Surface and interface structures of epitaxial silicon nitride on Si(111)

Abstract

Surface and interface structures of an ultrathin silicon nitride film grown epitaxially on the Si(111) surface are investigated by core-level and valence-band photoelectron spectroscopy using synchrotron radiation. The Si $2p$ photoelectron spectra reveal a characteristic series of components for the Si species not only in stoichiometric ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ $({\mathrm{Si}}^{4+})$ but also in the intermediate nitridation states with one $({\mathrm{Si}}^{+})$ or three $({\mathrm{Si}}^{3+})$ nitrogen nearest neighbors. The Si $2p$ core-level shifts for the ${\mathrm{Si}}^{+},$ ${\mathrm{Si}}^{3+},$ and ${\mathrm{Si}}^{4+}$ components are determined to be 0.64, 2.21, and 2.74 eV, respectively. In sharp contrast to the well-known ${\mathrm{SiO}}_{2}/\mathrm{Si}(111)$ case, no trace of the ${\mathrm{Si}}^{2+}$ species is observed, indicating an atomically abrupt and defect-free interface in accordance with a recent interface model of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}/\mathrm{Si}(111).$ In addition, the origin of the characteristic N $1s$ spectra and a strong surface-state emission observed in the valence-band spectra are discussed.