Preparation of cobalt-doped colloidal silica abrasives and their chemical mechanical polishing performances on sapphire

Cobalt (Co)-doped colloidal silica abrasives were synthesised by seed-induced growth method. Time-of-flight secondary ion mass spectroscopy was used to characterise the composition of the obtained abrasives. The morphology of the abrasives was measured by using scanning electron microscopy. The chemical mechanical polishing (CMP) performances of the Co-doped colloidal silica abrasives on sapphire substrates were investigated. Experiment results indicate that the Co-doped colloidal silica abrasives exhibit lower surface roughness and higher material removal rate (MRR) than that of pure colloidal silica abrasive under the same testing conditions. Furthermore, the inductively coupled plasma-atomic emission spectrometry and X-ray photoelectron spectroscopy were also used to investigate the acting mechanism of the Co-doped colloidal silica in sapphire CMP. Analysis results show that cobalt aluminate appears after polishing, implying the tribochemistry reaction occurs during CMP. The chemical reaction between element cobalt and sapphire surface during CMP can promote the chemical effect in CMP and lead to the increasing of MRR.