Reverse polarity effect in Cu/Sn-9Zn/Ni interconnect under high current density at high temperature

Synchrotron radiation real-time imaging technology was conducted to in situ observe the interfacial reaction in line-type Cu/Sn-9Zn/Ni interconnect under a current density of 2.0 × 10⁴ A/cm² at 230 °C. The reverse polarity effect in Cu/Sn-9Zn/Ni interconnects undergoing L-S EM was verified by the continuous growth of the intermetallic compound (IMC) layer at the cathode while the thinning of that at the anode under both flowing directions of electrons. This provided a clear evidence that Zn atoms migrated from the anode toward the cathode undergoing L-S EM, which is different from the normal diffusion behavior of atoms under the effect of electron current stressing. Since there was no back-stress in L-S EM, it is deduced that the abnormal diffusion behavior of Zn atoms was attributed to the electromigration flux, Jem, being greater than the chemical potential gradient flux, Jchem, during L-S EM under a high current density.