The presented paper describes a study concerning the synthesis of copper nitride layers by means of the pulsed magnetron sputtering (PMS) method that can work under conditions of various frequencies of modulation. The morphology and phase composition of the layers were determined as a function of the process parameters: the power (P) and frequency of power modulation - gating frequency (f(mod)). During the synthesis process, a plasma diagnostic was performed by optical emission spectroscopy (OES). We have observed that the structure of Cu-N layers strongly depends on these parameters. The interpretation of the obtained results of the phase composition was based on OES measurements, focusing mainly on elementary processes in plasma. The duration of target sputtering in each pulse of plasma, controlled by the frequency of power modulation, has been pointed out as the cause of observed differences in the phase composition of the layers. The results of the reported study proved the correct selection of the parameters of Cu3N synthesis. Moreover, they showed that the gating frequency can be considered a significant parameter of the magnetron sputtering process affecting the final state of the product of synthesis.