Mechanisms of Stress Relief in Thin Films

The stress required to form a dislocation loop of the size of a grain has been calculated for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present. It is shown that in typical polycrystalline films this value of the stress is comparable to the observed stresses in films before plastic flow sets in. In the case of single crystal epitaxial films with a high grown-in dislocation density the plastic strain realizable is shown on the basis of a simple model to be a few percent. The model is based on a simple nearest neighbor dislocation interaction and is shown to explain the tensile behavior of thin single crystal films.