THE EFFECT OF DOPING PROFILE VARIATIONS UPON DEEP-SUBMICROMETER MOSFETS

The variations in current induced by variations in the (horizontal) do ping profile between channel and drain or source can be described in t erms of variations in the effective channel length L(EFF) induced by t he variations in the doping profile of source or drain. Sensitivity to profile variations becomes severe as L(EFF) --> 0, because the curren t in the L(EFF) --> 0 regime depends exponentially on the barrier pote ntial. Likewise, because of the exponential dependence of current on p otential in the subthreshold region, sensitivity is particularly stron g in subthreshold for variations in the (vertical) channel profile tha t determines the device threshold and turn-off. The centroid of the ve rtical profile must be controlled to sub-Debye length accuracy to keep subthreshold current variations below a few percent.