In this paper, samples of copper nitride, a thermally unstable semiconducting material, were synthesized as layers, using the pulsed magnetron sputtering method. Synthesis was performed under different pure nitrogen pressure points, which aimed at obtaining layers differentiated in terms of their structure. The deposited layers have been subjected to heat treatment to achieve a better understanding of the thermal evolution of the structure of the material. A series of treatments were carried out in different temperatures starting from within studied one phase materials stability range (T∼230°C), through the intermediate range of a two-phase structure: Cu3N, Cu (∼230°C<T<330°C) up to the point of complete thermal decomposition (T∼400°C), enabling to better describe stoichiometry contributions of copper nitride to the thermal stability of the material. Crystalline phase and lattice constants of the deposited layers were characterized with X-ray diffraction measurements for samples from each temperature point. The phase composition was confirmed by Raman spectroscopy. Optical studies were performed by spectroscopic ellipsometry and resistivity by the Kelvin measurement method. Studies were evaluated and plotted as a function of annealing temperature. Deposited samples exhibited an anti-ReO3 polycrystalline structure with its lattice constant corresponding with literature data. The results showed changes in the structure of copper nitride layers induced by temperature. Higher temperatures caused visible structural changes. Depending on the stoichiometry of copper nitride layers, the thermal stability of the material was different. The reported changes were discussed and attributed to the stoichiometry of the material layers.