Thermal-stress-induced voiding in narrow, passivated Cu lines

Copper is being considered as an alternative to aluminum-based metallizations in microelectronic circuits, both because copper is a better conductor and because it is expected to be more resistant to thermal stress and electromigration induced failure. However, thermal stresses are found to cause significant voiding in passivated copper lines, in a manner very similar to that commonly observed for passivated aluminum lines.