The miniaturization of devices has become more and more important over the past few years, with an accompanying increase in complexity. As macroscale tests are not applicable for such small components, miniaturized tests have to be applied to study the materials response of the complex arrangements used in state of the art and future devices at small length scales. Especially residual stresses can play an important role in thin film systems concerning performance and lifetime, thus they have to be fully accounted when determining fracture mechanical quantities.
In this work, we concentrate on recent developments regarding the local determination of residual stresses and their influence on the fracture behaviour of thin films. The materials investigated are sputter deposited Cu-W-Cu and W-Cu-W trilayer systems, with an individual layer thickness of 500 nm, on a Si substrate. Samples are fabricated via cross section polishing and focused ion beam (FIB) milling. Initially, the residual stress depth profiles are determined by means of an improved ion beam layer removal (ILR) method. Here, the stress is calculated from the deflection of a cantilever that changes when parts of the film are removed. Subsequently, fracture experiments parallel and perpendicular to the interface are performed in-situ in the SEM to obtain comprehensive knowledge of the fracture and interface toughness. An accompanying finite element based modelling approach is introduced to determine crack-driving forces in the presence of interfaces and residual stresses.
With our findings we emphasize the importance of elastic and plastic incompatibilities and residual stresses when addressing fracture mechanical quantities of multi-layered thin film systems. Challenges and benefits of our approaches will be discussed.