A medium-long wave infrared antireflection protective film and a preparation method thereof

Abstract

The application provides a kind of middle long wave infrared antireflection protective film and its preparation method, belong to optical protective film technical field, the component of the protective film includes chemical formula M3N4 nitride;Wherein, M represents metal element, is Zr or Hf;Nitride is cubic crystal system, crystal space group is I43d;The mole proportion of N element in protective film is 54%~60%.The preparation method of the protective film includes the following steps: cleaning substrate;In Ar gas environment, the substrate is plasma cleaned;With metal element as target material, in Ar and N2 mixed gas environment, by high power pulse magnetron sputtering, the target material is sputtered, so that metal element and N2 react to generate nitride and deposit on the substrate, to obtain middle long wave infrared antireflection protective film on the substrate.The middle long wave infrared antireflection protective film is a single layer structure, simple structure, and has high hardness, and has high transmittance in the wavelength range of 8-16 μm.

Description

Technical Field

[0001] This invention belongs to the field of optical protective film technology, and particularly relates to a mid-to-long-wave infrared anti-reflection protective film and its preparation method. Background Technology

[0002] Infrared optical materials are primarily used in key components of photoelectric detectors, such as lenses and windows, which are in direct contact with the external environment. With the rapid development of modern advanced military optical systems, the performance requirements for infrared window materials are becoming increasingly stringent in applications such as missile-borne infrared precision guidance systems and airborne infrared search and track systems. To meet the operational needs of infrared detection and guidance, infrared windows must possess sufficient mechanical strength to withstand impacts from solid particles such as dust and hail during high-speed flight, especially resisting wind and sand impacts and rain corrosion. Furthermore, infrared windows must also possess excellent optical performance, namely, sufficiently high transmittance within the infrared band.

[0003] Silicon (Si) is one of the most important infrared optical materials currently available, and it can be used to prepare mid-to-long-wave infrared window materials. However, the high refractive index of Si in the infrared band leads to significant reflection loss, resulting in a substantial reduction in its transmittance for infrared light with wavelengths greater than 8 μm. Simultaneously, Si has poor mechanical properties, making it susceptible to erosion from raindrops and sand in outdoor environments. Therefore, when using Si as an optical window, it is necessary to coat it with an infrared anti-reflection protective film to improve its optical transmittance and effectively protect the infrared window. The quality of the infrared anti-reflection protective film directly determines the performance of the photodetector and is an indispensable key component in modern photoelectric detection systems.

[0004] Currently, infrared antireflective protective films typically employ a multi-layer structure design, requiring layer-by-layer deposition during fabrication, which is a complex process. Furthermore, if the film is too thick, it is prone to peeling due to stress accumulation, while if the film is too thin, control errors are likely to occur, leading to a decline in optical performance.

[0005] Therefore, how to provide a mid-to-long-wave infrared antireflection protective film that is simple in structure, easy to prepare, and has excellent performance is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a mid-to-long-wave infrared antireflection protective film and its preparation method. The mid-to-long-wave infrared antireflection protective film has a single-layer structure, is simple in structure, has high hardness, and has high transmittance in the wavelength range of 8-16μm.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a mid-to-long-wave infrared antireflection protective film. The protective film comprises a nitride with the chemical formula M3N4, wherein M represents a metal element, such as Zr or Hf; the nitride has a cubic crystal system and a crystal space group of I43d; and the molar proportion of N element in the protective film is 54% to 60%.

[0009] In some of these embodiments, the molar ratio of nitrogen in the protective film is 57%.

[0010] In some embodiments, the thickness of the protective film is 200 nm to 950 nm.

[0011] The present invention also provides a method for preparing the mid-to-long-wave infrared antireflection protective film as described in any of the above technical solutions, comprising the following steps:

[0012] Clean the substrate;

[0013] Plasma cleaning of the substrate was performed in an Ar atmosphere.

[0014] Using metal elements as the target material, the target material is sputtered in an Ar and N2 mixed gas environment by high-power pulsed magnetron sputtering, so that the metal elements react with N2 to generate nitrides and deposit them on the substrate, thereby obtaining a mid-to-long-wave infrared anti-reflection protective film on the substrate.

[0015] In some embodiments, during high-power pulsed magnetron sputtering, the average power is 200W to 500W, the duty cycle is 1% to 5%, the frequency is 800Hz to 1200Hz, the Ar to N2 flow ratio is 40:(6 to 12), the sputtering pressure is 0.5Pa to 1.0Pa, and the substrate bias is -50V to -100V.

[0016] In some embodiments, no additional heating of the substrate is applied during sputtering, and the deposition time is no less than 30 minutes.

[0017] In some of these embodiments, the deposition time is 60 minutes.

[0018] In some of these embodiments, the purity of the target material is above 99%.

[0019] In some embodiments, the plasma cleaning is performed at a pressure of 1.0 Pa and a cleaning power of 300 W.

[0020] In some embodiments, the specific steps for cleaning the substrate are as follows: the substrate is cleaned sequentially using anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the substrate is cleaned, it is placed in an ultrasonic cleaner containing the cleaning solution.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0022] 1. The mid-to-long-wave infrared antireflection protective film provided by the present invention is composed of cubic Zr3N4 or Hf3N4 with a crystal space group of I43d. Due to its good crystallinity, it can effectively reduce light absorption caused by defect states. Moreover, its refractive index is between that of air and Si. Therefore, it can play a good antireflection effect on Si in the mid-to-long-wave infrared wavelength range of 8-16μm. When the mid-to-long-wave infrared antireflection protective film is deposited on Si material, it can increase the average transmittance of Si material by about 5%.

[0023] 2. The mid-to-long-wave infrared anti-reflection protective film provided by the present invention is a single-layer structure, which is simple in structure and easy to prepare. In addition, the single-layer infrared anti-reflection protective film has high transmittance, hardness exceeding 20GPa, and good hydrophobicity, which can meet the requirements of infrared detection and guidance. It has good application prospects in the fields of photoelectric detectors, missile-borne infrared precision guidance systems and airborne infrared search and tracking systems.

[0024] 3. The method for preparing the mid-to-long-wave infrared antireflective protective film provided by the present invention is pollution-free, low-cost, simple and easy to implement, and has a short protective film growth cycle. At the same time, the prepared mid-to-long-wave infrared antireflective protective film has good crystallinity, effectively avoids light absorption caused by defects in the protective film, improves the transmittance of the protective film in the wavelength range of 8-16μm, has high density, and has a smooth surface. Attached Figure Description

[0025] Figure 1 The protective films on the Si substrates prepared in Examples 1-4 and Comparative Example 1 of this invention, and the transmittance curves of the Si substrates in the wavelength range of 8-16 μm;

[0026] Figure 2 The protective film on the Si substrate prepared in Example 5 of the present invention and the transmittance curve of the Si substrate in the wavelength range of 8-16 μm are shown.

[0027] Figure 3 The contact angle measurement results are for the Si substrate protective films prepared in Examples 1-4 and Comparative Examples 1 and 3 of this invention; wherein, (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, (d) corresponds to Example 4, (e) corresponds to Comparative Example 1, and (f) corresponds to Comparative Example 3.

[0028] Figure 4 The contact angle measurement results are for the Si substrate protective film prepared in Example 5 of this invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a mid-to-long-wave infrared antireflection protective film. The protective film comprises a nitride with the chemical formula M3N4, wherein M represents a metal element, such as Zr or Hf; the nitride has a cubic crystal system and a crystal space group of I43d; and the molar proportion of N element in the protective film is 54% to 60%.

[0031] The aforementioned mid-to-long-wave infrared antireflection protective film is composed of cubic Zr3N4 or Hf3N4 with a crystal space group of I43d. Due to its good crystallinity, it can effectively reduce light absorption caused by defect states. Furthermore, its refractive index is between that of air and Si, thus providing excellent antireflection protection for Si in the 8-16 μm mid-to-long-wave infrared wavelength range. When this mid-to-long-wave infrared antireflection protective film is deposited on Si material, it can increase the average transmittance of Si material by approximately 5%. Simultaneously, the aforementioned mid-to-long-wave infrared antireflection protective film is a single-layer structure, simple in structure and easy to prepare. In addition to high transmittance, this single-layer infrared antireflection protective film has a hardness exceeding 20 GPa and good hydrophobicity, meeting the requirements for use in infrared detection and guidance fields. It has promising application prospects in photoelectric detectors, missile-borne infrared precision guidance systems, and airborne infrared search and track systems.

[0032] In some embodiments, the molar ratio of nitrogen (N) in the protective film is 57%. This embodiment provides an optimal molar ratio of N in the protective film, under which the antireflection effect on single-crystal Si is optimal, while also exhibiting good mechanical properties and hydrophobicity.

[0033] In some embodiments, the thickness of the protective film is 200 nm to 950 nm. In this embodiment, a preferred thickness range for the protective film is given, which allows the protective film within this preferred thickness range to simultaneously achieve both infrared light transmittance and hardness.

[0034] This invention also provides a method for preparing the above-mentioned mid-to-long-wave infrared antireflection protective film, comprising the following steps:

[0035] S1: Clean the substrate.

[0036] In this step, it should be noted that the substrate includes, but is not limited to, glass, quartz glass, single-crystal Si, ZnS, Si3N4, Al2O3, Ge, CaF, AlN, GaN, and BeF. It should also be noted that the specific steps for cleaning the substrate are as follows: the substrate is cleaned sequentially with anhydrous ethanol, ultrapure water, acetone, and then anhydrous ethanol again. Each time, the substrate is placed in an ultrasonic cleaner containing the cleaning solution.

[0037] S2: Plasma cleaning of the substrate in an Ar atmosphere.

[0038] In this step, it should be noted that the pressure during plasma cleaning is 1.0 Pa and the cleaning power is 300 W. Plasma cleaning can improve the adhesion of the substrate, thereby extending the service life of the protective film.

[0039] S3: Using metal elements as the target material, the target material is sputtered in a mixed Ar and N2 gas environment by high-power pulsed magnetron sputtering, so that the metal elements react with N2 to generate nitrides and deposit them on the substrate, thereby obtaining a mid-to-long-wave infrared anti-reflection protective film on the substrate.

[0040] In this step, it should be noted that high-power pulsed magnetron sputtering is an existing technology, and its specific operation steps are well known to those skilled in the art, and will not be elaborated here. Preferably, during high-power pulsed magnetron sputtering, the average power is 200W to 500W, the duty cycle is 1% to 5%, the frequency is 800Hz to 1200Hz, the Ar to N2 flow ratio is 40:(6 to 12), the sputtering pressure is 0.5Pa to 1.0Pa, and the substrate bias voltage is -50V to -100V. Using the above-mentioned preferred sputtering parameter range during high-power pulsed magnetron sputtering can improve the crystallinity of the nitride, thereby obtaining a protective film with high transmittance in the 8-16μm wavelength range. It should also be noted that the purity of the target material is above 99%, preferably above 99.95%, which helps to reduce the impurity content in the protective film. In addition, no additional heating is applied to the substrate during the sputtering process, and the deposition time is no less than 30 minutes, preferably 60 minutes. The protective film prepared in this way has a better anti-reflection effect in the wavelength range of 8-16 μm (mid-long infrared band).

[0041] The above-mentioned method for preparing mid-to-long-wave infrared antireflective protective films is pollution-free, low-cost, simple, and has a short growth cycle. Furthermore, the mid-to-long-wave infrared antireflective protective films prepared using this method exhibit good crystallinity, effectively avoiding light absorption caused by defects in the protective film, improving the transmittance of the protective film in the 8-16 μm wavelength range, and possessing high density and a smooth surface.

[0042] To provide a clearer and more detailed description of the mid-to-long-wave infrared antireflection protective film and its preparation method provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0043] Example 1

[0044] (1) The Si substrate was cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the Si substrate was cleaned, it was placed in an ultrasonic cleaner containing the cleaning solution for 15 minutes.

[0045] (2) The Si substrate was plasma cleaned in an Ar atmosphere with a pressure of 1.0 Pa, a cleaning power of 300 W, and a cleaning time of 10 min.

[0046] (3) Using Hf as the target material with a purity of 99.95%, a nitride was deposited on a Si substrate using high-power pulsed magnetron sputtering to obtain a protective film. The specific steps were as follows: the target material was sputtered in an Ar and N2 mixed gas environment using high-power pulsed magnetron sputtering, and the resulting nitride was deposited on the Si substrate. Specific parameters were: average power of 300 W, duty cycle of 2%, frequency of 1000 Hz, Ar flow rate of 40 sccm, N2 flow rate of 6 sccm, gas pressure maintained at 0.9 Pa during sputtering, substrate bias of -50 V, no additional heating of the Si substrate during sputtering, and deposition time of 60 min. The thickness of the obtained protective film was 500 nm, and the molar ratio of N element was 57%.

[0047] Example 2

[0048] (1) The Si substrate was cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the Si substrate was cleaned, it was placed in an ultrasonic cleaner containing the cleaning solution for 15 minutes.

[0049] (2) The Si substrate was plasma cleaned in an Ar atmosphere with a pressure of 1.0 Pa, a cleaning power of 300 W, and a cleaning time of 10 min.

[0050] (3) Using Hf as the target material with a purity of 99.95%, a nitride was deposited on a Si substrate using high-power pulsed magnetron sputtering to obtain a protective film. The specific steps were as follows: the target material was sputtered in an Ar and N2 mixed gas environment using high-power pulsed magnetron sputtering, and the resulting nitride was deposited on the Si substrate. Specific parameters were: average power of 500 W, duty cycle of 4%, frequency of 800 Hz, Ar flow rate of 40 sccm, N2 flow rate of 12 sccm, gas pressure maintained at 0.5 Pa during sputtering, substrate bias of -100 V, no additional heating of the Si substrate during sputtering, and deposition time of 60 min. The thickness of the obtained protective film was 950 nm, and the molar ratio of N element was 55%.

[0051] Example 3

[0052] (1) The Si substrate was cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the Si substrate was cleaned, it was placed in an ultrasonic cleaner containing the cleaning solution for 15 minutes.

[0053] (2) The Si substrate was plasma cleaned in an Ar atmosphere with a pressure of 1.0 Pa, a cleaning power of 300 W, and a cleaning time of 10 min.

[0054] (3) Using Hf as the target material with a purity of 99.95%, a protective film was obtained by depositing nitrides on a Si substrate using high-power pulsed magnetron sputtering technology. The specific steps were as follows: the target material was sputtered in an Ar and N2 mixed gas environment using high-power pulsed magnetron sputtering, and the resulting nitrides were deposited on the Si substrate. Specific parameters were: average power of 400 W, duty cycle of 5%, frequency of 1200 Hz, Ar flow rate of 40 sccm, N2 flow rate of 8 sccm, gas pressure maintained at 1.0 Pa during sputtering, substrate bias of -80 V, no additional heating of the Si substrate during sputtering, and deposition time of 60 min. The thickness of the obtained protective film was 700 nm, and the molar ratio of N element was 54%.

[0055] Example 4

[0056] (1) The Si substrate was cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the Si substrate was cleaned, it was placed in an ultrasonic cleaner containing the cleaning solution for 15 minutes.

[0057] (2) The Si substrate was plasma cleaned in an Ar atmosphere with a pressure of 1.0 Pa, a cleaning power of 300 W, and a cleaning time of 10 min.

[0058] (3) Using Hf as the target material with a purity of 99.95%, a nitride was deposited on a Si substrate using high-power pulsed magnetron sputtering to obtain a protective film. The specific steps were as follows: the target material was sputtered in an Ar and N2 mixed gas environment using high-power pulsed magnetron sputtering, and the resulting nitride was deposited on the Si substrate. Specific parameters were: average power of 200 W, duty cycle of 1%, frequency of 1000 Hz, Ar flow rate of 40 sccm, N2 flow rate of 10 sccm, gas pressure maintained at 0.5 Pa during sputtering, substrate bias of -50 V, no additional heating of the Si substrate during sputtering, and deposition time of 60 min. The thickness of the obtained protective film was 200 nm, and the molar ratio of N element was 60%.

[0059] Example 5

[0060] (1) The Si substrate was cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol as cleaning solutions. Each time the Si substrate was cleaned, it was placed in an ultrasonic cleaner containing the cleaning solution for 15 minutes.

[0061] (2) The Si substrate was plasma cleaned in an Ar atmosphere with a pressure of 1.0 Pa, a cleaning power of 300 W, and a cleaning time of 10 min.

[0062] (3) Using Zr as the target material with a purity of 99.9%, a protective film was obtained by depositing nitrides on a Si substrate using high-power pulsed magnetron sputtering technology. The specific steps were as follows: the target material was sputtered in an Ar and N2 mixed gas environment using high-power pulsed magnetron sputtering, and the resulting nitrides were deposited on the Si substrate. Specific parameters were: average power of 300 W, duty cycle of 4%, frequency of 1000 Hz, Ar flow rate of 40 sccm, N2 flow rate of 6 sccm, gas pressure maintained at 0.9 Pa during sputtering, substrate bias of -50 V, no additional heating of the Si substrate during sputtering, and deposition time of 60 min. The thickness of the obtained protective film was 350 nm, and the molar ratio of N element was 57%.

[0063] Comparative Example 1

[0064] The difference from Example 1 is that in step (3), the parameters for high-power pulsed magnetron sputtering are: average power of 600W, duty cycle of 8%, frequency of 1500Hz, Ar flow rate of 40sccm, N2 flow rate of 15sccm, gas pressure maintained at 1Pa during sputtering, and substrate bias of -100V. The thickness of the prepared protective film is 400nm, and the molar ratio of N element is 61%.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that the Si substrate was not subjected to the plasma cleaning in step (2), and no substrate bias was applied during the high-power pulsed magnetron sputtering in step (3).

[0067] Comparative Example 3

[0068] The difference from Example 1 is that in step (3), the parameters for high-power pulsed magnetron sputtering are: average power of 1000W, duty cycle of 10%, frequency of 1000Hz, Ar flow rate of 80sccm, N2 flow rate of 4sccm, gas pressure maintained at 0.4Pa during sputtering, substrate bias of -150V, and Si substrate heated to 200℃ during sputtering. The thickness of the prepared protective film is 1100nm, and the molar ratio of N element is 50%.

[0069] Performance testing

[0070] The transmittance of the Si-based protective films prepared in Examples 1-5 and Comparative Example 1 in the 8-16 μm wavelength range was detected using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). The test results are as follows: Figure 1 and Figure 2 As shown. It should be noted that in Comparative Example 2, because the substrate was not ion-cleaned during the film preparation process, the resulting Si-based protective film exhibited film detachment, making transmittance testing impossible; the Si-based protective film prepared in Comparative Example 3 was a conductor, exhibiting virtually no infrared transmittance. Figure 1 As can be seen, the protective film prepared in Comparative Example 1 exhibits significantly improved transmittance compared to the Si substrate in the 8-12 μm and 14-16 μm wavelength ranges, but no significant improvement in transmittance in the 12-14 μm wavelength range. The protective films prepared in Examples 1-4 all show significantly improved transmittance compared to the Si substrate in the 8-16 μm wavelength range. Figure 2 As can be seen, the protective film prepared in Example 5 also has a significantly improved transmittance in the 8-16 μm wavelength range compared to the Si substrate.

[0071] The hardness of the Si-based protective films prepared in Examples 1-5 and Comparative Examples 1 and 3 was tested using nanoindentation technology, and the results are shown in Table 1. It should be noted that in Comparative Example 2, because the substrate was not ion-cleaned during film preparation, the Si-based protective film exhibited film detachment and could not be subjected to nanoindentation testing. As shown in Table 1, the hardness of the protective films prepared in Examples 1-4 ranged from 19.8 to 22.0 GPa, which was higher than that of the protective film prepared in Comparative Example 1, indicating better mechanical strength. The protective film prepared in Comparative Example 3 showed a significant change in elemental composition, essentially transforming into HfN, resulting in a higher hardness of 24.0 GPa. In Example 5, because Zr was used, the hardness of the protective film differed from that of Examples 1-4, with a hardness of 8.8 GPa, also exhibiting good mechanical strength.

[0072] Table 1. Hardness of the Si-based protective films prepared in Examples 1-5 and Comparative Examples 1-3

[0073]

[0074] The contact angles between the Si-based protective films prepared in Examples 1-5 and Comparative Examples 1 and 3 and water at room temperature were measured using a contact angle meter. The test results are as follows: Figure 3 and Figure 4 As shown. It should be noted that in Comparative Example 2, because the substrate was not ion-cleaned during the thin film preparation process, the resulting Si-based protective film exhibited film detachment, making contact angle testing impossible. Figure 3 As can be seen, the contact angles of the protective films prepared in Examples 1-4 are significantly higher than those in Comparative Example 1 and Comparative Example 3. Figure 4 As can be seen, the contact angle of the protective film prepared in Example 5 reached over 108°. This indicates that the mid-to-long-wave infrared antireflective protective film prepared by the present invention has good hydrophobicity, making it difficult for rainwater and other substances to remain on its surface, and possesses self-cleaning ability.

Claims

1. A method for preparing a mid-to-long-wave infrared antireflective protective film, characterized in that, The protective film comprises a nitride with the chemical formula M3N4; wherein M represents a metallic element, such as Zr or Hf; the nitride is cubic with a crystal space group of I43d; the molar proportion of nitrogen in the protective film is 54%~60%; the preparation method includes the following steps: Clean the substrate; The substrate was subjected to plasma cleaning in an Ar atmosphere; Using a metal element as the target material, the target material is sputtered in an Ar and N2 mixed gas environment by high-power pulsed magnetron sputtering, so that the metal element reacts with N2 to generate nitrides and deposits them on the substrate, thereby obtaining a mid-to-long-wave infrared anti-reflection protective film on the substrate. The substrate is a single-crystal Si. During the high-power pulsed magnetron sputtering, the average power is 200W~500W, the duty cycle is 1%~5%, the frequency is 800Hz~1200Hz, the Ar to N2 flow ratio is 40:(6~12), the sputtering pressure is 0.5Pa~1.0Pa, the substrate bias is -50V~-100V, no additional heating is applied to the substrate during sputtering, and the deposition time is not less than 30min.

2. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, The molar ratio of nitrogen in the protective film is 57%.

3. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, The thickness of the protective film is 200nm~950nm.

4. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, The deposition time was 60 minutes.

5. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, The purity of the target material is above 99%.

6. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, During the plasma cleaning, the pressure is 1.0 Pa and the cleaning power is 300 W.

7. The method for preparing the mid-to-long-wave infrared antireflective protective film according to claim 1, characterized in that, The specific steps for cleaning the substrate are as follows: the substrate is cleaned sequentially with anhydrous ethanol, ultrapure water, acetone and anhydrous ethanol. Each time the substrate is cleaned, it is placed in an ultrasonic cleaner containing the cleaning solution.

Images