A Robust All-Wet-Etching Process for Mesa Formation of InGaAs–InP HBT Featuring High Uniformity and High Reproducibility

Abstract

A simple InP-based heterojunction bipolar transistors (HBT) fabrication process featuring high uniformity and high reproducibility is introduced. No dry etching method was utilized for triple-mesa formation to avoid plasma damage to the device surface. An all-wet etching method was specially developed. This process is relatively simple compared to the conventional HBT fabrication process with respect to the emitter mesa formation by one-step selective etching. Uniformity of the current gain over a 3-in diameter wafer was approximately 2.9%, and the variation of the current gain of 17 wafers was 2.9 (max.-min.). The current gain cutoff frequency and the maximum oscillation frequency were 145 and 174 GHz, respectively. The mean time to failure was over 5 /spl times/ 10/sup 6/ h at 150/spl deg/ C whose criterion was over 3% changes in the current gain. This process is suitable for mass production of ultrahigh speed ICs in high yield.