X-ray diffraction study on residual stress and preferred orientation in thin titanium films subjected to a high ion flux during deposition

Abstract

The structural properties of thin Ti films were studied by x-ray scattering techniques aiming at an improved understanding of residual stress and preferred orientation in thin metal films when subjected to a high ion flux during deposition. The samples were prepared by gas-flow sputtering and by subjecting the substrate to a midfrequency bias during deposition. Large arrival ratios of ions over deposited atoms, Ji∕Ja, could be realized by this processing. Some hundred nanometers thin Ti layers were characterized by x-ray reflectometry, symmetric θ∕2θ diffraction, pole figure analysis, and residual stress measurements by the sin2ψ and by the scattering vector technique, the latter method enabling a depth-resolved determination of stress fields. Whereas the stress state in an unbiased sample turned out to be tensile accompanied by a dominating (00.l) texture component, the biased samples were found to exhibit an overall compressive stress and a (h0.0) fiber texture. The results for the unbiased sample could be explained by a minimization of the elastic energy density which favors the preferred orientation of crystallographic c axes normal to the substrate plane. The biased samples closely resembled macroscopic Ti workpieces that were subjected to severe plastic deformation as was indicated by (i) the (h0.0) fiber texture along the load direction, (ii) the large compressive in-plane residual stress σ⊥, and (iii) the depth-resolved course of σ⊥(z). It is concluded that a high ion flux onto a growing Ti film has the same effect as a uniaxial mechanical load stress would have.