Microstructural and comparative analysis for wire electric discharge machining on edge trimming of semi-insulating silicon carbide wafers

Semi-insulating silicon carbide (SI-SiC) wafer is a crucial third-generation semiconductor for high-power and high-frequency electronic devices. However, conventional mechanical edge trimming for this material is inefficient, inducing subsurface damage and severe tool wear. This study employed wire electric discharge machining (WEDM) with an assisting electrode (AE) technique to achieve precise radius trimming on single-crystal 4H SI-SiC wafers featuring high electrical resistivity (> 10 5 Ωcm). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the machined surface and subsurface characteristics. Microstructural analysis showed that the material removal mechanism involves a combination of melting, vaporization, thermal spalling, and oxidation. Energy-dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) analyses confirmed that the trimmed subsurface consists of three distinct zones: a recast layer, a heat-affected zone (HAZ) with lattice dislocations, and the unaffected single-crystal bulk material. Response surface method (RSM) demonstrates a clear trade-off where higher open voltage and pulse-on time accelerate material removal but reduce radius precision and increase surface roughness. Crucially, a comparative evaluation against micro-EDM drilling reveals that the lower discharge energy of traveling-wire WEDM trimming dramatically minimizes thermal damage, yielding a thinner recast layer and a smaller HAZ. These findings provide critical optimization pathways for preserving the microstructural and functional integrity of processed SI-SiC wafers.