Low-damage gas cluster ion beam polishing of the C-face of 4H-SiC

Successful polishing of the C-face of 4H-SiC has been achieved with a 2-step Ar⁺_n gas cluster ion beam (GCIB) sputtering process. While limiting subsurface damage due to its inherent properties, GCIB enabled surface cleaning by physically etching contaminants and native oxide. The emphasis was on recipes that minimize both chemical and structural damage while providing a high-quality finish for downstream processes such as direct wafer bonding, which requires extreme cleanliness, oxide-free conditions, high uniformity, and very low roughness (R_q < 0.5nm for fusion bonding). After bombardment, the scratches were shallower, and significant surface improvements (R_q decreased from 2.1nm to 0.86nm) were achieved with low-energy recipes (< 6 eV/atom) on the C-face, which behaves differently from the Si-face. In situ x-ray photoelectron spectroscopy and atomic force microscopy are reported to highlight the surface evolution. These initial findings pave the way for process improvement that would highlight the potential of GCIB for surface preparation of hard materials in wafer bonding applications.