X-ray photoelectron spectroscopy investigation on the chemical structure of amorphous silicon nitride (a-SiNx)

Abstract

Amorphous silicon nitride a-SiNx (0<x<1.7) thin films, prepared by dual ion beam sputtering, were investigated by means of high-energy resolution photoelectron spectroscopy using an x-ray monochromatized radiation. The variation of the position, width and line shape of the Si 2p photoemission peak, as a function of the alloy composition, was explained in terms of an overlapping of five chemically shifted unresolved components corresponding to the five tetrahedral silicon bonding configurations Si–Si4−nNn (n=0,1,...,4). Considering each component as a convolution of the spin-orbit doublet Si 2p1/2–Si 2p3/2, we experimentally determined their binding energy and full width at half-maximum. We thus obtained, by a curve-fitting process, the Si–Si4−nNn distribution as a function of atomic composition and compared it with the predictions of the most used growth models: the random bonding model and stoichiometric statistical model. These two models were in disagreement with the experimental data, thus a third model was proposed based on the invariant coordination of nitrogen to three silicon neighbors, and includes also a nucleation of possible stoichiometric clusters in the a-SiNx films. Moreover, methodological aspects such as artifacts induced by ion sputtering, used to clean the sample surface before x-ray photoelectron spectroscopy measurements, were taken into account.