Characterization of machined surface in semi-conductive SiC wafer subjected to micro-EDM drilling

Abstract

Semi-conductive silicon carbide (semi-SiC) wafers are essential in the semiconductor industry, but their high hardness and brittleness make traditional machining difficult. Electric discharge machining (EDM) is an alternative method for machining semi-SiC wafer. This study investigates the effects of discharge energy parameters, such as pulse-on time and peak current, on the surface and subsurface characteristics of semi-SiC wafers subjected to micro-EDM drilling. The machined surface and subsurface morphology and microstructure were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). SEM micrographs revealed the presence of craters, resolidified material, cracks, and micro-pores on the machined surface, influenced by the thermal energy generated during the EDM process. The material removal mechanisms identified include melting, vaporization, spalling, and oxidation. EDS analyses indicated a larger discharge energy led to an increase in carbon and oxygen concentrations on the machined surfaces, likely due to the decomposition of SiC and oxidation during EDM. XPS analysis identified the presence of graphite, SiO₂, Cu particles, Cu₂O, and CuO on the machined surface. TEM micrographs revealed three distinct regions in the subsurface, namely a recast layer, a heat-affected zone (HAZ), and the unaffected bulk SiC. These layers exhibited different microstructures, with the thickness of the recast layer and HAZ being dependent on the discharge energy. This study highlights the advantages of micro-EDM over other techniques, achieving a thin recast layer and minimal HAZ, thereby preserving the surface and subsurface integrity of the semi-SiC wafer.