Dose-Dependent Etching Selectivity in SiO2by Focused Ion Beam

The dose-dependent etching characteristics of SiO2 films irradiated with 40 keV Si2+ focused ion beams (FIBs) were comprehensively investigated. The etching rate in a buffered HF increased with increasing dose (8 ×1013–1 ×1015 cm-2), however it decreased for doses exceeding a critical value (1 ×1015 cm-2). The maximum selectivity of the etching rate of the irradiated region to the nonirradiated region was about 14, which was obtained for irradiation with the critical dose. The numerical simulation indicated that all of the Si atoms in SiO2 were displaced by irradiation with this critical dose. A simple model for the etching characteristics was proposed, in which the enhancement of etching by vacancies and the retardation of etching by implanted Si atoms were considered. The etching characteristics obtained by the experiments were quantitatively explained by the model.