Selective etching of TiN over TaN and vice versa in chlorine-containing plasmas

Selectivity of etching between physical vapor-deposited TiN and TaN was studied in chlorine-containing plasmas, under isotropic etching conditions. Etching rates for blanket films were measured in-situ using optical emission of the N2 (C3Πu→B3Πg) bandhead at 337 nm to determine the etching time, and transmission electron microscopy to determine the starting film thickness. The etching selectivity in Cl2/He or HCl/He plasmas was poor (<2:1). There was a window of very high selectivity of etching TiN over TaN by adding small amounts (<1%) of O2 in the Cl2/He plasma. Reverse selectivity (10:1 of TaN etching over TiN) was observed when adding small amounts of O2 to the HCl/He plasma. Results are explained on the basis of the volatility of plausible reaction products.