  We explore the effect of faceting on possible mechanisms for mass transport
around electromigration voids in aluminum interconnects. Motivated by linear
response estimates which suggest that particle flux would be much higher along
steps than across terraces on a clean aluminum surface, we study step
nucleation in the presence of a small driving force along a surface. We find
that step nucleation, even on a nearly defect-free void surface, would be slow
if the step energy is equal to that calculated for a clean aluminum surface. In
the presence of a uniform electromigration force, the creation of new steps
between existing ones should not occur unless the free energy cost of a step is
much less than thermal energies. We conclude that voids cannot move
intragranularly at $\mu$m/hr rates without help from other factors such as
local heating and impurities.
