HCl-free selective epitaxial Si-Ge growth by LPCVD for high-frequency HBTs

Low-temperature HCl-free selective silicon germanium epitaxial growth using low-pressure chemical vapor deposition was developed. By utilizing the incubation period of the poly-SiGe growth on SiO₂, sufficient selectivity was obtained without the use of HCl gas. The advantages of this HCl-free process are sufficient growth rate at low temperature (660°C) and capability of high-concentration boron doping without surface roughening. The thickness uniformity of the selectively grown layers throughout a wafer was good and the local loading effect did not appear. These results show the process can be used for fabricating heterojunction bipolar transistors (HBTs). The HBTs fabricated using the process have excellent yields and high-frequency characteristics, that is, 80-GHz cutoff frequency and 160-GHz maximum oscillation frequency. These characteristics and good uniformity of cutoff frequency throughout a wafer show that developed selective growth process can be applied to production of SiGe HBTs.