Local plasticity of Al thin films as revealed by x-ray microdiffraction.

Grain-to-grain interactions dominate the plasticity of Al thin films and establish effective length scales smaller than the grain size. We have measured large strain distributions and their changes under plastic strain in 1.5-microm-thick Al 0.5% Cu films using a 0.8-microm-diameter white x-ray probe at the Advanced Light Source. Strain distributions arise not only from the distribution of grain sizes and orientation, but also from the differences in grain shape and from stress environment. Multiple active glide plane domains have been found within single grains. Large grains behave like multiple smaller grains even before a dislocation substructure can evolve.

Scanning X-ray microdiffraction with submicrometer white beam for strain/stress and orientation mapping in thin films.

Scanning X-ray microdiffraction (microSXRD) combines the use of high-brilliance synchrotron sources with the latest achromatic X-ray focusing optics and fast large-area two-dimensional-detector technology. Using white beams or a combination of white and monochromatic beams, this technique allows for the orientation and strain/stress mapping of polycrystalline thin films with submicrometer spatial resolution. The technique is described in detail as applied to the study of thin aluminium and copper blanket films and lines following electromigration testing and/or thermal cycling experiments. It is shown that there are significant orientation and strain/stress variations between grains and inside individual grains. A polycrystalline film when investigated at the granular (micrometer) level shows a highly mechanically inhomogeneous medium that allows insight into its mesoscopic properties. If the microSXRD data are averaged over a macroscopic range, results show good agreement with direct macroscopic texture and stress measurements.