Elucidating Defect Effects on Surface Diffusivity and Enhanced Electromigration Resistance Using Density Functional Theory

Density functional theory (DFT) calculations can be regarded as a cornerstone in modern materials science to facilitate the materials design in nanotechnology. The introduction of nanoscale coherent twin-boundary defects into Cu nanowires can modify the atomic surface structure, reduce surface diffusion and further enhance the electromigration resistance. However, a more in-depth understanding of how the twin structure affect the electromigration behavior is still unclear. In this study, we discuss the reduction of Cu surface diffusivity using DFT elucidation. We focus on (1) the geometric effect and (2) the electronic structure effect on the surface diffusivity. We show that introducing twin structure can enhance diffusion barrier for Cu atomic migration around a specific twin concave junction. Therefore, a lower effective surface diffusivity can be achieved by around two orders of magnitude under 100°C, compared to twin-free systems. The root cause of varying the diffusivity of Cu surfaces mainly attribute to different coordination numbers of the surrounding Cu atoms. This study provides defect-engineering routes against diffusion-induced instability of Cu interconnects.