The role of copper in electromigration: the effect of a Cu-vacancy binding energy

The effect of a Cu-vacancy binding energy on electromigration transport in Al-Cu alloys is studied in detail. A lattice-gas model for electromigration is developed which accounts for the Cu-vacancy binding energy. Expressions for the diffusion coefficients are derived in the limit of low vacancy concentrations and calculated using Monte Carlo simulations. The diffusion equations are solved for the failure times and concentration profiles. Our results show that for a binding energy of about 0.2 eV there is a dramatic increase in the failure time for copper doping levels of only 1%. The concentration profiles are consistent with 'incubation time' phenomena in experiments where the copper is found to drift away from the blocking boundary before failure occurs.