High-performance uniform stepper-based InP double-heterojunction bipolar transistor (DHBT) on a 3-inch InP substrate

In this paper, InP Double-Heterojunction Bipolar Transistors (DHBTs) on a 3-inch InP substrate is demonstrated through stepper-based photolithography. The performance of the fabricated InP DHBTs such as DC characteristics, high-frequency characteristics, and uniformity of the 3-inch wafer is investigated to verify the stepper-based fabrication process. To improve the high-frequency characteristics, the self-aligned base-emitter contact is realized by using the high height-to-width ratio and vertical sidewall emitter profile of the Au electroplating process. The fabricated DHBTs with W_E = 0.6 μm and L_E = 15 μm exhibits current gain (β) = 50 at V_CE = 1.0 V and an open-base common-emitter breakdown voltage (BV_CEO) of 5.7 V at J_C = 0.01 mA/µm² and 7.5 V at J_C = 0.1 mA/µm², respectively. Moreover, the fabricated DHBTs with W_E = 0.6 μm and L_E = 15 μm show excellent f_T of 244 GHz and f_max of 221 GHz at J_C = 4.4 mA/μm² and V_CE = 1.6 V. In order to evaluate the uniformity of the fabricated DHBTs, we measure current gain (β) and high-frequency characteristics with W_E = 0.6 μm and L_E = 15 μm and the average values and standard deviation of the β, f_T, and f_max are β = 49.3 ± 1.9, f_T = 241.4 ± 3.8 GHz, and f_max = 221.5 ± 4.0 GHz, respectively. Thanks to the optimized stepper-based fabrication process, the fabricated InP DHBTs exhibit well-balanced high-frequency characteristics and excellent uniformity.