XPS study of interface formation of CVD SiO2 on InSb

Abstract

The interfacial chemistry of CVD SiO2 films deposited on thin native oxides grown on InSb substrates is investigated using x-ray photoemission and chemical depth profiling. The SiO2 films are grown through thermal decomposition of silane in a N2/O2 ambient. The chemical composition of these films is determined through the use of a relatively benign chemical- etching method together with an intensity analysis of the XPS spectra. Absolute peak positions are utilized to determine the different local chemical environments as well as to follow the details of surface potential variations which correlate with the chemical depth profile. Before deposition, the InSb surface is covered by a 15–20 Å native oxide overlayer composed of In2O3 and Sb2O3 in a 3:1 ratio. During deposition of SiO2 on InSb, significant interaction between deposited and native species was found. Reaction of the substrate with oxygen resulted in an In-rich native oxide and 1–2 monolayers of excess elemental Sb at the native-oxide/substrate interface. Incompletely oxidized silane reduced the native oxide, leaving ≲1 monolayer of elemental In at the SiO2/native oxide interface. Etch removal of this thin In-rich layer leads to a change in substrate surface potential of 0.06 eV, corresponding to a net increase in positive charge. The experimental observations are shown to be consistent with simple thermodynamic considerations, and a comparison is made with previous studies of deposited insulators on III–V compound semiconductors.