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PBr3 Adsorption and Dissociation on the Si(100) Surface

Vladimir M. Shevlyuga, Yulia A. Vorontsova, Tatiana V. Pavlova

TL;DR

This paper investigates PBr3 as a phosphorus precursor for halogen-mask–assisted near-atomic doping of Si(100). The authors combine STM experiments in UHV at room temperature with DFT/NEB calculations to study adsorption, fragmentation, and dissociation barriers on the Si(100)-2×1 surface, reporting that PBr3 largely dissociates to P and Br on three neighboring dimers and that the most stable fragment (p-1) matches observed STM features with Br atop Si and P in end-bridge positions; dissociation barriers reach up to $0.78$ eV, enabling room-temperature dissociation on experimentally relevant timescales (roughly $10$ s) via at least one low-energy pathway with $0.39$ eV. Annealing the PBr3-covered surface to 400°C triggers phosphorus incorporation evidenced by Si ejection and island formation, with residual Br on the surface. The results support using PBr3 with a halogen mask as a practical alternative to phosphine for controlled phosphorus incorporation into Si, offering a route to near-atomic precision doping.

Abstract

The adsorption of PBr3 on the Si(100)-2$\times$1 surface was studied by scanning tunneling microscopy (STM) and density functional theory (DFT). The PBr3 molecule completely dissociates on the Si(100) surface at room temperature into P and Br atoms. In most cases, the dissociated molecule was observed in STM on three neighboring Si dimers. DFT calculations confirm that the PBr3 molecule can completely dissociate at room temperature. After annealing the sample to 400$^{\circ}$C, phosphorus is incorporated into silicon, as evidenced by the Si atoms ejected to the surface. These findings are useful for the insertion of individual phosphorus atoms into silicon by PBr3 adsorption through a halogen mask.

PBr3 Adsorption and Dissociation on the Si(100) Surface

TL;DR

This paper investigates PBr3 as a phosphorus precursor for halogen-mask–assisted near-atomic doping of Si(100). The authors combine STM experiments in UHV at room temperature with DFT/NEB calculations to study adsorption, fragmentation, and dissociation barriers on the Si(100)-2×1 surface, reporting that PBr3 largely dissociates to P and Br on three neighboring dimers and that the most stable fragment (p-1) matches observed STM features with Br atop Si and P in end-bridge positions; dissociation barriers reach up to eV, enabling room-temperature dissociation on experimentally relevant timescales (roughly s) via at least one low-energy pathway with eV. Annealing the PBr3-covered surface to 400°C triggers phosphorus incorporation evidenced by Si ejection and island formation, with residual Br on the surface. The results support using PBr3 with a halogen mask as a practical alternative to phosphine for controlled phosphorus incorporation into Si, offering a route to near-atomic precision doping.

Abstract

The adsorption of PBr3 on the Si(100)-21 surface was studied by scanning tunneling microscopy (STM) and density functional theory (DFT). The PBr3 molecule completely dissociates on the Si(100) surface at room temperature into P and Br atoms. In most cases, the dissociated molecule was observed in STM on three neighboring Si dimers. DFT calculations confirm that the PBr3 molecule can completely dissociate at room temperature. After annealing the sample to 400C, phosphorus is incorporated into silicon, as evidenced by the Si atoms ejected to the surface. These findings are useful for the insertion of individual phosphorus atoms into silicon by PBr3 adsorption through a halogen mask.
Paper Structure (7 sections, 2 equations, 4 figures)

This paper contains 7 sections, 2 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Experimental methods
  4. Computational methods
  5. Results and discussion
  6. Conclusions
  7. Acknowledgement

Figures (4)

  • Figure 1: (a) Empty ($U_s =+2.2$ V) and (b) filled ($U_s =-3.5$ V) state STM images (30.1$\times$18.2 nm$^2$, I$_t$ = 1.5 nA) of the Si(100) surface after PBr3 adsorption at room temperature. The most frequently observed object on the PBr3-dosed surface is marked with a white circle. One of the other observed objects is indicated by a white square. (c) Empty ($U_s =+2.5$ V, I$_t$ = 2.2 nA) and (d) filled ($U_s =-3.5$ V, I$_t$ = 1.3 nA) state STM images (11.1$\times$8.8 nm$^2$) of the Si(100) surface after Br2 adsorption. Two different surface areas are shown in (c) and (d). The gaps between rows of Si dimers are marked with green lines.
  • Figure 2: Identification of the most frequently observed object on the PBr3-dosed Si(100) surface. (a) Empty ($U_s =+2.5$ V, I$_t$ = 1.0 nA) and (b) filled ($U_s =-4.5$ V, I$_t$ = 2.0 nA) state STM images of the object. Si dimers are marked with green dumbbells. (c) Top and side views of the model of the object (the p-1 structure in SM). Si atoms are shown in grey, Br in red and P in blue. (d) Simulated empty (U$_s =+2.5$ V) and (e) filled (U$_s = -4.5$ V) state STM images of the model shown in (c).
  • Figure 3: Energy barrier diagram of PBr3 dissociative adsorption on the Si(100)-2$\times$1 surface. PBr3 adsorption on electrophilic Si ('down atom') and nucleophilic Si ('up atom') are shown to the right and left of the initial state, respectively. Stable structures are shown at the bottom, transition states are shown at the top. The top-view schematics of the stable structures can be found in Fig. S3 in SM. Si atoms are marked in gray, Br in red, and P in blue. All energies are given in electronvolts relative to the initial state energy. Red numbers indicate activation barriers.
  • Figure 4: The PBr3-dosed surface after annealing to 400$^{\circ}$C for 5 min. (a) Empty state STM image (19.3$\times$19.3 nm$^2$, $U_s =+2.2$ V, I$_t$ = 2.0 nA) of the Si(100) surface with silicon islands. (b) Empty ($U_s =+2.5$ V, I$_t$ = 2.0 nA) and (c) filled ($U_s =-4.3$ V, I$_t$ = 2.0 nA) state STM images of the large silicon island on Si(100). The PBr3 adsorption was carried out at a partial pressure of $7 \cdot 10^{-10}$ Torr for ten minutes at room temperature.