1. A method for designing and preparing a thin film antireflection coating for a silicon-based lens having a thickness of 8-4 μm.

Abstract

This paper provides a design and fabrication method for a 1.8-4 μm silicon-based lens antireflection film. The design method includes the following steps: Sa, the film system design uses 550 nm as the reference wavelength for optical film design, and employs the film stack formula: Sub / 0.3M. 0.8N(HL)^3K / AIR, Sub is coated with the same film system on both sides, where Sub is the silicon substrate, AIR represents air. In the film stack formula, H represents 1 / 4 wavelength thick high refractive index material ZnS, L represents 1 / 4 wavelength thick low refractive index material YbF3, M represents 1 / 4 wavelength thick base layer material SiO, N represents 1 / 4 wavelength thick connecting layer material Ge, K represents 1 / 4 wavelength thick protective layer material Al2O3 (alumina), Sb, through the input film stack formula, generates a film structure of Sub / SiO / Ge / ZnS / YbF3 / Al2O3 / Air; Sc, the film thickness is optimized using thin film design software to obtain the optimal film thickness, and the transmittance of the optimized film structure in the 1.8-4μm band meets the requirements; Sd, the optimized film thickness is input into the control computer of the coating machine.

Description

Technical Field

[0001] This disclosure relates to the field of infrared optical thin film technology, and more specifically to a design method and preparation method of a 1.8-4μm silicon-based lens antireflection film. Background Technology

[0002] Silicon, due to its excellent infrared optical and physical properties and good transparency in the 1.5-14μm wavelength range, is widely used in infrared thermometry, thermal imaging, uncooled infrared focal plane array detection, wafer packaging windows, and military guidance. However, silicon substrates are easily oxidized in the atmosphere, and their coefficients of thermal expansion differ significantly from those of common infrared coating materials. Furthermore, some silicon substrates have convex surfaces (for example, silicon convex mirrors can be used to focus and adjust laser beams in laser cutting and welding processes, improving the accuracy and efficiency of laser processing, and can also be used in optical measuring instruments), resulting in poor adhesion between the film and the substrate, increasing the difficulty of film fabrication. In addition, in the 1.8-4μm wavelength range, some commonly used coating materials exhibit some absorption, leading to low transmittance of the resulting lenses, which cannot meet the requirements of different applications. Therefore, the selection of coating materials, the design of the film system, and the improvement of the specific coating process all become more challenging. Summary of the Invention

[0003] In view of the problems existing in the background art, one object of this disclosure is to provide a design method and a preparation method for a 1.8-4μm silicon-based lens antireflection film, which enables the designed and prepared silicon substrate and the film system on both sides to achieve the required transmittance in the 1.8-4μm band.

[0004] Another objective of this disclosure is to provide a design and fabrication method for a 1.8-4μm silicon-based lens antireflection film, which enables the designed and fabricated silicon substrate and the film system on both sides to meet the requirements of different applications.

[0005] Therefore, a design method for a 1.8-4μm silicon-based lens antireflection film includes the following steps: Sa, the film system design uses 550nm as the reference wavelength for optical film design, and uses the film stack formula: Sub / 0.3M0.8N(HL)^3K / AIR, Sub is coated with the same film system on both sides, where Sub is the silicon substrate, AIR represents air, and in the film stack formula, H represents a 1 / 4 wavelength thick high refractive index material ZnS (zinc sulfide), L represents a 1 / 4 wavelength thick low refractive index material YbF3 (ytterbium fluoride), and M represents a 1 / 4 wavelength thick base layer material S. iO (silicon monoxide), N represents the 1 / 4 wavelength thick connecting layer material Ge (germanium), K represents the 1 / 4 wavelength thick protective layer material Al2O3 (aluminum oxide), Sb, through the input film stack formula, generates a film structure of Sub / SiO / Ge / ZnS / YbF3 / Al2O3 / Air; Sc, the film thickness is optimized using thin film design software to obtain the optimal film thickness, and the transmittance of the optimized film structure in the 1.8-4μm band meets the requirements; Sd, the optimized film thickness is input into the control computer of the coating machine.

[0006] A method for preparing a 1.8-4μm silicon-based lens antireflection film includes the following steps: S1, cleaning the silicon substrate and the substrate to be coated before deposition, and preparing five film materials: SiO, Ge, ZnS, YbF3, and Al2O3; S2, configuring the deposition process conditions and process documents, including deposition temperature, pre-deposition base vacuum, film thickness, deposition mode of the film materials, deposition rate of the film materials, and the use and parameters of ion source-assisted deposition. The optimal film thickness is based on the aforementioned 1.8-4μm silicon-based lens antireflection method. The optimal film thickness is stored in the control computer of the coating machine as described in the thin film design method; S3, the cleaned lens is placed into the tooling fixture, the tooling fixture with the lens is hung into the cavity of the coating machine, the door is closed, vacuum is drawn and heated; S4, the film material is pre-melted; S5, the lens is cleaned with an ion source; S6, film coating and monitoring, the first side of the lens is coated according to the coating process conditions and process document configuration in step S2; S7, constant temperature is maintained after coating; S8, the part is cooled and removed; S9, steps S1 to S8 are repeated to coat the second side of the lens.

[0007] The beneficial effects of this disclosure are as follows.

[0008] In the design method of the 1.8-4μm silicon-based lens antireflection film according to this disclosure, SiO has a similar coefficient of thermal expansion to the silicon substrate and is used as the underlayer to enhance the adhesion between the film and the substrate. Ge has good adhesion to both SiO and ZnS films, but Ge has significant absorption near 1.8μm, so Ge ​​is used as the bonding layer. ZnS and YbF3 are used as high and low refractive index materials to improve the transmittance of the film. Al2O3 is used as the outermost protective layer, which is both waterproof and abrasion resistant. Therefore, the designed film structure not only meets the transmittance requirements in the 1.8-4μm band, but also considers the adhesion between the underlayer and the silicon substrate on both sides of the film system, and the ability of the two film systems to meet the requirements of different applications.

[0009] In the method for preparing a 1.8-4μm silicon-based lens antireflection film according to this disclosure, based on steps S1 to S9 and the optimal film thickness stored in the control computer of the coating machine as described in the aforementioned design method for a 1.8-4μm silicon-based lens antireflection film, as verified by testing, the transmittance of the prepared silicon substrate substrate and the film system on both sides can meet the requirements in the 1.8-4μm band. At the same time, it can meet the requirements of water immersion test, salt spray test, adhesion test, moderate friction test, constant temperature and humidity test, low temperature test and high temperature test, thereby meeting the requirements of different applications. Attached Figure Description

[0010] Figure 1 This is a schematic structural diagram of the silicon substrate and the film system on both sides, according to the design and fabrication method of the 1.8-4μm silicon-based lens antireflection film according to the present disclosure.

[0011] Figure 2 The transmittance curve is the result of the design method of the 1.8-4μm silicon-based lens antireflection film in Example 1.

[0012] Figure 3 This is a transmittance curve of the substrate and the film system on both sides after the coating is completed, showing the preparation method of the 1.8-4μm silicon-based lens antireflection film in Example 1.

[0013] Figure 4 The images show the preparation method of the 1.8-4μm silicon-based lens antireflection film in Example 1, and the product before and after moderate friction after coating. Detailed Implementation

[0014] It is understood that the disclosed embodiments are merely examples of this disclosure, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this disclosure in various ways.

[0015] [Design Method of 1.8-4μm Silicon-based Lens Anti-reflection Film]

[0016] Reference Figure 1 and Figure 2 The design method for 1.8-4μm silicon-based lens antireflection films according to this disclosure includes the following steps:

[0017] Sa, the film system design uses 550nm as the reference wavelength for optical thin film design, and uses the film stack formula: Sub / 0.3M0.8N(HL)^3K / AIR, where Sub is coated with the same film system on both sides, and Sub represents silicon substrate, AIR represents air. In the film stack formula,

[0018] H represents ZnS (zinc sulfide), a high-refractive-index material with a thickness of 1 / 4 wavelength.

[0019] L represents YbF3 (ytterbium fluoride), a low-refractive-index material with a thickness of 1 / 4 wavelength.

[0020] M represents the SiO (silicon monoxide) substrate material with a thickness of 1 / 4 wavelength.

[0021] N represents Ge (germanium), a bonding layer material with a thickness of 1 / 4 wavelength.

[0022] K represents Al2O3 (alumina), a protective layer material with a thickness of 1 / 4 wavelength.

[0023] Sb, through the input membrane stack formula, generates a membrane structure of Sub / SiO / Ge / ZnS / YbF3 / Al2O3 / Air;

[0024] Sc, by optimizing the film thickness using thin film design software, obtained the optimal film thickness. The transmittance of the optimized film structure in the 1.8-4μm band meets the requirements.

[0025] Sd inputs the optimized film thickness into the control computer of the coating machine.

[0026] In the design method of the 1.8-4μm silicon-based lens antireflection film according to this disclosure, SiO has a similar coefficient of thermal expansion to the silicon substrate and is used as the underlayer to enhance the adhesion between the film and the substrate. Ge has good adhesion to both SiO and ZnS films, but Ge has significant absorption near 1.8μm, so Ge ​​is used as the bonding layer. ZnS and YbF3 are used as high and low refractive index materials to improve the transmittance of the film. Al2O3 is used as the outermost protective layer, which is both waterproof and abrasion resistant. Therefore, the designed film structure not only meets the transmittance requirements in the 1.8-4μm band, but also considers the adhesion between the underlayer and the silicon substrate on both sides of the film system, and the ability of the two film systems to meet the requirements of different applications.

[0027] In one example, in step Sc, the optimal coating thickness for each of the two sides of the lens is:

[0028] The SiO film thickness is 25 nm.

[0029] The thickness of the Ge film is 25 nm.

[0030] The thickness of the ZnS film is 280.31 nm.

[0031] The thickness of the YbF3 film is 393.64 nm.

[0032] The thickness of the Al2O3 film is 153 nm.

[0033] In one example, in step Sc, the average transmittance of the optimized film structure in the 1.8–4 μm band is greater than 99.5%.

[0034] In one example, in steps Sa to Sc, the software is designed as TFCalc or Essential Macleod.

[0035] [Preparation method of 1.8-4μm silicon-based lens antireflection film]

[0036] The method for preparing the 1.8-4 μm silicon-based lens antireflection film according to this disclosure includes the following steps:

[0037] S1. Before plating, the silicon substrate product used as the lens and the accompanying coating are cleaned and the five film materials SiO, Ge, ZnS, YbF3 and Al2O3 are prepared.

[0038] S2, Configuration of coating process conditions and process documents. The configuration of coating process conditions and process documents includes coating temperature, pre-coating base vacuum, film thickness, film material coating mode, film material deposition rate, use and parameters of ion source assisted deposition. Among them, the optimal film thickness is based on the optimal film thickness stored in the control computer of the coating machine as described in the aforementioned design method of 1.8-4μm silicon-based lens antireflection film.

[0039] S3, the cleaned lenses are placed into the tooling fixture, the tooling fixture with the lenses is hung into the cavity of the coating machine, the door is closed, vacuum is drawn and heating is performed;

[0040] S4, pre-melting of film material;

[0041] S5, ion source cleaning of lenses;

[0042] S6, Coating and monitoring: Coating is performed on the first surface of the lens according to the coating process conditions and process document configuration in step S2.

[0043] S7, maintain constant temperature after coating is completed;

[0044] S8, cooling down before picking up the item;

[0045] S9. Repeat steps S1 to S8 to apply a coating to the second surface of the lens.

[0046] In the method for preparing a 1.8-4μm silicon-based lens antireflection film according to this disclosure, based on steps S1 to S9 and the optimal film thickness stored in the control computer of the coating machine as described in the aforementioned design method for a 1.8-4μm silicon-based lens antireflection film, as verified by subsequent tests, the prepared silicon substrate substrate and the film system on both sides can achieve the required transmittance in the 1.8-4μm band, and can also meet the requirements of water immersion test, salt spray test, adhesion test, moderate friction test, constant temperature and humidity test, low temperature test and high temperature test, thereby meeting the requirements of different applications.

[0047] In one example, in step S1, the product is a (50±0.1)mm×(10±0.1)mm convex mirror, and the accompanying plate is a (25±0.1)mm×(2±0.1)mm circular plate.

[0048] The cleaning in step S1 ensures a clean lens surface, which is beneficial for the adhesion and bonding of the coating. In one example, in step S1, the lens is polished with an alumina polishing slurry, followed by ultrasonic cleaning with pure water. For example, the alumina polishing slurry used is a 0.1μm polycrystalline diamond slurry from Nanjing Hengrui Precision Optics Co., Ltd.

[0049] In one example, in step S2, the coating temperature is 150±2℃; the pre-coating base vacuum is (1.3±0.1)×10 -3 Pa; The film thickness in the coating process conditions and process documentation configuration is based on the optimal film thickness stored in the control computer of the coating machine as described in the aforementioned design method for 1.8-4μm silicon-based lens antireflective films; the film deposition mode is as follows: SiO is evaporated using resistance heating, Ge is evaporated using electron beam heating, ZnS and YbF3 are evaporated using resistance heating, and Al2O3 is evaporated using electron beam heating; the film deposition rate is as follows: the deposition rate of the SiO film is... The Ge film deposition rate is The ZnS film deposition rate is The deposition rate of the YbF3 film is: The deposition rate of the AL2O3 film is The use of ion source-assisted deposition is as follows: the ion source is not turned on when depositing Ge film, but the ion source is turned on for the other film layers.

[0050] In one example, in step S2, the coating machine is a Seawalk 1350.

[0051] In one example, in step S2, the ion source is a Hall source with the following parameters: neutralization current 0.6±0.01A, neutralization gas flow rate 7±0.1sccm, anode voltage 120±2V, anode current 1±0.01A, no oxygen is supplied throughout the process, and the proportion of argon in the neutralization gas is 100%.

[0052] In one example, in step S3, a vacuum is first drawn to 5 × 10⁻⁶. -2 Pa, after which the cavity of the coating machine is heated. This prevents the silicon substrate from oxidizing under humid and hot conditions.

[0053] In step S4, the pre-melted membrane material undergoes degassing and impurity removal to ensure its purity. In one example, in step S4, when the vacuum reaches (4.0-5.0)×10⁻⁶... -3 At step Pa, the film material is pre-melted. After pre-melting, the temperature of the cavity of the coating machine reaches 150℃ and is maintained at a constant temperature for 10 minutes. Specifically, for example, in step S4, the pre-melting treatment uses both electron beam heating and resistance heating. For SiO film material, the resistance heating current is 620-660mA; for Ge film material, the electron beam heating current is 260-290mA; for ZnS film material, the resistance heating current is 720-760mA; for YbF3 film material, the resistance heating current is 860-900mA; and for Al2O3 film material, the electron beam heating current is 180-210mA.

[0054] Step S5, the ion source cleaning, removes the surface oxide layer and attached particles from the silicon substrate, making the silicon substrate surface cleaner and increasing the adhesion of the film. In one example, in step S5, the cavity vacuum level reaches (1.3 ± 0.1) × 10⁻⁶. -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source with the following parameters: neutralization current 0.6±0.01A, neutralization gas flow rate 7±0.1sccm, anode voltage 120±2V, anode current 0.8±0.01A, neutralization gas is argon, and cleaning time is 300±2s.

[0055] In one example, in step S6, when depositing each film layer, no gas is introduced from outside the coating machine into the cavity of the coating machine, and the cavity of the coating machine is kept evacuated and the coating temperature is kept at 150°C; each film layer is deposited at a temperature of 150°C in the cavity of the coating machine; the film thickness is monitored by using the crystal oscillator method with the corresponding crystal oscillators of multiple crystal oscillators of the crystal controller; after ion source cleaning, the crystal controller controls the new crystal oscillator among the multiple crystal oscillators to work accordingly, and the crystal oscillator frequency is not less than 5850Hz.

[0056] In one example, in step S7, after the plating is completed, the cavity is kept at 150±2°C for 30 minutes.

[0057] In one example, in step S8, after step S7 is completed, the temperature is first lowered to 130±2℃ at 1℃ / min and held for 5min, then lowered to 110±2℃ at 1℃ / min and held for 5min, and finally lowered to below 80±2℃ at 1℃ / min, and the door is opened to retrieve the item.

[0058] [test]

[0059] Example 1

[0060] Part 1: Design Methods for 1.8-4μm Silicon-based Lens Antireflection Films

[0061] The design method for 1.8-4μm silicon-based lens antireflection films involves the following steps:

[0062] Sa, the film system design uses 550nm as the reference wavelength for optical thin film design. In TFCalc, the film stack formula is used: Sub / 0.3M 0.8N(HL)^3K / AIR, where Sub has the same film system deposited on both sides, and Sub is the silicon substrate, while AIR represents air.

[0063] H represents ZnS (zinc sulfide), a high-refractive-index material with a thickness of 1 / 4 wavelength.

[0064] L represents YbF3 (ytterbium fluoride), a low-refractive-index material with a thickness of 1 / 4 wavelength.

[0065] M represents the SiO (silicon monoxide) substrate material with a thickness of 1 / 4 wavelength.

[0066] N represents Ge (germanium), a bonding layer material with a thickness of 1 / 4 wavelength.

[0067] K represents Al2O3 (alumina), a protective layer material with a thickness of 1 / 4 wavelength.

[0068] Sb, through the input membrane stack formula, generates a membrane structure of Sub / SiO / Ge / ZnS / YbF3 / Al2O3 / Air;

[0069] The film thickness was optimized using the thin film design software TFCalc to obtain the optimal film thickness. The transmittance of the optimized film structure in the 1.8-4μm wavelength range met the requirements.

[0070] In step Sc, the optimal coating thickness for each of the two surfaces of the lens is:

[0071] The SiO film thickness is 25 nm.

[0072] The thickness of the Ge film is 25 nm.

[0073] The thickness of the ZnS film is 280.31 nm;

[0074] The thickness of the YbF3 film is 393.643 nm;

[0075] The thickness of the Al2O3 film is 153 nm;

[0076] Sd inputs the optimized film thickness into the control computer of the coating machine, which is a Siewoc 1350.

[0077] Part 2: Preparation method of 1.8-4μm silicon-based lens antireflection film

[0078] The preparation method of the 1.8-4μm silicon-based lens antireflection film adopts the following steps:

[0079] S1. Before plating, the silicon substrate product and the accompanying plating sheet are cleaned and five kinds of film materials, namely SiO, Ge, ZnS, YbF3 and Al2O3, are prepared. The product is a 50mm×10mm convex mirror and the accompanying plating sheet is a 25mm×2mm circular sheet. The lens is polished with alumina polishing liquid and then ultrasonically cleaned with pure water. The alumina polishing liquid is a 0.1μm polycrystalline diamond liquid from Nanjing Hengrui Precision Optics Co., Ltd.

[0080] S2, Configuration of coating process conditions and process documents. The configuration of coating process conditions and process documents includes coating temperature, pre-deposition base vacuum, film thickness, film deposition mode, film deposition rate, use and parameters of ion source-assisted deposition. Among them, the optimal film thickness is based on the optimal film thickness stored in the control computer of the coating machine as described in the design method of 1.8-4μm silicon-based lens antireflection film in Part I above.

[0081] In step S2,

[0082] The coating temperature is 150℃;

[0083] The base vacuum before plating is 1.3 × 10⁻⁶. -3 Pa;

[0084] The film thickness in the coating process conditions and process document configuration is based on the optimal film thickness stored in the control computer of the coating machine as described in the design method of the 1.8-4μm silicon-based lens antireflection film in Part I above;

[0085] The evaporation modes of the film materials are as follows: SiO is evaporated using resistance heating, Ge is evaporated using electron beam heating, ZnS and YbF3 are evaporated using resistance heating, and Al2O3 is evaporated using electron beam heating.

[0086] The deposition rate of the film material is: the deposition rate of the SiO film layer is The Ge film deposition rate is The ZnS film deposition rate is The deposition rate of the YbF3 film is:

[0087] The deposition rate of the AL2O3 film is

[0088] The use of ion source-assisted deposition is as follows: the ion source is not turned on when depositing Ge films, but the ion source is turned on for all other films.

[0089] The ion source is a Hall source with the following parameters: neutralization current 0.6A, neutralization gas flow rate 7sccm, anode voltage 120V, anode current 1A. No oxygen is supplied throughout the process, and argon accounts for 100% of the neutralization gas.

[0090] S3. Place the cleaned lenses into the fixture, hang the fixture with the lenses in it into the cavity of the coating machine, close the door, and first evacuate to 5×10. -2 Pa, then the cavity of the coating machine is heated;

[0091] S4, pre-melting of the film material, when the vacuum reaches 4.5×10 -3 When Pa, the film material is pre-melted. After the film material is pre-melted, the temperature of the cavity of the coating machine reaches 150℃ and is kept constant for 10 minutes.

[0092] In step S4, the pre-melting process employs both electron beam heating and resistance heating:

[0093] For SiO film material, the resistance heating current is 640mA.

[0094] For Ge film materials, the electron beam heating current is 265mA;

[0095] For ZnS film material, the resistance heating current is 740mA;

[0096] For YbF3 film material, the resistance heating current is 880mA;

[0097] For Al2O3 film material, the electron beam heating current is 195mA;

[0098] S5, ion source cleaning lens, cavity vacuum reaches 1.3×10 -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source. The parameters of the ion source are: neutralization current 0.6A, neutralization gas flow rate 7sccm, anode voltage 120V, anode current 0.8A, neutralization gas is argon, and cleaning time is 300s.

[0099] S6, Coating and Monitoring: Following the coating process conditions and process documentation from step S2, coating is applied to the first surface of the lens.

[0100] In step S6,

[0101] When depositing each film layer, no gas is introduced from outside the coating machine into the cavity of the coating machine, and the cavity of the coating machine is kept evacuated while maintaining the coating temperature at 150°C.

[0102] Each film layer is deposited at a temperature of 150°C in the cavity of the coating machine;

[0103] The crystal oscillator method uses multiple crystal oscillators of a crystal controller to monitor the film thickness. After ion source cleaning, the crystal controller controls the corresponding new crystal oscillator among the multiple crystal oscillators to operate.

[0104] The crystal oscillator frequency is 5990Hz;

[0105] S7, after plating, keep the cavity at 150℃ for 30 minutes;

[0106] S8, first cool down to 130℃ at 1℃ / min and hold for 5min, then cool down to 110℃ at 1℃ / min and hold for 5min, and finally cool down to 80℃ at 1℃ / min, then open the door and take out the part;

[0107] S9. Repeat steps S1 to S8 to apply a coating to the second surface of the lens.

[0108] Comparative Example 1

[0109] Except for the ion source with the same parameters used in step S2 for depositing the Ge film, the rest is the same as in Example 1.

[0110] Comparative Example 2

[0111] Except for replacing Al2O3 with Y2O3 in steps S1, S2, and S4 (i.e., only the film material changes), the rest is the same as in Example 1.

[0112] Comparative Example 3

[0113] Except for replacing SiO with Si in steps S1, S2, and S4 (i.e., only the film material changes), the rest is the same as in Example 1.

[0114] Comparative Example 4

[0115] Except for the coating temperature of 180°C in step S2, the temperature of the cavity of the coating machine reaching 180°C in step S4, the coating temperature being maintained at 180°C in step S6, and the coating of each film layer being completed at a temperature of 180°C in the cavity of the coating machine, the rest is the same as in Example 1.

[0116] Comparative Example 5

[0117] Except for the pre-plating base vacuum of 4.0 × 10⁻⁶ in step S2. -3 Pa, the cavity vacuum in step S5 reaches 4.0 × 10⁻⁶. - 3 Except for Pa, the rest is the same as in Example 1.

[0118] Comparative Example 6

[0119] Except for the Ge film deposition rate in step S2, which is And the deposition rate of YbF3 film is Except for the above, the rest is the same as in Example 1.

[0120] Comparative Example 7

[0121] Except for the ion source parameters in step S2, which are oxygen-filled throughout and have a total neutralization gas flow rate of 10 sccm, and an argon to oxygen ratio of 7:3, the rest are the same as in Example 1.

[0122] Comparative Example 8

[0123] In addition to introducing argon gas from outside the coating machine into the cavity of the coating machine in step S6, maintaining the evacuation of the cavity of the coating machine and ensuring that the coating vacuum degree is maintained at 5×10 -3 Except for Pa, the rest is the same as in Example 1.

[0124] Figure 2 This is a transmittance curve obtained from the design method of the 1.8-4μm silicon-based lens antireflection film in Example 1. From... Figure 2 It can be seen that the average transmittance of the silicon substrate and the film system on both sides is 99.7% in the 1.8-4μm band.

[0125] Figure 3 This is a transmittance curve of the substrate and the film system on both sides after the preparation method of the 1.8-4μm silicon-based lens antireflection film of Example 1 is completed. Figure 3 It can be seen that the average transmittance of the substrate and the film system on both sides in the 1.8-4μm band is 98.6% (i.e., more than 98%).

[0126] The average transmittance of the substrates in the 1.8-4 μm band, along with the films on both sides, for Comparative Examples 1-8 are listed in Table 1.

[0127] The products of Example 1 and Comparative Examples 1-8, along with the film systems on both sides, were subjected to the following overall performance tests.

[0128] Water immersion test: Take tap water and conduct a water immersion test for 2 hours, and observe whether the film layer on each surface is peeled off or whether the film layer on each surface is cracked.

[0129] Salt spray test: Neutral salt spray test for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0130] Adhesion test: Apply 3M tape by hand and pull the tape in the opposite direction to the adhesive end on each side to observe whether the film layer is pulled up.

[0131] Moderate friction test: The membrane layer is subjected to 50 rubs with a rubber friction head wrapped with degreased cloth at a pressure of 4.9N, and the presence of scratches or damage is observed.

[0132] Constant temperature and humidity test: In a constant temperature and humidity chamber, at 50℃ and 95% relative humidity for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0133] Low temperature test: In a low temperature chamber, at -40℃ for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0134] High temperature test: In a high temperature chamber, at 85℃ for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0135] Table 1 shows the average transmittance of Example 1 and Comparative Examples 1-8, as well as the results of various tests.

[0136] Table 1 shows the average transmittance of Examples 1 and Comparative Examples 1-8, and the results of various tests.

[0137]

[0138] Figure 4 The preparation method of the 1.8-4μm silicon-based lens antireflection film of Example 1 is given, along with photographs of the product before and after moderate friction after coating.

[0139] Several exemplary embodiments have been described in detail above, but this document is not intended to limit itself to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form several other combinations, which are not shown for simplicity.

Claims

1. A method for designing a 1.8-4μm silicon-based lens antireflective film, characterized in that, Including the following steps: Sa, the film system design uses 550nm as the reference wavelength for optical thin film design, and uses the film stack formula: Sub / 0.3M 0.8N(HL)^3K / AIR, where Sub has the same film system deposited on both sides, where Sub is the silicon substrate and AIR represents air. In the film stack formula, H represents ZnS (zinc sulfide), a high-refractive-index material with a thickness of 1 / 4 wavelength. L represents YbF3 (ytterbium fluoride), a low-refractive-index material with a thickness of 1 / 4 wavelength. M represents the SiO (silicon monoxide) substrate material with a thickness of 1 / 4 wavelength. N represents Ge (germanium), a bonding layer material with a thickness of 1 / 4 wavelength. K represents Al2O3 (alumina), a protective layer material with a thickness of 1 / 4 wavelength. Sb, through the input membrane stack formula, generates a membrane structure of Sub / SiO / Ge / ZnS / YbF3 / Al2O3 / Air; Sc, by optimizing the film thickness using thin film design software, obtained the optimal film thickness. The transmittance of the optimized film structure in the 1.8-4μm band meets the requirements. Sd inputs the optimized film thickness into the control computer of the coating machine; In step Sc, the optimal coating thickness for each of the two surfaces of the lens is: The SiO film thickness is 25 nm. The thickness of the Ge film is 25 nm. The thickness of the ZnS film is 280.31 nm. The thickness of the YbF3 film is 393.64 nm. The thickness of the Al2O3 film is 15 nm; In step Sc, the average transmittance of the optimized film structure in the 1.8-4μm band is greater than 99.5%.

2. A method for preparing a 1.8-4 μm silicon-based lens antireflection film, characterized in that, Including the following steps: S1. Before plating, the silicon substrate product used as the lens and the accompanying coating are cleaned and the five film materials SiO, Ge, ZnS, YbF3 and Al2O3 are prepared. S2, Configuration of coating process conditions and process documents, including coating temperature, pre-coating base vacuum, film thickness, coating mode of film material, deposition rate of film material, use and parameters of ion source assisted deposition, wherein the optimal film thickness is based on the optimal film thickness stored in the control computer of the coating machine according to the design method of the 1.8-4μm silicon-based lens antireflection film according to claim 1. S3, the cleaned lenses are placed into the tooling fixture, the tooling fixture with the lenses is hung into the cavity of the coating machine, the door is closed, vacuum is drawn and heating is performed; S4, pre-melting of film material; S5, ion source cleaning of lenses; S6, Coating and monitoring: Coating is performed on the first surface of the lens according to the coating process conditions and process document configuration in step S2. S7, maintain constant temperature after coating is completed; S8, cooling down before picking up the item; S9. Repeat steps S1 to S8 to apply a coating to the second surface of the lens.

3. The method for preparing the 1.8-4μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S1, The product is a (50±0.1)mm×(10±0.1)mm convex mirror, and the accompanying plate is a (25±0.1)mm×(2±0.1)mm circular plate. The lenses are polished with aluminum oxide polishing solution and then ultrasonically cleaned with pure water.

4. The method for preparing the 1.8-4μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S2, The coating temperature is 150±2℃; The base vacuum before plating was (1.3±0.1)×10 -3 Pa; Film thickness in coating process conditions and process documentation configuration The optimal film thickness is stored in the control computer of the coating machine based on the preparation method of the 1.8-4μm silicon-based lens antireflection film according to claim 2. The evaporation modes of the film materials are as follows: SiO is evaporated using resistance heating, Ge is evaporated using electron beam heating, ZnS and YbF3 are evaporated using resistance heating, and Al2O3 is evaporated using electron beam heating. The deposition rate of the film material is: the deposition rate of the SiO film layer is / s, Ge film deposition rate is The ZnS film deposition rate is / s. The deposition rate of the YbF3 film is / s. The Al2O3 film deposition rate is / s. / s; The use of ion source-assisted deposition is as follows: the ion source is not turned on when depositing Ge films, but the ion source is turned on for all other films. The ion source is a Hall source, and the ion source parameters are: neutralization current 0.6±0.01A, neutralization gas flow rate 7±0.1sccm, anode voltage 120±2V, anode current 1±0.01A, no oxygen is supplied throughout the process, and the proportion of argon in the neutralization gas is 100%.

5. The method for preparing the 1.8-4μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S3, a vacuum is first drawn to 5×10⁻⁶. -2 Pa, then the cavity of the coating machine is heated.

6. The method for preparing the 1.8-4μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S4, when the vacuum reaches (4.0-5.0)×10 -3 When Pa, the film material is pre-melted. After the film material is pre-melted, the temperature of the cavity of the coating machine reaches 150℃ and is kept constant for 10 minutes. The pre-melting process employs both electron beam heating and resistance heating. For SiO film materials, the resistance heating current is 620-660mA; For Ge film materials, the electron beam heating current is 260-290mA; For ZnS film materials, the resistance heating current is 720-760mA; For YbF3 film material, the resistance heating current is 860-900mA; For Al2O3 film material, the electron beam heating current is 180-210mA.

7. The method for preparing the 1.8-4 μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S5, The cavity vacuum level reached (1.3±0.1)×10 -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source with the following parameters: neutralization current 0.6±0.01A, neutralization gas flow rate 7±0.1sccm, anode voltage 120±2V, anode current 0.8±0.01A, neutralization gas is argon, and cleaning time is 300±2s.

8. The method for preparing the 1.8-4 μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S6, When depositing each film layer, no gas is introduced from outside the coating machine into the cavity of the coating machine, and the cavity of the coating machine is kept evacuated, and the coating temperature is kept at 150℃. Each film layer is deposited at a temperature of 150°C in the cavity of the coating machine; The crystal oscillator method is used to monitor the film thickness by using the corresponding crystal oscillators of multiple crystal oscillators in the crystal controller. After cleaning with the ion source, the crystal controller controls the new crystal oscillator in the multiple crystal oscillators to work accordingly, and the crystal oscillator frequency is not less than 5850Hz.

9. The method for preparing the 1.8-4μm silicon-based lens antireflection film according to claim 2, characterized in that, In step S7, after the plating is completed, the cavity is kept at 150±2℃ for 30 minutes; In step S8, after step S7 is completed, the temperature is first lowered to 130±2℃ at 1℃ / min and held for 5min, then lowered to 110±2℃ at 1℃ / min and held for 5min, and finally lowered to below 80±2℃ at 1℃ / min, and the door is opened to take out the part.

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