Silicon Nitride Surface Modification by Ion Bombardment with Physisorbed Hydrofluorocarbons: Theoretical Assessment

We present key pathways involved in bombardment-induced modification of amorphous silicon nitride (SiN) surfaces with physisorbed hydrofluorocarbons (HFCs), based on tight binding molecular dynamics (TBMD) simulations. Under 35 eV argon (Ar) atom bombardment, the surface layers are predicted to decrease in atomic density due to bombardment-induced damage while accumulating a significant amount of fluorine (F) as a function of the HFC stoichiometry; comparable amounts of carbon (C) are also predicted to be incorporated. The surface chemical modification is found to be strongly dependent on the nonequilibrium effects of Ar bombardment, especially the creation of surface defects induced by the bombardment. The defects play a critical role in facilitating surface reactions with fragments of dissociated species. Our TBMD results also suggest the potential for further evolution with continued bombardment, resulting in the implantation of HFC species beneath the SiN surface layer.