X-Ray Photoelectron Spectroscopy of SiO2-Si Interfacial Regions: Ultrathin Oxide Films

The composition and width of the interfacial region formed between thin thermally-grown oxide films and single-crystal Si substrates were nondestructively characterized by means of x-ray photoelectron spectroscopy. Data obtained from variations in core-level binding energies, from variations in photoelectron line intensities, and from variations in photoelectron linewidths indicate the presence of a nonstoichiometric oxide-Si transition region. The composition and width of this region are dependent upon substrate orientation, but are invariant with change in other oxidation processing parameters. Transition regions formed on 〈100〉 oriented substrates are narrower and more completely oxidized than those formed on 〈111〉 oriented substrates. Although both Si-Si bonds and SiO-Si groups are present in this nonstoichiometric region, they do not appear to be a mixture of Si and SiO
2
. Instead, a continuous distribution of Si tetrahedra, Si-(O)
x
(Si)
4−x
, are formed, in which x changes from 0 to 4 as one proceeds from the substrate to the stoichiometric SiO
2
film.