Diffusion of boron in heavily doped <i>n</i>- and <i>p</i>-type silicon

Willoughby, A. F. W.; Evans, A G R; Champ, P; Kevin, Y.; Godfrey, D. J.; Dowsett, M. G.

doi:10.1063/1.336340

Cited by 40 publications

(19 citation statements)

References 15 publications

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“…B TED appears to be enhanced with increasing B concentration, leading to shouldering in the diffusion profiles. The shouldering behavior is consistent with a previous experimental observation 4 that shows B diffusion enhancement at high B concentration; that is, 10 B diffusion increased at the presence of high concentrations (Ϸ10 19 cm Ϫ3 ) of background boron 11 B. In fact, the concentration-dependent B diffusion has been explained by the variation of charged defect concentrations under extrinsic conditions ͑i.e., Fermi level shift effect, vide infra͒.…”

supporting

confidence: 79%

Shouldering in B diffusion profiles in Si: Role of di-boron diffusion

Hwang

Goddard

2003

Applied Physics Letters

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The role of di-boron diffusion in evolution of B diffusion profiles has been investigated. We find that boron pair (B s -B i ) diffusion can become as important as boron-interstitial pair (B s -Si i ) diffusion when both boron concentration and annealing temperature are very high, leading to concentration-dependent B diffusion. Our simulated B diffusion profiles with dramatic shouldering are in excellent agreement with experimental ones reported by Schroer et al. ͓Appl Boron doping is an essential ingredient in the fabrication of silicon-based semiconductor devices. As gate dimensions shrink to nanometer scales ͑р100 nm͒, it becomes critical to gain precise control of doping profiles. Consequently, a great deal of effort is being devoted to understanding and controlling transient enhanced diffusion ͑TED͒ of boron during implantation and postimplantation annealing.While it is understood that a mobile boron-silicon interstitial pair (B-Si i ) plays an important role in B TED, 1,2 still little is known about underlying reasons for the enhancement ͑or the retardation͒ of B diffusion at high concentrations of boron (Ͼ10 18 cm Ϫ3 ) ͑or impurities, such as carbon or oxygen͒.We were particularly intrigued by the diffusion profiles ͑Fig. 1͒ determined by Schroer et al. 3 using secondary ion mass spectroscopy ͑SIMS͒. Their results show clearly a concentration-dependent behavior; that is, B diffusion is enhanced as the B concentration increases. They implanted boron at energies ϳ500 eV with a dose of 10 15 cm Ϫ2 into a p-type, epitaxially grown ͑epi͒ silicon layer on Si͑001͒. Then, the substrate was annealed at 1200°C. The concentrations of oxygen and carbon in the epi-Si layer are typically less than 10 15 cm Ϫ3 . Hence, impurities are likely to play an insignificant role in determining the doping profiles in these experiments. In addition, high temperature annealing at 1200°C results in fast dissolution of B clusters formed at the very early stages of annealing. Therefore, the density of immobile large boron clusters, if any, is too low to influence diffusion profile evolution. This suggests that only Si interstitials and mobile B species should be considered in explaining these experiments. In the absence of concentrationdependent and/or transient effects, single component diffusion should lead to a Gaussian distribution ͑once the diffusion profile is fully developed͒, but the experimental results 3 in Fig. 1 differ substantially from a simple Gaussian. B TED appears to be enhanced with increasing B concentration, leading to shouldering in the diffusion profiles. The shouldering behavior is consistent with a previous experimental observation 4 that shows B diffusion enhancement at high B concentration; that is, 10 B diffusion increased at the presence of high concentrations (Ϸ10 19 cm Ϫ3 ) of background boron 11 B. In fact, the concentration-dependent B diffusion has been explained by the variation of charged defect concentrations under extrinsic conditions ͑i.e., Fermi level shift effect, vide infra͒. 10 In this letter...

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supporting

confidence: 79%

Shouldering in B diffusion profiles in Si: Role of di-boron diffusion

Hwang

Goddard

2003

Applied Physics Letters

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“…This most likely indicates that dopant pairing reactions Sb++B -(Sb+B ), P++B -(P+B ), (10.23) are effectively reducing diffusion below that predicted by Fermi-level effects alone. This pairing reaction is the most reasonable explanation for the same large retarded diffusion observed for B diffusing in layers heavily doped with As (Willoughby et al , 1986). Donor-acceptor pairing has been observed on an atomic scale using In with the perturbed angular correlation (PAC) technique.…”

Section: Isoconcentration Studiesmentioning

confidence: 87%

“…These very recent results are quite surprising and show that isoconcentration experiments may not be as easy to interpret as previously thought. It should be mentioned that self-diffusion has also been studied by the isoconcentration method, but the results are ambiguous [see the review article by Frank, Gosele, Mehrer, and Seeger (1984) Recent examples of isoconcentration studies are the investigation of ' B diffusing in a region heavily doped with "B (Miyake, 1985a;Willoughby et al , 1986) and Sb diffusion in the presence of high concentrations of As (Fair, Manda, and Wortman, 1986) or P (Nishi, Sakamoto, and Ueda, 1986). As expected, with increasing "B doping above n; (and thus increasing hole concentration) the diffusivity of ' B increases and demonstrates what was already known from nonisoconcentration studies:…”

Section: Isoconcentration Studiesmentioning

confidence: 98%

Point defects and dopant diffusion in silicon

1989

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Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects {vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

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“…20 However, more extensive diffusion studies using iso-concentration p-type and n-type backgrounds have shown that the contributions of charged and neutral point defects to intrinsic boron diffusion (the dopant concentration is less than the intrinsic carrier concentration) are of similar magnitude. 21,22 This rules out a strong reduction in intrinsic B diffusion due to band gap narrowing. Another explanation involves the pairing of boron and germanium atoms in the alloy, 11 consistent with the fact that the two atoms introduce compensating strain in the silicon lattice.…”

Section: Introductionmentioning

confidence: 95%

First-principles study of the origin of retarded diffusion of boron in silicon in the presence of germanium

2004

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Dopant diffusion plays an important role in the formation of ultrashallow junctions. To avoid unwanted transient enhanced diffusion of dopants, especially boron, other species (e.g., Ge, C, N, and F) are introduced into the Si substrate. Here, ab initio calculations have been carried out using a density functional theory code, DFT+ +, to investigate the origin of the experimentally observed retardation of boron diffusion in SiGe alloys. The formation energies of individual Si, B, and Ge point defects, and Si-B, Ge-B, and Si-Ge pair defects were calculated. Based on these calculations, the energetics of Si: Ge: B systems suggest that one mechanism to retard boron diffusion involves the effect of Ge atoms to decrease the number of available Si self-interstitials by increasing the migration energy and, concomitantly, to increase the migration energy of boron atoms. Our results also show that it is difficult for a Ge interstitial to approach a substitutional boron atom compared with a Si self-interstitial.

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Diffusion of boron in heavily doped n- and p-type silicon

Cited by 40 publications

References 15 publications

Shouldering in B diffusion profiles in Si: Role of di-boron diffusion

Shouldering in B diffusion profiles in Si: Role of di-boron diffusion

Point defects and dopant diffusion in silicon

First-principles study of the origin of retarded diffusion of boron in silicon in the presence of germanium

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