Preparation method of chalcogenide glass dual-band wide-spectrum antireflection film

Abstract

The invention discloses a preparation method of a chalcogenide glass dual-band wide-spectrum antireflection film. The method comprises the steps of substrate cleaning, vacuum baking, ion source cleaning, sequential deposition of nine layers of thin films with specific materials and thicknesses, constant-temperature treatment after plating, cooling and workpiece taking, and double-sided plating. According to the invention, by optimizing the film system design and key process parameters, especially selectively using the ion source to assist deposition, the anti-reflection film with high transmittance (higher than 91.7% and 94.6% respectively) at the two wavebands of 3-5 [mu] m and 8-12 [mu] m is successfully prepared on the chalcogenide glass substrate. The film layer is strong in adhesive force, high in compactness, capable of passing multiple strict environmental reliability tests, excellent in comprehensive performance, good in process repeatability and suitable for a high-performance infrared optical system.

Description

Technical Field

[0001] This invention relates to the field of optical thin film preparation technology, and specifically to a method for preparing a broadband antireflective film for chalcogenide glass substrates that has high transmittance in both the 3–5 μm and 8–12 μm wavelength bands. Background Technology

[0002] With the continuous development of infrared technology, traditional optical devices based on single-band response can no longer meet the ever-growing demands. Dual-band infrared antireflection coatings (3-5μm + 8-12μm) break through the limitations of single-band by simultaneously integrating mid- and long-wave infrared detection capabilities, achieving full coverage of 3-5μm (high temperature) and 8-12μm (normal temperature). This significantly improves system stability in complex scenarios such as day-night cycles. At the same time, cross-validation using dual-band radiation characteristics enhances anti-interference and target recognition accuracy. Ultimately, a multi-dimensional sensing upgrade is achieved with a single optical system, greatly reducing the cost of multi-sensor configuration.

[0003] However, existing technologies still have many shortcomings in achieving high-performance dual-band antireflection films on chalcogenide glass substrates. For example, Chinese patent CN108627889 discloses a germanium-based broadband infrared antireflection optical window. This patent provides a broadband film system on a germanium substrate that can achieve 96% transmittance in the 7.5-14μm range. However, this film system can only be applied to far-infrared antireflection and cannot meet the application requirements of dual-band response. At the same time, this patent does not provide a feasible method for preparing the film system, and the optical components prepared based on this patent are costly and not conducive to practical applications.

[0004] For example, Chinese patent CN119506777 discloses a method for preparing a germanium dual-band film system. This patent provides a film system with a transmittance of less than 30% in the 2-5μm band and a transmittance of more than 95% in the 7.5-14μm band, and also provides a reliable preparation method. However, the film system involved in this patent is prepared on a germanium substrate. Since chalcogenide glass and germanium have different refractive indices, it cannot be directly transferred to a chalcogenide glass substrate. Moreover, the film system provided by this patent has a transmittance of only 30% in the 2-5μm band, which cannot be applied to the 2-5μm band, nor can it meet the application requirements of dual-band response. Furthermore, the optical components prepared based on this method are costly.

[0005] For example, Chinese patent CN120028947 discloses a design and preparation method for a durable antireflective film with dual-band infrared wavelengths in the medium and long wavelengths on a chalcogenide glass substrate. The transmittance of this film structure is 99.7% in the medium wavelength range of 3.7-4.8μm and 98.6% in the long wavelength range of 7.7-10.5μm. The relatively narrow working wavelength range results in problems such as low light flux and poor resolution. Moreover, without changing the film structure, it is not possible to broaden the working wavelength range to fully cover the two atmospheric windows of 3-5μm and 8-12μm by simply adjusting the thickness of each layer. Therefore, its application scope is limited in practical applications and it is only suitable for civilian fields, which cannot meet the high-performance requirements of military applications.

[0006] In summary, existing antireflective coating solutions generally suffer from one or more of the following problems: inability to simultaneously and efficiently cover both the 3-5μm and 8-12μm dual-band wavelengths; incomplete band coverage and low average transmittance even when targeting both bands; membrane system design tied to specific substrates (such as germanium), making it unsuitable for chalcogenide glasses; insufficient environmental durability; or complex and costly fabrication processes. Therefore, developing a method for preparing an antireflective coating specifically for chalcogenide glass substrates, capable of fully covering both the 3-5μm and 8-12μm dual-band wavelengths, and possessing high transmittance, excellent environmental adaptability, and good process economy has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing a dual-band broadband antireflection film for chalcogenide glasses. This method has well-defined process parameters, good repeatability, and the prepared antireflection film exhibits high average transmittance in both atmospheric windows of 3–5 μm and 8–12 μm. Furthermore, the film is robust and exhibits excellent environmental stability.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a chalcogenide glass dual-band broadband antireflection film, comprising the following steps: (1) Ultrasonic cleaning of chalcogenide glass substrates; (2) Load the substrate into the coating machine, evacuate it and then bake it by program heating from room temperature to 120°C at a rate of ≤3°C / min and keep it at that temperature for 1 hour to remove the water vapor adsorbed on the substrate and the cavity and to improve the surface energy of the substrate. The baking has two main purposes: first, to reduce the moisture in the coating machine. After vacuuming and baking, the water molecule content in the cavity can be kept at a very low level, thus avoiding the influence of water vapor on the coating; second, to improve the surface energy of the lens. When the film molecules reach the lens surface, the higher surface energy can enable the film molecules to have enough kinetic energy to move to the appropriate position to form a film, which can improve the density and uniformity of the film and enhance the adhesion of the film. (3) Using an ion source to bombard and clean the substrate surface removes the oxide layer on the surface and increases the surface roughness so that the film molecules can better adhere to the substrate surface, thereby improving the adhesion of the film layer. (4) Using a combination of electron beam evaporation and resistance evaporation, nine thin films are deposited sequentially with the assistance of an ion source, following a specific film layer sequence and precisely controlled thickness. (5) After deposition, the film is kept at 120°C for 10 minutes. The purpose of the constant temperature is to give the film molecules a certain amount of time to move. The film molecules will automatically find the gaps in the film and fill them to make the film more compact and ensure the strength of the film. (6) Cooling and removing the parts: Stop heating and allow the coating chamber to cool naturally to below 40°C. Remove the coating substrate by breaking the vacuum to avoid impact on the coating quality due to the large temperature difference between the inside and outside. (7) Double-sided deposition: Flip the substrate and repeat steps (1) to (6) to prepare the same film structure on the other surface of the substrate; Preferably, the materials and deposition order of the nine thin films are as follows: the first layer is a Ge film, the second layer is a YbF3 film, the third layer is a Ge film, the fourth layer is a YbF3 film, the fifth layer is a Ge film, the sixth layer is a YbF3 film, the seventh layer is a ZnS film, the eighth layer is a YbF3 film, and the ninth layer is a ZnS film. Preferably, in step (4), the first, third, and fifth Ge films are deposited by electron beam evaporation at a deposition rate of 3–4 Å / s; the seventh and ninth ZnS films and the second, fourth, sixth, and eighth YbF3 films are deposited by resistive evaporation, wherein the deposition rate of the ZnS film is 10–12 Å / s and the deposition rate of the YbF3 film is 8–10 Å / s. Preferably, during the ion source cleaning in step (3) and the film deposition process in step (4), an APS ion source is used for assisted deposition to enhance the adhesion between the film and the substrate and the density of the film layer; wherein: the ion source is activated when depositing the first Ge film, the second, fourth, sixth, and eighth YbF3 films, and the ninth ZnS film; when depositing the YbF3 film and the ZnS film, the ion source parameters are set as follows: radio frequency current 50 A, bias voltage 140 V, and high-purity argon gas flow rate 13 sccm; when depositing the Ge film, the ion source parameters are set as follows: radio frequency current 40 A, bias voltage 140 V, and high-purity argon gas flow rate 13 sccm. The use of an ion source for the YbF3 film is to improve the density of the film layer, because the naturally formed YbF3 film has a loose structure and poor density, and also to improve the film layer's strength. The use of an ion source for the ZnS film is only on the outermost layer to improve the density of the film and enhance its mechanical strength; Preferably, the physical thicknesses of each film layer deposited in step (4) are as follows: the first Ge film is 99.6 nm; the second YbF3 film is 146.36 nm; the third Ge film is 158.3 nm; the fourth YbF3 film is 279.37 nm; the fifth Ge film is 92.23 nm; the sixth YbF3 film is 351.07 nm; the seventh ZnS film is 323.41 nm; the eighth YbF3 film is 515.03 nm; and the ninth ZnS film is 88.56 nm. Preferably, the base vacuum degree of the coating cavity in step (2) is 5.0 × 10⁻⁶. -4 Pa; Preferably, the planetary disk in step (2) has a revolution frequency of 4–5 Hz during the baking stage and a revolution frequency of 9–10 Hz during the film deposition stage.

[0009] The beneficial effects of this invention are as follows: 1. Excellent optical performance: After the film system provided by this invention is coated on both sides of chalcogenide glass (such as HBL206), the average transmittance of the element reaches more than 91.7% in the 3-5μm band and more than 94.6% in the 8-12μm band, effectively covering two important atmospheric infrared windows.

[0010] 2. High environmental stability: Through optimized ion source-assisted deposition process and post-deposition heat treatment, the density and adhesion of the film are significantly improved. The prepared antireflective membrane can successfully pass multiple environmental reliability tests specified in GJB 2485A-2019 standard, including salt spray, damp heat, thermal shock, water immersion, and adhesion tests, meeting the requirements for use in harsh environments.

[0011] 3. Good process controllability: It provides detailed process parameters (such as vacuum degree, temperature, deposition rate, ion source parameters, film thickness, etc.), the process steps are clear and highly repeatable, which is conducive to industrialization.

[0012] 4. High cost-effectiveness: This invention provides a method for preparing a dual-band broadband antireflection film suitable for chalcogenide glass substrates. Compared with the preparation method for germanium substrates, it can significantly reduce costs while ensuring performance. Attached Figure Description

[0013] Figure 1 This is a transmittance curve diagram of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a sample of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0015] In this embodiment, a double-sided dual-band antireflection film was prepared using chalcogenide glass of grade HBL206 as a substrate.

[0016] Cleaning: Place the cut and polished chalcogenide glass lens into an ultrasonic cleaner and clean it with a mixture of special optical cleaning agent and deionized water. Loading the furnace: Load the clean lens into the special coating fixture, ensuring that the fixture is secure and the force is even, and hang the fixture on the planetary disk of the coating machine (model: Leybold ARES 1350); Vacuuming and Baking: Close the coating chamber door and start the vacuum system to evacuate air. When the vacuum level reaches 5.0 × 10⁻⁶... -2 When the pressure reaches Pa, turn on the baking system. Set the program: increase the temperature from 25℃ to 120℃ at a rate of 2.5℃ / min, and maintain this temperature for 60 minutes after reaching 120℃. The final working vacuum level is maintained at 5.0 × 10⁻⁶. -4 Pa. The orbital frequency of the planetary disk during baking was set to 4.5 Hz.

[0017] Pre-melting of film material: In the later stage of baking, the Ge material in the electron gun crucible and the ZnS and YbF3 material in the molybdenum boat are pre-melted in sequence to remove particles, impurities and other substances that are not conducive to film formation that remain on the surface of the film material during contact with the external environment, thereby improving the quality of the film. Ion source cleaning: After baking, turn on the APS ion source, set the RF current to 50 A, the bias voltage to 140 V, and introduce 12 sccm of high-purity argon gas to perform ion bombardment cleaning on the substrate surface for 600 seconds.

[0018] Film deposition: Film deposition begins immediately after cleaning. Specific process parameters are as follows: Deposition rates and methods: Ge (electron beam evaporation): 3.5 Å / s; ZnS (barrier evaporation): 11 Å / s; YbF3 (barrier evaporation): 9 Å / s.

[0019] Planetary disk rotation speed: The orbital frequency during deposition was set to 9.5 Hz.

[0020] Ion source usage: Ion source-assisted deposition is only activated during the deposition of the first Ge layer, the second, fourth, sixth, and eighth YbF3 layers, and the ninth ZnS layer. Ion source parameters for YbF3 and ZnS deposition: RF current 50 A, bias voltage 140 V, argon gas 13 sccm; ion source parameters for Ge deposition: RF current 40 A, bias voltage 140 V, argon gas 13 sccm.

[0021] Film thickness control: The thickness was monitored using a crystal oscillator. Deposition of each layer was stopped after reaching the following physical thicknesses: First layer Ge: 99.6 nm; Second layer YbF3: 146.36 nm; Third layer Ge: 158.3 nm; Fourth layer YbF3: 279.37 nm; Fifth layer Ge: 92.23 nm; Sixth layer YbF3: 351.07 nm; Seventh layer ZnS: 323.41 nm; Eighth layer YbF3: 515.03 nm; Ninth layer ZnS: 88.56 nm. Post-deposition heat treatment: After all film layers have been deposited, maintain vacuum and 120°C temperature conditions for 10 minutes. Cooling and Removing the Part: Turn off the baking and allow the coating chamber to cool naturally. When the chamber temperature drops to 40°C, fill the chamber with dry nitrogen to atmospheric pressure, open the door and remove the lens with one side coated.

[0022] Coating the other side: Flip the lens over and repeat steps 1 to 8 to coat the other side of the lens with the exact same coating structure.

[0023] Performance testing: The double-sided coated sample prepared in Example 1 above was tested: Spectral performance: The transmittance profiles in the 2–13 μm band were measured using Fourier transform infrared spectroscopy (FTIR). The results showed that the average transmittance of the sample was 91.7% in the 3–5 μm band and 94.6% in the 8–12 μm band.

[0024] Environmental adaptability: The following tests were conducted on the samples according to GJB 2485A-2019 standard: Adhesion test (tape method): Pass, no film peeling.

[0025] Water immersion test (24-hour room temperature immersion): Passed, no blistering or peeling of the film layer.

[0026] Damp heat test (60℃, 96% RH, 48 hours): Passed, no change in the film layer.

[0027] Salt spray test (35℃, 5% NaCl solution, 48 hours): Passed, no corrosion spots or peeling of the film.

[0028] Thermal shock test (-40℃↔60℃, 10 cycles): Passed, no cracking or peeling of the film layer.

[0029] All tests were passed successfully, indicating that the antireflective membrane has excellent environmental stability and mechanical strength.

[0030] Comparative analysis: To illustrate the role of key processes, two comparative examples were set up: Comparative Example 1: Except for not using an ion source during the first Ge deposition, the other process parameters were exactly the same as in Example 1.

[0031] Comparative Example 2: Except for not using an ion source to assist in the deposition of ZnS in the ninth layer (outermost layer), the rest was the same as in Example 1.

[0032] The following tests were performed on Example 1 and Comparative Examples 1 and 2: Water immersion test: Soak the sample in an appropriate amount of tap water for 24 hours, then take it out and observe whether there is any film peeling or peeling.

[0033] Adhesion test: Use 3M tape to quickly pull the sample vertically in different directions three times and observe whether the film layer peels off.

[0034] Damp heat test: Place the sample in a damp heat test chamber, set the temperature to 60℃ and the humidity to 96%Rh, keep it for 48 hours, and then take it out to observe whether the film layer has peeled off or is damaged.

[0035] Thermal shock test: Place the sample in a thermal shock test chamber and set the temperature to -40℃ to 60℃. After 10 cycles, take out the sample and observe whether it falls off or breaks.

[0036] Salt spray test: Place the sample in a salt spray test chamber, set the temperature to 35℃, spray with neutral salt spray for 48 hours, and observe whether the film layer is peeled off or damaged.

[0037] Table 1. Environmental Adaptability Test Records for Examples and Comparative Examples Water bubble test Adhesion test Damp heat test thermal shock test Salt spray test Example 1 qualified qualified qualified qualified qualified Comparative Example 1 qualified Demolding —— —— —— Comparative Example 2 Demolding —— —— —— —— Comparing Example 1 and Comparative Example 1, the test results showed that Comparative Example 1 failed the adhesion test (the film peeled off after being pulled off with tape). This indicates that the ion source assistance of the first Ge film is crucial to enhancing the adhesion between the film and the substrate. Applying an ion source to the first Ge film can improve the adhesion strength between the substrate and the underlying film, thereby improving the overall adhesion of the film.

[0038] Comparing Example 1 and Comparative Example 2, the test revealed that Example 1 failed the water immersion test (the membrane blistered), indicating that the ion source assistance of the outermost ZnS layer can significantly improve the membrane's density and water resistance. As the outermost ZnS membrane layer, which also provides some protection, applying an ion source can effectively improve the membrane's density, greatly enhance the waterproof effect, and thus extend the membrane's lifespan.

[0039] The above embodiments and comparative examples demonstrate that the specific membrane structure combined with the ion source-assisted deposition process of the key layer used in this invention is a necessary condition for obtaining high-performance, high-durability dual-band antireflection membranes.

Claims

1. A method for preparing a chalcogenide glass dual-band broadband antireflection film, characterized in that, Includes the following steps: (1) Substrate pretreatment: Ultrasonic cleaning of chalcogenide glass substrates; (2) Loading and baking: Load the cleaned substrate into the coating fixture and install it onto the planetary disk of the coating machine; evacuate the coating chamber and heat it to 120°C at a rate of no more than 3°C / min, and keep it at that temperature for 1 hour; (3) Ion source cleaning: Start the ion source and perform ion bombardment cleaning on the substrate surface; (4) Film deposition: Nine thin films are deposited sequentially on the surface of the substrate according to a specific film layer order and precisely controlled thickness; (5) Post-deposition heat treatment: After deposition, maintain a constant temperature of 120℃ for 10 minutes; (6) Cooling and removing the parts: Stop heating and allow the coating chamber to cool naturally to below 40°C. Remove the coated substrate by breaking the vacuum. (7) Double-sided deposition: Flip the substrate and repeat steps (1) to (6) to prepare the same film structure on the other surface of the substrate.

2. The method for preparing a chalcogenide glass dual-band broadband antireflection film according to claim 1, characterized in that... The materials and deposition order of the nine thin films in step (4) are as follows: the first layer is a Ge film, the second layer is a YbF3 film, the third layer is a Ge film, the fourth layer is a YbF3 film, the fifth layer is a Ge film, the sixth layer is a YbF3 film, the seventh layer is a ZnS film, the eighth layer is a YbF3 film, and the ninth layer is a ZnS film.

3. The method for preparing a chalcogenide glass dual-band broadband antireflective coating according to claim 1 or 2, characterized in that, In step (4), the first, third, and fifth Ge films are deposited by electron beam evaporation at a deposition rate of 3–4 Å / s; the seventh and ninth ZnS films and the second, fourth, sixth, and eighth YbF3 films are deposited by resistive evaporation, wherein the deposition rate of the ZnS film is 10–12 Å / s and the deposition rate of the YbF3 film is 8–10 Å / s.

4. The method for preparing a chalcogenide glass dual-band broadband antireflective coating according to claim 1 or 2, characterized in that, In step (3) the ion source cleaning process and in step (4) the film deposition process, an APS ion source is used for assistance; wherein: The ion source is activated during the deposition of the first Ge film, the second, fourth, sixth, and eighth YbF3 films, and the ninth ZnS film. When depositing YbF3 and ZnS films, the ion source parameters were set as follows: radio frequency current 50 A, bias voltage 140 V, and high-purity argon gas flow rate 13 sccm. When depositing the Ge film, the ion source parameters were set as follows: RF current 40 A, bias voltage 140 V, and high-purity argon gas flow rate 13 sccm.

5. The method for preparing a chalcogenide glass dual-band broadband antireflective coating according to claim 1 or 2, characterized in that, The physical thicknesses of the deposited films in step (4) are as follows: the first Ge film is 99.6 nm; the second YbF3 film is 146.36 nm; the third Ge film is 158.3 nm; the fourth YbF3 film is 279.37 nm; the fifth Ge film is 92.23 nm; the sixth YbF3 film is 351.07 nm; the seventh ZnS film is 323.41 nm; the eighth YbF3 film is 515.03 nm; and the ninth ZnS film is 88.56 nm.

6. The method for preparing a chalcogenide glass dual-band broadband antireflective coating according to claim 1 or 2, characterized in that, The base vacuum degree of the coating cavity in step (2) is 5.0 × 10⁻⁶. ⁻4 Pa.

7. The method for preparing a chalcogenide glass dual-band broadband antireflective coating according to claim 1 or 2, characterized in that, The planetary disk described in step (2) has a revolution frequency of 4–5 Hz during the baking stage and a revolution frequency of 9–10 Hz during the film deposition stage.

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