Effect of the SiO₂/Si interface on self-diffusion in SiO ₂ upon oxidation

The effect of the SiO₂/Si interface on Si self-diffusion in SiO₂ during thermal oxidation was investigated using silicon isotopes. Samples with ^natSiO₂/²⁸Si heterostructures were oxidized at 1150 - 1250°C and the ³⁰Si diffusion in ²⁸SiO₂ during the thermal oxidation was investigated by secondary ion mass spectrometry (SIMS) measurements. Near the SiO₂/Si interface, a significant profile broadening of the ³⁰Si isotope from ^natSiO₂ toward the newly grown ²⁸SiO₂ was observed. This ³⁰Si self-diffusivity sharply decreases with oxidation time and hence with increasing distance between ³⁰Si diffusion region and the interface. This distance-dependent ³⁰Si self-diffusion was simulated taking into account the effect of Si species generated at the interface upon oxidation and diffusing into SiO₂ to enhance Si self-diffusion. The simulation fits the SIMS profiles and these results indicate that Si species, most likely SiO, are emitted from the SiO₂/Si interface upon Si thermal oxidation to release the oxidation-induced stress, as has been predicted by recent theoretical studies. Furthermore, combined with our recent results on O self-diffusion, the diffusion behavior of the emitted SiO near the SiO ₂/Si interface is discussed.