Estimating the yield strength of metal films in ILD stacks using optimization-based inverse finite element analysis

The fabrication process-induced variation in the yield strength of metal films in microelectronic devices critically impacts the reliability of inter-layer dielectric (ILD) stacks. However, estimation of the yield strength of buried films in multilayer stacks remains a significant challenge. The indentation technique, whose advantage is that it does not require a freestanding film, has been widely used to characterize thin films, but traditional analyses mostly focus on characterizing the top layer of the stack. In this paper, we propose an optimization-based inverse finite element analysis (IFEA) technique to estimate the yield strength of a buried metal film in the ILD stack. The technique is demonstrated by estimating the yield strength of the buried aluminum film in a TEOS-Al-Si3N4-Si stack. We carryout the optimization from multiple initial points in the parameter space to ensure the uniqueness of the estimated yield strength.