Simulations for nanoindentation on thin metal films and the potential influence of creep

Thin metal films have been present in microelectronic packaging for a long time as e.g. RDL and BEOL structures, terminal metal or shielding layers. In most use cases, thin metal layers will be thermo-mechanically loaded, leading e.g. to disruption due to high thermal transients, or to fatigue cracks due to periodic sub-critical bending, thus causing reliability problems. In order to understand, describe and model the underlying failure mechanisms within a physics-of-failure approach, it is important to characterize thin metal films for their thermo-mechanical properties. It is known, that thin metals are highly process dependent in their properties. Also, the small thickness introduces size effects, so methods requiring thick or bulk samples are not of much use. This paper discusses the applicability and challenges of combining nanoindentation (NI) on thin metal films with FE simulations to obtain material properties. To that end, nanoindentation and atomic force microscopy (AFM) measurements on Ni, Cu, and Al are investigated together with finite element simulations to obtain elastic-plastic material properties. As there are some differences observed between experimental and simulated loading curves, the potential influence of creep on the simulation results is considered.