Selective and non-selective growth of self-aligned SiGe HBT structures by LPCVD epitaxy

Abstract

Silicon-germanium (SiGe) heterojunction bipolar transistors (HBT) have become increasingly important for high speed applications. Novel device structures are often required to fully exploit the advantages from incorporation of a heterojunction. In this work, a growth technique is described which uses both selective and non-selective growth of Si and SiGe to produce an advanced SiGe HBT structure. The surface morphology of the material grown is examined using Nomarski contrast optical microscopy and scanning electron microscopy (SEM), and the surface of the epitaxial areas appears smooth with a low defect density. The growth surface is reasonably planar, as needed for further device processing, which suggests the required thicknesses of both selective and non-selective epitaxy were achieved. The Ge and B profiles of the material are measured using secondary ion mass spectroscopy (SIMS), and the layer thicknesses are found to meet the device specification. The crystallinity and defects in the material are examined by transmission electron microscopy (TEM). The material produced is shown to be suitable for fabrication into the proposed device.