Method of fabricating bipolar transistors and insulated gate field

Abstract

A method of fabricating a semiconductor device includes the steps of: forming at least one first semiconductor region of a first conductivity type and at least one second semiconductor region of a second conductivity type in a main surface of a semiconductor layer of the first conductivity type; forming a three-layer film having a desired shape on each of the first and second semiconductor regions, the three-layer film being made up of a bottom layer which is a conductive film, an intermediate layer which is a silicon nitride film, and a top layer which is a polycrystalline silicon film doped with one of arsenic and phosphorus; forming a first insulating layer on the side wall of the three-layer film; forming a second polycrystalline silicon film on the whole surface, and diffusing one of arsenic and phosphorus from the first polycrystalline silicon film into the second polycrystalline silicon film; selectively etching off the first polycrystalline silicon film and that portion of the second polycrystalline silicon film, in which one of arsenic and phosphorus has been diffused; forming a second insulating layer at least on the surface of the portion of the second polycrystalline silicon film which exists on the second semiconductor region; removing the silicon nitride film and the conductive film which exist on the second semiconductor region, while using the second insulating layer as a mask, to form an aperture; and forming a third polycrystalline silicone film so that the aperture is covered by the third polycrystalline silicon film.