Selective Wet Etching of SiO2 through Fluorine Species Control

The selective wet etching of silicon dioxide (SiO 2 ) over silicon nitride (Si 3 N 4 ) is a critical process in semiconductor fabrication. In this study, the etching behavior of SiO 2 in HF solution was investigated by analyzing the individual contributions of F – , HF, and HF 2 – . Contrary to the previously proposed etching mechanism of SiO 2 , the etching of SiO 2 was observed even when the HF 2 – concentration was significantly low. This suggests that F – and HF also participate in the reaction. A rate equation describing the SiO 2 etching behavior was derived by fitting the experimental data, showing that F – , HF, and HF 2 – all contribute to the reaction. Since HF 2 – contributes the most to the etching of SiO 2 , increasing its proportion was considered for selective etching of SiO 2 over Si 3 N 4 . To increase the proportion of HF 2 – , the concentrations of HF and NH 4 F were increased while keeping their mixing ratio constant, based on the understanding that HF 2 – plays the most significant role in SiO 2 etching. As a result, the etching selectivity of SiO 2 over Si 3 N 4 improved significantly. These results demonstrate that highly selective SiO 2 etching could be achieved by tuning the fluorine species distribution in BOE.