Synchrotron X-ray micro-diffraction analysis on microstructure evolution in Sn under electromigratton

White Sn (ß-Sn) thin film stripe shows a voltage drop about 10% when subjected to electromigration testing. Since ß-Sn has anisotropic crystal structure, it possesses different resistivity along a-, b- and c axis. The direction of the axes determines the resistance in each grain. Under electromigration, low resistance grain tends to grow in the expense of the neighboring high resistance grains. The changes of grain orientation in the Sn stripe before and after electromigration was studied by synchrotron x-ray microdiffraction (~lnm diameter) to achieve grain-by-grain analysis. Grain growth involves grain boundary migration and rotation of neighboring high resistance grains. A model different from normal grain growth is proposed to describe the condition and mechanism of microstructural evolution under electromigration.