Electromigration-induced failures in thin-film Al-Cu conductors

The effect of CuAl₂ precipitates on the electromigration lifetime of thin film Al-Cu conductors was studied by varying the Cu concentration in the 0–12 wt per cent range. Experiments show that the conductor lifetime does not increase monotonically with an increase in precipitate content. It is shown that the precipitates, when present in sufficient quantity, can greatly modify the grain size distribution and hence can affect the electromigration lifetime. These results are interpreted in terms of a model relating the vacancy and the copper atom flux along the grain boundaries. The roles of annealing treatments, copper concentration, structural non-homogeneities and test temperatures are explained by the present model.