ULTRAHIGH-VACUUM RAPID THERMAL CHEMICAL-VAPOR-DEPOSITION OF EPITAXIALSILICON ON (100)SILICON .2. CARBON INCORPORATION INTO LAYERS AND AT INTERFACES OF MULTILAYER STRUCTURES

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 ca rbon contamination as a function of deposition temperature, film growt h rate, and partial pressure of hydrocarbons. The results show that at higher deposition temperatures (750 and 800 degrees C) carbon levels in epitaxial layers are lower compared to levels in layers grown at lo wer temperatures (650 and 700 degrees C). It is proposed that at highe r temperatures, the carbon concentration in Si is determined by the ad sorption-desorption equilibrium and this results in a growth rate inde pendent incorporation process. At lower temperatures, carbon incorpora tion is limited by the availability of sites for chemisorption. Site a vailability is determined by hydrogen coverage on Si during growth, an d this produces a growth rate dependent incorporation process. Hydroca rbon 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 i nterfaces of multilayer structures was found to depend strongly on the growth temperature. Higher interfacial carbon levels were obtained fo llowing growth at higher temperatures when temperature cycling was use d to start and stop the growth processes. When gas switching was used for this purpose, interfacial carbon contamination was observed at low er temperatures (650 and 700 degrees C). This is tentatively attribute d to loss of hydrogen coverage when Si2H6 is evacuated from the chambe r for gas switching and inefficient desorption of physisorbed species from the surface at lower temperatures.