Incorporation of Ambient Oxygen During Silicon Deposition and the Effects of Argon Ion Bombardment

The composition of SiOx films deposited by electron-beam evaporation of silicon in an oxygen atmosphere was measured as a function of silicon deposition rate and oxygen pressure. The compositions varied between X = 0.03 and 2.1 depending on the ratio of O2 molecules to Si atoms arriving at the substrate. Bombardment with 500 eV argon ions caused X to decrease at low arrival ratio and to increase at higher arrival ratio. The results are analyzed using an adsorption model in which chemisorption of O2 occurs after physisorption into one of two states: one on silicon and one on SiO2. A fit to the data for the unbombarded samples is achieved if physisorption occurs only on silicon. From this fit a sticking coefficient of 0.05 is obtained for O2 chemisorption on silicon. The effects of ion bombardment are consistent with the model if bombardment allows O2 to also physisorb on SiO2 and migrate to silicon where it chemisorbs.