Molecular dynamics simulation of Si trench etching with SiO2 hard masks

Molecular dynamics simulations were performed to demonstrate nanometer-scale silicon (Si) trench etching with silicon dioxide (SiO2) hard masks by chlorine (Cl+) ion beams possibly with low-energy chlorine (Cl) radicals. Although the sputtering yield of SiO2 is typically much lower than that of Si, the etch rates of SiO2 and Si can be comparable because of the lower Si atomic density of SiO2. This implies that the erosion of the mask can significantly affect etched structures. This study has demonstrated that although the fluxes of incident ions and radicals are uniform in space and constant in time, the individuality of incident ions and radicals causes atomic-scale surface roughness, which cannot be neglected for nanometer-scale etched structures. Furthermore, some transient effects of surface etching, such as initial swelling of the Si surface due to incorporation of Cl atoms and preferential sputtering of oxygen, can affect the profiles of etched structures. The insufficiency of the local mechanical strengths of nanometer-scale materials also enhances their erosion, leading to the formation of nanometer-scale roughness on the sidewalls of masks and etched structures.