Effect of surfactant based abrasive free slurry on CMP polishing rate and planarization of semi-polar (11–22) GaN surface

Abstract

An abrasive free slurry has been formulated using ionic and non-ionic surfactants with KMnO4 as an oxidiser. Subsequently, the effect of these surfactants on the material removal rate (MRR) and surface planarity of semi-polar (11–22) GaN surface have been studied using chemical mechanical planarization (CMP) process. The formulated polishing slurries were characterized for their rheological properties such as shear thickening, thinning and viscosity as a function of shear rate. It was found that the polishing rate and surface planarity depend on the type of surfactant and its concentration. The estimated MRR values of various surfactants are seen to decrease from anionic to cationic to non-ionic in the order SDS > CTAB > TX-100 and the maximum MRR has been found to be 2.58μm/hr for 0.5 wt% SDS surfactant containing slurry, under optimized conditions of other CMP parameters. In compared to the cationic (CTAB) and non-ionic surfactants (TX-100), anionic surfactant (SDS) offered relatively good surface planarity with a remarkable root-mean-square (rms) surface roughness (Rq) of 2 Å over a scan area of 1 × 1 μm.2.