X-ray photoelectron spectroscopy investigations of ultrathin layers grown by ultraviolet-assisted oxidation of SiGe

X-ray photoelectron spectroscopy (XPS) investigations of the composition and chemical bonding of layers grown on Si _0.8 Ge _0.2 samples at 300 °C by a vacuum ultraviolet (VUV)-assisted dry oxidation process have been performed. The VUV source was an array of three Xe ₂ * excimer VUV lamps emitting at 172 nm, a power density of around 25 mW/cm ² . XPS investigations showed that the layers grown for shorter periods of time contain mostly SiO ₂ with a very low percent of GeO ₂ . Most of Ge atoms initially present in the surface SiGe layer were segregated and accumulated at the interface between the grown oxide and remaining SiGe. Angle-resolved XPS showed that the formed GeO ₂ was buried under the grown SiO ₂ layer and located adjacent to the remaining SiGe layer. When the grown SiO ₂ layer reached a thickness around ∼70 Å and the fraction of Ge accumulated in the segregated layer was more than double the initial value, a sudden increase in Ge oxidation rate was observed.