Effect of chemical oxide layers on platinum-enhanced oxidation of silicon

Si oxidation promoted by a platinum (Pt) overlayer has been investigated using x-ray photoelectron spectroscopy and synchrotron radiation ultraviolet photoelectron spectroscopy. Heat treatments of the specimens with 〈∼5-nm-Pt/0.5–1-nm-chemical oxide/Si(100)〉 structure at 300–400 °C increase the oxide thickness to 4–5 nm. The amounts of the suboxide species, a(Si+), a(Si2+), and a(Si3+), in the chemical oxide layers formed in hydrochloric acid (HCl) plus hydrogen peroxide (H2O2) are in the order of a(Si+)>a(Si2+)>a(Si3+), while those for the oxide layers formed in nitric acid (HNO3) have an order of a(Si3+)>a(Si2+)≈a(Si+). The amounts of the suboxide species in the former oxide layers are much higher than those in the latter oxide layers. These results indicate that the HNO3 oxide layers are more highly oxidized, probably resulting in a higher atomic density and a lower defect density. Although the initial chemical oxide layers formed in HCl+H2O2 are thinner than those grown in HNO3, the former oxide layers become thicker than the latter after the Pt deposition and the heat treatments below 200 °C. This result is attributed to the lower atomic density and the higher defect density of the chemical oxide layers produced in HCl+H2O2, which enhance the diffusion of oxidizing species. It is suggested that the variation in the atomic density of the chemical oxide layers cause the different energy distribution of interface states in the Si band gap.