High etching rates of bulk Nb in Ar/Cl2 microwave discharge

Plasma-based Nb surface treatment provides an excellent opportunity to eliminate surface imperfections and increase the cavity quality factor in important applications such as particle accelerators and cavity quantum electrodynamics, as well as Josephson junctions. In this study, plasma etching of bulk Nb is performed on the surface of disk-shaped samples with the goal of eliminating nonsuperconductive pollutants in the penetration depth region and the mechanically damaged surface layer. The authors have demonstrated that in the microwave glow discharge, an etching rate of 1.5 mu m/min can be achieved using Cl-2 as a reactive gas. The influence of plasma parameters such as input power, pressure, and concentration of the reactive gas on the etching rate is determined. Simultaneously, plasma emission spectroscopy was used to estimate the densities of Cl, Cl+, and Cl-2 under various plasma conditions.