Effect of substrate constraint on stress-induced cracking of sputtered tungsten thin film

A comparative investigation was performed on the stress-induced surface cracking of tungsten films sputter deposited on polyimide (PI) and Si substrates. Microscopic observations suggest that with the same film thickness， two different types of cracking behaviors were observed. Wedge-shaped cracks are formed on the surface of film deposited on the Si substrate. However， the cracks of film deposited on the polyimide consist of aligned grains. The localized plastic deformation in the nanocrystalline W film on polyimide is mediated by the alignment of grains， which results from the grain rotation along the in-plane and out-of-plane directions. However， on the Si substrates the wedge-shaped cracks originate from the in-plane rotation of grains. The analysis implies that the different deformation behaviors are associated with the evolution of stress in the film and the substrate constraint.