A simulation study to evaluate the feasibility of midgap workfunction metal gates in 25 nm bulk CMOS

The performance of 25 nm metallurgical channel length bulk MOSFETs with midgap workfunction metal gates has been compared with conventional polysilicon gates and bandedge workfunction metal gates. Device design using pocket halo implants was implemented to achieve the required off-state leakage specification. Highly accurate, full device simulations have been performed with a linear chain of inverters taking quantum effects into consideration. Drain induced barrier lowering (DIBL) was used as an indicator of short channel effects, and the stage delay of a linear chain of inverters and the on state drive current (I/sub on/) have been identified as metrics for performance. Compared to bandedge metal gates, midgap gates suffer from lower drive currents for both NMOS and PMOS devices. On the other hand, midgap devices were comparable in their performance to N/sup +/ polysilicon gated devices and exceeded that of P/sup +/ polysilicon devices. This high performance was attributed to a lack of poly depletion in midgap metal devices and a higher degree of DIBL which resulted in a lower V/sub t/ under high drain bias providing high drive current. Conclusions have been drawn on the feasibility of using midgap metal gates to simplify process integration in future generation CMOS devices.