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

Abstract

Under maximum substrate current (lsub.max) stress (i.e. Vg ≈ Vd/2), the hot-carrier induced degradation of tungsten polycide gate (WSix) 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 (Ig,max) stress (i.e. Vg = Vd), the WSix n-MOSFETs showed higher hot-carrier induced degradation than the PolySi devices. In contrast, WSix p-MOSFETs showed higher degradation compared with the PolySi p-MOSFETs under both lg,max (i.e. Vg < Vd/2) and ISUb,max (i.e. Vg ≈ Vd/2) stresses. An explanation, substantiated by charge-pumping measurements, is proposed to explain the phenomena observed. The hot-carrier lifetime of WSix p-MOSFETs is found to limit the operation of WSix CMOS circuits.