Point Defects In Silicon Research Articles

Atomistic simulation of point defects in silicon at high temperature

The Stillinger–Weber interatomic potential is used in molecular dynamics simulations to compute estimates of the equilibrium and transport properties of self-interstitials and vacancies in crystalline silicon at high temperature. Equilibrium configurations are predicted as a 〈110〉 dumbbell for a self-interstitial, and as an inwardly relaxed configuration for a vacancy. Both structures show considerable delocalization with increasing temperature, which leads to a strong temperature dependence of the entropy of formation, as suggested by diffusion experiments. Diffusion coefficients and mechanisms are predicted as a function of temperature. The predictions are discussed in the context of experiments and first-principle calculations.

Structure, energetics, clustering and migration of point-defects in silicon

We present a theoretical investigation on point-defect formation, migration, and clustering in silicon by tight-binding molecular dynamics. We also provide, by means of first-principles Hartree-Fock calculations, a detailed chemical characterization of the Si-Si bond at the split ⟨110⟩ self-interstitial defect.

Properties of intrinsic point defects in silicon determined by zinc diffusion experiments under nonequilibrium conditions.

The present paper deals with self- and foreign-atom diffusion processes in Si. We focus on the foreign-atom Zn whose diffusion behavior is shown to be influenced by intrinsic point defects like Si self-interstitials (I) and vacancies (V). Diffusion experiments with Zn in dislocation-free Si were carried out between 1208 and 870 \ifmmode^\circ\else\textdegree\fi{}C applying a special method to perform isothermal diffusion anneals as short as a few seconds. Concentration-depth profiles measured with the help of spreading-resistance analysis are completely described by simultaneous diffusion via the kickout and dissociative mechanism. The evolution of Zn diffusion with time is characterized by short-, intermediate-, and long-time diffusion regimes. Profiles belonging to the long-time regime are suitable to extract transport capacities of intrinsic defects given by the product of thermal equilibrium concentration and diffusion coefficient. Zn profiles after intermediate diffusion times are shown to be sensitive to the prevailing thermal equilibrium concentration of Si self-interstitials. Results are presented for the thermal equilibrium concentrations of self-interstitials and vacancies as well as their transport properties. From the temperature dependence of these quantities the formation and migration enthalpy of I and V are obtained. These data are compared to previous experimental results as well as theoretical calculations.

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.

New Effect of Interaction between Moving Dislocation and Point Defects in Silicon

New Effect of Interaction between Moving Dislocation and Point Defects in Silicon

Reactions between Point Defects in Silicon Doped with Germanium

Reactions between Point Defects in Silicon Doped with Germanium

Consistent quantitative model for the spatial extent of point defect interactions in silicon

The silicon point defect properties which control the spatial extent of their interactions (e.g., interstitial diffusivity) have been calculated by many researchers. However, large discrepancies exist in the reported values of these parameters, and it is essential to have a consistent set of parameters for use in process simulation. To meet this need, we present here a model which includes important interactions which have been ignored in previous analyses, specifically bulk recombination of interstitials with vacancies and segregation of interstitials to surface oxide films. We assess the effectiveness of the model in predicting the spatial extent of point defect interactions by comparing simulation results with a wide range of experimental data. Although this same experimental data previously gave large differences in calculated parameter values, we obtain a single set of model parameters which can account for the full range of data in a consistent manner.

Diffusion and interactions of point defects in silicon: Molecular dynamics simulations

Diffusion and interactions of point defects in silicon: Molecular dynamics simulations

Diffusion and interactions of point defects in silicon: molecular dynamics simulations

We have simulated the motion and clustering of vacancies and interstitials in silicon using molecular dynamics methods. The diffusion coefficients of isolated defects were calculated from atomic displacements in simulations performed over a wide range of temperatures. The results give an apparent migration energy barrier of E ( M) V =0.43 eV for vacancies and E ( M) 1=0.9 eV for interstitials. The diffusion coefficients are between 10 −6 and 10 −5 cm 2/s at 800°C, and are in approximate agreement with recent first-principles calculations, although they are many orders of magnitude larger than the most direct experimental measurements. Simulations with high concentrations of defects show that like defects aggregate into stable clusters, and that individual defects are bound to these clusters with energies in the range of 0.6–2.3 eV. Defect clusters have mobilities which can differ substantially from those of the individual defects. The di-interstitial has a dramatically smaller diffusion barrier, E ( M) 21 ≈ 0.2 eV, whereas the tri-interstitial has a mobility which is so small that it is difficult to measure accurately by molecular dynamics simulations. We discuss some of the implications of these simulations for diffusion under silicon device-processing conditions.

Point defect-based modeling of diffusion and electrical activation of ion implanted boron in crystalline silicon

The time evolution of the transient enhanced diffusion and of the electrical activation of boron in crystalline silicon during thermal annealing subsequent to boron ion implantation is modeled by a system of diffusion-reaction equations for the dopant species and the silicon point defects. The concept of point defect impurity pair diffusion under equilibrium conditions is used to describe the diffusion process. Outdiffusion of implantation-induced silicon self-interstitials and the kick-out reaction Bi■Bs+I are assumed to be the leading mechanisms for boron activation. In the case of low-dose boron ion implantation, we start from a defect distribution of Gaussian shape with one interstitial per implanted boron atom. For higher boron doses, the area density of this interstitial distribution is constant, but the depth position of its peak depends on boron dose. Local equilibrium for the reactions between the point defects and the boron species is postulated to be realized before the onset of diffusion. The computed boron depth profiles are compared to data from the literature. Implantation doses from 2×1014 cm−2 up to 5×1015 cm−2 are analyzed, annealing temperatures and times are considered over the ranges 800–1000 °C and 10 s–8 h, respectively. Although this approach is characterized by a number of simple assumptions, essential deficiencies are only found in certain cases of annealing subsequent to high-dose boron implantation. Trapping of free interstitials by extended defects seems to become important at low temperatures and for long annealing times. If the depth region with maximum boron concentration is in its as-implanted state close to amorphization, a boron overactivation which is beyond the present model can be found. For all other cases it is possible to achieve a reasonable modeling of transient enhanced diffusion and of electrical activation.

Observation of defects in crystal surface layers by grazing-incidence diffraction X-ray topography

Threading dislocations in gallium arsenide and point defects in silicon were observed for the first time by X-ray topography under grazing-incidence diffraction conditions. A new type of contrast on polished surfaces has been resolved for single crystals with defects. The characteristics of grazing-incidence diffraction topography are discussed.

Chemistry of Point Defect in Silicon and its Applications in Semiconductor Technology

AbstractThe chemistry of the interactions between point defects and impurities is discussed by considering first the general thermodynamic and kinetic aspects of these reactions, deserving major attention to the identity of of the stable chemical species eventually formed and to the boundary conditions for diffusion controlled and reaction controlled interaction processes.The second part of the paper is instead dedicated to the analysis of the chemistry of carbon, oxygen, hydrogen and point defects in silicon, which is a system of major technological interest.We postulate that at low enough temperatures, when homogeneous nucleation processes are slow, spinodal decomposition assists oxygen aggregation phenomena. We postulate, also, on the basis of the existing knowledge, that carbon and hydrogen favour alternative reaction paths for oxygen in the due of clustering processes and discuss the hydrogen-enhanced oxygen diffusivity in the frame of a conventional trapping model.

Point and Swirl Defects in Silicon

In the previous paper [Jpn. J. Appl. Phys. 32 (1993) L856], vacancy and silicon self-interstitial thermal equilibrium concentrations, i.e., C V0= 2.1×1017 cm-3 and C I0= 3.4×1016 cm-3, were determined at 1100°C from an analysis of experimental data of P and Sb diffusions in silicon during thermal oxidation. From the relationship between these values and the Boltzmann factor, C V0 and C I0 are obtained as functions of the absolute temperature, T. Vacancy and self-interstitial diffusivities, D V and D I, are also given as functions of T by using the equation of D VC V0 or D IC I0 derived from Au diffusion experiments in silicon. Furthermore, the silicon self-diffusion mechanism is discussed and a successful model on the swirl defect formation mechanism is also proposed, using the obtained C V0, C I0, D V and D I. Consequently, C I0<C V0 and D V<D I relations hold for arbitrary T. That is, the dominant thermal equilibrium defects in silicon are vacancies. It was also found that self-diffusion is mainly governed by the interstitialcy or vacancy mechanism for T>1158 K or T≤1158 K.

Fast neutron irradiation for Czochralski grown silicon

In this investigation, Czochralski grown silicon (CZ-Si) was irradiated by a fast neutron which can introduce irradiated defects into silicon and change the quality and density of point defects in silicon, by the interaction between irradiated defects and oxygen, the controlled precipitation of oxygen, and an excellent intrinsic gettering structure in CZ-Si during heat treatment cycles can be obtained easily.

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.

Similar point defects in crystalline and amorphous silicon.

The microscopic nature of defects in ion-implanted crystalline silicon (c-Si) and amorphous silicon (a-Si) has been studied using M\"ossbauer spectroscopy. The evolution of the local structure around the probe atoms is followed during thermal annealing of ion-beam-created amorphous and ion-beam-damaged crystalline Si. Direct comparison of the M\"ossbauer parameters of $^{119}\mathrm{Sb}$ in c-Si and a-Si demonstrates that Sb occupies two distinct sites in each material with similar local environments in both materials. These sites are identified as fourfold-coordinated substitutional Sb and Sb-vacancy complexes. Annealing of ion-beam-damaged c-Si at 150 \ifmmode^\circ\else\textdegree\fi{}C causes the Sb-vacancy complex to change from a substitutional Sb adjacent to a vacancy to a more complicated complex. Annealing of a-Si is shown to reduce distortions in the network, consistent with structural relaxation.

Vibrational and elastic effects of point defects in silicon.

We calculate the free energies and normal modes associated with point defects in silicon. The dynamical matrices of a large relaxed supercell of perfect silicon and supercells containing defects are calculated. Diagonalization gives all the vibrational frequencies, and localized defect modes are found from the eigenvectors. The elastic effect of the defects is found by a method involving inversion of the dynamical matrices. The free energy and vibrational entropy of the defects are found by standard statistical techniques.

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

Determination of silicon point defect properties from oxidation enhanced diffusion of buried layers

In order to characterize fundamental silicon point defect properties, the enhanced diffusion of phosphorous buried layers as a function of depth into the silicon substrate was measured during interstitial injection via thermal oxidation of the wafer surface. The measurements were used to calculate the effective interstitial diffusivity in epitaxial silicon at 1100 °C. The experimental results were also interpreted using a physical model which includes bulk recombination of interstitials with vacancies and a fast interstitial diffusivity calculated from metal gettering. The model effectively accounted for the experimental data, and through comparison of the data with model simulations, the ratio of the concentrations of vacancies and interstitials in equilibrium was obtained.

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