SiGe-base, poly-emitter heterojunction bipolar transistors

Si and graded-SiGe-base bipolar transistors with extremely narrow base-widths (50-75 nm) and low base-sheet resistances have been successfully fabricated in a poly-emitter bipolar process. Ideal junction characteristics were obtained for both Si and SiGe-base devices. The SiGe-base transistors have collector currents which are 10 times higher than those of Si-base devices having the same pinched base resistance. The SiGe-base transistors also show improved low-temperature behavior, with extremely high current gains (1600) being obtained at LN2 temperature for devices having low base sheet resistance (7.5 kΩ/□). These results clearly demonstrate some of the advantages that SiGe heterojunction bipolar transistors offer for future bipolar technologies, and that excellent junction quality be obtained with these devices in a poly-emitter process.