Effects of slurry pH on chemical and mechanical actions during chemical mechanical polishing of YAG

Abstract

Yttrium aluminum garnet (YAG) single crystal has become a promising substrate for the high-power solid-state laser. It needs to be processed into a defect-free surface by chemical mechanical polishing (CMP). The preparation of polishing slurry is critical for the material removal efficiency and surface quality, which relies on understanding the removal mechanism of polished materials. In this study, the impacts of slurry pH on the chemical and mechanical actions of YAG in CMP process are investigated. Chemical reaction mechanisms are revealed by X-ray photoelectron spectroscopy analysis. And mechanical actions of abrasives are analyzed by the theory of Derjaguin–Landau–Verwey–Overbeek and the measured coefficient of friction. The results indicate that the material removal depends on the formation of bridge bonds at the interface and the dissociation of work surface bonds when the slurry pH is below 12. In comparison, it is based on forming a softer reaction layer and removed mechanically at pH 13. More abrasives interact with YAG under the acidic condition and it contributes to elevating the material removal rate. The colloidal silica at pH 6 is preferred for CMP of YAG. This study helps to understand the material removal mechanism and optimize the polishing process.