Thermal stability, microstructure and electrical property of molybdenum nitride film were studied for application of ULSI's DRAM capacitor electrode and copper diffusion barrier. Phase transformation from Mo to γ-Mo2N was observed at 20% N2/(Ar+N2) flow ratio and γ-Mo2N and Δ-MoN phases coexisted at 50% N2 flow ratio. γ-Mo2N film was found to crystallize at 400°C. Amorphous γ-Mo2N deposited at 300 °C remained stable upon 750 °C heat treatment. Breakdown strengths of Y -Mo2N/Ta2O&/Si MOS capacitor before and after 850 °C annealing were 2.4 MV/cm and 1.85 MV/cm at 1×10-6 A/cm2, respectively. After 850 °C annealing, dielectric constant of Ta2Os film decreased to 19.