A method of producing a diamond material for an optical window

Abstract

The application belongs to the technical field of diamond material preparation, and discloses a preparation method of diamond material for optical windows. The steps are as follows: S1, preparing an optical-grade polycrystalline diamond film, and then cutting, grinding, polishing and cleaning the film; S2, etching an optical anti-reflection microstructure layer on the surface of the diamond film prepared in step S1 by ICP, and cleaning and drying the film after etching, and then placing the film in a vacuum dish for standby; S3, using a magnetron sputtering technology to coat a rare earth oxide anti-reflection film on the surface of the optical anti-reflection microstructure layer of the diamond film prepared in step S2, and setting the thickness of the coated rare earth oxide anti-reflection film according to the refractive index of the diamond film with the optical anti-reflection microstructure layer prepared in step S2 and the theory of optical anti-reflection film; the magnetron sputtering technology is a combination of pre-coating and variable-speed coating. The diamond material prepared by the application has high infrared transmittance and excellent thermal stability, and is particularly suitable for application requirements in the field of infrared windows.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diamond material preparation, and particularly relates to a preparation method of diamond material for optical windows. BACKGROUND

[0002] The long-wave infrared window located at the front end of a hypersonic aircraft is one of the key components of an infrared imaging seeker, which not only needs to withstand the load impact of air dynamics, but also needs to resist the erosion and damage of space particles to the optical infrared imaging system. Therefore, a material with excellent optical transmittance, high strength, high temperature resistance and excellent chemical stability needs to be selected. At present, gallium arsenide (GaAs), gallium phosphide (GaP), zinc sulfide (ZnS), zinc selenide (ZnSe) and diamond are commonly used materials for infrared windows, but with the rapid development of infrared technology, GaAs, GaP, ZnS and ZnSe are difficult to meet the requirements of harsh service environment due to low strength, which further leads to the failure of infrared target attack. Diamond has the advantages of wide infrared transmittance band (0.25-3 μm, 5-100 μm), the highest thermal conductivity (2000 W / m·K), good chemical stability and small thermal expansion coefficient, and becomes the best choice for infrared window materials.

[0003] Optical grade chemical vapor deposition (CVD) self-supporting diamond polycrystalline film can almost match high-quality natural single crystal diamond in all performance, but due to the properties of diamond material, the theoretical transmittance of single crystal in the long-wave infrared band is only 71%, and that of polycrystal is lower than the theoretical value. At present, the main ways to improve the performance of diamond film include adding surface microstructure and plating high-performance film. Based on the bionic fly-eye, an optical anti-reflection microstructure is obtained on the surface of diamond by inductively coupled plasma (ICP) etching, so as to improve the infrared transmittance of diamond. The simulation calculation of the fly-eye microstructure prepared on the surface of diamond can improve the infrared transmittance of diamond to 85%, but the microstructure cannot improve the thermal shock resistance of diamond film. Plating of rare earth oxide anti-reflection film with high thermal stability and excellent optical performance can realize the infrared transmittance of diamond up to 90%. Due to the limitation of polycrystalline diamond film itself, it is difficult to break through the theoretical infrared transmittance of 71%, and more can only ensure the infrared transmittance of polycrystalline diamond film of 68%. Therefore, the combination of the above microstructure and anti-reflection film can not only solve the optical limitation problem, but also realize high infrared optical transmittance.

[0004] Patent CN 107219722 A proposes a preparation method of high-transmittance surface microstructure and a prepared microstructure. The surface microstructure is designed on the optical component surface by nano-imprinting, thereby overcoming the influence of reflection caused by the difference in surface refractive index on the performance of the device. Patent CN 210720786 U designs an optical anti-reflection film with a multi-layer film structure, which adopts a multi-layer transmission structure, grooves, and light guide holes and other multi-structure designs to achieve the wear resistance and service life of optical materials. However, the multi-layer transmission film structure has problems such as poor refractive index matching and interface stress, which leads to the peeling of the anti-reflection film and the failure of the anti-reflection effect. Patent CN 114488362 A proposes a sapphire window with double-sided anti-reflection microstructure and a preparation method thereof, which points out that the anti-reflection method of preparing a microstructure array on both sides of sapphire or on one side, or a microstructure array on one side and an optical thin film on the back, can solve the problems of corrosion resistance, high temperature resistance, and improvement of sapphire transmittance.

[0005] In the currently reported anti-reflection structures of optical windows, whether it is a multi-layer anti-reflection film or a microstructure, although it can achieve optical material anti-reflection, it still has problems such as not changing the intrinsic properties of diamond materials and the phonon scattering problem of the concave-convex surface of the microstructure in the light field. SUMMARY

[0006] In order to overcome the deficiencies in the prior art, the purpose of the present application is to provide a preparation method of diamond material for optical window, which can greatly improve the phonon transmission in the light field and improve the infrared optical transmittance.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of diamond material for optical window, characterized by the following preparation steps:

[0009] S1, preparing an optical-grade polycrystalline diamond film, and then cutting, grinding, polishing and cleaning it;

[0010] S2, ICP etching an optical anti-reflection microstructure layer on the surface of the diamond film prepared in step S1, and then cleaning, drying, and placing it in a vacuum dish for standby after etching;

[0011] S3, using a magnetron sputtering technology to coat a rare earth oxide anti-reflection film on the surface of the optical anti-reflection microstructure layer of the diamond film prepared in step S2, and setting the thickness of the coated rare earth oxide anti-reflection film according to the refractive index of the diamond film with the optical anti-reflection microstructure layer prepared in step S2 and the theory of optical anti-reflection film, to obtain the diamond material for optical window of the present application; the magnetron sputtering technology is a combination of pre-coating and variable-speed coating.

[0012] Preferably, in step S1, the thickness of the optical-grade polycrystalline diamond film is controlled to be 1-2 mm, and the optical-grade polycrystalline diamond film can be prepared by any prior art, including but not limited to the preparation of the optical-grade polycrystalline diamond film by the microwave plasma chemical vapor deposition method, the deposition temperature is 800-900℃, and the deposition rate is 1-5 μm / h.

[0013] Preferably, in step S1, the surface roughness Ra of the diamond film after grinding and polishing is 1-2 nm.

[0014] Preferably, in step S2, the thickness of the optical anti-reflection microstructure layer is controlled to be 50-100 nm, and the parameters of ICP etching are set as follows: etching ICP power 700-1000 W, radio frequency power 40-80 W, etching oxygen flow rate 3-6 sccm, etching argon flow rate 8-12 sccm, etching sulfur hexafluoride flow rate 20-40 sccm, etching pressure 1-2 Pa, and etching rate 10-50 nm / min.

[0015] Preferably, in step S3, the pre-deposition process is as follows: the target sputtering power (marked as 1# target sputtering power) is 100-200 W, the oxygen flow rate is 1-3 sccm, the Ar flow rate is 35-50 sccm, and the sputtering time is 10-30 min; then the target shutter is closed, and 1-2 min is waited, and the variable-speed deposition is started; the variable-speed deposition process is as follows: the target sputtering power (marked as 2# target sputtering power) is increased to 150-180 W, the target shutter is opened, the sputtering time is 20-25 min, then the target shutter is closed, the target sputtering power (marked as 3# target sputtering power) is reduced to 120-150 W, and then the target shutter is opened until the sputtering is completed; during the whole pre-deposition process and the variable-speed deposition process, the oxygen flow rate and the Ar flow rate are kept consistent, and 3# target sputtering power < 1# target sputtering power < 2# target sputtering power.

[0016] Preferably, in step S3, the rare earth oxide anti-reflection film is an erbium oxide anti-reflection film, a yttrium oxide anti-reflection film, a lanthanum oxide anti-reflection film, or a rare earth element-doped other optical oxide film.

[0017] Preferably, in step S3, the thickness of the pre-deposited rare earth oxide anti-reflection film is controlled to be 50-100 nm.

[0018] The optical anti-reflection microstructure layer in the present application refers to the convex and concave surface of the diamond film after ICP etching, and the optical anti-reflection refers to the reduction of optical reflection.

[0019] The application adopts a combination of pre-plating and variable-speed plating to obtain a rare earth oxide anti-reflection film with nanocrystalline grain size on the surface of an optical anti-reflection microstructure layer, wherein the pre-plating process is to increase the nucleation area of the anti-reflection film on the microstructure surface and provide high nucleation density for the growth of the subsequent film, and the variable-speed plating process is based on the growth of the rare earth oxide film crystal nucleus on the surface of the pre-plated diamond film to ensure the integrity and uniformity of the nanocrystalline structure of the rare earth oxide anti-reflection film.

[0020] The key of the implementation process of the application is that (i) the inductively coupled plasma etching (ICP) optical anti-reflection microstructure must meet a high degree of consistency, and the etched surface should not have a large area of carbonization, at the same time, the optical anti-reflection microstructure avoids the position of the large-angle grain boundary to reduce the further expansion of the grain boundary defects and the absorption loss of the optical field; (ii) the application adopts a combination of pre-plating and variable-speed plating to increase the nucleation surface area of the convex and concave surface of the optical anti-reflection microstructure, increase the nucleation density of the anti-reflection film, ensure the thickness uniformity of the nanocrystalline structure of the rare earth oxide anti-reflection film, reduce the high phonon scattering in the diamond microstructure anti-reflection film optical field due to the thickness difference, and improve the CVD diamond infrared transmittance.

[0021] Advantages:

[0022] (1) By designing the diamond film surface optical anti-reflection microstructure and plating the rare earth oxide anti-reflection film, the optical field phonon transmittance can be greatly improved, and the infrared optical transmittance can be improved;

[0023] (2) The diamond material prepared by the application has high infrared transmittance and excellent thermal stability, and can be directly used as an infrared window material in the far infrared 8~12 μm wave band, solving the poor low infrared transmittance and thermal stability of the diamond infrared window material in the atmospheric environment, and realizing the diversified use of the diamond infrared window material in harsh environments. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 : The flowchart of the preparation method of the application;

[0025] Figure 2 : The infrared transmittance test results of the polycrystalline diamond film prepared in step S1, the diamond film with an optical anti-reflection microstructure layer prepared in step S2, and the diamond material prepared in S3 of Example 1. DETAILED DESCRIPTION

[0026] In order to make the application clearer and more explicit, the application will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0027] Example 1

[0028] A method for preparing a diamond material for an optical window, the preparation steps being as follows:

[0029] S1, preparing an optical-grade polycrystalline diamond film by a microwave plasma chemical vapor deposition method: using a 2-inch single crystal silicon as a deposition substrate material, hetero-epitaxially growing a CVD polycrystalline film, the deposition parameters mainly including: a deposition temperature of 800 DEG C, a methane / hydrogen ratio of 300 / 15 (flow rate ratio), a power of 3900 W, a deposition rate of 2 μm / h, a deposition time length of 500 h, and then removing the silicon substrate by using a hydrogen fluoride reagent to obtain a 1.0 mm-thick polycrystalline diamond film, as shown in Figure 1 (a); then cutting, grinding, polishing (to a surface roughness Ra of 1 nm) and cleaning the polycrystalline diamond film;

[0030] S2, etching an optical anti-reflection microstructure layer on the surface of the diamond film prepared in step S1 by using an inductively coupled plasma (ICP) technology, the ICP etching power being 900 W, the radio frequency power being 70 W, the etching oxygen flow rate being 4 sccm, the argon flow rate being 10 sccm, the sulfur hexafluoride flow rate being 32 sccm, the etching pressure being 1.4 Pa, the etching rate being 15 nm / min, and the etching thickness being 60 nm, as shown in Figure 1 (b); after the etching is completed, sequentially cleaning by using acid washing (nitric acid and sulfuric acid), alcohol and acetone to remove part of residual carbonized graphite on the surface due to etching, then transferring to a drying box for 200 DEG C heat preservation for 60 min, and after the end, timely transferring into a vacuum tray for standby;

[0031] S3, transferring the diamond film with the optical anti-reflection microstructure layer prepared in step S2 into a multifunctional magnetron sputtering device, vacuumizing to below 2*10 -4 Pa, then heating the deposition table, the heating temperature being 400 DEG C, and then coating a rare earth oxide anti-reflection film on the surface of the optical anti-reflection microstructure layer: based on the optical requirement design of the infrared optical anti-reflection film thickness, first coating a 50 nm-thick rare earth oxide film on the diamond film with the optical anti-reflection microstructure layer, the pre-coating process being: a target sputtering power of 140 W, an oxygen flux of 1 sccm, an Ar gas flux of 40 sccm, and a coating time of 10 min; then closing the target shutter, waiting for 1 min, and starting variable-speed coating; the variable-speed coating process being: increasing the target sputtering power to 160 W, opening the target shutter, an oxygen flux of 1 sccm, an Ar gas flux of 40 sccm, sputtering for 20 min, then closing the target shutter, reducing the target sputtering power to 120 W, and then opening the target shutter, an oxygen flux of 1 sccm, an Ar gas flux of 40 sccm, until the sputtering is completed, to obtain the diamond material for the optical window (the diamond with a microstructure and an oxide target anti-reflection film on the surface) of the present application, as shown in Figure 1(c) shown.

[0032] The infrared transmittance of the polycrystalline diamond film prepared in step S1, the diamond film with the optical anti-reflection microstructure layer prepared in step S2 and the diamond material prepared in step S3 in the far infrared waveband (8-12 μm) was calculated by using optical simulation software, and the test results are shown in Figure 2 As shown in (a), (b) and (c), the infrared transmittance of the polycrystalline diamond film (a) prepared in step S1 is 65%, the infrared transmittance of the diamond film with the optical anti-reflection microstructure layer (b) prepared in step S2 is 82.5%, and the infrared transmittance of the diamond material (c) prepared in step S3 is 97.5%.

[0033] Example 2

[0034] A preparation method of a diamond material for an optical window, the preparation steps are as follows:

[0035] S1, preparing an optical-grade polycrystalline diamond film by using a microwave plasma chemical vapor deposition method: using a 2-inch single crystal silicon as a deposition substrate material, heteroepitaxially growing a CVD polycrystalline film, the deposition parameters mainly include: a deposition temperature of 820 ℃, a methane / hydrogen ratio of 300 / 15 (flow rate ratio), a power of 4100 W, a deposition rate of 2.5 μm / h, a deposition time of 500 h, and then removing the silicon substrate by using a hydrogen fluoride reagent to obtain a 1.0 mm-thick polycrystalline diamond film, as shown in Figure 1 (a); and then cutting, grinding, polishing (to a surface roughness Ra of 1 nm) and cleaning the polycrystalline diamond film;

[0036] S2, etching an optical anti-reflection microstructure layer on the surface of the diamond film prepared in step S1 by using an inductively coupled plasma (ICP) technology, the ICP etching power is 800 W, the radio frequency power is 70 W, the etching oxygen flow rate is 6 sccm, the argon flow rate is 11 sccm, the sulfur hexafluoride flow rate is 25 sccm, the etching pressure is 1.8 Pa, the etching rate is 30 nm / min, and the etching thickness is 70 nm, as shown in Figure 1 (b); after etching, sequentially cleaning by using acid washing (nitric acid and sulfuric acid), alcohol and acetone to remove part of the residual carbonized graphite on the surface due to etching, and then transferring to a drying box for 200 ℃ heat preservation for 60 min, and then timely transferring into a vacuum tray for standby;

[0037] S3, transferring the diamond film with the optical anti-reflection microstructure layer prepared in step S2 into a multifunctional magnetron sputtering device, and vacuumizing to 2×10 -4Pa, the deposition table is heated again, the heating temperature is 400 DEG C, and then a rare earth oxide antireflection film is plated on the surface of the optical antireflection microstructure layer: based on the optical requirements of the thickness of the infrared optical antireflection film layer, a 70 nm thick rare earth oxide film is first pre-plated on the diamond film with the optical antireflection microstructure layer, the pre-plating process is as follows: the target sputtering power of the rare earth element is 160 W, the oxygen flux is 2 sccm, the Ar gas flux is 35 sccm, and the plating time is 8 min; then the rare earth target shutter is closed, and 2 min is waited, and then variable speed plating is started; the variable speed plating process is as follows: the rare earth target sputtering power is increased to 170 W, the rare earth target shutter is opened, the oxygen flux is 2 sccm, the Ar gas flux is 35 sccm, and sputtering is performed for 25 min, then the rare earth target shutter is closed, the rare earth target sputtering power is reduced to 130 W, the rare earth target shutter is opened again, the oxygen flux is 2 sccm, the Ar gas flux is 35 sccm, and sputtering is performed until the end, thereby obtaining the diamond material for optical windows (diamond with a microstructure and an oxide antireflection film on the surface) of the present application, as shown in Figure 1 (c) shown.

Claims

1. A method for preparing a diamond material for optical windows, characterized in that, The preparation steps are as follows: S1. Prepare an optical-grade polycrystalline diamond film, and then cut, grind, polish and clean it; S2. ICP etching of the optical antireflection microstructure layer on the surface of the diamond film prepared in step S1. After etching, clean and dry the film and place it in a vacuum dish for later use. S3. Using magnetron sputtering technology, a rare earth oxide antireflective film is deposited on the surface of the optical antireflective microstructure layer of the diamond film prepared in step S2 to obtain diamond material for optical windows. The magnetron sputtering technology combines pre-deposition and variable-speed deposition. The pre-deposition process is as follows: target sputtering power 100-200 W, oxygen flux 1-3 sccm, Ar gas flux 35-50 sccm, sputtering time 10-30 min; then the target baffle is closed, wait 1-2 min, and start variable-speed deposition. The variable-speed deposition process is as follows: increase the target sputtering power to 150-180 W, open the target baffle, sputtering time 20-25 min, then close the target baffle, reduce the target sputtering power to 120-150 W, and then open the target baffle again until sputtering is completed. Throughout the pre-deposition and variable-speed deposition processes, the oxygen flux and Ar gas flux remain consistent.

2. The method for preparing diamond material for optical windows as described in claim 1, characterized in that: In step S1, the thickness of the optical-grade polycrystalline diamond film is controlled at 1-2 mm. The optical-grade polycrystalline diamond film is prepared by microwave plasma chemical vapor deposition at a deposition temperature of 800-900℃ and a deposition rate of 1-5 μm / h.

3. The method for preparing diamond material for optical windows as described in claim 1, characterized in that: In step S1, the surface roughness Ra of the diamond film after grinding and polishing is 1-2 nm.

4. The method for preparing diamond material for optical windows as described in claim 1, characterized in that: In step S2, the thickness of the optical antireflective microstructure layer is controlled at 50-100 nm, and the parameters for ICP etching are set as follows: etching ICP power 700-1000 W, radio frequency power 40-80 W, etching oxygen flow rate 3-6 sccm, argon flow rate 8-12 sccm, sulfur hexafluoride flow rate 20-40 sccm, etching pressure 1-2 Pa, and etching rate 10-50 nm / min.

5. The method for preparing diamond material for optical windows as described in claim 1, characterized in that: In step S3, the rare earth oxide antireflection film is an erbium oxide antireflection film, a yttrium oxide antireflection film, a lanthanum oxide antireflection film, or other optical oxide films doped with rare earth elements.

6. The method for preparing diamond material for optical windows as described in claim 1, characterized in that: In step S3, the thickness of the pre-deposited rare earth oxide antireflection film is controlled at 50-100 nm.

Images