Electromigration Characteristics for Electron Down-Flow in Copper Interconnects

Abstract

In this study, electron down-flow electromigration (EM) behavior of Copper (Cu) interconnects was characterized in terms of the line width and the via number. For a single-via structure, slit-like voiding underneath the via and line-depletion modes were observed. The slit-like voiding mode is a fatal EM failure for the narrow and wide Cu lines with a single-via structure due to a relatively short lifetime. This failure mode can be eliminated by optimizing via clean process or increasing redundant via. The linedepletion mechanism can be further distinguished into two kinds of failure modes in terms of the voiding location and shows the different line width dependence EM behaviors. For line-depletion failure mode with the voiding location away from via, the EM failure times increase with increasing the metal width. On the other hand, the failure times are similar in the wide and narrow metal lines for line-depletion mode with the voiding location originated from the edge of the via.