Super-smooth processing of CVD-SiC using combined electrolytic in-process dressing grinding and fixed softer-than-diamond abrasive grinding

Chemical vapor-deposited silicon carbide (CVD-SiC) is ideal for optical applications owing to its superior strength, thermal stability, and optical performance. However, chemical mechanical polishing (CMP) generates numerous surface steps, which hampers the application of CVD-SiC. This study proposes an innovative machining technology that combines an electrolytic in-process dressing grinding (preprocessing) and a fixed softer-than-diamond abrasive (FSTDA) grinding (finishing) process to achieve a super-smooth CVD-SiC surface while avoiding step formation. To this end, first, the characteristics of CVD-SiC substrates, including their surface morphology, composition, and crystal orientation, were analyzed. Subsequently, the finishing performances of three FSTDA grinding wheels (poly-CeO₂, conventional alumina, and poly-SiC) were evaluated using confocal laser scanning microscopy, with a focus on their effects on surface morphology and roughness. The results confirmed the effectiveness of fixed abrasive grinding in suppressing step formation during CVD-SiC finishing. Additionally, scanning electron microscopy was employed to investigate the wear characteristics of the abrasive grains before and after usage. The results reveal a strong correlation between abrasive hardness and surface quality. For comparison, CMP was applied to CVD-SiC under same preprocessing conditions, thereby confirming the superior step suppression and surface planarization of FSTDA grinding. Experimental results indicate that finishing with a conventional alumina grinding wheel achieved a flat, scratch-free surface, therefore outperforming CMP in both step suppression and surface planarization. Thus, this study establishes an efficient and reliable technological approach for achieving super-smooth CVD-SiC surfaces, thereby laying a foundation for their broader application in high-precision optical systems.