Abstract: The chemical mechanical polishing (CMP) performance of Si-face 6H-SiC substrates are compared between two different oxidizers (KMnO₄ and H₂O₂) under different pH values, using colloidal silica nanoparticles as abrasives. The surface morphology of the polished SiC substrate is characterized using atomic force microscope (AFM). The Zeta potentials of silica particles in different solutions are investigated using zeta potential analyzer and the chemical composition of the polished surfaces is studied using X-ray photoelectron spectroscopy (XPS). The results indicate that there is a significant difference in the material removal rates (RRs) of 6H-SiC under different pH values. For the KMnO₄ based slurries, the maximum RRs (185 nm/h) with an average roughness Ra of 0.25 nm is achieved at pH 6; for the H₂O₂ based slurries, the maximum RRs (110 nm/h) with an average roughness Ra of 0.32 nm is achieved at pH 8. Negative charged silica particles are expected to be attracted by positive charged SiC surface below pH 5, which might reduce the oxidation and removal of the SiC substrate; the electrostatic repulsive force of silica particles in the H₂O₂ based slurries is less than in the KMnO₄ based slurries, thus influencing the dispersion properties of silica particles. The concentrations of the oxidized species of Si-C (Si-C-O, Si₄C_4-xO₂ and Si₄C₄O₄) are higher in the SiC surface polished with KMnO₄ than in the pre-polished SiC surface and the surface polished with H₂O₂, which due to the higher oxidizing ability of KMnO₄ than H₂O₂.

Key words: chemical mechanical polishing (CMP), H₂O₂, KMnO₄, silica particles, silicon carbide (SiC)