Effects of film thickness on critical crack tip opening displacement in single-crystalline and polycrystalline submicron Cu films

We performed in-situ field emission scanning electron microscopy fracture toughness tests on single-crystalline and polycrystalline submicron-thick Cu films. In all specimens, the notch root became blunt, and a crack was initiated from the blunted notch root. The critical crack tip opening displacement (CTOD) for crack initiation, δi, was thickness dependent, where δi decreased with a decrease in the thickness. The critical CTOD normalized by the thickness, δi/B, values of the films were similar (δi/B = 1.4–1.9), irrespective of the film thickness and microstructure. This suggested that the local fractures of the submicron Cu films were similar.