEMS core mold to remove the residual photoresist after etching, and then use KOH etching solution to strip the stop layer (metal film). Then use wet BOE etching to remove the oxide layer (SiO2). After drying, use plasma peroxide to clean the surface of the MEMS core mold to obtain the MEMS core mold (such as Figure 5 shown).

[0042] Example 2

[0043] A method for preparing a MEMS core mold comprises the following steps:

[0044] S1. Use an automated rotary spreader to apply a 3μm layer of adhesive (positive resist process) to one side of a 4-inch double-sided oxidized polished silicon wafer. Then, use a photolithography machine to pattern and expose the wafer, dry it, and then develop it. Next, place the patterned 4-inch wafer in a RIE etcher and etch it (etching parameters: CHF3:Ar = 1:1 sccm, pressure 32 mTorr, etching time 24 minutes for three cycles). After etching, clean the wafer with NMP as a desmear, rinse with pure water, and dry it. Repeat these steps to pattern the other side of the 4-inch wafer.

[0045] S2. Using an automated rotary coating process, apply 3μm of adhesive (positive resist) to one side of the double-sided patterned 4-inch silicon wafer in S1. A photolithography machine is used to expose the secondary overlay pattern, which is then developed. After development, the surface pattern integrity is inspected. A 6-inch wafer is used as the lamination substrate, and a pyrolytic film is applied to the surface of the 6-inch wafer. The surface must be flat and free of bubbles. The double-sided patterned 4-inch silicon wafer is bonded to the 6-inch wafer. The secondary overlay pattern is etched to the desired depth using the DRIE-Bosch process. The 4-inch silicon wafer and 6-inch wafer are separated by heating at 130°C. The wafers are then debonded, cleaned, and dried.

[0046] S3. Bond the 4-inch silicon wafer etched in S2 to the 6-inch wafer. Continue to use the DRIE-Bosch process to etch the exposed silicon surface for a second time, using the surface oxide layer as a secondary barrier layer (composite mask process). After etching is completed, heat at 150°C to separate the 4-inch silicon wafer from the 6-inch wafer.

[0047] S4. After the etching in S3 is completed, the thickness of the deposited pattern side of the 4-inch silicon wafer is The gold film is used as a stop layer.

[0048] S5. Perform photoresist treatment on the back side of the 4-inch wafer (the thickness of the photoresist is 3μm), pattern it using a photolithography machine, and observe the pattern integrity after development; bond the metal film side of the 4-inch silicon wafer to the 6-inch wafer using a pyrolytic film, and use the DRIE-Bosch process to etch the back side pattern to form the MEMS core mold body.

[0049] S6. Heat at 150℃ to separate the MEMS core mold body from the 6-inch wafer, clean the MEMS core mold to remove the residual photoresist from etching, then use KOH etching solution to strip off the stop layer (metal film), and then use wet BOE etching to remove the oxide layer (SiO2). After drying, use plasma peroxide to clean the surface of the MEMS core mold to obtain the MEMS core mold.

[0050] Example 3

[0051] A method for preparing a MEMS core mold comprises the following steps:

[0052] S1. Use an automated rotary spreader to apply a 3μm layer of adhesive (positive resist process) to one side of a 4-inch double-sided oxidized polished silicon wafer. Then, use a photolithography machine to pattern and expose the wafer, dry it, and then develop it. Next, place the patterned 4-inch wafer in a RIE etcher and etch it (etching parameters: CHF3:Ar = 1:1 sccm, pressure 32 mTorr, etching time 24 minutes for three cycles). After etching, clean the wafer with NMP as a desmear, rinse with pure water, and dry it. Repeat these steps to pattern the other side of the 4-inch wafer.

[0053] S2. Using an automated rotary coating process, apply 3μm of adhesive (positive resist) to one side of the double-sided patterned 4-inch silicon wafer in S1. Use a photolithography machine to expose the secondary overlay pattern, then develop it. After development, inspect the surface pattern integrity. Use a 6-inch wafer as the lamination substrate and apply a pyrolytic film to the surface of the 6-inch wafer. The surface must be flat and free of bubbles. Bond the double-sided patterned 4-inch silicon wafer to the 6-inch wafer. Use the DRIE-Bosch process to etch the secondary overlay pattern to the desired depth. Heat at 130°C to separate the 4-inch silicon wafer from the 6-inch wafer. Remove the adhesive, clean it, and dry it.

[0054] S3. Bond the 4-inch silicon wafer etched in S2 to the 6-inch wafer. Continue to use the DRIE-Bosch process to etch the exposed silicon surface for a second time, using the surface oxide layer as a secondary barrier layer (composite mask process). After etching is completed, heat at 130°C to separate the 4-inch silicon wafer from the 6-inch wafer.

[0055] S4. After the etching in S3 is completed, the thickness of the deposited pattern side of the 4-inch silicon wafer is The chromium film is used as a stop layer.

[0056] S5. Perform photoresist treatment on the back side of the 4-inch wafer (the thickness of the photoresist is 3μm), pattern it using a photolithography machine, and observe the pattern integrity after development; bond the metal film side of the 4-inch silicon wafer to the 6-inch wafer using a pyrolytic film, and use the DRIE-Bosch process to etch the back side pattern to form the MEMS core mold body.

[0057] S6. Heat at 130℃ to separate the MEMS core mold body from the 6-inch wafer, clean the MEMS core mold to remove the residual photoresist from etching, then use KOH etching solution to strip the stop layer (metal film), and then use wet BOE etching to remove the oxide layer (SiO2). After drying, use plasma peroxide to clean the surface of the MEMS core mold to obtain the MEMS core mold.

[0058] Comparative Example 1

[0059] A method for preparing a MEMS core mold includes steps substantially the same as those in Example 1, except that the pyrolysis film in steps S2 and S5 is replaced with lubricating oil (FOMBLIN-YL VAC 25 / 6).

[0060] Comparative Example 2

[0061] A method for preparing a MEMS core mold includes steps substantially the same as those in Example 1, except that the pyrolysis film in steps S2 and S5 is replaced by photoresist.

[0062] Performance Testing

[0063] The core molds prepared in Example 1, Comparative Example 1 and Comparative Example 2 were compared to detect the effects of different preparation methods on MEMS core mold contamination. The test results are shown in Tables 1 and Figures 6 to 8 shown.

[0064] Table 1 Test results

[0065]

[0066] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a MEMS core mold, characterized in that: The following steps are involved: S1. Take a silicon wafer A having an oxide layer on at least one side, and bond the oxide layer side to the wafer substrate by a pyrolytic film; Deep reactive ion etching is used to etch the desired pattern on the side of silicon wafer A away from the wafer substrate to obtain silicon wafer B, and then silicon wafer B is separated from the wafer substrate by heating; S2. Depositing a metal film on the patterned side of silicon wafer B in S1 and bonding the metal film side to the wafer substrate via a pyrolysis film; using deep reactive ion etching to form the desired pattern on the side of silicon wafer B away from the metal film to obtain silicon wafer C; then, thermally separating silicon wafer C from the wafer substrate, peeling off the metal film and removing the oxide layer to obtain the MEMS core die; The pyrolysis films in S1 and S2 are composed of a polyethylene terephthalate base film and acrylic adhesive layers coated on both sides of the base film.

2. The preparation method according to claim 1, characterized in that The average thickness of the pyrolysis films in steps S1 and S2 is 100 to 300 μm.

3. The preparation method according to claim 1, characterized in that: In step S1 , both sides of the silicon wafer A have an oxide layer.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S1, the oxide layer of silicon wafer A is first etched to form a desired pattern, and then the oxide layer side is bonded to the wafer substrate via a pyrolysis film.

5. The preparation method according to any one of claims 1 to 3, characterized in that The thickness of the oxide layer in step S1 is 1 μm to 2 μm.

6. The preparation method according to any one of claims 1 to 3, characterized in that As described in step S2 7. The preparation method according to claim 6, characterized in that: The thickness of the metal film is 8. The preparation method according to claim 6, characterized in that: The metal film is any one of an aluminum film, a chromium film and a gold film.

9. The preparation method according to claim 1, characterized in that: The heating and separation temperatures in steps S1 and S2 are both 90-160°C.

10. The preparation method according to claim 9, characterized in that: The temperature for heating and separating in steps S1 and S2 is 130-150°C.

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