Segregation of Cu to grain boundaries by aging treatment and its effect on EM resistance for AlCu/TiN lines

The electromigration (EM) resistance of AlCu(0.5 wt.%) multilayered lines improved by a factor of 10 after a low-temperature annealing at 250/spl deg/C for 10 hrs. The authors use the term "aging treatment" in this paper to describe such low-temperature annealing. Redistribution of Cu atoms after aging treatment was observed using TEM and energy dispersive X-ray spectroscopy (EDX). In addition to CuAl2 precipitates, segregated Cu, which was invisible by standard TEM imaging, was detected at grain boundaries after the aging treatment. However, aging treatments that were too long decreased both the EM lifetime and the segregated invisible Cu. The same temporal variation of EM lifetime and segregated Cu implies that the microstructure in which grain boundaries were coated with diffused Cu atoms during the aging treatment is that which improves EM resistance.<>