XPS study of silicon oxycarbide formation on SiC surfaces at ambient temperatures

The Si 2p binding energies for various silicon oxycarbides species have been established using X-ray Photoelectron Spectroscopy (XPS) analysis of single phase compounds and multicomponent silicon oxycarbide glasses. A simplified Pauling charge model was used to interpret the measured binding energies in terms of the local bonding environment of the silicon; this model successfully described the data obtained in this study as well as the data reported in previous studies of silicon oxycarbides. The oxygen and carbon concentrations required to satisfy the distribution of Si 2p components measured in silicon oxycarbide glass samples were compared to the concentrations calculated independently using the Si, O and C photoelectron intensities.; The established binding energies were used to identify the species formed during the initial oxidation of SiC surfaces. Amorphous SiC as well as the two polar faces of single-crystal {dollar}alpha{dollar}-SiC (C-face and Si-face) were exposed to various oxygen sources at room temperature. The oxygen sources included the residual gas in a UHV environment, ambient air, ozone and oxygen plasma, all of which are typical oxidizing environments encountered during fabrication of microelectronic devices. In general, the relative rate and extent of oxidation of the various SiC materials obeyed the following relation: Si-face {dollar}<{dollar} C-face {dollar}<{dollar} amorphous SiC. However, no significant oxygen uptake was detected after exposure of the C-face SiC to air. XPS was used to follow changes in the surface composition and to determine the local bonding environment of the Si-atoms. It was found that silicon oxycarbide species are formed when these SiC materials are initially exposed to oxygen. With extended exposure of amorphous SiC to ambient air, a SiO{dollar}sb2{dollar} layer is subsequently formed over the silicon oxycarbide. However, the native oxide on the single-crystal Si-face SiC consists mainly of silicon oxycarbide species. After exposures to more active oxygen (i.e., O{dollar}sb3{dollar} and oxygen plasma) SiO{dollar}sb2{dollar} was observed on all samples and silicon oxycarbide species were detected at the interface. The extent of oxidation was found to be related to the thickness of the silicon oxycarbide layer. A model is proposed to explain the observed differences in oxidation behaviors for the investigated SiC materials.