The relaxation of thermal stress in a thin film adhering to a substrate of differing expansion coefficient is discussed. Good agreement is found between literature data on relaxation during isothermal anneals of Pb films at up to 350/sup 0/K and model calculations based on a state variable description of plastic flow. The stress system during relaxation is explored, and the absence of diffusional creep is explained. The plasticity-dominated relaxation process suggested by this analysis is shown to be in good qualitative agreement with data on rapid relaxation over the course of a cycle between room and cryogenic temperatures. The implications …
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The relaxation of thermal stress in a thin film adhering to a substrate of differing expansion coefficient is discussed. Good agreement is found between literature data on relaxation during isothermal anneals of Pb films at up to 350/sup 0/K and model calculations based on a state variable description of plastic flow. The stress system during relaxation is explored, and the absence of diffusional creep is explained. The plasticity-dominated relaxation process suggested by this analysis is shown to be in good qualitative agreement with data on rapid relaxation over the course of a cycle between room and cryogenic temperatures. The implications of this for long-range material transport in the film are discussed. It is shown that hillock volume should increase over the course of a temperature cycle. Finally, a mechanism for hillock nucleation based on grain boundary sliding is suggested.
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