NbNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability. NbNx thin films with NbN0.49, NbN1.08, NbN1.71, NbN2.25, NbN2.75 were prepared using radio frequency (RF) sputter. The experimental results showed that the contact angle at 20 degrees C go up with raising N-2 content to 109.2 degrees at beginning, corresponding to NbN1.71, and then drop off. In addition, the contact angle components decreased with increasing surface temperature. The total SFE at 20 degrees C decreases with N-2 content to raise to 36 mN m(-1) (NbN1.71) at the start, and then increase. The total SFE, dispersive SFE and polar SFE of NbNx films decreased with increasing surface temperature. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. (c) 2007 Elsevier B.V. All rights reserved.