A selective-epitaxial-growth SiGe-base HBT with SMI electrodes featuring 9.3-ps ECL-gate delay

An ultra-high-speed selective-epitaxial-growth SiGe-base heterojunction bipolar transistor (HBT) with self-aligned stacked metal/in-situ doped poly-Si (IDP) (referred to as SMI) electrodes is developed. A 0.5-μm-wide SiGe base self-aligned to the 0.1-μm-wide emitter was selectively grown by using a UHV/CVD system. This self-aligned structure effectively reduces collector capacitance. In SMI technology, a tungsten film is selectively stacked on all poly-Si electrodes (base, emitter, and collector) in a self-aligned manner by using selective deposition without any heat treatment. So this technology does not cause unwanted diffusion of the base dopants and keeps a shallow intrinsic base profile. SMI technology can therefore provide low parasitic resistances and is well-suited to an SiGe-base HBT. A 2-μm-wide BPSG/SiO₂ refilled trench was introduced in order to reduce the substrate capacitance. The low dielectric constant of BPSG/SiO₂ and the wide trench are very effective in reducing the sidewall element of substrate capacitance. This technology makes it possible to obtain ultra-high-speed operation with a 9.3-ps-gate-delay emitter-coupled-logic (ECL) circuit.