Molecular dynamics simulation of Si and SiO₂ reactive ion etching by fluorine-rich ion species

One of the most difficult challenges in the fabrication of three-dimensional (3D) NAND flash memory devices is high-aspect-ratio etching to make deep hole channels through a polycrystalline silicon (Si) (or silicon nitride) and silicon dioxide (SiO₂) stacked layers. In this study, classical molecular dynamics (MD) simulation is performed to examine ion-surface interactions in reactive ion etching (RIE) of Si and SiO₂ surfaces by C₂F₅ ⁺ and NF₂ ⁺ ions with ion incident energy ranging from 500 eV to 2000 eV. These ions are selected for this study as sample cases where each incident ion contains a relatively large number of fluorine atoms, which enhance chemical etching of both Si and SiO₂. Such highly reactive ions generated in a plasma are expected to etch through stacked Si and SiO₂ layers with high etching yields. The etching yields obtained from MD simulation are found to be consistent with experimental results and highly dependent on the impact ion energy as well as the amount of fluorine involved in the etching process. The depth profile study has also shown that dense accumulation of F atoms on the surface formed during the ion bombardment significantly contributes to the bond breaking of surface atoms, which enhances the etching yields.