bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady-State Creep of Thick and Thin-Film Multilayers
Authors: Shen Y.-L. , Suresh S.
Published: April 2011

The steady-state creep response of multilayered polycrystalline materials subjected to cyclic variations in temperature is analyzed. The approach presented here is capable of predicting the evolution of curvature, the thermal stresses, and the dominant deformation mechanisms at any through-thickness location of each layer for prescribed layer geometries and thermo-mechanical properties of the constituent layers. The Al-Al2O3 model system is considered, where the dominant relaxation mechanism in Al is studied as the layer thickness is systematically varied. Creep due to grain boundary diffusion is found to become more significant in thin layers with a three-dimensional equiaxed grain structure. The effects of columnar grain structure in Al thin films on the thermal cycling response are also discussed.
Ultrasmooth, Conducting Films Composed of Mo/Si Multilayers
Authors: Stearns D. G. , Baker S. L. , Wall M. A.
Published: April 2011

We investigate the variation of microstructure and electron transport with layer thickness in Mo/Si multilayer films deposited by magnetron sputtering.
Effect of the Grain Growth Process on the Characteristics for the Excimer Laser Crystallized Poly-Si Thin Film Transistors
Authors: Okumura Hiroshi , Tanabe Hiroshi , Okumura Fujio
Published: April 2011

We have found, for excimer laser crystallized poly-Si thin films, that there are two different grain growth processes that depend on the energy density. Columnar grains grow laterally at lower energy densities. The other grain growth process at higher energy densities is shown to be secondary grain growth caused by a less oriented structure with fine granular grains. A TFT with the maximum mobility is obtained at the border for the lower energy grain growth. Grain boundary and intragrain defects around grain boundary formed through the secondary grain growth reduce the mobility in spite of considerable grain enlargement.
Surface Morphology of P-Doped LPCVD Silicon Films
Authors: Plugaru Rodica , Vasile E. , Cosmin P. , Cosmin Silvia , Cobianu C. , Dascalu D.
Published: April 2011

The formation of silicon hillocks at the surface of amorphous and polycrystalline LPCVD silicon films, as a function of phosphorus doping was investigated by SEM, TEM replica and X-ray diffraction techniques. The phosphorus doping was performed in the concentration range from 9 × 1019cm-3 tol.5 × 1020cm-3. It was observed that the hillocks size increases with the dopant concentration for the as-doped and for annealed films. The experimental data were analysed in a model involving diffusion of silicon during the doping and recrystallization processes.
Effective Conductivity Modelling of Polycrystalline ZnO Thin Films
Authors: Robles M. , Tagüeña-Martínez J. , Río J. A. Del
Published: April 2011

Chemically deposited thin films have multiple applications, in particular for low cost solar cells production. However, due to their inhomogeneous structure, it is very difficult to predict their physical properties. In this work we present a mean field approximation to model the effective electrical conductivity of the polycrystalline ZnO chemical deposited thin films. Our model considers elliptical inclusions randomly distributed in a matrix. We compare with the experimental results of two different deposition methods: spray pyrolysis [1] and successive ion layer adsorption and reaction (SILAR) [2]. Supported by the structural information of these samples, we select the elliptical geometrical parameters. We obtain a good fit of the experimental measurements with our calculation.
Piezoresistance Gauge Factors in Heavily Boron-Doped Polysilicon from Infrared Piezoreflectance
Authors: Cali J. , Bustarret E. , Kleimann P. , Berre M. Le , Barbier D.
Published: April 2011

Heavily boron-doped (4×1019 < [B] >1021 cm-3) polycrystalline silicon thin films on oxidized silicon cantilevers were studied by FTIR spectroscopy. The experimental reflectance spectra (400–7000 cm-l) were compared to those expected for a poly-Si/SiO2/c-Si/SiO2 multilayer where the doped layer is described by a simple Drude model. The resulting free carrier concentration and conductivity were checked against electrical measurements.

The optical response of the polycrystalline layer in the medium infrared range (400–3000 cmn−1) was shown to be affected by a static uniaxial stress applied along the film plane by a four point bending mechanical device. The resulting microscopic piezoresistivity longitudinal gauge factors in the 15 - 25 range are in close agreement with those deduced from conventional electrical piezoresistivity measurements on sub-millimeter size patterns. The effective range of applicability of this contactless method and the potential application of such layers to temperature-independent miniature pressure sensors are discussed
Blanket and Local Crystallographic Texture Determination in Layered Al Metallization
Authors: Rodbell K. P. , Hurd J. L. , DeHaven P. W.
Published: April 2011

The effect of microstructure, including average grain size, grain size distribution, precipitate distribution and crystallographic texture, on the reliability of Al and Al-alloys is well documented. In this paper, the various x-ray methods available for measuring preferred orientation in blanket films are compared and contrasted in an effort to find the fastest, most accurate method to acquire crystallographic texture information. I(111)/I(200)ratios from Bragg-Brentano scans (θ/2θ), rocking curves, and complete pole figures (fiber plots) were compared for four Ti/AlCu films having greatly different crystallographic texture components. The results show that it matters how texture is measured in a thin film; only pole figures (fiber plots) are unambiguous. In addition, the local texture in a series of stress-voided 0.48 um wide Ti/AICuSi/TiN lines was measured using Backscattered Kikuchi Diffraction (BKD). Samples were chosen from two sets of identically prepared wafers (processed at different times) showing large differences in stress-voiding driven resistance versus time behavior. The more strongly textured (111 ) films had decreased stress-voiding lifetimes and tended to have smaller average grain sizes with slightly larger grain size distributions. This is in apparent contradiction with previous results in Al films, where improved stress-voiding and electromigration behavior were found in those films with the strongest (111 ) texture.
Direct Observation of the Effects of Cu Distribution on Electromigration Phenomena in Submicron Al Interconnects
Authors: Theiss Silva K. , Prybyla J. A.
Published: April 2011

We have performed time-resolved studies of the electromigration (EM) – induced formation, growth, migration, and spatial distribution of Al2Cu precipitates in submicron Al(0.5 wt. % Cu) runners. Of particular interest is the formation of the precipitates in relationship to the local microstructure of the runners, and the formation of voids and hillocks with respect to the location of the Al2Cu precipitates. Runners of widths 0.3, 0.5, 0.8, and 1.0 ýtm were tested at a current density of 2×106 A/cm2 and temperatures between 200 and 300°C. The evolution of the microstructure of the runners was evaluated using plan-view TEM, SEM, and EDX. The formation of voids and hillocks, and the growth of precipitates proceeds more rapidly as the width of the runners increases. However, a far greater number of precipitates nucleate in the 0.3 μm-wide line than in any of the others. As expected, voids are most likely to form near the cathode and hillocks near the anode. Large Al2Cu precipitates form near the anode long before failure occurs. Interestingly, the cathode-side bonding pad is not observed to serve as a good reservoir of Cu for the runners. Although the formation of voids near the cathode seems to be associated with the depletion of Cu in this region, hillocks and voids elsewhere are more likely to form at precipitates than in other parts of the line. Thus Al2Cu precipitates can act as sites for preferential EM-damage, reducing interconnect reliability.
ACRES: Adaptive Coordinate Real-Space Electronic Structure
Authors: Modine N. A. , Zumbach Gil , Kaxiras Efthimios
Published: April 2011

A real space approach to electronic structure calculations has several important advantages. A regular real-space mesh produces a sparse, local, and highly structured Hamiltonian, which enables effective use of iterative numerical methods and parallel computer architectures. However, a regular real space mesh has equal resolution everywhere, while actual physical systems are inhomogeneous. To remedy this inherent inefficiency without losing the advantages of a regular mesh, we carry out computations on a regular mesh in curvilinear space. There are several choices involved in the implementation of the method. These include the choice of the coordinate transform, the form of the discretized Laplacian, the regularization of the ionic potential for all-electron calculations, and the method of calculating the forces. Of particular interest is the use of error analysis to optimize the grid for a given physical system. The adaptive grid is versatile enough to describe accurately a very wide class of systems, including ones with highly inhomogeneous electronic distributions. We report all-electron calculations for atoms and molecules with is and 2p valence electrons, and pseudopotential calculations for molecules and solids.
The Massively Parallel O[N] LSMS-Method: Alloy Energies and Non-Collinear Magnetism
Authors: Stocks G. M. , Wang Yang , Nicholson D. M. C. , Shelton W. A. , Temmerman W. M. , Szotek Z. , Harmon B. N. , Antropov V. P.
Published: April 2011

We present an overview of the locally self-consistent multiple scattering (LSMS) method. The method is based on real space multiple scattering theory, is naturally highly parallel, and has been implemented on Intel Paragon parallel platforms within the Center for Computational Sciences at Oak Ridge National Laboratory. O(N)-scaling is demonstrated for unit cells as large as 1000-atoms. We discuss in detail how the real space convergence properties of the method can be controlled by taking advantage of the stationary properties of a finite temperature Harris-Foulkes free energy functional. We show how the LSMS method can be combined with spin-dynamics to treat non-collinear magnetic states of materials. We show some preliminary results for the ground state magnetic structure of FCC Fe0.6 5Ni 0.35 alloys that indicate the possible existence of non-collinear arranges of magnetic moments in this system.
Ab Initio and Model Calculations on Different Phases of Zirconia
Authors: Schönberger Uwe , Wilson Mark , Finnis Michael W.
Published: April 2011

In order to get a better understanding of the energetics of ZrO2 (zirconia) ab initio calculations with the full potential linear muffin tin orbital method ( fp LMTO) have been performed on the tetragonal structure over a range of c/a and sublattice displacement. A new semi-empirical shell model is developed which makes use of Hartree-Fock calculations and includes compressible anions and quadrupolar distortions. The empirical model predicts energies for tetragonal distortion in agreement with the fp LMTO calculations. Furthermore, it enables us to understand why the seven-fold coordinated monoclinic phase is the low temperature equilibrium structure.
Distribution of Rings and Intermediate Range Correlations in Silica Glass Under Pressure-A Molecular Dynamics Study
Authors: Rino José Pedro , Gutiérrez Gonzalo , Ebbsjö Ingvar , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

Using the molecular dynamics (MD) method, we have studied the effect of pressure on the distribution of rings and their relationship to intermediate range correlations manifested as the first sharp diffraction peak (FSDP) for Si02 glass. A systematic analysis of the modifications observed in the FSDP for densities ranging from 2.0 to 3.2 g/cm3 and temperatures from 0 to 1500 K is reported. The decrease in the height of the FSDP with increasing density is found to be proportional to the decrease in the number of 6-fold rings. For the density and temperature ranges studied in SiO2 glass, the full width at half maximum (FWHM) of the FSDP remains unchanged.
Atomistic Monte Carlo Simulations of Surface Segregation in (FexMn1-x)O and (NixCo1-x)O
Authors: Battaile C. , NajafBdi R. , Srolovitz D. J
Published: April 2011

An atomistic Monte Carlo (MC) method has been used to predict equilibrium segregation of isovalent cations to (001) surfaces in (Fex.Mn-x)O and (NixCol-x)O. The surface is found to be enriched with solvent in both systems. Long-range electrostatic interactions and atomic motions that occur on small time scales make the MC approach very computationally demanding. The Free Energy Minimization (FEM) method is a more efficient alternative for performing such segregation simulations, but involves several approximations. Comparison of the surface segregation profiles determined using the MC and FEM simulation methods show that the two are essentially indistinguishable. The FEM results can be obtained about 1,000 times faster than the MC predictions. Therefore, the FEM method is a practical and accurate alternative to the more cumbersome MC approach.
Tight-Binding Initialization for Generating High-Quality Initial Wave Functions: Application to Defects and Impurities in GaN
Authors: Neugebauer Jörg , Walle Chris G. Van De
Published: April 2011

We describe a new method that allows an efficient construction of high-quality initial wavefunctions which are required as input for iterative total-energy methods. The key element of the method is the reduction of the parameter space (number of wavefunctions) by about two orders of magnitude by projecting the plane-wave basis onto an atomic basis. We show that the wave functions constructed within this basis set are very close to the exact plane-wave wavefunctions, resulting in a rapid total-energy convergence.
Native Point Defect Densities and Dark Line Defects in ZnSe
Authors: Berding M. A. , Sher A. , Schilfgaarde M. Van
Published: April 2011

Native point defect densities (including vacancies, antisites and interstitials) in ZnSe are calculated using a quasichemical formalism, including both vibrational and electronic contributions to the defect free energy. The electronic contribution to the defect formation free energy is calculated using the self-consistent first-principles full-potential linearized muffin-tin orbital (FP-LMTO) method and the local-density approximation (LDA). Gradient corrections are included so that absolute reference to zinc atoms in the vapor phase can be made. We find that the Frenkel defect formation energy is ∼0.3 eV lower at a stacking fault than in the bulk lattice. Nonradiative-recombination-induced Frenkel defect generation at stacking faults is proposed as a mechanism responsible for the limited device lifetimes.
First-Principles Calculations of the Elastic Properties of the Nickel-Based L12 Intermetallics
Authors: Iotova D. , Kioussis N. , Lim S. P. , Sun S. , Wu R.
Published: April 2011

The elastic constants of the L12-type ordered nickel-based intermetallics Ni3X (X = Mn, Al, Ga, Si, Ge), have been calculated by means of ab initio total-energy electronic structurecalculations based on the full-potential linear-muffin-tin-orbital (FLMTO) method. Theorigins in the electronic structure of the variation of the elastic constants, bulk and shearmoduli are investigated across the series, and the effects of the anisotropy of bonding chargedensity on the shear anisotropy factor and the degree of ductility is discussed.
Molecular Dynamics Simulations of a Siloxane-Based Liquid Crystal Using an Improved Fast Multipole Algorithm Implementation
Authors: McKenney Alan , Pachter Ruth , Patnaik Soumya , Adams Wade
Published: April 2011

In our continuing efforts towards designing materials with controlled optical properties, largescale molecular dynamics simulations of a molecular cluster of a liquid crystalline cyclic siloxane are still limited by the size of the molecular system. Such simulations enable evaluation of the orientation order parameter of the system, as well as modelling the behavior of the material in bulk. This study summarizes improvements in the implementation of the fast multipole algorithm for computing electrostatic interactions which is included in the molecular dynamics program PMD[7, 8], such as the elimination of computations for empty cells and the use of optimal interaction lists. Moreover, an improved implementation of a 3-D Fast Multipole Method (FMM3D) based on the algorithm previously proposed[1, 2] is described in detail. The structure of the module, details of the expansions, parallelization, and its integration with the molecular dynamics simulation code are explained in detail. Finally, the utility of this approach in the study of liquid crystalline materials is briefly illustrated.
First-Principles Determination Of The Effects Of Boron And Sulfur On The Ideal Cleavage Fracture In Ni3Al
Authors: Sun Sheng N. , Kioussis Nicholas , Ciftan Mikael , Gonis A.
Published: April 2011

The effects of boron and sulfur impurities on the ideal cleavage fracture properties of Ni3Al under tensile stress are investigated for the first time using the full-potential linearmuffin- tin-orbital (FLMTO) total-energy method, with a repeated slab arrangement of atoms simulating an isolated cleavage plane. Results for the stress-strain relationship, ideal cleavage energies, ideal yield stress and strains with and without impurities are presented, and the electronic mechanism underlying the contrasting effects of boron and sulfur impurities on the ideal cleavage of Ni3Al is elucidated.
Investigation Of Cracking Mechanisms Of Plasma Sprayed Alumina-13% Titania By Acoustic Emission
Authors: Lin C.K. , Leigh S.H. , Gansert R.V. , Murakami K. , Sampath S. , Herman H. , Berndt C.C.
Published: April 2011

Free standing alumina-13% titania samples were manufactured using high power water stabilized plasma spraying. Heat treatment was performed at 1450°C for 24 hours and then at 1100°C for another 24 hours. Four point bend tests were performed on the as-sprayed and heat-treated samples in both cross section and in-plane orientations with in situ acoustic emission monitoring to monitor the cracking during the tests. Catastrophic failure with less evidence of microcracking was observed for as-sprayed samples. Energy and amplitude distributions were examined to discriminated micro- and macro-cracks. It was found that the high energy (> 100) and high amplitude (say > 60 dB) responses can be characterized as macro-cracks. Physical models are proposed to interpret the AE responses under different test conditions so that the cracking mechanisms can be better understood.
Parallel Simulations Of Rapid Fracture
Authors: Abraham Farid F.
Published: April 2011

Implementing molecular dynamics on the IBM SP2 parallel computer, we have studied the fracture of two-dimensional notched solids under tension using million atom systems. Brittle materials are modelled through the choice of interatomic potential function and the speed of the failure process, and our interest is to learn about the dynamics of crack propagation in ideal materials. Recent laboratory findings occur in our simulation experiments, one of the most intriguing is the dynamic instability of the crack tip as it approaches a fraction of the sound speed. A detailed comparison between laboratory and computer experiments is presented, and microscopic processes are identified. In particular, an explanation for the limiting velocity of the crack being significantly less than the theoretical limit is provided.
Temporal Instabilities (Dissipative Structures) In Cyclically Deformed Metallic Alloys
Authors: Glazov Michael V. , Williams David R. , Laird Campbell
Published: April 2011

The existing models for the “classical” Portevin-Le-Chatelier effect have been analyzed, and the non-linear dynamical model has been proposed in order to quantify the nature of temporal instabilities in fatigued metallic alloys. The model employs the concept of a positive feed-back among the populations of mobile, immobile and Cottrell-type dislocations with atmospheres of point defects. Three major types of loading have been numerically simulated: pure sinusoidal, creep fatigue (“the Lorenzo-Laird bursts”) and ramp loading (“the Neumann bursts”, when the amplitude of otherwise cyclic loading grows linearly with time). Computer movies of the temporal evolution of stress and dislocation densities have been prepared as an aide for analysis and illustration. The model successfully reproduces stress serrations in terms of the underlying dislocation mechanisms and thus for the first time establishes a fundamental link between the micro-and macromechanics of cyclic deformation.
Plan-View Transmission Electron Microscopy Of Crack Tips In Bulk Materials
Authors: Saka H. , Nagaya G. , Sakuishi T. , Abe S. , Muroga A.
Published: April 2011

A focused ion beam (FIB) system has been applied to prepare a thin foil specimen of Si, MgO and alumina which contained cracks in the plane of foil. It was possible to observe a much larger area at and near a crack tip than has been hitherto possible. FIB was also applied to observation of microstructure near a crack tip evolved during severe rolling contact fatigue in a steel.
New Routes To Nitrides: Synthesis Of A Highly Colored Lithium Tantalum Oxynitride
Authors: Houmes Joel D. , Loye Hans-Conrad Zur
Published: April 2011

The synthesis of a new lithium tantalum oxynitride is described. The compound, LiTaO3-3xN2x was synthesized by reacting LiTaO3 with anhydrous ammonia at temperatures ranging from 773 K to 1173 K. Depending on the reaction temperature the sample color changes from white to tan (773 K) to bright orange (973 K) to red (1123 K). The color appears to be the result of a p-d transition consistent with a charge transfer from localized nitrogen states to a band of predominately metal character. Electrical and magnetic measurements indicate that the material is a diamagnetic insulator.
Synthesis and Modification of beta-C3N4 Materials by Ion-beam Processing
Authors: Ren Zhong-Min , Du Yuan-Cheng , Ying Zhi-Feng , Li Fu-Ming , Zhang Yafei
Published: April 2011

Covalent carbon nitride films have been synthesized by laser ablation and ion-beam coprocessing. Different laser ablations give different ablated graphite plasma. Beta- C3N4 polycrystalline has been found in the deposited films. Under laser energy of 50 mJ per pulse, the adoption of 532 nm laser used for ablation of graphite is proposed for the purpose of production of good carbon nitride films. The C-N crystal structures can be improved by followed ion-beam processing.
Epitaxial Growth of 3C-SiC by Pulsed Laser Deposition
Authors: Cosgrove J. E. , Rosenthal P. A. , Hamblen D. , Fenner D. B. , Yang C.
Published: April 2011

We have grown thin films of SiC by pulsed laser deposition on silicon (100) and vicinal and non-vicinal 6H SiC (0001) substrates using a quadrupled YAG laser and a high purity dense polycrystalline SiC target. Epitaxy on all three substrate types was confirmed by x-ray diffraction, transmission electron microscopy and electron diffraction. Composition of the films was measured by Rutherford backscattering spectrometry and Scanning Auger Microprobe.
The Interaction of HCl With polycrystalline β-SiC: Evidence for a Site-Blocking Mechanism for HCl Inhibition of SiC CVD
Authors: Schulberg Michelle T. , Allendorf Mark D. , Outka Duane A.
Published: April 2011

Chlorine-containing precursors are attractive for chemical vapor deposition (CVD) of SiC because they are less hazardous and more economical than silane precursors. The reactivity of HCl, a by-product of these reactions, on SiC is of particular interest because it has been reported that HCl inhibits SiC CVD, but the mechanism for this inhibition has not been identified. In this work the adsorption of HCl on polycrystalline β-SiC was examined with Auger Electron Spectroscopy (AES) and Temperature Programmed Desorption (TPD). HCl adsorbs readily on SiC, with an initial sticking probability of 0.1 at 300 K, and forms a strong bond, with an activation energy for desorption of 64 kcal/mol. The only product detected by TPD is HCl, which desorbs in a peak centered at 1010 K. There are no Si- or C-containing desorption products, demonstrating that HCl does not etch SiC under TPD conditions. These results are consistent with a site-blocking mechanism for HCl inhibition of SiC CVD, but not with an etching mechanism.
Plasma Surface Modification in Biomedical Applications
Authors: Loh I-H , Sheu M-S
Published: April 2011

Synthetic biomaterials are widely used for a variety of in vivo and in vitro biomedical applications. However, the performance, safety, and cost effectiveness of medical products are determined by desirable interactions between the physiological environments and biomaterial surfaces. Hence, development of surface modifications for biomaterials is strongly demanded by the biomedical industry. High energy techniques, such as glow discharge plasma, have been developed to impart specific chemical functionality to the biomaterial surfaces or to deposit new polymer films with desired properties. The use of plasma surface modification for biomedical applications is reviewed in this paper.
Vertically-Stacked InAs Islands Between GaAs Barriers Grown by Chemical Beam Epitaxy
Authors: Miller Mark , Jeppesen Søren , Georgsson Kristina , Kowalski Bernhard , Malm Jan-Olle , Pistol Mats-Erik , Samuelson Lars
Published: April 2011

We report vertically-aligned InAs islands separated by GaAs barriers thin enough for electronic coupling. Thinner barriers reduced the InAs critical-thickness for island formation. Transmission electron microscopy revealed well-aligned islands with all detected islands in complete stacks. Atomic force microscopy showed the top islands of uncapped stacks are fully formed. The photoluminescence peak was sharper and shifted to lower energy compared to a single-layer growth. We attribute this shift to island-to-island electronic coupling and to the smaller compressive strain in the center of the composite structure.
Temperature-Dependent Strain Relaxation and Islanding of Ge/Si(111)
Authors: Deelman P. W. , Schowalter L. J. , Thundat T.
Published: April 2011

In order to understand Ge island nucleation and evolution, we have studied strain relaxation and clustering of Ge grown on Si(111) by molecular beam epitaxy (MBE) with in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Our goal is to tailor the size and density of the nanocrystals by controlling thermodynamics and kinetics. At low temperature (∼ 450°C), we observe a sharp 2D–3D growth mode transition after 2.5ML ±0.1ML (we define a thickness of 1ML to be one-third the length of the body diagonal of the Ge conventional unit cell), when transmission diffraction features appear in RHEED and the surface lattice constant begins to relax. The mechanisms of island growth and strain relaxation change with growth temperature. At ∼ 700°C, transmission diffraction spots never appear in RHEED for Ge/Si(111) and strain relaxation occurs gradually. After 37ML of growth, the apparent in-plane lattice parameter increases only 1.5% over that of the Si substrate. This behavior is explained by the different manner in which islands initially nucleate and grow in the two temperature regimes. At low temperature, small islands nucleate and grow on a relatively rough wetting layer (which itself provides preferential sites for dislocation introduction). The areal density of the small islands is relatively high. At high temperature, a small number of islands grow very large from the outset. A general model indicates how, at low temperature. The relative difficulty of overcoming the barrier to dislocation formation actually results in an apparent larger degree of strain relief than at high temperature.
Optical Characteristics of Tensilely Strained GaInP/AIGaInP Mqw for Laser Diode Applications
Authors: Ono K. , Motoda T. , Tsugami M. , Hayafuji N. , Sonoda T. , Takamiya S.
Published: April 2011

Availability of tensilely strained GaInP/AIGaInP quantum well, which is essential to laser diodes operating at 635–650nm, is investigated by combining conventional and time-resolved photoluminescence measurements. It is found that optical characteristics are improved by introducing tensile strain into barrier layers in addition to well layers, while samples with unstrained or compressively strained barrier layers reveal inferior characteristics. Experimantal data indicate that these optical characteristics are not determined by interfacial stress, but by the energy band discontinuity between well and barrier layer.
Improved Copper Chemical Vapor Deposition Process by Applying Substrate Bias
Authors: Lee Won-Jun , Rha Sa-Kyun , Lee Seung-Yun , Kim Dong-Won , Chun Soung-Soon , Park Chong-Ook
Published: April 2011

The substrate bias was applied during the chemical vapor deposition (CVD) process of copper in an effort to change the adsorption behaviors of the reactant. Copper films were deposited on TiN and SiO2 from Cu(hfac)(tmvs) with the substrate bias and without one. The surface morphology, the thickness, the sheet resistance and the purity of the films were investigated. When the negative substrate bias of -30 V was applied to the substrate, the deposition rate of copper increased both on TiN and SiO2. No change was observed in the chemical composition of the copper film deposited with substrate bias in comparison with that of the copper film deposited with no bias. It was calculated that Cu(hfac) has the dipole moment whose direction is from copper to hfac. Under the d. c.electric field, dipole tends to align along the poling direction. Resulting from the overlapping population (OP) value analysis, the improvement of deposition rate under negative substrate bias was explained due to the adsorption of copper atom in Cu(hfac) species directly onto the substrate by the electric field applied between the substrate and the gas showerhead.
A Complete Stochastic Wiring Distribution for Gigascale Integration (GSI)
Authors: Davis Jeffrey A. , Eble John C. , De Vivek K. , Meindl James D.
Published: April 2011

Based on Rent's Rule, a well established empirical relationship, a rigorous derivation of a complete wire length distribution for on-chip random logic networks is performed. The distribution is then used to describe an optimal architecture for a multilevel wiring network that provides maximum interconnect density and minimum chip size for a ULSI system. In addition, this new distribution has been incorporated into a Generic System Simulator (GENESYS), that projects overall performance of future ULSI systems. Assuming various interconnect materials such as copper, aluminum, silicon dioxide, and low dielectric polymers, GENESYS has been used to examine the effects that each material has on overall performance of ASIC's over the next 15 years.
New Surface Cleaning Method for Heavily-Doped Silicon and Its Application to Selective Cvd-W Clad Layer Formation on Single- and Poly-Crystalline Silicon
Authors: Kosugi T. , Sato Y , Ishii H. , Arita Y
Published: April 2011

We have developed a new method of cleaning p+-Si surfaces by plasma hydrogenation and subsequent HF treatment prior to selective W-CVD by SiH4 reduction. The hydrogenation enhances the hydrogen-termination of p+-Si surfaces in HF solution significantly, resulting in high controllability in selective W-CVD on p+-Si surfaces. Contact resistivity was 0.5 to 3×10-7 Ω cm2 for single- and poly-crystalline p+-Si. The increase in junction leakage current was fairly small because of low Si consumption.
Chemical Vapor Deposition of Tin for Ulsi Applications
Authors: Eizenberg M.
Published: April 2011

TiN has been recognized as an excellent barrier material for W as well as Al planarization gap filling of contacts and vias. The need for conformality over extreme topography necessitates the use of CVD rather than sputtering for the deposition of TiN. In this paper we will first review the various deposition techniques of CVD TiN. Then, we will present a recently developed approach: thermal decomposition of TDMAT followed by nitrogen-based rf plasma treatments for resistivity reduction. This approach utilizes the advantages of thermal decomposition: excellent step coverage, good barrier properties, and low particle content. The resistivity reduction of the post deposition plasma treatment is followed by excellent stability upon long term air exposure. Vias and salicide contacts utilizing this unique process exhibit resistance values equivalent to those obtained when sputtered TiN is used. Conformal films as thin as 200Å can be utilized as excellent barriers for deep sub-0.5μm devices with large aspect ratios, where sputtered TiN can not be used any more.
Thermal Metalorganic Chemical Vapor Deposition of Ti-Si-N Films for Diffusion Barrier Applications
Authors: Custer J. S. , Smith Paul Martin , Jones Ronald V. , Maverick A. W. , Roberts D. A. , Norman J. A. T. , Hochberg A. K.
Published: April 2011

Structurally disordered refractory ternary films such as titanium silicon nitride (Ti-Si-N) have potential as advanced diffusion barriers in future ULSI metallization schemes. Here we present results on purely thermal metalorganic chemical vapor deposition (CVD) of Ti-Si-N. At temperatures between 300 and 450°C, tetrakis(diethylamido)titanium (TDEAT), silane, and ammonia react to grow Ti-Si-N films with Si contents of 0-20 at.%. Typical impurity contents are 5-10 at.%H and 0.5 to 1.5 at.% C, with no O or other impurities detected in the bulk of the film. Although the film resistivity increases with increasing Si content, it remains below 1000 μΩ-cm for films with less than 5 at.% Si. These films are promising candidates for advanced diffusion barriers.
X-Ray Microdiffraction for VLSI
Authors: Wang P.-C. , Cargill G. S. , Noyan I. C. , Liniger E. G. , Hu C.-K. , Lee K. Y.
Published: April 2011

We describe how x-ray microbeam diffraction is being used to measure strain with micronscale spatial resolution. Micron-scale x-ray beams can be obtained using tapered glass capillaries. With the high brightness and broad energy spectrum of synchrotron radiation and the energy dispersive capabilities of commercially available, liquid nitrogen cooled x-ray detectors, spatially resolved strains in a sample can be determined along different directions without having to rotate the sample, in contrast with more conventional methods using monochromatic x-ray diffraction. This is a major advantage in achieving micron-scale spatial resolution. Strain sensitivities on the order of 2×10−4 have been achieved in such measurements. White beam x-ray microdiffraction has been applied for the first time in real-time studies of thermal and electromigration related strain distributions in passivated Al-on-Si conductor lines. Results of measurements on a single 10μm-wide line are described.
Synthesis and Characterization of Siof Thin Films Deposited by Ecrcvd for Ulsi Multilevel Interconnections
Authors: Lee Seoghyeong , Park Jong-Wan
Published: April 2011

Low dielectric constant fluorine doped silicon oxide films were deposited by using ECR plasma CVD with SiF4 and O2 as source gases diluted in Ar gas. Characterization of films was carried out in terms of various gas flow ratios (SiF4/O2 = 0.2 ∼ 1.6). The microwave power and substrate temperature during deposition were fixed at 700W and 300°C, respectively. The chemical bonding structure of the films was evaluated by Fourier transform infrared spectroscopy (FTIR), fluorine concentration by X-ray photoelectron spectroscopy (XPS) and refractive index by ellipsometry. Dielectric constant was determined from C-V measurements at 1MHz. FTIR spectra shows that as the fluorine concentration increases, peak intensities of Si-F bonding and shoulder peak at around 1160cm−1 of Si-O stretching mode increased. Moreover, with increasing the fluorine concentration in the SiOF film, the peak position of Si-O stretching mode shifts to the higher wavenumber side. The Si-F2 bond peak is observed to rise when the SiF4/O2 gas flow ratio is larger than 1.0. Refractive index and film density decreased with increasing the SiF4/O2 gas flow ratio. The SiOF film deposited at SiF4/O2 gas flow ratio of 1.0 exhibited fluorine content of 11.8 at.% and dielectric constant of 3.14.
The Band at “960”
Authors: Schwarz S. , Corbin D. R. , Vega A. J.
Published: April 2011

Mesoporous silicas were modified with titanium alkoxide precursors. Results are consistent with a model that describes the resultant silica surface as a mixture of Si–OH groups, isolated Si–O–Ti type species, and oligomeric (-Ti-O-)n ensembles. Decreasing the rate of hydrolysis of the precursor by using chelated Ti-alkoxides increases the fraction of isolated Ti.
Preparation of Continuous Mesoporous Films on Porous and Dense Substrates
Authors: Liu J. , Bontha J. R. , Kim A. Y. , Baskaran S.
Published: April 2011

High quality, continuous mesoporous films are prepared on both porous and dense substrates. An interfacial reaction mechanism is used to grow mesoporous films within the pores of porous supports using a diffusion cell reactor. The porous support was placed between two compartments containing a silicate solution in one compartment and a surfactant solution in the other. The silicate and surfactant solutions diffused into the support to form a mesoporous film at the liquid-liquid interface. This method produces a transparent film free from large defects. Spincoating technique is also used to prepare mesoporous films on dense substrates. These films have uniform thickness and show well-defined interference depending on the film thickness.
Nanostructural Study of Luminescent Porous Polycrystalline Silicon
Authors: Poon M. C. , Han P. G. , Sin J. K. O. , Wong H.
Published: April 2011

Luminescent porous poly-Si films with large areas or micron-sized patterns have been obtained by anodization or stain etching of phosphorus-doped poly-Si films deposited by low pressure chemical vapor deposition onto Si, thermal oxide or CVD nitride. The anodized film is composed of spherical Si grains with nano-pores formed around the surface. However, the stainetched film has large rectangular Si grains, and no nano-pores can be observed. The intensity of photoluminescence is enhanced after nitric acid boiling or stain etching, and is found to be closely related to the crystallinity of the porous Si layers.
Synthesis, Characterization and Catalytic Properties of Al2O3-TiO2 Mixed Oxides Prepared by Sol-Gel
Authors: Montoya A. , Melé;ndez-Hernindez J. , Domínguez J. M. , Sandoval-Robles G.
Published: April 2011

Some synthesis parameters like R-OH/OBu, H20/OBu and composition (Al/Ti) ratios influence the textural and catalytic properties of the mixed Al2O3 -TiO2 oxides. The Radial Distribution Function of the pure and mixed oxides shows that Ti4+ incorporation favors the long-range-order in the mixed aggregates as well as the surface area loss at high temperatures, i.e. 900 °C. The catalytic dehydration of isopropanol towards propylene and the HDS of light gasoils indicate that catalytic properties of the sol-gel mixtures are comparable to the activity of reference catalysts, i.e. Al2O3and Ni/Al2O3.
Sol-Gel Processed Alumina based Materials in Microcalorimeter Sensor Device Fabrication for Automotive Applications
Authors: Nakouzi S. R. , McBride J. R. , Nietering K. E. , Narula C. K.
Published: April 2011

The application of sol-gel processed materials in a variety of sensors has been proposed. We describe microcalorimeter sensor devices employing sol-gel processed alumina based materials which can be used to monitor pollutants in automotive exhaust. These sensors operate by measuring changes in resistance upon catalysis and are economically acceptable for automotive applications. It is important to point out that automobiles will be required to have a means of monitoring exhaust gases by on-board sensors as mandated by the EPA and the California Air Resources Board (OBD-II).
Optical Interference Filters Made of Porous Silicon
Authors: Thönissen M. , Berger M. G. , Krüger M. , Billat S. , Arens-Fischer R. , Glück O. , Lüth H. , Hilbrich S. , Theiss W. , Grosse P.
Published: April 2011

Porous silicon (PS) layers can easily be formed by an electrochemical etch process using a mixture of hydrofluoric acid (HF) and ethanol. The microstructure and porosity of the layers depend on the HF concentration, the doping level of the substrate and the current density applied during the etch process. Changing the current density during the etch process will result in a well defined layer structure consisting of layers with different porosities. Each single layer can be treated as an effective medium exhibiting a refractive index depending mainly on the porosity of the layer. Using reflectance measurements we have investigated the dependence of the refractive index of PS layers on the formation current density for different substrates. In addition the etch rate was determined by thickness measurements with an electron microscope. Based on these results various kinds of optical interference filters were studied. We have formed samples consisting of discrete single layers with different porosities (e.g. Bragg reflectors) as well as samples with continuous variation of the refractive index (rugate filters). Combining these PS filters with standard photolithography steps, microoptical devices such as spectral sensitive photodiodes can be realized.
Resorcinol-Formaldehyde and Carbon Aerogel Microspheres
Authors: Alviso C. T. , Pekala R. W. , Gross J. , Lu X. , Caps R. , Fricke J.
Published: April 2011

Aerogels are a unique class of materials possessing an open-cell structure with ultrafine cells/pores (<100nm), high surface area (400–1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10nm. Although monolithic aerogels are ideal candidates for many applications (e.g. transparent window insulation), current processing methods have limited their introduction into the commercial marketplace. Our research focuses on the formation of resorcinol-formaldehyde (RF) aerogel microspheres which offer an attractive alternative to monolith production. An inverse emulsion polymerization is used to produce these spherical gel particles which undergo solvent exchange followed by supercritical drying with carbon dioxide. This process yields aerogel microspheres (10–80μ diameter) which can be used as loosely packed powders, compression molded into nearnet shapes using a polymer binder, or used as additives in conventional foaming operations to produce new aerogel composites with superior thermal properties. The emulsification procedure, thermal characterization, mechanical properties, and potential applications of RF aerogel microspheres will be discussed.
Direct Synthesis of Acidic Aluminosilicate Mesoporous Molecular Sieves
Authors: Mokaya Robert , Jones William
Published: April 2011

A simple and versatile synthetic route, whereby primary amine surfactants are the template in the assembly of aluminosilicate inorganic species, is used to prepare aluminosilicate mesoporous molecular sieves in which Brønsted acidity is generated by simply calcining the as-synthesised material. Al incorporation is accompanied by charge-balancing protonated amine molecules. Si and Al are incorporated into the mesoporous framework to yield materials with textural properties similar to those of MCM-41 but with substantially higher Brønsted acidity.
Periodic Mesoporous Silica Gels
Authors: Anderson M. T. , Martin J. E. , Odinek J. G. , Newcomer P. , Wilcoxon J. P.
Published: April 2011

We have synthesized monolithic particulate gels of periodic mesoporous silica by adding tetramethoxysilane to a homogeneous alkaline micellar precursor solution. The gels exhibit 5 characteristic length scales over 4 orders of magnitude: fractal domains larger than the particle size (>500 nm), particles that are ˜150 to 500 nm in diameter, interparticle pores that are on the order of the particle size, a feature in the gas adsorption measurements that indicates pores ˜10–50 nm, and periodic hexagonal arrays of ˜3 nm channels within each particle. The wet gel monoliths exhibit calculated densities as low as ˜0.02 g/cc; the dried and calcined gels have bulk densities that range from ˜0.3–0.5 g/cc. The materials possess large interparticle (˜1.0–2.3 cc/g) and intraparticle (˜0.6 cc/g) porosities.
The Effect of Heat Generation on the Development of Vermicular α-Al 2O3 in Alumina Films
Authors: Bagwell R.B. , Messing G.L.
Published: April 2011

The transformation of transition aluminas (i.e. θ-A12O3) to α-A12O3 results in an interconnected, porous microstructure that is commonly described as ‘wormy’ or‘vermicular’. The effect of heat generated during the exothermic transformation at the θ-Al2O3/α-Al2O3 interface on the development of the vermicular α-A12O3 morphology was analyzed in boehmite-derived thin films. The vermicular structure may arise in an analogous manner to the thermal dendrites formed in metals during solidification. However, the analysis shows that heat generation and transfer at the interface does not play a significant role in the development of α-A12O3 dendrites.
Boehmite and Yttrium Oxide Coatings on Silicon Nitride From Aqueous Sols
Authors: Buchta Michael , Shih Wei-Heng
Published: April 2011

To improve the processing of silicon nitride, boehmite and yttrium oxide were coated on silicon nitride particles by an aqueous sol-gel method. It is shown that boehmite and Y2O3 can be coated on Si3N4 particles from aqueous solutions. However, the Y2O3 coating is not as complete as boehmite coating. The coating of a yttria coating followed by a boehmite coating was attempted and the TEM showed a coating twice as thick as the Y2O3 or AlOOH coating. Hydrothermal treatment of yttrium nitrate hydrous hydroxide results in the formation and growth of Y(OH)3 fibers which can be calcined and transformed into Y2O3 fibers at 500°C.
Dielectric and Ferroelectric Properties of Pulsed Laser Deposited Strontium Barium Niobate Thin Films
Authors: Liu Y. , Ong C.W. , Choy C.L. , Chan P.W.
Published: April 2011

The dielectric and ferroelectric properties of pulsed laser deposited strontium barium niobate (SBN) thin films were investigated. The samples were prepared using a Q-switched Nd:YAG laser with a wavelength of 355 nm and a fluence of 8 J cm−2. The oxygen ambient pressure and substrate temperature were set at 50 mTorr and 700 °C, respectively. The measurements of x-ray diffraction show that the films have tungsten-bronze- type structure. Pt/SBN/Pt capacitor structure was made on (111) silicon wafer to perform the ferroelectric and dielectric measurements. From the observations of the P-E loops, the saturation polarization, remanent polarization and coercive field at 25°C are equal to 40.7 μC cm−2, 32.5 μC cm−2 and 3.8 kV cm−1. The shape of the P-E loop becomes slimmer at temperatures above 150 °C, indicating that a ferroelectric-to-paraelectric transition occurs. The dielectric constant and loss tangent of the films at 10 kHz were found to be equal to 240 and 0.4, respectively. The saturation and remanent polarization remain almost unchanged after 109 switching cycles, indicating that pulsed laser deposited SBN films have good fatigue endurance.