Influence of barriers on the reliability of dual damascene copper contacts

In this paper we investigate the reliability of Cu contacts with both Ta and W based barriers using thermal and electrical stressing. The Ta based barrier showed superior resistance to electrical stressing, with a time-to-failure approaching that of the W-plug reference and a via like failure mode. However early fails reduce the t50 due to high process induced stress imposed by the pre-metal dielectric. These initial results suggest, with further process optimization to reduce thermal stress and improve barrier uniformity, Cu contacts with Ta based barriers can be as reliable as vias in higher metals layers and the traditional W contacts.