Effect of electromigration on interfacial reaction in Cu/Sn-9Zn/Cu and Cu/Sn-9Zn/Ni interconnects

The interfacial reaction in Cu/Sn-9Zn/Cu and Cu/Sn-9Zn/Ni interconnects during electromigration (EM) were investigated under a current density of 5.0 × 10³ A/cm² at 150 °C. An obvious reverse polarity effect in Cu/Sn-9Zn/Cu and Cu/Sn-9Zn/Ni interconnects during EM was demonstrated, i.e., the interfacial IMCs at the cathode grew continuously and were remarkably thicker than those at the anode. The formed IMC was always Cu₅Zn₈ at the cathode and anode interfaces during EM in Cu/Sn-9Zn/Ni interconnect. And a little Cu₆Sn₅ phase formed at the cathode interface after EM for 400h. When electrons flowed from the Cu side to the Ni side in Cu/Sn-9Zn/Ni interconnect, the (Ni,Cu)₃(Sn,Zn)₄ replaced Ni5Zn21 at the Ni/Sn-Zn interface, while the formed IMC was always Cu₅Zn₈ at Cu/Sn-Zn interface. More Zn atoms diffused toward Sn-9Zn/Cu interface (cathode) in Cu/Sn-9Zn/Ni interconnect during EM and the Cu₅Zn₈ layer at the cathode in Cu/Sn-9Zn/Cu interconnect is obviously thicker than that in Cu/Sn-9Zn/Ni interconnect during EM for 400h.