ECR plasma etching enhanced mechanical polishing CVD diamond

Use electron cyclotron resonance (ECR) plasma etching and mechanical polishing to polish chemical vapor deposition (CVD) diamond, use scanning electron microscope and Raman spectroscopy to observe and analyze the surface morphology and quality changes of diamond after etching and polishing And compared with pure mechanical polishing, the effect of plasma etching on subsequent mechanical polishing was studied. The result found that the amorphous carbon content of diamond is reduced to a certain extent after ECR plasma etching, and the etching process is on the diamond crystal surface. The formed loose surface is conducive to mechanical polishing, and the average roughness of the diamond surface decreases more quickly. Comparative experiments show that plasma etching has a more obvious enhancement effect on the polishing efficiency in the early stage of mechanical polishing. The roughness of diamond samples after ECR plasma etching is reduced from 7.284 to 1.054μm after 10 minutes of mechanical polishing, while the direct mechanical The surface roughness of diamond after polishing for 30 minutes is 1.133 μm. In the initial stage of mechanical polishing, the mechanical polishing efficiency after plasma etching is 3 times that of pure mechanical polishing. Finally, after three repeated etchings and mechanical polishing, the diamond surface roughness was reduced to 0.045 m.

Diamond combines excellent physical and chemical properties. It is recognized by many experts as the most promising engineering material in the 21st century. It has great development and application prospects and huge market value. Since Eversole used the chemical vapor deposition (CVD) method to artificially synthesize diamond in 1962, various CVD methods for manufacturing diamond have appeared one after another, mainly including hot filament CVD (HFCVD), microwave (MPCVD) and direct current plasma torch CVD (DC Plasma-jet CVD) method and so on. Nowadays, the surface roughness of synthetic diamond using these methods generally reaches tens of microns, while industrial applications such as thermal, optics, and microelectronics require diamond surface roughness to reach tens of nanometers or even higher. Therefore, the subsequent surface polishing treatment of diamond is very necessary.

Today, diamond polishing treatment methods mainly include mechanical polishing, laser polishing, thermochemical polishing, chemically assisted mechanical polishing, ion reactive etching and so on. The mechanical polishing cost is low, but its polishing efficiency is low. Although laser polishing has high polishing efficiency and can quickly reduce the surface roughness of diamond, it will cause greater damage to the diamond. Thermal chemical polishing and chemical-assisted mechanical polishing have lower costs, but the residues of chemical agents cause serious pollution to the diamond surface. ECR plasma etching belongs to ion reactive etching. In the preliminary work of the laboratory, a method of polishing large-area CVD diamond with ECR plasma was invented. It has the advantages of less pollution to the diamond surface and higher polishing efficiency, but generally It takes several hours to ten hours of polishing time, which increases the polishing cost. It can be seen from these that a single polishing method has certain defects. Therefore, under the premise of considering the polishing cost, polishing efficiency and diamond integrity, the vacuum technology network (http://www.chvacuum.com/) proposed a polishing method combining ECR plasma and mechanical polishing. This article uses a combination of ECR plasma etching and mechanical polishing to polish CVD diamond. Compared with pure mechanical polishing CVD diamond, it is found that adding ECR plasma etching in mechanical polishing can significantly enhance the efficiency of mechanical polishing, especially in In the early stage of mechanical polishing, the combined polishing efficiency is 3 times that of mechanical polishing.

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The sample preparation device is a microwave plasma device with a compressed waveguide resonant cavity structure made by the laboratory. The working gas is methane and hydrogen, and a polycrystalline diamond film sample is prepared by depositing on a molybdenum substrate. The following are the specific process parameters: methane and hydrogen flow rates are 2 and 200mL/min (standard state), working pressure is 18kPa, microwave power is 800W, substrate temperature is 1000℃, and the film thickness is 988&mu after 140h of deposition; m, a diamond film with a diameter of 22mm, and the surface thickness and morphology are relatively uniform. Its surface morphology is as shown. A roughness meter was used to test the diamond film, and the initial average surface roughness Ra was 7.284μm. Use the HQ-103 laser precision cutting machine to cut the diamond film to obtain a series of 3mm×3mm diamond film.

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The etching of CVD diamond film is carried out in the self-designed ECR plasma system. For the magnetic field configuration used, the use of a convergent magnetic field configuration is beneficial to confine the plasma in the cavity, thereby increasing the plasma density in the cavity. The working gas is oxygen, and the magnetoelectric heating method is used to make the plasma ion temperature reach more than ten electron volts, which is higher than the general ECR plasma, which enhances the etching effect. Mechanical polishing adopts UNIPOL-802 mechanical polishing machine. Sample 1 uses pure mechanical polishing; Sample 2 uses ECR plasma etching for 1 hour and then mechanical polishing for 30 minutes. This process is repeated several times to obtain the polishing result. The TR200 roughness meter was used to measure the variation of the average roughness Ra of the CVD diamond surface during the polishing process. During the mechanical polishing process, the polishing load, polishing disk, and polishing speed remain unchanged.

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This paper studies the mechanical polishing of CVD diamond after ECR plasma etching, and compares it with the mechanical polishing of unetched CVD diamond. The result shows that ECR plasma etching can significantly improve the mechanical polishing efficiency. This result is also more obvious in the initial stage of mechanical polishing. The reason is that etching removes a part of the non-diamond phase in the diamond sheet, and also produces a defect layer, which makes the top area of the surface loose. In the initial stage of polishing, the defect layer area is quickly removed, resulting in a higher polishing efficiency, and then the polishing efficiency begins to approach that of pure mechanical polishing. Therefore, ECR plasma etching can greatly improve the efficiency of CVD diamond mechanical polishing in the early stage of polishing. Finally, after three repeated etchings and mechanical polishing, the diamond surface roughness dropped to 0.045 m.

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Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.