Electromigration-induced drift failure of via contacts in multilevel metallization

Abstract

Much effort has been expended to improve metal sidewall coverage of via contacts in multilevel metallization schemes because of the possibility of an enhanced rate of electromigration failure at the sidewall. Multilayered conductors, which incorporate a refractory material beneath an Al alloy layer, will be more resistant to these voiding failures. These metallizations are not ideal, however, because of the discontinuities in the flux of electromigrating atoms at the Al/refractory interfaces of the via, which render the interfaces vulnerable to voiding. This paper examines the relative importance of electromigration at the sidewall and metal interface of vias containing AlSiCu/TiN multilayer conductors. Our results demonstrate that voiding failure is not associated with poor metal step coverage, and that the interface between the metal levels is the region most vulnerable to voiding. Formation of voids between the metal levels occurs by drift of the Al layer away from the Al/TiN interface, and there is a strong dependence of failure on the direction of electron flow through the via. This directional dependence arises because the Al drift velocity is determined by the current density in the stripes attached to the via. We present an expression for the via failure time that incorporates the stripe current density.

Electromigration in isolated aluminum vias probed by resistance changes and 1/f noise

“…Similar samples have been used in previous studies of mean time to failure and drift velocity. 16,17 The vias were connected by runners of 120 m in length.…”

System-level modeling and reliability analysis of microprocessor systems

“…This is because the via and the line below it are formed by separate deposition steps, which creates a vulnerable interface. Hence, although EM can be observed in interconnect lines, it is much more likely to be seen at via interfaces [85], [86]. Therefore, this work focuses on EM in vias, rather than in the significantly less vulnerable interconnect lines.…”

Experimental Studies of Al Interconnections

“…For multilevel metallization, flux divergence occur at the line/stud contact (Endicott, Bouldin and Miller 1992;Oates, Nkansah and Chittipeddi 1992;Hu, Small and Ho 1993). Cu is found to be important in determining the rate of mass depletion at the line/stud contact.…”