Immortal interconnects-prevent cracking and limit void size

This paper considers an aluminum line in a multilevel interconnect structure. Upon cooling from the processing temperature, differential thermal contraction causes a triaxial tensile stress state in the aluminum line; voids may initiate and grow to relax the stress. When a direct voltage is applied, the electric current causes aluminum atoms to diffuse. The interconnect will evolve to a state with a high pressure at the anode, and a large void at the cathode. The pressure may crack the surrounding insulator or debond an interface, extruding aluminum. The void may uncover the via contact area, substantially increasing electrical resistance. Provided neither failure mode occurs, aluminum electromigration will stop and the interconnect will function forever. This paper examines the conditions under which the interconnect is immortal.