Influence of slurry pH on material removal rate and surface roughness of super-precision polishing of LBO crystal

Abstract

LBO crystal with high quality surface, which must be defect-free and super smooth, is urgently needed because of its applications in high energy laser system. Chemical mechanical polishing (CMP) is adopted to raise surface quality and processing efficiency in super precision polishing of LBO crystal. The polyurethane pad and colloidal SiO2 slurry are chosen and the polishing experiments are performed on Logitech PM5 Precision Lapping & Polishing Machine. The slurry pH is changed and its influence on material removal rate (MRR) and surface roughness is studied. The polished surface roughness is measured by using atomic force microscope. MRR is calculated through the difference of the crystal thickness between before and after polishing by polishing time. In the pH range from 2 to 6, MRR of LBO crystal increases with pH decreasing and there is an optimal pH for surface roughness. While in the pH range from 7 to 13, MRR and surface roughness vibrate with pH. The maximal MRR reaches 758 nm/min when slurry pH is kept at 2 and the best surface roughness reaches 0.197 nm RMS when it at 4.