Reliability of copper-based interconnections for power devices

Abstract

A new type of interconnections in power devices could be based on copper due to higher electrical and thermal conductivity, and significantly lower material price than for Au. This work presents fabrication technology of Cu-based interconnections for high power transistors and results of interconnections reliability. Magnetron co-sputtering deposition method was applied to create Cu alloys with Ru, Hf, Nb, NbN additives, as well as adhesion layers of Ti, NbN or NbTiN. Interconnection reliability was evaluated on test structures, where Cu lines were protected by thin metallic or dielectric cap against oxidation in air. Crystal structure of the Cu film is stabilized by small amount of Nb or NbN additive. Formed interconnections ensure resistivity below 5 μΩcm. Resistance of the Cu interconnection is stable after ageing in air at 250oC and at current stress of 5 MA/cm2 for few hundred hours, while an insignificant increase in resistance is observed after 200 h ageing at 300oC and current stress of 2 MA/cm2.