An isotopic labeling study of the diffusion mechanism during oxidation of Si(100) in water vapor by successive oxidation

The diffusion mechanism during the wet oxidation of Si(100) at 1373 K was investigated by successive oxidations finally containing isotopic water. SiO₂ was first thermally grown on Si in non-labeled oxidizing ambient (dry O₂ or H₂O) followed by isotopic water (H₂¹⁸O) to trace ¹⁸O species in SiO₂. The distributions of ¹⁶O and ¹⁸O in the oxide film were analyzed by means of secondary ion mass spectroscopy (SIMS). SIMS depth profiles show that there was a wide overlap of both isotopes (¹⁸O and ¹⁶O) throughout the SiO₂ layer, no matter whether the first oxidation step was carried out in dry O₂ or H₂O, and the concentration gradient of ¹⁸O decreased with increasing oxidation time at the second oxidation step by H₂¹⁸O. The results suggest that the diffusion mechanism in SiO₂ during water vapor oxidation is exchange diffusion; H₂O related oxidizing species diffuse through the network with significant exchange with the pre-existing oxygen in it.