Analysis by surface-sensitive second harmonic generation of Si(111)7 × 7 exposed to high-purity ozone jet for oxide film formation

We observed an in situ process of ozone adsorption on Si(111)7 × 7 at different temperatures by second harmonic generation (SHG). On ozone exposure, the second harmonics (SH) intensity descreased close to a detectable limit on the surface at room temperature (RT). However, we observed the appearance of another SH intensity during ozone exposure at elevated substrate temperatures between 260 °C and 400 °C, after it decreased in the same way as that at RT. On these surfaces, the profile of SH intensity recovery by desorption of adsorbed species indicated that different adsorbed species were formed during surface exposure to ozone at different substrate temperatures: those at RT are weakly adsorbed species for termination of dangling bonds and insertion into backbonds, and those at higher temperatures have an Si-O-Si network which is more stable and desorbs at higher temperatures than 700 °C. We conclude that the SH intensity that appeared on the surfaces at elevated temperatures is due to more stable SiO₂-like Si-O-Si bonding as an initial step of oxide formation.