STRUCTURAL CHARACTERIZATION OF A UHV CVD-GROWN SIGE HBT WITH GRADED BASE/

SiGe/Si base heterostructure bipolar transistors (HBTs) were structura lly characterized using a variety of techniques. The SiGe base regions were linearly graded with various peak Ge concentrations and boron do ping levels, and were grown with a production-ready, ultrahigh vacuum chemical vapor deposition system. The peak Ge composition was determin ed using photoluminescence (PL), high-resolution X-ray diffraction, an d Auger electron spectroscopy (AES). Boron doping levels were measured by secondary ion mass spectroscopy (SIMS), field-emission scanning el ectron microscopy, and four-point probe (4-pp). PL was found to be esp ecially useful for determining the peak Ge concentration, while AES wa s 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 do pant atoms are electrically active within the range 7 x 10(18)-2.2 x 1 0(19) cm(-3). (C) 1998 Elsevier Science S.A. All rights reserved.