Mechanical analysis of interconnected structures using process simulation

An elastoplastic model has been implemented in a technology computer-aided design (TCAD) program with the aim of predicting the mechanical behavior of polycrystalline materials used in silicon-based technology in microelectronics. In order to analyze microstructures combining both nonlinear viscoelastic and elastoplastic materials, we propose a computational process with quick convergence. This model is now included in a stress simulation system, thus allowing the prediction of variations in stress according to the stage of the process. The modeling takes into account not only thermal stress but also intrinsic/extrinsic stresses and etching-related stress. The stress evolution of aluminum copper (Al–Cu) periodic lines embedded within silicon dioxide has been examined. The tensile and compressive yield strengths of thin-film Al–Cu have been characterized using the von Mises criterion for various film thicknesses. Comparisons with experimental results, based on passivated and unpassivated line structures, show that von Mises yield stress is independent of linewidth. It was also found that the correct prediction of the principal stresses strongly depends on the accurate characterization of thin-film yield strength. The use of incorrect values can lead to large errors in the determination of the line aspect ratio giving the maximum principal stresses. Finally, the analysis of an industrial back end of line process is performed to demonstrate what we can now carry out with TCAD to solve stress-related reliability problems in interconnects.