A novel chemical mechanical polishing slurry for yttrium aluminum garnet crystal

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) crystal is widely used for laser applications. However, due to its high hard and brittle nature, high surface quality and high material removal rate (MRR) are difficult to be achieved. In this study, to solve the problem, a novel CMP slurry was developed, which contains 8 wt% ZrO₂ abrasives, 5 wt% Na₂SiO₃·5H₂O, 0.3 wt% MgO and deionized water. After polishing, the surface roughness and MRR achieved 0.08 nm Ra and 34 nm/min respectively. The reaction mechanism during polishing was elucidated based on the results of grazing incidence small angle X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The results show that AlOOH and YOOH generated from hydration reaction react with Si–OH in Na₂SiO₃ aqueous solution to form soft andalusite and yttrium silicate, then MgO combines with andalusite to produce montmorillonite. All soft products are removed mechanically by ZrO₂ abrasives, obtaining the ultra-smooth surface of YAG crystal.