Identifying the First Layer to Fail in Dual-Layer ${\rm SiO}_{\rm x}/{\rm HfSiON}$ Gate Dielectric Stacks

We use the thermo-chemical model of bond breakage to investigate the degradation occurring in dual-layer SiO_x/HfSiON gate dielectric stacks during low-compliance soft breakdown (BD) experiments, with the ultimate goal of identifying the first layer that degrades. Time-dependent dielectric breakdown experiments reveal that the degradation of conventional SiON and SiO_x/HfSiON dielectric stacks have the same kinetics, i.e., activation energy and field acceleration factor. This finding, supported by physics-based BD simulations, shows that the degradation in SiO_x/HFSiON stacks is governed by the defect generation in the silicon oxide interfacial layer, which is the first that degrades in the multilayer stack.