Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon on (100) Silicon: II . Carbon Incorporation info Layers and at Interfaces of Multilayer Structures

Abstract

In this study, we have investigated carbon incorporation in epitaxial Si layers and at interfaces of multilayer epitaxial structures due to desorption of hydrocarbons from chamber walls at elevated temperatures. The experiments were conducted in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV‐RTCVD) reactor. We have investigated carbon contamination as a function of deposition temperature, film growth rate, and partial pressure of hydrocarbons. The results show that at higher deposition temperatures (750 and 800°C) carbon levels in epitaxial layers are lower compared to levels in layers grown at lower temperatures (650 and 700°C). It is proposed that at higher temperatures, the carbon concentration in Si is determined by the adsorption‐desorption equilibrium and this results in a growth rate independent incorporation process. At lower temperatures, carbon incorporation is limited by the availability of sites for chemisorption. Site availability is determined by hydrogen coverage on Si during growth, and this produces a growth rate dependent incorporation process. Hydrocarbon desorption from the chamber walls increases with increasing hold time at elevated temperatures, resulting in a time dependent increase in the carbon level within epitaxial layers. Carbon contamination at interfaces of multilayer structures was found to depend strongly on the growth temperature. Higher interfacial carbon levels were obtained following growth at higher temperatures when temperature cycling was used to start and stop the growth processes. When gas switching was used for this purpose, interfacial carbon contamination was observed at lower temperatures (650 and 700°C). This is tentatively attributed to loss of hydrogen coverage when is evacuated from the chamber for gas switching and inefficient desorption of physisorbed species from the surface at lower temperatures.