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

The V_t variability in scaled FinFETs with gate length (L_g) down to 25 nm was systematically investigated, for the first time. By investigating the gate oxide thickness (T_ox) dependence of V_t variation (VTV), the gate-stack origin, i.e., work-function variation (WFV) and gate oxide charge (Q_ox) 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 (T_Si) fluctuations, but also the reduction of gate-stack origin VTV. Moreover, it was experimentally found that the V_t of multi-FinFETs with the same gate area reduces with increasing the number of fins.