Polyurea films deposited by molecular layer deposition for surface and sidewall passivation during HF plasma etching of high-aspect-ratio structures

Molecular layer deposition (MLD) was used to deposit polyurea films using toluene diisocyanate and ethylenediamine as precursors. Polyurea was deposited on SiO2 and SiNx blanket films and exposed to an HF plasma to evaluate plasma-surface interactions. The surface composition was monitored using in situ infrared spectroscopy. During the initial stages of HF plasma exposure, polyurea was sacrificially etched, while etching of the underlying SiO2 or SiNx films was negligible. Once polyurea was completely consumed by reactions with plasma species, the underlying SiO2 or SiNx films were etched at their baseline etch rates. Despite the high porosity of the MLD films, the presence of polyurea prevented etching of the underlying material, showing that polyurea efficiently consumed the reactive plasma species. Fluorination of polyurea was observed prior to its removal, suggesting that polyurea was removed as hydrofluorocarbons during HF plasma etching. Finally, polyurea was deposited on ∼65:1 aspect-ratio holes in SiO2-SiNx stacks and then exposed to an etching plasma to evaluate the sidewall passivation. We show that polyurea was deposited throughout the entire hole using the saturation doses for a flat surface, although the thickness on the sidewalls was lower than the planar surface. After MLD, in the second etch step, the polyurea film preserved the critical dimension throughout the high-aspect-ratio feature.