Resistivity anisotropy of tilted columnar W and W[sbnd]Cu thin films

Abstract

Electrical resistivity of tilted columnar thin films is theoretically and experimentally investigated considering the anisotropic structure of the columns. To this end, W and WCu thin films were deposited by the GLAD co-sputtering technique. These films were prepared using two different sputtering pressures: 2.5 × 10−3 and 15 × 10−3 mbar. Their morphological and crystallographic properties were studied in order to understand the correlations between some structural characteristics and electrical behaviors of these structured films. The influence of the sputtering pressure on the film's morphology was demonstrated and related to the electronic transport properties in these columnar films. For WCu films, the copper was chemically etched in order to tune even more the electrical properties. By rotating the sample along its azimuthal axis, it was shown that the measured resistivity in the axis perpendicular to the particle flux is maximum, but decreases significantly along the axis parallel to the flux, leading to an anisotropic resistivity coefficient higher than 1.9 for some films. Similarly, an analytical model based-on effective medium approximations was successfully applied to determine the evolution of electrical resistivity versus azimuthal axis for W, WCu and etched WCu thin films.