Three-dimensional simulation of VLSI MOSFET's - The three-dimensional simulation program WATMOS

A computer simulation program based on a three-dimensional model for small-geometry MOSFET's is described. The effect of Si-SiO2 interface charge, ion implantation in the channel, p(+) isolation field ion implant (channel isolations), and the shape of the field oxide are all addressed in the model. The three-dimensional simulations offer new insight into VLSI MOSFET devices. The effective channel width under certain bias conditions is found to decrease to 63% of its nominal value. The punchthrough current per unit width as a function of channel width is found for the first time to decrease rapidly as the channel width is reduced below 5 microns. A decrease of punchthrough current by three orders of magnitude is observed as the channel width is reduced from 2 to 1 micron. It is also found that the breakdown voltage of small-geometry devices increases as the channel width decreases.