Atomic-level surface formation of large-size SiC substrates by chemical mechanical polishing: Interfacial chemistry and removal mechanism

Abstract

Large-size SiC substrates are essential for next-generation power and high-frequency electronic devices, but achieving atomic-level surfaces with effective material removal remains challenging because of their high hardness and chemical inertness. In this work, a CeO₂-based fine chemical mechanical polishing slurry was developed for high-quality surface formation of 8-inch 4H-SiC substrates through component screening, orthogonal optimization, surface/subsurface characterization, and atomistic mechanism analysis. The optimized slurry, consisting of 2.0 wt% CeO₂ abrasives with a particle size of 90 nm, 0.4 wt% KMnO₄, 0.20 wt% PVP, 0.15 wt% NaHCO₃, and a pH of 7.5, achieved a material removal rate of 646 nm h⁻¹ and an ultra-low surface roughness Sa of 0.073 nm. SEM, AFM, and cross-sectional TEM confirmed the formation of an ultra-smooth surface with suppressed subsurface damage. More importantly, first-principles calculations combined with XPS analysis revealed that CeO₂ abrasives act not only as mechanical removal media, but also as chemically active interfacial species. Stable Ce–O–Si bridge bonds are formed between CeO₂ abrasives and the oxidized SiO₂/4H-SiC surface, enabling effective load transfer to the reaction layer. Because these interfacial bonds are stronger than several internal Si–O bonds within the oxide layer, the weaker internal bonds rupture preferentially under polishing load. These results clarify how CeO₂-mediated interfacial chemistry enables selective removal of the oxidized reaction layer and promotes atomic-level surface formation on large-size SiC substrates.