On "effective channel length" in 0.1-μm MOSFETs

The conventional, 1-D definition of "effective channel length" (L/sub eff/) is examined in light of the spatial dependence of channel sheet resistance in 0.1-μm MOSFETs calculated from a 2-D device model. For short-channel devices, the sheet resistance deviates significantly from the uniform, long-channel behavior that L/sub eff/ in general is different from the "metallurgical channel length", L/sub met/. While geometrical (charge-sharing) effects tend to make L/sub eff/ slightly shorter than L/sub met/, lateral source-drain doping gradients, especially when coupled with retrograde channel doping, can make L/sub eff/ substantially longer than L/sub met/. The latter might help explain the apparent "excess" short channel effect often observed in 0.1-μm CMOS devices.