Development of electrolytic in-process dressing ELID) grinding of GaN wafers sliced from bulk GaN crystals by ammonothermal growth

Significant effort has been exerted to develop cost-effective ammonothermal growth of bulk GaN crystals; however, due to extreme hardness and chemical stability, the wafering process for bulk GaN crystals has not been established yet. Currently, chemical mechanical polishing CMP) to achieve damage-free, atomically-flat wafer surface is so inefficient that ~150 hours are required to finish the surface. To achieve a time and cost efficient process to finish the surface epi-ready, we need to develop a wafer shaping process which minimizes subsurface damage and therefore CMP time. This project proposes a novel grinding method called electrolytic in-process dressing ELID) grinding, which can replace the conventional steps of grinding, lapping and polishing. In addition, ELID grinding potentially causes less subsurface damage than the conventional process. During Phase I, an ELID grinding machine is constructed by adding necessary components to SixPoint's existing grinding machine and the process conditions of ELID grinding will be optimized using small-sized ~10 mm) GaN wafers. At the same time, subsurface damage of the conventional wafering process will be characterized in detail so that we can compare the damage by ELID grinding with the conventional process. After successful demonstration of a proof of concept, we will expand the capacity to 2" GaN wafers in Phase II. The developed ELID grinding process will be incorporated in the wafering process at SixPoint, which will significantly reduce the production cost of GaN substrates.