Atomic layer etch process for Nb and Ta using CF4/H2 plasma

Cyclic atomic layer etch (ALE) processes were developed for sputtered Nb and Ta thin films using CF4/H2 ICP plasma and Ar+ irradiation. The processes were investigated as a function of CF4/H2 dose time, Ar+ exposure time, and RF substrate bias. Etch per cycle, synergy, and surface roughness before and after etch are reported. Etch rates were similar for both materials for identical process conditions. A soft-saturated ALE process had etch rates of 0.23±0.02 nm/cycle for Nb and 0.23±0.01 nm/cycle for Ta with a total cycle time of 16 s. Synergies were 87% and >99% for Nb and Ta, respectively. Selectivity to Si is also reported. These processes are promising for real-world devices, which are sensitive to etch-induced damage, such as superconducting resonators.