High temperature MCP process suitable for extremely hard high functional SiC wafers

The need for SiC single crystals as the next generation, high-power electronic and optoelectronic devices is increasing. Mechanochemical Polishing (MCP) is suitable for the final, damage-free surface finishing process for such extremely hard and high functional materials. Cr2O3 is already known as one of the useful MCP abrasives for finishing SiC crystals. However, there is some hesitation on the actual use of Cr2O3 abrasive in the production field because of the formation of Cr6+ as a highly toxic substance. In this paper, the possibility of α-Fe2O3 powder as an environmentally safe MCP abrasive is investigated. Polycrystalline SiC wafers are MCPed on a newly developed, high temperature polishing machine. Results obtained are the following. First, α-Fe2O3 abrasive produces the highest polishing efficiency at a polishing temperature of about 230°C, which is more efficient than that obtained by Cr2O3 abrasive polishing at any experimental temperature between RT (room temperature) and 330°C. Second, the polishing efficiency of the Cr2O3 abrasive decreases at temperatures higher than 230°C. This is because of the excessive adhesion of the abrasive grains to the wafer surface. Third, no mechanical scratches are detected, suggesting that there is no subsurface damage. Fourth, unevenness per each crystal grain resulting in large surface roughness Ra over several tens nm is observed, which is peculiar to MCP of polycrystalline anisotropic materials.