Optimized processing for differentially molecular beam epitaxy-grown SiGe(C) devices

Abstract

Nanoimpurities at a silicon surface are able to disturb the structural and electrical properties of epitaxially grown films. A sophisticated ex situ cleaning procedure should remove most of these contaminants. X-Ray photoelectron spectroscopy as well as minority carrier recombination and generation lifetime measurements show the necessity of a careful modification of the wet chemical cleaning in relation to annealing prior to epitaxial growth of transistor relevant structures. H-passivated Si surface is preferred to reaction chemical agents cleaning, because of the weaker in situ thermal treatment. The allowed contact time to air as well as ultra high vacuum (UHV) conditions are discussed. To evaluate the quality of SiGe molecular beam epitaxy (MBE) layers using optimized wafer processing, we grew heterobipolar transistor (HBT) structures on topological surfaces. The obtained output characteristics (Gummel plot, Early voltage, high-frequency behavior) and yields are compatible with our in-house chemical vapor deposition HBTs. We introduced carbon into the SiGe epitaxy to weaken the film sensitivity against boron outdiffusion of the film in post-growth thermal processes to stabilize (weaken process margins) the HBT production. Improvement of HBTs with SiGe(C) base fabricated in a standard bipolar is demonstrated. The additional introduction of carbon into an HBT by MBE advances the transistor parameters without creating memory effects in the chamber.