Influence of Cu-Ion Migration and Fine-Line Effect on Time-Dependent Dielectric Breakdown Lifetime of Cu Interconnects

The time-dependent dielectric breakdown (TDDB) of sub-half-micron Cu interconnects was investigated with respect to the waiting time between Cu chemical mechanical polishing (CMP) and barrier dielectric deposition. Breakdown voltage and TDDB lifetime between adjacent Cu wires decrease markedly if the waiting time in air exceeds 5 days. This is due to Cu-ion migration phenomenon on the CMP surface. The degradation can be improved by keeping the samples in a N2 box or adopting post-CMP cleaning. This TDDB degradation has been observed for various Cu barrier dielectrics in this study. In addition, a "fine-line effect" on Cu TDDB lifetime has been discovered. As Cu wire width becomes smaller, the TDDB lifetime also decreases because of the intensification of the electric field at the CMP surface.