Mechanistic difference between Si-face and C-face polishing of 4H–SiC substrates in aqueous and non-aqueous slurries

Abstract

The traditional aqueous-based polishing slurries have been extensively used in the ultra-precision machining process of SiC substrates, but their processing efficiency remains a major challenge in making SiC wafers with high surface quality. SiC polishing slurries based on non-aqueous solvents have been explored and reported, however, the mechanism for the accelerated SiC material removal rate (MRR) remains unknown. In this work, the Si-face and C-face of the SiC wafer were polished with water and methanol as polishing liquid carriers, respectively. The MRR of Si-face using the methanol-based slurry, can reach 260.9 nm/h, and the polished Si-face surface roughness Ra reduces to 0.150 nm. In contrast, the MRR of Si-face by using the aqueous-based slurry, is 66.8 nm/h, the polished Si-face surface roughness Ra is 0.691 nm. However, the results of MRR and Ra for C-face are opposite. The reaction between the polishing liquid carriers and the atomic structures of Si-face and C-face lead to differences of the MRRs by analyzing contact angle, XPS, and molecular dynamics (MD) simulation results. The newly revealed polishing mechanisms shined light for speeding up the development of SiC polishing slurries based on the specific aspects of the polishing surface of SiC.