VDMOS transistor with reduced projective area of source region

Claim 1

A semiconductor device comprising: (a) a semiconductor substrate of a first conductivity type having a first conductivity type epitaxial layer, said substrate forming a drain region of the semiconductor device; (b) an insulating material disposed over said substrate to define an active region; (c) a gate electrode for said device disposed over said substrate adjacent the active region; (d) a trench in said substrate and adjacent a side of said gate electrode, said trench having: (i) first sidewalls which intersect said substrate essentially normal to a major surface thereof and extend in a direction normal to said major surface for a predetermined distance, and second sidewalls then converging towards each other as the depth of the trench in said epitaxial layer increases; (e) pockets of first conductivity type material, said pockets having a first conductivity type impurity concentration greater than that of said epitaxial layer, said pockets being disposed immediately adjacent the first sidewalls, below said gate electrode, without being immediately adjacent said second sidewalls; and (f) a region of second conductivity type material surrounding said trench and said pockets of first conductivity type material.