Research on R-Plane Sapphire Substrate CMP Removal Rate Based on a New-Type Alkaline Slurry

Abstract

Chemical mechanical polishing (CMP) is widely used as one of the most effective methods to achieve atomic-scale smooth surface. In order to investigate the mechanism of sapphire (α-Al2O3) substrate CMP, the X-ray photo-emission spectroscopy (XPS) was applied to analyze the chemical state of elements. From XPS analysis it was demonstrated that AlO(OH) whose hardness was lower than α-Al2O3, existed only in c-plane sapphire after c- and r-plane polishing, so it's difficult to get high removal rate for r-plane CMP. But GaN epitaxial film grown on the r-plane sapphire substrate is semi-polar, and the luminous efficiency of the thin film is significantly improved. In order to improve r-plane sapphire substrate processing efficiency and accuracy, effects of pH regulator, KNO3 concentration and surfactant concentration on r-plane sapphire CMP were studied. Higher removal rate of r-plane was obtained when KNO3 concentration was 0.1 wt%, which was attributed to the particle size increase and new chemical reaction. But the removal rate decreased slightly due to the broadening of particle size distribution scope at higher ionic strengths. Anionic surfactant could improve removal rate and surface quality due to its good dispersion and stability to prevent nano-SiO2 sol agglomeration. For r-plane sapphire, removal rate and surface roughness Sq can reach 1.43 um/h and 0.173 nm respectively, which provides guiding significance for the development of industrial sapphire ultra precise processing.