Microwave HBT fabrication by using a self-aligned technology with a perpendicular side-wall

A HBT self-aligned technology with a perpendicular side-wall mesa has been adopted in microwave HBT fabrication by virtue of a high selectivity chemical wet etchant. Principal features and technological processes of the method are discussed. The gap of ∼0.1μm between the emitter mesa edge and base contact metallization edge has been formed repeatedly by the method. The experimental results of the developed microwave HBT for test purpose is given.