X-ray microdiffraction: local stress distributions in polycrystalline and epitaxial thin films

When investigated by X-ray microdiffraction, the stress states in thin metal films are found to be more complex than as assumed by the simple models that have been formulated to describe their behavior. In this paper, the local differences in stress have been measured in a polycrystalline Al(0.5 wt% Cu) film on Si and an epitaxial Cu film on Al 2O 3. Significant differences in stress state are apparent between grains, but also within grains. While both types of film display a local variation in residual stress state, the width of the distribution is much broader in the polycrystalline film. The reasons for this are discussed in terms of grain size distribution and dislocation nucleation.