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Microscale torsion test to investigate initial yielding phenomenon of a single crystal copper

Mechanical property of copper is very important for the reliable design of semiconductor devices, because the interface between a copper line and the dielectric barrier layer is the week point in the device. In general, the line width of copper line is in the range from tens nanometer to micrometer, and the plastic property of a crystalline metal with small dimensions is highly sensitive to its dimension [1]. In addition, it appears that the loading condition significantly affects the plastic behavior of a micron scale metal. C Motz et al found the follow stress of almost 1GPa (i.e. nearly equal to theoretical strength of copper crystal) at the micro-bending test [2]. Considering these reports, in order to comprehend deformation behavior of the copper embedded in semiconductor device, we need to investigate mechanical response of the copper with small dimensions under heterogeneous stress distribution. In this paper, we twisted micron copper specimens with different dimensions, and investigated the size effect of its plasticity, especially focused on the initial yielding.