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 Si0.8Ge0.2 samples at 300 °C by a vacuum ultraviolet (VUV)-assisted dry oxidation process have been performed. The VUV source was an array of three Xe2∗ excimer VUV lamps emitting at 172 nm, a power density of around 25 mW/cm2. XPS investigations showed that the layers grown for shorter periods of time contain mostly SiO2 with a very low percent of GeO2. 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 GeO2 was buried under the grown SiO2 layer and located adjacent to the remaining SiGe layer. When the grown SiO2 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.