Stress concentrations in thin films bonded to substrates

Several problems associated with the stresses in a thin film bonded to a substrate of a different material under conditions of mismatch strain are studied in the context of elasticity, anisotropy, plasticity and fracture. These problems are: (1) Determination of the concentration of elastic stresses near the free edges along the interface in polycrystalline (isotropic) thin films in a state of residual stress. Issues of edges effects, stress singularities, size effects and proximity effects are addressed. (2) The effect of anisotropy on elastic stresses and singularities in epitaxially grown films of material parameters typical of metallic and semiconducting films. The inhomogeneous stresses near the free edge and the uniform stresses far from the free edge are calculated. (3) The effect of inelastic deformation in relaxing stresses in thin films by dislocation slip. That plastic deformation significantly reduces the stress levels near the interface is discussed. (4) Mechanical failure of thin films by interface cracking and decohesion. Both external and internal boundaries which are responsible for delamination of thin films are investigated. Complex stress intensity factor and associated energy release rate are determined by employing the interface fracture mechanics concepts. The techniques from applied mechanics (finite elements, fracture analysis) are used throughout this study.