Shape modulation due to sub-surface damage difference on N-type 4H–SiC wafer during lapping and polishing

Abstract

The technology enhancement of obtaining 4H–SiC wafers with a concave Si face shape has improved the performance of GaN-on-SiC. For manufacturers, the wafer shape has a tremendous impact on the deposited films quality by increasing defects generation or causing undesirable strain. Therefore, it is crucial to control the wafer shape and explore the mechanism. This study recorded the wafer shape evolution by flatness tester during the machining process of lapping, mechanical polishing (MP), and chemical mechanical polishing (CMP). The varying shapes of SiC wafers are due to surface damage and intrinsic stress caused by the early lapping process, but the intrinsic stress is dominant. The measurement results show that double side MP and single side CMP make the wafer more convex and concave. It indicates that the residual surface stress is involved in shape formation. Perfect symmetrical shape between (0001) Si face and (000 1‾) C face suggests that there is indeed bending stress within the wafer. In this study, atomic force microscopy (AFM), high-resolution X-ray diffractometry (HRXRD), and scanning electron microscopy (SEM) was used to investigate the surface damage between SiC polar faces. According to the results, the damage to the Si face is more severe than that to the C face after double-sided mechanical polishing, leading to the wafer becoming more convex.