Effect of structure and processing on electromigration-induced failure in anodized aluminum

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Abstract
The effect of barrier and porous anodizations, either singly or sequentially, on the electromigration resistance of aluminumfilms was characterized. Samples were tested for current densities in the 4×105−2×106‐A/cm2 range and temperatures between 150 and 280°C with the median failure time being used as a basis for comparison of lifetimes. An initial barrier anodization was found to be necessary in order to consistently enhance lifetime. The addition of a porous layer as well led to the best result—an increase in lifetime by a factor of 23 at 227°C. All lifetime increases were attributable to increased activation energy for the electromigration‐failure process. An increase of 0.14 eV was obtained for the double anodic structure. Results for structures having a barrier layer adjacent to aluminum were considered in terms of surface sealing of the aluminum and/or response to mechanical constraints of the overlayer. Direct porous anodization resulted in preferential oxidation at grain boundaries, thereby widening these regions, in pitting at grain boundaries, and in general cratering characteristic of this type of anodization. It was concluded that the widening phenomenon was most instrumental in reducing activation energy and lifetime.