Chinese semiconductor industry

Shanghai Institute of Optics and Mechanics has made progress in research on silicon carbide surface femtosecond laser modification to improve polishing efficiency​

　　Recently, the Center Laboratory of Precision Optical Manufacturing and Testing of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences has made progress in the research of femtosecond laser modification of silicon carbide surface to improve polishing efficiency. It is found that the surface modification layer with bonding strength of 55.46N can be obtained by modifying the surface of RB-SiC pre-coated with Si powder by femtosecond laser. And the surface of the modified RB-SiC can be polished for only 4.5 hours to obtain an optical surface with a surface roughness Sq of 4.45nm. Compared with direct grinding and polishing, the polishing efficiency is increased by more than 3 times. The research results expand the surface modification method of RB-SiC, and the controllability of the laser and the simplicity of the method make it applicable to the surface modification of RB-SiC with complex profiles. Relevant results were published in Applied Surface Science ("Applied Surface Science").

　　As a silicon carbide ceramic, RB-SiC has excellent performance and has become one of the best and most feasible materials for light-weight large-scale telescope optical components (especially large-size and complex-shaped mirrors). However, RB-SiC is a typical high-hardness, multi-phase material. When liquid Si reacts with C during sintering, 15%-30% of residual silicon remains in the green body. The difference in the polishing properties of these two materials will form micro-steps at the junction of the SiC phase and the Si phase components during the surface precision polishing process, which is prone to diffraction, which is not conducive to obtaining a high-quality polished surface, and will affect the subsequent polishing belt. Here comes the great challenge.

　　Aiming at the above problems, a femtosecond laser surface modification pretreatment method was proposed. Using femtosecond laser to modify the RB-SiC surface pre-coated with silicon powder can not only solve the problem caused by the difference in two-phase polishing performance. Surface scattering problem, and can effectively reduce the polishing difficulty of RB-SiC substrate and improve polishing efficiency. The research results show that the pre-coated Si powder on the surface of RB-SiC is oxidized under the action of femtosecond laser, and as the oxidation gradually penetrates into the interface, the modified layer forms a bond with the RB-SiC matrix. By optimizing the laser scanning parameters to adjust the oxidation depth, a high-quality modified layer with a bonding strength of 55.46N was obtained. Compared with the RB-SiC substrate, the modified layer is easier to polish, so that the surface roughness of the pretreated RB-SiC can be reduced to Sq4.5nm in just a few hours of polishing, and the abrasive polishing of the RB-SiC substrate Compared with that, the polishing efficiency has increased by more than 3 times. In addition, the method is simple to operate, has low requirements on the surface profile of the RB-SiC substrate, can be applied to more complex RB-SiC surfaces, and significantly improves the polishing efficiency.​