Cu-ion-migration phenomena and its influence on TDDB lifetime in Cu metallization

Time-dependent dielectric breakdown (TDDB) of sub-half-micron Cu interconnects was investigated with regard to the waiting time between Cu-CMP and barrier dielectric deposition. Breakdown voltage and TDDB lifetime between adjacent Cu wires deteriorated abruptly as the waiting time in air passed 4 days. This is due to Cu-ion migration phenomena on the CMP-surface. The degradation can be improved by keeping the samples in a N₂-box or adopting post-cleaning. This TDDB degradation was observed on any Cu barrier dielectrics in this experiment. In addition, another phenomenon related to Cu TDDB lifetime was discovered, namely a ´fine line effect´. As Cu wire width becomes finer, the TDDB lifetime also decreases further because of the interaction of the electric field at the CMP-surface. It was predicted that the TDDB lifetime for next-generation technology was possibly insufficient for 10-year reliability by testing several low-k dielectrics and Cu barrier dielectrics.