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Reduction of electromigration in aluminum films by copper doping

 Award plaque by I. Ames,
F. M. d'Heurle,
and R. E. Horstmann

We have found that the lifetime of aluminum films subjected to high current densities at elevated temperatures can be increased by the addition of copper. Previous studies have indicated that the failure mechanism is a combination of electromigration-induced phenomena, including nucleation and growth of voids, which are gated primarily by material transport along grain boundaries. On the basis of the present study, it appears that the presence of copper causes an appreciable retardation in the rate at which this overall combination of processes takes place, thereby producing a considerable increase in lifetime.

Originally published:

IBM Journal of Research and Development, Volume 14, Issue 4, pp. 461-463 (1970).

Significance:

In the 1960s, it was observed that aluminum interconnects in transistor circuits developed irregularities and failures after prolonged current flow or accelerated testing. The irregularities were associated with the movement of aluminum in the interconnections during current flow and were attributed to aluminum atom electromigration. During their studies, Ames et al. observed that the addition of 4% copper to aluminum significantly reduced electromigration and increased the lifetimes of the aluminum lines by a factor of about 70. Until the late 1990s, IBM used aluminum/copper (4%) alloy to interconnect computer circuits.

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