Evaluation of Surface Roughness and Subsurface Damage of 4H-SiC Processed by Different Finishing Techniques

Abstract

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 diamond abrasives lapping, chemical mechanical polishing (CMP) and plasma assisted polishing (PAP). Scratches were introduced through diamond abrasives lapping due to the high hardness of diamond, which resulted in the worsening of surface roughness. A damage layer was observed in the cross-sectional transmission electron microscopy (XTEM) images. A scratch-free surface was obtained through CMP, but it’s not atomically flat since step/terrace structure couldn’t be clearly observed. PAP was newly proposed for the finishing of difficult to machine materials. In PAP, water vapor plasma oxidation and soft abrasive polishing were repeatedly conducted. Ceria which is much softer than SiC was used as the abrasive material. PAP was proved very effective to achieve surfaces out of scratches. Also, due to the low hardness of ceria, no damage layers were introduced. The roughness of PAP processed surface was decreased to about 0.1 nm rms. The surface was also observed by XTEM, which proved an atomically flat surface without crystallographical damage was obtained.