Channel-length dependence of substrate current characteristic of LDD MOSFET's

The substrate current versus gate voltage characteristic of short-channel LDD structures showed a second peak for large spacer widths and low n - concentrations. The effect of channel length on the two regions of the characteristic (i.e., in the neighborhood of the first and the second peaks) is investigated. While the substrate current at the first peak normalized to the drain current remains independent of the channel length, the normalized substrate current at the second peak increases as the channel length decreases. These observations are explained on the basis of the drain depletion region extended beyond the gate edge. A previously published model by Ko et al. [4] was extended to an LDD structure to quantitatively explain this phenomena.