Three-dimensional effects due to the field oxide in MOS devices analyzed with MINIMOS 5

The MINIMOS simulation program has been extended to three dimensions to investigate the parasitic effects at the channel edge on MOSFET device characteristics. The box integration method after Forsythe has been applied for discretization. This method is suitable for nonplanar interfaces. The most important nonplanar interface occurs at the transition of the gate oxide to the field oxide called the bird´s beak. Approximating this interface as a rectangular shape leads to unrealistic results. The oxide-body is defined by analytical functions, so it is easy to investigate a wide range of applications. An automatic grid-refinement algorithm is used to generate the specific grid. The simulation shows that the influence of the channel edge is not negligible for channel widths less than 2 μm. The total drain current for narrow channel MOSFETs is either increased or decreased by parasitic three-dimensional effects compared to wide channel (two-dimensional) MOSFETs depending on the bias conditions