504-baumvol-apl-1999-1872 - Isotopic substitution of N, O,...

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Unformatted text preview: Isotopic substitution of N, O, and Si in the thermal oxidation of nitrogen-deposited silicon I. J. R. Baumvol a) Instituto de Fı´sica, Universidade Federal do Rio Grande do Sul, 9500 Porto Alegre - RS, Brazil 91509-900 T. D. M. Salgado, F. C. Stedile, C. Radtke, and C. Krug Instituto de Quı´mica, Universidade Federal do Rio Grande do Sul 9500 Porto Alegre - RS, Brazil 91509-900 ~ Received 17 August 1998; accepted for publication 3 February 1999 ! Nitrogen was deposited on the surface of Si ~ 100 ! wafers by ion implantation at a very low energy ~ approximately 20 eV ! , at fluences between 1 and 10 3 10 14 cm 2 2 . The samples were thermally oxidized in dry O 2 at temperatures between 800 and 1050 °C. Atomic transport of the chemical species involved in the process was investigated by isotopic tracing of N, O, and Si, using depth profiling with nanometric resolution. The obtained results indicate that: ~ i ! the nitrogen atoms deposited on the Si surface are redistributed during thermal oxidation in O 2 within the silicon oxide ~ oxynitride ! film, with maxima at the near-surface and near-interface regions; ~ ii ! during growth, O is fixed not only in the near-interface and near-surface regions like in the thermal growth of SiO 2 films on Si, but also in the bulk of the growing oxide ~ oxynitride ! film; and ~ iii ! Si is immobile during the thermal oxidation process. The observed modifications in the mechanisms of thermal growth of SiO 2 (SiO x N y ) films on Si due to the presence of N are discussed. © 1999 American Institute of Physics. @ S0003-6951 ~ 99 ! 01113-4 # In a recent publication 1 we reported on the thermal oxi- dation in dry O 2 of Si ~ 100 ! wafers whose surfaces were pre- viously covered with around 1/30–1 ML of N atoms by N 1 implantation at 20 eV. This kind of processing has recently been considered as a convenient route to prepare silicon ox- ynitride ultrathin films for gate dielectrics in ultra-large-scale integration ~ ULSI ! metal–oxide–semiconductor field-effect transistor ~ MOSFET ! devices. 2–5 The presence of N atoms at the surface of Si at these concentrations significantly de- creased the growth rate of the silicon oxide film, 1 whereas the N atoms were partially removed from the system as ther- mal oxidation proceeded. Several questions arose from this previous work: ~ i ! What is the depth distribution of the re- maining N atoms? ~ ii ! Which are the mobile species and which are the atomic transport mechanisms taking place dur- ing the thermal growth of the silicon oxide ~ oxynitride ! film? ~ iii ! What is the mechanism by which N reduces the thermal growth rate? This last question, in particular, has been the subject of many debates in the literature in the context of the thermal growth of silicon oxynitride films in N 2 O and NO....
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504-baumvol-apl-1999-1872 - Isotopic substitution of N, O,...

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