Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures

High-temperature stability of Cu-based interconnects is of technological importance for electronic circuits based on wide band gap semiconductors. In this study, different metal stack combinations using Ta or TaN as capping- and/or barrier-layer, in the configuration cap/Cu/barrier, are evaluated electrically and morphologically prior to and after high-temperature treatments. The symmetric combinations Ta/Cu/Ta and TaN/Cu/TaN are characterized by a low and stable sheet resistance after annealing up to 700 °C. Asymmetric combinations of Ta/Cu/TaN and TaN/Cu/Ta, however, display an increase in sheet resistance values after annealing at 500 °C and above. This increase in sheet resistance is considered to result from Ta diffusion into the grain boundaries of the Cu film. The preliminary electromigration studies on the TaN/Cu/Ta and TaN/Cu/TaN structures show a twofold higher activation energy and a tenfold longer lifetime for the former, thus suggesting an important role of the interface between Cu and the cap and/or barrier