Effects of barrier height (ΦB) and the nature of bi-layer structure on the reliability of high-k dielectrics with dual metal gate (Ru & Ru-Ta alloy) technology

In this work, we present the effects of barrier height on the reliability of HfO₂ with dual metal gate technology in terms of Weibull slope, soft breakdown characteristics, defect generation rate, critical defect density and charge-to-breakdown. It was found that the lower Weibull slope of high-k dielectrics (compared to SiO₂) is partially attributed to the lower barrier height of high-k dielectrics which in turn results in larger current increase. Thus, defect generation rate increases and charge-to-break down decreases, while critical defect density remains constant. In addition, it has been found that there is distinct bi-modal defect generation rate for high-k/SiO₂ stack. Two-step breakdown process was clearly observed; and Weibull slope of soft breakdown (1^st breakdown) shows lower β value compared to that of hard breakdown (2^nd breakdown). Soft breakdown characteristics were dependent on the barrier heights. The bi-modal defect generations are believed to be resulted from the breakdown in interface and bulk layer.