Atomic-scale characterization of subsurface damage and structural changes of single-crystal silicon carbide subjected to electrical discharge machining

Single-crystal silicon carbide (SiC) is an important semiconductor material used in power electronics. Due to its high hardness and brittleness, SiC is very difficult to machine using mechanical methods. Electrical discharge machining (EDM) has recently garnered extensive research interest as a potential machining method for SiC. However, this technique induces severe subsurface damage on the workpiece. To date, mechanisms leading to EDM-induced subsurface damage in SiC have not been clarified. This study aims to investigate the atomic-scale subsurface damage in SiC induced by EDM using Raman spectroscopy and transmission electron microscopy (TEM). In cross-sectional TEM observations, three regions of subsurface damage were identified, namely, the re-solidified layers, heat-affected zones, and microcracks. It was found that SiC decomposed into silicon and carbon in the re-solidified layers, and the degree of decomposition depended on the discharge energy and workpiece polarity. The re-solidified layer was a mixture of crystalline/amorphous silicon, crystalline/amorphous carbon, and nano-crystalline SiC. The presence of an extremely thin graphite layer was observed in the re-solidified layer. The heat-affected zone remained crystalline but showed a different crystal structure distinct from that of the bulk.