  In this work, we integrate different computational tools based on
multi-phase-field simulations to account for the evolution of morphologies and
crystallographic defects of Cu/Sn/Cu sandwich interconnect structures that are
widely used in three dimensional integrated circuits (3DICs). Specifically,
this work accounts for diffusion-driven formation and disappearance of multiple
intermetallic phases during accelerated electromigration and takes into account
the non-equilibrium formation of vacancies due to electromigration. The work
compares nucleation, growth, and coalescence of intermetallic layers during
transient liquid phase bonding and virtual joint structure evolution subjected
to accelerated electromigration conditions at different temperatures. The
changes in the rate of dissolution of Cu from intermetallics and the
differences in the evolution of intermetallic layers depending on whether they
act as cathodes or anodes are accounted for and are compared favorably with
experiments. The model considers non-equilibrium evolution of vacancies that
form due to differences in couplings between diffusing atoms and electron
flows. This work is significant as the point defect evolution in 3DIC solder
joints during electromigration has deep implications to the formation and
coalescence of voids that ultimately compromise the structural and functional
integrity of the joints.
