An electromigration model was developed in order to simulate the reliability of interconnects. A polynomial expression for the free energy of solution was used to calculate the chemical potential for Al and Cu, while the diffusivities were based upon a Cu-trapping model. The effects of Cu upon stress evolution and lifetime were investigated in all-bamboo or near-bamboo stud-to-stud structures. The significance of the effect of mechanical stress upon the diffusivity of Al and Cu was determined for all-bamboo and near-bamboo lines. Void nucleation and growth was simulated in 200µ stud-to-stud lines. The current-density scaling behavior for void nucleation-limited failure and void growth-limited failure was simulated in long stud-to-stud lines. Current-density exponents of 2, for void-nucleation failure, and of 1, for void-growth failure, were found for pure Al and Al-Cu lines.

Simulations of Stress Evolution and the Current Density Scaling of Electromigration-Induced Failure Times in Pure and Alloyed Interconnects. Y.J.Park, V.K.Andleigh, C.V.Thompson: Journal of Applied Physics, 1999, 85[7], 3546-55