The possibility was considered of improving the electromigration resistance, of thin-film conductors with so-called quasi-bamboo structures, by means of post-pattern annealing treatments that decreased the maximum polygranular segment length. Pure Al, Al-2Cu, and A1-2Cu-1Si lines were patterned and annealed at temperatures that were high enough to stimulate grain growth. Appropriate annealing treatments produced predominant bamboo structures with short polygranular segments. These grain structures exhibited a high median time-to-failure, with a relatively low deviation of that parameter. Metallography showed that the polygranular segment length was a principal factor in determining the failure site. Post-pattern annealing led to a preferential shortening of the relatively long polygranular segments that caused early failures. But after annealing, failure still occurred at the longest residual polygranular segments; even when these were significantly shorter than the so-called Blech length for those conditions. Statistical analysis of the failure of alloy lines revealed a simple exponential relationship between the failure time and the longest polygranular segment length within a line.

S.H.Kang, C.Kim, J.W.Morris, F.Y.Génin: Journal of Applied Physics, 1996, 79[11], 8330-5