Resistivity Scaling in CuTi and CuAl₂ Intermetallics for Narrow Interconnects

The electrical resistivity <i>ρ</i> as a function of thickness <i>d</i> = 5.8-149/10.2-141 nm of epitaxial CuTi(001) and CuAl₂(001) layers is measured to quantify the resistivity size effect of these compound conductors and evaluate their promise as a replacement material for Cu in highly scaled interconnect lines in microelectronic devices. The layers are deposited by magnetron co-sputtering onto MgO(001) substrates and their epitaxy is confirmed by x-ray diffraction <i>θ</i>-2<i>θ</i> scans, <i>ω</i> rocking curves and <i>φ</i>-scans. The surface morphology is quantified by x-ray reflectivity and atomic force microscopy, and the composition measured by photoelectron spectroscopy and Rutherford backscattering. Data fitting of the measured <i>ρ</i> vs <i>d</i> yields room-temperature electron mean free paths <i>λ</i> = 12.5 and 15.6 nm for CuTi and CuAl₂, respectively, and bulk resistivities <i>ρ_o</i> = 19.2 ± 0.8 and 7.7 ± 0.4 μΩ cm. Air exposure causes surface oxidation and a resistivity increase for both intermetallic compounds which is attributed to a transition from partially specular to completely diffuse electron surface scattering. CuTi in direct contact with SiO₂ exhibits a 500 times longer failure time than Cu during room-temperature time-dependent dielectric breakdown (TDDB) tests using a 3 MV/cm bias. The overall analysis yields <i>ρ_oλ</i> benchmark values of 24 × 10^-16 and 12× 10^-16 Ωm², respectively, indicating that the evaluated compound conductors exhibit a conductivity advantage against Cu only if their higher cohesive energies and stability is exploited to achieve liner-free lines.