Selective interface toughness measurements of layered thin films

Driven by the ongoing miniaturization and increasing integration in microelectronics devices, very thin metallic films became ever more important in recent years. Accordingly also the capability of determining specific physical and mechanical properties of such arrangements gained increasing importance. Miniaturized testing methods to evaluate, for example, the mechanical properties of thin metallic multilayers are therefore indispensable. A novel in-situ micromechanical approach is examined in the current study and compared to existing methods regarding their capability to determine the interface toughness of specific interfaces in multilayer configurations. Namely, sputter deposited copper and tungsten thin films with a thickness of approx. 500 nm on a stress-free silicon (100) substrate are investigated. The multilayer stacks consist of different materials that vary in microstructure, elastic properties and residual stress state. We examine the interface toughness via double cantilever beam tests, nanoindentation and novel miniaturized shear tests. The choice of a proper test method is indispensable when addressing strong interfaces, such as the W-Cu interface, in the presence of weaker ones. Finally, it is demonstrated that miniaturized shear testing is a very promising approach to test such strong interfaces as the interface of interest to fail is predefined by the sample geometry.