Investigation into the effect of a PECVD-deposited SiOx chamber coating on the selective, radical-based NF3 etching of TaN with respect to BEOL low-k

This paper explores the use of a low temperature inductively coupled plasma discharge containing an NF3/Ar mixture for the isotropic, dry etching of TaN with selectivity to low-k dielectric; relying on radically based etch, without nonselective ion bombardment. With a clean chamber condition, no etch selectivity is found between TaN and the low-k dielectric, but when the chamber condition is manipulated by the addition of a plasma-deposited SiOx coating to the chamber wall, selectivity between TaN and the low-k dielectric is achieved. Deposition occurred on the low-k dielectric when the coating was applied to the chamber walls before etch, and while the TaN film etch rate did decrease with a coating applied, an etching regime was still observed. The coating was found to add significant atomic oxygen to the etch processes and decreased etching of the low-k dielectric. The deposition regime apparent for the low-k dielectric was made possible by the inability of the fluorine radicals to volatize silicon oxyfluoride compounds, causing deposition of a silicon oxyfluoride film on the low-k surface. The same etching inhibition was not observed on TaN, allowing selective etching.