Multi-link statistical test structures were used to study the effect of low k dielectrics on EM reliability of Cu interconnects. Experiments were performed on dual-damascene Cu interconnects integrated with oxide, CVD low k, porous MSQ, and organic polymer ILD. The EM activation energy for Cu structures was found to be between 0.8 and 1.0 eV, indicating mass transport is dominated by diffusion at the Cu/SiNx cap-layer interface, independent of ILD. Compared with oxide, the decrease in lifetime and (jL)c observed for low-k structures can be attributed to less dielectric confinement in the low k structures. An effective modulus B obtained by finite element analysis was used to account for the dielectric confinement effect on EM. For all the ILDs studied, (jL)c showed no temperature dependence.