Image Number 7 for United States Patent #6924201.
A heterojunction bipolar transistor of the present invention is produced from a wafer including a substrate and a collector layer of a first conductivity type, a base layer of a second conductivity type and an emitter layer of the first conductivity type sequentially laminated on the substrate in this order. First, the wafer is etched up to a preselected depth of the collector layer via a first photoresist, which is formed at a preselected position on the emitter layer, serving as a mask. Subsequently, the collector layer etched with at least the sidewalls of the base layer and collector layer, which are exposed by the first etching step, and a second photoresist covering part of the surface of the collector layer contiguous with the sidewalls serving as a mask.
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