Highly-efficient slurryless finishing of GaN by plasma-assisted polishing using a resin bonded grinding stone

摘要

GaN is a promising material for the next generation semiconductor power devices which operate at high temperature and have a small power loss since GaN has a wide bandgap and a high electric breakdown field. For device fabrication, the surface of GaN must be scratch-free, damage-free and atomically flat. Chemical mechanical polishing (CMP) is widely used as the finishing technique for GaN. However, its material removal rate (MRR) is very low due to the high hardness and chemical inertness of GaN. We proposed a novel polishing technique named plasma-assisted polishing (PAP) which combined surface oxidation by irradiation of atmospheric-pressure plasma and removal of the oxide layer by soft abrasive polishing. PAP is applied to difficult-to-machine materials such as GaN and SiC to realize a scratch-free and damage-free polishing with high MRRs. In our preliminary study, we developed a prototype PAP machine for polishing of 3 inch wafers and the fundamental polishing characteristics of the PAP machine were evaluated. In this paper, the relationship between the surface morphology of the grinding stone and the MRR of PAP was investigated. Intermittent dressing of the resin bonded grinding stone enabled us to obtain a high MRR of about 200 nm/h for GaN substrate, which was about 2.5 times higher than that of conventional CMP.