Anomalous Short-channel Body Coefficients Due To Transient Enhanced Diffusion

The threshold voltage and its variation with back-gate bias (body effect) are among the key parameters of a digital MOSFET model. For long-channel devices formed by conventional processing, both are routinely predicted by a combination of process and device simulation to better than 0.1 V [2]. For short-channel devices, particularly those formed with a very small thermal budget, anomalous diffusion effects can strongly influence the final doping profile and lead to incorrect threshold predictions. We report here on short (0.45/spl mu/m coded) and long (2/spl mu/m) channel length devices which show threshold shifts which are not predicted by conventional diffusion models. It is shown that transient enhanced diffusion caused by the source-drain implant must be influencing the channel profile. If the point defects generated by the source-drain implant are taken into account in the diffusion simulation, an accurate channel profile is obtained. Using correct diffusion profiles, the experimental threshold behavior is reproduced in device simulation.