Impact of Redundancy and Line Extension on Short-Length Effect in Electromigration Reliability

This study investigates electromigration in a double-redundancy interconnect configuration, commonly found at standard-cell level in the power delivery networks, under downstream electron flow conditions, using both experiments and physics-based simulations. This work sheds light on the critical jL product, (jL)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf>, in presence of a parallel path. Due to double redundancy, for our samples coming from a 28nm commercial technology node, the critical current density j<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> was found to increase by 1.15-fold and 1.1-fold, for 5% and 20% R-shift failure criteria, respectively. The impact of line extension on (jL)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> was also investigated. A 37% decrease in (jL)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> was observed for a single line with a passive line extension acting as a sink, undermining the short-length effect, regardless of the failure criterion. For the same target lifetime, a 1.2-fold increase in maximum allowable current density, based on a 50% target failure percentile and 10 years lifetime criterion, was obtained when comparing the single and double redundancy configurations for 5% R-shift.