The effect of growth temperature on electrical conductivity and on the structure of thin refractory metal films, grown by laser ablation deposition

The investigation of the growth-temperature effect on electrical conductivity, measured at room and helium temperatures, as well as on structure, defined by reflection high-energy electron diffraction measurement, of thin tungsten and niobium films, grown by laser ablation deposition on a sapphire R-plane under ultra high vacuum, was made. It was shown that for the films with thickness of 60–80 nm the residual resistance ratio (RRR), which is used as the film quality parameter, is in limits of 12–80 and 7–20 for Nb and W, respectively. It increases rapidly if the substrate temperature, at which the film is grown, exceeds 350°C due to the growth of a perfect monocrystallinc epitaxial film, which has a bec structure with the [100] axis perpendicular to the substrate plane and with the [111] axis parallel to the c axis of the substrate. The film resistivity is close to the bulk monocrystal resistivity and smoothly depends on film growth temperature while the residual film resistivity diminishes as temperature increases. Both RRR and residual film resistivity are saturated at substrate temperature greater than 400–500 °C. Such dependence can be explained by the presence of an imperfect “bulk” phase, whose concentration is low at a high film growth temperature and rapidly increases with its diminishing to lower than 400–500°C. As a result, the scattering of conducting electrons is defined by film surface scattering under low concentration of the bulk phase at high and by bulk scattering on “static” defects of the imperfect bulk phase at low growth temperatures.