Investigation on Material Removal Mechanisms in Photocatalysis-Assisted Chemical Mechanical Polishing of 4H–SiC Wafers

Photocatalysis-assisted chemical mechanical polishing, in which the photocatalysis oxidation and silica abrasives polishing are combined, is a novel finishing technique for 4H–SiC wafer. This paper characterizes the effect of pressure and abrasives on the MRR and surface quality and discusses mechanical and chemical interaction based three slurries that resulted in maximum material removal rate (1.18 μm/h) with PCMP slurry. The polished silicon carbide wafer was examined with atomic force microscope, transmission electron microscope and X-ray photoelectron spectroscopy for surface quality and material removal mechanism. The results show that an atomically smooth and flat 4H–SiC (0001) surface (Ra about 0.247 nm) was obtained by PCMP. The interface of crystal and amorphous layer of 4H–SiC wafer was flat without introducing crystallographic subsurface damage, and the atoms and lattice fringes of the crystal layer are arranged in regular order. The existence of a thin silicon oxycarbide layer, which are various forms of functional groups such as Si–C, Si–C–O, Si–O, Si4C4O4, C–O, and C = O, at the interface. And, it also demonstrates that the amorphous layer is composed of oxide layer (4–6 nm) and distorted layer. The silicon carbide surface is mechanically activated, oxidized and mechanically removed in turn, which is the main method of material removal.