A high-temperature anneal-resistant process, which enables high-speed SiGe HBTs to embed scaled CMOS, is optimized in SiGe BiCMOS technology. This process, called promoting emitter diffusion (PED), is based on enhanced phosphorous diffusion from poly-Si emitter electrodes at high temperature to fabricate thin base layers and shorten the base transit time. By investigating the dependence of high-frequency performance on diffusion temperature, as-grown base layer thickness, and Si cap thickness, the methodology for PED optimization was yielded. In addition, this PED process is effective in reducing an extrinsic base resistance due to deep boron diffusion from poly-Si base electrodes. This indicates that the PED process is very effective at improving the tradeoff relationship between cutoff frequency fT and maximum oscillation frequency fmax in self-aligned SiGe HBTs using selective epitaxial growth. As a consequence, both fT and fmax of more than 200 GHz were successfully obtained.
- Communication systems
- Diffusion processes
- Epitaxial growth
- Heterojunction bipolar transistors (HBTs)
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering