Method for coating pressure-resistant medium-wave infrared protective film on zone-melting single-crystal silicon substrate

Abstract

The present invention discloses a method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate, comprising the following steps: ultrasonically cleaning the zone-melting single-crystal silicon substrate to remove polishing residues on the surface; immersing the substrate in a chemical solution to remove the oxide layer on the surface; preparing a C:H protective film on the surface of the substrate under high bias conditions by an RF-PECVD method, with a thickness not exceeding 150 nm; and preparing a C:H protective film under low bias conditions to have a thickness not exceeding 400 nm, thereby obtaining the pressure-resistant medium-wave infrared protective film on the zone-melting single-crystal silicon substrate. The present invention specifically adopts a surface cleaning treatment and an oxide layer removal process before coating, effectively solving the problem that residues on the zone-melting single-crystal silicon substrate affect the film-substrate bonding strength. At the same time, based on the deposition principle of PECVD, a coating process method combining high and low bias voltages is adopted, thereby reducing the temperature distribution gradient during the film deposition process, solving the problem of poor reliability and difficulty in film formation during film coating, and improving its environmental weather resistance and reliability.

Description

Technical Field

[0001] The invention belongs to the technical field of optical thin films, and in particular relates to a method for plating a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate. Background Art

[0002] Due to its high purity, high resistivity, and high strength, zone-melting single-crystal silicon is widely used in the semiconductor industry and plays an important role. Compared with Czochralski single-crystal silicon, it has better electrical insulation properties. When a certain thickness (thickness ≥ 25mm) of zone-melting single-crystal silicon is used as a pressure-resistant optical window and placed in an underwater environment, it will exhibit more stable resistance to electrochemical corrosion. In order to improve the medium-wave infrared transmittance of the zone-melting single-crystal silicon substrate and meet the needs of long-term use in underwater environments, a method of coating a dense medium-wave infrared protective film on the zone-melting single-crystal silicon substrate is adopted to meet both optical and functional requirements.

[0003] Medium-wave infrared protective films on single-crystal silicon substrates are often made from C:H thin films deposited using RF-PECVD. The C:H thin film structure lies somewhere between graphite and diamond phases. When pressure-resistant medium-wave infrared protective films are deposited on single-crystal silicon substrates using PECVD, the deposited films often exhibit high stress due to the material properties and high thickness of the substrate, which can easily cause film shedding.

[0004] How to prepare a C:H protective film with good optical properties, high environmental weather resistance and good pressure resistance on a zone-melting single-crystal silicon substrate using the PECVD method has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation process method for depositing a pressure-resistant medium-wave infrared protective film on a zone-melting silicon window substrate with a thickness of ≥25 mm. By deeply optimizing and improving the zone-melting single-crystal silicon substrate plating process chain, a C:H protective film with good optical properties, high environmental weather resistance and good pressure resistance is prepared on its surface, meeting the application requirements of pressure-resistant zone-melting single-crystal silicon.

[0006] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0007] A method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate comprises the following steps:

[0008] 1) Ultrasonic cleaning is used to clean the zone-melting single crystal silicon substrate to remove polishing residues on the surface;

[0009] 2) Soak in a chemical solution to remove the surface oxide layer;

[0010] 3) A C:H protective film with a thickness not exceeding 150 nm is prepared on its surface by RF-PECVD method under high bias conditions; a C:H protective film with a thickness not exceeding 400 nm is prepared under low bias conditions, thereby obtaining a pressure-resistant medium-wave infrared protective film for the zone-melting single crystal silicon substrate.

[0011] According to the above solution, the resistivity of the zone-melting single crystal silicon substrate is ≥2000Ω.cm, the diameter or diagonal length is ≥300mm, and the thickness is not less than 25mm;

[0012] According to the above scheme, the ultrasonic cleaning agent in step 1 includes but is not limited to one of KOH, hydrochloric acid, and H2O2, and is dried by air drying.

[0013] According to the above scheme, the chemical solution in step 2 includes but is not limited to one of HF, NH4HF2, and NH4F.

[0014] According to the above scheme, during the preparation process under the high bias condition in step 3, the power is 1KW to 2KW, and the deposition bias is not less than 800V.

[0015] According to the above scheme, the power of the preparation process under the low bias condition in step 3 is 1KW to 2KW, and the deposition bias is not higher than 750V.

[0016] According to the above scheme, step 3 is completed by multiple film formation methods, and after each plating is completed, it is cooled to room temperature and then taken out; the C:H protective film is prepared under low bias conditions in two times, and the thickness of each time does not exceed 200nm.

[0017] According to the above scheme, the method further includes step 4: using an infrared spectrometer to test the medium-wave infrared optical transmittance;

[0018] Step 5: Conduct two cycles of low-temperature, high-temperature, and damp-heat tests in accordance with GJB2485A-2019 General Specifications for Optical Coatings, and five cycles of salt spray tests in accordance with GJB150.11A Salt Spray Test Methods.

[0019] Step 6: Carry out pressure screening test. After the test is completed, the membrane layer is qualified if there is no peeling, wrinkling or falling off.

[0020] According to the above scheme, in step 4, it is confirmed that the single-side optical transmittance of the mid-wave infrared is not less than 92%.

[0021] According to the above scheme, in step 5, the low temperature is -45°C, the high temperature is 70°C, the humidity is 95% RH, and the salt spray test is a 24-hour salt spray + 24-hour drying test.

[0022] According to the above scheme, a multi-cycle cyclic pressure screening test is used in step 6. The film layer should be observed under a 60W yellow light and pass the test if there is no peeling, wrinkling or shedding.

[0023] This invention addresses the application needs of pressure-resistant protective films for melt-zone single-crystal silicon substrates. Taking advantage of their high resistivity, large resistivity gradient, and low thermal conductivity, it employs a targeted pre-coating surface cleaning and oxide layer removal process, effectively addressing the problem of residual melt-zone single-crystal silicon substrates impacting film-substrate adhesion. Furthermore, based on the deposition principles of PECVD, a coating process combining high and low bias voltages is employed to reduce the temperature gradient during film deposition, addressing the challenges of poor film deposition reliability and difficulty in film formation, and improving environmental resistance and reliability.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention is the first to use zone-melting single-crystal silicon material as a pressure-resistant optical window, placed in an underwater environment for application. To meet the long-term use requirements of zone-melting single-crystal silicon in a pressure-resistant environment, ultrasonic surface treatment and oxide layer removal processes are used before coating to fundamentally remove silicon surface residues and oxide layers that affect the adhesion of the film to the substrate. The PECVD preparation process under high and low voltage conditions is also used to effectively reduce the surface temperature of the zone-melting single-crystal silicon film formation process, solving the problem of high stress and easy shedding of the film layer caused by the high resistivity and low thermal conductivity coefficient of the zone-melting single-crystal silicon window. At the same time, strict environmental tests are used after coating to effectively complete the screening process, forming a full process chain manufacturing.

[0026] The zone-melting single crystal silicon substrate pressure-resistant medium-wave infrared protective film obtained by the present invention has good reliability and environmental weather resistance, and has passed the environmental adaptability screening tests such as low temperature, high temperature, humidity and heat, salt spray and pressure tests specified in the "GJB2485A-2019 General Specifications for Optical Film Layers" at one time.

[0027] The combination of high and low voltages and the rational allocation of tooling effectively improves the bonding strength between the film layer and the substrate, solves the problem of high internal stress caused by high film deposition temperature, and effectively improves the reliability of the film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Example 1 Design curve of pressure-resistant medium-wave infrared protective film on zone-melting single crystal silicon substrate.

[0029] Figure 2 : Measured curve of the pressure-resistant medium-wave infrared protective film on the zone-melting single crystal silicon substrate in Example 1.

[0030] Figure 3 : Example 1: Process for preparing a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate. DETAILED DESCRIPTION

[0031] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0032] The specific embodiment provides a method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate, comprising the following steps:

[0033] 1) Ultrasonic cleaning is used to clean the zone-melting single crystal silicon substrate to remove polishing residues on the surface;

[0034] 2) Soak in a chemical solution to remove the surface oxide layer;

[0035] 3) A C:H protective film with a thickness not exceeding 150 nm is prepared on its surface by RF-PECVD method under high bias conditions; a C:H protective film with a thickness not exceeding 400 nm is prepared under low bias conditions, thereby obtaining a pressure-resistant medium-wave infrared protective film for the zone-melting single crystal silicon substrate.

[0036] Specifically, the resistivity of the zone-melting single crystal silicon substrate is ≥2000Ω.cm, the diameter or diagonal length is ≥300mm, and the thickness is not less than 25mm;

[0037] Specifically, the ultrasonic cleaning agent in step 1 includes but is not limited to one of KOH, hydrochloric acid, and H2O2, and is dried by air drying;

[0038] Specifically, the chemical solution in step 2 includes but is not limited to one of HF, NH4HF2, and NH4F.

[0039] Specifically, during the preparation process under high bias conditions in step 3, the power is 1KW to 2KW, and the deposition bias is not less than 800 V. During the preparation process under low bias conditions, the power is 1KW to 2KW, and the deposition bias is not higher than 750 V. Preparation is completed by multiple film formations, and after each plating is completed, the film is cooled to room temperature before being removed.

[0040] A specific embodiment may further include step 4: using an infrared spectrometer to test the mid-wave infrared optical transmittance of the protective film prepared by the RF-PECVD method;

[0041] Step 5: Conduct two cycles of low-temperature, high-temperature, and damp-heat tests in accordance with GJB2485A-2019 General Specifications for Optical Coatings, and five cycles of salt spray tests in accordance with GJB150.11A Salt Spray Test Methods.

[0042] Step 6: Carry out pressure screening test. After the test is completed, the membrane layer is qualified if there is no peeling, wrinkling or falling off.

[0043] Specifically, in step 4, it is confirmed that the mid-wave infrared single-side optical transmittance is not less than 92%.

[0044] Specifically, in step 5, the low temperature is -45°C, the high temperature is 70°C, the wet heat is 95% RH, and the salt spray is a 24-hour salt spray (5% concentration NaCl solution) + 24-hour drying (35°C) test.

[0045] Specifically, in step 6, a multi-cycle cyclic pressure screening test is used and the film is observed under a 60W yellow light. The film layer should be qualified if there is no peeling, wrinkling or shedding.

[0046] Example 1

[0047] A 200mm×110mm×30mm thick zone-melting single crystal silicon substrate was used, and KOH, HCl, and H2O2 were used as cleaning agents for continuous ultrasonic semi-automatic cleaning. After cleaning, the surface was dried and the surface quality was observed under a 60W yellow light to check whether it met the required surface finish.

[0048] The single crystal silicon in the zone was immersed in a 10% NH4F solution for 2 minutes. After the immersion, the surface was washed with deionized water and dried.

[0049] According to the design curve thickness (see Appendix Figure 1 ), a 550nm thick C:H film was prepared on a zone-melting single crystal silicon substrate using the PECVD method. The plating process was divided into three passes. The first pass was 150nm, the power was 1.7KW, the bias voltage was adjusted to 800V, and the temperature was lowered to room temperature after the plating was completed. The second pass was 200nm, the power was 1.4KW, the bias voltage was adjusted to 730V, and the temperature was lowered to room temperature after the plating was completed. The third pass was 200nm, the bias voltage was adjusted to 730V, and the temperature was lowered to room temperature after the plating was completed to obtain a pressure-resistant medium-wave infrared protective film for the zone-melting single crystal silicon substrate. The measured curve of the pressure-resistant medium-wave infrared protective film for the obtained zone-melting single crystal silicon substrate is shown in the attached figure. Figure 2 shown.

[0050] After coating, the window film properties were tested using an infrared spectrometer, and the optical transmittance was higher than 93%.

[0051] Place the finished product in an environmental test chamber. For specific test procedures, see the attached Figure 3 As shown, according to the requirements of the "GJB2485-2019 General Specification for Optical Coatings," two cycles of high temperature (70°C), low temperature (-45°C), and damp heat (95% RH, 24 hours) testing were conducted. After the test, the surface was inspected to confirm that there was no peeling, wrinkling, or film peeling. After that, five cycles of salt spray (5% NaCl solution continuous spray for 24 hours followed by 35°C drying for 24 hours) were conducted. After all tests, the film showed no peeling, wrinkling, or shedding, and no corrosion spots were found on the surface when placed under a 50X microscope.

[0052] After the environmental screening test is completed, the finished product is placed in a pressure vessel and subjected to a specific cycle of pressure testing. After the test is completed, the surface is observed and the film layer is free of peeling, wrinkling, or shedding. The pressure resistance test of this embodiment can withstand a pressure of 1000m underwater.

[0053] Example 2

[0054] A 220mm×110mm×30mm single-crystal silicon zone was used as the substrate, and KOH, HCl, and H2O2 were used as cleaning agents for continuous ultrasonic semi-automatic cleaning. After cleaning, the surface was dried and the surface quality was observed under a 60W yellow light to check whether it met the required surface finish.

[0055] The single crystal silicon in the zone was treated by soaking in 8% HF solution for 1.5 minutes. After soaking, the surface was washed with deionized water and dried.

[0056] According to the design curve thickness (see Appendix Figure 1 ), a 550nm thick C:H film was prepared on a zone-melting single crystal silicon substrate using the PECVD method. The plating process was divided into three passes. The first pass was 150nm, the power was 1.8KW, the bias voltage was adjusted to 810V, and the temperature was lowered to room temperature after the plating was completed. The second pass was 200nm, the power was 1.5KW, the bias voltage was adjusted to 740V, and the temperature was lowered to room temperature after the plating was completed. The third pass was 200nm, the bias voltage was adjusted to 740V, and the temperature was lowered to room temperature after the plating was completed, to obtain a pressure-resistant medium-wave infrared protective film for the zone-melting single crystal silicon substrate.

[0057] After coating, the window film properties were tested using an infrared spectrometer, and the optical transmittance was higher than 93%.

[0058] The finished product was placed in an environmental testing chamber and subjected to two cycles of high-temperature (70°C), low-temperature (-45°C), and damp-heat (95% RH, 24 hours) testing in accordance with the requirements of the "GJB2485-2019 General Specification for Optical Coatings." After the tests, the surface was inspected to confirm that there was no peeling, wrinkling, or film peeling. Five cycles of salt spray (5% NaCl solution sprayed continuously for 24 hours followed by drying at 35°C for 24 hours) were then performed. After all tests, the film showed no peeling, wrinkling, or shedding, and no corrosion spots were observed under a 50X microscope.

[0059] After the environmental screening test is completed, the finished product is placed in a pressure vessel and subjected to a specific cycle of pressure testing. After the test is completed, the surface is observed and the film layer is free of peeling, wrinkling, or shedding. The pressure resistance test of this embodiment can withstand a pressure of 1000m underwater.

Claims

1. A method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single-crystal silicon substrate, characterized in that The following steps are involved: 1) Ultrasonic cleaning of a zone-melting single crystal silicon substrate to remove polishing residue from the surface; the zone-melting single crystal silicon substrate has a resistivity of ≥2000Ω.cm, a diameter or diagonal length of ≥300mm, and a thickness of not less than 25mm; 2) Soak in chemical solution to remove the surface oxide layer; 3) Using RF-PECVD method to prepare C:H protective film on its surface under high bias conditions, with a thickness not exceeding 150nm; under low bias conditions, preparing C:H protective film with a thickness not exceeding 400nm, a pressure-resistant medium-wave infrared protective film can be obtained on the zone-melting single crystal silicon substrate; The preparation is completed by multiple film formations, and after each plating is completed, the film is cooled to room temperature and then taken out; the C:H protective film is prepared in two steps under low bias conditions, and the thickness of each step does not exceed 200nm; During the preparation process under the high bias condition, the power is 1KW~2KW, and the deposition bias is not lower than 800V; during the preparation process under the low bias condition, the power is 1KW~2KW, and the deposition bias is not higher than 750V.

2. The method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single crystal silicon substrate as claimed in claim 1, characterized in that In step 1, the ultrasonic cleaning agent contains one of KOH, hydrochloric acid, and H2O2, and is dried by air drying.

3. The method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single crystal silicon substrate as claimed in claim 1, characterized in that The chemical solution in step 2 contains one of HF, NH4HF2, and NH4F.

4. The method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single crystal silicon substrate as claimed in claim 1, wherein Also includes step 4): using an infrared spectrometer to test the medium-wave infrared optical transmittance; confirming that the medium-wave infrared single-side optical transmittance is not less than 92%; Step 5): Conduct 2 cycles of low temperature, high temperature and humidity tests according to GJB2485A-2019 "General Specification for Optical Films", and conduct 5 cycles of salt spray test according to GJB150.11A salt spray test method; Step 6): Carry out pressure screening test. After the test is completed, the membrane layer is qualified without peeling, wrinkling or falling off.

5. The method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single crystal silicon substrate as claimed in claim 4, characterized in that In step 5, the low temperature is -45°C, the high temperature is 70°C, the humidity is 95%RH, and the salt spray test is a 24-hour salt spray + 24-hour drying test.

6. The method for coating a pressure-resistant medium-wave infrared protective film on a zone-melting single crystal silicon substrate as claimed in claim 4, wherein In step 6, a multi-cycle cyclic pressure screening test is used and the film is observed under a 60W yellow light. The film should be qualified if there is no peeling, wrinkling or shedding.

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