Chemical Mechanical Polishing of Gallium Nitride with Colloidal Silica

In this report, chemical mechanical polishing (CMP) of gallium nitride (GaN) with colloidal silica was studied. It was confirmed that colloidal silica based slurry could be used for gallium face of GaN. Removal rate of GaN was 17 nm/h under typical polishing conditions. An atomically flat surface with Ra = 0.1 nm was achieved after CMP. Detailed observation of the scratch density was done during the CMP process. Cathode luminescence (CL) imaging was used to understand the sub-surface damage induced by mechanical polishing process and its removal by CMP with colloidal silica based slurry. Combining the optical microscope, atomic force microscope (AFM), CL imaging, and reflection high energy electron diffraction (RHEED) observations before, after and at intermediate stages of the CMP process, the schematic model of the removal of scratch and damage layer from Ga-faced GaN substrate by CMP process was proposed.