| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for controlling an interval between an emitter mesa and a base ohmic metal of a heterojunction bipolar transistor, in order to obtain high gain and low parasitic base resistance. SOLUTION: An emitter, a base 24 and a collector layer 22 are epitaxial- grown on a base body 20, and a sacrificial layer of dielectric film is made to stick on the emitter layer. After an emitter mesa is patterned using a lithography technique, the sacrifice layer is etched to form an undercut. Then the emitter layer is etched, and the first photoresist layer, used for patterning the emitter mesa, and the entire device are coated with a lift-off resist 46, and it is lastly patterned, so as to form reentrant inclination on a base layer 24. An ohmic metal 48 for base is made to stick on the resist 46, and both the second resist layer and the resist on the emitter mesa are dissolved and lifted-off. The sacrificial layer is peeled off by isotropic etching, and base metal around the emitter mesa is left at an interval decided by undercut of the layer.
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