Fatigue damage in thin film Al interconnects at ultra high frequency: A finite element analysis approach

In order to investigate the behavior of thin metal films under high cyclic stress surface acoustic waves (SAW) test devices with frequencies up to several GHz can be used. Resulting from the microstructural damage formation a significant degradation in form of a shift of the resonance frequency in SAW test devices takes place. In the present paper, we analyze the influence of the amount of damage on the observed frequency shift in detail. It is shown that Finite Element (FEM) calculations simulate very well the sensitivity of the resonance frequency to the damage formation in the form of cracking, voiding and extrusion growth. The experimentally observed linear correlation between damage density and frequency shift is reproduced by the FEM model. Furthermore, the FEM simulations predict a significant deviation from the linear correlation for very high damage densities.