High-current reliability of carbon nanotube via interconnects

We have improved the high-current reliability of carbon nanotube (CNT) via interconnects by chemical mechanical polishing (CMP) and vacuum in situ metal deposition processes. These processes enable us to decrease the contact resistance of a CNT via to the upper and lower Cu lines, and also increase the number of CNTs contributing to current flow. Consequently, the current density per CNT was decreased, and current tolerance properties were improved. As a result, the CNTs via interconnects were able to withstand a high current density of 4 × 10⁷ A/cm² per via, i.e., 1.7 × 10 ⁸ A/cm² per CNT. In addition, we found that the failure mode of Cu-line/CNT-via/Cu-line interconnects with a CNT density of 3 × 10¹¹ tubes/cm² was the slit void formation at the Cu line under the via, which is similar to that of Cu via interconnects. Furthermore, we discussed how to further increase the tolerance of electromigration (EM), taking advantage of their high thermal conductivity.