Silicon Oxynitride Thin Films Grown by Reactive HiPIMS

Amorphous silicon oxynitride (SiOxNy) thin films were grown by reactive high power impulse magnetron sputtering from a pure silicon target in Ar/N2O plasmas. The elemental composition of the films was shown to depend on the target surface conditions during the film deposition, as well as on the reactive gas flow rate. When the target was sputtered under poisoned surface conditions, the film composition was predominantly silicon oxide, whereas films deposited in the transition regime between poisoned and metallic target surface conditions showed higher nitrogen concentrations, as measured by X-ray photoelectron spectroscopy (XPS) and elastic recoil detection analysis (ERDA). The different target surface conditions were identified based on the evolution of the target current waveforms upon variation of the deposition parameters. The average electron temperatures during the peak target current were determined by Langmuir probe measurements, to assist with the explanation of the observed target current behavior and target poisoning characteristics. The chemical composition of the films was shown to range from silicon-rich to effectively stoichiometric silicon oxynitrides, where no Si−Si contributions were found in the XPS Si 2p core level spectra. The film optical properties, the refractive index n and the extinction coefficient k, were shown to depend on the film chemical bonding, with the effectively stoichiometric films displaying optical properties falling between those of SiO2 and Si3N4.