Effects of annealing and current stressing on the intermetallic compounds growth kinetics of Cu/thin Sn/Cu bump

Thermal annealing and electromigration (EM) tests were performed at 125–175 °C with 2.2 × 104 A/cm2 conditions in order to investigate the growth kinetics of intermetallic compound (IMC) in Cu/thin Sn/bump. Cu3Sn was formed and grown at the Cu pillar/Cu6Sn5 interface with increasing annealing and current stressing times. IMC thickness increased linearly with the square root of annealing time while it increased linearly with the current stressing time, which means that current stressing accelerated the interfacial IMC reaction. Cu3Sn phases continuously grew with stressing time while thickness of Cu6Sn5 phase decreased due to very thin Sn thickness wrt Cu thickness. Change in the IMC growth slopes is closely related to the phase transition from Cu6Sn5 to Cu3Sn phases after complete consumption of the remaining Sn phase due to the limiting amount of Sn phase in Cu/thin Sn/Cu bump, which can be divided with stages 1 and 2. The complete consumption time of Sn phase in EM condition was faster than that in annealing condition. The activation energies for current stressing are lower than that for annealing, which might be closely related to the change in dominant reaction mechanism by electron wind force.

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► The IMC growth behaviors in Cu/thin Sn/Cu bumps during both annealing and current stressing conditions were investigated.
► Cu3Sn phases are continuously thickened while Cu6Sn5 phase are thinned.
► Change in the IMC growth slopes was occurred.
► The phase transition from Cu6Sn5 to Cu3Sn phases occurs after complete consumption of the remaining Sn phase.
► The IMCs growth is accelerated by the influence of the electron wind force.