Photonic effects during low-temperature ultraviolet-assisted oxidation of SiGe

Abstract

The behavior of Ge atoms during dry oxidation of Si0.8Ge0.2 films at 300°C under 10 mbar of oxygen induced by vacuum-ultraviolet (VUV) illumination from an array of Xe2* excimer lamps (λ=172 nm) has been studied. During VUV oxidation, samples are exposed to both a high concentration of ozone and atomic oxygen and a large flux of energetic photons. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy investigations showed that the layers grown for shorter periods of time contain mostly SiO2 with a few percent GeO2. Most of the Ge atoms, initially present uniformly within the SiGe layer, were segregated and accumulated at the interface between the grown oxide and remaining SiGe. Angle-resolved XPS showed that the amount of GeO2 within the grown oxide layer decreased for longer irradiation times and was located adjacent to the SiGe layer. When the grown SiO2 layer reached a thickness around ∼70 A and the amount of Ge that had accumulated in the segregated layer more than doubled, a sharp increase in the Ge oxidation rate was observed. Continuing the oxidation for longer irradiation times resulted in the formation of a mixed oxide layer. The Ge segregation was not previously observed during other low-temperature oxidation treatments, including ozone-assisted oxidation, which provides the same oxidation species as VUV-assisted oxidation and similar growth rates. It is, therefore, concluded that a VUV photon-irradiation enhancement effect on Si and Ge interdiffusion has been introduced, possibly involving either Si-Si or Si-Ge bond softening or even breaking.