Stress relaxation in film samples was investigated by means of  in situ  stress measurements. A simple viscous flow model was used to explain the kinetics of stress relaxation in thin films. The activation energy for stress relaxation was estimated to be 190kJ/mol; and was attributed to the lattice diffusion of vacancies. It was found that a Nabarro-Herring creep model could be used to correlate the viscosity, lattice diffusion coefficient, and grain size of the films. An estimate was obtained for the lattice diffusion coefficient for vacancy motion during relaxation. The observed time which was required for complete relaxation was found to be in agreement with theoretical values. Hillock formation which resulted from grain boundary sliding was suggested to contribute to stress relaxation in the early stages. The grain growth which resulted from lattice diffusion was expected to play a major role in stress relaxation.

C.C.Li, S.B.Desu: Journal of Vacuum Science and Technology A, 1996, 14[1], 7-12