Evaluation of surface roughness and subsurface damage of 4H-SiC processed by different finishing techniques

摘要

Single crystal SiC is one of the most attractive semiconductor materials for next generation power device applications. However, it is very difficult to be precisely machined due to its high hardness and chemical inertness. We evaluated the machining characteristics of 4H-SiC using different processes including chemical mechanical polishing (CMP), diamond abrasive polishing, and plasma assisted polishing (PAP). Scratches were introduced through diamond abrasive polishing due to the high hardness of diamond, which caused increase1 in surface roughness. Lack of surface atoms was observed in the cross-sectional transmission electron microscopy (XTEM) image. A scratch-free surface was obtained through CMP, but slight crystallographical damage was introduced. PAP was newly proposed for the finishing of difficult to machine materials. In PAP process, oxidation using water vapor plasma and polishing using soft abrasive were sequentially conducted. Ceria, which was much softer than SiC, was used as the abrasive material for glass polishing. PAP was proved very effective to obtain high-integrity surfaces without introducing scratches. Also, due to the low hardness of ceria, no damage layers were introduced. The roughness of PAP processed surface was decreased to 0.17 nm rms. The PAP processed surface was also observed by XTEM, which proved that an atomically flat surface without crystallographical damage was obtained.