Formation of ultra-shallow base with high boron-doping concentration for high-performance SiGe HBTs

High-concentration in-situ boron-doping technique has been successfully developed to fabricate an ultra-shallow base layer of SiGe HBTs. Extremely high-concentration doping with abrupt profiles in the Si/SiGe layers can be achieved without high-temperature activation annealing, and good crystallinity of the grown layer has been obtained. Too high boron-doping has an impact on the crystallinity and on Ge content of boron-doped SiGe layers. High-resolution X-ray diffraction indicated that good crystallinity was achieved at B2H6 flow rate of below 0.25 sccm. By optimizing epitaxial growth conditions, an extremely high-concentration of boron-doping was achieved, and the resultant good crystallinity of the boron-doped SiGe layer gave a very high carrier concentration of 5 × 1020 cm−3. Accordingly, the high-concentration in-situ boron-doping combined with our continuous epitaxial growth technique is a powerful technique to fabricate future ultra-high-speed and low-power SiGe HBTs.