UV-TiO2 photocatalysis-assisted chemical mechanical polishing 4H-SiC wafer

The objective of this study is to propose a photocatalysis-assisted chemical mechanical polishing (PCMP) method for atomic smoothing SiC wafer based on the powerful oxidability of UV photo-excited hydroxyl radical on nano-TiO2 particles. The study identifies five slurries of different photocatalyst, electron capturer, UV light, and pH value by measuring oxidation reduction potential and static oxidation experiment. After PCMP process, a SiC wafer is examined with optical microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy for information on surface finish and quality, material removal and mechanisms. The study demonstrates that photocatalyst, UV light, electron capturer, and acid environment are necessaries for PCMP process. Among the five PCMP slurries, the one with 1 g of TiO2, 0.3 g of (NaPO3)6, 10 ml H2O2, 5 g SiO2 abrasives under UV light irradiation provides the highest material removal rate of 0.95 µm/h and the best surface finish (Ra = 0.35 nm) and surface quality. It then discusses how UV light irradiation promotes the chemical oxidation of hydroxyl radical with SiC by forming “Si–C–O,” “Si–O,” “C–O,” and “C˭O” on SiC surface. The study concludes that the proposed PCMP is effective and clean manufacturing method for SiC wafer without releasing toxic chemicals to environment and human health.