It was recalled that, in narrow metal interconnects, electromigration flux divergences occurred at the intersections between polycrystalline cluster segments (where grain boundaries offered a rapid diffusion path), and bamboo segments (where there were no grain boundaries oriented along the length). In confined passivated metal interconnects, these flux divergences were linked to the appearance of significant mechanical stresses. A quasi-steady stress distribution built up quickly in the cluster segments, and remained unchanged until the stress profiles between cluster segments began to overlap and the clusters began to interact. A significant increase in stress above the quasi-steady state could result from cluster interactions; thus increasing the possibility of electromigration and stress-induced damage. When the cluster separation was small, this stress increase could occur on a time-scale which was short in comparison with the stress evolution at the interconnect line as a whole.

D.D.Brown, J.E.Sanchez, M.A.Korhonen, C.Y.Li: Applied Physics Letters, 1995, 67[3], 439-41