SENSITIVITY ISSUES IN MODELING THE SUBSTRATE CURRENT FOR SUBMICRON N-CHANNEL AND P-CHANNEL MOSFETS

A well known source of uncertainty in device/process simulation is the exact lateral diffusion profile forming the source/drain junction under the edge of the MOSFET gate. In order to deal with this limitation, the common practice among TCAD users is to employ a calibrated local-field substrate current model to indirectly infer the details of the lateral diffusion of the source/drain region. Typically, the estimate of the lateral diffusion is adjusted to make the simulated substrate current agree with the measured substrate current. Using the standard local-field model and our recently published two-dimensional energy-dependent (non local-field) substrate current models that have a more correct physical basis, we have performed simulations to determine the sensitivity of these substrate current models to changes in the ratio of lateral diffusion to junction depth. It has been found that the local-field model can introduce an artificially high and misleading degree of sensitivity in substrate current, whereas the more physically correct energy-dependent model does not show as much sensitivity. This artificial sensitivity can lead to uncertainty as well as error in the extracted lateral diffusion profile; therefore, a calibrated local-field model may lead to erroneous results when determining the lateral diffusion and the relationship between effective channel length and physical gate length.