Effect of surfactant and electrolyte on surface modification of c-plane GaN substrate using chemical mechanical planarization (CMP) process

Abstract

This study demonstrates the effect of surfactant and electrolyte on the colloidal stability of a KMnO4/Al2O3 suspension and their subsequent effects on the material removal rate (MRR) and roughness of a c-plane GaN (0 0 0 1) surface polished by chemical mechanical planarization (CMP) process. It was found that the material removal rate and surface roughness strongly depend on the type and concentration of surfactant and electrolyte used. The maximum material removal rate (MRR) has been found to be 123.5 nm/hr and 234 nm/hr for SDS as surfactant and NaCl as electrolyte, respectively, under optimized conditions of 38 kPa polishing pressure, 90 rpm platen velocity, 30 rpm carrier velocity, slurry pH of 1 and 0.3 M KMnO4 concentration. A remarkable rms surface roughness (Rq), 1-2 Å,has been obtained on polished c-plane GaN (0 0 0 1) surface over a scan area of 1 μm × 1 μm for slurries containing 0.55 wt.% SDS or 0.05 M NaCl. The mechanism of colloidal stability of the surfactant based slurry used in this investigation and its subsequent effect on material removal rate has been proposed.