ELASTIC STRAIN GRADIENTS AND X-RAY-LINE BROADENING EFFECTS AS A FUNCTION OF TEMPERATURE IN ALUMINUM THIN-FILMS ON SILICON

Grazing incidence x-ray scattering (GIXS) with a synchrotron source wa s used to measure elastic strain gradients as a function of temperatur e in aluminum and aluminum alloy thin films of different thicknesses o n silicon. The stresses in the films are induced as a result of the di fference in thermal expansion coefficient between film and substrate. Disregarding minor deviations at the surface, it is shown that there a re no gross strain gradients in these films in the range of temperatur es (between room temperature and 400 degrees C) considered. Significan t x-ray line broadening effects were observed, suggesting an accumulat ion of dislocations on cooling the films and their annealing out as th e films were being reheated. The variation of the dislocation density during thermal cycling compares well in nature with that of the concur rent variation in film stress, indicating that large strain hardening effects contribute toward the film flow stress.