Etch rate retardation of Ga+-ion beam-irradiated silicon

Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in SF6/O-2 plasma of high-dose Ga+-implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and X-ray 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 in more detail by angle-resolved XPS. In the case of dry reactive ion etching (RIE) 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/O-2 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 reveals a stoichiometry of almost 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. (c) 2005 The Electrochemical Society. All rights reserved.