TABLE OF CONTENTS In this section, we discuss the present understanding of the surface chemistry of common reactant gases used in low temperature epitaxial growth using the chemical vapor deposition method which is a commercial technique in Si and group-IV alloy technology. The deposition chemistry is simple in solid source MBE since a chemical reaction does not take place. However, complex surface reactions and gas chemistry are involved in both CVD based and gas-source MBE processes. In CVD, however, the growth rate strongly decreases with temperature. A high temperature is required for the precursor gases to decompose, while a low temperature is necessary to prevent dislocation formation and islanding during the growth.
Although most of the early work on SiGe alloy films was carried out by MBE, CVD is more acceptable in production and thus there has been considerable work on the development of CVD processes for group-IV alloy films. An extremely broad range of deposition conditions and reactor designs has been employed. For high temperature (above 1000 C) and at atmospheric pressure, the deposition/growth rate is determined mainly by mass transport through the gas phase, a process which is not very sensitive to temperature. At lower temperatures ( ? 750 1000 C) and pressures (0.001 0.1 Torr), the chemical reaction becomes slower and the transport properties of the species in the gas phase change and become a function of complicated diffusion phenomena and chemical reaction rates. In the lower pressure range (mTorr range) the process can become more complicated. A...
