Experimental evidence of B clustering in amorphous Si during ultrashallow junction formation

Salvador, D. De; Bisognin, G.; Marino, M. Di; Napolitani, E.; Carnera, A.; Graoui, H.; Foad, M.A.; Boscherini, Federico; Mirabella, S.

doi:10.1063/1.2402905

Cited by 20 publications

(19 citation statements)

References 20 publications

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“…16 Moreover, sheet resistance measurements after low temperature recrystallization are also consistent with maximum levels of B activation of around $2 Â 10 20 B/cm 3 . 7,8 All these observations support the hypothesis of formation of immobile BICs in amorphous Si at B concentrations higher than that limit value, as experimentally verified by De Salvador et al 17 By using theoretical calculations, Mattoni and Colombo have characterized the formation kinetics of some BICs during recrystallization and found that B 2 I, B 3 I and B 4 I 2 configurations could play the major role in the evolution of recrystallized B-doped Si. 18 However, there are still some uncertainties about the configurations of BICs after recrystallization and the kinetics of their nucleation in amorphous Si is generally not modeled in detail.…”

Section: Introductionsupporting

confidence: 76%

Kinetics of large B clusters in crystalline and preamorphized silicon

Aboy

Pelaz

Bruno

et al. 2011

Journal of Applied Physics

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We present an extended model for B clustering in crystalline or in preamorphized Si and with validity under conditions below and above the equilibrium solid solubility limit of B in Si. This model includes boron-interstitial clusters (BICs) with BnIm configurations—complexes with n B atoms and m Si interstitials—larger (n > 4), and eventually more stable, than those included in previous models. In crystalline Si, the formation and dissolution pathways into large BICs configurations require high B concentration and depend on the flux of Si interstitials. In the presence of high Si interstitial flux, large BICs with a relatively large number of interstitials (m ≥ n) are formed, dissolving under relatively low thermal budgets. On the contrary, for low Si interstitial flux large BICs with few interstitials (m ≪ n) can form, which are more stable than small BICs, and whose complete dissolution requires very intense thermal budgets. We have also investigated the kinetics of large BICs in preamorphized Si, both experimentally and theoretically. B was implanted at a high-dose into preamorphized Si, and the B precipitation was studied by transmission electron microscopy and by sheet resistance and Hall measurement techniques. A simplified model for B clustering and redistribution in amorphous Si is proposed, including the experimental value for the B diffusivity in amorphous Si and the energetics of BICs. Our model suggests that B2, B3I, B4I and B4I2 clusters are the most energetically favored configurations, with relative abundance depending on B concentration. After recrystallization, thermal anneals up to 1100 °C evidence that BICs evolve under very low flux of Si interstitials under the particular experimental conditions considered. Simulations indicate that for very high B concentrations and low Si interstitial flux a significant fraction of the initial small BICs evolves into larger and very stable BIC configurations that survive even after intense thermal budgets, as confirmed by energy filtered transmission electron microscopy analyses. The correlation between simulations and Hall measurements on these samples suggest that hole mobility is significantly degraded by the presence of a high concentration of BICs.

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Section: Introductionsupporting

confidence: 76%

Kinetics of large B clusters in crystalline and preamorphized silicon

Aboy

Pelaz

Bruno

et al. 2011

Journal of Applied Physics

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“…II), even if to a lower extent than in crystalline Si, and then these clusters are transferred to the crystalline structure during the SPER. 6,12,13 Such B clusters, even if formed in preamorphized Si, can evolve towards BICs as large as 8 nm if a high B concentration is present and subjected to a proper I supersaturation, as shown by B chemical mapping and energyfiltered TEM investigations. 96 In summary, the non equilibrium clustering of B induced by a supersaturation of Is gives out B:Si complexes, named BICs, whose size and thermal stability depend on the starting conditions.…”

Section: B-i Clusters Formation and Dissolutionmentioning

confidence: 99%

“…Actually, the formation of B-B pairs during the very early stages of annealing at 550 C, while B is still in the amorphous phase of Si, has been evidenced by x-ray absorption near-edge spectroscopy measurements of p þ /n ultrashallow junctions realized by solid-phase epitaxy. 13 The clustered B, formed in a-Si, is then transferred to the c-Si once the SPER is complete, being responsible for the B deactivation measured in the final device.…”

Section: B Main Features Of B Migrationmentioning

confidence: 99%

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Mechanisms of boron diffusion in silicon and germanium

Mirabella

Salvador

Napolitani

et al. 2013

Journal of Applied Physics

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103

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B migration in Si and Ge matrices raised a vast attention because of its inﬂuence on the production of conﬁned, highly p-doped regions, as required by the miniaturization trend. In this scenario, the diffusion of B atoms can take place under severe conditions, often concomitant, such as very large concentration gradients, non-equilibrium point defect density, amorphous-crystalline transition, extrinsic doping level, co-doping, B clusters formation and dissolution, ultra-short high-temperature annealing. In this paper, we review a large amount of experimental work and present our current understanding of the B diffusion mechanism, disentangling concomitant effects and describing the underlying physics. Whatever the matrix, B migration in amorphous (a-) or crystalline (c-) Si, or c-Ge is revealed to be an indirect process, activated by point defects of the hosting medium. In a-Si in the 450-650 C range, B diffusivity is 5 orders of magnitude higher than in c-Si, with a transient longer than the typical amorphous relaxation time. A quick B precipitation is also evidenced for concentrations larger than 2 x10^20 B/cm3. B migration in a-Si occurs with the creation of a metastable mobile B, jumping between adjacent sites, stimulated by dangling bonds of a-Si whose density is enhanced by B itself (larger B density causes higher B diffusivity). Similar activation energies for migration of B atoms (3.0 eV) and of dangling bonds (2.6 eV) have been extracted. In c-Si, B diffusion is largely affected by the Fermi level position, occurring through the interaction between the negatively charged substitutional B and a self-interstitial (I) in the neutral or doubly positively charged state, if under intrinsic or extrinsic (p-type doping) conditions, respectively. After charge exchanges, the migrating, uncharged BI pair is formed. Under high n-type doping conditions, B diffusion occurs also through the negatively charged BI pair, even if the migration is depressed by Coulomb pairing with n-type dopants. The interplay between B clustering and migration is also modeled, since B diffusion is greatly affected by precipitation. Small (below 1 nm) and relatively large (5-10 nm in size) BI clusters have been identiﬁed with different energy barriers for thermal dissolution (3.6 or 4.8 eV, respectively). In c-Ge, B motion is by far less evident than in c-Si, even if the migration mechanism is revealed to be similarly assisted by Is. If Is density is increased well above the equilibrium (as during ion irradiation), B diffusion occurs up to quite large extents and also at relatively low temperatures, disclosing the underlying mechanism. The lower B diffusivity and the larger activation barrier (4.65 eV, rather than 3.45 eV in c-Si) can be explained by the intrinsic shortage of Is in Ge and by their large formation energy. B diffusion can be strongly enhanced with a proper point defect engineering, as achieved with embedded GeO2 nanoclusters, causing at 650 °C a large Is supersaturation. These aspects of B diffusion are presented and discus...

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“…After amorphization, the channel dopants experience diffusion in the a-Si layer. For the B diffusion in the a-Si during the SPER annealing stage, enhanced B diffusion [2] and B clustering phenomenon [18] are also considered. The LA process based on multiple laser stripe overlays leads to microscopic variations of Rs [19] and transistor properties [6].…”

Section: Pocket Dopant Deactivation Analysismentioning

confidence: 99%

Atomistic Modeling of Pocket Dopant Deactivation and Its Impact on <inline-formula> <tex-math notation="LaTeX">$V_{\textrm {th}}$ </tex-math></inline-formula> Variation in Scaled Si Planar Devices Using an Atomistic Kinetic Monte Carlo Approach

Noda

Vrancken

Vandervorst

2015

IEEE Trans. Electron Devices

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An analysis of pocket dopant deactivation and its impact on V th variation for scaled Si devices using an atomistic kinetic Monte Carlo approach are shown in this paper. B 5 keV, 5 × 10 13 /cm 2 + As 1 keV, 1 × 10 15 /cm 2 implants were used for B pocket deactivation study. An effect of laser annealing (LA) before spike-Rapid Thermal Annealing (RTA) was investigated. In case of B pocket implant, a stable B cluster configuration is changed from B 3 I (>1020°C) to BI 2 at spike-RTA temperature ∼1020°C. BI 2 is a source of B pocket deactivation with lower temperature than 1020°C. LA before low-temperature spike-RTA (<1020°C) is useful to improve B pocket activation. The V th mismatch figure of merit extracted from Pelgrom plot (Avt) degradation in nFET is shown as spike-RTA temperature is reduced. LA before spike-RTA shows a better short channel effect with lower drain-induced barrier lowering in nFET. LA + spike-RTA at 1000°C shows better Avt than spike-RTAonly. The difference of pocket deactivation is one of possible important reasons for the higher V th mismatch for nFET than for pFET.

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Experimental evidence of B clustering in amorphous Si during ultrashallow junction formation

Cited by 20 publications

References 20 publications

Kinetics of large B clusters in crystalline and preamorphized silicon

Kinetics of large B clusters in crystalline and preamorphized silicon

Mechanisms of boron diffusion in silicon and germanium

Atomistic Modeling of Pocket Dopant Deactivation and Its Impact on <inline-formula> <tex-math notation="LaTeX">$V_{\textrm {th}}$ </tex-math></inline-formula> Variation in Scaled Si Planar Devices Using an Atomistic Kinetic Monte Carlo Approach

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