Conductivity modulated MOSFET

Claim 1

A conductivity modulated metal oxide semiconductor field effect transistor, comprising: a semiconductor substrate having a base layer of first conductivity type, a drain layer of second conductivity type formed on a first surface of said base layer, and an emitter region of the second conductivity type formed on a second surface of said base layer; an oxide film deposited on said substrate so that it spans over a part of a surface of said emitter region and a part of a surface of said base layer; a first polycrystalline silicon layer of the second conductivity type deposited so that it comes into contact with only said oxide film; a second polycrystalline silicon layer of the first conductivity type deposited so that it spans over said emitter region and said oxide film, and so that it comes into contact with a first side wall of said first polycrystalline silicon layer; a third polycrystalline silicon layer of the first conductivity type deposited so that it spans over said base region and said oxide film, and so that it comes into contact with a second side wall of said first polycrystalline silicon layer; a gate polycrystalline silicon layer deposited so that it spans over from said first polycrystalline silicon layer to said third polycrystalline silicon layer through an insulating layer; a source electrode coming into contact with said emitter region and said second polycrystalline silicon layer; a gate electrode coming into contact with said gate polycrystalline silicon layer; and a drain electrode coming into contact with said drain layer.