bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of Grain Structure Evolution and its Impact on the Reliability of Al(Cu) Thin Film Interconnects
Authors: Riege S. P. , Andleigh V. , Thompson C. V. , Frost H. J. 
Published: April 2011

ABSTRACTWe have extended a 2D simulation of grain growth to treat the effects of precipitates on the evolution of interconnect grain structures during post-patterning processing. It is known from experiments that different annealing histories result in different precipitate sizes and locations. Precipitates capture and effectively pin grain boundaries and inhibit grain growth and evolution toward bamboo structures. We find that even a small volume fraction of precipitates prevent an interconnect strip from reaching the fully bamboo structure by retarding grain growth and lowering the average grain size. At a late stage of evolution, cluster regions are pinned by precipitates on both sides, preventing further transformation to the by far more reliable bamboo structure. The results from grain growth simulations have been used with our electromigration simulator MTT/EmSim to investigate the dependence of interconnect reliability on linewidth and precipitate distribution. We find that in lines with precipitates the bamboo structure is not reached during post-pattern annealing even if the line width is smaller than the average grain diameter. Furthermore, it is found that while Cu in solid solution improves interconnect reliability, Al2Cu precipitates can inhibit post-patterning grain structure evolution to more reliable bamboo or near-bamboo structures so much that similar lines made of pure Al would be more reliable. Linked grain structure evolution and electromigration simulations allow process optimization for maximum interconnect reliability.
Simulation Study of IBE Process for III-V Compounds in Mesa and Trenches
Authors: Houlet L. , Rhallabi A. , Turban G. 
Published: April 2011

ABSTRACTThe Ion Beam Etching (IBE) model is developed assuming the analogy between the evolution of hydrodynamic surfaces and that of vacuum-solid interfaces. The main physical phenomenon in the IBE is the ion sputtering where the transfer of ion energy to the surface allows to eject the surface atoms. The local etching rate is thus proportional to the energetic flux and to the sputtering yield. Mask erosion and shadowing are taken into account in the model. The angular dependence of the sputtering yield permits to underscore the faceting and trenching phenomena which respectively represent the formation of the facets in mask comers and the overetching in the trench sides. Besides, the effect of mask erosion on pattern transfer of both trench and mesa structures is studied. In comparison with the experimental profile, the simulated etching profile of the mesa, based on the IBE model, shows a good agreement.
Effects of Compositional Segregation and Short Channel on Threshold Voltage of nMOSFET
Authors: Lee Julie Y. H. , Lee Tom C. H. , Embry Mike , Evans Keenan , Koch Dan , Tucker Robert 
Published: April 2011

ABSTRACTThis study calculates the threshold voltage (VT) roll-off behavior caused by short channel effect (SCE) as a result of scaling and the reverse short-channel effect (RSCE) due to B segregation around source and drain junctions by using the 2D device simulator - SILVACO™-ATLAS. The simulation results are comparable with the experimental data. It suggests that the drift diffusion physics can predict SCE and RSCE very well to sub-0.25μ Si n-MOSFET devices. The modeling results indicate the VT roll off at shorter channel length for devices with higher substrate doping concentration. VT increases if the local p-dopant segregation exists around the source and drain junction. It is observed that RSCE is more significant for devices with lower substrate doping concentration and shorter channel length.
Computationally Efficient Model for 2D Ion Implantation Simulation
Authors: Temkin Misha , Chakarov Ivan 
Published: April 2011

ABSTRACTA computationally efficient method for ion implantation simulation is presented. The method allows two-dimensional ion implantation profiles in arbitrary shaped structures to be calculated and is valid for both amorphous and crystalline materials. It uses an extension of the one-dimensional dual Pearson approximation into the second dimension.
Atomic Dynamics During Silicon Oxidation and the Nature of Defects at the Si-SiO2 Interface
Authors: Pantelides S. T. , Ramamoorthy M. 
Published: April 2011

ABSTRACTOxidation of thin-film Si, oxygen precipitation in bulk crystalline Si, and the formation of buried oxide layers (as in the SIMOX process for SOI) have been studied extensively for decades but the underlying atomic scale processes have remained elusive. Furthermore, common features of these phenomena have not been generally appreciated, in part because the kinetics are substantially different in the different cases. In this paper we review recent theoretical research based on atomic-scale first-principles calculations that provides a unified description of the three phenomena. In particular, we account for both the normal and enhanced mode of oxygen diffusion that leads to the formation of oxygen clusters known as thermal donors and their subsequent annealing and evolution into SiO2-like precipitates. It is proposed that a novel family of interface defects that are akin to thermal donors, composed of “frustrated” Si-O bonds, are a natural by-product of thin-film oxidation. An explicit mechanism for the emission of Si interstitials, which occurs during both oxidation and oxygen precipitation, is obtained. It is shown that emission of Si interstitials eliminates the frustrated-bond defects, thus explaining the high quality of the resulting interfaces. It is proposed that frustrated-bond defects are responsible for much of the behavior observed at the Si-SiO2 interface that cannot be accounted by dangling bonds and for the amphoteric traps that occur in high concentrations in SOI material.
Cohesive Energies of Be and Mg Chalcogenides
Authors: Porcu M. , Satta G. , Casula F. , Mula G. 
Published: April 2011

ABSTRACTWe have calculated the cohesive energies, bulk moduli and equilibrium volumes of Be and Mg oxides, sulphides and selenides, in both zincblende and rocksalt structures. The calculations have been performed with the Discrete-Variational-Method (DVM), a real space first-principle local-density-functional approach. Comparisons with the experiment and with other first-principles approaches show that the electronic and structural properties of solids can be computed with DVM at least as accurately as with the usual plane-wave pseudopotential methods. This result is especially interesting in view of the fact that an order N implementation of DVM, based on the W. Yang's divide and conquer method, has been recently developed.
Quantum Monte Carlo Simulations of Disordered Magnetic and Superconducting Materials
Authors: Scalettar R. T. , Denteneer P. J. H. , Huscroft C. , Mcmahan A. , Pollock R. , Randeria M. , Trivedi N. , Ulmke M. , Zimanyt G. T. 
Published: April 2011

ABSTRACTOver the last decade, Quantum Monte Carlo (QMC) calculations for tight binding Hamiltonians like the Hubbard and Anderson lattice models have made the transition from addressing abstract issues concerning the effects of electron-electron correlations on magnetic and metal-insulator transitions, to concrete contact with experiment. This paper presents results of applications of “determinant” QMC to systems with disorder such as the conductivity of thin metallic films, the behavior of the magnetic susceptibility in doped semiconductors, and Zn doped cuprate superconductors. Finally, preliminary attempts to model the Kondo volume collapse in rare earth materials are discussed.
Reliable Estimates of Quasi-Particle Energies and Exci-Tonic Effects in Clusters Through Discrete-Variational-Method Total Energy Calculations
Authors: Cappellini Giancarlo , Casula Francesco , Bechstedt Friedhelm 
Published: April 2011

ABSTRACTSelf-energy corrections to the DFT-LDA HOMO-LUMO gap for clusters have been calculated through an efficient method based on ΔSCF theory. Total energies for the clusters are obtained via discrete variational method (DVM). Good results in comparison with experiments and available theoretical data for the sodium tetramer Na4 and C60 have been obtained. The localization properties of DVM basis-functions play a fundamental role in obtaining the above results with a strongly reduced computational effort in comparison with ab-initio schemes. For the two systems under study an estimate of the first excitonic transition energy is also given.
Environment-Dependent Tight-Binding Model for Molybdenum
Authors: Haas H. , Wang C. Z. , Fähnle M. , Elsässer C. , Ho K. M. 
Published: April 2011

ABSTRACTA transferable orthogonal tight-binding model for molybdenum is developed which goes beyond the traditional two-center approximation. The elements of the Hamiltonian matrix as well as the repulsive potential are allowed to depend on the environment. Several bulk, atomic defect and surface properties are calculated and compared with ab-initio data and experimental results to check the accuracy of the model.
The Environment-Dependent Interatomic Potential Applied To Silicon Disordered Structures And Phase Transitions
Authors: Bazant Martin Z. , Kaxiras Efthimios , Justo J. F. 
Published: April 2011

ABSTRACTThe recently developed Environment-Dependent Interatomic Potential (EDIP) holds the promise of a new degree of transferability in describing bulk phases and defects of elemental covalent solids with a simple theoretically motivated functional form. Here we explore to what extent the environment-dependence of the model can extrapolate successes of the fitted version for Si for bulk defects to disordered phases, which involve local configurations very different from those used in fitting. We find that EDIP-Si provides an improved description of the metallic bonding bond angles of the liquid and is the first empirical potential to predict a quench directly from the liquid to the amorphous phase. The resulting amorphous structure is in closer agreement with ab initio and experimental results than with any artificial prepration method. We also show that melting of the bulk crystal and premelting of the (100)2×1 surface are reasonably well described by EDIP-Si in spite of its not being fit to any such properties.
Transferable Tight-Binding Approach Of Si-H Interactions
Authors: Kim Eunja , Lee Seung Mi , Lee Young Hee 
Published: April 2011

ABSTRACTWe construct transferable tight-binding parameters of silicon-hydrogen interactions, reproducing the electronic energy levels and vibrational frequencies of the silane(SiH4) molecule accurately. The potential function was rescaled with the exponential factor in order to ensure that the potential energy is smooth at an appropriate cut-off distance, which is very important in molecular-dynamics simulations. The parameters have been applied to other molecules and various surfaces such as hydrogenated Si(100) surfaces, for example, monohydride, dihydride, and (3×1) phase.
Tight-binding Electron-ion Dynamics: A Method for treating nonadiabatic processes and Interactions with Electromagnetic Radiation
Authors: Graves J. S. , Allen R. E. 
Published: April 2011

ABSTRACTA method is introduced for simulations of the coupled dynamics of electrons and ions in a molecule or material. It is applicable to general nonadiabatic processes, including interactions with an arbitrarily intense radiation field. The field is included in the electronic Hamiltonian through a time-dependent Peierls substitution. The time-dependent Schrödinger equation is solved with an algorithm that preserves orthogonality, and the atomic forces are obtained from a generalized Ehrenfest theorem. Calculations for GaAs and Si demonstrate that the method is reliable and quantitative.
Atomic Structure of a Polar Ceramic/Metal Interface: {222}MgO/Cu
Authors: Benedek R. , Shashkov D. A. , Seidman D. N. , Muller D. A. , Silcox J. , Chisholm M. F. , Yang L. H. 
Published: April 2011

ABSTRACT{222}MgO/Cu is one of the most extensively characterized ceramic/metal interfaces, in view of the atom-probe field-ion-microscopy, Z-contrast scanning-transmission-electron-microscopy (STEM), and spatially-resolved electron-energy-loss-spectroscopy (EELS) measurements performed by the present authors, as well as the high-resolution electron microscopy (HREM) of this system by others. Atomistic simulations with local density functional theory (LDFT) and molecular dynamics (MD) have been performed to gain additional insight into the structure of this interface. This presentation describes an interface interatomic potential for {222}MgO/Cu derived from LDFT total energy calculations, and its application to structural properties, including the terminating species, the absence of dislocation standoff, and the symmetry of the interfacial dislocation network.
Equilibrium Structure and Schottky Barriers at Eras/Gaas Interfaces
Authors: Petukhov A. G. , Hemmelman B. T. , Lambrecht W. R. L. 
Published: April 2011

ABSTRACTThe equilibrium structures as well as the electronic Schottky barriers for (100) Erbium-Arsenide/Gallium-Arsenide (ErAs/GaAs) arsenic and gallium terminated interfaces have been determined by ab-initio calculations using the local-density approximation and a full-potential linear-muffin-tin-orbital method. In both cases the arsenic sublattice was chosen to be continuous across the interface in accordance with experiments on Rutherford backscattering channeling. Band structures, densities of states, and charge density distributions were also determined for the interfaces. The comparison of the total supercell energies reveals that the gallium terminated (chain) interface is more energetically stable than the arsenic terminated (shadow) interface. It also shows that the equilibrium interface separation for the arsenic terminated interface corresponds to an ideal structure when arsenic forms undistorted face-centered cubic lattice. The separation in the gallium terminated interface is quite substantial and is 60% larger than that of the ideal situation. The model also predicts that no buckling of the ErAs interface monolayer will occur for either structure. The computed Schottky barriers for holes (after a semi-empirical quasiparticle self-energy correction) are 0.6 eV for the chain interface and 0.4 eV for the shadow interface.
Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals
Authors: Elsässer C. , Beck O. , Ochs T. , Meyer B. 
Published: April 2011

ABSTRACTAtomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.
Monte Carlo and Molecular Dynamics Simulations of Liquid Semiconductor Surfaces
Authors: Wang Zhiqiang , Yu Wenbin , Stroud David 
Published: April 2011

ABSTRACTWe have numerically studied the surface tension and surface profiles of several liquid semiconductors, including Si, Ge, GaAs, CdTe, and their alloys, as a function of temperature and concentration. Two kinds of simulations have been carried out: direct free-energy calculations using Monte Carlo methods, and force summations using molecular dynamics. We use empirical two- and three-body interatomic interactions based on the form originally proposed by Stillinger and Weber for Si, in conjunction with simulation cell sizes ranging from 216 to as large as 8000 atoms and several novel numerical techniques including a direct calculation of the surface entropy. In the case of alloys, we find a striking segregation of the low-surface-tension component to the surface even when the alloy components are miscible at all concentrations.
Thickness Dependencies in the Calculated Properties of Metallic Ultra-Thin Films
Authors: Boettger J. C. 
Published: April 2011

ABSTRACTUltra-thin film (UTF) electronic structure calculations are a common tool for investigating surface properties. In this work, electronic structure calculations for A1(111) films ranging from one to twelve atoms thick are used to illustrate some of the difficulties that can arise when one attempts to determine surface properties of metals with UTF calculations.
Ab-Initio Theory of Initial Oxidation of Silicon (001) Surfaces
Authors: Modine N. A. , Zumbach G. , Kaxiras E. 
Published: April 2011

ABSTRACTThe oxidation of the Si(001) surface is an important process on both technological and theoretical grounds. Experimental studies have not provided a clear picture of even the relevant atomic structures during the initial stages of oxidation, while previous theoretical studies of these processes have yielded contradictory results. Using careful first principles total-energy calculations based on density functional theory, we study several mechanisms of incorporating a sub-monolayer coverage of oxygen into the characteristic p(2 × 1) dimer reconstruction of the Si(001) surface. Our recently developed Adaptive Coordinate Real-space Electronic Structure (ACRES) method allows us to obtain results that are adequately converged with respect to the numerous computational parameters associated with this difficult system. We compare our results with previous theoretical work and propose a physically motivated two step pathway for the initial incorporation of an oxygen atom into the dimerized surface. Based on our results, we can explain what formerly appeared to be puzzling Ultraviolet Photoelectron Spectroscopy measurements which indicated that each initial oxygen atom saturates two surface dangling bonds.
Mechanism for Breakage of Si-O Networks of SiO2 Films in HF Solutions
Authors: Oku Tomoki , Hattori Ryo , Sato Kazuhiko 
Published: April 2011

ABSTRACTAn extended Hiickel calculation was employed to calculate the total electronic energy and the electron density during the breakage of the Si-O networks of a (F3SiO)2FSiOSiF(OSiF3)2 cluster modelled on the a-cristobalite structure. The Si-O networks are opened by the attack of F- ions on the silicon atoms, and the reaction is exthothermic by 2.7 eV through the attack of H+ ions on the oxygen atoms. Although the hydrogen termination of the oxygen atoms is an early reaction, the fluorine termination of the silicon atoms is a late reaction. The atomic bond population on the Si-O bonds decreases to zero by opening the Si-O networks. We conclude that the a-cristobalite and a-quartz SiO2 are dissolved in HF solutions since the Si-O networks are easily opened by the attack of F- ions. Our conclusion indicates that both cosite and stishovite SiO2, which are not dissolved in the HF solutions, are composed of Si-O networks that can be hardly opened by the attack of F- ions. Moreover, we propose the continual breakage of Si-O networks without the desorption of H2O molecules as an etching mechanism of SiO2 films.
The Effect of the Interface on the Overall Thermal Conductivity of Multi-Phase Composites
Authors: Lipton Robert 
Published: April 2011

ABSTRACTMulti-phase particle reinforced heat conducting composites are considered. We treat the case when there is an interfacial thermal barrier between phases. We indicate how the particle size distribution and particle geometry influences the overall properties of the suspension. These results apply immediately to the mathematically analogous case of DC electrical conductivity in the presence of electrical contact resistance between phases.
Magnetic Effects at Surfaces and Interfaces (Including Grain Boundaries)
Authors: Freeman A. J. , Wu Ruqian , Chen Lujun , Zhong Lieping 
Published: April 2011

ABSTRACTFirst-principles electronic structure studies based on local spin density functional theory and performed on extremely complex simulations of ever increasingly realistic systems, play a very important role in explaining and predicting surface and interface magnetism. This has led to solving even more challenging problems like the embrittlement of the Fe grain boundary, discussed here. Now, a major issue for first-principles theory is the treatment of the weak spin-orbit coupling (SOC) in magnetic transition metals and their alloys and its subsequent effects: (i) A major breakthrough in eliminating the numerical randomness for the determination of the magneto-crystalline anisotropy was made with the state-tracking and torque approaches. This now enables us to treat magnetostriction and its inverse effect, strain-induced magnetic anisotropy in transition metal bulk, thin films and alloys, (ii) The magneto-optical Kerr effects and x-ray magnetic circular dichroism are now directly calculated and compared with experiment. In all this work, and more recently, on the first-principles calculations of giant magneto-resistance in multilayers, extensive first-principles calculations and model analyses provide simple physical insights and guidelines to search for new magnetic recording and sensor materials.
Atomistic Study on Nano Stress-Strain Curves of α-Fe
Authors: Hu Shenyang , Ludwig Matthias , Farrissey Liam , Schmauder Siegfried 
Published: April 2011

ABSTRACTThe atomistic processes and stress-strain-curves during uniaxial tensile deformation of a single α-Fe nanocrystal have been studied with the molecular static method. Periodic boundary conditions are imposed along one direction perpendicular to the tensile axis to model plane strain conditions. The effects of the model sizes in plane, boundary conditions and crystal orientations on the stress-strain curves are systematically analyzed. Various deformation evidences such as dislocation movement, dislocation piling up and twinning are clearly observed. The deformation and fracture characteristics of a-Fe and their dependencies on the boundary conditions are investigated.
Micromorphology, Microstructure and Magnetic Properties of Sputtered Garnet Multilayers
Authors: Marcelli R. , Padeletti G. , Gambacorti N. , Simeone M. G. , Fiorani D. 
Published: April 2011

ABSTRACTThe growth technique, the micromorphological and microstructural characterization by means of atomic force microscopy (AFM) and secondary ions mass spectrometry (SIMS) as well as the magnetic properties of a novel class of magnetic multilayers, based on radio frequency (RF) sputtered thin amorphous garnet films, are presented. One, three and five thin film multilayers composed by amorphous pure yttrium iron garnet (a:YIG) and amorphous gadolinium gallium garnet (a:GGG) have been grown on GGG single crystal substrates. The multilayer interfaces have been found to be comparable in both, the three and five-layers structure. Low field susceptibility measurements, showed a paramagnetic behaviour for the single layer YIG film. For the three and five layers samples, irreversibility effects were observed, giving evidence of magnetic clusters at the interface YIG/GGG.