Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar+N-2 atmosphere with different pressure ratios of Ar and N-2. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and difftision barrier property were investigated. It was found that the fraction of a metastable beta-phase in the Ta film deposited at the substrate bias voltage of -50 V films decreased by adding nitrogen gas, while the alpha-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of -50 V under Ar (9 Pa)+N-2 (3 Pa) atmosphere showed a dominant alpha-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier. (c) 2007 Elsevier B.V. All rights reserved.