Effect of surface/subsurface damage on the photoelectrochemical oxidation process of 4H-SiC

As one of the third-generation wide-bandgap semiconductor materials, SiC has high surface processing difficulty due to its intrinsic properties, making it challenging to prepare atomically smooth and damage-free substrate. Photoelectrochemical mechanical polishing (PECMP) has successfully demonstrated its potential for high-efficiency precision machining by leveraging the synergy of energy fields to enhance oxidation reaction and material removal. However, the residual damage from prior lapping processe significantly affects the PEC treated surface. Here, we systematically investigate the influence of surface scratch on PEC oxidation. Nanoscratching was performed along two representative crystal directions, i.e., < 1 1 ̅ 00 > and < 11 2 ̅ 0 > , and the PEC oxidation was conducted afterwards. The results show that anodic oxidation preferentially and rapidly occurs at scratch sites, thus forming nano-to-submicron-scale protrusions. Furthermore, cross-sectional FIB/STEM characterizations observed a load-dependent oxide layer formation rate, which was highly correlated with subsurface damage. In contrast, certain stress-free regions exhibited mild oxidation, which further evidenced the defect/strain-induced PEC oxidation enhancement. Notably, the uniformity of the oxide layer was regulated by the stress accumulation status, particularly in the edge regions of scratches, where stress relaxation leads to the formation of voids. Our work provides fundamental insights into PEC anodization, and we anticipate these findings will offer valuable guidance for future optimization of SiC PECMP process. ● The effects of surface scratches and subsurface defects on photoelectrochemical oxidation have been investigated. ● Anodic oxidation preferentially and rapidly occurs at scratch sites. ● Defects and strain exhibit an induced enhancement effect on photoelectrochemical oxidation. ● Load-regulated defect density drives the evolution of the stress field and affects the characteristics of the oxide layer.