Cu5Zn8 Growth Reversion in Cu/Sn-8Zn-3Bi/Cu During Discontinuous Electromigration

A Cu/Sn-8Zn-3Bi/Cu structure was used to investigate the intermetallic compound (IMC) growth behavior during discontinuous electromigration under current density of 10⁴ A/cm² at 70°C. Cu₅Zn₈ IMC formed at both the anode and the cathode interfaces, and the thickness increased with the stressing time. With prolonging the current stressing time, a bulged Cu₅Zn₈ layer was squeezed out between the former Cu₅Zn₈ layer and Cu substrate in the samples to relax the excess compressive stress. Additionally, due to the back stress gradient built up by the Sn diffusion, the Zn atomic flux reacted with Cu to form Cu₅Zn₈ at the cathode side when the power was turned off. Finally, the total IMC thickness of the anode and the cathode under discontinuous current stressing showed a "reversion" in the 69 h and 310 h samples.