Ta diffusion barriers have been deposited on Si (100) substrate by applying a negative substrate bias voltage. The effect of the substrate bias voltage on the properties of the Ta films was investigated. In the case of the Ta films deposited without the substrate bias voltage, a columnar structure and small grains were observed distinctly, and the electrical resistivity of the deposited Ta films was very high (250 $muOmega$cm). By applying the substrate bias voltage, no clear columnar structure and grain boundary were observed. The resistivity of the Ta films decreased remarkably and at a bias voltage of -125 V, reaching a minimum value of 40 $muOmega$cm, which is close to that of Ta bulk (13 $muOmega$cm). The thermal stability of Cu(100 mm)/Ta(50 mm)/Si structures was evaluated after annealing in H2 atmosphere for 60 min at various temperatures. The Ta films deposited by applying the substrate bias voltage were found to be stable up to $600^{circ}C$, while the Ta films deposited without the substrate bias voltage degraded at $400^{circ}C$.