It is well known that the kind of disorder in amorphous materials have a great influence on their properties and the determination of the structure is necessary to understand the physical mechanisms governing these properties. The structure of ternary compounds, such as silicon oxynitride, could be mainly described by two models: the Random Bonding Mode (RBM) and the Random Mixture Model (RMM).
Amorphous silicon oxynitride (a-SiOxNy) thin films were obtained by sputtering a pure silicon target under different argon-oxygen-nitrogen gas mixtures. A large range of compositions, between Si3N4 and SiO2, was obtained by varying only the reactive gas flow ratio. The deposit structure was investigated by mean of IRTF and XPS analysis. The absorption spectra showed a large band located between 600 cm-1 and 1300 cm-1 with a continuous shift of the absorption maximum towards higher wave numbers when the oxygen concentration increases. We also noticed that the Si3N4 and SiO2 absorption peaks clearly appear. The Si 2p photoelectron peak maximum shifts towards higher binding energies (from 102.4 to 103.3 eV) and the full width at half maximum slightly decrease (from 2.9 to 2.7 eV) when the oxygen content increases. The XPS spectra were decomposed into five components corresponding to the polysubstituted tetrahedra SiOjN4-j following the RBM model but we noticed an excess of SiN4 and SiO4 configurations for N-rich and O-rich films respectively. It was also found that Auger parameter exhibits a non linear behaviour and that shoulders appear on the Si KLL Auger transition spectra. Such results support the SiN4 and SiO4 configurations excess. Finally a comparison between the theoretical expectations and experimental values of the presence of the different tetrahedra allowed us to conclude that our material contains Si3N4 and SiO2 phases incorporated in amorphous SiOxNy one.
|