Iso-concentration study of atomistic mechanism of B diffusion in Si (original) (raw)

Mechanism of boron diffusion in silicon-1999

2014

An exhaustive first-principles study of the energetics of B-Si interstitial complexes of various configurations and charge states is used to elucidate the diffusion mechanism of B in Si. Total energy calculations and molecular dynamics simulations show that B diffuses by an interstitialcy mechanism. Substitutional B captures a Si interstitial with a binding energy of 0.90 eV. This complex is itself a fast diffuser, with no need to first "kick out" the B into an interstitial channel. The migration barrier is about 0.68 eV. Kinetic Monte Carlo simulations confirm that this mechanism leads to a decrease in the diffusion length with increasing temperature, as observed experimentally.

Mechanisms of boron diffusion in silicon and germanium

Journal of Applied Physics, 2013

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 Â 10 20 B/cm 3. 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 GeO 2 nanoclusters, causing at 650 C a large Is supersaturation. These aspects of B diffusion are presented and discussed, modeling the key role of point defects in the two different matrices. V

Mechanism of boron diffusion in silicon: An ab initio and kinetic Monte Carlo study

Physical review letters, 1999

Experimental investigations of boron diffusion mechanisms in crystalline and amorphous silicon

Materials Science and Engineering: B, 2008

Boron, as the main p-type dopant in Si, has been extensively investigated both experimentally and theoretically in order to understand its diffusion mechanisms for modelling and optimization of advanced devices. Crystalline Si matrix was mostly studied, but quite recently increased interest emerged on the behaviour of B in amorphous Si. In this work we present our recent progress in understanding these fundamental processes. Extensive investigation about the room temperature diffusion of B induced by the analyzing beam during secondary ion mass spectrometry, allowed to give information about diffusion mechanism of B both in crystalline and in amorphous phase. Moreover this put the basis for accurate measurements that allowed to investigate the key parameters describing the B diffusion in different equilibrium conditions, i.e. in wide ranges of temperature and doping level. On this basis, a comprehensive, experimentally based, atomistic model for B diffusion has been assessed, advancing and clarifying in a coherent picture the wide existing literature, including the interactions among B and self-interstitial in different charge states. Also the amorphous phase shows a complex B diffusion mechanism, far from being Fick-like. By means of simulation modelling of extensive diffusion data, produced in a wide range of temperatures, times and B concentrations, we have demonstrated that B promotes the formation of dangling bonds and it interacts with them in order to diffuse. Peculiar physical features, such as diffusion shape and transient diffusion, are correctly described by the model.

Mechanism of boron diffusion in silicon and germanium

Effect of near atmospheric pressure nitrogen plasma treatment on Pt/ZnO interface J. Appl. Phys. 112, 116104 (2012) Observation of boron diffusion in an annealed Ta/CoFeB/MgO magnetic tunnel junction with standing-wave hard x-ray photoemission 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 Â 10 20 B/cm 3 . 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 GeO 2 nanoclusters, causing at 650 C a large Is supersaturation. These aspects of B diffusion are presented and discussed, modeling the key role of point defects in the two different matrices. V C 2013 American Institute of Physics. [http://dx.

Ab initio modeling study of boron diffusion in silicon

2001

We present investigations of boron diusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one-or two-step diusion mechanisms have been found for the dierent charge states. The predicted activation energy of 3.5±3.8 eV, migration barrier of 0.4±0.7 eV, and diusion-length exponent of À0:6 to À0:2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these ®rst-principles results can be used to create a physical B diusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diusion models.

First-Principles Study of Boron Diffusion in Silicon

Physical Review Letters, 1999

In this Letter we investigate boron diffusion as a function of the Fermi-level position in crystalline silicon using ab initio calculations. Based on our results, a new mechanism for B diffusion mediated by Si self-interstitials is proposed. Rather than kick out of B into a mobile channel, we find a direct diffusion mechanism for the boron-interstitial pair for all Fermi-level positions. Our activation energy of 3.5 3.8 eV, migration barrier of 0.4 0.7 eV, and diffusion-length exponent of 20.6 to 20.2 eV are in excellent agreement with experiment. PACS numbers: 66.30.Jt, 31.15.Ar, 71.55.Cn

Role of Si self-interstitials on the electrical de-activation of B doped Si

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006

The off-lattice displacement of B atoms in B-doped Si induced by the irradiation with light ion beam at room temperature has been investigated. A proton beam with energy ranging from 300 to 1300 keV was used to irradiate the single crystal Si samples containing a 400 nm thick surface layer (grown by molecular beam epitaxy) uniformly doped with B at a concentration of 1 · 10 20 B/cm 3 . Channelling analyses along the h1 0 0i axis using the 11 B(p, a) 8 Be reaction (at 650 keV proton energy) were used to detect the off-lattice displacements of B during irradiation. B is substitutional in the as-grown sample. During irradiation the normalized channelling yield of B v B increases with the ion fluence and saturates at a value v F smaller than unity, being this value independent of the energy of the irradiating beam. No change on the Si channelling yield was detected. The B displacement rate decreases with increasing the beam energy, it is controlled by the generation rate of Si self-interstitials, and it can be fitted by the following formula

Boron diffusion in silicon in the presence of other species

Applied Physics Letters, 2000

Modeling and experimental investigation of B equilibrium diffusivity and its activation in Si in the presence of other species, including ab initio calculations, are presented here. The results suggest that incorporating other species along with B into the Si substrate can achieve shallower junctions and higher B activation in semiconductor device applications.

Iso-concentration study of atomistic mechanism of B diffusion in Si (original) (raw)

Related papers