Interface crack initiation due to nano-scale stress concentration

In order to investigate the mechanical factors dominating interfacial crack initiation in nano-meter-scale components, we prepared two types of specimens, which possessed different stress conditions due to the shapes, containing an interface between a 20-nm-thick copper (Cu) thin film and a silicon (Si) substrate. In one type, the stress concentration was at the interface edge, while in the other type, it was in the interior. In the former, a crack was initiated at the Cu/Si interface edge under a stress concentration of about 1 GPa extending over 20–30 nm. In the latter, using a cantilever specimen with a step, a crack was initiated in the interior at the Cu/Si interface at a stress concentration of about 1 GPa extending over 60 nm, which coincides fairly well with that at the interface edge. These results demonstrate the applicability of a unified criterion for interface crack initiation, though the interior is slightly more resistant to cracking.