Semiconductor device

A method of fabricating a semiconductor device wherein a heterojunction bipolar transistor is fabricated by successively forming semiconductor layers comprising a subcollector layer, collector layer, base layer, emitter layer and emitter cap layer on one surface of a semiconductor substrate, said subcollector layer, collector layer, base layer, emitter layer and emitter cap layer are formed by etching a predetermined semiconductor layer of said semiconductor layers in a predetermined pattern, an emitter electrode is formed on said emitter layer, a base electrode is formed whereof an inner edge part overlaps the periphery of said emitter layer, a collector electrode is formed on said collector layer, and the base electrode is electrically connected to the base layer via an alloy layer by alloying the emitter layer under said base electrode, said method comprising the steps of:

• successively forming said semiconductor layers comprising the subcollector layer, collector layer, base layer, emitter layer and emitter cap layer on one surface of said semiconductor substrate,
• selectively forming a first electrode layer comprising the emitter electrode on the semiconductor layer which is the emitter cap layer,
• forming the emitter cap layer so that its periphery lies further inside than the edge of said emitter electrode by etching the semiconductor layer which is the emitter cap layer using said first electrode layer as an etching mask,
• forming an etching mask to cover the first electrode layer comprising said emitter cap layer and said emitter electrode, and then forming the emitter layer by etching the semiconductor layer which is the emitter layer,
• removing said etching mask, forming a photoresist mask on the whole of one surface of said semiconductor substrate, forming an electrode layer and lifting off unnecessary parts, forming the base electrode by said electrode layer extending from the periphery of said emitter layer across the semiconductor layer which is the base layer, and forming the emitter electrode by said first electrode layer and a second electrode layer comprising said electrode layer which exactly overlaps said first electrode layer, and
• forming an etching mask so that the outer edge of said base electrode is exposed and said emitter layer and emitter electrode are covered, and undercut etching the semiconductor layers which are the base layer and collector layer.

A method of fabricating a semiconductor device wherein a heterojunction bipolar transistor is fabricated by successively forming semiconductor layers comprising a subcollector layer, collector layer, base layer, emitter layer and emitter cap layer on one surface of a semiconductor substrate, said subcollector layer, collector layer, base layer, emitter layer and emitter cap layer are formed by etching a predetermined semiconductor layer of said semiconductor layers in a predetermined pattern, an emitter electrode is formed on said emitter layer, a base electrode is formed whereof an inner edge part overlaps the periphery of said emitter layer, a collector electrode is formed on said collector layer, and the base electrode is electrically connected to the base layer via an alloy layer by alloying the emitter layer under said base electrode, said method comprising the steps of:

• successively forming said semiconductor layers comprising the subcollector layer, collector layer, base layer, emitter layer and emitter cap layer on one surface of said semiconductor substrate,
• selectively forming a first electrode layer comprising the emitter electrode on the semiconductor layer which is the emitter cap layer,
• forming the emitter cap layer so that its periphery lies further inside than the edge of said emitter electrode by etching the semiconductor layer which is the emitter cap layer using said first electrode layer as an etching mask,
• forming an etching mask to cover the first electrode layer comprising said emitter cap layer and said emitter electrode, and then forming the emitter layer by etching the semiconductor layer which is said emitter layer,
• removing said etching mask, forming a photoresist mask of the whole of one surface of said semiconductor substrate, forming an electrode layer and lifting off unnecessary parts, forming the base electrode by said electrode layer extending from the periphery of said emitter layer across the semiconductor layer which is the base layer, and forming the emitter electrode by said first electrode layer and a second electrode layer comprising said electrode layer which exactly overlaps said first electrode layer, and
• forming an etching mask so that the outer edge of said base electrode is exposed and said emitter layer and emitter electrode are covered, and undercut etching so that the edges of said base layer and collector layer are situated further inside than the edge of said emitter layer to prevent said base electrode and said base layer from coming in direct contact.