On the gate-stack origin threshold voltage variability in scaled FinFETs and multi-FinFETs

The Vt variability in scaled FinFETs with gate length (Lg) down to 25 nm was systematically investigated, for the first time. By investigating the gate oxide thickness (Tox) dependence of Vt variation (VTV), the gate-stack origin, i.e., work-function variation (WFV) and gate oxide charge (Qox) variation (OCV) origin VTV were successfully separated. It was found that the atomically flat Si-fin sidewall channels fabricated by using the orientation dependent wet etching contribute to, not only the reduction of fin thickness (TSi) fluctuations, but also the reduction of gate-stack origin VTV. Moreover, it was experimentally found that the Vt of multi-FinFETs with the same gate area reduces with increasing the number of fins.