Electromigration in 0.15-10 mu m wide and 0.3 mu m thick Cu lines deposited
by physical vapor deposition has been investigated using both resistance a
nd edge displacement techniques in the sample temperature range 255-405 deg
rees C. For wide polycrystalline lines (>1 mu m), the dominant diffusion me
chanism is a mixture of grain boundary and surface diffusion, while in narr
ow lines (<1 mm) the dominant mechanism is surface transport. The activatio
n energy for grain-boundary transport is approximately 0.2 eV higher than t
hat of surface transport. (C) 1999 American Institute of Physics. [S0003-69
51(99)03920-0].