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

Abstract

The influence of the silane (SiH 4 ) pressure on the dopant incorporation during LPCVD silicon deposition at 550 • C using silane and phosphine (PH 3 ) or diborane (B 2 H 6 ) 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 (SiH 2 ) at high pressure. At low pressure, SiH 4 and PH 3 or B 2 H 6 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.

Effect of diborane on the microstructure of boron-doped silicon nanowires

“…In particular, for LPCVD growth of Si at 550 1C, the growth rate enhancement with B 2 H 6 became significant when the boron concentration in the film exceeded a threshold of about 10 19 cm À3 [12], which is similar to the boron levels measured in the highly doped SiNWs. A reduction in the activation energy for Si thin-film deposition was also observed with B 2 H 6 addition.…”

“…The addition of B 2 H 6 has previously been reported to result in an increased growth rate of Si thin films grown by CVD [9], plasma-enhanced CVD (PECVD) [7,8] and low-pressure CVD (LPCVD) [10][11][12] using SiH 4 as the Si source. In particular, for LPCVD growth of Si at 550 1C, the growth rate enhancement with B 2 H 6 became significant when the boron concentration in the film exceeded a threshold of about 10 19 cm À3 [12], which is similar to the boron levels measured in the highly doped SiNWs.…”

“…A growth-rate enhancement is observed frequently when B 2 H 6 is used as a dopant in Si thin-film chemical vapor deposition (CVD) [9][10][11][12]. Intentional doping of SiNWs, however, is fundamentally different from CVD since the growth is via a vapor-liquid-solid (VLS) mechanism.…”

Silicon nanowire-based solar cells

“…The addition of a dopant gas to silane is known to induce some variations of the growth rate of silicon (e.g. [12]) and for nanowire growth changes in morphology and structure have been observed [13,14]. absorption of a 375 μm thick Si wafer.…”

Peculiarities of axial and radial Ge–Si heterojunction formation in nanowires: Monte Carlo simulation

“…In [26], radial shell growth was "turned on" by the addition of diborane, which serves to lower the decomposition temperature of silane. Based on experimental work [30] where diboran introduction in the growth chamber results in an increase in the polysilicon film growth rate, diboran was believed to enhance the precursor dissociation rate [26]. However, impurity (boron) could also change Si solubility in the catalyst drop or change the Si surface diffusion length.…”