Effect of Polishing Parameters on Chemical Mechanical Planarization of C-Plane (0001) Gallium Nitride Surface Using SiO₂ and Al₂O₃ Abrasives

Abstract

In this study, Chemical Mechanical Planarization (CMP) of (0001) GaN surface, using two different slurries containing colloidal silica and alumina as abrasive nanoparticles, has been reported. Effect of processing parameters, such as concentration of the oxidizer, downward pressure, head rpm, base rpm, pH of the slurries, and type and concentration of abrasive particles, on the material removal rate (MRR) and surface quality (roughness) have been studied in details. The maximum MRR has been found to be ∼39 nm/hr and ∼85 nm/hr for slurries containing SiO₂ and Al₂O₃ abrasives, respectively, under 38 kPa pressure, 90 rpm base speed (100 rpm for Al₂O₃ containing slurry), 30 rpm carrier speed, slurry pH 1 (2 for Al₂O₃ containing slurry), 0.3 M Oxidizer concentration, and 3.75 wt% abrasive particle concentration. RMS surface roughness of 1.3 Å and 0.7 Å, over scanning area of 10 μm × 10 μm and 5 μm × 5 μm, respectively, has been achieved on polished Ga-faced GaN surface for SiO₂ containing slurry using optimized slurry chemistry and processing parameters.