High performance 110 nm InGaAs/InP DHBTs in dry-etched in-situ refractory emitter contact technology
We report a 110 nm InP/In<inf>0.53</inf>Ga<inf>0.47</inf>As/InP double heterojunction bipolar transistor (DHBT) demonstrating a simultaneous f<inf>t</inf>/f<inf>max</inf> of 465/660 GHz and operating at power densities in excess of 50 mW/µm<sup>2</sup>. To our knowledge this is the smallest junction width reported for a III–V DHBT. The narrow 110 nm emitter junction permits the devices to be biased simultaneously at high voltages and high current densities (J<inf>e</inf>) with peak RF performance at 41 mW/µm<sup>2</sup> (J<inf>e</inf> = 23.6 mA/µm<sup>2</sup>, V<inf>ce</inf> = 1.75 V). Devices incorporate low contact resistance, refractory, in-situ Mo emitter contact to a highly doped, regrown InGaAs cap. A low stress, sputter deposited, refractory, dry-etched W/Ti<inf>0.1</inf>W<inf>0.9</inf> emitter metal process was developed demonstrating both high emitter yield and scalability to sub-100 nm junctions. Previously reported dry etch processes involving Ti/Ti<inf>0.1</inf>W<inf>0.9</inf> metals could not be scaled below 180 nm junction widths due to high metal stress resulting in very low emitter yield [1, 2]. The emitter metal contacts reported here are 100 nm wide and the emitter-base junction width is 110 nm. On-wafer Through-Reflect-Line (TRL) calibration structures were used to measure the RF performance of devices from 140 – 180 GHz.