Different diffusion behavior of Cu, Ni and Zn atoms in Cu/Sn-9Zn/Ni interconnects during liquid-solid electromigration

Different diffusion behavior of Cu, Ni and Zn atoms in Cu/Sn-9Zn/Ni interconnects during liquid-solid electromigration (L-S EM) were investigated under a current density of 5.0 × 10³ A/cm² at 230 ^oC. When Cu atoms were under downwind diffusion, L-S EM enhanced the cross-solder diffusion of Cu atoms to the opposite Ni side compared with the liquid-solid reaction case, resulting in the formation of interfacial Cu₅Zn₈ at Ni/Sn-Zn interface, and its thickness increased at the beginning and then decreased. For the Ni atoms, L-S EM significantly enhanced the diffusion of Ni atoms to the Cu side when Ni atoms were under downwind diffusion, resulting in the formation of a large amount of (Ni, Cu)₃(Sn, Zn)₄ at the Cu side. Under the combined effect of chemical potential gradient and electronic wind force, the Zn atoms with positive effective charge number would directional diffuse towards Cu side under both downwind and upwind diffusion conditions, as a result, the interfacial Cu₅Zn₈ formed at the Cu side, and its thickness continuously increased.