14.4 Epitaxial growth of tetragonal CuAl2 as a conductor for high conductivity interconnects

Epitaxial tetragonal CuAl2(110) and CuAl2(001) layers with thicknesses d = 7–350 nm are deposited on MgO(001), with and without a TiN(001) wetting layer, to quantify the CuAl 2 resistivity scaling and evaluate its potential as next -generation interconnect material. X-ray diffraction confirms phase -pure strongly oriented CuAl2 within a narrow stoichiometric window, while off -stoichiometric growth leads to polycrystalline films. Increasing the deposition temperature from Tₛ = 100 to 300 °C results in a transition from two -domain CuAl2(110) epitaxy to single-crystal CuAl2(001) layers and a resistivity ρ reduction from 8.14 to 6.39 μΩ-cm, reflecting suppressed electron scattering at domain walls in CuAl2(110) films. However, elevated temperatures Tₛ ≥ 300 °C lead to dewetting and discontinuous microstructures. TiN(001) nucleation layers improve wetting and facilitate ρ vs d measurements, yielding a value for the ρoλ product for tetragonal θ-CuAl2 of (2.8 ± 1.2) × 10-15 Ω m2.