Improved thermal stability of ultrathin silicon oxynitride layer due to nitrogen incorporation at the interface

This paper describes the effect of annealing on ultrathin oxynitride films on Si 100.surface prepared by the dissociative interaction of nitric oxide NO.at room temperature. Ultraviolet and X-ray photoelectron spectroscopy UPS and XPS.and Auger electron spectroscopy AES. have been employed to understand the clustering phenomenon of approximately monolayer thick oxynitride layer. On annealing the oxynitride at ;5008C, nitrogen atoms move preferentially towards the interface. In the UPS, absence of the reappearance of surface states even after annealing the oxynitride to ;7208C suggests a resistance to clustering of the oxynitride layer. This is in contrast to the annealing behavior of pure SiO2 film where clustering begins at temperatures as low as 1908C. On further annealing of the oxynitride film at 8308C, the SiN species remain on the surface due to the selective desorption of SiO species. Upon exposing oxygen to this surface, selective adsorption takes place on the bare Si areas exposed by the desorption of SiO. We believe that the enhanced thermal stability of ultrathin silicon oxynitride is due to the stabilization of the interface by the nitrogen atoms incorporated preferentially at the SirSiO2 interface. q1998 Elsevier Science B.V. All rights reserved.