Effects of Non-Degenerately Doped Polysilicon on the Hot-Carrier Reliability of Tungsten Polycide Gate PMOSFETs

Polysilicon depletion effect is observed for the non-degenerately doped Polysilicon layer of the tungsten-polycide gate of buuried-channel PMOSFETs. Lower current drive and transconductance coupled with higher subthreshold slope are observed for PMOSFETs with lower doped Polysilicon layer. The potential drop across the lower doped polysilicon layer of the PMOSFETs results in lower gate current. Consequently, PMOSFETs with lower doped polysilicon layer are more resistant to hot-carrier degradation and have higher hot-carrier lifetimes. There exists an optimum polysilicon doping concentration for tungsten-polycide devices depending on the desired electrical performances and hot-carrier reliability of the buried-channel PMOSFETs.