Electromigration Induced Drift and Noise in a Single Aluminum Via

We have examined small changes in the resistance of a single aluminum via test structure with a resolution of 10-8 ohms. The via is roughly one cubic micron and contains a well defined TiN diffusion barrier. The high resolution of these resistance measurements allows the observation of atomic drift rates corresponding to roughly 100 atoms/second into and out of the well defined via structure. Resistance changes are observed with moderate current densities in the temperature range of 100°C to 200°C. We observe reversible increases and decreases in the resistance caused by the accumulation of atoms at the diffusion barrier within the via. Comparisons can be made to recent models for the transient electromigration induced vacancy drift. We are able to extract microscopic electromigration parameters as well as differentiate between copper and aluminum as the initial diffusing element.