Etch rate retardation of Ga+ ion beam irradiated silicon

Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in SF6/O2 plasma of high dose Ga+ implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and x-ray induced photoelectron spectroscopy (XPS). During wet chemical etching in a KOH/H2O solution a thin layer of GaOx of < 1 nm thickness is formed, which has been investigated more in detail by angle-resolved XPS.. In the case of dry reactive ion etching the surface chemistry is quite different. In this case a more enhanced oxidation of Ga takes place due to the high reactivity of atomic oxygen from the SF6/O2 plasma. SIMS results show that during RIE a Ga rich surface layer forms and therefore an enhanced Ga oxidation takes place leading to a thicker GaOx layer compared to wet chemical treatment. XPS depth profiling points at a stoichiometry of nearly completely oxidized Ga (Ga2O3) layer free from Si with a thickness of about 5 ... 10 nm. The etch rate lowering in Ga+ as- implanted silicon is ascribed to the formation of gallium oxide at the Si surface during the etch processes.