Reliability evaluation of carbon nanotube interconnect in a silicon CMOS environment

Conventional copper conductor suffered from electromigration induced by high current density. This calls for a more reliable conductive material. Carbon nanotubes (CNTs), with excellent electrical properties and extremely high thermal conductivity, have been suggested for future interconnects. Although different integration schemes have been demonstrated for CNT interconnects, the reliability of CNT interconnects in the silicon CMOS environment has not been evaluated. The purpose of this study is to investigate the reliability of CNT interconnect under electrical and thermal stress. We first studied the electrical properties of a single CNT exposed in air. It was found that CNT did not fail in the continuous, accelerating manner typical of electromigration failure. An abrupt decrease of conductance was observed when certain level power is supplied. This possibly is caused by the oxidation of the CNT outer shell by Joule heating in air. We then fabricated another CNT via test structure. The reliability of the new test structure is improved due to the heat-sinking effect of surrounding dielectrics. But still the CNT interconnect in the new test structure failed when additional thermal stress is applied. By filling the voids between CNTs with copper, the CNT interconnect becomes more reliable.