Electromigration Path in Cu Thin Film Lines

Electromigration in 0.15 µm to 10 µm wide 0.3 µm thick Cu lines deposited by physical vapor deposition has been investigated using both resistance and edge displacement techniques in the sample temperature range 255°C - 405°C. For wide polycrystalline lines (>1 µm), the dominant diffusion mechanism is a mixture of grain boundary and surface diffusion, while in narrow lines (<1 µm) the dominant mechanism is surface transport. The activation energy for grain boundary transport is approximately 0.2eV higher than that of surface transport.