Control of selective SiGe etching by enhanced formation of hydroxyl radicals and by surface passivation in peracetic acid solution

The selective etching of SiGe over Si is a crucial process in the fabrication of advanced 3D semiconductor devices. During the etching process, highly selective SiGe etching is required to obtain precise etch profiles. In this study, the enhancement of the selective SiGe etching in a peracetic acid (PAA) etchant solution by adding hydroxylamine and pentyl acetate was investigated. The addition of hydroxylamine increased the SiGe etching rate and SiGe/Si etching selectivity owing to the more vigorous oxidation of the SiGe surface produced by hydroxyl radicals. The SiGe/Si etching selectivity was also increased through the addition of pentyl acetate owing to the larger decrease in the Si etching rate when compared to that in SiGe. This is due to the stronger passivation effect of pentyl acetate on the Si surface, which suppresses its oxidation more effectively than on the SiGe surface. The SiGe etching rate and SiGe/Si etching selectivity were significantly increased from 223.3 nm/min and 125 to 310.8 nm/min and 557, respectively, through the simultaneous addition of hydroxylamine and pentyl acetate to the PAA etchant solution. Consequently, a mechanism for the selective etching of SiGe on vertically stacked SiGe/Si trench structures using the PAA etchant solution was proposed.