Effects of gate electrodes and barrier heights on the breakdown characteristics and Weibull slopes of HfO2 MOS devices

In this work, we present the effect of gate electrodes and barrier heights on the breakdown characteristics and Weibull slopes of HfO₂ MOS devices. Higher Weibull slope (β) of Ru gate electrode has been observed when compared that of Ru-Ta alloy. The higher β in Ru devices is due to smaller charge fluence which results from relatively higher barrier height. Varying SiO₂ and HfO₂ were investigated in order to understand ultra-thin HfO₂ gate stack structure. We found that there is bi-modal defect generation rate on High-k/SiO₂ stack. Two-steps breakdown process was clearly observed and Weibull slope of soft breakdown (1st 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. Weibull slope of high-k gate stacks is a strong function of the inter-face layer thickness and the barrier height by gate electrode workfunction, whereas it is a weak function of high-k layer thickness.