Hot-carrier induced degradation of polysilicon and tungsten polycide gate MOSFETs under maximum substrate and gate current stresses

Abstract

Under maximum substrate current (I sub,max ) stress (i.e. V g ≈ V d /2), the hot-carrier induced degradation of tungsten polycide gate (WSi x ) n-MOSFETs in the linear drain current and maximum linear transconductance is lower, and the shift in the threshold voltage is higher than that of polysilicon gate (PolySi) n-MOSFETs. However, under maximum gate current (I g,max ) stress (i.e. V g = V d ), the WSi x n-MOSFETs showed higher hot-carrier induced degradation than the PolySi devices. In contrast, WSi x p-MOSFETs showed higher degradation compared with the PolySi p-MOSFETs under both I g,max (i.e. V g < V d /2) and I sub,max (i.e. V g ≈ V d /2) stresses. An explanation, substantiated by charge-pumping measurements, is proposed to explain the phenomena observed. The hot-carrier lifetime of WSi x p-MOSFETs is found to limit the operation of WSi x CMOS circuits.