Ion beam deposition of α-Ta films by nitrogen addition and improvement of diffusion barrier property

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N₂ atmosphere with different pressure ratios of Ar and N₂. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β-phase in the Ta film deposited at the substrate bias voltage of - 50 V films decreased by adding nitrogen gas, while the α-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of - 50 V under Ar (9 Pa) + N₂ (3 Pa) atmosphere showed a dominant α-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.