Bismuth trichloride as a molecular precursor for silicon doping

Abstract

Dopant impurity species can be incorporated into the silicon (001) surface via the adsorption and dissociation of simple precursor molecules. Examples include phosphine (PH3), arsine (AsH3), and diborane (B2H6) for the incorporation of phosphorus, arsenic, and boron, respectively. Through exploitation of precursor surface chemistry, the spatial locations of these incorporated dopants can be controlled at the atomic scale via the patterning of a hydrogen lithographic resist layer using scanning tunneling microscopy (STM). There is strong interest in the spatial control of bismuth atoms incorporated into silicon for quantum technological applications; however, there is currently no known precursor for the incorporation of bismuth that is compatible with this STM-based lithographic method. Here, we explore the precursor chemistry (adsorption, diffusion, and dissociation) of bismuth trichloride (BiCl3) on Si(001). We show atomic-resolution STM images of BiCl3 exposed Si(001) surfaces at low coverage and combine this with density functional theory calculations to produce a model of the surface processes and the observed features. Our results show that, at room temperature, BiCl3 completely dissociates to produce bismuth ad-atoms, ad-dimers, and surface-bound chlorine, and we explain how BiCl3 is a strong candidate for a bismuth precursor compound compatible with lithographic patterning at the sub-nanometer scale.

Adsorption and Thermal Decomposition of Triphenyl Bismuth on Silicon (001)

“…We also find two types of large and bright protrusion features, as shown in Figure i,j. These are consistent with surface bismuth ad-dimers. , Bismuth ad-dimers on the Si(001) surface have been reported after exposing a clean Si(001) surface to the evaporated elemental bismuth, and also after exposing a clean Si(001) surface to molecular bismuth chloride (BiCl 3 ) . In both cases, bismuth ad-atoms form on the surface and rapidly diffuse at room temperature until two bismuth ad-atoms meet and pair up to form a bismuth ad-dimer.…”

“… 29 , 30 Bismuth ad-dimers on the Si(001) surface have been reported after exposing a clean Si(001) surface to the evaporated elemental bismuth, and also after exposing a clean Si(001) surface to molecular bismuth chloride (BiCl 3 ). 13 In both cases, bismuth ad-atoms form on the surface and rapidly diffuse at room temperature until two bismuth ad-atoms meet and pair up to form a bismuth ad-dimer. The barriers for bismuth diffusion and the pairing of two bismuth ad-atoms to form an ad-dimer have been shown by previous DFT calculations to be less than 0.44 eV, and these processes, therefore, occur rapidly at room temperature.…”

“…The barriers for bismuth diffusion and the pairing of two bismuth ad-atoms to form an ad-dimer have been shown by previous DFT calculations to be less than 0.44 eV, and these processes, therefore, occur rapidly at room temperature. 13 , 31 The bismuth ad-dimers are thermally stable at room temperature and do not diffuse on the time scale of a typical STM experiment. The two bismuth ad-dimers shown in Figure 1 i,j correspond to configurations where the ad-dimers are on top of the dimer row and aligned parallel ( Figure 1 i) and perpendicular ( Figure 1 j) to the dimer rows.…”

“…24 The LANL2DZ basis set was chosen for its balance of computational efficiency and accuracy, suitable for our aim of exploring a range of possible adsorption structures. Larger basis sets or additional refinements such as zero-point energy corrections (such as those we have employed when studying a smaller bismuth compound on Si(001) 13 ) while potentially providing more precise results, would significantly increase the computational cost and time. In the context of this study, where our aim was to explore a broad range of possible adsorption structures rather than definitively assign structures to experimental observations, we deemed the use of the LANL2DZ basis set to be a suitable and pragmatic approach.…”

“…10−12 In this article, we explore the potential of using the adsorption and thermal transformation of triphenyl bismuth [Bi(C 6 H 5 ) 3 , or TPB] on the silicon (001) surface to control the introduction of bismuth into silicon crystals. TPB is a carbon-based bismuth precursor and as such this work is complementary to our recent investigation of the chlorinebased bismuth precursor, bismuth trichloride (BiCl 3 ), 13 and other recent efforts to evaluate carbon-based precursors for aluminum (trimethyl aluminum and triethyl aluminum). 14 Using atomic-resolution scanning tunneling microscopy (STM), synchrotron-based X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, we show that TPB adsorption at room temperature leads to molecular adsorption via Si−Bi and Si−C bonding, and dissociative adsorption involving the cleaving of a bismuth− phenyl bond.…”