The mechanism of thermal oxidation of silicon in dry oxygen was studied using 18O as the tracer. SiO2 layers first grown in natural oxygen (1300–3000 Å) were further grown in highly 18O-enriched oxygen for 8.5 h at 930 °C. 18O profiling was carried out using the 629-keV narrow resonance in the nuclear reaction 18O(p,α)  15N. The resulting SiO2 films consist of two 18O-rich layers, 7% near the SiO2 surface and 93% near the Si-SiO2 interface, while the bulk 18O concentration is very low. The results suggest that the oxide grows mainly through long-range migration of oxygen, favoring models based on the transport of molecular oxygen.

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A method has been developed for the determination of very small quantities of the stable isotopes of oxygen.