Copper nitride films were prepared by the rf magnetron sputtering method using Ar and N-2 as working gas. The nitrification degree of the films was studied by changing the N-2 fraction or the substrate temperature under the N-2 fraction of 30%. The films deposited under different N-2 fraction were also annealed at temperature range of 100-300 degrees C in order to study the thermal stability of the films. X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films. It was shown that the films grow along the [100] orientation and the preferential growth becomes heavier with increasing N-2? fraction. The size of the Cu3N grain is estimated to be on the order of nanometers, and the grain size increases with increasing N-2;? fraction. The Cu3N phase is thermally unstable in vacuum even at 100 degrees C. During the deposition under the N-2 fraction of 30%, the highest substrate temperature to form the Cu3N phase ranges from 200 to 250 degrees C. Good agreement between XRD and XPS analysis was obtained in characterizing the film structures. The observed phenomena are discussed briefly.