Redeposition of etch products on sidewalls during SiO_2 etching in a fluorocarbon plasma. Ⅲ. Effects of O_2 addition to CF_4 plasma

摘要

The effect of added O_2 on the etching of SiO_2 sidewalls in a CF_4 plasma was examined using a transformer-coupled plasma etcher, for two cases when the sidewall was either affected or unaffected by particles emitted from the bottom SiO_2 surface. The deposition rate on the sidewall decreased in proportion to the amount of added O_2. This occurred because the increased amount of F radicals enhanced the re-etching of SiO_2, which is present beneath the surface polymer layer, and of etch products, which are redeposited from the bottom. The surface polymer layer on the sidewall, affected by particles emitted from the bottom, became thin and smooth as a result of the reaction with O radicals. The chemical etch rate of the sidewall, unaffected by energetic ions and bottom-emitted particles, and the bottom etch rates were the highest for oxygen concentrations of 10% and 20%, respectively. These concentrations were lower than an O_2 concentration of 30%, which yields the maximum concentration of F radicals. The mismatch in the O_2 concentrations arises because the O_2 concentration required to obtain the maximum etch rate on the sidewall or bottom surface is determined by competitive reactions among F, CF_2, O radicals, and incident ions.