Patent ID: 6287929
Filing Date: 2001-09-11
Classification: H01L

Abstract:
A method of forming a bipolar transistor, comprising the steps of:selectively etching laminations of a base polysilicon film and an insulation film overlying said base polysilicon film to form an opening on an intrinsic base region, wherein said laminations extends on a first silicon oxide film which further extends on an epitaxial layer, so that an upper surface of said first silicon oxide film is shown on said intrinsic base region;carrying out a first ion-implantation of first impurity ions into said epitaxial layer on said intrinsic base region and under said opening to selectively form a collector in said epitaxial layer;carrying out an isotropic etching to said first silicon oxide film to selectively remove said first silicon oxide film under said opening and also under adjacent portions of said laminations to said opening, thereby forming a gap under said adjacent portions of said laminations;entirely forming a dummy polysilicon film which extends over said laminations and on said side walls and a bottom of said opening as well as extends to fill said gap, so that said dummy polysilicon film has a gap-filling part in said gap;carrying out a heat treatment to oxidize said dummy polysilicon film except for said gap-filling parts, so that said dummy polysilicon film is made into a dummy silicon oxide film except for said gap-filling part;removing said dummy silicon oxide film to leave said gap-filling part in said gap;carrying out a second ion-implantation of second impurity ions through said opening to form a base region under said opening and also over said collector;selectively forming an emitter polysilicon film having an impurity within and over said opening so that a bottom of said emitter polysilicon film is made into contact with a top surface of said base region; andcarrying out a heat treatment to cause a thermal diffusion of said impurity in said emitter polysilicon film to an upper region of said base region so as to form an emitter in said upper region of said base region.