Papers by Author: M. Wohlschlögel

Abstract: Thin film diffusion couples (Pd-Cu, individual layer thicknesses: 50 nm) have been prepared by DC-magnetron sputtering on silicon substrates coated with amorphous inter-layers (Si3N4 on top of SiO2). The microstructural development, phase formation and the stress evolution during diffusion annealing have been investigated employing Auger-electron spectroscopy in combination with sputter depth profiling, ex-situ and, in particular, in-situ X-ray diffraction measurements. Upon annealing at relatively low temperatures (175°C to 250°C) for durations up to 100 hours, considerable diffusional intermixing occurs. Interdiffusion is accompanied by the sequential formation of a new phase (Cu3Pd). The detected stress changes are discussed in terms of possible mechanisms of stress generation.

Abstract: Stress gradients have been investigated employing a measurement strategy for diffraction measurements at constant penetration/information depths. Two examples have been considered: (i) sputter-deposited copper thin films on silicon wafers and (ii) γ’-Fe4N1-x layers on α-Fe substrates obtained by gaseous nitriding. In the Cu thin films rather low tensile stresses, increasing in magnitude with increasing penetration/information depth have been found. An evaluation of the measured lattice strains has been performed on the basis of the f(ψ) method, where the X-ray elastic constants (XEC’s) have been calculated as weighed averages of the corresponding Voigt and Reuss XEC’s and the weighing parameter has been taken as a fitting parameter. This evaluation reveals that the grain interaction changes with increasing penetration/information depth from near-Reuss type towards Neerfeld-Hill type. In the γ’-Fe4N1-x layers stress gradients occur due to surface relaxation near the surface and deeper in the layer due to a nitrogen concentration gradient which is built up during nitriding. First measurements in a laboratory diffractometer show the effect of surface relaxation on the stress-depth profile near the surface. As no single-crystal elastic constants are available for γ’-Fe4N1-x, the mechanical elastic constants have been employed in diffraction stress analysis. The results indicated that single-crystal elastic anisotropy occurs. From the measured data also a concentration – depth profile has been deduced.

Abstract: A rigorous strategy for (X-ray) diffraction stress measurements at fixed penetration/information depths is described. Thereby errors caused by lack of penetration-depth control in traditional (X-ray) diffraction (sin2ψ) measurements are annulled. The ranges of accessible penetration/information depths and experimental aspects are briefly discussed. The power of the method is illustrated by the analysis of an only small stress gradient in a sputter-deposited nickel layer.