High-temperature-resistant antireflection film for silicon carbide single crystal and preparation method of high-temperature-resistant antireflection film

Abstract

The invention relates to a high-temperature-resistant antireflection film for a silicon carbide single crystal and a preparation method of the high-temperature-resistant antireflection film. The structure of the high-temperature-resistant antireflection film for the silicon carbide single crystal comprises a silicon carbide substrate, wherein the silicon carbide substrate comprises a first surface and a second surface which are opposite to each other; the first coating film layer is deposited on the first surface; and the second coating film layer is deposited on the second surface.

Description

Technical Field

[0001] This invention belongs to the field of optical film material technology, specifically relating to a high-temperature resistant antireflective film for silicon carbide single crystals and its preparation method. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, possesses low visible-to-near-infrared spectral loss, high thermal conductivity, excellent mechanical strength, and chemical stability, making it an ideal substrate material for high-performance integrated photonics, especially in the field of augmented reality (AR) waveguides. In near-eye display devices such as AR glasses, waveguides need to achieve high-efficiency light transmission and coupling within extremely thin dimensions. This places stringent requirements on the material's refractive index contrast, thermal management capabilities, and mechanical reliability, and SiC demonstrates unique potential in these areas.

[0003] However, while SiC's high refractive index (n≈2.6) provides strong light confinement capabilities, it also leads to significant Fresnel reflection losses at the optical coupling interface. In AR waveguides, this directly manifests as reduced optical input and output efficiency, wasting system optical energy. Furthermore, the decreased image contrast and ghosting caused by reflected stray light severely limit the brightness, energy efficiency, and image quality of the final display. Therefore, developing high-efficiency antireflection films suitable for SiC waveguides is a crucial prerequisite for unlocking their optical potential and propelling them towards practical application.

[0004] Antireflective coatings are a key technology for improving the transmittance of optical components. Common single-layer antireflective coatings typically achieve optimal antireflection for only a single wavelength, making them insufficient for broad-spectrum applications. While multilayer antireflective coatings can achieve good antireflection, they are costly and inefficient to manufacture. Optical components in AR devices also face challenges such as localized high thermal loads, severe process thermal stress, and long-term environmental reliability. Therefore, developing an antireflective coating that achieves high-efficiency antireflection, withstands the aforementioned high-temperature and stress environments, and bonds firmly to a silicon carbide substrate is crucial for promoting the large-scale application of silicon carbide in high-end consumer electronics optics. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-temperature resistant antireflective film for silicon carbide single crystals and its preparation method. This structure not only achieves efficient antireflection in the visible to near-infrared wavelength range but also withstands high-temperature environments, ensuring that its optical performance and structure remain stable when subjected to localized high thermal loads from miniature light sources in AR devices. This provides a reliable surface treatment solution for the application of silicon carbide optical components in AR glasses, automotive HUDs, and other fields.

[0006] In a first aspect, the present invention provides a high-temperature resistant antireflective film for silicon carbide single crystals, the structure of which includes: A silicon carbide substrate, the silicon carbide substrate including a first surface and a second surface facing away from each other; A first coating layer deposited on the first surface; and, A second coating layer deposited on the second surface.

[0007] Preferably, the silicon carbide substrate has a refractive index of 2.55-2.77 and a thickness of 0.05-2 mm, more preferably 0.5 mm.

[0008] Preferably, the materials of the first and second coated layers include high-purity SiO2, with a purity preferably ≥99.99%, and the film system is for a center wavelength of 380-750nm, preferably 580nm, and has a refractive index of 1.45-1.48, preferably 1.47.

[0009] Preferably, the thickness of both the first coating layer and the second coating layer is 67nm-130nm, and more preferably 97nm.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned high-temperature resistant antireflective film for silicon carbide single crystals. The preparation method includes the following steps: depositing a first coating layer and a second coating layer on a first surface and a second surface opposite to each other on a silicon carbide substrate by vacuum electron beam evaporation coating method, respectively, to obtain the high-temperature resistant antireflective film for silicon carbide single crystals.

[0011] Preferably, the process parameters of the vacuum electron beam evaporation coating method include: working disk temperature 80-150℃, preferably 120℃, monitoring plate temperature 150-250℃, preferably 200℃, and vacuum degree below 1.0×10⁻⁶. -3 Pa.

[0012] Preferably, the deposition rate of the first and second vapor-deposited film layers is 2-15 Å / s, and more preferably 8 Å / s.

[0013] Beneficial effects (1) Based on the high reflection loss of the original silicon carbide substrate, the present invention proposes to deposit an antireflection film on its double surface, thereby reducing the light reflection loss at the interface between the upper and lower air-silicon carbide substrates, significantly improving the light transmittance of the system, increasing the transmittance of the 438-938nm band to more than 90%, and the peak transmittance to 95%, effectively reducing the reflection loss of light in the visible and near-infrared range. (2) The present invention deposits the film structure on the surface of silicon carbide substrate by electron beam evaporation. The evaporation process uses electron beam, which has extremely high energy density, thus achieving high temperature, and therefore can deposit high melting point materials such as SiO2. This process has a fast film formation rate and good repeatability, making it suitable for industrial production. Electron beam evaporation can obtain a uniform and dense film with good intrinsic thermal stability. (3) The SiO2 film material used in this invention is consistent with the thermal expansion behavior of the surface oxide layer of silicon carbide at high temperature. It can avoid the interlayer stress caused by the interface reaction at high temperature, which can lead to film cracking or deformation. Moreover, SiO2 material has excellent high temperature stability and oxidation resistance. It can still maintain structural integrity and optical performance stability after high temperature annealing at 1000℃. This makes the components using this film layer able to easily withstand the internal thermal environment of AR devices and subsequent high temperature packaging processes. Attached Figure Description

[0014] Figure 1 A schematic diagram of an exemplary structure of a high-temperature antireflective film for silicon carbide single crystals provided by the present invention; Figure 2 A comparison of the transmittance spectra of an uncoated silicon carbide single crystal substrate, a high-temperature antireflective film for silicon carbide single crystals prepared in Example 1, and a high-temperature antireflective film for silicon carbide single crystals after annealing at 1000°C. Figure 3 SEM image of a high-temperature antireflective coating on a silicon carbide single crystal after annealing at 1000℃; Figure label: 1. Silicon carbide substrate; 2. First coating layer; 3. Second coating layer. Detailed Implementation

[0015] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0016] First, such as Figure 1 As shown, this invention provides a high-temperature resistant antireflective film for silicon carbide single crystals. The structure of the high-temperature resistant antireflective film for silicon carbide single crystals may include: A silicon carbide substrate, the silicon carbide substrate including a first surface and a second surface facing away from each other; A first coating layer deposited on the first surface; and, A second coating layer deposited on the second surface.

[0017] In some embodiments, the refractive index of the silicon carbide substrate can be 2.55-2.77, and the thickness can be 0.05-2 mm, preferably 0.5 mm. By setting the thickness of the SiO2 film, the anti-reflection effect of the crystal can be ensured in the wavelength range of 400 nm to 2000 nm. The refractive index range of the silicon carbide substrate specified in this application is derived from the test results of high-purity 4H-SiC material and the intrinsic dispersion properties of the material itself. Preferably, the refractive index refers to the measured value at the center wavelength of 580 nm in the visible light spectrum to ensure optimal optical matching with subsequent films. The thickness range (0.05-2 mm) covers the commonly used and achievable range in the industry, with 0.5 mm being the preferred industrial standard thickness, balancing mechanical strength, processing efficiency, and cost. If the parameters exceed the limits, it will lead to a reduction in mechanical properties, processing performance, and optical efficiency, affecting the stability and performance of the final product.

[0018] In some embodiments, the silicon carbide substrate may be circular, rectangular, square, elliptical, polygonal, irregular, or other shapes suitable for a specific application, and is not limited thereto.

[0019] In some embodiments, the materials of the first and second coating layers may include high-purity SiO2, preferably with a purity of ≥99.99%, the film system may be for a center wavelength of 380-750nm, preferably 580nm, and the refractive index may be 1.45-1.48, preferably 1.47.

[0020] For silicon carbide substrates with a refractive index as high as approximately 2.6, theoretical calculations indicate that a refractive index of approximately 1.63 is required to achieve optimal single-layer antireflection at a specific wavelength (e.g., 580 nm). Although the refractive index of SiO2 (~1.47) is slightly lower than this ideal value, it can still achieve extremely high transmittance exceeding 95% within the target narrow wavelength range. More importantly, SiO2 exhibits excellent thermal expansion coefficient matching with the silicon carbide substrate. This characteristic significantly suppresses interfacial thermal stress during film deposition and subsequent temperature changes in the device, fundamentally avoiding failures such as film cracking, wrinkling, or peeling caused by thermal mismatch. This advantage endows the optical element of this invention with superior high-temperature environmental stability and long-term reliability, which is difficult to achieve with other materials (such as MgF2, certain organic materials, etc.) that have similar initial antireflection effects even at room temperature. Therefore, choosing SiO2 is a crucial and non-obvious technical decision for achieving a balance between high performance, high reliability, and high environmental adaptability.

[0021] In some embodiments, the thickness of both the first and second coating layers can be 67nm-130nm, preferably 97nm.

[0022] The specified thickness range enables peak transmittance in the visible light range. When the thickness is less than 67 nm, the optical impedance modulation effect of the coating layer weakens, peak transmittance is limited, and physical stability decreases. When the thickness is greater than 130 nm, film stress problems are easily introduced, affecting adhesion and film performance. The preferred film thickness enables peak transmittance at the center of the visible light spectrum, which is beneficial for improving transmittance within the visible spectrum.

[0023] The theoretical basis of this invention lies primarily in the fact that, according to Fresnel's law, to achieve optimal antireflection in a single layer, the refractive index of the membrane material must satisfy n... 2 =n A n S , where n is the optimal refractive index of the film material, n A n is the refractive index of air. S Let n be the refractive index of the silicon carbide substrate. For the silicon carbide substrate, its refractive index n in the visible to near-infrared band (e.g., 400-1000 nm) is... s The refractive index is approximately 2.55-2.77. Calculations show that, corresponding to the substrate's refractive index range, the optimal theoretical refractive index range for the matched film is approximately 1.60-1.66. To achieve high-temperature resistance, the film needs to match the thermal expansion of the substrate and the interface at high temperatures, and this is the design criterion. The subtraction of the interfacial reflected light interference in a single-layer film system must satisfy: Δ=2dn=kλ, where Δ is the optical path difference of the reflected light from the air-film interface, d is the physical thickness of the film, k is a positive integer, and λ is the wavelength of the incident light. The refractive index of the SiO2 film is approximately 1.47, slightly lower than this ideal value. However, a significant anti-reflection effect can still be achieved by designing according to λ / 4, and a thermally oxidized SiO2 layer will form at the interface between silicon carbide and the film at high temperatures. Therefore, SiO2 film is the best material for high-temperature resistant silicon carbide optical components.

[0024] The antireflection film provided by this invention is deposited on the surface of a silicon carbide single-crystal substrate. It exhibits high transmittance and excellent high-temperature stability in the visible to near-infrared band. The film maintains structural integrity and stable optical performance even at a high temperature of 1000℃, making it suitable for AR optical components. Simultaneously, this invention utilizes the principle of thin-film interference to effectively reduce light reflection loss in the visible and near-infrared range, significantly improving the optical transmittance of silicon carbide in the visible to near-infrared band.

[0025] In some embodiments, the high-temperature antireflective coating for silicon carbide single crystals, after being annealed at 1000°C for 1 hour in an air atmosphere, has an average transmittance of not less than 90% in the 400nm to 1000nm wavelength band.

[0026] The following is an exemplary description of a method for preparing a high-temperature resistant antireflective coating for silicon carbide single crystals provided by the present invention. The preparation method may include the following steps: depositing a first coating layer and a second coating layer on opposite surfaces of a silicon carbide substrate using a vacuum electron beam evaporation deposition method, thereby obtaining the double-sided antireflective coating for silicon carbide single crystals.

[0027] In some embodiments, the process parameters of the vacuum electron beam evaporation coating method may include: working disk temperature 80-150℃, preferably 120℃, monitoring plate temperature 150-250℃, preferably 200℃, and vacuum degree below 1.0×10⁻⁶. -3 Pa.

[0028] The working plate temperature is generally set according to the type of membrane material and adhesion requirements. Excessive temperature may lead to delamination, while insufficient temperature may affect membrane density. The optimal monitoring plate temperature effectively reduces water and volatile matter adsorption, improving membrane quality. Increasing the temperature helps reduce moisture or gas adsorption, but excessively high temperatures can cause monitoring plate deformation or coating stress problems. Within a reasonable process window, parameters can repeatedly achieve excellent membrane quality.

[0029] In some embodiments, the deposition rate of the first and second vapor-deposited film layers can be 2-15 Å / s, preferably 8 Å / s. By controlling the deposition rate within a suitable range, film density, optical uniformity, and preparation efficiency can be balanced.

[0030] It should be noted that the present invention differs fundamentally from conventional technical solutions: (1) The present invention aims to solve the performance stability problem of silicon carbide components in high-temperature environments such as local high heat load of micro light source in AR devices, and puts forward extreme requirements for the thermal stability, adhesion and thermal matching of the film layer. Conventional technical solutions often only solve the problem of broadband anti-reflection and moisture protection of ordinary optical glass at room temperature, without involving any high temperature or high heat load scenarios; or, only involve the anti-reflection of glass / crystal, focusing on chemical stability and self-cleaning. The composite films such as "Al2O3-SiO2" used are generally prepared by sol-gel method. Their mechanical strength, density and thermal stability are fundamentally different from the dense films prepared by physical vapor deposition (such as electron beam evaporation), and are not designed for high temperature applications. (2) The present invention uses a single-layer SiO2 film on one side of the substrate. The fewer interfaces greatly reduce the risk of interface failure due to mismatch of thermal expansion coefficients at high temperatures. Conventional technical solutions often use multi-layer composite films of unequal thickness. Under this design, the multi-layer interface is very easy to delaminate and crack due to stress accumulation when the temperature changes, which is completely unsuitable for high temperature or thermal cycling environments. (3) The present invention selects SiO2 because of its better matching coefficient of thermal expansion with silicon carbide (which is the physical basis for achieving high-temperature stability), a characteristic that other commonly used antireflective materials (such as MgF2, ZrO2, etc.) do not possess. The SiO2 film itself has high density, high chemical stability, high hardness and low absorption. Combined with electron beam evaporation process, it can form a robust and durable protective layer. The material selection of conventional technical solutions is entirely based on refractive index matching (to achieve broadband antireflection) or chemical function (self-cleaning), without considering the thermomechanical matching problem between the material and the substrate at high temperatures.

[0031] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0032] Example 1 The high-temperature resistant antireflective film for silicon carbide single crystals and its preparation method provided in this embodiment are as follows: (1) The structure of the high-temperature antireflective coating for silicon carbide single crystal includes: a silicon carbide substrate, the silicon carbide substrate including a first surface and a second surface opposite to each other; a first coating layer deposited on the first surface; and a second coating layer deposited on the second surface; The silicon carbide substrate has a refractive index of 2.63 and a thickness of 0.5 mm; The first and second coating layers are made of high-purity SiO2 with a refractive index of 1.47 and a thickness of 97 nm. (2) The method for preparing the high-temperature resistant antireflective film for silicon carbide single crystals includes the following steps: First, the surface of the silicon carbide substrate is cleaned, as are the crucible, electron gun, vacuum chamber interior and edges. Then, the cleaned silicon carbide substrate is clamped into the working fixture of the vacuum chamber, the required film material is placed in the crucible, and the vacuum degree of the vacuum chamber is reduced to 4×10⁻⁶. -3 After Pa, melting begins. The working plate temperature is set to 120℃, and the monitoring plate temperature is set to 200℃. The vacuum level in the vacuum chamber is then reduced to below 1.0 × 10⁻⁶. -3 Pa, automatically start the film deposition; deposit SiO2 on the silicon carbide substrate to obtain the first film layer, and control the film deposition rate to 8 Å / s; Finally, the process conditions of the first coating layer are repeated to deposit a second SiO2 coating layer on the other side of the silicon carbide substrate to obtain the high-temperature antireflective film for silicon carbide single crystals.

[0033] To evaluate the high-temperature resistance of the antireflective membrane of this invention, the samples were annealed at 1000°C in air (holding temperature for 1 hour, heating / cooling rate 200°C / h). The samples before and after annealing were characterized using a UV-Vis spectrophotometer and a scanning electron microscope (SEM).

[0034] Figure 2 The figures show a comparison of the transmittance spectra of an uncoated silicon carbide single crystal substrate, the high-temperature antireflective film for silicon carbide single crystals prepared in Example 1, and the high-temperature antireflective film for silicon carbide single crystals annealed at 1000℃. As can be seen from the figures, the film structure of this invention increases the transmittance in the 438-938 nm wavelength band to over 90%, effectively reducing light reflection loss in the visible and near-infrared range, and significantly improving the optical transmittance of silicon carbide in the visible to near-infrared wavelength range; furthermore, after annealing at 1000℃, the average transmittance of the sample in the 400 nm to 1000 nm wavelength range is still not less than 90%.

[0035] Figure 3 This is a SEM image of a high-temperature antireflective coating on a silicon carbide single crystal after annealing at 1000℃. The image shows that the film layer is continuous and dense after annealing at 1000℃, with good adhesion to the substrate and no visible cracks or peeling.

[0036] Comparative Example 1 The technical solution in this comparative example is the technical solution in Chinese patent CN 114609702 A.

[0037] Analysis reveals that the substrate used in Comparative Document 1 is optical glass, employing a five-layer (unequal thickness) Al2O3 / ZrO2 / MgF2 multilayer system. While achieving excellent broadband high transmittance in the visible-near infrared region, the structure is complex, involving numerous processes, complex interfaces between film layers, and difficult process control, demanding higher standards for cost and consistency stability. Furthermore, it struggles to meet high-temperature performance requirements. This invention designs a single-layer film structure on a silicon carbide substrate, making anti-reflection even more challenging. The SiO2 film material used exhibits thermal expansion behavior consistent with the surface oxide layer of silicon carbide at high temperatures, preventing interlayer stress caused by interfacial reactions at high temperatures from leading to film cracking or deformation. Moreover, SiO2 possesses excellent high-temperature stability and oxidation resistance, maintaining structural integrity and stable optical performance even after annealing at 1000℃.

[0038] Comparative Example 2 The technical solution in this comparative example is the technical solution in Chinese Patent CN 105130204 A.

[0039] Analysis shows that the coating method used in Comparative Document 2 is the sol-gel method, which usually forms porous or organic-inorganic hybrid films. Its hardness, density and high temperature resistance are far lower than those of physical vapor deposition films, and it cannot be applied to the high temperature / high heat load scenarios targeted by this invention.

[0040] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A high-temperature resistant antireflective film for silicon carbide single crystals, characterized in that, The structure of the high-temperature antireflective coating for silicon carbide single crystals includes: A silicon carbide substrate, the silicon carbide substrate including a first surface and a second surface facing away from each other; A first coating layer deposited on the first surface; and, A second coating layer deposited on the second surface.

2. The high-temperature resistant antireflective film for silicon carbide single crystals according to claim 1, characterized in that, The silicon carbide substrate has a refractive index of 2.55-2.77 and a thickness of 0.05-2 mm, preferably 0.5 mm.

3. The high-temperature resistant antireflective film for silicon carbide single crystals according to claim 1 or 2, characterized in that, The materials of the first and second coating layers include high-purity SiO2, preferably with a purity of ≥99.99%, and the film system is for a center wavelength of 380-750nm, preferably 580nm, with a refractive index of 1.45-1.48, preferably 1.

47.

4. The high-temperature resistant antireflective film for silicon carbide single crystals according to any one of claims 1-3, characterized in that, The thickness of both the first and second coating layers is 67nm-130nm, preferably 97nm.

5. A method for preparing a high-temperature resistant antireflective film for silicon carbide single crystals according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: depositing a first coating layer and a second coating layer on the first and second surfaces opposite to each other on a silicon carbide substrate by vacuum electron beam evaporation coating method, respectively, to obtain the high-temperature antireflective film for silicon carbide single crystal.

6. The preparation method according to claim 5, characterized in that, The process parameters for the vacuum electron beam evaporation coating method include: working disk temperature 80-150℃, preferably 120℃; monitoring plate temperature 150-250℃, preferably 200℃; and vacuum degree below 1.0×10⁻⁶. -3 Pa.

7. The preparation method according to claim 5 or 6, characterized in that, The deposition rate of the first and second vapor-deposited film layers is 2-15 Å / s, preferably 8 Å / s.

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