Effect of ZnO-SiO2 Composite Abrasive on Sapphire Polishing Performance and Mechanism Analysis

Abstract

Sapphire is widely used because of its excellent physical and chemical properties, and the requirements for its surface quality and processing efficiency are becoming more stringent. Chemical mechanical polishing (CMP) has been widely used to achieve non-damaged and atomically smooth surfaces on sapphire wafers. To promote the removal rate and surface quality, the effect of ZnO-SiO2 composite abrasive on sapphire CMP performance was studied. A higher material removal rate and lower Root mean squared surface roughness (Sq) (less than 0.3 nm) were obtained with the ZnO nano-particle slurry. HSC chemistry software was used to calculate the Gibbs free energy of possible chemical reactions between sapphire, SiO2, H2O, and ZnO to determine whether new reactions can occur. At the same time, the action and removal mechanism of sapphire using the ZnO-SiO2 composite slurry were investigated. X-ray photoelectron spectroscopy showed that the new reaction was produced and the product of the solid-state reaction was ZnAl2O4. In addition, only a hydration layer was observed on the surface of soaked sapphire in ZnO-based slurry, while the solid-state reaction products of Al2SiO5/Al2SiO5(OH)4 and ZnAl2O4 existed on the surface of polished sapphire. This indicates that mechanical processing provides energy or conditions which can promote chemical effects during CMP and lead to solid-phase reactions. Finally, a mechanochemical effect is introduced to explain the mechanism of solid state reaction in sapphire CMP process, which has a certain guiding significance to the mechanism analysis of CMP for different materials.