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105-baumvol-apl-1996-2385 - Nitrogen transport during rapid...

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Nitrogen transport during rapid thermal growth of silicon oxynitride films in N 2 O I. J. R. Baumvol a) Instituto de Fisica, UFRGS, Porto Alegre, RS, 91540-000, Brasil F. C. Stedile Instituto de Quimica, UFRGS, Porto Alegre, RS, 91540-000, Brasil J.-J. Ganem, I. Trimaille, and S. Rigo Groupe de Physique des Solides, URA 17-CNRS, Universite ´s Paris 6 et Paris 7, 75251 Paris-CEDEX 05, France ~ Received 21 May 1996; accepted for publication 1 August 1996 ! We investigated the transport of nitrogenous species during rapid thermal growth of silicon oxynitride films on Si in N 2 O, using N isotopic tracing and high resolution depth profiling techniques. The results indicate that the diffusion of nitrogenous species ~ most probably NO ! through the growing oxynitride film to react with Si at the oxynitride/Si interface, induces the incorporation of N near this interface. This mechanism acts in parallel with a site-to-site jump mechanism ~ interstitialcy or vacancy ! of diffusion and chemical reaction of nitrogenous species in the volume of the growing oxynitride film. The characteristic N accumulation only near the interface obtained by rapid thermal processing growth in N 2 O is due to the removal of N from the near surface region of the films, here attributed to atomic exchanges O N taking place during growth. Furthermore, N N exchange was also observed. © 1996 American Institute of Physics. @ S0003-6951 ~ 96 ! 00642-0 # As metal-oxide-semiconductor ~ MOS ! devices are scaled down to the deep submicron, a gate dielectric more reliable than SiO 2 is required. Recently, there has been inter- est in using nitrous oxide ~ N 2 O ! to grow thin ~ , 10 nm ! dielectric films on Si by rapid thermal processing ~ RTP ! . 1–5 The thermal growth of the oxynitride films seems to be self- limited to thicknesses between 4 and 12 nm, depending on the RTP temperature, whereas the N concentration in the films grows continuously with the RTP time. 6,7 In the oxyni- tride films grown by RTP, N is located near the oxynitride/Si interface, being absent from the surface and from the bulk until a certain depth. 2,7,8 Carr et al. 8 attributed to O 2 the lead- ing role in the growth of the oxynitride films, by means of the oxidation of Si. The reaction of NO with Si was thought to be the main cause of nitrogen incorporation into the ox- ynitride films. The peak N concentration in the films depends linearly on the NO concentration in the gas phase. 9–11 The removal of N from the near surface region of the oxynitride film grown by RTP in N 2 O was demonstrated to be due to the action of O, which is produced in the vicinity of the Si wafer. 8 Aiming to investigate the atomic transport processes tak- ing place, we report here on the first studies of isotopic trac- ing of N during thermal growth of oxynitride films in N 2 O using a RTP furnace. All the treatments were performed at 1050 °C, under a N 2 O pressure of 30 mbar ~ i.e., 3 kPa ! . The two gases used for film growth were pure N 2 O containing N and O isotopes in their natural abundances ( 14 N 2 O),and 97% 15 N-enriched N 2 O ( 15 N 2 O). The total amounts of the differ-
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