In situ doping of silicon deposited by LPCVD:: pressure influence on dopant incorporation mechanisms

The influence of the silane (SiH4) pressure on the dopant incorporation during LPCVD silicon deposition at 550 degrees C using silane and phosphine (PH3) or diborane (B2H6) is examined, for a range of pressure from 1 to 100 Pa. We conclude that different deposition and dopant incorporation mechanisms occur according to the deposition pressure. It is shown that, under low-pressure conditions, silane remains the preponderant host species, while it is silylene (SiH2) at high pressure. At low pressure, SiH4 and PH3 or B2H6 are separately but not independently adsorbed. At high pressure, the presence of silylene promotes the formation of monosilylphosphine and monosilylborane which are found to be the adsorbed dopant species. The usual change of the growth rate caused by the addition of the dopant, i.e. a reduction with phosphine and an increase with diborane, is a function of the silane pressure; the dopant content of the solid films causes a significant variation of the growth rate only when it is superior to a threshold of about 10(19) cm(-3) in both cases.