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.