Challenges of future high-precision polishing methods for hard-to-process materials by the fusion of environmental control and plasma technology

Wide-band-gap semiconductors such as silicon carbide, gallium nitride, and diamond are known as hard-to-process materials. In this study, two types of chemical mechanical polishing (CMP)-related processing equipment were designed to create novel high-efficiency and high-quality processing technology for these crystal substrates. Applying these apparatuses, the processing mechanisms are discussed and the processing characteristics of the hard-to-process substrates investigated. The two types of prototype processing equipment were the closed chamber-type processing environment control CMP equipment and the plasma fusion CMP equipment. In the former, high-efficiency processing was attempted by introducing a photocatalytic reaction while adding ultraviolet (UV) irradiation to a high-pressure oxygen atmosphere. In the latter, we expected a synergistic effect that could bring out the features of atmospheric pressure plasma chemical vaporization machining (P-CVM) and CMP, especially with a diamond substrate that is very hard and chemically stable. When the processing mechanisms of these equipment were examined, the processing was promoted while forming reaction products such as hydrated and oxide films on the extreme surface. Therefore, the chamber-type CMP equipment by UV irradiation was particularly effective in a high-pressure oxygen environment. In the plasma fusion CMP equipment, high-efficiency processing of the diamond substrate was possible when P-CVM and CMP were simultaneously operated in an oxygen atmosphere. Furthermore, based on the studied processing mechanism, a "cyclic processing method" consisting of two steps, a pseudo radical field / reaction product formation step and a new surface contact magnetorheological finishing step, was proposed as a highly efficient processing process.