Improving polishing efficiency of RB-SiC through femtosecond laser pretreatment

Abstract

It is a great technical challenge to precisely and efficiently polish RB-SiC substrates due to their two-phase structure and extreme hardness, especially for large-optics fabrication. Here, a simple laser pretreatment process is demonstrated for improving the polishing efficiency using femtosecond laser to modify the RB-SiC surface pre-coated with silicon powder. Material characterization and finite-element analyses reveal that the pre-coated surface is oxidized under femtosecond laser irradiation. As oxidation gradually penetrates deeper into the interface, the modified layer forms a bonding with the RB-SiC substrate. By optimizing laser scanning parameters to adjust the oxidation depth, a high-quality modified layer with stronger adhesion strength can be obtained. The approach is capable of delivering a modified layer that is easier to polish and tightly bonded to the RB-SiC substrate with an adhesion strength of 55.46 N. Thanks to the femtosecond laser modification, the surface roughness of the pretreated RB-SiC can be reduced to Sq 4.5 nm in just a few hours of polishing, which increases polishing efficiency over 3 times compared with direct abrasive polishing. Low requirements for substrate surface profile and simple operation make this laser pretreatment approach possible to be applied to more complex RB-SiC surfaces and significantly improve polishing efficiency.