Analyses and design for electrochemical migration suppression by alloying indium into silver

Abstract

Silver electrochemical migration (ECM) is a serious reliability issue for fine pitch as well as power electronic devices that employ silver as interconnection materials. In this study, a method to suppress the ECM behavior of silver was proposed and implemented. Solid solutions of Ag–In and intermetallic compounds were fabricated and their ECM properties were studied through the water drop test (WDT). The WDT was performed on alumina substrate in deionized water at 3 V, where the leakage current was measured. The results show that Ag–In alloy samples have considerably longer lifetime before reaching short circuit than pure silver samples. As indium concentration in Ag–In solid solution increases, the resistance to ECM also increases. The migration process is completely inhibited when the indium concentration reaches 19 at.%. The morphologies of the dendrites and surfaces of the anode and cathode were also investigated. A model was established to explain the anti-ECM mechanism of Ag–In alloys. By forming indium oxide on the surface of the anode under electric field in a humid environment, the anode gets passivated and the silver dissolution path is completely blocked, and thus inhibiting the ECM process. It was discovered that the quality of electrode surfaces is essential in realizing the full potential of the inherent anti-ECM ability of Ag–In alloys. In conclusion, the results of this investigation have shown that Ag–In alloys can be promising and valuable candidates for conductors, metallization, and interconnect materials in fine pitch and high power electronic devices.