  As the semiconductor industry turns to alternate conductors to replace Cu for
future interconnect nodes, much attention as been focused on evaluating the
electrical performance of Ru. The typical hexagonal close-packed (hcp) phase
has been extensively studied, but relatively little attention has been paid to
the face-centered cubic (fcc) phase, which has been shown to nucleate in
confined structures and may be present in tight-pitch interconnects. Using
\emph{ab initio} techniques, we benchmark the performance of fcc Ru. We find
that the phonon-limited bulk resistivity of the fcc Ru is less than half of
that of hcp Ru, a feature we trace back to the stronger electron-phonon
coupling elements that are geometrically inherited from the modified Fermi
surface shape of the fcc crystal. Despite this benefit of the fcc phase, high
grain boundary scattering results in increased resistivity compared to Cu-based
interconnects with similar average grain size. We find, however, that the line
resistance of fcc Ru is lower than that of Cu below 21 nm line width due to the
conductor volume lost to adhesion and wetting liners. In addition to studying
bulk transport properties, we evaluate the performance of adhesion liners for
fcc Ru. We find that it is energetically more favorable for fcc Ru to bind
directly to silicon dioxide than through conventional adhesion liners such as
TaN and TiN. In the case that a thin liner is necessary for the Ru deposition
technique, we find that the vertical resistance penalty of a liner for fcc Ru
can be up to eight times lower than that calculated for conventional liners
used for Cu interconnects. Our calculations, therefore, suggest that the
formation of the fcc phase of Ru may be a beneficial for advanced,
low-resistance interconnects.
