X-ray photoelectron spectroscopy and structural analysis of amorphous SiOxNy films deposited at low temperatures

Abstract

We establish, using a tetrahedral model, the bonding properties of amorphous silicon oxynitride (a-SiOxNy) films deposited at low temperatures (LTs) by electron-cyclotron resonance chemical-vapor deposition (ECRCVD) on several substrates and under various conditions of gas flows and total gas pressure in a dilute mixture of SiH4+N2 in Ar. The atomic percentage of each tetrahedral unit incorporated in the film network is calculated from the deconvolution of the high-resolution x-ray photoelectron spectroscopy (XPS) spectra in the Si 2p3∕2 region and corroborated by the results obtained from both survey scans and the high-resolution XPS spectra in the N 1s region. The Si3N4 phase is the most important one and the only bonding unit which is incorporated in all our LT ECRCVD SiOxNy films. The incorporation of all the other component tetrahedrons depends strongly on growth conditions. The threshold values of the N∕Si atomic ratio for which intrinsic defects, such as Si–Si bonds, are not incorporated in the network depend on the O∕Si ratio incorporated in the films, mainly due to the competition between oxygen and nitrogen atoms in their reaction with silicon dangling bonds. The effect of the total gas pressure on the atomic percentages of the oxidation states present in the LT ECRCVD SiOxNy films is qualitatively similar to the effect of the ion bombarding energy or the plasma density. O–N bonds are present only in samples having high amount of oxygen and nitrogen in their networks. For these films, our results show unambiguously the presence of the N–Si2O tetrahedron and suggest that N–Si3−νOν tetrahedrons with ν⩾2 are not incorporated in their networks. A correlation is observed between the N–Si2O and the Si–O3(ON) tetrahedrons whose component peak is localized at (104.0±0.2)eV in the Si 2p3∕2 region of the XPS data, which suggests that both bonding units coexist in these films as some sort of complex bonding configuration.