Degradation and failure analysis of copper and tungsten contacts under high fluence stress

The reliability of Cu and W contacts under high fluence stress mimicking source/drain contacts in the on-state of a transistor is evaluated. We use Kelvin structures to study the contact degradation and to determine the lifetime as a function of voltage and temperature. Failure analysis reveals significant damage created in the proximity of the contacts. It is concluded that not electromigration alone, but also Joule heating of the contact and the contact interfaces triggers failure.