Temperature dependence of structural and electrical properties of Ta-Si thin alloy films

In situ electrical resistivity measurement and structural analysis methods including MeV ⁴He⁺ ion backscattering, x-ray diffraction, Auger electron spectroscopy combined with Ar⁺ sputtering, scanning and transmission electron microscopies have been used to investigate the properties and characteristics of the Ta-Si thin alloy film system as a function of temperature. Stoichiometric TaSi₂ films were deposited by double electron-gun coevaporation on Si, oxidized Si, and sapphire substrates. A distinct drop in resistivity near 300 °C has been determined to be a transformation of the amorphous to crystalline phase. The kinetics of the transformation has been obtained by isothermal treatment over the temperature interval of 240-280 °C. The results are interpreted in terms of a classical solid-state phase transformation model with a t⁴ (time) dependence and an apparent activation energy of 1.85 eV. Subsequent annealing causes further decrease of resistivity. The microstructures of films at various stages of annealing have been studied by x-ray diffraction and transmission electron microscopy. Correlation between the resistivity and microstructure is given and discussed. In situ resistivity of annealed films below room temperature has been measured. Crystalline TaSi₂ thin films do not become superconductive at 1.5 °K. Ion-beam mixed, coevaporated TaSi₂ film and films varying in composition from TaSi_3.4 to TaSi_1.2 prepared by cosputtering have also been studied. The results are compared and discussed.