Effect of post-pattern annealing on the grain structure and reliability of Al-based interconnects

The possibility is addressed of improving the electromigration resistance of Al and Al–Cu thin‐film conductors with ‘‘quasi‐bamboo’’ structures by post‐pattern anneals that decrease the maximum polygranular segment length. Pure Al, Al–2Cu, and Al–2Cu–1Si lines were patterned and annealed at temperatures high enough to stimulate grain growth. Appropriate anneals led to predominantly bamboo structures with short polygranular segments. These grain structures had a high median time to failure with a relatively low deviation of the time to failure. Metallographic analyses showed that polygranular segment length was a dominant factor in determining the failure site. Post‐pattern annealing promotes a preferential shortening of the relatively long polygranular segments that cause early failures. However, even after annealing, failure occurred at the longest residual polygranular segments, even when these were significantly shorter than the ‘‘Blech length’’ under the test conditions. Statistical analysis of the fa...