Resistivity Scaling in Epitaxial CuAl2(001) Layers

Epitaxial CuAl
₂
(001) layers with thickness
${d}$
= 10.2–141 nm are deposited by co-sputtering onto MgO(001) substrates at 300 °C and their resistivity
$\rho $
is measured
in situ
to quantify the CuAl
₂
resistivity scaling. A combination of X-ray diffraction
$\theta $
-
$2\theta $
scans,
$\omega $
rocking curves, and
$\varphi $
-scans confirms the single-crystal microstructure with a 45°-rotated epitaxy with CuAl
₂
(001)
$\vert \vert $
MgO(001) and CuAl
₂
(100)
$\vert \vert $
MgO(110). The measured
$\rho $
increases with decreasing
${d}$
, which is well described by the Fuchs–Sondheimer model, yielding a room-temperature electron mean free path
$\lambda $
= 15.6 nm with a bulk resistivity
$\rho _{o}$
=
$7.7 ~\mu \Omega \cdot cm$
. The latter value is 18% above the previously reported
$\rho _{o}$
, which is attributed to electron scattering at Al vacancies with a concentration of 6.4% per site, as quantified by Rutherford backscattering and X-ray reflectivity. Transport measurements at 77 K confirm that
$\rho _{o}\lambda $
= (12 ± 1)
$\times 10^{-16} \Omega \text{m}$
²
is temperature-independent. This value is 79% larger than for Cu, indicating a more pronounced resistivity size effect in CuAl
₂
. Thus, CuAl
₂
is promising only as Cu-replacement interconnect metal if its low melting point facilitates large grains and its high cohesive energy provides reliability benefits and an associated reduction in liner thickness.