Cracking and debonding in integrated microstructures

Internal stresses inevitably arise in integrated microstructures. This paper reviews a fracture mechanics approach to devising design rules to avert cracking. The smallness of the feature size permits a strategy different from that conventionally used to analyze the fracture of bulk materials. In an integrated microstructure, high tensile stress is localized in small regions. The elastic energy stored in each region scales with its volume. The surface energy associated with the creation of a crack scales with the surface area of the crack. Thermodynamics dictates that a flaw cannot grow if the stored elastic energy is lower than the created surface energy. Consequently, for a sufficiently small feature size, the volume-to-area ratio is small, and no flaw can grow. Our design rules do not depend on flaw size. They are deterministic, and rely on well-specified geometric and physical parameters. Furthermore, the stress singularity at corners does not cause any particular difficulty. As an example, the thermal misfit cracking in a multilevel interconnect test structure is investigated.