A method for preparing a SiC substrate surface modification layer

Abstract

The present invention belongs to the field of thin film deposition technology, and specifically relates to a novel preparation technology of SiC substrate surface modification layer. Different from the current mainstream magnetron sputtering technology for preparing SiC substrate modification layer, the present invention uses radio frequency ion beam sputtering technology. The main principle is to use a high-purity single crystal silicon target as the raw material. Under vacuum, a pollution-free radio frequency ion source is used to emit a high-energy ion beam to bombard the silicon target. When the energy of the bombarding particles is greater than the work function of the material, Si atoms are sputtered out of the target surface and deposited on the SiC substrate surface with extremely high momentum, eventually forming a modified layer. This preparation technology can deposit a very thick Si modification layer (more than 25um), and the prepared Si modification layer crystal form is an isotropic amorphous state with excellent polishability. The embodiment obtains a surface roughness of 0.15nm.

Description

Technical Field

[0001] The invention belongs to the technical field of thin film deposition, and in particular relates to a novel preparation technology of a SiC substrate surface modification layer. Background Art

[0002] SiC material has excellent properties such as high specific stiffness, high thermal conductivity, low thermal expansion coefficient and low density. It is an ideal material for space reflective optical elements and is widely used in various space payloads. When preparing the reaction-sintered SiC substrate used for space payloads, it is necessary to infiltrate Si material into SiC, resulting in the SiC substrate actually having two components - Si and SiC. For the same polishing process, it is difficult to achieve the same removal speed for Si and SiC. The removal speed of Si is fast, while that of SiC is extremely slow. Therefore, the polishing process will inevitably cause steps or even holes to form at the boundary of the two components. Therefore, it is extremely difficult to form an ultra-smooth optical surface on the polished SiC surface. This requires the SiC surface to be modified into a single-component surface so that the subsequent optical polishing can reach the level of precision optics.

[0003] The surface modification of SiC substrate is to deposit a dense, thick and well-bonded modified layer on its surface to cover the defect holes of the original substrate. The modified layer must also have good polishability. After deposition, the modified layer is precisely optically polished to achieve the purpose of obtaining a precise optical surface. At present, the mainstream technology at home and abroad is to deposit Si modified layers. The direction of the modified layer technology is low stress, high density, high bonding force and large thickness. Among them, low stress ensures that the modified layer has less stress release during the polishing process, which is more conducive to processing; high density makes the surface roughness smaller and the defects less after polishing; high bonding force is the basic guarantee of polishability; large thickness can provide a larger processing allowance for optical polishing, which is conducive to the manufacture of more complex optical surfaces.

[0004] The most reported technologies for preparing SiC surface modification layers are electron beam evaporation and magnetron sputtering. For example, Chinese patent CN201010614356.6 uses electron beam evaporation technology to prepare Si modification layers. However, even if electron beam evaporation technology uses high-energy Ar ions for auxiliary deposition, it still requires the manufacture of a buffer layer, which has a complex process, relatively weak bonding force, and limited thickness of the modification layer. At present, electron beam evaporation technology is not the mainstream technology for SiC surface modification.

[0005] At present, magnetron sputtering technology is the mainstream of SiC surface modification technology. CN201410833359.7 introduces in detail a method of sputtering a Si modified layer using magnetron sputtering technology. This technology overcomes the shortcomings of the complex process of electron beam evaporation technology, and directly deposits a deposition layer with a thickness of up to 25um on the SiC substrate, with good bonding force and good machinability. The paper published by its team shows that its structure is a polycrystalline structure, and a surface roughness of the order of 0.9nm is obtained after polishing. However, magnetron sputtering also has two obvious limitations: first, it is difficult to continue to thicken the modified layer, and currently 25um is the thickest thickness reported; second, it is difficult to obtain an ultra-smooth surface below 0.3nm after polishing the polycrystalline structure.

[0006] In view of this situation, we need to propose the use of ion beam sputtering technology to prepare a Si modified layer on the SiC surface to obtain a smoother and more complex ultra-precision optical surface. Summary of the invention

[0007] The purpose of the present invention is to obtain a thicker SiC surface modification layer which is more conducive to polishing an ultra-smooth surface.

[0008] The novel SiC substrate surface modification layer preparation technology of the present invention adopts the following basic technical route:

[0009] A. Use Si target (single crystal silicon or polycrystalline silicon) as the material source;

[0010] B. Use a radio frequency ion source as a sputtering energy source to bombard the Si target, bombard Si atoms out of the target, and deposit them on the surface of the SiC substrate;

[0011] C. Use a radio frequency ion source to clean the surface of the SiC substrate;

[0012] D. The ion source uses a cathode-free radio frequency neutralizer as the electron emission source;

[0013] The present invention discloses a novel SiC substrate surface modification layer preparation technology, which has the following process:

[0014] A. Process 1: Prepare coating conditions; weld and bind the Si target to the water-cooled back plate, and install the water-cooled back plate into the coating machine; clean the surface of the SiC substrate workpiece, fix it on the workpiece plate of the coating machine, evacuate, heat and bake to the background vacuum;

[0015] B. Process 2: SiC substrate surface cleaning: the cleaning ion source is filled with working gas, and after radio frequency discharge, the ion source is pulled out to bombard the SiC substrate surface;

[0016] C. Process three: Si modified layer deposition; the sputtering ion source is filled with working gas, and after radio frequency discharge, the ion source is pulled out to bombard the surface of the Si target material, so that Si is deposited on the surface of the SiC substrate at a stable deposition rate, and finally a Si modified layer is obtained.

[0017] The present invention discloses a novel SiC substrate surface modification layer preparation technology, the process of which is mainly characterized by:

[0018] A. The background vacuum described in process 1 is 4×10 -4 Pa-2×10 -5 Pa;

[0019] B. The heating and baking temperature described in process 1 is 60°C-120°C;

[0020] C. The target material described in process 1 is a single crystal silicon or polycrystalline silicon target material;

[0021] D. The working gas described in process 2 is Ar gas, with a maximum concentration of 15 sccm-25 sccm.

[0022] E. The ion beam voltage described in process 2 is about 100V-400V, and the current is about 100mA-400mA.

[0023] F. The cleaning time described in process 2 is about 100s-600s.

[0024] G. The working gas described in process three is Ar, Kr or Xe gas, and the gas filling amount is about 15sccm-30sccm.

[0025] H. The ion beam voltage described in process 3 is about 900V-1450V, and the current is about 500mA-800mA.

[0026] I. The stable speed described in process 3 is 0.15nm / s-0.5nm / s.

[0027] J. The thickness of the modified layer described in process 3 can reach a range of 10um-50um. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 SiC substrate sample

[0029] Figure 2 Coating equipment diagram

[0030] Figure 3 XRD pattern

[0031] Figure 4 Transmission spectrum test to determine film thickness

[0032] Figure 5 Roughness of the surface modification layer after polishing. DETAILED DESCRIPTION

[0033] The following examples are specific embodiments of the present invention and are only used to illustrate the present invention, rather than to limit the present invention.

[0034] Example: Preparation of SiC thick surface modification layer (50um) and subsequent polishing effect

[0035] Step 1: Preparation before coating

[0036] This example uses a 5N grade high purity single crystal silicon target, which is bound to the water-cooled target back plate of the equipment. A 50 mm diameter reaction sintered SiC is used as the surface modified sample ( Figure 1 ). The coating equipment uses a dual ion beam sputtering coating machine, in which the main ion source is used to sputter Si, and the auxiliary ion source is used to clean the workpiece surface. Both ion sources are three-grid radio frequency ion sources. The internal settings of the equipment are as follows: Figure 2 .

[0037] After the SiC substrate is cleaned with an environmentally friendly wiper, it is loaded into the equipment, vacuumed, and heated to 80°C. Step 2: Ion cleaning of the SiC surface

[0038] When the vacuum reaches 5×10 -5 After Pa, the auxiliary ion source was filled with 15 sccm of Ar gas. After RF ignition, the ion beam voltage was set to 200 V and the beam current was 200 mA. Then the ion beam was extracted to bombard the surface of the SiC workpiece for 300 s to remove contamination and enhance the bonding force.

[0039] Step 3: Preparation of modified layer

[0040] The main ion source was filled with Kr gas at a flow rate of 25 sccm. After the ion source was ignited by radio frequency, the ion beam voltage was set to 1350 V, the beam current was set to 500 mA, the deposition rate was set to 0.34 nm / s, and the coating thickness was set to 50 microns. Finally, the coating was completed.

[0041] After plating, the performance of the modified layer is characterized by:

[0042] 1. Phase determination

[0043] Figure 3 From the XRD spectrum, it can be seen that the Si modified layer prepared by the preparation technology involved in the present invention is completely different from the reported Si modified layer deposited by magnetron sputtering, and is in an isotropic amorphous state, which means that there is no problem in the polishing process caused by thin film crystallization.

[0044] 2. Thickness measurement

[0045] The transmission spectrum at 2500nm-1500nm was obtained by using the accompanying coating film deposited on the glass. The thickness was calculated to be 48.321um ( Figure 4 ).

[0046] 3. Roughness test after polishing

[0047] After polishing, an ultra-smooth surface with a thickness better than 0.15nm was obtained. Figure 5 ), indicating that the SiC surface modification layer prepared by the present invention has excellent polishability.

Claims

1. A method for preparing a surface modification layer of a SiC substrate, characterized in that: The following basic technical routes are adopted: A) Use high-purity single crystal silicon target as the material source; B) Using a radio frequency ion source as a sputtering energy source to bombard a Si target, bombarding Si atoms out of the target and depositing them on the surface of the SiC substrate; C) Using a radio frequency ion source to clean the surface of the SiC substrate; D) The ion source uses a cathode-less radio frequency neutralizer as the electron emission source; The preparation process of the SiC substrate surface modification layer is as follows: Process 1: Preparation of coating conditions; welding and binding the Si target to the water-cooled back plate, and installing the water-cooled back plate into the coating machine; cleaning the surface of the SiC substrate workpiece, fixing it on the workpiece plate of the coating machine, evacuating, heating and baking to the background vacuum; Process 2: SiC substrate surface cleaning; the cleaning ion source is filled with working gas, and after radio frequency discharge, the ion source is pulled out to bombard the SiC substrate surface; Process three: Si modified layer deposition; the sputtering ion source is filled with working gas, and after radio frequency discharge, the ion source is pulled out to bombard the surface of the Si target material, so that Si is deposited on the surface of the SiC substrate at a stable deposition rate, and finally a Si modified layer is obtained; In process three, the ion beam voltage is 900V-1450V and the current is 500mA-800mA; The deposition rate described in process 3 is 0.15nm / s-0.5nm / s; The final thickness of the Si modified layer can reach a range of 10 μm to 50 μm.

2. The method for preparing the surface modification layer of the SiC substrate according to claim 1, characterized in that: The background vacuum in process 1 is 4×10 -4 Pa-2×10 -5 Pa; The heating and baking temperature described in process 1 is 60°C-120°C.

3. The method for preparing the surface modification layer of the SiC substrate according to claim 1, characterized in that: The working gas in process 2 is Ar gas, and the filling amount is 15sccm-25sccm; The ion beam voltage in process 2 is 100V-400V, and the current is 100mA-400mA; The cleaning time described in process 2 is 100s-600s.

4. The method for preparing the surface modification layer of the SiC substrate according to claim 1, characterized in that: The working gas described in process three is one or more of Ar, Kr or Xe gases, and the gas filling amount is 15sccm-30sccm.

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