Nitrogen doped amorphous carbon (a-C:N) films are a material that may successfully compete with DLC coatings, which have high hardness, high wear resistance, and a low friction coefficient. The a-C: N films were prepared on silicon substrate by a closed-field unbalanced magnetron sputtering method with a graphite target and using the Ar/N-2 mixture gases. And, we investigated the effects of various DC bias voltages from 0 to - 300 V on the structural and tribological properties of the a-C: N films. This study was focused on improving physical properties of the a-C: N film by controlling process parameters like negative substrate DC bias voltage. The maximum hardness of the a-C: N film was 23 GPa, the friction coefficient was 0.08, and the critical load was 25 N on a Si wafer. Consequently, the structural and tribological properties of the a-C: N film showed a clear dependence on the energy of ions bombardment and the density of the sputtering and the reaction gases during film growth. (C) 2008 Elsevier B. V. All rights reserved.