Resistivity scaling in CuTi determined from transport measurements and first-principles simulations

The resistivity size effect in the ordered intermetallic CuTi compound is quantified using in situ and ex situ thin film resistivity rho measurements at 295 and 77 K, and density functional theory Fermi surface and electron-phonon scattering calculations. Epitaxial CuTi(001) layers with thickness d = 5.8-149 nm are deposited on MgO(001) at 350 ? and exhibit rho vs d data that are well described by the classical Fuchs and Sondheimer model, indicating a room-temperature effective electron mean free path lambda = 12.5 +/- 0.6 nm, a bulk resistivity rho(o) = 19.5 +/- 0.3 mu omega cm, and a temperature-independent product rho(o)lambda = 24.7 x 10(-16) omega m(2). First-principles calculations indicate a strongly anisotropic Fermi surface with electron velocities ranging from 0.7 x 10(5) to 6.6 x 10(5) m/s, electron-phonon scattering lengths of 0.8-8.5 nm (with an average of 4.6 nm), and a resulting rho(o) = 20.6 +/- 0.2 mu omega cm in the (001) plane, in excellent agreement (7% deviation) with the measurements. However, the measured rho(o)lambda is almost 2.4 times larger than predicted, indicating a break-down of the classical transport models. Air exposure causes a 6%-30% resistivity increase, suggesting a transition from partially specular (p = 0.5) to completely diffuse surface scattering due to surface oxidation as detected by x-ray photoelectron spectroscopy. Polycrystalline CuTi layers deposited on SiO2/Si substrates exhibit a 001 texture, a grain width that increases with d, and a 74%-163% larger resistivity than the epitaxial layers due to electron scattering at grain boundaries. The overall results suggest that CuTi is a promising candidate for highly scaled interconnects in integrated circuits only if it facilitates liner-free metallization.

Automated summary

The resistivity size effect in the ordered intermetallic CuTi compound was quantified using in situ and ex situ thin film resistivity measurements, as well as density functional theory calculations. The results showed that the measured resistivity and electron mean free path were in agreement with theoretical calculations, but the measured resistivity mean free path product was almost 2.4 times larger than predicted, indicating a breakdown of classical transport models.