GROWTH-MECHANISM OF THIN SILICON-OXIDE FILMS ON SI(100) STUDIED BY MEDIUM-ENERGY ION-SCATTERING

The growth of ultrathin oxide films by the thermal oxidation of Si(100 ) at 1020-1170 K and in 10(-1)-10(-3) Torr O-2 pressure has been studi ed by high-resolution medium-energy ion-scattering spectroscopy (MEIS) . To develop a fundamental understanding of very thin oxide film growt h, we utilize sequential isotopic exposures (O-18(2) followed by O-16( 2)). MEIS readily distinguishes O-18 from O-16 and the depth distribut ion for both species can be determined quantitatively with high accura cy. Our results show that the traditional phenomenological models for silicon oxidation cannot be applied to the initial oxidation. For very thin oxide films (15-25 Angstrom), we find overlapping isotope depth profiles in the film. For thicker films ( > 40 Angstrom), we find that several key aspects of the Deal-Grove model (oxygen diffusion to the Si-SiO2 interface and oxide formation at and/or near that interface) a re consistent with our results. We also observe O-18 loss from the sur face after reoxidation in O-16(2). The complex oxidation behavior duri ng the initial oxidation is likely to be a combination of interfacial, near-interfacial, and surface reactions.