B diffusion and clustering in ion implanted Si: The role of B cluster precursors (original) (raw)

Mechanism of de-activation and clustering of B in Si at extremely high concentration

It is known that B deactivation and clustering occur in the presence of an excess of Si self-interstitials (Is). First principle calculations predicted the path of clusters growth, but the precursor complexes are too small to be visible even by the highest resolution microscopy. Channeling with nuclear reaction analyses allowed to detect the location of small B-Is complexes into the lattice formed as a consequence of the B interaction with the Is.

B cluster formation and dissolution in Si: A scenario based on atomistic modeling

Applied Physics Letters, 1999

A comprehensive model of the nucleation, growth, and dissolution of B clusters in Si is presented. We analyze the activation of B in implanted Si on the basis of detailed interactions between B and defects in Si. In the model, the nucleation of B clusters requires a high interstitial supersaturation, which occurs in the damaged region during implantation and at the early stages of the postimplant anneal. B clusters grow by adding interstitial B to preexisting B clusters, resulting in B complexes with a high interstitial content. As the annealing proceeds and the Si interstitial supersaturation decreases, the B clusters emit Si interstitials, leaving small stable B complexes with low interstitial content. The total dissolution of B clusters involves thermally generated Si interstitials, and it is only achieved at very high temperatures or long anneal times.

Activation and deactivation of implanted B in Si

Applied Physics Letters, 1999

The temporal evolution of the electrically active B fraction has been measured experimentally on B implanted Si, and calculated using atomistic simulation. An implant of 40 keV, 2ϫ10 14 cm Ϫ2 B was examined during a postimplant anneal at 800°C. The results show a low B activation ͑ϳ25%͒ for short anneal times ͑р10 s͒ that slowly increases with time ͑up to 40% at 1000 s͒, in agreement with the model proposed by Pelaz et al. ͓Appl. Phys. Lett. 74, 3657 ͑1999͔͒. Based on the results, we conclude that B clustering occurs in the presence of a high interstitial concentration, in the very early stages of the anneal. For this reason, B clustering is not avoided by a short or low-temperature anneal. The total dissolution of B clusters involves thermally generated Si interstitials, and therefore, requires long-or high-temperature anneals.

Physical insight into the phenomenon of B clustering in Si at room temperature

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

The interaction between the crystal defects and the implanted dopants in Si is at the origin of the diffusion and the electrical de-activation that are detrimental for the realization of the ultra-shallow junctions required by the semiconductor technology roadmap. In this contest, the B clustering phenomenon under non-equilibrium conditions is of particular interest for the scientific community. It has been shown that ion channeling technique is an extremely powerful tool to reveal the room temperature formation of small boron-interstitial-clusters (BICs) through the detection of subnanometric B off-lattice displacement. In this paper, we review our recent results on BIC formation in B-doped Si samples on a large range of B concentration (10 19-10 21 at/ cm 3). At room temperature B atoms undergo an off-lattice displacement, with a characteristic channeling mark, if a supersaturation of Si self-interstitials (Is) is maintained by ion irradiation. The B displacement rate is limited by the fluence of excess Is per B atom and can be reproduced using a simple model of B-Is interaction with the formation of small B clusters. In the early stage of Is injection the formation of B 2 I clusters with the structure of split (1 0 0) has been detected by performing channeling angular scans along the <1 0 0> and <1 1 0> crystal axes.

Kinetics of large B clusters in crystalline and preamorphized silicon

Journal of Applied Physics, 2011

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.

Iso-concentration study of atomistic mechanism of B diffusion in Si

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007

B diffuses in crystalline Si by reacting with Si self-interstitial (I) with a frequency g, forming a BI complex that can migrate for an average length k. We experimentally measured both g and k as a function of the hole concentration p by means of iso-concentration experiments on B delta-layers both under p-and n-doping conditions. On the basis of these data, we propose a comprehensive model that fixes the interplay among free charge, I and BI charge states that determines the B diffusion. Pairing effect with donors was also considered.

Dissolution kinetics of boron-interstitital clusters in silicon

In this work, we have investigated the stoichiometry of boron-interstitial clusters ͑BICs͒ produced in a molecular-beam-epitaxy-grown B box by Si implantation and annealing, and their dissolution during further prolonged annealing cycles. Low-concentration B delta doping was used to quantitatively monitor the interstitial (I) flux. A stoichiometric ratio of about 1.2 between I and B was found for the BICs formed at 815°C. The BIC dissolution kinetics was investigated by analyzing the concentration profiles at different times and temperatures ͑in the range 815-950°C͒ with a simulation code able to deconvolve the processes of B diffusion and B release from clusters. We found that the main mechanism for cluster dissolution is the release of interstitial boron atoms, with a thermal activation energy of 3.2Ϯ0.4 eV. These data are discussed and compared with existing literature data.

First-principles-based predictive simulations of B diffusion and activation in ion implanted Si

2000

We present a kinetic Monte Carlo model for boron diffusion, clustering and activation in i o n implanted silicon. The input to the model is based on a combination o f experimental data and ab i n i t i o calculations. The model shows that boron diffusion and activation are low while vacancy clusters are present in the system. As the vacancy clusters dissociate, boron becomes substitutional and the active fraction increases rapidly. At the same time, the total boron diffusion length also increases rapidly while interstitial clusters ripen. The final burst of boron diffusion occurs a s the large interstitial clusters d i s s o l v e , but most of the transient diffusion of the implanted boron has already taken place by this time. We show that these results are in excellent agreement with experimental data on annealed dopant profiles and dopant activation as a function of annealing time.

Experimental evidences for two paths in the dissolution process of B clusters in crystalline Si

Applied Physics Letters, 2005

We show that B clusters, produced by self-interstitial interaction with substitutional B in crystalline Si, dissolve under annealing according to two distinct paths with very different characteristic times. The two regimes generally coexist, but while the faster dissolution path is predominant for clusters formed at low B concentration ͑1 ϫ 10 19 B/cm 3 ͒, the slower one is characteristic of clusters formed above the solubility limit and dominates the dissolution process at high B concentration ͑2 ϫ 10 20 B/cm 3 ͒. The activation energies of both processes are characterized and discussed. It is showed that the faster path can be connected to mobile B direct emission from small clusters, while the slower path is demonstrated not to be self-interstitial limited and it is probably related to a more complex cluster dissolution process.

Formation and evolution of small B clusters in Si: ion channeling study

B off-lattice displacement in B-doped Si was observed under Si self-interstitials ͑Is͒ supersaturation induced by ion irradiation at room temperature. B lattice location has a characteristic channeling mark and was studied by nuclear reaction analyses and ion channeling technique, through the comparison of the performed angular scans along the ͗100͘ and ͗110͘ crystal axes and the simulated scans by FLUX code. Solid and liquid-phase epitaxies and molecular beam epitaxy were used to prepare B-doped Si samples in order to investigate samples with B concentration in the range between 10 19 and 10 21 at/ cm 3 . B off-lattice displacement is limited by the fluence of excess Is per B atom. Small B-Is clusters ͑BICs͒ were formed as consequence of the interaction with Is produced during the ion irradiation. Clusters structures were investigated by simulating the channeling angular scans of cluster configurations predicted by theoretical calculations. In the early stage of Is injection, experimental observations are consistent with the presence of the predicted B 2 I clusters. These small BICs evolved into different structures under further ion irradiation.