Structural characterization of a UHV/CVD-grown SiGe HBT with graded base

SiGe/Si base heterostructure bipolar transistors (HBTs) were structurally characterized using a variety of techniques. The SiGe base regions were linearly graded with various peak Ge concentrations and boron doping levels, and were grown with a production-ready, ultrahigh vacuum chemical vapor deposition system. The peak Ge composition was determined using photoluminescence (PL), high-resolution X-ray diffraction, and Auger electron spectroscopy (AES). Boron doping levels were measured by secondary ion mass spectroscopy (SIMS), field-emission scanning electron microscopy, and four-point probe (4-pp). PL was found to be especially useful for determining the peak Ge concentration, while AES was used to verify the linearity of the grade. A comparison of SIMS and 4-pp data on several HBT structures indicates that all of the boron dopant atoms are electrically active within the range 7 x 10(18)-2.2 x 10(19) cm(-3). (C) 1998 Elsevier Science S.A. All rights reserved.