The NbMoTaW high entropy alloy (HEAs) films with equal proportion and excellent single-phase solid solution were fabricated by DC magnetron sputtering. A 70 nm-thick NbMoTaW film shows excellent thermal stability and maintains good electrical properties about 75 μΩ-cm after 500°C annealing. A 15 nm-thick NbMoTaW film was prepared as a diffusion barrier. It was found that the structure is complete, and no diffusion occurs after 500℃ annealing. Moreover, Cu/HEAs/Si interface become obscure slightly after 700℃ annealing that is superior to the Cu/Ti/Si interface, which become rough at 500℃. It indicates that the critical point of failure of the HEA diffusion barrier was improved. The results also suggest a high opportunity of NbMoTaW film to replace the conventional Ti, Ta and other binary alloys/nitrides with the advantages of low resistivity and thermal stability, being a potential candidate in Cu/Si interconnects as a diffusion barrier.