The electromigration effect revisited: non-uniform local tensile stress-driven diffusion

• Main Authors: Shih-kang Lin, Yu-chen Liu, Shang-Jui Chiu, Yen-Ting Liu, Hsin-Yi Lee
• Format: Article
• Language: English
• Published: Nature Publishing Group 2017-06-01
• Series: Scientific Reports
• Online Access: https://doi.org/10.1038/s41598-017-03324-5

Abstract The electromigration (EM) effect involves atomic diffusion of metals under current stressing. Recent theories of EM are based on the unbalanced electrostatic and electron-wind forces exerted on metal ions. However, none of these models have coupled the EM effect and lattice stability. Here, we performed in situ current-stressing experiments for pure Cu strips using synchrotron X-ray diffractometry and scanning electron microscopy and ab initio calculations based on density functional theory. An intrinsic and non-uniform lattice expansion – larger at the cathode and smaller at the anode, is identified induced by the flow of electrons. If this electron flow-induced strain is small, it causes an elastic deformation; while if it is larger than the yield point, diffusion as local stress relaxation will cause the formation of hillocks and voids as well as EM-induced failure. The fundamental driving force for the electromigration effect is elucidated and validated with experiments.