Isotopic labeling studies of interactions of nitric oxide and nitrous oxide with ultrathin oxynitride layers on silicon

The interaction of nitric (NO) and nitrous (N2O) oxide with ultrathin (simi lar to 1.5-3.5 nm) oxide and oxynitride films on silicon has been studied b y performing high resolution depth profiling using medium energy ion scatte ring and isotopic labeling methods. We observe that, after NO annealing at 850 degrees C, both O and N incorporate near the SiO2/Si interface. There i s no nitrogen and little newly incorporated oxygen observed at the surface, implying that NO diffuses through the oxide film and dissociates and react s at the interface. For N2O annealing, atomic oxygen resulting from decompo sition of the gas can replace oxygen atoms in both oxide and oxynitride fil ms. This replacement is most important at the surface, but also, to a small er extent, occurs in the middle of the film. For ultrathin oxynitride films , oxide growth during reoxidation is faster in N2O than in pure O-2. Atomic oxygen also influences the nitrogen distribution, which moves further into the film and accumulate at the new interface. We discuss the roles of atom ic oxygen and peroxyl bridging oxygen species in explaining the observed ph enomena. (C) 2000 American Institute of Physics. [S0021-8979(00)01303-7].