The initial stages of the formation of holes and hillocks in thin films under equal biaxial stress

The theory of thermal grooving under stress is extended to explain the formation of holes and hillocks in very thin films undergoing thermal cycling. Previous experimental work and attempts to model holes and hillocks are first reviewed. A theoretical model based on the review is then developed to quantify the surface topological evolution at triple junctions in thin films with large columnar grains. The surface profiles are computed for various applied stresses and angles of intersecting grain boundaries, and the model is applied to describe a 120° triple junction in a Cu thin film through an annealing cycle from room temperature to 325°C. The simulation, which uses experimentally determined stress and materials property data, illustrates how this model can predict the failure of films undergoing a given thermal cycle.