Optical film coating method

Abstract

The invention relates to the technical field of coating, and discloses an optical film coating method which comprises the following steps: step 1, placing a substrate in an evaporation coating machine, and starting an ion source to clean the substrate; 2, after cleaning is completed, the surface of the substrate is plated with a germanium layer in the mode that an ion source is combined with electron beam coating; 3, after the germanium layer is plated, a zinc sulfide layer is plated on the surface of the germanium layer in the mode that an ion source is combined with evaporation-resistant evaporation coating, and the optical thin film is obtained; wherein the screen electrode voltage of the ion source is 500-550V. According to the method, the coating uniformity can be improved, so that demolding is avoided.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and more specifically, relates to an optical thin film coating method. Background Technology

[0002] Optical thin films are thin film materials with specific optical properties (such as anti-reflection, reflection, and filtering) formed by deposition on the surface of a substrate through specific preparation processes. They are widely used in high-end fields such as consumer electronics, laser technology, and aerospace. Their performance directly determines the imaging quality, reliability, and lifespan of optical devices.

[0003] "Film peeling" (film detachment, peeling) in optical thin film fabrication refers to the phenomenon where the film layer detaches locally or entirely from the substrate or multilayer film due to insufficient adhesion during the fabrication process. It is a core process defect that has long constrained the quality and reliability of optical devices. Optical thin film peeling can seriously affect the optical performance (such as transmittance and reflectance drift), mechanical stability, and lifespan of optical components. Summary of the Invention

[0004] The main objective of this invention is to provide an optical thin film coating method that uses an ion source to assist coating and improves coating uniformity by adjusting the process parameters of the ion source, thereby solving the problem of coating peeling.

[0005] According to a first aspect of the present invention, an optical thin film coating method is provided, comprising the following steps:

[0006] Step 1: Place the substrate in the evaporation coating machine and turn on the ion source to clean the substrate;

[0007] Step 2: After cleaning, a germanium layer is deposited on the surface of the substrate using an ion source combined with electron beam deposition.

[0008] Step 3: After the germanium layer is deposited, a zinc sulfide layer is deposited on the surface of the germanium layer by means of ion source combined with barrier evaporation to obtain an optical thin film; wherein, the plate voltage of the ion source is 500-550V.

[0009] In some embodiments of the present invention, in step 3, the plate voltage of the ion source is preferably 500V, 510V, 520V, 530V, 540V, or 550V.

[0010] In a specific embodiment of the present invention, in step 1, the parameters for cleaning the substrate by the ion source are as follows: beam current of 20-30 mA, cathode current of 9-13 A, anode voltage of 60-70 V, accelerating voltage of 240-280 V, neutralizing current of 9-13 A, plate voltage of 280-320 V, argon flow rate of 31-35 sccm, and cleaning time of 4-8 min.

[0011] In some embodiments of the present invention, the parameters for cleaning the substrate by the ion source are as follows: the beam current is preferably 20mA, 22mA, 24mA, 26mA, 28mA, or 30mA; the cathode current is preferably 9A, 11A, or 13A; the anode voltage is preferably 60V, 62V, 64V, 66V, 68V, or 70V; the accelerating voltage is preferably 240V, 250V, 260V, 270V, or 280V; the neutralization current is preferably 9A, 11A, or 13A; the plate voltage is preferably 280V, 290V, 300V, 310V, or 320V; the argon flow rate is preferably 31sccm, 33sccm, or 35sccm; and the cleaning time is preferably 4min, 6min, or 8min.

[0012] In a specific embodiment of the present invention, in step 2, the parameters of the ion source are: beam current of 85-90 mA, cathode current of 13-17 A, anode voltage of 65-75 V, accelerating voltage of 180-220 V, neutralization current of 13-17 A, plate voltage of 400-420 V, argon flow rate of 28-32 sccm, bias voltage of 35-45 V, and bias current of 90-105 mA; the parameters of the electron beam coating are: coating temperature of 70-85 °C and coating rate of 4-8 Å / s.

[0013] In some embodiments of the present invention, in step 2, the parameters of the ion source are as follows: the beam current is preferably 85mA, 87mA, or 90mA; the cathode current is preferably 13A, 15A, or 17A; the anode voltage is preferably 65V, 70V, or 75V; the accelerating voltage is preferably 180V, 190V, 200V, 210V, or 220V; the neutralization current is preferably 13A, 15A, or 17A; the plate voltage is preferably 400V, 410V, or 420V; the argon flow rate is preferably 28sccm, 30sccm, or 32sccm; the bias voltage is preferably 35V, 40V, or 45V; and the bias current is preferably 90mA, 95mA, 100mA, or 105mA. The parameters of the electron beam coating are as follows: the coating temperature is preferably 70℃, 75℃, 80℃, or 85℃; and the coating rate is preferably 4Å / s, 6Å / s, or 8Å / s.

[0014] In a specific embodiment of the present invention, in step 3, the zinc sulfide used for plating the zinc sulfide layer includes large-particle zinc sulfide and small-particle zinc sulfide, wherein the particle size of the large-particle zinc sulfide is 6-9 mm, the particle size of the small-particle zinc sulfide is 2-5 mm, and the mass ratio of large-particle zinc sulfide to small-particle zinc sulfide is 6-10:1.

[0015] In some embodiments of the present invention, in step 3, the particle size of the large-diameter zinc sulfide is preferably 6mm, 7mm, 8mm, or 9mm, and the particle size of the small-diameter zinc sulfide is preferably 2mm, 3mm, 4mm, or 5mm. The mass ratio of the large-diameter zinc sulfide to the small-diameter zinc sulfide is preferably 6:1, 7:1, 8:1, 9:1, or 10:1.

[0016] In a specific embodiment of the present invention, in step 3, before plating the zinc sulfide layer, the zinc sulfide needs to be cleaned and baked. Specifically, the zinc sulfide is placed in a crystallizing dish, deionized water is added to the crystallizing dish, and the zinc sulfide in the crystallizing dish is ultrasonically cleaned. The cleaning temperature is 65-75°C and the cleaning time is 15-25 minutes. After cleaning, the crystallizing dish is baked at a temperature of 200-300°C for 20-28 hours.

[0017] In some embodiments of the present invention, the cleaning temperature is preferably 65℃, 70℃, or 75℃, the cleaning time is preferably 15min, 20min, or 25min, the baking temperature is preferably 200℃, 220℃, 240℃, 260℃, 280℃, or 300℃, and the baking time is preferably 20h, 22h, 24h, 26h, or 28h.

[0018] In a specific embodiment of the present invention, in step 3, the parameters of the ion source are: beam current of 45-50 mA, cathode current of 11-15 A, anode voltage of 75-85 V, accelerating voltage of 140-180 V, neutralization current of 11-15 A, argon flow rate of 33-37 sccm, bias voltage of 35-45 V, and bias current of 50-70 mA; the parameters of the electron beam coating are: coating temperature of 70-85 °C and coating rate of 6-10 Å / s.

[0019] In some embodiments of the present invention, in step 3, the parameters of the ion source are as follows: the beam current is preferably 45mA, 47mA, or 50mA; the cathode current is preferably 11A, 13A, or 15A; the anode voltage is preferably 75V, 80V, or 85V; the accelerating voltage is preferably 140V, 160V, or 180V; the neutralization current is preferably 11A, 13A, or 15A; the argon flow rate is preferably 33sccm, 35sccm, or 37sccm; the bias voltage is preferably 35V, 40V, or 45V; and the bias current is preferably 50mA, 60mA, or 70mA. The parameters of the electron beam coating are as follows: the coating temperature is preferably 70℃, 75℃, 80℃, or 85℃; and the coating rate is preferably 6Å / s, 8Å / s, or 10Å / s.

[0020] In one specific embodiment of the present invention, the substrate is made of silicon.

[0021] In a specific embodiment of the present invention, the thickness of the germanium layer is 95-100 nm; the thickness of the zinc sulfide layer is 1200-1400 nm.

[0022] In some embodiments of the present invention, the thickness of the germanium layer is preferably 95nm, 97nm, or 100nm, and the thickness of the zinc sulfide layer is preferably 1200nm, 1300nm, or 1400nm.

[0023] One of the above-described technical solutions of the present invention has at least one of the following advantages or beneficial effects:

[0024] The coating method of the present invention uses an ion source-assisted coating and adjusts the process parameters of the ion source according to the different materials of the film layer, thereby improving the uniformity of the coating and reducing the probability of film removal.

[0025] Furthermore, by using zinc sulfide with different particle sizes to compound the zinc sulfide, the heating of the zinc sulfide is made more uniform. Combined with the process parameters of the ion source, the bonding force between the zinc sulfide layer and the germanium layer is improved, thereby further reducing the probability of delamination. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application shown herein can generally be arranged and designed in various different configurations.

[0027] The following disclosure provides many different implementations or examples for different ways of implementing the present invention.

[0028] Example 1

[0029] An optical thin film coating method includes the following steps:

[0030] Step 1: Place the substrate in the evaporation coating machine and turn on the ion source to clean the substrate;

[0031] In this embodiment, the substrate is a silicon wafer, the ion source is a Kaufman ion source, and the parameters for cleaning the substrate by the ion source are: beam current of 25mA, cathode current of 11A, anode voltage of 65V, accelerating voltage of 260V, neutralization current of 11A, plate voltage of 300V, argon flow rate of 33sccm, and cleaning time of 6min.

[0032] Step 2: After cleaning, a germanium layer is deposited on the surface of the substrate using an ion source combined with electron beam deposition.

[0033] In step 2, electron beam deposition, aided by a Kaufman ion source, is used to deposit a germanium layer on the surface of the silicon wafer. The germanium used in the germanium layer has a particle size of 4 mm. The parameters of the Kaufman ion source are: beam current 87 mA, cathode current 15 A, anode voltage 70 V, accelerating voltage 200 V, neutralization current 15 A, plate voltage 410 V, argon flow rate 30 sccm, bias voltage 40 V, and bias current 97 mA. The parameters of the electron beam deposition are: vacuum degree 1.3 × 10⁻⁶. -3 Pa, coating temperature 80℃, coating rate 6Å / s, and germanium layer thickness 97nm.

[0034] Step 3: After the germanium layer is deposited, a zinc sulfide layer is deposited on the surface of the germanium layer by means of ion source combined with barrier evaporation to obtain an optical thin film;

[0035] In step 3, the zinc sulfide used for the zinc sulfide plating layer has a particle size of 7mm. First, the zinc sulfide is cleaned and baked. Specifically, the zinc sulfide is placed in a crystallization dish, and deionized water is added to the crystallization dish until the water level is 1cm above the crystallization dish. Then, the crystallization dish is placed in an ultrasonic cleaner, and deionized water is added to the ultrasonic cleaner until the water level in the ultrasonic cleaner is 2cm higher than the water level in the crystallization dish. Then, the zinc sulfide in the crystallization dish is ultrasonically cleaned 6 times at a cleaning temperature of 70℃ and a cleaning time of 20min. Then, the crystallization dish is placed in an oven, and the opening of the crystallization dish is covered with a lint-free cloth. The zinc sulfide in the crystallization dish is baked at a baking temperature of 250℃ for 24h.

[0036] After baking, the zinc sulfide is placed in an evaporation coating machine and coated using a barrier evaporation coating method, assisted by a Kaufman ion source, to deposit a zinc sulfide layer on the surface of the germanium layer. The ion source is a Kaufman ion source with the following parameters: beam current 47mA, cathode current 13A, anode voltage 80V, accelerating voltage 160V, neutralization current 13A, plate voltage 520V, argon flow rate 35sccm, bias voltage 40V, and bias current 60mA. The barrier evaporation coating parameters are: coating temperature 80℃, coating rate 8Å / s, and zinc sulfide layer thickness 1300nm.

[0037] After coating, keep warm for 20 minutes to obtain an optical thin film.

[0038] Example 2

[0039] This embodiment is basically the same as embodiment 1, except that: Step 1: Place the substrate in the evaporation coating machine and turn on the ion source to clean the substrate;

[0040] In this embodiment, the substrate is a silicon wafer, the ion source is a Kaufman ion source, and the parameters for cleaning the substrate by the ion source are: beam current of 30mA, cathode current of 13A, anode voltage of 70V, accelerating voltage of 280V, neutralization current of 13A, plate voltage of 320V, argon flow rate of 35sccm, and cleaning time of 8min.

[0041] Step 2: After cleaning, a germanium layer is deposited on the surface of the substrate using an ion source combined with electron beam deposition.

[0042] In step 2, electron beam deposition, aided by a Kaufman ion source, is used to deposit a germanium layer on the surface of the silicon wafer. The germanium used in the germanium layer has a particle size of 4 mm. The parameters of the Kaufman ion source are: beam current 90 mA, cathode current 17 A, anode voltage 75 V, accelerating voltage 220 V, neutralization current 17 A, plate voltage 420 V, argon flow rate 32 sccm, bias voltage 45 V, and bias current 105 mA. The parameters of the electron beam deposition are: vacuum degree 1.3 × 10⁻⁶. -3 Pa, coating temperature 85℃, coating rate 8Å / s, germanium layer thickness 100nm.

[0043] Step 3: After the germanium layer is deposited, a zinc sulfide layer is deposited on the surface of the germanium layer by means of ion source combined with barrier evaporation to obtain an optical thin film;

[0044] In step 3, the zinc sulfide used for the zinc sulfide plating layer has a particle size of 9mm. First, the zinc sulfide is cleaned and baked. Specifically, the zinc sulfide is placed in a crystallization dish, and deionized water is added to the crystallization dish until the level of deionized water is 1cm above the crystallization dish. Then, the crystallization dish is placed in an ultrasonic cleaner, and deionized water is added to the ultrasonic cleaner until the level of deionized water in the ultrasonic cleaner is 2cm higher than the level of deionized water in the crystallization dish. Then, the zinc sulfide in the crystallization dish is ultrasonically cleaned 6 times at a cleaning temperature of 65℃ and a cleaning time of 15min. Then, the crystallization dish is placed in an oven, and the opening of the crystallization dish is covered with a lint-free cloth. The zinc sulfide in the crystallization dish is baked at a baking temperature of 200℃ for 20h.

[0045] After baking, the zinc sulfide is placed in an evaporation coating machine and coated using a barrier evaporation coating method, with the assistance of a Kaufman ion source, to deposit a zinc sulfide layer on the surface of the germanium layer. The ion source is a Kaufman ion source with the following parameters: beam current 50mA, cathode current 15A, anode voltage 85V, accelerating voltage 180V, neutralization current 15A, plate voltage 550V, argon flow rate 37sccm, bias voltage 45V, and bias current 50mA. The barrier evaporation coating parameters are: coating temperature 85℃, coating rate 10Å / s, and zinc sulfide layer thickness 1400nm.

[0046] After coating, keep warm for 20 minutes to obtain an optical thin film.

[0047] Example 3

[0048] This embodiment is basically the same as embodiment 1, except that: Step 1: Place the substrate in the evaporation coating machine and turn on the ion source to clean the substrate;

[0049] In this embodiment, the substrate is a silicon wafer, the ion source is a Kaufman ion source, and the parameters for cleaning the substrate by the ion source are: beam current of 20mA, cathode current of 9A, anode voltage of 60V, accelerating voltage of 240V, neutralizing current of 9A, plate voltage of 280V, argon flow rate of 31sccm, and cleaning time of 4min.

[0050] Step 2: After cleaning, a germanium layer is deposited on the surface of the substrate using an ion source combined with electron beam deposition.

[0051] In step 2, electron beam deposition, aided by a Kaufman ion source, is used to deposit a germanium layer on the surface of the silicon wafer. The germanium used in the layer has a particle size of 4 mm. The parameters of the Kaufman ion source are: beam current 85 mA, cathode current 13 A, anode voltage 65 V, accelerating voltage 180 V, neutralization current 13 A, plate voltage 400 V, argon flow rate 28 sccm, bias voltage 35 V, and bias current 90 mA. The parameters of the electron beam deposition are: vacuum degree 1.3 × 10⁻⁶. -3 Pa, coating temperature 70℃, coating rate 4Å / s, germanium layer thickness 95nm.

[0052] Step 3: After the germanium layer is deposited, a zinc sulfide layer is deposited on the surface of the germanium layer by means of ion source combined with barrier evaporation to obtain an optical thin film;

[0053] In step 3, the zinc sulfide used for the zinc sulfide plating layer has a particle size of 2mm. First, the zinc sulfide is cleaned and baked. Specifically, the zinc sulfide is placed in a crystallization dish, and deionized water is added to the crystallization dish until the level of deionized water is 1cm above the crystallization dish. Then, the crystallization dish is placed in an ultrasonic cleaner, and deionized water is added to the ultrasonic cleaner until the level of deionized water in the ultrasonic cleaner is 2cm higher than the level of deionized water in the crystallization dish. Then, the zinc sulfide in the crystallization dish is ultrasonically cleaned 6 times at a cleaning temperature of 65℃ and a cleaning time of 15min. Then, the crystallization dish is placed in an oven, and the opening of the crystallization dish is covered with a lint-free cloth. The zinc sulfide in the crystallization dish is baked at a baking temperature of 200℃ for 20h.

[0054] After baking, the zinc sulfide is placed in an evaporation coating machine and coated using a barrier evaporation coating method, with the assistance of a Kaufman ion source, to deposit a zinc sulfide layer on the surface of the germanium layer. The ion source is a Kaufman ion source with the following parameters: beam current 45mA, cathode current 11A, anode voltage 75V, accelerating voltage 140V, neutralization current 11A, plate voltage 500V, argon flow rate 33sccm, bias voltage 35V, and bias current 50mA. The barrier evaporation coating parameters are: coating temperature 70℃, coating rate 6Å / s, and zinc sulfide layer thickness 1200nm.

[0055] After coating, keep warm for 20 minutes to obtain an optical thin film.

[0056] Example 4

[0057] This embodiment is basically the same as embodiment 1, except that in step 3, the zinc sulfide particles used for the zinc sulfide plating layer are 3mm in diameter.

[0058] Example 5

[0059] This embodiment is basically the same as embodiment 1, except that: in step 3, the zinc sulfide used for the zinc sulfide coating includes large-particle zinc sulfide and small-particle zinc sulfide, wherein the particle size of the large-particle zinc sulfide is 7 mm, the particle size of the small-particle zinc sulfide is 3 mm, and the mass ratio of large-particle zinc sulfide to small-particle zinc sulfide is 8:1.

[0060] Example 6

[0061] This embodiment is basically the same as embodiment 1, except that in step 3, the zinc sulfide particles used for the zinc sulfide plating layer are 11 mm in diameter.

[0062] Comparative Example 1

[0063] This comparative example is basically the same as Example 1, except that in step 3, the plate voltage of the ion source is 450V.

[0064] Comparative Example 2

[0065] This comparative example is basically the same as Example 1, except that in step 3, the plate voltage of the ion source is 600V.

[0066] The optical thin film was coated using the methods of Examples 1-6 and Comparative Examples 1-2, respectively. The transmittance at different locations of the optical thin film was detected by Fourier transform infrared spectroscopy, specifically the transmittance at three points A, B and C of the optical thin film, to obtain the uniformity of the coating.

[0067] The results are shown in Table 1:

[0068] Table 1: Test Results of Optical Thin Films

[0069] Group Transmittance at point A Point B transmittance C-point transmittance Example 1 83.67% 82.87% 83.17% Example 2 82.86% 81.46% 81.86% Example 3 84.55% 84.75% 84.35% Example 4 84.77% 84.41% 84.73% Example 5 84.49% 84.99% 84.69% Example 6 81.74% 80.12% 78.44% Comparative Example 1 51.62% 55.51% 61.62% Comparative Example 2 81.24% 78.35% 80.52%

[0070] Results analysis:

[0071] In optical thin films, the transmittance is high at the non-delamination position and low at the delamination position. Therefore, when using a Fourier transform infrared spectrometer to detect the transmittance of an optical thin film, by detecting different positions of the optical thin film, if the transmittance at each position is not much different, it reflects that the film layer has good uniformity. If the transmittance at each position is much different, it reflects that the film layer has poor uniformity.

[0072] According to Examples 1-4, we can see that using zinc sulfide particles with a particle size of 2-9 mm and within a plate voltage range of 500-550 V can yield a zinc sulfide film with good uniformity. Furthermore, from the transmittance of Examples 1-4, we can see that when the zinc sulfide particle size is smaller, the transmittance of the zinc sulfide film is better, and the transmittance at the three detection points is not significantly different, indicating good uniformity of the film. This may be because the smaller the zinc sulfide particle size, the more uniformly the zinc sulfide is heated during sublimation, thus enabling the overall zinc sulfide to sublimate uniformly, thereby improving the uniformity of the zinc sulfide film.

[0073] Based on Examples 1 and 6, we can see that when the particle size of zinc sulfide is too large, the transmittance will decrease. Moreover, the fluctuation difference of the three detection points of the optical film is greater than that of the three detection points in Example 1. That is, the uniformity of the film layer in Example 6 is worse than that in Example 1. The reason may be that the zinc sulfide particle size is larger and the gap between adjacent zinc sulfides is larger. During the heating process, the heat transfer effect between zinc sulfides is poor, which leads to the zinc sulfide not being heated uniformly and reducing the uniformity of the zinc sulfide film layer.

[0074] According to Examples 4 and 5, when zinc sulfide with a larger particle size (7 mm) and zinc sulfide with a smaller particle size (3 mm) are blended, the transmittance of the resulting zinc sulfide film is not significantly different from that obtained by using zinc sulfide with a smaller particle size. Moreover, the fluctuation difference between the three detection points is small. In other words, the effect of blending larger and smaller particle sizes is similar to that of using smaller particle sizes. However, since the price of zinc sulfide with a smaller particle size is higher than that of zinc sulfide with a larger particle size, blending larger and smaller particle sizes can reduce the amount of smaller zinc sulfide used, thereby reducing the cost of zinc sulfide. Therefore, blending larger and smaller particle sizes with a plate voltage of 500-550V is the optimal choice for zinc sulfide film.

[0075] Based on Example 1 and Comparative Examples 1-2, we can see that in Comparative Example 1, when the plate voltage is too low, the transmittance of the entire optical film is low, film peeling occurs, and the fluctuations at the three detection points are significant, resulting in poor uniformity of the zinc sulfide film. In Comparative Example 2, when the plate voltage is too high, the transmittance decreases, and the uniformity of the film also decreases. From an economic perspective, excessively high plate voltage leads to low energy utilization and generally poor coating quality.

[0076] In summary, a zinc sulfide film with good coating quality can be obtained when the plate voltage is 500-550V. When zinc sulfide with larger particle size (6-9mm) and zinc sulfide with smaller particle size (2-5mm) are compounded, and the plate voltage is in the range of 500-550V, a zinc sulfide film with good coating quality and low cost can be obtained.

Claims

1. An optical thin film coating method, characterized in that, Includes the following steps: Step 1: Place the substrate in the evaporation coating machine and turn on the ion source to clean the substrate; Step 2: After cleaning, a germanium layer is deposited on the surface of the substrate using an ion source combined with electron beam deposition. Step 3: After the germanium layer is deposited, a zinc sulfide layer is deposited on the surface of the germanium layer by means of ion source combined with barrier evaporation to obtain an optical thin film; wherein, the plate voltage of the ion source is 500-550V.

2. The optical thin film coating method according to claim 1, characterized in that, In step 1, the parameters for cleaning the substrate using the ion source are as follows: beam current 20-30 mA, cathode current 9-13 A, anode voltage 60-70 V, accelerating voltage 240-280 V, neutralizing current 9-13 A, plate voltage 280-320 V, argon flow rate 31-35 sccm, and cleaning time 4-8 min.

3. The optical thin film coating method according to claim 1, characterized in that, In step 2, the parameters of the ion source are: beam current 85-90 mA, cathode current 13-17 A, anode voltage 65-75 V, accelerating voltage 180-220 V, neutralizing current 13-17 A, plate voltage 400-420 V, argon flow rate 28-32 sccm, bias voltage 35-45 V, and bias current 90-105 mA; the parameters of the electron beam coating are: coating temperature 70-85 °C and coating rate 4-8 Å / s.

4. The optical thin film coating method according to claim 1, characterized in that, In step 3, the zinc sulfide used for the zinc sulfide plating layer includes large-particle zinc sulfide and small-particle zinc sulfide. The particle size of the large-particle zinc sulfide is 6-9 mm, and the particle size of the small-particle zinc sulfide is 2-5 mm. The mass ratio of large-particle zinc sulfide to small-particle zinc sulfide is 6-10:

1.

5. The optical thin film coating method according to claim 1, characterized in that, In step 3, before plating the zinc sulfide layer, the zinc sulfide needs to be cleaned and baked. Specifically, the zinc sulfide is placed in a crystallization dish, deionized water is added to the crystallization dish, and the zinc sulfide in the crystallization dish is ultrasonically cleaned. The cleaning temperature is 65-75℃ and the cleaning time is 15-25 minutes. After cleaning, the crystallization dish is baked at a temperature of 200-300℃ for 20-28 hours.

6. The optical thin film coating method according to claim 1, characterized in that, In step 3, the parameters of the ion source are: beam current 45-50 mA, cathode current 11-15 A, anode voltage 75-85 V, accelerating voltage 140-180 V, neutralization current 11-15 A, argon flow rate 33-37 sccm, bias voltage 35-45 V, and bias current 50-70 mA; the parameters of the electron beam coating are: coating temperature 70-85 °C and coating rate 6-10 Å / s.

7. The optical thin film coating method according to claim 1, characterized in that, The substrate is made of silicon.

8. The optical thin film coating method according to claim 1, characterized in that, The thickness of the germanium layer is 95–100 nm; the thickness of the zinc sulfide layer is 1200–1400 nm.