Role of a New Type Chelating Agent in Chemical Mechanical Polishing of R-Plane Sapphire Substrate

Abstract

Since the GaN epitaxial film grown on the r-plane sapphire substrates is semi-polar, the strong built-in electric field inside the thin film cannot be produced, and the luminous efficiency of the thin film is significantly improved. However, the breaking energy of Al-O bond of r-plane is higher than the Al-Al bond of c-plane. So it's difficult to get high removal rate for r-plane CMP. The influence of different chelating agents on r-plane sapphire CMP was studied in order to improve the processing efficiency and accuracy. The removal rate of r-plane sapphire is only about 0.5 μm/h without adding such new chelating agent to the slurry. But the removal rate increased rapidly to 1 μm/h when adding 0.2 vol% of such new chelating agent to the slurry. Removal rate was significantly improved at least in surface layer thickness of 20 um after the r-plane sapphire wafer was soaked in the new chelating agent for one week. For the soaked wafers, the removal rate can reach 2.48 μm/h and the surface roughness Sq is 0.148 nm. From the analysis, such new type chelating agent takes the action of pH-regulator, complexing, chelating, softening and osmosis.