Chemical Mechanical Polishing of the C-Face of 6H-SiC and Mechanisms Elucidated by Reactive Force Field Molecular Dynamics

Abstract

Due to its strong Si–C covalent bonds, high hardness, and strong chemical inertness, single-crystal SiC still faces challenges in chemical mechanical polishing (CMP), including low material removal rates, difficulty in controlling surface and subsurface damage, and an unclear understanding of the chemical–mechanical coupling mechanism. In this study, focusing on the C-face of 6H-SiC, we combined Fenton/Electro-Fenton CMP experiments with reactive force field molecular dynamics (ReaxFF-MD) simulations that account for initial nanoscale roughness to investigate the effect of ·OH concentration on polishing performance and atomic-scale removal mechanisms. Experimental results show that as the total ·OH generation increased from 15158.97 μmol to 54105.03 μmol, the material removal rate (MRR) increased from 1199.279 nm/h to 2066.794 nm/h, and the surface roughness Ra decreased from 0.705 to 0.321 nm; at the highest ·OH concentration, the MRR increased by 72.3% compared to the lowest concentration, and Ra decreased by 34.0%. To explain these macroscopic experimental trends, ReaxFF-MD simulations revealed that ·OH promotes the breaking of Si–C bonds and the formation of oxygen-containing structures such as Si–O–H and Csub–O–H bonds, inducing oxidation reactions in the surface layer. This breaks the strong Si–C covalent bonds and causes amorphization of the crystal structure, thereby softening the mechanical properties of the surface material and ultimately making it easier to remove under the shearing action of diamond abrasive grains; the evolution of interfacial bonds further reveals the dynamic evolution mechanism of “oxidation activation─interfacial bonding─shear fracture─structural rearrangement.” Experimental results demonstrate that increasing the ·OH concentration enhances MRR and reduces Ra, while simulation results explain the origin of this chemical–mechanical coupling at the atomic scale. The study indicates that increasing the ·OH concentration can effectively improve the CMP efficiency of the C-face of 6H-SiC and enhance surface flatness; however, it is still necessary to balance this with the control of subsurface amorphization damage. This provides experimental evidence and an atomic-scale mechanistic explanation for optimizing high-efficiency, low-damage polishing processes for SiC wafers.