Electromigration characteristics of vias in Ti:W/Al-Cu(2 wt.%) multilayered metallization

The electromigration (EM) performance and failure mechanisms for 1.2- mu m vias fabricated in a passivated Ti:W/Al-Cu(2 wt.%) metallization were investigated. Single van der Pauw via structures were stressed at 175 degrees C and 200 degrees C and at accelerated current densities. The via resistance was monitored independently of the metal feed lines and a difference in activation energy, failure mode, and mean time to fail was observed depending on the direction of current flow. When electrons flowed into the via, the via sustained a 20% increase in resistance before failing catastrophically. Conversely, when electrons flowed out of the via, a monotonic increase in resistance was observed, and yet the via remained intact. Concerns of poor aluminum step coverage in the vias were addressed. Reliability comparisons were made between vias and flat metal stripes.<>