Effects of deposition methods on the temperature-dependent resistivity of tunasten films

Abstract

The resistivity of tungsten films prepared by magnetron sputtering, electron gun evaporation, and chemical vapor deposition was measured in the 4.2-297 K temperature range. The resistivityp ρ in all films decreases linearly with temperature down to 60 K, indicating that scattering by lattice phonons is responsible for most of the resistivity at higher temperatures. Residual resistivity decreases with increasing grain size as determined from transmission electron microscopy (TEM). Residual resistivity ratio (RRR) values are in the 2–7 range and this includes the epitaxially grown film investigated for comparison. Annealing, in general, increases RRR and in the case of epifilm, a value of 20.5 is obtained after 1000 °C anneal. The temperature coefficient of resistivity is found to decrease with increasing ρ297K, reflecting a growing contribution from defects and impurities. The effect of impurities is interpreted in terms of the grain boundary scattering model with reflection coefficient R, varying with deposition technique and thus with the amount of impurities incorporated in the films. Evaporated films have R less than 0.4, suggestive of low impurity content. In these films, defects observed in TEM play a major role. Cracks, precipitates, and dislocation loops contribute more significantly to ρ4.2Kthan to ρ297K. The contribution of defects can be reduced by raising substrate temperature (ρ297K = 6.39 μΩ cm) or by anneal at 1000 °C. © 1986, American Vacuum Society. All right reserved.