Investigation of ultra-thin gate oxide reliability behavior by separate characterization of soft breakdown and hard breakdown

It is shown in this work that the soft breakdown can follow a significantly different temperature and field acceleration behavior than the dielectric breakdown (hard breakdown). These properties have a strong influence on reliability prediction of ultra-thin oxides and can result in misinterpretation if soft breakdown and hard breakdown events are mixed up during gate oxide reliability testing. The activation energy and the field acceleration of the soft breakdown are compared to the disturbed-bond breakage process proposed in the thermochemical E-model. It is concluded that soft breakdown can be caused by H-Si and H-O bond breakage due to the electric field in the oxide. The activation energy for soft breakdown also indicates that formation of a soft breakdown path is influenced by hydrogen diffusion in the oxide.