Thin film cracking and the roles of substrate and interface

Cracks in thin films caused by residual tension are examined. Attention is focused on film cracking, subject to either interface debonding or substrate cracking. For crack channeling along the film, the driving force is found to depend on the channel cross-section, as governed by the fracture properties of the interface and the substrate, in addition to known effects of film thickness, residual stress and elastic moduli. The critical film thickness needed to avoid cracking is determined to be lower if the crack extends into the substrate. Conditions for thin film spalling and constrained debonding are prescribed. Finally, the T-stress is used to account for crack branching in substrates.