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 〈$\mathrm{\sim 5-nm-Pt/0.5–1-nm-chemical\hspace{0.17em}oxide/Si(100)}$ 〉 structure at 300–400 °C increase the oxide thickness to 4–5 nm. The amounts of the suboxide species, $\mathrm{a(}{\mathrm{Si}}^{\mathrm{+}}\mathrm{),}$ $\mathrm{a(}{\mathrm{Si}}^{\mathrm{2+}}\mathrm{),}$ and $\mathrm{a(}{\mathrm{Si}}^{\mathrm{3+}}\mathrm{),}$ in the chemical oxide layers formed in hydrochloric acid (HCl) plus hydrogen peroxide $({\mathrm{H}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{2}})$ are in the order of $\mathrm{a(}{\mathrm{Si}}^{\mathrm{+}}\mathrm{)>a(}{\mathrm{Si}}^{\mathrm{2+}}\mathrm{)>a(}{\mathrm{Si}}^{\mathrm{3+}}\mathrm{),}$ while those for the oxide layers formed in nitric acid $({\mathrm{HNO}}_{\mathrm{3}})$ have an order of $\mathrm{a(}{\mathrm{Si}}^{\mathrm{3+}}\mathrm{)>a(}{\mathrm{Si}}^{\mathrm{2+}}\mathrm{)\approx a(}{\mathrm{Si}}^{\mathrm{+}}\mathrm{).}$ 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 ${\mathrm{HNO}}_{\mathrm{3}}$ oxide layers are more highly