Via-depletion electromigration in copper interconnects

Via-depletion electromigration was studied under a number of conditions in a 65-nm technology. Observed failure distributions were either single mode or bimodal, depending on the structural configuration. The distribution and the time to fail for the early-fail mode of the bimodal distributions varied with linewidth, via redundancy, and via current density. Additionally, it was observed that for bimodal failure distributions, the length of the extension of the line past the via determined the fraction of early fails in the via. The bimodal behavior was suppressed by optimization of the via liner deposition process.