ANALYSIS BY SURFACE-SENSITIVE 2ND-HARMONIC GENERATION OF SI(111)7X7 EXPOSED TO HIGH-PURITY OZONE JET FOR OXIDE FILM FORMATION

We observed an in situ process of ozone adsorption on Si(111)7 x 7 at different temperatures by second harmonic generation (SHG). On ozone e xposure, the second harmonics (SH) intensity descreased close to a det ectable limit on the surface at room temperature (RT). However, we obs erved the appearance of another SH intensity during ozone exposure at elevated substrate temperatures between 260 degrees C and 400 degrees 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 speci es indicated that different adsorbed species were formed during surfac e exposure to ozone at different substrate temperatures: those at RT a re weakly adsorbed species for termination of dangling bonds and inser tion into backbonds, and those at higher temperatures have an Si-O-Si network which is more stable and desorbs at higher temperatures than 7 00 degrees C. We conclude that the SH intensity that appeared on the s urfaces at elevated temperatures is due to more stable SiO2-like Si-O- Si bonding as an initial step of oxide formation. (C) 1997 by John Wil ey & Sons, Ltd.