  This paper discusses the influence of the channel impurity distribution on
the transport and the drive current in short-gate MOSFET. In this purpose, a
careful description of electron-ion interaction suitable for the case of
discrete impurities has been implemented in a 3D particle Monte Carlo
simulator. This transport model is applied to the investigation of 50 nm MOSFET
operation. The results show that a small change in the number of doping
impurities or in the position of a single discrete impurity in the inversion
layer may significantly influence the drain current. This effect is not only
related to threshold voltage fluctuations but also to variations in transport
properties in the inversion layer, especially at high drain voltage. The
results are analyzed in terms of local fluctuations of electron velocity and
current density. In a set of fifteen simulated devices the drive current Ion,
determined at VGS = VDS = 0.6 V, is found to vary in a range of 23% according
to the position of channel impurities.
