Narrow BF/sub 2/ implanted bases for 35 GHz/24 ps high-speed Si bipolar technology

Abstract

The authors report on a high-speed Si bipolar self-aligned technology featuring deep trench isolation for low capacitances, a production-compatible 15-keV BF/sub 2/ base implantation for high cutoff frequency, and an advanced composite material spacer formation process which avoids any etch removal of the base profile allowing for perfect control of the base charge. This process results in extremely reproducible device characteristics. The authors fabricated transistors with measured cutoff frequencies in excess of 35 GHz and realized CML ring oscillators which achieved a minimum delay time of 24 ps/gate. To check for degradation effects arising from residues of fluorine due to BF/sub 2/ implantation they processed reference transistors with B bases implanted at effectively identical energies as the BF/sub 2/ devices. With respect to base/emitter breakdown characteristics, no significant difference between the two sets of samples was observed. Thus, it is concluded that a 15 keV BF/sub 2/ implantation for narrow base formation is a viable approach for realizing bipolar devices for high-speed ICs.<>