Threshold stress behavior in thin film electromigration

Thin film electromigration is simulated using simple models for constitutive relations. Inhomogeneities in the mass deposition and stress fields can explain many features of the phenomenon. They imply that the threshold stress depends on the thin film microstructure and texture. The vacancy Z* parameter derived from the Blech threshold is increased in magnitude, in better agreement with experiments than earlier estimates. The predicted transient vacancy flux displays shorter decay times than the commonly used stress model, possibly in better agreement with experiment below threshold. Finally, nonlinear stress-strain relations are shown to be consistent with the behavior that is seen above threshold in passivated and unpassivated interconnects. (C) 1999 American Institute of Physics. [S0021-8979(99)05611-X].