Patent ID: 7001820

Claim:
A method for fabricating a heterojunction bipolar transistor, comprising the steps of: successively forming, on the principal surface of a semi-insulating substrate, a heavily-doped n-type first subcollector layer, a heavily-doped n-type second subcollector layer made of a material having a smaller band gap than the first subcollector layer, an i-type or a lightly-doped n-type collector-layer-forming film, a heavily-doped p-type base-layer-forming film, an n-type emitter-layer-forming film made of a material having a larger band gap than the base-layer-forming film, a heavily-doped n-type emitter-cap-layer-forming film, and a heavily-doped n-type emitter-contact-layer-forming film made of a material having a smaller band gap than the emitter-cap-layer-forming film; patterning the emitter-contact-layer-forming film and the emitter-cap-layer-forming film to expose a base electrode formation region of the emitter-layer-forming film, thereby forming an emitter contact layer and an emitter cap layer; patterning the emitter-layer-forming film, the base-layer-forming film and the collector-layer-forming film to expose a collector electrode formation region of the second subcollector layer, thereby forming an emitter layer, a base layer and a collector layer; forming an emitter electrode made of one or a plurality of conductive layers on an emitter electrode formation region of the emitter contact layer; forming a base electrode made of one or a plurality of conductive layers on the base electrode formation region of the emitter layer; forming a collector electrode made of one or a plurality of conductive layers on the collector electrode formation region of the second subcollector layer; and forming, by heat treatment, a first alloying reaction layer, a second alloying reaction layer and a third alloying reaction layer in a part of the emitter contact layer located under the emitter electrode, a part of the emitter layer located under the base electrode and a part of the second subcollector layer located under the collector electrode, respectively.