Electromigraton activation energy dependence on AlCu interconnect linewidth and microstructure

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Abstract
Al 1.5% Cu interconnects with linewidths from 0.8 to 10 μm and median grain size of 3.0 μm were stressed at current densities from 2–3×106 A cm−2 and at film temperatures between 140 and 300 °C. The activation energy dependence of the linewidth and grain size distribution, along with evidence for electromigration damage at specific sites within the film grain structure provides support for a line segment model in which the mass transport mechanism is dependent on the microstructure of the film. The results suggest that the contribution of nongrain boundary diffusion mechanisms to mass transport is more significant than previously believed for lines having comparable grain size and linewidth dimensions. In the context of interconnect reliability in integrated circuits, the data indicates that interconnect design rules which are driven by reliability constraints must include the microstructural properties of the film for accurate assessment.