Void nucleation and growth contributions to the critical current density for failure of Cu vias

We investigate the critical current density for electromigration failure, j
_c
, as a function of voiding failure mode for Cu dual damascene vias. We demonstrate experimentally the variation of (jL) product with via failure mode showing that it is not possible to characterize vias by a single (jL). We suggest that, in general, j
_c
for failure is determined by the sum of void nucleation and growth components, and we present a model for j
_c
based on these concepts.