Performance of colloidal silica and ceria based slurries on CMP of Si-face 6H-SiC substrates

Abstract

Colloidal silica and ceria based slurries, both using KMnO4 as an oxidizer, for chemical mechanical polishing (CMP) of Si-face (0001) 6H-SiC substrate, were investigated to obtain higher material removal rate (MRR) and ultra-smooth surface. The results indicate that there was a significant difference in the CMP performance of 6H-SiC between silica and ceria based slurries. For the ceria based slurries, a higher MRR was obtained, especially in strong acid KMnO4 environment, and the maximum MRR (1089nm/h) and a smoother surface with an average roughness Ra of 0.11nm was achieved using slurries containing 2wt% colloidal ceria, 0.05M KMnO4 at pH 2. In contrast, due to the attraction between negative charged silica particles and positive charged SiC surface below pH 5, the maximum MRR of silica based slurry was only 185nm/h with surface roughness Ra of 0.254nm using slurries containing 6wt% colloidal silica, 0.05M KMnO4 at pH 6. The polishing mechanism was discussed based on the zeta potential measurements of the abrasives and the X-ray photoelectron spectroscopy (XPS) analysis of the polished SiC surfaces.