Molecular dynamics simulation for reactive ion etching of Si and SiO2 by SF 5 + ions

Abstract

Silicon (Si)-based materials such as Si and silicon dioxide ( SiO 2) are commonly used as basic components of advanced semiconductor devices. For example, alternating stacks of poly-Si and SiO 2 layers are used in three-dimensional (3D) NAND flash memory devices. Fabrication of high-aspect-ratio deep holes through such stacked materials by plasma etching may be achieved by highly energetic and chemically reactive ion injections to the surface. Etching by sulfur hexafluoride ( SF 6) plasmas can produce ions carrying multiple fluorine (F) atoms and therefore exhibit high etch rates for both Si and SiO 2. In this study, reactive ion etching of Si and SiO 2 materials by SF 5 + ions was examined with the use of molecular dynamics (MD) simulation. For this purpose, a simplified interatomic potential functions model for sulfur (S) was developed that approximately represents molecular moieties or molecules SF n ( n ≤ 6) based on density-functional-theory (DFT) calculations. The etching yields of Si and SiO 2 by SF 5 + ions evaluated by MD simulations with these new potential functions were found to be in good agreement with those obtained from multibeam injection system experiments, which implies that the etching process is essentially due to sputtering enhanced by chemical reactions of F atoms with the surface materials. Analyses of the depth profiles of atomic concentrations of etched surfaces and desorbed species obtained from MD simulations also indicate that the presence of excess F atoms on the surface enhances the etching yield of Si and SiO 2 significantly over corresponding physical sputtering.