A new approach based on anisotropic relaxation time evaluation for size-dependent electrical conductivity

As the device size becomes smaller in modern CMOS technology, its resistivity increases too rapidly, so copper would not be appropriate for future interconnect applications. One of the most significant challenges is to search for other materials to replace copper for interconnect in future single-digit nanosized CMOS technology. For this purpose, we investigate the electrical transport properties of not only various single element metals but also binary and ternary metal alloys to find candidate materials. We use first-principles calculations to compute their electronic structures and phonon dispersions and to evaluate the electron-phonon interaction yielding the momentum- and energy-dependent electron relaxation time or mean free path. We then solve the Boltzmann transport equation to predict their conductivity tensors. We further develop a method to evaluate the size dependence of the momentum- and energy-dependent electronic mean free path to include the surface scattering effect on the resistivity. It turns out that our method produces the results in good agreement with available experimental data. We present a few materials with strongly anisotropic Fermi surfaces, the resistivity of which becomes comparable to or even lower than copper as their size becomes smaller.