Semiconductor high-power mosfet device

Claim 1

In a high power metal oxide semiconductor field effect transistor device comprising: a semiconductor chip having first and second parallel opposite surfaces; an upper layer on said chip of a relatively low conductivity region of one of the conductivity types extending to said first surface; a plurality of substantially identical polygonal base regions of the other of said conductivity types extending from said first surface into said upper layer, said plurality of base regions being symmetrically laterally disposed over said first surface and having peripheries which are spaced from peripheries of adjacent base regions by a given distance; a respective generally annular source region extending from said first surface into each of said base regions; the lateral outer periphery of each of said source regions being laterally spaced along said first semiconductor surface from the lateral outer periphery of its said respective base region, thereby to define respective channels of the opposite conductivity type which can be inverted; a gate oxide extending over each of said channels and a gate electrode atop said gate oxide; and source electrode means connected to each of said source regions and to respective adjoining portions of their associated base regions at respective contact areas; the improvement comprising, in combination with the foregoing: said polygonal base regions each having a depth of less than about 0.25 mil, having a flat bottom portion substantially coextensive with the area of said base region at said first surface, and being free of any further portion extending deeper than said flat bottom portion; a central region of each of said base regions having a lower extent situated above its associated flat bottom portion and an upper extent coextensive with said first surface and being in contact with said source electrode means, said central region having an increased conductivity compared to that of the remainder of said base region, said central region being deeper than its associated source region and extending laterally at least coextensively with the associated source electrode contact area; said central region extending laterally beneath at least a portion of its said source region, thereby to reduce the lateral electrical resistance of the source region beneath at least a portion of the lateral extent of said source.