Ab-initio molecular dynamics simulations of the reactivity of MoS2 towards F2 molecules: Implications for etching processes

Abstract

We investigated the reactivity of fluorinated monolayer and bilayer MoS2 in relation to etching processes. We considered both the energetics and the dynamics of the different processes: a) interaction of fluorine species in the gas phase with MoS2, b) the surface chemistry of SF, SF2, and SF3 groups and c) the desorption of fluorine-containing molecules into the gas phase. The dissociative adsorption of F2 occurs at very low temperatures (100 K) and the surface becomes populated by SF, SF2 (the most stable), and SF3 groups. Etching processes begin with the desorption of the SF3 group and only at very high temperatures the desorption of SF2 was observed. Sulfur vacancies left by the removal of S atoms are rapidly filled by F atoms due to the formation of strong MoF bonds. The formation of a sulfur vacancy induces the subsequent formation of S-vacancies on adjacent surface sites, and this finally promotes the desorption of MoF5 or MoF6 species, thus leaving a surface pit defect. For a MoS2 bilayer with the top layer fluorinated on both sides, the etching of the top layer was observed as a consequence of the release of SFx species within the interlayer region.