Finite element analysis of fatigue cracks formation in power metallisation of a semiconductor device subjected to active cycling

This contribution presents a finite element method (FEM) study of fatigue crack formation in Cu metallisation of a power MOSFET device during active cycling using a shear strain based critical plane approach. After a short description of the fatigue model and the procedure for identification of the critical planes, a two-dimensional FEM model of a DMOS cell aimed at computation of detailed stress-strain fields resulting from temperature loading during electrical power pulses is presented. Accumulation of plastic strains, evolution of stresses during the cyclic loading and predictions of the fatigue model is discussed. The predicted most dangerous critical planes satisfactorily correspond to the experimentally observed crack locations in the Cu metallisation showing the potential of the selected methodology.