Method of manufacturing a bipolar transistor

Claim 1

A method of manufacturing a bipolar transistor, said method comprising the sequential steps of; forming a covering layer on a surface of a semiconductor substrate, said substrate being of a first conductivity type; forming an aperture in said covering layer to expose a section of said surface of said substrate; forming a side wall layer made of material resistant to oxidation on a peripheral part of said section and on said covering layer within said aperture to expose a center part of said section; carrying out a heat treatment under oxidizing atmosphere to form an oxide film on said exposed center part of said section of said surface; removing said side wall layer to expose said peripheral part of said section of said surface; introducing impurities of a second conductivity type, opposite to said first conductivity type, into said peripheral part to form an extrinsic base portion of said second conductivity type contacting an edge of said oxide film; forming a concavity in said peripheral part of said surface section at a position adjacent said edge of said oxide film such that (1) first wall portions of said concavity, including the bottom of said concavity remote from said edge of said oxide film, are of said second conductivity type constituted by said extrinsic base portion and (2) second wall portions of said concavity in contact with and in the vicinity of said edge of said oxide film are of said first conductivity type; forming an insulating film within said concavity to entirely cover said first and second wall portions; forming an intrinsic base portion of said second conductivity type in said center part of said surface section and along said cavity and in contact with said extrinsic base portion; and forming an emitter region of said first conductivity type within said intrinsic base portion such that said emitter region is in contact with said insulating film within said concavity at its side.

Claim 2

A method of manufacturing a bipolar transistor, said method comprising the sequential steps of; forming a covering layer on a surface of a semiconductor substrate, said substrate being of a first conductivity type; forming an aperture in said covering layer to expose a section of said surface of said substrate; forming a side wall layer made of material resistant to oxidation on a peripheral part of said section and on said covering layer within said aperture to expose a center part of said section; carrying out a heat treatment under oxidizing atmosphere to form an oxide film on said exposed center part of said section of said surface; removing said side wall layer to expose said peripheral part of said section of said surface; introducing impurities of a second conductivity type, opposite to said first conductivity type, into said peripheral part to form an extrinsic base portion of said second conductivity type contacting an edge of said oxide film; forming a concavity in said peripheral part of said surface section at a position adjacent said edge of said oxide film such that (1) first wall portions of said concavity, including the bottom of said concavity remote from said edge of said oxide film, are of said second conductivity type constituted by said extrinsic base portion and (2) second wall portions of said concavity in contact with and in the vicinity of said edge of said oxide film are of said first conductivity type; forming an insulating film within said concavity to entirely cover said first and second wall portions; forming an intrinsic base portion of said second conductivity type in said center part of said surface section and along said cavity and in contact with said extrinsic base portion; and forming an emitter region of said first conductivity type within said intrinsic base portion such that said emitter region is in contact with said insulating film within said concavity at its side.