Vibration-assisted fixed abrasive polishing CaF₂ crystal

In order to improve polished surface quality of CaF₂ crystal and increase material removal rate, the method of vibration-assisted fixed abrasive polishing of CaF₂ crystal is proposed, which combined ultrasonic vibration with fixed abrasive polishing effectively. The effect of process parameters on material removal rate and surface quality are investigated by orthogonal experiment. The optimal parameters of CaF₂ crystal polishing is obtained with rotational speed 40 r/min, vibration frequency 40 kHz, slurry pH value 9, and rotation speed ratio 0.95. Under the optimal parameters, material removal rate is 324 nm/min, and surface roughness S_a is 1.92 nm in vibration-assisted fixed abrasive polishing CaF₂ crystal process. Compared with the results of fixed abrasive polishing without vibration, material removal rate is increased by 57% and surface roughness S_a is reduced by 35%. Vibration-assistance can increase material removal rate and enhance surface quality of the wafer by cavitation and intermittent contact in fixed abrasive polishing process.