Isotopic Labeling Studies of Oxynitridation in Nitric Oxide (NO) of Si and SiO2

Rapid thermal oxynitridation in nitric oxide (NO) of a thick (14 nm) Si02 film grown on Si(001) is studied as a first stage towards understanding of atomic transport mechanisms occuring during NO annealing of thin SiO2 films. The SiO2 films were grown in an ultra high vacuum rapid thermal processing (RTP) furnace in static pressure of natural O2 (16O2). These films were then annealed in N and 180-enriched NO (15N18O) for 20 and 80 s. Total amounts of nitrogen and oxygen (areal densities in at.cm-2) and heavy isotopes depth distribution were measured using non resonant and resonant nuclear reactions analysis. The results are discussed in terms of atomic depth profiles and growth mechanisms. These first results are more likely explained by two mechanisms occuring in parallel. In the first one, NO diffuses through the silica network without reacting with it and both N and O are fixed in the near interface region. In the second one, 18O is fixed near the oxide surface due to a mechanism related with a step-by-step motion of network oxygen atoms, by a simple diffusion process, induced by the presence of network defects, involving O only. This latter mechanism leads mostly to an exchange of oxygen atoms between the oxide network and the gas phase.