Molecular dynamics study of SiO2 nanohole etching by fluorocarbon ions

As the sizes of semiconductor devices continue to shrink, the fabrication of nanometer-scale device structures on material surfaces poses unprecedented challenges. In this study, molecular dynamics simulations of CF3+ ion beam etching of SiO2 were performed with carbon masks to form holes with a diameter of 4 nm. It is found that, when the ion energy is sufficiently high and the etching continues, tapered holes are formed by the ion beam etching. This is because the etching under these conditions is essentially due to physical sputtering, so that tapered surfaces having high etching yields appear as the sidewalls and sputtered Si-containing species are redeposited. Furthermore, preferential removal of oxygen from SiO2 surfaces occurs, which leads to the formation of Si-rich sidewall surfaces. It is also found that, with simultaneous irradiation of CF3 radicals, the etching yield of a flat SiO2 surface by energetic CF3+ ion beams can double, but too large a flux of CF3 radicals causes etch stop.