Epitaxial-base transistors with ultrahigh vacuum chemical vapor deposition (UHV/CVD) epitaxy: enhanced profile control for greater flexibility in device design

Abstract

A discussion is presented of the fabrication of small-geometry (1.0 mu m*20 mu m) epitaxial-base n-p-n bipolar transistors with high-doped bases of less than 100-nm width and base sheet-resistances of approximately 8 k Omega per square. An ultrahigh-vacuum chemical vapor deposition (UHV/CVD) 550 degrees C epitaxy process was used. The impurity profiles are found to be much more uniform than possible with other techniques so that intrinsic base sheet resistance and base width are largely decoupled. This allows fabrication of narrow-base bipolar devices with little temperature dependence of the I-V characteristics for operation below room temperature. The better control over thickness, combined with high doping levels, improves the flexibility in device design. >