18-baumvol-apl-1998-2999 - Incorporation of oxygen and...

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Unformatted text preview: Incorporation of oxygen and nitrogen in ultrathin films of SiO 2 annealed in NO I. J. R. Baumvol a) Instituto de Fisica, UFRGS, Porto Alegre, RS, 91509-900 Brazil J.-J. Ganem, L. G. Gosset, I. Trimaille, and S. Rigo Groupe de Physique des Solides, UMR 77-88—CNRS, Universite ´s Paris 6 et Paris 7, 2, Place Jussieu, 75251 Paris, Cedex 05, France ~ Received 24 November 1997; accepted for publication 3 April 1998 ! The areal densities of oxygen and nitrogen incorporated into ultrathin films of silicon dioxide during rapid thermal processing in nitric oxide, as well as the regions where these incorporations took place, were determined by combining nuclear reaction analysis and narrow nuclear resonance depth profiling with isotopic enrichment of the processing gas. Oxygen is seen to incorporate in the near-surface and near-interface regions of the oxynitride films, whereas nitrogen is incorporated only in the near-interface regions. The growth of the oxynitride film is very moderate as compared to that of a SiO 2 film in dry O 2 . The thermal oxynitridation of ultrathin SiO 2 films takes place by two mechanisms in parallel: the major part of the NO molecules, which react with the silica, decompose in the near-surface region, the O atoms being exchanged for O atoms preexistent in this region of the SiO 2 films; a minor portion of the NO molecules diffuse through the silica film in interstitial sites, without reacting with it, to react at the oxynitride/Si interface. © 1998 American Institute of Physics. @ S0003-6951 ~ 98 ! 01823-3 # Recent publications 1–4 reported on complementary metal–oxide–semiconductor ~ CMOS !-based devices in which the gate dielectric was made of ultrathin ~ between 2.5 and 8 nm ! silicon oxynitride films, produced by either direct thermal growth in NO, or by thermal oxynitridation of an ultrathin SiO 2 film in NO. These oxynitride films exhibit several properties superior to thermal O 2 oxides, the most important ones being supression of boron penetration, en- hanced reliability, and reduced hot-electron induced degra- dation. The direct thermal growth in NO is self-limited 5–7 to a maximum thickness of about 2.5 nm for temperatures be- low 1100 °C, most probably due to the high concentration of nitrogen in the near-interface region. For temperatures at and above 1100 °C, the oxynitride films were observed to grow at a much higher rate, up to a thickness of 80 nm. 5 On the other hand, the production of oxynitride films by thermal nitridation of SiO 2 films in NO provides a flexible method of tailoring continuously the film thickness in the range 2–20 nm, as well as the nitrogen concentration in the range 0.5–5.0%. 8,9 NO is believed 10–13 to be the species respon- sible for nitrogen incorporation into the SiO 2 films. In this work we report on the kinetics of oxygen and nitrogen incor- poration, as well as on the depth profiles of the incorporated O and N atoms, during thermal annealing of SiO 2 films in NO....
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18-baumvol-apl-1998-2999 - Incorporation of oxygen and...

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