Effect of oxygen inclusion on microstructure and thermal stability of copper nitride thin films

Copper oxynitride thin films with a minor oxygen content were prepared on silicon wafers at 100 °C by reactive magnetron sputtering using a gas mixture of nitrogen and oxygen. Addition of oxygen immediately improves the compactness of the deposits, which otherwise comprise ragged Cu₃N nanocrystallites. With an oxygen content <10.0 at.%, the deposits reveal some sporadic Cu₂O nanocrystals under transmission electron microscopy, but their x-ray diffraction (XRD) patterns exhibit reflections only from the Cu₃N phase. The decomposition temperature, at which the sample after prolonged annealing shows Cu reflections on its XRD pattern, can be raised from 300 °C for stoichiometric Cu₃N to 360 °C. The decomposition product after annealing at 450 °C is pure copper having an electrical resistivity of 8.94 × 10⁻⁸ Ω·m at room temperature, which can be taken as a good conductor and stands in strong contrast with the oxynitride matrix with an electrical resistivity of 6.87 × 10⁻² Ω·m. These results constitute progress in the search of directly writable copper nitride-based materials.