Electromigration‐induced failure by edge displacement in fine‐line aluminum‐0.5% copper thin film conductors

摘要

Electromigration mass transport rates in Al‐0.5% Cu film conductors have been measured by the Blech‐Kinsbron technique, and the data extrapolated so as to predict times‐to‐failure under typical conditions of service, due to open circuit at silicon‐to‐aluminum contacts. In tests between 260 and 400 °C, average drift velocities ranging from 0.01 to 10 μm/h were measured. The observed activation energy is 0.44 eV for the extra‐fine‐grained film (grain‐boundary diffusion control) but 1.2 eV for the coarser‐grained film which had been patterned to form a strip 1.5 μm wide (lattice diffusion control). At a given temperature, transport is much faster in finer‐ as compared to coarser‐grained films. For the extra‐fine‐grained films deposited by evaporation from an induction‐heated source, the predicted time‐to‐failure in use is well within the normal‐service lifetime. The inferred safe current density design level for extra‐fine‐grained material is well below previously recommended values. We conclude that deposition processes which result in extra‐fine‐grained aluminum are probably unsuitable for use in integrated circuit fabrication. Even for coarser‐grained aluminum conductors, additional work will be required to define conservative current density design limits to avoid contact failure by this mechanism.