Diffusion of the Diboron Pair in Silicon

Hwang, Gyeong S.; Goddard, William A.

doi:10.1103/physrevlett.89.055901

Cited by 14 publications

(11 citation statements)

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“…Binding energies of B m I n clusters. These energies are obtained from Theiss et al [3] and Cowern et al [9,10].…”

Section: Discussionmentioning

confidence: 99%

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Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion

Hwang¹,

Won²

2009

Molecular Simulation

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In this paper, we report our study on the minimised atomistic model (MAM) and the determination of an evolution path for dominant B m I n clusters during boron diffusion in kinetic Monte Carlo (KMC). It has been known that clusters generated after ion implantation play a decisive role in the enhanced boron diffusion at the tail region while being immobile at the peak region. Our MAM, based on the simple continuum model and the simple atomistic model, takes the smallest number of intermediate clusters into account as well as dominant clusters for the evolution path of interstitial clusters during boron diffusion. We find that intermediate clusters such as B 2 I 3 and B 3 I 3 play a significant role during the evolution of clusters despite the fact that the lifetimes of the corresponding intermediate clusters are relatively short due to low binding energies. Also, through our simulation results, we find the main evolution path of dominant clusters from B 2 I to B 3 I during thermal annealing in the MAM. Furthermore, our investigation reveals that the density of BI 2 clusters increases at the beginning of the annealing process while the density of B 3 I increases at a later stage. KMC simulation results are compared with experimental SIMS data, which support our theoretical model.

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“…Binding energies of B m I n clusters. These energies are obtained from Theiss et al [3] and Cowern et al [9,10].…”

Section: Discussionmentioning

confidence: 99%

“…If an interstitial happens to react with boron in the lattice site, BI is formed and migrated. It is called the interstitialcy mechanism [10]. Thereafter, extended defects are formed from individual defects by encounter.…”

Section: Minimised Atomistic Model and Evolution Path Of Dominant Clumentioning

confidence: 99%

Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion

Hwang¹,

Won²

2009

Molecular Simulation

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“…Within our modeling, we neglect for now the mobility of larger BICs and interstitial clusters like, e.g., B 2 I , which has been reported in the literature [45].…”

Section: Summary Of the Energy States Of Boron Clustersmentioning

confidence: 99%

Theoretical Study of Boron Clustering in Silicon

Windl

2005

J Comput Electron

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Ion implantation is the method of choice to introduce dopants such as boron into silicon. Thermal anneals are used to heal the implant damage as well as to activate the dopant electrically. The implant-anneal cycle causes transient enhanced diffusion (TED) of boron and clustering of boron atoms at concentrations far below the solubility limit. The formation of these small immobile boron-interstitial clusters (BICs) causes the deactivation of boron. In this work, we use density-functional theory calculations to study the boron clustering process in Si. We determine the minimum-energy structures of these clusters at different sizes embedded in bulk Si and calculate the energy and charge state of each cluster within density-functional theory. Special care is taken with regard to structural minimization, charge state effects and energy corrections. In contrast to previous work, we argue that substitutionalboron clusters as defined previously are meaningless due to the high repulsive energy of nearest-neighbor boron atoms. We compare the larger clusters to the phase of precipitates at higher boron concentrations, Si 1.8 B 5.2 , and suggest the boron icosahedron as logical final BIC before the formation of more macroscopic precipitates in the absence of kinetic constraints. We also describe in detail the implementation of our ab-initio results into a continuum model, which we have used in previous work to simulate diffusion and deactivation of boron.

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“…Our kinetic simulation shows that, as the total boron concentration is increased, the B s -B i concentration increases almost quadratically, but in contrast the B s -Si i concentration increases sublinearly at a high B concentration region (Ͼ10 18 cm Ϫ3 ) due to suppression by B s -B i cluster formation. 5 As a result, at 10 20 cm Ϫ3 , the equilibrium concentration of B s -B i becomes four orders of magnitude larger than the B s -Si i one. 5 We calculate that ␥Ϸ1.4 when C B ϭ10 20 cm Ϫ3 ͑it increases linearly with C B ) using the diffusivities and the binding energies listed before.…”

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confidence: 99%

“…5 As a result, at 10 20 cm Ϫ3 , the equilibrium concentration of B s -B i becomes four orders of magnitude larger than the B s -Si i one. 5 We calculate that ␥Ϸ1.4 when C B ϭ10 20 cm Ϫ3 ͑it increases linearly with C B ) using the diffusivities and the binding energies listed before. Here, the prefactor of B s -B i and B s -Si i dissociation rates is estimated based on the Debye frequency (ϭ10 13 s Ϫ1 ).…”

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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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Diffusion of the Diboron Pair in Silicon

Cited by 14 publications

References 20 publications

Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion

Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion

Theoretical Study of Boron Clustering in Silicon

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

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Diffusion of the Diboron Pair in Silicon

Cited by 14 publications

References 20 publications

Minimised atomistic model and main evolution path for dominant BmInclusters in boron diffusion

Minimised atomistic model and main evolution path for dominant BmInclusters in boron diffusion

Theoretical Study of Boron Clustering in Silicon

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

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Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion

Minimised atomistic model and main evolution path for dominant B_mI_nclusters in boron diffusion