TABLE OF CONTENTS In this section, we discuss the different approaches that have been used for surface preparation for low temperature epitaxy and the conditions that must be satisfied for pseudomorphic growth. The important requirements for high-quality epitaxial growth include: an atomically clean substrate surface, contamination free (ultrahigh vacuum or inert) environment, source purity, a source-substrate geometry that allows uniform deposition, uniform substrate temperature, absence of particulate and undesired impurity atoms, compatibility with analytical tools to allow in situ monitoring of growth quality and control of layer composition and thickness.
Perhaps the single most important issue in silicon-based epitaxy is wafer preparation and in situ cleaning prior to epitaxial growth. Epitaxial layer growth is degraded by submonolayer surface coverage of oxygen and carbon. Poor surface cleaning results in defects at the epitaxial interface that are independent of the lattice mismatch between Si and the grown film. Improper surface preparation prior to epitaxial growth and/or particulates from the reactor determine the number of threading dislocations in an as-deposited film. To prevent reoxidation or contamination of the cleaned surface, at least the final stages of the cleaning process are preferably done in situ under UHV conditions. Because a native oxide forms on Si shortly after exposure to oxygen, even at room temperature, in situ cleaning prior to epitaxial growth is needed.
In general, the requirements for cleaning elemental group-IV substrates are more stringent than those for cleaning III-V compound semiconductor substrates. Conventional Si substrate cleaning techniques fall into...
