AlInAs/InGaAs based heterojunction bipolar transistors fabricated by electron cyclotron resonance etch

A dry etch fabrication technology for high-speed AlInAs/InGaAs heterojunction bipolar transistors (HBTs) utilizing low-damage electron cyclotron resonance (ECR) CH4/H2/Ar plasma etching is detailed. Small-area (2×4 to 3×9 μm2 ) devices demonstrated current gains up to 160, unity gain cutoff frequency ( fT) of 57 GHz and a maximum oscillation frequency ( fmax) of 35 GHz. The dry etch process uses triple self-alignment of the emitter and base metals and the base mesa, minimizing the base-collector capacitance (CBC). These results represent the first report of a truly scalable process for In-based HBTs and demonstrate the ability of ECR plasma etching to provide smooth, degradation-free etching of III–V semiconductors.