Effect of metal line width on electromigration of BEOL Cu interconnects

Electromigration reliability of BEOL Cu interconnects with various metal line widths and via sizes has been studied. EM lifetime significantly improves from minimum width to three times the minimum width, and then saturates. In addition, the EM lifetime of the wide metal lines was not dependent on via size. The proposed mechanism for EM lifetime improvement is larger grains in wider lines leading to a suppression of grain boundary diffusion. Cu grain size and Cu drift velocity were correlated to the EM lifetime behavior, saturating at the same line width, and kinetic studies found activation energies consistent with grain boundary diffusion.