Point Defects In Crystalline Silicon Research Articles

Diffusion of point defects in crystalline silicon using the kinetic activation-relaxation technique method

We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.

Global Parameterization of Multiple Point-Defect Dynamics Models in Silicon

The task of determining globally robust estimates for the thermophysical properties of intrinsic point defects in crystalline silicon remains challenging. Previous attempts at point-defect model regression have focused on the use of a single type of experimental data but as of yet no single parameter set has produced predictive models for a variety of point-defect related phenomena. A stochastic optimization technique known as simulated annealing is used to perform simultaneous regression of multiple models. Specifically, zinc diffusion in Si wafers and the dynamics of the so-called interstitial-vacancy boundary during Czochralski crystal growth are used to systematically probe point-defect properties. A fully transient model for point-defect dynamics during crystal growth is presented which employs a sophisticated adaptive mesh refinement algorithm to minimize the computational expense associated with each optimization. The resulting framework leads to a quantitatively coherent picture for both experimental systems, which are modeled with a single set of point-defect thermophysical properties. The results are shown to be entirely consistent with other recent model-fitting estimates and indicate that as the number of experiments considered simultaneously within this framework increases it should be possible to systematically specify these properties to higher precision. © 2003 The Electrochemical Society. All rights reserved.

Structure and Dynamics of Point Defects in Crystalline Silicon

Ab-initio theoretical methods are increasingly being used to study the properties of defects in covalent materials such as silicon. Static properties include potential energy surfaces, binding energies, and electronic structures. The dynamics involve diffusion, vibrational properties, and defect reactions. This paper describes a powerful combination of methods used to study the interactions involving vacancies, self-interstitials, and impurities in Si. The methods are Hartree-Fock in molecular clusters and density-functional based molecular-dynamics simulations in periodic supercells. Three examples of applications are discussed: 1. the dissociation of interstitial H 2 molecules by vacancies and self-interstitials. and the formation of H 2 * , 2. the aggregation of vacancies leading to the formation of the ring-hexavacancy (V 6 ), and 3. the trapping of interstitial copper at V 6 and the origin of the electrical activity of copper precipitates.

Interaction and Migration Properties of Ion Beam Induced Point Defects in Crystalline Silicon: Basic Research and Technological Relevance

Interaction and Migration Properties of Ion Beam Induced Point Defects in Crystalline Silicon: Basic Research and Technological Relevance

Intrinsic point defects in crystalline silicon: Tight-binding molecular dynamics studiesof self-diffusion, interstitial-vacancy recombination, and formation volumes

Tight-binding molecular dynamics simulations are performed to study self-diffusion, interstitial-vacancy recombination, and formation volumes of point defects in crystalline silicon. The results show that (i) self-diffusion is dominated by vacancies (V) at low temperature and by interstitials (I) at high temperature; (ii) interstitial-vacancy recombination at room temperature leads to formation of a metastable I-V complex, which has an annihilation energy barrier of 1.1 eV; (iii) interstitial and vacancy relaxation volumes in silicon are approximately equal in magnitude and opposite in sign.

Room temperature migration of ion beam injected point defects in crystalline silicon

We have investigated the room temperature diffusion and trapping phenomena of ion beam generated point defects in crystalline Si by monitoring their interaction with dopants, native contaminants such as C and O, and other defects. Spreading resistance measurements show that a small fraction (∼ 10 −7–10 −6) of the defects generated at the surface by a 40 keV Si implant is injected into the bulk. These defects undergo trap-limited diffusion and produce dopant deactivation and/or partial annihilation of preexisting deep (several micron) defect markers, produced by MeV He implants. It is found that in highly pure, epitaxial Si layers, these effects extend to several microns from the surface, demonstrating a long range migration of point defects at room temperature. A detailed analysis of the experimental evidences allows us to identify the Si self-interstitials injected into the bulk as the major responsible of both dopant deactivation and partial annealing of vacancy-type defects (divacancies, phosphorus-vacancy and oxygen-vacancy) generated by the implants. Finally, a lower limit of ∼ 6 × 10 −11 cm 2/s is obtained for the room temperature diffusivity of Si self-interstitials.

Ion Beam Injected Point Defects in Crystalline Silicon: Migration, Interaction and Trapping Phenomena

AbstractOur recent work on the room temperature migration and trapping phenomena of ion beam generated point defects in crystalline Si is reviewed. It is shown that a small fraction (˜10−6) of the defects generated at the surface by a shallow implant is injected into the bulk. These defects undergo a long range trap-limited diffusion and interact with both impurities, dopants and preexisting defects along their path. In particular, these interactions result in dopant deactivation and/or partial annihilation of pre-existing vacancy-type defect markers. It is found that in highly pure, epitaxial Si layers, these effects extend to several microns from the surface, demonstrating a long range migration of point defects at room temperature. By a detailed analysis of the experimental evidences we have identified the Si self-interstitials as the major responsible for the observed phenomena. This allowed us to give a lower limit of 6 × 10−11 cm2/s for the room temperature diffusion coefficient of the Si self-interstitials. Room temperature trap-limited migration of vacancies is also detected as a broadening in the divacancy profile of as implanted samples. In this case the room temperature diffusion coefficient of vacancies has been found to be ≥3 × 10−12 cm2/s. These data are presented and their implications discussed.

Ion Beam Injected Point Defects in Crystalline Silicon: Migration, Interaction and Trapping Phenomena

AbstractOur recent work on the room temperature migration and trapping phenomena of ion beam generated point defects in crystalline Si is reviewed. It is shown that a small fraction (∼ 10−6) of the defects generated at the surface by a shallow implant is injected into the bulk. These defects undergo a long range trap-limited diffusion and interact with both impurities, dopants and preexisting defects along their path. In particular, these interactions result in dopant deactivation and/or partial annihilation of pre-existing vacancy-type defect markers. It is found that in highly pure, epitaxial Si layers, these effects extend to several microns from the surface, demonstrating a long range migration of point defects at room temperature. By a detailed analysis of the experimental evidences we have identified the Si self-interstitials as the major responsible for the observed phenomena. This allowed us to give a lower limit of 6×10−11-cm2/s for the room temperature diffusion coefficient of the Si self-interstitials. Room temperature trap-limited migration of vacancies is also detected as a broadening in the divacancy profile of as implanted samples. In this case the room temperature diffusion coefficient of vacancies has been found to be ≥3 × 10−12 cm 2/s. These data are presented and their implications discussed.

Point defects in MeV ion-implanted silicon studied by deep level transient spectroscopy

This paper reviews recent work using deep level transient spectroscopy (DLTS) for studying point defects in crystalline silicon implanted with H, B, C, O, Si, Ge and Sn ions. Doses between 10 7 and 10 10 cm −2 and energies from 0.4 to 8 MeV were used. Different intrinsic and impurity-related defects like divacancy and vacancy-oxygen centers are identified and their formation has been studied as a function of dose, dose rate, sample depth, implantation temperature and ion mass. Recombination between vacancies and Si self-interstitials is found to play a major role and only a few percent of the generated vacancies form stable defects. Furthermore, in direct contrast to that for damage accumulation at doses above ∼ 10 12 cm −2, the production of vacancy-type defects increases with increasing implantation temperature and decreases with increasing dose rate. These effects are qualitatively simulated using a simple model for the defect generation kinetics and attributed to enhanced vacancy annihilation by overlapping Si self-interstitials from adjacent ion tracks.

Nonequilibrium point defects and diffusion in silicon

Abstract Many surface and bulk processes generate or consume point defects in crystalline silicon. Some such processes that commonly occur in silicon device fabrications include impurity/dopant diffusion, thermal oxidation, thermal nitridation, silicidation, plasma treatment, ion implantation and oxygen precipitation. These processes can cause the concentrations of point defects to depart from their thermal equilibrium values. Nonequilibrium point defects can profoundly affect dopant diffusion. They may also engender extended defects, such as stacking faults and dislocations. Understanding of the causes and effects of nonequilibrium point defects is a prerequisite for the prediction and control of dopant diffusion in the fabrication of modern submicron devices. This report reviews technologically important processes that cause nonequilibrium point defects in silicon, and our current understanding of them.

Point defects in crystalline silicon, their migration and their relation to the amorphous phase

Vacancies and selfinterstitials in silicon have been studied extensively both experimentally and theoretically and many of their properties have been established. We review briefly some of the recent results obtained by ab initio calculations and by atomistic simulations using empirical interatomic potentials. These results yield a comprehensive picture of defect structure, migration paths, and relative contributions to self-diffusion. We elucidate the details of the atomic migration process by analyzing one of the migration paths of the self-interstitial in terms of the lattice normal modes (phonons). Finally, we report new calculations to clarify further similarities between crystals containing large concentrations of point defects and amorphous silicon. In addition to a notable trend in the density of crystals containing increasingly higher self-interstitial concentrations, we find strong similarities in the vibrational and structural properties.

Generation of point defects in crystalline silicon by MeV heavy ions: Dose rate and temperature dependence.

Si(100) samples have been implanted with low doses (10 7 -10 9 cm -2 ) of MeV 76 Ge and 120 Sn ions. Deep level transient spectroscopy was used for sample analysis, and the generation or vacancy-related point defects is round to increase with increasing implantation temperature and to decrease with increasing ion dose rate. These results are in direct contrast to that for damage buildup at high doses (≥10 12 cm -2 ), and the effect is attributed to rapidly diffusing Si self-interstitials which overlap and annihilate vacancies created in adjacent ion tracks

Fully relaxed point defects in crystalline silicon.

We have studied intrinsic point defects in crystalline silicon via a tight-binding molecular-dynamics scheme. The intrinsic defects studied in this work are the vacancy, the interstitial, the divacancy, the split divacancy, and the vacancy-interstitial complex. Fully relaxed geometries, gap states, and formation energies are investigated. It is shown that the relaxation effects cannot be neglected, in particular, in the peak position of band-gap states

Erbium point defects in silicon.

The possible technological importance of rare-earth-doped semiconductors has led to great interest in these materials. However, little at the atomic level is hitherto known about such defects in the host lattice. Using first-principles calculations, the nature of erbium point defects in crystalline silicon is investigated. The total energy of an erbium point defect at several high-symmetry sites and with two different oxidation states is computed. Among the configurations studied, the minimum-energy one is ${\mathrm{Er}}^{3+}$ at a tetrahedral interstitial site. The nature of the Er-related defect levels is determined.