Etching Mechanism of Niobium in Coaxial Ar/Cl2 RF Plasma

TL;DR

This study investigates the plasma etching mechanisms of niobium in coaxial Ar/Cl2 RF plasma, focusing on factors affecting etch rate and uniformity for superconductive cavity surface modification.

Contribution

It provides a detailed analysis of how pressure, power, bias, gas composition, and geometry influence niobium etching in coaxial RF plasma, advancing understanding of etching uniformity.

Findings

Etch rate varies with gas flow and plasma parameters.

Sheath potential and surface temperature significantly affect etch rate.

Optimal conditions improve uniformity of niobium etching.

Abstract

The understanding of the Ar/Cl2 plasma etching mechanism is crucial for the desired modification of inner surface of the three dimensional niobium (Nb) superconductive radio frequency cavities. Uniform mass removal in cylindrical shaped structures is a challenging task, because the etch rate varies along the direction of gas flow. The study is performed in the asymmetric coaxial RF discharge with two identical Nb rings acting as a part of the outer electrode. The dependence of etch rate uniformity on pressure, RF power, DC bias, Cl2 concentration, diameter of the inner electrode, temperature of the outer cylinder and position of the samples in the structure is determined. To understand the plasma etching mechanisms, we have studied several factors that have important influence on the etch rate and uniformity, which include the plasma sheath potential, Nb surface temperature, and the gas flow rate.