MEASUREMENT OF LATTICE STRAIN IN METALS BY QUANTITATIVE CONVERGENT BEAM ELECTRON DIFFRACTION. J. Mayer, C. Deininger, S. Streiffer^*, A. Weickenmeier, Max-Planck-Institut für Metallforschung, Seestr. 92, 70174 Stuttgart, Germany, ^*now at: Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907

Lattice strain in metals or alloys is an important factor controlling the performance and failure mechanisms in compound systems. In combination with ceramics or semiconductors, the metal is always the elastically and plastically softer material. Therefore most of the strain is localised within the metal. In such systems, temperature changes lead to lattice strain caused by the difference in thermal expansion coefficients. Convergent Beam Electron Diffraction (CBED) makes it possible to measure lattice strain with high spatial resolution. Strain can e.g. be measured as a function of distance from an interface. We have studied Al thin films on SiC and Si substrates. In particular the latter one serves as a good model system for interconnects in semiconductor devices. The samples were studied in cross-section and plan-view geometry. The CBED patterns were acquired on an energy-filtering Zeiss EM 912 Omega transmission electron microscope. The energy-filter removes the inelastically scattered electrons which increases the accuracy of the measurements and makes possible to study thicker specimen areas. The CBED patterns were recorded at different temperatures to study the effect of the differences in thermal expansion coefficients. The arrangement of the higher order Laue zone (HOLZ) lines in the central disc was simulated using a fully dynamical Bloch wave program. A refinement algorithm was used to vary the strain state in the simulation until a best fit between the experimental and simulated patterns was obtained. The results indicate that in the thin films strains of up to 0.5% can occur. Strong deviations from a simple equibiaxial strain state were observed in a polycrystalline <111> textured film. A sensitivity to variations in lattice parameter of approximately 10^-4 was obtained. Possible stress relaxations in the thin TEM sections will be discussed.