Superhard antireflection protective film for microscope eyepiece and its preparation method

Abstract

This invention discloses an ultra-hard anti-reflective protective film for microscope eyepieces and its preparation method. The prepared ultra-hard anti-reflective protective film includes an anti-reflective layer and a protective layer disposed on a substrate from bottom to top. The anti-reflective layer is composed of silicon nitride films with a thickness of 14-240 nm and aluminum oxide films with a thickness of 14-160 nm, which are spaced apart. There are 5 layers of silicon nitride film and 5 layers of aluminum oxide film. The advantage is that the high hardness and high wear resistance of silicon nitride and aluminum oxide are utilized, and the two materials are cross-stacked to form a multilayer film structure. Through the combination of the two, the hardness and wear resistance of the film can be significantly improved while ensuring high optical transmittance, without significantly increasing the film stress. In addition, as silicon nitride and aluminum oxide are high and low refractive index materials, respectively, according to the light interference effect, high optical transmittance can be obtained by simply adjusting the thickness of each layer.

Description

Technical Field

[0001] This invention relates to an optical protective film for a microscope eyepiece and its preparation method, and more particularly to an ultra-hard anti-reflective protective film for a microscope eyepiece and its preparation method. Background Technology

[0002] Existing microscope eyepieces are directly exposed to the external environment, inevitably leading to the accumulation of dust and impurities on their surface. During cleaning, surface scratches are easily encountered, which can typically be addressed by applying an ultra-hard anti-reflective coating. However, while providing high film hardness and optical transparency, the ultra-hard anti-reflective coating significantly increases the stress on the film, causing micro-deformation of the lens, resulting in wavefront distortion and aberrations. This leads to image blurring and increased stray light, directly affecting the eyepiece's imaging performance. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an ultra-hard anti-reflective protective film for microscope eyepieces and its preparation method.

[0004] One of the technical solutions adopted by the present invention to solve the above-mentioned technical problems is: an ultra-hard anti-reflective protective film for a microscope eyepiece, comprising an anti-reflective layer and a protective layer disposed on a substrate from bottom to top, wherein the anti-reflective layer is composed of overlapping silicon nitride films with a thickness range of 14~240nm and aluminum oxide films with a thickness range of 14~160nm, wherein each of the silicon nitride film and the aluminum oxide film consists of 5 layers.

[0005] Compared with existing technologies, the advantages of this invention lie in utilizing the high hardness and high wear resistance of silicon nitride and aluminum oxide, and cross-stacking these two materials to form a multilayer film structure. This combination significantly improves the hardness and wear resistance of the film while maintaining high optical transmittance, without significantly increasing film stress. Furthermore, as high and low refractive index materials, silicon nitride and aluminum oxide, based on the light interference effect, allow for high optical transmittance simply by adjusting the thickness of each layer.

[0006] Preferably, a stress buffer layer is disposed between the substrate and the antireflective layer, and the silicon nitride film is in contact with the stress buffer layer. The stress buffer layer is used to form compensating stress between the substrate and the antireflective layer, thereby reducing the interfacial stress between the substrate and the antireflective layer and improving adhesion.

[0007] Preferably, the stress buffer layer is a silicon oxynitride thin film with a thickness ranging from 6 to 8 nm. The nitrogen content of the silicon oxynitride thin film gradually increases from the bottom up, forming compensating stress between the substrate and the antireflection layer. The gradual increase in nitrogen content from the bottom up results in compressive stress for nitrogen-rich SiOxNy and tensile stress for oxygen-rich SiOxNy, creating low compensating stress. Using this as the underlayer can reduce the interfacial stress between the substrate layer and the functional layer, and improve the film's adhesion.

[0008] Preferably, the protective layer is a short-chain fluorocarbon compound waterproof and oil-resistant film with a thickness ranging from 8 to 11 nm.

[0009] Preferably, a silicon dioxide film with a thickness ranging from 50 to 55 nm is disposed between the antireflective layer and the protective layer.

[0010] The above-mentioned method for preparing an ultra-hard antireflective protective film for a microscope eyepiece is as follows: the silicon nitride film is deposited using a high-purity silicon planar target under an argon and nitrogen atmosphere via radio frequency sputtering. The preparation parameters are: vacuum level range of 4.0 × 10⁻⁶. -4 ~5.0×10 -4 The conditions were: Pa, temperature 300℃, silicon target power range 2~3kW, nitrogen flow rate range 40~50sccm, and argon flow rate range 300~320sccm; the alumina film was deposited using a high-purity aluminum planar target under an argon and oxygen atmosphere via radio frequency sputtering, with the following preparation parameters: vacuum level range 4.0×10⁻⁶. -4 ~5.0×10 -4 The sputtering power ranges from 10 to 11 kW, the oxygen flow rate is 80 sccm, and the argon flow rate is 300 sccm. This invention optimizes the silicon nitride thin film fabrication process, primarily focusing on the control of sputtering power and gas flow rate. Experimental results show that reducing sputtering power, decreasing nitrogen flow rate, and increasing argon flow rate (increasing overall gas pressure) can reduce the compressive stress caused by high-energy particle bombardment. Simultaneously, the excess silicon atoms can induce lattice expansion, providing the driving force for stretching, thus reducing the compressive stress of the silicon nitride thin film and contributing to a reduction in overall stress.

[0011] Preferably, the stress buffer layer is a silicon oxynitride thin film prepared by magnetron sputtering. By adjusting the oxygen / nitrogen ratio, the nitrogen content gradually increases from the bottom up, achieving a stepwise change from nitrogen-rich to oxygen-rich. Through the compressive stress of nitrogen-rich and the tensile stress of oxygen-rich, compensating stress is formed between the substrate and the antireflection layer, reducing the interfacial stress between the substrate and the antireflection layer and improving adhesion.

[0012] Preferably, the thickness of the silicon oxynitride thin film is in the range of 6~8 nm, and the specific preparation method is as follows: high-purity silicon target material is used for deposition using a radio frequency power supply in an atmosphere of argon, nitrogen and oxygen, and the vacuum degree during the preparation process is in the range of 4.0 × 10⁻⁶. -4 ~5.0×10 -4 The sputtering power ranges from 3 to 7 kW, the argon flow rate ranges from 230 to 240 sccm, the nitrogen flow rate ranges from 40 to 120 sccm, and the oxygen flow rate ranges from 40 to 120 sccm. By controlling the sputtering power and the nitrogen-oxygen gas flow rate ratio, the nitrogen content of the prepared silicon oxynitride gradually increases from the bottom up. Nitrogen-rich SiOxNy represents compressive stress, while oxygen-rich SiOxNy represents tensile stress, forming a low compensating stress. Using this as the underlayer can reduce the interfacial stress between the substrate layer and the functional layer, and improve the film adhesion.

[0013] Preferably, the protective layer is a short-chain fluorocarbon compound waterproof and oil-resistant thin film with a thickness ranging from 8 to 11 nm. The specific preparation method is as follows: it is prepared by evaporation deposition, with the following parameters: vacuum degree range of 4.0 × 10⁻⁶. -4 ~5.0×10 -4 Pa, evaporation current is 200A.

[0014] Preferably, a silicon dioxide thin film with a thickness ranging from 50 to 55 nm is disposed between the antireflection layer and the protective layer. The specific preparation method is as follows: high-purity silicon planar target material is used for radio frequency sputtering deposition under an argon and oxygen atmosphere. Preparation parameters: vacuum degree range of 4.0 × 10⁻⁶. -4 ~5.0×10 -4 Pa, silicon target power is 7kW, oxygen flow rate is 120sccm, and argon flow rate is 240sccm. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an ultra-hard anti-reflective protective film for a microscope eyepiece, provided in an embodiment of the present invention.

[0016] The numbers in the figure are: 11, substrate; 21, stress buffer layer; 31, silicon nitride film; 32, aluminum oxide film; 41, silicon dioxide film; 51, protective layer. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example

[0018] This invention provides an ultra-hard anti-reflective protective film for microscope eyepieces, the structure of which is as follows: Figure 1As shown, from bottom to top, the structure consists of a substrate 11, a stress buffer layer 21, a silicon nitride film 31, and an aluminum oxide film 32 forming an antireflection layer, a silicon dioxide film 41, and a protective layer 51. The stress buffer layer 21 is a silicon nitride film deposited by radio frequency magnetron sputtering; the antireflection layer is obtained by radio frequency magnetron sputtering, consisting of overlapping silicon nitride films 31 and aluminum oxide films 32; the silicon dioxide film 41 is obtained by radio frequency magnetron sputtering; and the protective layer 51 is a short-chain fluorocarbon compound waterproof and oil-resistant film deposited by evaporation. The preparation method of this ultra-hard antireflection protective film is as follows:

[0019] First, a silicon oxynitride thin film is deposited on the surface of substrate 11 as a stress buffer layer 21. Substrate 11 is the microscope eyepiece. The deposition vacuum level is set to 5.0 × 10⁻⁶. -4 With the argon gas flow rate at 240 sccm, the silicon target power supply was turned on, and the power and nitrogen / oxygen gas flow rates were set in three stages. The first stage was set to a power of 3 kW, a nitrogen flow rate of 120 sccm, and an oxygen flow rate of 40 sccm; the second stage was set to a power of 5 kW, a nitrogen flow rate of 80 sccm, and an oxygen flow rate of 80 sccm; the third stage was set to a power of 7 kW, a nitrogen flow rate of 40 sccm, and an oxygen flow rate of 120 sccm. The thickness of the deposited silicon oxynitride film was 7 nm.

[0020] A silicon nitride film 31 and an aluminum oxide film 32 were deposited alternately on the surface of a silicon oxynitride film. The silicon target power supply was turned on, and the power was set to 3 kW, the nitrogen flow rate to 40 sccm, the argon flow rate to 320 sccm, and the vacuum degree to 5.0 × 10⁻⁶. -4 At a pressure of 300℃ and a pressure of Pa, the thicknesses of the deposited silicon nitride thin film 31, from bottom to top, are 15 nm, 166 nm, 166 nm, 236 nm, and 166 nm, respectively. The aluminum target power supply is turned on, with a power of 5 kW, an oxygen flow rate of 100 sccm, an argon flow rate of 240 sccm, and a vacuum degree of 5.0 × 10⁻⁶. -4 Pa, the thicknesses of the deposited alumina thin film 32 from bottom to top are 36 nm, 15 nm, 150 nm, 15 nm and 35 nm respectively.

[0021] A silicon dioxide film 41 is deposited on the surface of the uppermost alumina film 32. The silicon target power supply is turned on, and the power is set to 7kW, the oxygen flow rate to 120sccm, the argon flow rate to 240sccm, and the vacuum degree to 5.0×10⁻⁶. -4 Pa, the thickness of the deposited silicon dioxide thin film 41 is 52 nm.

[0022] A short-chain fluorocarbon compound waterproof and oil-resistant film 51 is deposited on the surface of the silica film 41 as a protective layer. The anti-evaporation power supply is turned on, and the current is set to 200A and the vacuum degree is 5.0×10⁻⁶. -4Pa, the thickness of the deposited fluorocarbon waterproof and oil-resistant film is 10 nm. Example

[0023] As provided in Example 1, an ultra-hard antireflective protective film for a microscope eyepiece is formed by overlapping deposition of a silicon nitride film 31 and an aluminum oxide film 32 on the surface of a substrate 11. The silicon target power supply is turned on, with the power set to 3 kW, nitrogen flow rate to 40 sccm, argon flow rate to 320 sccm, and vacuum level to 5.0 × 10⁻⁶. -4 At a pressure of 300℃, the thicknesses of the deposited silicon nitride film 31, from bottom to top, are 15 nm, 144 nm, 239 nm, 144 nm, and 221 nm. The aluminum target power supply is turned on, with a power of 5 kW, an oxygen flow rate of 100 sccm, an argon flow rate of 240 sccm, and a vacuum degree of 5.0 × 10⁻⁶. -4 The thicknesses of the deposited alumina thin film 32, from bottom to top, are 47 nm, 33 nm, 32 nm, 155 nm, and 81 nm, respectively. Example

[0024] As provided in Example 1, an ultra-hard antireflective protective film for a microscope eyepiece is formed by overlapping deposition of a silicon nitride film 31 and an aluminum oxide film 32 on the surface of a substrate 11. The silicon target power supply is turned on, with the power set to 3 kW, nitrogen flow rate to 40 sccm, argon flow rate to 320 sccm, and vacuum level to 5.0 × 10⁻⁶. -4 At a pressure of 300℃ and a pressure of Pa, the thicknesses of the deposited silicon nitride film 31, from bottom to top, are 15 nm, 260 nm, 132 nm, 130 nm, and 124 nm, respectively. The aluminum target power supply is turned on, with a power of 5 kW, an oxygen flow rate of 100 sccm, an argon flow rate of 240 sccm, and a vacuum degree of 5.0 × 10⁻⁶. -4 Pa, the thicknesses of the deposited alumina thin film 32 from bottom to top are 40 nm, 158 nm, 163 nm, 315 nm and 77 nm, respectively.

[0025] Comparative Example 1:

[0026] The structure is as described in Example 1, a superhard antireflective protective film for a microscope eyepiece, wherein a silicon nitride film and a silicon oxide film are deposited overlappingly on the surface of a substrate. The silicon target power supply is turned on, with the power set to 3kW, nitrogen flow rate to 40sccm, argon flow rate to 320sccm, and vacuum level to 5.0×10⁻⁶. -4 At a pressure of 300℃, the thicknesses of the deposited silicon nitride films, from bottom to top, were 15 nm, 147 nm, 136 nm, 153 nm, and 157 nm. The silicon target power supply was turned on, set to 7 kW, oxygen flow rate of 120 sccm, argon flow rate of 240 sccm, and vacuum level of 5.0 × 10⁻⁶. -4Pa, the thicknesses of the deposited silicon oxide films from bottom to top are 52 nm, 180 nm, 183 nm, 170 nm and 67 nm, respectively.

[0027] Comparative Example 2:

[0028] The structure is as described in Example 1, a superhard antireflective protective film for a microscope eyepiece, wherein a silicon nitride film and a silicon oxide film are deposited overlappingly on the surface of a substrate. The silicon target power supply is turned on, with the power set to 7 kW, nitrogen flow rate to 80 sccm, argon flow rate to 240 sccm, and vacuum level to 5.0 × 10⁻⁶. -4 The thicknesses of the deposited silicon nitride films, from bottom to top, are 15 nm, 147 nm, 136 nm, 142 nm, and 142 nm, respectively. The silicon target power supply is turned on, set to 7 kW, oxygen flow rate to 120 sccm, argon flow rate to 240 sccm, and vacuum level to 5.0 × 10⁻⁶. -4 Pa, the thicknesses of the deposited silicon oxide films from bottom to top are 52 nm, 180 nm, 184 nm, 174 nm and 93 nm, respectively.

[0029] The samples provided in the examples and comparative examples were tested for performance according to the following criteria:

[0030] Reflectance test: Take a sample coated on a frosted quartz glass surface and use a Shibuya MSP-100B reflectance spectrometer to measure the reflectance of the sample in the wavelength range of 400nm~700nm. Take the average value in the wavelength range as the result. The smaller the value, the smaller the reflectance and the higher the transmittance.

[0031] Transmittance test: The transmittance of the prepared sample was measured using an Agilent Cary 6000 UV-Vis-NIR spectrophotometer in the wavelength range of 400nm to 700nm. The average value within the wavelength range was taken as the result. The higher the value, the better the transmittance performance.

[0032] Abrasion resistance test: The abrasion resistance of the samples was tested using an abrasion testing machine. "#0000" steel wool was selected, with a load of 300g, a friction head area of ​​20mm × 20mm, a speed of 20 cycles / min, a stroke of 20mm, and 1000 cycles. After friction, the abrasion resistance was determined by the number of abrasion marks (N) and the transmittance loss (ΔT) on the sample surface. A smaller value indicates less transmittance loss and correspondingly better abrasion resistance.

[0033] Surface pencil hardness test: The Mohs hardness of the sample is tested using a hardness pencil (with metal or alloy tips of different hardness). The load is 750g, the speed is 5mm / s, and the stroke is 10mm. After the scratch test, the hardness is determined by whether the remaining marks on the sample surface can be erased. If the remaining marks on the sample surface can be erased, it indicates that the hardness is high.

[0034] Stress testing: Using a Zygo laser interferometer, the reflective surface profile of the sample was determined. The wavelength was set to 632.8 nm, the measurement area was the entire surface, and the measured value was the PV value. The stress could be calculated using the Stoney formula. The smaller the measured PV value, the lower the stress in the film layer.

[0035] Table 1 shows the performance test results of the samples provided in the examples and comparative examples.

[0036] Table 1

[0037]

[0038] Comparative Example 2 is a common ultra-hard antireflective membrane, which is composed of silicon nitride and silicon dioxide stacked into a multilayer membrane structure. It has a good transmittance of 97.9% and a Mohs hardness of up to 9, but poor wear resistance. After 1000 rubs, the sample surface has obvious scratches, the transmittance decreases by 12%, and the membrane stress is relatively large (-723 MPa).

[0039] Compared to Comparative Example 2, Comparative Example 1, by adjusting the process parameters of silicon nitride, reduced the sputtering power to 3kW, reduced the nitrogen flow rate to 40sccm, and increased the argon flow rate to 320sccm. The prepared low-stress silicon nitride multilayer film had a transmittance of 96.2%, and its wear resistance and surface hardness were basically the same as those of Comparative Example 2, while the film stress was significantly reduced to -454MPa.

[0040] In Example 3, compared to Comparative Example 1, silicon dioxide was replaced with alumina, which is more wear-resistant, harder, and has lower stress. It was then overlapped with low-stress silicon nitride. The transmittance was 96.1%, which is close to that of Comparative Example 1. The Mohs hardness remained unchanged. After friction, there were slight scratches on the surface, and the transmittance decreased by less than 1%, indicating that the wear resistance was significantly improved and the film stress was reduced to -253 MPa.

[0041] Compared to Example 3, Example 2, with a smaller film thickness, adjusted the thickness of silicon nitride and aluminum oxide, changing the original silicon nitride thickness to be slightly smaller than the aluminum oxide thickness, so that the total thickness ratio of silicon nitride and aluminum oxide exceeded 2:1. The resulting silicon nitride / alumina multilayer film had a transmittance of 95.4%, and the wear resistance and surface hardness remained basically unchanged, while the film stress was further reduced to -151 MPa.

[0042] Compared to Example 2, Example 1 introduces a silicon oxynitride film as a stress buffer layer 21 and a silicon dioxide film 41, and a short-chain fluorocarbon waterproof and oil-repellent film as a protective layer 51, and further optimizes the thickness ratio of the silicon oxynitride film 31 and the aluminum oxide film 32. The nitrogen-rich layer at the bottom of the silicon oxynitride film provides compressive stress, and the oxygen-rich layer at the top provides tensile stress, serving as a stress buffer layer 21 between the substrate 11 and the multilayer films of silicon oxynitride film 31 / alumina film 32 to balance stress. The silicon dioxide film 41 and the protective layer 51 provide optical transparency and waterproof and oil-repellent properties. The thickness ratio of the silicon oxynitride film 31 to the aluminum oxide film 32 is further adjusted to approximately 3:1, resulting in a product with a high transmittance of 98.2%, high abrasion resistance, unchanged Mohs hardness, low stress as low as -83 MPa, and a waterproof angle of 125°, exhibiting good hydrophobicity.

[0043] Example 1 employs the optimal preparation process, achieving high wear resistance and low stress while maintaining good optical transmittance and high hardness, and also achieving waterproof and oil-proof effects, making it the optimal implementation scheme of the present invention.

Claims

1. A super-hard antireflective protective film for a microscope eyepiece, comprising an antireflective layer and a protective layer disposed on a substrate from bottom to top, characterized in that, The antireflection layer consists of overlapping silicon nitride films with a thickness ranging from 14 to 240 nm and aluminum oxide films with a thickness ranging from 14 to 160 nm, with five layers of each film. The total thickness ratio of the silicon nitride film to the aluminum oxide film exceeds 2:

1. A stress buffer layer is disposed between the substrate and the antireflection layer, with the silicon nitride film in contact with the stress buffer layer. The stress buffer layer is used to compensate for stress between the substrate and the antireflection layer. The stress buffer layer is a silicon oxynitride film with a thickness ranging from 6 to 8 nm, with the nitrogen content gradually increasing from the bottom up. The stress buffer layer is a 6-8 nm thick silicon oxynitride film prepared using magnetron sputtering technology. Specifically, it is prepared by using a high-purity silicon target and depositing it with an RF power supply in an atmosphere of argon, nitrogen, and oxygen. The vacuum level during the preparation process is 4.0-5.0 × 10⁻⁶. -4 Pa, sputtering power: 3-7 kW, argon flow rate: 230-240 sccm, nitrogen flow rate: 40-120 sccm, oxygen flow rate: 40-120 sccm.

2. A superhard antireflective protective film for microscope eyepieces according to claim 1, characterized in that The protective layer is a short-chain fluorocarbon compound waterproof and oil-resistant film with a thickness of 8-11 nm.

3. The ultra-hard anti-reflective protective film for a microscope eyepiece according to claim 2, characterized in that, A silicon dioxide film with a thickness of 50-55 nm is disposed between the antireflective layer and the protective layer.

4. The method for preparing an ultra-hard antireflective protective film for a microscope eyepiece according to claim 1, characterized in that, The alumina thin film was deposited using a high-purity aluminum planar target under an argon and oxygen atmosphere via radio frequency sputtering. The fabrication parameters were: vacuum degree 4.0 - 5.0 × 10⁻⁶. -4 Pa, aluminum target power 10-11kW, oxygen flow rate 80 sccm, argon flow rate 300 sccm.

5. A method of making a superhard antireflective protective film for a microscope ocular according to claim 4, wherein, The silicon nitride thin film was formed using a high-purity silicon planar target and by radio frequency sputtering deposition under an argon and nitrogen atmosphere. The preparation parameters were: vacuum level range of 4.0 × 10⁻⁶. -4 Pa ~ 5.0 × 10 -4 Pa, temperature 300℃, silicon target power range 2~3kW, nitrogen flow rate range 40~50sccm, argon flow rate range 300~320sccm.

6. The method for preparing an ultra-hard antireflective protective film for a microscope eyepiece according to claim 4, characterized in that, The protective layer is a short-chain fluorocarbon compound waterproof and oil-resistant thin film with a thickness of 8-11 nm. The specific preparation method is as follows: it is prepared by evaporation deposition, with the following parameters: vacuum degree 4.0 - 5.0 × 10⁻⁶. -4 Pa, evaporation current 200 A.

7. The method for preparing an ultra-hard antireflective protective film for a microscope eyepiece according to claim 4, characterized in that, A 50-55 nm thick silicon dioxide film is disposed between the antireflection layer and the protective layer. The specific preparation method is as follows: high-purity silicon planar target material is used for radio frequency sputtering deposition under an argon and oxygen atmosphere. Preparation parameters: vacuum degree 4.0 - 5.0 × 10⁻⁶. -4 Pa, silicon target power 7 kW, oxygen flow rate 120 sccm, argon flow rate 240 sccm.

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