The effect of contact resistance on current crowding and electromigration in ULSI multi-level interconnects

Electromigration (EM) has been the most persistent interconnect reliability issue over the decades. In general, EM damages tend to occur at atomic flux divergence sites. The EM failure rate can be further accelerated by current crowding, which occurs when current flows between inter-level wires. In this work, we used two different via etch schemes to study the effect of contact resistance on current crowding and EM. We found that the etch stop structures show longer EM lifetimes than the over etch. The contact resistance of the etch stop is higher than that of the over etch. Two-dimensional simulation results show that the higher contact resistance in the etch stop can suppress current crowding and improve EM lifetimes. Differences in void morphology between the over etch and etch stop as a result of current crowding are discussed.