Transport mechanisms of ions and neutrals in low-pressure, high-density plasma etching of high aspect ratio contact holes

Transport mechanisms of ions and neutrals in high aspect ratio contact hole s during low-pressure, high-density plasma etching were investigated by bot h experiments and numerical simulations. Etching experiments were performed in electron cyclotron resonance plasmas with a C4F8/O-2 gas mixture, toget her with measurements of plasma parameters. The SiO2 etch rate decreased, a nd the deposition rate of polymer film during over-etching increased with d ecreasing hole diameter. The trajectories of ions and neutrals were investi gated by numerical simulations that took into account the local charging ef fect for ions and Knudsen transport for neutrals. The etch rate distributio n on the hole bottom was estimated by an etching model that included ion sp uttering and ion-assisted etching. A sub-trench profile of the Etch rate wa s obtained for a low aspect ratio hole, while a flat profile was observed f or a high aspect ratio hole. This numerical result was in good agreement wi th the experimental results. Moreover, the dependence of polymer film thick ness on over-etch duration was explained by a deposition model that include d both the polymer formation by ion-assisted deposition and polymer removal by oxygen atoms. (C) 2000 Elsevier Science S.A. All rights reserved.