Improvement of Ta barrier film properties in Cu interconnection by using a non-mass separated ion beam deposition method

Abstract

Ta/Si (100) and Cu/Ta/Si (100) film structures were fabricated by using ion beam deposition with a modified RF sputter-type ion source, in which a strong RF discharge was introduced in order to enhance the plasma density. For Ta/Si structures, Ta films were deposited at various bias voltages. When the substrate bias voltage was not applied, the Ta film showed a columnar structure and had a high resistivity of 2600 nΩm. On the other hand, when the substrate bias voltage of -50 - -200V was applied, the cross-sectional observation did not show columnar structure at all. In this case, film deposition was considered to be sufficient migration energy by the accelerated Ta+ ions. In particular, Ta films deposited at a bias voltage of -125 V had a very small resistivity of 360 nΩm. Thermal stability of Cu(100 nm)/Ta(50 nm)/Si films, where Ta plays a role of diffusion barrier, was evaluated after annealing in H2 atmosphere for 60 min at various temperatures. Non-columnar structure Ta films deposited at substrate bias voltages of -50 V and -125 V were found to be stable up to 600°C, while columnar structure Ta films deposited at zero bias voltage degraded at 300°C. This result indicates that the thermal stability of the Ta films is mainly governed by the film microstructure of the deposited layer.