Mechanisms of thermal stress relaxation and stress-induced voiding in narrow aluminum-based metallizations

Thermal stress-induced voiding in narrow aluminum-based metallizations used as interconnects in microelectronic circuits has recently become a serious reliability concern. Room-temperature stress relaxation and associated physical phenomena in passivated and unpassivated aluminum-based metallizations, subsequent to exposure to high temperatures, are analyzed based both on theoretically estimated and experimentally determined thermal stresses. It is shown that stress relaxation at longer times involves mainly dislocation climb, while short-term relaxation during cool down from higher temperatures, and immediately thereafter, involves significant dislocation glide. Void growth, frequently observed in passivated metallizations, provides a new source of atoms to feed stress relaxation by the same processes as in the absence of voiding.