339-lu-apl-1995-1742 - An isotopic labeling study of the...

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Unformatted text preview: An isotopic labeling study of the growth of thin oxide films on Si(100) H. C. Lu and T. Gustafsson Department of Physics and Astronomy, and Laboratory for Surface Modification, Rutgers University, Piscataway, New Jersey 08855-0849 E. P. Gusev and E. Garfunkel a) Department of Chemistry, and Laboratory for Surface Modification, Rutgers University, Piscataway, New Jersey 08855-0939 ~ Received 4 May 1995; accepted for publication 13 July 1995 ! The mechanism of thin ~ , 8 nm ! oxide growth on Si ~ 100 ! has been studied by high-resolution medium energy ion scattering in combination with oxygen isotope substitution in the T 5 800– 900 °C and 0.1–1 Torr oxygen pressure regime. Isotopic labeling experiments demonstrate that the Deal–Grove model breaks down for these films. In addition to the traditional oxidation reaction at the Si/SiO 2 interface, two other spatially specific reactions take place during thermal oxidation: an exchange reaction at the oxide surface and an oxidation reaction in the near-interfacial region. © 1995 American Institute of Physics. The growth of thin oxide films during the thermal oxi- dation of silicon is still not well-understood. 1–6 Oxidation kinetics for thick ~ . 20 nm ! films is described by the Deal– Grove model, in which oxide growth proceeds via molecular oxygen diffusion to the Si–SiO 2 interface and reaction with silicon at the interface. 7 However, early studies 4,8 demon- strated that the oxidation kinetics for ultrathin ~ , 10 nm ! oxides could not be explained by this model. Recently, we have used sequential exposures of oxygen isotopes in combination with medium energy ion scattering ~ MEIS ! to elucidate the growth mechanism of 2–5 nm oxide films. 9,10 This technique 11 provides a determination of the isotope depth distributions with an accuracy ~; 0.4 –0.5 nm ! , significantly better than NRA 5 and SIMS 12 which have pre- viously been used to study the growth of thicker oxides. In particular, we showed that 18 O 2 followed by 16 O 2 oxidation results in overlapping depth profiles of the isotopes for 2–3 nm films ~ isotopic mixing ! , a behavior not expected from the traditional Deal–Grove model. We also observed 18 O loss after 16 O 2 exposures, the result of an oxygen exchange reac- tion near oxide surface. A new ‘‘interfacial 1 near-interfacial 1 surface exchange reaction’’ model was proposed to account for these results. 10 Neither the near-interfacial nor the surface exchange re- actions were directly resolved in our previous experiments. In this letter, we present results of an MEIS study of thicker ~; 6 nm ! Si 16 O 2 films reoxidized in 18 O 2 to final thicknesses up to ; 8 nm. Since the thickness of the initial oxide is now greater than the thickness of the two reaction regions ~ which have a width on the order of 2 nm ! , two well-separated 18 O peaks are observed in the MEIS spectra after the reoxi- dation; one corresponds to an 18 O oxide near the surface, the other to...
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339-lu-apl-1995-1742 - An isotopic labeling study of the...

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