Plasma-based isotropic etching polishing of synthetic quartz

To efficiently eliminate the surface defects and subsurface damage layer of synthetic quartz introduced by grinding, a plasma-based isotropic etching polishing (plasma-IEP) technique is proposed in this study. The smoothing of synthetic quartz by plasma-IEP is attributed to the formation, overlapping and merging of numerous and ultra-smooth etch pits formed by isotropic etching of SiO2 using inductively coupled plasma. Plasma diagnostics have revealed the existence of large amounts of etching radicals. The input radio frequency power and CF4 flow rate have been proved to be the two determinant factors of the material removal rate (MRR) of plasma-IEP. Under the optimized conditions, a maximum MRR of 5.62 gm/min of a 2-inch wafer has been achieved which is much higher than that of the conventional CMP process. After plasma-IEP for 30 min, the Sa roughness of the ground synthetic quartz decreases from 270.6 nm to 17.4 nm and the inner surface of the isotropic etch pits is smooth at the atomic level. The results presented in this paper demonstrate that plasma-IEP is a promising approach for the highly efficient and damage-free semi-finishing of synthetic quartz.