Electric‐Current‐Induced Phase Transformation in Cu ₆ Sn ₅ Below Its Equilibrium Transition Temperature

ABSTRACT As semiconductor interconnects scale toward sub‐2 nm nodes, they are subjected to increasingly high current densities that challenge materials reliability. While phase transformations are traditionally interpreted through thermal equilibrium, electric current can introduce additional nonequilibrium effects that influence structural evolution. Here, we report a current‐driven monoclinic‐to‐hexagonal transformation in Cu ₆ Sn ₅ occurring under a measured bulk temperature of ∼120°C, below the equilibrium η′ ↔ η transition temperature of 186°C–189°C. Using an ex situ synchrotron X‐ray diffraction series on separate current‐stressed samples together with transmission electron microscopy, we show that matched bulk‐temperature thermal aging alone did not reproduce the same transformation within the examined time window, whereas current stressing progressively converted η′‐Cu ₆ Sn ₅ to η‐Cu ₆ Sn ₅ . The transformed state also exhibits a higher measured indentation modulus and hardness than the monoclinic reference under the present test conditions. These results demonstrate that electric current can drive unconventional structural evolution in Cu ₆ Sn ₅ below the equilibrium transition temperature and provide a basis for understanding current‐assisted phase stability in conductive intermetallics.