A study of the corner effect in trench-like isolated structures

In trenchlike isolated devices, several parasitic effects exist. In a real-case test simulation, two such effects are shown. The most difficult to handle is the corner effect at the convex and concave corners in the structure. The corner effect is studied for two simple structures where no other parasitic effect exists. This makes it possible to look at the controlling factors of the effect and to formulate possible solutions of the corner effect. Results show that the corner effect is very strong, even with low gate bias and oxide charge density (Q_f) values. To eliminate the inversion of the convex corner, doping levels higher than 1E17/cm³ are necessary when Q_f⩾1E11/cm². It is shown that rounding the convex corner is a very effective way to eliminate the effect. However, to minimize the area loss, a compromise must be chosen between the substrate doping concentration (N _sub), oxide thickness, and rounding radius. Furthermore, the carrier concentration in the corner is controlled by the neighborhood of a biased drain (well). This can have an important influence on the leakage currents along a trench. The corner effect in a concave structure seems to have a very strong pinning function on the potential. Sharp corners prevent leakage currents around a trench, even with a relatively low N_sub