The influence of grain structure on the reliability of narrow Al- based interconnects

The work reported here concerns the effect of grain structure on electromigration failure in pure A1 and A1-2wt.% Cu-1 wt.% Si lines. The grain structure of fine lines were controlled by annealing after pattering to promote the formation of ``bamboo`` structures. Significant improvements in the median time to failure (MTF) and the deviation of the time to failure (DTF) were observed with the development of near-bamboo structures with polygranular-segment lengths shorter than {approximately} 5 {mu}m. The most common failure sites are voids or slits across bamboo grains at the upstream ends of polygranular segments. The time-to-failure decreases with the polygranular segment length, and can be significantly enhanced by controlling the grain structure