The Role of Incomplete Interstitial-Vacancy Recombination on Silicon Amorphization (original) (raw)
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Stability of defects in crystalline silicon and their role in amorphization
Physical Review B, 2001
Using molecular-dynamics simulation techniques, we have investigated the role that point defects and interstitial-vacancy complexes have on the silicon amorphization process. We have observed that accumulation of interstitial-vacancy complexes in concentrations of 25% and above lead to homogeneous amorphization. However, we have determined the basic properties of the interstitial-vacancy complex, and showed that it is not as stable at room temperature as previously reported by other authors. From our simulations we have identified more stable defect structures, consisting of the combination of the complex and Si self-interstitials. These defects form when there is an excess of interstitials or by incomplete interstitial-vacancy recombination in a highly damaged lattice. Unlike the interstitial-vacancy complex, these defects could survive long enough at room temperature to act as embryos for the formation of extended amorphous zones and/or point defect clusters.
The role of the bond defect on silicon amorphization: a molecular dynamics study
Computational Materials Science, 2003
We have studied the influence of the so called ''bond defect'' in the silicon amorphization process using molecular dynamics simulation techniques. The bond defect consists in a local distortion of the silicon lattice with no excess or deficit of atoms, and it can be formed during ion-beam irradiation. Even though the bond defect lifetime is too short to justify damage accumulation at usual implantation temperatures, we have observed however that the interaction between close bond defects can generate more stable structures which behave as the amorphous pockets created by ion irradiation. We have seen as well that the recombination of a given amount of damage created by bond defect accumulation depends of its spatial distribution.
Structural transformations from point to extended defects in silicon: A molecular dynamics study
Physical Review B, 2008
We use classical molecular dynamics simulation techniques to study how point defects aggregate to form extended defects in silicon. We have found that ͗110͘ chains of alternating interstitials and bond defects, a generalization of the Si di-interstitial structure, are metastable at room temperature but spontaneously transform into ͕311͖ defects when annealed at higher temperatures. Obtained atomic configurations and energetics are in good agreement with experiments and previous theoretical calculations. We have found a ͕311͖ structural unit which consists of two interstitial chains along ͗110͘ but arranged differently with respect to the known ͕311͖ units.
Ion-beam-induced amorphization and recrystallization in silicon
Journal of Applied Physics, 2004
Ion beam induced amorphization in Si has attracted significant interest since the beginning of the use of ion implantation for the fabrication of Si devices. A number of theoretical calculations and experiments were designed to provide a better understanding of the mechanisms behind the crystalto-amorphous transition in Si. Nowadays, a renewed interest in the modeling of amorphization mechanisms at atomic level has arisen due to the use of preamorphizing implants and high dopant implantation doses for the fabrication of nanometric-scale Si devices. In this review we will describe the most significant experimental observations related to the ion-beam-induced amorphization in Si and the models that have been developed to describe the process. Amorphous Si formation by ion implantation is the result of a critical balance between the damage generation and its annihilation. Implantation cascades generate different damage configurations going from isolated point defects and point defect clusters in essentially crystalline Si to amorphous pockets and continuous amorphous layers. The superlinear trend in the damage accumulation with dose and the existence of a ion-mass depending critical temperature above which it is not possible to amorphize, are some of the intriguing features of the ion-beam-induced amorphization in Si. Phenomenological models were developed in an attempt to explain the experimental observations, as well as other more recent atomistic models based on particular defects. Under traditional models, amorphization is envisaged to occur through the overlap of isolated damaged regions created by individual ions (heterogeneous amorphization) or via the build-up of simple defects (homogeneous amorphization). The development of atomistic amorphization models requires the identification of the lattice defects involved in the amorphization process and the characterization of their annealing behavior. Recently, the amorphization model based on the accumulation and interaction of bond defects or IV pairs has been shown to quantitatively reproduce the experimental observations. Current understanding of amorphous Si formation and its recrystallization, predictive capabilities of amorphization models and residual damage after regrowth are analyzed.
Solid State Electronics, 2008
An atomistic model for self-interstitial extended defects is presented in this work. The model is able to predict a wide variety of experimental results by using a limited set of assumptions about the shape and emission frequency of extended defects, and taking as parameters the interstitial binding energies of extended defects versus their size. The model accounts for the whole extended defect evolution, from the initial small irregular clusters to the {3 1 1} defects and to the more stable dislocation loops. It predicts the extended defect dissolution, supersaturation and defect size evolution with time, and it takes into account the thermally activated transformation of {3 1 1} defects into dislocation loops. Moreover, the model is also used to explore a two-phase exponential decay observed in the dissolution of {3 1 1} defects.
Dominant structural defects in amorphous silicon
Journal of Physics: Condensed Matter, 2015
The nature of disorder in amorphous silicon (a-Si) is explored by investigating the spatial arrangement and energies of coordination defects in a numerical model. Spatial correlations between structural defects are examined on the basis of a parameter that quantifies the probability for two sites to share a bond. Pentacoordinated atoms are found to be the dominant coordination defects. They show a tendency to cluster, and about 17% of them are linked through three-membered rings. As for tricoordinated sites, they are less numerous, and tend to be distant by at least two bond lengths. Typical local geometries associated to under and overcoordinated atoms are extracted from the model and described using partial bond angle distributions. An estimate of the formation energies of structural defects is provided. Using molecular-dynamics calculations, we simulate the implantation of high-energy atoms in the initial structure in order to study the effect of relaxation on the coordination defects and their environments.
Atomistic analysis of the annealing behavior of amorphous regions in silicon
Journal of Applied Physics, 2007
We have analyzed the features of recrystallization of amorphous regions, using an atomistic amorphization-recrystallization model that considers the Si interstitial-vacancy pair as the building block for the amorphous phase. Both small amorphous pockets and large continuous amorphous layers are modeled as an accumulation of Si interstitial-vacancy pairs. In our model recrystallization is envisioned as a local rearrangement of atoms, the recrystallization rate of Si interstitial-vacancy pairs being determined by their local coordination. This feature explains the differences in the annealing behavior of amorphous regions with different topologies, the faster regrowth velocity of the damage tail compared with the continuous amorphous layer, and the independence of the regrowth velocity on the amorphous layer depth.
Stability of Si-Interstitial Defects: From Point to Extended Defects
Physical Review Letters, 2000
Trends in the growth of extended interstitial defects are extracted from extensive tight-binding and ab inito local density approximation simulations. With an increasing number of interstitials, the stable defect shape evolves from compact to chainlike to rodlike. The rodlike ͕311͖ defect, formed from (011) interstitial chains, is stabilized as it grows, elongating in the chain direction. Accurate parametrization of the defect-formation energy on the number of interstitials and interstitial chains, together with the anisotropy of the interstitial capture radius, enables macroscopic defect-growth simulations.
Microscopic Description of the Irradiation-Induced Amorphization in Silicon
Physical Review Letters, 2003
We have investigated the atomistic mechanism behind the irradiation-induced amorphization in Si using molecular dynamics simulation techniques. The microscopic description of the process is based on the defect known as bond defect or IV pair. IV pairs recombine very fast when isolated, but if they interact to each other they survive longer times and thus accumulate giving rise to amorphization. This fact accounts for the superlinear behavior of the accumulated damage with dose and the different activation energies for recrystallization observed in the experiments. The molecular dynamics results have been used to define an atomistic model for amorphization and recrystallization which has been implemented in a kinetic Monte Carlo code. The model is able to reproduce quantitatively the dependence of the critical crystal-amorphous transition on the irradiation parameters.
Atomistic analysis of defect evolution and transient enhanced diffusion in silicon
Journal of Applied Physics, 2003
Kinetic Monte Carlo simulations are used to analyze the ripening and dissolution of small Si interstitial clusters and ͕113͖ defects, and its influence on transient enhanced diffusion of dopants in silicon. The evolution of Si interstitial defects is studied in terms of the probabilities of emitted Si interstitials being recaptured by other defects or in turn being annihilated at the surface. These two probabilities are related to the average distance among defects and their distance to the surface, respectively. During the initial stages of the defect ripening, when the defect concentration is high enough and the distance among them is small, Si interstitials are mostly exchanged among defects with a minimal loss of them to the surface. Only when defects grow to large sizes and their concentration decreases, the loss of Si interstitials through diffusion to the surface prevails, causing their dissolution. The presence of large and stable defects near the surface is also possible when the implant energy is low-small distance to the surface-but the dose is high enough-even smaller distance among defects. The exchange of Si interstitials among defects sets a interstitial supersaturation responsible for the temporary enhancement of the diffusivity of interstitial diffusing dopants. The transitory feature of the enhancement is well correlated to the extinction of the Si interstitial defects.