Electromigration damage in mechanically deformed Al conductor lines: dislocations as fast diffusion paths

The role of dislocations in the generation of electromigration damage in model experiments is considered. Continuous segments of polycrystalline and single-crystal pure aluminum conductor lines were plastically deformed using nanoindentation methods. The lines were subsequently subjected to accelerated electromigration tests, in part in-situ in a scanning electron microscope. Electromigration damage was generated at plastically deformed segments in the single-crystal conductor lines, but not in polycrystalline lines. Diffusion paths and the origins of flux divergences that lead to electromigration damage are discussed. Investigations of the microstructure using focused ion beam (FIB) and electron back-scattered diffraction (EBSD) techniques did not show signs of fine-grain recrystallization in the indented regions. This and numerical estimates of the diffusivities involved suggest that electromigration damage arises by fast diffusion along dislocations with reasonable densities (of order 1015/m2).