Microplasticity of copper thin films on silicon substrates

Internal friction in polycrystalline copper films 0.2-1.5 w m thick on silicon substrates has been measured as a function of strain amplitude. The internal friction in the films increases with increasing strain amplitude but at a value of the strain amplitude that is at least two orders of magnitude greater than the similar increase in bulk copper. Analysis of the amplitude-dependent internal friction provides the plastic strain of the order of 10 -9 as a function of effective stress on dislocation motion. Since the grain size is larger than the film thickness, the microflow stress at a constant level of plastic strain varies inversely with the film thickness. The film thickness effect in the microplastic range can be explained on the basis of a dislocation-bowing model.