Method of manufacturing bipolar transistor with reduced numbers of steps without increasing collector resistance

A method of manufacturing a semiconductor device having a collector of one conductivity type, a base of an opposite conductivity type, and an emitter of the one conductivity type which are formed on a semiconductor substrate, comprising the steps of:

• doping an impurity of the one conductivity type in a major surface portion of said semiconductor substrate to form a buried layer of the one conductivity type and growing an epitaxial layer on an entire surface on a major surface of said semiconductor substrate;
• forming a diffusion region of the opposite conductivity type in an emitter formation region on the major surface of said semiconductor substrate and forming a base connecting region in a base formation region in contact with said diffusion region of the opposite conductivity type;
• forming an insulating interlayer on the major surface of said semiconductor substrate including said diffusion region of the opposite conductivity type and said base connecting region;
• forming an emitter electrode contact hole reaching said diffusion region of the opposite conductivity type in an emitter formation region in said insulating interlayer and forming a collector region hole reaching said epitaxial layer in a collector formation region in said insulating interlayer;
• depositing a polysilicon film on said insulating interlayer and in said emitter electrode contact hole and said collector region hole;
• forming a patterning mask on said polysilicon film in said emitter formation region and part of said collector formation region, patterning said patterning mask to leave portions of said polysilicon film serving as an emitter electrode layer and part of a collector electrode layer in said collector formation region, and, at the same time, removing said epitaxial layer in said collector formation region by etching to form a collector groove;
• and
• doping an impurity of the one conductivity type in said emitter electrode layer and then diffusing the impurity of the one conductivity type to a major surface portion of said diffusion region of the opposite conductivity type to form an emitter region, and doping an impurity of the one conductivity type in at least a bottom surface portion of said collector groove and then diffusing the impurity of the one conductivity to said epitaxial layer to form a collector diffusion region.