Self-aligned selective-epitaxial-growth SiGe HBTs: Process, device, and ICs

We review the fabrication and device technologies of a high-speed self-aligned selective-epitaxial-growth (SEG) SiGe-base heterojunction bipolar transistor (HBT), and its potential application in ICs for optical-fiber-link systems. A 0.54-μm-wide SiGe base, self-aligned to the 0.14-μm-wide emitter to reduce collector capacitance, was selectively grown by using a UHV/CVD system. A self-aligned stacked metal/in situ doped poly-Si electrode technology enables low parasitic resistance, and allows the intrinsic base profile to be kept shallow, so it is well-suited to a SiGe-base HBT. A 2-μm-wide insulator refilled trench was introduced to reduce substrate capacitance. This SiGe HBT makes it possible to obtain 95-GHz cutoff frequencies and 97-GHz maximum oscillation frequencies, and ultra-high-speed emitter-coupled-logic (ECL) circuits with an 8-ps gate delay. The technology was applied in ICs required for optical-fiber-link systems, including a 1/8 static frequency divider with a maximum operating frequency of up to 50 GHz, a time-division multiplexer and a demultiplexer operating at 40 Gb/s, a preamplifier with a bandwidth of 35 GHz, an AGC amplifier core with a bandwidth of 32 GHz, and a decision circuit operating at 40 Gb/s.