| We have used rapid thermal chemical vapor deposition along with a zero thermal budget transistor process to demonstrate the first Si/Si1-x-y GexCy/Si heterojunction bipolar transistors (HBT) and to investigate the influence of carbon incorporation on the electrical characteristics of Si1-xGex HBTs. We have used the temperature dependence of transistor collector saturation currents to measure a difference in bandgap between Si1-x-yGexCy and Si1-xGe x of +26 meV/%C for carbon fractions less than 1%.We have used Si1-x-yGexCy base HBTs to discover that high carbon concentrations have a profound influence on boron diffusion in Si1-x-yGexCy alloys. Using the electrical characteristics of these transistors, we demonstrate that thermal diffusion of boron is reduced in Si1-x-yGexCy alloys. As measured both electrically and by SIMS, boron transient enhanced diffusion caused by an arsenic emitter implant and activation anneal is suppressed in Si1-x-yGexCy alloys. However, we show that for these discoveries to useful in HBT applications, the doped Si 1-x-yGexCy base layers must be separated from the transistor depletion regions by doped, carbon-free Si1-xGex spacer layers. These results are explained qualitatively. This discovery of the positive effects of carbon incorporation on boron diffusion may enable Si1-xGe x HBTs to be more easily integrated with mainstream silicon technology. |
