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 condu ctivity, measured at room and helium temperatures, as well as on struc ture, defined by reflection high-energy electron diffraction measureme nt, of thin tungsten and niobium films, grown by laser ablation deposi tion on a sapphire R-plane under ultra high vacuum, was made. It was s hown that for the films with thickness of 60-80 nm the residual resist ance ratio (RRR), which is used as the film quality parameter, is in l imits of 12-80 and 7-20 for Nb and W, respectively. It increases rapid ly if the substrate temperature, at which the film is grown, exceeds 3 50 degrees C due to the growth of a perfect monocrystalline epitaxial film, which has a bcc structure with the [100] axis perpendicular to t he substrate plane and with the [111] axis parallel to the c axis of t he substrate. The film resistivity is close to the bulk monocrystal re sistivity and smoothly depends on film growth temperature while the re sidual film resistivity diminishes as temperature increases. Both RRR and residual film resistivity are saturated at substrate temperature g reater than 400-500 degrees C. Such dependence can be explained by the presence of an imperfect ''bulk'' phase, whose concentration is low a t a high film growth temperature and rapidly increases with its dimini shing to lower than 400-500 degrees C. As a result, the scattering of conducting electrons is defined by film surface scattering under low c oncentration of the bulk phase at high and by bulk scattering on ''sta tic'' defects of the imperfect bulk phase at low growth temperatures.