Effect of deposit thickness during electroplating on Kirkendall voiding at Sn/Cu joints

Abstract Electroplating process was widely used for preparing Cu metallization in semiconductor devices, while Kirkendall voids (KVs) were usually observed at Cu3Sn/electroplated Cu interface. In this paper, the effect of the thickness of the electroplated Cu film on the voiding behaviors has been investigated. High current density, 50 mA/cm2, was used during electroplating. It is found that as the deposit thickness was 2 μm, no obvious KVs were found even after aged at 150 °C for 30 days. However, as the deposit thickness was 10 μm, a large number of KVs were observed just after soldering, at Cu6Sn5/Cu interface. During aging, the KVs gradually condensed into a continuous crack. And further prolonging the holding time, the crack was found to transfer to a large opening. The Cu3Sn layer became thinner during the whole stage. It seems that thicker deposit film would induce more impurities and vacancies, which further promoting Kirkendall voiding, as well as consuming the Cu3Sn layer.