HOT-CARRIER RELIABILITY OF NON-DEGENERATELY DOPED TUNGSTEN POLYCIDE GATE BURIED-CHANNEL P-MOSFETS

Apolysilicon-depletion effect is observed for the non-degenerately dop ed polysilicon layer of a tungsten silicide-polysilicon gate stack of buried-channel p-MOSFETs, but not for n-MOSFETs with a polysilicon lay er of the same doping concentration. A lower current drive and transco nductance, coupled with a higher subthreshold slope, will result in po orer dynamic performance for p-MOSFETs having a lower doped polysilico n layer. The potential drop across the lower doped polysilicon layer r esults in lower gate currents. Consequently the p-MOSFETs with a lower doped polysilicon layer are more resistant to hot-carrier induced deg radation and have higher hot-carrier lifetimes; Thus there exists an o ptimum polysilicon doping concentration for tungsten-polycide devices and the latter is dependent on the desired electrical performance and hot-carrier reliability of buried-channel p-MOSFETs. (C) 1997 Elsevier Science Ltd.