A molecular dynamics investigation of fluorocarbon based layer-by-layer etching of silicon and $SiO2$

A molecular dynamics model is used to understand the layer-by-layer etching of Si and $SiO2$ using fluorocarbon and $Ar+$ ions. In these two-step etch processes, a nanometer-scale fluorocarbon passivation layer is grown on the material’s surface using low energy $CFx+$ ions or radicals. The top layers of the material are then reactive ion etched by $Ar+$ ions utilizing the fluorocarbon already present on the material surface. By repeating these two steps, Si or $SiO2$ can be etched with nanometer-scale precision and the etch rate is considerably faster than what traditional atomic layer etching techniques provide. The modeling results show that fluorocarbon passivation films can be grown in a self-limiting manner on both Si and $SiO2$ using low energy $CF2+$ and $CF3+$ ions. The fluorocarbon passivation layer is a few angstroms thick, and its thickness increases with the fluorocarbon ion’s energy. Increasing the ion energy, however, amorphizes the top atomic layers of the material. In addition, the fluorocarbon film becomes F rich with increasing ion energy. Simulations of fluorocarbon passivated $SiO2$ surface show that $Ar+$ ions with energy below $50eV$ etch Si (within $SiO2$⁠) in a self-limiting manner. Si etching stops once F in the fluorocarbon passivation layer is exhausted or is pushed too deep into the substrate. Oxygen within $SiO2$ is more easily sputtered from the material surface than Si, and the top layers of $SiO2$ are expected to become O deficient during $Ar+$ ion bombardment. $Ar+$ ion etching of fluorocarbon passivated Si also appears to be self-limiting below $30eV$ ion energy, and etching stops once F on the material surface is either consumed or becomes inaccessible.