In-Situ Observation on Liquid-Solid Electromigration Behavior of (111) nt-Cu/Sn/Cu Interconnects

The microstructural evolution of (111) nt-Cu/Sn/polycrystalline Cu solder interconnects undergoing L-S EM was characterized in-situ and real-time by synchrotron radiation X-ray imaging. The growth rate of interfacial inter metallic compound (IMC) at the polycrystalline Cu anode (5.8μm/min) was 29 % higher than that at the (111) nt-Cu anode (4.5 μm/min). The consumption rate of nt-Cu UBM acting as the cathode was 2.0 μm/min, which was 20 % lower than that of Cu UBM (2.4 μm/min). Moreover, after L-S EM for 12 min, (111) nt-Cu remained original orientation feature accompanied by horizontal lamellar structures and no recrystallization or abnormal grain growth was observed, indicating the superior stability of nt-Cu UBM. The high electromigration resistance of (111) nt-Cu was attributed to the following factors. Firstly, the (111) exhibits the lowest surface energy among all crystal planes, resulting in lowest migration of atoms under the current stressing in (111) nt-Cu. Secondly, the twin boundary structure of (111) nt-Cu significantly impedes migration of Cu atoms. Additionally, tri-junction points formed by the intersection of twin boundaries with grain boundaries also hindered electromigration of Cu atoms.