Copper interconnect electromigration (EM) performance was examined in three low-k materials (k=2.65/spl sim/3.6) using advanced back end of line (BEOL) technology. Comparable time to failure distributions were achieved after process optimization for each material. The Ea and n ranged from 0.8 eV to 0.9 eV and 1.1 to 1.4, respectively, and agree well with the interface diffusion mechanism and void nucleation mechanism. Various testing structures were designed to identify the EM failure modes. Extensive failure analysis was carried out to understand the failure phenomena of various test structures. Results of the present study suggest that the interface of Cu interconnects is the key factor for EM lifetime performance for advanced BEOL technology design rules. The weak links of the interconnect system were also identified.