High resolution x-ray photoelectron spectroscopy has been used to determine the valence band alignment at ultrathin SiO 2 /Si interfaces. In the oxide thickness range 1.6-4.4 nm the constant band-offset values of 4.49 and 4.43 eV have been obtained for the dry SiO 2 /Si͑100͒ and the wet SiO 2 /Si͑100͒ interfaces, respectively. The valence band alignment of dry SiO 2 /Si͑111͒ ͑4.36 eV͒ is slightly smaller than the case of the dry SiO 2 /Si͑100͒ interface. © 1997 American Institute of Physics. ͓S0021-8979͑97͒00203-X͔ Ultralarge scale integration ͑ULSI͒ of metal-oxidesemiconductor ͑MOS͒ devices will need reliable gate oxides thinner than 5.0 nm in the near future. In order to predict the tunneling leakage current through the ultrathin gate oxides, an accurate description of the energy band profile at the ultrathin SiO 2 /Si interfaces or a precise knowledge on the value of the valence band alignment and the conduction band barrier height is required.1 Although the energy band profile of thick SiO 2 /Si interfaces has been determined by an internal photoemission technique, 2 reliable values for the electron or hole barrier height at ultrathin SiO 2 /Si interfaces remain an unresolved issue. Among the various attempts that have been made in the past to gain a comprehensive understanding of the barrier height or the energy band profile for ultrathin SiO 2 /Si interfaces, 3-8 the consistent picture of the energy band profile has not yet been drawn. Horiguchi and Yoshino 3 have reported that the barrier height for SiO 2 /Si͑100͒ decreases when the oxide thickness becomes thinner than 3.1 nm. On the other hand, by using an electron-beam-assisted scanning tunneling microscopy technique, Heike et al. 4 have concluded that the barrier height at the SiO 2 /Si͑100͒ interfaces keeps a constant value of 2.7 eV in the oxide thickness range 1.8-4.5 nm. Grunthaner and Grunthaner 9 have measured valence band spectra of ϳ6-nm-thick SiO 2 thermally grown on Si͑111͒ by using x-ray photoelectron spectroscopy and found the valence band offset of 4.5 eV. Also, Himpsel et al. 10 have obtained a valence band alignment of 4.3 eV for the SiO 2 /Si͑100͒ interface by using the Si 2 p core level spectrum. Thus well established values of the valence band alignment or the barrier height at ultrathin SiO 2 /Si interfaces are not available.The purpose of our study is to directly determine the magnitude of the valence band alignment or the hole barrier height at the ultrathin SiO 2 /Si interface and derive a value for the conduction band barrier height by using a measured SiO 2 band gap, based on the valence band density of states ͑VB-DOS͒ for ultrathin gate oxides ͑below 5.0 nm͒ thermally grown on Si͑100͒ and Si͑111͒ surfaces by employing highresolution x-ray photoelectron spectroscopy ͑XPS͒.Ultrathin gate oxides were grown at 1000°C in a 2% dry O 2 gas diluted with N 2 or at 850°C in wet ambient. Hydrogen-terminated p-type Si͑100͒ substrates ͑10 ⍀ cm͒ were obtained by modified RCA cleaning with a low concentration of NH 4 OH followed by a chemical...

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Nitrogen doped silicon ͑NIDOS͒ films have been deposited by low-pressure chemical vapor deposition from silane SiH 4 and ammonia NH 3 at high temperature ͑750°C͒ and the influences of the NH 3 /SiH 4 gas ratio on the films deposition rate, refractive index, stoichiometry, microstructure, electrical conductivity, and thermomechanical stress are studied. The chemical species derived from silylene SiH 2 into the gaseous phase are shown to be responsible for the deposition of NIDOS and/or ͑silicon rich͒ silicon nitride. The competition between these two deposition phenomena leads finally to very high deposition rates ͑Ϸ 100 nm/min͒ for low NH 3 /SiH 4 gas ratio (RϷ0.1). Moreover, complex variations of NIDOS film properties are evidenced and related to the dual behavior of the nitrogen atom into silicon, either n-type substitutional impurity or insulative intersticial impurity, according to the Si-N atomic bound. Finally, the use of NIDOS deposition for the realization of microelectromechanical systems is investigated.

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