Strain distribution in thin aluminum films using x-ray depth profiling

Thin polycrystalline Al films deposited on oxidized Si(100) substrates have been studied using grazing incidence x-ray scattering techniques. The films become strained after high-temperature annealing due to the differential thermal expansion of the substrate and film. By varying the grazing angle of incidence on the surface, the penetration depth of the incident x rays can be varied from a minimum of roughly 30 Å to a maximum which is deeper than the film thickness. By measuring the change in the Al in-plane peak position with penetration depth, the strain distribution within the film can be determined. For thin films (less than 3000 Å) the strain is uniform throughout much of the film, decreasing only very near the surface. Strain relaxation with time occurs uniformly throughout the film over the first 4000 min.