Electromigration mass flow in Cu damascene lines which were connected to W blocking barrier contacts and were capped with either a CoWP, Ta, Ta/TaN, Pd, SiNx, or SiCxNyHz layer was investigated. Cu lines, fabricated with body centered cubic alpha- or tetragonal beta-Ta liners, were also investigated. A thin electroless CoWP, physical vapor deposition (PVD) Ta, PVD Pd or PVD Ta/TaN cap on top of the Cu line significantly reduced the interface diffusivity and remarkably improved the electromigration lifetime when compared with lines capped with SiNx or SiCxNyHz. Activation energies for electromigration in bamboo-like Cu lines were found to be 2 eV with a CoWP cap, 1.4 eV with a PVD Pd, Ta or Ta/TaN cap, and 0.9-1 eV with a SiCxNyHz or SiNx cap. The Ta phase was found to have an insignificant effect on the Cu mass flow rate, as did the Cu texture. (c) 2005 Elsevier B.V. All rights reserved.