Resistivity Scaling in Epitaxial CuAl2(001) Layers

Epitaxial CuAl2(001) layers with thickness d = 10.2-141 nm are deposited by co-sputtering onto MgO(001) substrates at 300 degrees C and their resistivity rho is measured in situ to quantify the CuAl2 resistivity scaling. A combination of X-ray diffraction theta-2 theta scans, omega rocking curves, and phi-scans confirms the single-crystal microstructure with a 45 degrees-rotated epitaxy with CuAl2(001) parallel to MgO(001) and CuAl2 (100) parallel to 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 . 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) x 10(-16) Omega m(2) is temperature-independent. This value is 79% larger than for Cu, indicating a more pronounced resistivity size effect in CuAl2. Thus, CuAl2 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.

Automated summary

Epitaxial CuAl2 layers with different thicknesses were deposited on MgO substrates by co-sputtering and their resistivity was measured. The results show that the resistivity of CuAl2 increases with decreasing thickness, with electron scattering at Al vacancies playing a significant role. The Fuchs-Sondheimer model was used to describe the resistivity scaling and the electron mean free path at room temperature. Transport measurements at 77K indicate a more pronounced resistivity size effect in CuAl2.