A silicon diamond infrared composite window material and a preparation method thereof

Abstract

The application discloses a silicon-diamond infrared composite window material, which comprises optical silicon and a diamond film deposited on the surface of the optical silicon, and the thickness of the diamond film is 80-120 microns. The silicon-diamond infrared composite window material has high transmittance and surface bonding capacity. The application further provides a preparation method of the silicon-diamond infrared composite window material, which comprises the following steps: pretreating 5-10 minutes on the optical silicon by using a diamond micro-powder suspension liquid, so that scratches are generated on the surface of the optical silicon; growing a diamond layer on the surface of the optical silicon obtained in step (1) by using a CH4 / H2 mixed gas as a reaction gas through a MPCVD (microwave plasma chemical vapor deposition) method at a temperature of 800-950 DEG C for 50-80 hours; and grinding and polishing the diamond layer to obtain the silicon-diamond infrared composite window material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of infrared optical materials, and particularly relates to a silicon-diamond infrared composite window material and a preparation method thereof. BACKGROUND

[0002] The research and application of infrared technology has become an important direction of the development of modern optical technology, and has a wide application in the manufacture of lenses, prisms, windows, radomes and the like in infrared optical instruments such as infrared thermal imagers and infrared homing heads. The infrared guidance technology is mainly used for detecting and tracking the thermal radiation of a target, so as to guide the aircraft to accurately detect the target. Infrared optical materials commonly use germanium, silicon, zinc selenide, zinc sulfide and sapphire. With the harshness of the application environment, such as the acceleration of flight speed, the aerodynamic effect caused by air friction is also stronger, especially at high Mach numbers, the strong aerodynamic effect will cause the heat on the surface of the infrared window to be unable to be quickly dissipated, causing local heat accumulation, resulting in a large temperature difference between the window stagnation point and other parts, thereby causing a large thermal stress, and further possibly leading to the destruction of the infrared window. There are few materials available under the environment of super-high-speed flight, only sapphire and zinc sulfide, but their thermal conductivities are very low (only 10-30 W / mK), and the heat resistance is not good. How to improve the heat resistance and expand its application range is a problem to be solved at present.

[0003] Diamond has excellent thermal, optical and mechanical properties (strength above 450 MPa), and its ultra-high thermal conductivity (theoretical value 2200 W / mK), making diamond infrared material an excellent choice for extreme environment applications. However, the cost of diamond thin film material preparation is relatively high, and the technology is not mature enough, and there is intrinsic absorption in the mid-wave infrared band (3-5 μm). Based on the principle that the optical intrinsic absorption increases with the thickness, the mid-wave infrared intrinsic absorption will also decrease with the decrease of the thickness of the optical material. Therefore, when a thin layer of diamond is deposited on the traditional mid-infrared window material, it is expected to realize the application of diamond in the mid-infrared band, and if it can be combined with traditional low-thermal-conductivity mid-infrared materials, it can provide good heat dissipation performance for traditional infrared window materials.

[0004] However, the thermal expansion coefficients and lattice constants of diamond film and traditional infrared materials are significantly different, which leads to insufficient density of the interface of the composite material, thereby affecting the performance of the composite material. The current commonly used method is to pre-deposit an intermediate layer on the substrate, and then grow diamond on the intermediate layer. Considering the size, cost, stability and thermal expansion coefficient and the like, silicon and sapphire have become the two most commonly used substrate materials.

[0005] In general, the main reason that diamond is difficult to be combined with the traditional infrared optical material substrate is that the thermal expansion coefficient of diamond is low, the stress generated when the temperature changes is small, the size changes little, while the thermal expansion coefficient of the traditional infrared optical material is high, the stress generated when the temperature changes is large, the size changes greatly, so that it is difficult for diamond to nucleate on the surface of the substrate, and the diamond layer is prone to collapse during the cooling process after growth. In addition, there is a large refractive index difference between diamond and the substrate, which has a great influence on the transmittance of the composite material. Therefore, the refractive index of the substrate should not be too different from that of diamond. SUMMARY

[0006] The application provides a silicon diamond infrared composite window material which has high transmittance and surface bonding capacity.

[0007] A silicon diamond infrared composite window material comprises optical silicon and a diamond film deposited on the surface of the optical silicon, wherein the thickness of the diamond film is 80-120 mu m.

[0008] The application reduces the intrinsic absorption of diamond in the mid-infrared band by providing a diamond film with a suitable thickness, so that the diamond film and the optical silicon can both refract the mid-infrared band with a refractive index close to each other, thereby achieving high transmittance in the mid-wave infrared band.

[0009] Since the thermal expansion coefficients of the optical silicon and the diamond film provided by the application are closest, and since the lattice matching degree is high and the interface is connected by molecular bonds, the surface bonding force is strong, so that it is not easy to produce cracking when the temperature changes.

[0010] Further, the application band of the optical silicon wafer and the diamond film is 3-5 mu m.

[0011] Further, the optical transmittance of the optical silicon wafer in the mid-wave infrared band is not less than 50%.

[0012] Since the refractive index and the application band of the optical silicon wafer and the diamond film are close or the same, the application first composites the optical silicon wafer and the diamond film to obtain an infrared composite material with high transmittance in the mid-wave infrared band.

[0013] Further, the size of the optical silicon wafer is not less than Φ25 mm, and the thickness is not less than 1 mm.

[0014] Further preferably, the thickness of the optical silicon wafer is 3-5 mm.

[0015] Further, the diamond film is used as the light incident medium, and the optical silicon is used as the light emitting medium.

[0016] The application further provides a preparation method of the silicon-diamond infrared composite window material, comprising the following steps:

[0017] (1) adopting a diamond micro-powder suspension liquid to pretreat the optical silicon for 5-10 minutes, so that scratches are generated on the surface of the optical silicon;

[0018] (2) through a MPCVD (microwave plasma chemical vapor deposition) method, using CH4 / H2 mixed gas as a reaction gas, growing a diamond layer on the surface of the optical silicon obtained in step (1) at a temperature of 800-950 DEG C for 50-80 hours, and grinding and polishing the diamond layer to obtain the silicon-diamond infrared composite window material.

[0019] The application uses the microwave plasma chemical vapor deposition technology to chemically bond two layers, so that the silicon-diamond infrared composite window material with high transmittance and high film layer bonding performance is obtained.

[0020] Further, before the pretreatment of the optical silicon wafer in step (1), the optical silicon wafer with a mid-wave infrared transmittance of not less than 50% is selected.

[0021] In step (2), the ratio of CH4 to H2 is 2:100-4:100, wherein the flow rate of H2 is 300-600 sccm; and the purity of CH4 and H2 is not less than 99.99%.

[0022] Further, before the deposition of the diamond layer, the optical silicon wafer obtained in step (1) is placed in a molybdenum holder with a height of 3-8 mm.

[0023] Further, the ratio of CH4 to H2 is 2:100-4:100, wherein the flow rate of H2 is 300-600 sccm; and the purity of CH4 and H2 is not less than 99.99%.

[0024] Further, the process parameters of the MPCVD are as follows: the deposition power is 3.0-4.5 kW, and the deposition gas pressure is 10-15 kPa.

[0025] Further, before the grinding and polishing of the diamond layer, the obtained diamond layer is cooled at a cooling rate of 5-30 DEG C / min.

[0026] Further, the diamond layer is ground and polished by using diamond powder with an average particle size of 0.5-2.0 microns. The use of the diamond powder with a smaller particle size for polishing makes the diamond surface smooth, which is beneficial to increase the light transmittance of the diamond layer.

[0027] The present application selects optical-grade silicon wafers as the substrate to reduce impurities and defects of the silicon wafers, so that the interface bonding strength is higher under high aerodynamic heat environment and the diamond is not easy to fall off. Moreover, the silicon with similar thermal expansion coefficient to diamond is used as the substrate, so that the diamond is not easy to fall off under high aerodynamic heat environment and the interface bonding strength is higher, chemical bonds are formed during the deposition process, the chemical bonds are not easy to be broken by heat, and the lattice parameters are relatively close, so that the interface bonding strength is further enhanced, the diamond layer is not easy to fall off under high aerodynamic heat environment, the transmittance of the middle-wave infrared band light is enhanced, and the transmittance is higher than 50%. Moreover, the surface thermal conductivity of the obtained infrared window is significantly improved due to the existence of the diamond layer.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] The present application uses the thinned diamond film, so that the application wave band of the diamond film is consistent with the application wave band of the optical silicon, that is, both are the middle-wave infrared band (3-5 mu m). Moreover, the refractive indexes of the diamond film and the optical silicon are relatively close, so that the silicon-diamond infrared composite window material obtained after compounding has higher transmittance. Moreover, the bonding force of the diamond film and the optical silicon is strong, and the expansion rates are relatively close, so that the diamond is not easy to fall off.

[0030] The present application deposits diamond by the MPCVD method, and then obtains the silicon-diamond infrared composite window material. The deposition method is simple and efficient, and provides a candidate scheme for the infrared window of a high-speed aircraft. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The structure schematic diagram of the silicon-diamond infrared composite window material provided by the embodiment of the present application is shown in the figure.

[0032] Figure 2 The Raman spectrum of the silicon-diamond infrared composite window obtained by the embodiment 1, the embodiment 2, the embodiment 3 and the comparative example 1 of the present application is shown in the figure.

[0033] Figure 3 The XRD graph of the silicon-diamond infrared composite window obtained by the embodiment 1, the embodiment 2, the embodiment 3 and the comparative example 1 of the present application is shown in the figure.

[0034] Figure 4 The transmittance graph of the silicon-diamond infrared composite window obtained by the embodiment 1, the embodiment 2, the embodiment 3 and the comparative example 1 of the present application is shown in the figure. DETAILED DESCRIPTION

[0035] In order to make the purpose, content and advantages of the present application more clear, the specific embodiments of the present application are further described in detail below in combination with the drawings and examples.

[0036] A specific embodiment of the present invention provides a silicon diamond infrared composite window material, such as... Figure 1 As shown, it includes optical silicon and a diamond film deposited on the surface of the optical silicon, the thickness of which is 80–120 μm.

[0037] A specific embodiment of the present invention also provides a method for preparing a silicon diamond infrared composite window material, comprising the following steps:

[0038] 1) An optical material with a certain optical transmittance is selected as a substrate for later use. Further, the optical material is an optical-grade silicon wafer with a size not less than Ф25mm, a thickness not less than 1mm (preferably 2–5mm), and an average optical transmittance of not less than 50% in the 3–5μm band.

[0039] 2) Sample A was obtained by uniformly rubbing a diamond micron powder suspension on a silicon substrate.

[0040] 3) Take sample A, place it on a metal molybdenum support of a certain thickness, and then place it together in the MPCVD equipment. Use a certain proportion of CH4 / H2 mixed gas as the reaction gas. Adjust the power and gas pressure to raise the temperature to 800–950℃ and continue to grow for 50–80 hours. Deposit a diamond layer on sample A. After slowly cooling to room temperature, take it out to obtain sample C.

[0041] Furthermore, the height of the molybdenum support is 3–8 mm; the ratio of CH4 to H2 is 2:100–4:100, with an H2 flow rate of 300–600 sccm; the gas purity is not less than 99.99%; the MPCVD operating power and gas pressure are set to 3.0–4.5 kW and 10.0–15.0 kPa, respectively; the cooling rate is controlled at 5–30 °C / min; and the thickness of the resulting diamond layer is 160–230 μm.

[0042] 4) Take sample C and polish the diamond growth surface to obtain sample D, which is the silicon diamond infrared composite window material. Further, the surface polishing process uses diamond powder with an average particle size of 0.5–2.0 μm as the polishing medium; the diamond layer thickness on sample D is controlled at 80–120 μm.

[0043] Example 1

[0044] (1) An optical silicon wafer with dimensions of Ф25mm×2mm was used as the substrate. The average optical transmittance of the optical silicon wafer in the 3–5μm band was 55%.

[0045] (2) Sample A1 was obtained by uniformly rubbing a diamond micro powder suspension on an optical silicon wafer substrate.

[0046] (3) Take sample A1, place it on a metal molybdenum support with a height of 6 mm, and then place it in an MPCVD device. Use a CH4 / H2 mixed gas with a volume ratio of 4:100 as the reaction gas, where the flow rate of H2 is 400 sccm, and the gas purity is 99.99%. Adjust the power and pressure to raise the temperature to 830°C, and grow a diamond layer on sample A1 for 50 hours. After slowly cooling to room temperature, take out sample C1. The MPCVD operating power and pressure are set to 4.1 kW and 12.4 kPa, respectively, and the cooling rate is controlled at 30°C / min. The thickness of the obtained diamond layer C1 is 180 μm.

[0047] (4) Take sample C1, polish the growth surface of diamond layer C1 to obtain sample D1, which is a silicon-diamond infrared composite window material.

[0048] The surface polishing step uses diamond powder with an average particle size of 2.0 μm as the polishing medium. The thickness of the diamond layer on sample D1 is 95 μm.

[0049] Example 2

[0050] (1) Take a silicon wafer with a size of Ф35 mm x 3 mm as the substrate for use. The average optical transmittance in the 3-5 μm band is 55%.

[0051] (2) Use diamond micro-powder suspension to uniformly rub the silicon substrate to obtain sample A2.

[0052] (3) Take sample A2, place it on a metal molybdenum support with a certain thickness, and then place it in an MPCVD device. Use a CH4 / H2 mixed gas with a certain ratio as the reaction gas. Adjust the power and pressure to raise the temperature to 880°C, and grow a diamond layer on sample A2 for 67 hours. After slowly cooling to room temperature, take out sample C2.

[0053] The height of the molybdenum support is 8 mm. The ratio of CH4 to H2 is 4:100, where the flow rate of H2 is 400 sccm. The gas purity is 99.99%. The MPCVD operating power and pressure are set to 3.5 kW and 12.25 kPa, respectively. The cooling rate is controlled at 20°C / min. The thickness of the obtained diamond layer is 213 μm.

[0054] (4) Take sample C2, polish the growth surface of the diamond to obtain sample D2, which is a silicon-diamond infrared composite window material.

[0055] The surface polishing step uses diamond powder with an average particle size of 2.0 μm as the polishing medium. The thickness of the diamond layer on sample D2 is 115 μm.

[0056] Example 3

[0057] (1) Take a silicon wafer with a size specification of Ф51mm x 4mm as a substrate for standby use. The average optical transmittance in the 3-5 μm band is 55%.

[0058] (2) Uniformly rub the silicon substrate with a diamond micro-powder suspension to obtain sample A3.

[0059] (3) Take sample A3, place it on a metal molybdenum holder of a certain thickness, and then place it together in an MPCVD device. Use a CH4 / H2 mixed gas with a certain ratio as the reaction gas. Adjust the power and gas pressure to raise the temperature to 950°C. Continue to grow for 63.5 hours to deposit a diamond layer on sample A3. Slowly lower the temperature to room temperature and then take it out to obtain sample C3.

[0060] Among them, the height of the molybdenum holder is 8mm; the ratio of CH4 to H2 is 3:100, in which the flow rate of H2 is 400sccm; the gas purity is 99.99%; the MPCVD operating power and gas pressure are set to 3.35kW and 12.2kPa, respectively; the cooling rate is controlled at 10°C / min; and the obtained diamond layer is 184μm thick.

[0061] (4) Take sample C3, polish the diamond growth surface to obtain sample D3, i.e., a silicon-diamond infrared composite window material.

[0062] Among them, the surface polishing step uses diamond powder with an average particle size of 2.0μm as the polishing medium; and the diamond layer on sample D3 is 117μm thick.

[0063] Comparative Example 1

[0064] (Note: Compared with the parameters of Example 2, only the optical-grade silicon substrate is replaced with a non-optical-grade silicon substrate)

[0065] (1) Take a silicon wafer with a size specification of Ф35mm x 3mm as a substrate for standby use.

[0066] (2) Uniformly rub the silicon substrate with a diamond micro-powder suspension to obtain sample A4.

[0067] (3) Take sample A4, place it on a metal molybdenum holder of a certain thickness, and then place it together in an MPCVD device. Use a CH4 / H2 mixed gas with a certain ratio as the reaction gas. Adjust the power and gas pressure to raise the temperature to 880°C. Continue to grow for 58 hours to deposit a diamond layer on sample A4. Slowly lower the temperature to room temperature and then take it out to obtain sample C4.

[0068] The molybdenum support has a height of 8 mm; the ratio of CH4 to H2 is 4:100, wherein the flow rate of H2 is 400 sccm; the gas purity is 99.99%; the MPCVD operating power and gas pressure are set to 3.5 kW and 12.25 kPa, respectively; the cooling rate is controlled to be 20 ℃ / min; and the obtained diamond layer has a thickness of 213 μm.

[0069] (4) Sample C4 is polished to obtain sample D4, i.e., a silicon-diamond infrared composite window material.

[0070] Further, the average particle size of the diamond powder used as the polishing medium in the surface polishing step is 2.0 μm; and the diamond layer on sample D4 has a thickness of 115 μm.

[0071] Comparative Example 2

[0072] (Note: Compared with the parameters of Example 2, only the optical-grade silicon substrate is replaced by sapphire)

[0073] 1) A sapphire piece with a size of Ф35 mm×3 mm is taken as a substrate and is ready for use.

[0074] 2) A diamond micro-powder suspension is used to uniformly rub the silicon substrate to obtain sample A5.

[0075] 3) Sample A5 is placed on a metal molybdenum support with a certain thickness, and then is placed in an MPCVD device. A certain ratio of CH4 / H2 mixed gas is used as a reaction gas. The temperature is increased to 880 ℃ by adjusting the power and gas pressure, and a diamond layer is deposited on sample A5 for 58 h. After slowly cooling to room temperature, sample C5 is obtained.

[0076] Further, the molybdenum support has a height of 8 mm; the ratio of CH4 to H2 is 4:100, wherein the flow rate of H2 is 400 sccm; the gas purity is 99.99%; the MPCVD operating power and gas pressure are set to 3.5 kW and 12.25 kPa, respectively; the cooling rate is controlled to be 20 ℃ / min; and the obtained diamond layer has a thickness of 213 μm.

[0077] 4) Sample C5 is polished to obtain sample D5, i.e., a sapphire-diamond infrared composite window material.

[0078] Further, the average particle size of the diamond powder used as the polishing medium in the surface polishing step is 2.0 μm; and the diamond layer on sample D5 has a thickness of 115 μm.

[0079] Performance analysis

[0080] The Raman spectra of the diamond layers on the surfaces of silicon-diamond infrared composite window samples C1, C2, C3, and C4 obtained in Examples 1, 2, and 3 of this invention, and Comparative Example 1, are as follows: Figure 2 As shown, this is the test result of the relationship between Raman shift and intensity. Figure 2 As shown in (a), the diamond layers obtained in Examples 1, 2, and 3 have very good crystal quality, with a characteristic peak (1332 cm⁻¹). -1 Clearly, without obvious other impurities, and with a narrow half-peak width, the sharper the Raman characteristic peak and the narrower the half-peak width, the better the diamond quality. Figure 2 As shown in (b), the diamond layer deposited on the non-optical grade silicon substrate has a larger half-peak width, indicating that its quality is poor.

[0081] The XRD patterns of silicon diamond infrared composite window samples D1, D2, D3, and D4 obtained in Examples 1, 2, and 3 of this invention and Comparative Example 1 are shown below. Figure 3 As shown in (a) and (b), the diffraction peaks of the diamond film (111), (220), and (311) are presented in the spectrum, and the diffraction peaks of the (111) crystal plane are stronger.

[0082] The specific transmittance of silicon diamond infrared composite window samples D1, D2, D3, and D4 obtained in Examples 1, 2, and 3 of this invention and Comparative Example 1 are as follows: Figure 4 As shown, the average transmittance of the three composite material windows deposited on optical-grade silicon wafers is 49% in the mid-infrared band (3–5 μm), while the transmittance of the composite material deposited on non-optical-grade silicon wafers is ~0%. This indicates that diamond deposited on optical-grade silicon wafers has excellent optical performance and is expected to be used as an infrared window.

[0083] To characterize the bonding strength of the diamond infrared composite window samples, thermal shock resistance tests were conducted. The specific methods and test results are shown in Table 1, obtained through rapid heating and cooling. Compared to control sample 2, i.e., the sapphire-diamond infrared composite window material with sapphire as the substrate, the silicon-diamond composite structures withstood the thermal shock tests without cracking or film detachment, while the sapphire-diamond composite structure cracked and the film detached. These results demonstrate that the composite structure samples provided by this invention possess excellent thermal shock resistance and excellent bonding performance.

[0084] Table 1. Film bonding performance of samples prepared in Examples 1-3 and Comparative Example 2 after thermal shock.

[0085]

[0086] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A silicon-diamond infrared composite window material, characterized in that, It includes an optical silicon wafer and a diamond film deposited on the surface of the optical silicon wafer, the thickness of which is 80–120 µm; The optical silicon wafer and diamond film are both used in the 3–5 μm wavelength band. The silicon diamond infrared composite window material is prepared by a method including the following steps: (1) Pre-treat the optical silicon wafer with diamond micro powder suspension for 5–10 min to create scratches on the surface of the optical silicon wafer; (2) Using the MPCVD method, with CH4 / H2 mixed gas as the reaction gas, a diamond layer is continuously grown on the surface of the optical silicon wafer obtained in step (1) for 50–80 h at a temperature of 800–950 °C. The diamond layer is then ground and polished to obtain a silicon diamond infrared composite window material.

2. The silicon-diamond infrared composite window material according to claim 1, characterized in that, The optical transmittance of the optical silicon wafer in the mid-infrared band is not less than 50%.

3. The silicon-diamond infrared composite window material according to claim 1, characterized in that, The optical silicon wafer has a size of not less than Φ25mm and a thickness of not less than 1mm.

4. The silicon-diamond infrared composite window material according to claim 2, characterized in that, The thickness of the optical silicon wafer is 3–5 mm.

5. The silicon-diamond infrared composite window material according to claim 1, characterized in that, Diamond film is used as the light incident medium, and optical silicon wafer is used as the light emitting medium.

6. The silicon-diamond infrared composite window material according to claim 1, characterized in that, In step (1), before pre-processing the optical silicon wafer, optical silicon wafers with a mid-wave infrared transmittance of not less than 50% are selected.

7. The silicon-diamond infrared composite window material according to claim 1, characterized in that, The volume ratio of CH4 to H2 is 2:100–4:100, with the flow rate of H2 being 300–600 sccm; the purity of both CH4 and H2 is not less than 99.99%.

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