UHV/CVD and related growth techniques for Si and other materials

This article discusses the growth of silicon and related materials using ultra-high vacuum chemical vapor deposition (UHV/CVD). This growth technique is well suited for deposition of strained epitaxial layers and also layers with metastable concentrations of impurities such as boron and carbon. In UHV/CVD, growth kinetics and the incorporation of various atoms other than silicon are determined by decomposition of the molecular reactants on the wafer surface. Growth rates, incorporation of dopants and alloy atoms, and various measures of the material quality are discussed. The common features shared with other CVD growth techniques are noted, and the differences are summarized. Description of UHV/CVD and Motivation Ultra-high vacuum chemical vapor deposition (UHV/CVD) has been used to describe a variety of growth techniques which have been used for epitaxial layer growth of silicon and related materials. The objectives of most researchers has been the growth of silicon and related materials such as GexSi1-x and GexSi1-x-yCy as uniformly strained epitaxial layers. One implementation that is of particular commercial interest is the multi-wafer UHV/CVD technique which was first reported [1] and later patented [2] by Meyerson. Notable characteristics of the multi-wafer UHV/CVD technique are the absence of both hydrodynamic boundary-layer effects and gas-phase chemical reactions. This is a consequence of the low total pressure during growth (near 10-3 Torr); at such low pressures the molecular mean free path is of the order of the chamber dimensions. Since collisions between molecules are infrequent gas phase reactions are unlikely. Also, a hydrodynamic boundary layer cannot form because transport is by molecular flow. As a result, the growth rate is determined by surface decomposition of the reactant molecules.