Diffusion barrier characteristics of molybdenum nitride thin films for Cu metallization were investigated as functions of annealing conditions by Rutherford backsattering spectroscopy, Nomarski microscope and electrical measurements. Molybdenum nitride thin films on Si were found to have molybdenu, silicide formed in the interface after annealing in $N_2$ at $700^{circ}C$for 30min. For $Si/{Gamma}-Mo_2N/Cu$ films, there was no indication of interdiffusion by conventaional depth profiling technique up to $600^{circ}C$ in $N_2$ for 30min. However, barrier failure was found to occur above $650^{circ}C$ by formation of silicide phases due to diffusion of Cu through the nitried layer to Si. The correlation between the structure and electrical properties of the molybdenum nitride films were discussed in terms of the barrier behavior.