Effect of Sub-Surface Damage Layer Removal by Sublimation Etching of 4H-SiC Bulk Wafers on PL Imaging of Crystal Defect Visibility

Improving the visibility of defects in nitrogen-doped 4H-SiC (0001) bare wafers by photoluminescence imaging (PLI) is essential for improving the epitaxial growth process and device yields. This study proposes sub-surface damage (SSD) introduced during the mechanical process of SiC wafers as a new factor in reducing defect visibility in PL images. To verify the effect of SSD, we observed the surface of a SiC wafer, which was thermally etched at about 3 μm. As a result, dramatic defect visibility improvement was observed when the surface roughness was sufficiently flat (Ra < 0.3 nm) after thermal etching. Thus, the results suggest that defect visibility in PL images can be improved by controlling SSD and surface roughness. Using the background noise reduction effect of the SSD removal, not only PLI but also many other wafer surface inspections are expected to be improved.