Low temperature oxidation of SiGe in ozone: Ultrathin oxides

Abstract

X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and spectral ellipsometry have been used to study ozone/atomic oxygen assisted direct oxidation of single crystalline SiGe. In situ Fourier transform infrared spectroscopy is used to monitor changes in the gas phase composition of O3/O2 gas mixtures. At all temperatures studied, 125–530 °C, XPS results indicate that Ge is incorporated into the growing oxide as GeO2. Increasing the oxidation temperature causes a decrease in the percentage of Ge incorporated in the growing oxide and an increase in the silicon content. Further, at oxidation temperatures of 400 °C and above, substantial Ge segregation is observed using SIMS. The change in composition is described using a temperature dependent flux model. Also, as the oxidation temperature increases, the oxide/SiGe interface becomes more abrupt with 1.9 monolayer (ML) of suboxide (Si+1, Si+2, Si+3) detected at 125 °C and 0.8 ML of suboxide at 530 °C. Based on thickness measurements from XPS and spectral ellipsometry, initial growth rates of 5 and ∼1 Å/min were achieved for ozone oxidation of Si0.85Ge0.15 at 530 and 125 °C, respectively. For the ultrathin regime (oxide thickness <25 Å), the effective activation energy for SiGe oxidation in 950 ppm of O3 is determined to be approximately 0.12 eV.