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

The influence of the silane (SiH4) pressure on the dopant incorporation dur ing LPCVD silicon deposition at 550 degrees C using silane and phosphine (P H3) or diborane (B2H6) is examined, for a range of pressure from 1 to 100 P a. We conclude that different deposition and dopant incorporation mechanism s occur according to the deposition pressure. It is shown that, under low-p ressure 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 presen ce of silylene promotes the formation of monosilylphosphine and monosilylbo rane 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 wit h phosphine and an increase with diborane, is a function of the silane pres sure; 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.