A Comparison between Different Post Grinding Processes on 4H-SiC Wafers

Abstract

The need of removing the mechanical damage and the stress introduced during the thinning step of device process flow is challenging for manufacturing of high quality SiC-based devices. In this respect we have identified two different back finishing approaches, based on material removal and material rearrangement. The first one includes dry polishing (DP) and chemical mechanical polishing (CMP); the second one includes bulk and laser annealing. Systematical investigation on wafer warpage, sample morphology and die mechanical reliability have been conducted and comparison between the two approaches has been done. The CMP and DP processes can remove the damage produced by back grinding, recovering wafer warpage and resulting in a smoother surface. Bulk thermal annealing has provided better roughness levels and has been successful in stress relief, although the wafer permanence at high temperature is not compliant with the device process flow. Under laser annealing process, the surface features keep almost unchanged as well as warpage level. Despite being not effective in stress relief, from a mechanical point of view, the laser annealing process, does not impact die reliability, representing a suitable back finishing process especially in the optic of its use in backside ohmic contact formation.