bluuebunny/crossref_metadata_2025 huggingface dataset:
High Efficiency Monolithic Multi-Junction Solar Cells Using Lattice-Mismatched Growth
Authors: Hoffman R.W. , Fatemi N.S. , Stan M.A. , Jenkins P. , Weizer V.G. , Scheiman D.A. , Brinker D.J.
Published: April 2011

The demand for spacecraft power has dramatically increased recently. Higher efficiency, multi-junction devices are being developed to satisfy the demand. The multi-junction cells presently being developed and flown do not employ optimized bandgap combinations for ultimate efficiency due to the traditional constraint of maintaining lattice match to available substrates. We are developing a new approach to optimize the bandgap combination and improve the device performance that is based on relaxing the condition of maintaining lattice match to the substrate. We have designed cells based on this approach, fabricated single junction components cells and tested their performance. We will report on our progress toward achieving beginning-of-life AMO multi-junction device conversion efficiencies above 30%.
Creep Mechanisms of Fully-Lamellar TiAl Based Upon Interface Sliding
Authors: Hsiung L. M. , Nieh T. G.
Published: April 2011

Deformation mechanisms of fully lamellar TiAl with a refined microstructure (γ lamellae: 100 ∼ 300 nm thick, α2 lamellae: 10 ∼50 nm thick) crept at 760°C have been investigated. As a result of a fine structure, the motion and multiplication of lattice dislocations within both γ and α2 lamellae are limited at low creep stresses (< 400 MPa). Therefore, the glide and climb of lattice dislocations are insignificant to creep deformation. The cooperative motion of interfacial dislocations on γ/α2 and -γ/γ interfaces (i.e. interface sliding) is proposed to be the dominant deformation mechanism at low stresses. Lattice dislocations impinged on lamellar interfaces are found to be the major obstacles impeding the motion of interfacial dislocations. The number of impinged lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations along the interfaces. Accordingly, deformation twinning activated by the pileup of interfacial dislocations is proposed to be the dominant deformation mechanism at high stresses (> 400 MPa).
Plastic Deformation of Ni3Nb Single Crystals
Authors: Hagihara Kouji , Nakano Takayoshi , Umakoshi Yukichi
Published: April 2011

Temperature dependence of yield stress and operative slip system in Ni3Nb single crystals with the DOastructure was investigated in comparison with that in an analogous L12structure. Compression tests were performed at temperatures between 20 °C and 1200 °C for specimens with loading axes perpendicular to (110), (331) and (270).

(010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {211} <107 13> twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 °C and 800 °C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni3Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L12-type compounds.
Microstructural Development of Mo(ss) + T2 Two-Phase Alloys
Authors: Sakidja R. , Wilde G. , Sieber H. , Perepezko J. H.
Published: April 2011

The microstructure evolution involving Mo-B-Si as-solidified alloys with compositions in the Mo solid-solution(ss) + T2 two-phase field has been examined following arc-melting and rapid solidification processing (RSP). Several solidification pathways in the arc-melted alloys have been identified. Compositional segregation during conventional solidification results in the formation of additional phases such as borides in the arc-melted alloys which require a prolonged solid-state annealing to obtain equilibrated two-phase microstructures. The RSP methods employed, splat-quenching (SQ) and powder drop tube processing (DTP), allow for significant microstructural modifications that facilitate the attainment of uniform dispersions of Mo(ss) phase in a T2 phase matrix.
Low Temperature Deformation Kinetics of Ruthenium Aluminide Alloys
Authors: Lu D. C. , Pollock T. M.
Published: April 2011

The kinetics of low temperature deformation were investigated in several different polycrystalline RuAl alloys with the use of strain rate change experiments at 77 K and 298 K. Compositions investigated include RuAl, RuAl+0.5%B, Ru51.5 A48.5, Ru52 Al48, RU53 A147+0.5%B, Ru54.5 Al45.5, and Ru52 Al43 Sc5. Flow stresses did not vary substantially with temperature between 77 K and 298 K. Rate sensitivities were low compared to other B2 compounds and similar in all compositions investigated. Analyses of dislocation substructures after low strain deformation were conducted. The deformation kinetics and substructural observations suggest a higher intrinsic deformability for RuAI alloys with respect to the other high temperature B2 aluminides.
Microstructure, Creep and Fracture Toughness of Directionally Solidified NiAl/(Cr,Mo) Alloys Modified with Hf, Si, Ta, Ti Additions
Authors: Locci I. E. , Raj S. V. , Whittenberger J. D. , Salem J. A. , Keller D. J.
Published: April 2011

A statistical design of experiments (DOE) strategy was implemented to optimize alloys based on the Ni-33AI-31Cr-3Mo eutectic system using small amounts of potential strengthening elements (Hf, Si, Ta, Ti). Following the analysis of the DOE results, several alloys were selected for directionally solidification (DS) utilizing a modified Bridgeman technique. The as-grown alloys were microstructurally examined by optical and scanning electron microscopy. They were also evaluated for fracture toughness at room temperature and compressive properties at 1300K. The microstructures and mechanical properties of these DS DOE alloys are discussed and compared to the directionally solidified Ni–33Al–3lCr–3Mo base composition.
Microstructural Evaluation During Mechanical Milling and Consolidation of ODS LI2-(AI,Cr)3Ti
Authors: Saage H. , Heilmaier M. , Eckert J. , Schultz L.
Published: April 2011

The effect of different oxide particles on the microstructure and the high temperature creep behavior of ODS ternary L12-(Al,Cr)3Ti intermetallic compounds, which were prepared by high energy ball milling, was analyzed. Particular attention was paid to the development of the dispersoid size and distribution after the milling process, the consolidation and the heat treatment.

X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the as-milled powders indicate that the ordered matrix can nearly be amorphizied during milling. Moreover, independent of the type of oxide the dispersoids with a mean diameter ≤ 20 nm are homogeneously distributed in the metallic matrix. Using hot pressing under protective atmosphere the powders were compacted to nearly full density, followed by heat treatment. This results in grain sizes varying between 200 nanometers and several micrometers. However, due to the nature of the dispersoids used different particle diameters were found after consolidation and annealing. Although known to be the thermodynamically most stable oxide the initial Y2O3powder has formed a mixed yttrium-aluminum oxide during manufacturing and, hence, significant particle growth has been observed. While CeO2shows a similar behavior, the line compound A12O3remains stable, but the average particle size of this oxide also increases during the heat treatment. First preliminary mechanical tests supported by TEM observations show the significant influence of the grain size on the creep resistance at high temperatures.
An Explanation for the Environmental Sensitivity of Ni3Al
Authors: Lillig D. B. , Legzdina D. , Robertson I. M. , Birnbaum H. K.
Published: April 2011

Secondary Ion Mass Spectrometry has been used to study the distribution of elements in and near grain boundaries in boron-free and boron-doped Ni76Al24 alloys with and without ∼220 wt. ppm of deuterium. In boron-free alloys, sulfur was distributed about the grain boundaries in both deuterium- free and deuterium-charged samples. The distribution of deuterium followed that of sulfur and was segregated to grain boundaries. In the boron-doped material, sulfur was not found at most grain boundaries in the uncharged material, but was in the charged material. No deuterium was found at the grain boundaries in the boron-doped material. It is proposed that in the boron-free material it is the synergistic effect of sulfur and hydrogen that is responsible for the environmental sensitivity of this alloy. In boron-doped material, boron segregation to the grain boundary prevents sulfur, and to some extent hydrogen, segregating to the grain boundary.
Effect of Nb Content and Temperature on the TiN Formation During the Oxidation of Ti3Al
Authors: Zhang Lanting , Wu Jiansheng , Jiang Kai , Wang Fei
Published: April 2011

Nb addition to Ti3Al has been found to be effective to improve its oxidation resistance. Recently, the beneficial effect of nitrogen in the oxidation behaviour of Nb contained T3AI-based alloys has been noticed. In this paper, the oxidation behaviour of five alloys with different Nb content from 0 to 20 at. % exposed in room air at different temperatures (from 600 to 950,C) has been examined with the focus on the TiN formation in the oxide scale. No TiN is detected in the scales of binary Ti3Al under all temperatures tested. On the contrary, in alloys containing Nb, TiN is identified in the scales irrespective of the oxidation temperature. The amount of TiN formation differs with differentNb content. EPMA analysis of the cross section of the scales is performed and discussion is made accordingly.
Creep of Mechanically-Alloyed NiAl Containing 13 Vol % Mo or Mo2C Dispersoids
Authors: Lakki A. , Dunand D. C.
Published: April 2011

Dispersion-strengthened nickel aluminide NiAl was synthesized by reactive mechanical alloying from elemental powders. The microstructure and creep properties of these materials was compared for two cases: (i) NiAl-Mo, where dispersoids are in the form of a ductile, metallic phase and (ii) NiAl- Mo2C, where the dispersoids are a brittle, ceramic phase. Also, the effect of annealing treatments which coarsened both matrix grains and dispersoids was investigated. Inhibited diffusional creep is identified as the rate-controlling creep mechanism.
Glide Mechanisms of <001> Dislocations in NiAl
Authors: Caillard D.
Published: April 2011

The glide properties of <001> dislocations have been studied by in situ straining experiments at and below room temperature, with the aim of studying slip, cross-slip, Peierls friction forces, and pinning at small obstacles. Most results are in a good agreement with atomistic calculations. It is concluded that unpinning from small extrinsic obstacles is probably the rate controlling mechanism in this temperature range and in the soft orientation.
Deformation Behavior And Internal Stress Of Icosahedral Al-Pd-Mn With Decagonal Phase Lamellae At Elevated Temperatures
Authors: Hirai H. , Tomita T. , Yoshida F. , Nakashima H.
Published: April 2011

Fine decagonal phase lamellae-bearing icosahedral Al-Pd-Mn quasicrystals were tested compressionally at temperatures of 997 to 1073 K and initial strain rate of 3 × 10−5. to I × 10−4 S−1, and stress relaxation tests were performed at various stages of deformation. The results confirmed the thermally activated nature of deformation, and the stress exponent of strain rate was around 4. Internal stress for deformation estimated by Kikuchi's method reached 50 to 90 % of applied stress. The effective stress exponent of strain rate was revealed to be about 1.3. At least a part of high internal stress was attributable to complicated dislocation microstructure.
On The Thermoelectric Power And Transport Properties Of Quasicrystals
Authors: Cyrot-Lackmann F.
Published: April 2011

Stable quasicrystals exhibit specific and unusual physical properties, such as, diamagnetism, low electrical conductivity, low thermal conductivity, and large themoelectric power at room temperature. These properties can be understood with a Bragg's reflexions scheme due to their dense filled reciprocal space.This leads to small gaps on the Fermi surface (some tenths of eV), much narrower than the usual Hume-Rothery ones (of order of 0.5 eV) which explain their stability. These gaps lead to the existence of quasi Umklapp processes, crucial for the interpretation of thermoelectric power. In some cases, the positive phonon drag contribution due to Umklapp processes, add with the electronic one's and dominates at room temperature with a large positive thermoelectric power. A crude estimate of the figure of merit gives some hope for applications of some quasicrystals and high approximants as new thermoelectric materials.
Thermal And Electronic Properties Of An AICoFeCr Approximant Of The Decagonal Phase
Authors: Archambault P. , Plaindoux P. , Belin-Ferre E , Dubois J. M.
Published: April 2011

We have studied the dependence versus nominal composition and temperature of the thermal conductivity in the AlCoFeCr system close to the region where an approximant of the decagonal phase forms. This compound of the Al5Co2type shows a melting temperature above 1100°C and is of interest because it dispays low thermal conductivity whereas its expansion coefficient is comparable to those of metallic substrates. Used as a coating, it is of potential value for the sake of producing thermal barriers. From a study of the occupied band by X-ray emission spectroscopy, we show that its poor thermal conductivity above room temperature fits with the recurrent localization scheme of electronic states.
Measurements Of The Hydrogen Absorption Pressurecomposition Isotherms IN Ti/Zr-Based Quasicrystals
Authors: Kim J. Y. , Majzoub E. H. , Gibbons P. C. , Kelton K. F.
Published: April 2011

The first hydrogen absorption pressure-composition isotherms (p-c-T) were measured in quasicrystalline Ti45Zr38Ni17. No evidence for a pressure plateau was found, indicating a distribution of energies for the hydrogen in interstitial sites. Fits to the p-c-T data confirmed this, giving energy peaks at -0.19 eV with a full width at half maximum (half-width) of 0.06 eV, and at -0.09 eV with a half-width of 0.08 eV. This is in contrast with the broad site energy distribution that is characteristic of a metallic glass. In agreement, fits to data taken from amorphous Ti45Zr27Ni20Si8 gave a single broad energy distribution at -0.10 eV with a half-width of 0.35 eV. Based on the weighted averages of the site energies for the pure components, the energies assigned to the tetrahedral sites in the Ti44Zr40Ni16 1/1 approximant phase are in qualitative agreement with the measured data for the quasicrystal, supporting a local structural similarity between these two phases. Almost all of the absorbed hydrogen can be desorbed at 650°C in one hour by pumping, without transforming the quasicrystal phase and without powdering the rapidly-quenched samples.
Holographic Grating Formed by Photochemical Phase Transition of Polymer Azobenzene Liquid Crystal
Authors: Yamamoto T. , Yoneyama S. , Hasegawa M. , Kanazawa A. , Shiono T. , Ikeda T.
Published: April 2011

We explored the formation of holographic gratings by means of a polymer azobenzene liquid crystal (PALC). When two writing beams (argon-ion laser, 488 nm, unpolarized) were interfered on the surface of the PALC film (thickness, 500 ∼ 600 nm), multiple diffraction beams were observed immediately, resulting from grating formation. Such generation of the diffraction beams was assumed to be due to a periodic induction of photochemical phase transition in the bright fringes of the interference pattern. The grating is namely made up of a periodic arrangement of nematic (N, dark fringes) and isotropic (I, bright fringes) phases. Observation of recorded interference patterns under a cross-polarized optical microscope supported our speculation for the structure of the grating. On the basis of these results, we succeeded in recording an image hologram of a photomask as an object.
Two-Dimensional Superlattice Self-Formed by Novel Ionic Liquid Crystals and Its Photofunctional Property
Authors: Kanazawa A. , Ikeda T.
Published: April 2011

Thermotropic liquid-crystalline behavior of various complex salts, which are structurally simple amphiphiles without rigid cores, was evaluated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. The phosphonium salts, consisting of positive phosphorus and negative chloride ions, were found to show a smectic A phase in which a homeotropic structure was formed spontaneously. It is significant that the phosphonium salts possess an advantageous feature as thermotropic liquid crystals and show a stable liquid-crystalline phase and a simple phase transition behavior in comparison with commonly available ammonium analogs. Furthermore, the introduction of divalent metal ions into the amphiphiles was revealed to result in enhancement of the thermal properties. Although the ammonium chlorides as parent compounds showed no liquid-crystalline phase (or indistinct transition behavior), the ammonium complexes possessing tetrachlorometalate ions exhibited clearly the smectic A phase in the expanded temperature range. Additionally, through the evaluation of dipolar alignment in the solid-state phosphonium assembly by second harmonic generation, it was assumed that the self-assembly can be regarded as layered polar thin films produced by two-dimensional ionic layers with an overall permanent electric polarization.
Electrooptic Characteristics of Polymer Stabilized Flcd: Application to field Sequential Fullcolor Display
Authors: Takahashi T. , Furue H. , Miyama T. , Shikaday M. , Kurihara R. , Kobayashi S.
Published: April 2011

Liquid crystal displays (LCDs) will be classified into miniature display, reflective type, projection type, direct view type, and holography type. All of these LCDs will be widely utilized in the coming multimedia network era. Along with this trends, in the first part of this paper we will discuss the social background of this research. In this paper we will place an emphasis on a polymer stabilized (PS) FLCD that is featured by fast response speed (40 µsec), high contrast (230:1) with grayscale, wide viewing angle, and high resolution (4001p/mmn). The PS-FLCD, which is referred to as Liquid Crystal Optical Diode owing to its strong asymmetric electrooptical characteristics, will be a promising technology for displaying a moving video image, and optical computing.
Microstructure and Surface Structure Evolution in AlCu Polycrystalline Thin Films
Authors: Lita Adriana E. , Sanchez John E.
Published: April 2011

The evolution of crystallographic texture, grain size and surface morphology in magnetron sputter deposited Al-0.5wt.% Cu polycrystalline thin films is reported as a function of film thickness for SiO2 and SiO2/Ti underlayers for several deposition rates. Regardless of the underlayer type, the initial ≈ 10 nm of the Al-Cu films is nearly randomly oriented, with the films developing a (111) out-of-plane texture which increases in strength with thickness during deposition. The AlCu films on sputtered Ti underlayers developed an exact (111) fiber orientation while Al-Cu films on oxide substrates were offset ≈ 5° from exact fiber orientation. Higher deposition rates were found to result in slightly better (111) textured 20 nm AlCu films. The surface morphology of films, determined by Atomic Force Microscopy (AFM), revealed two regimes of average roughness (Rrms) evolution during deposition. Rrms decreased early in the deposition process, followed by a roughening regime where Rrms increased with thickness. These results are discussed in terms of mechanisms such as grain growth, which help to determine microstructure development during film formation from the vapor.
Magnetic Anisotropy in Electrodeposited CO Films and spin-valves on Gaas Substrates
Authors: Attenborough K. , Cerisier M. , Boeve H. , De Boeck J. , Borghs G. , Celis J.-P.
Published: April 2011

We have studied the magnetic and structural properties of thin electrodeposited Co and Cu layers grown directly onto (100) n-GaAs and have investigated the influence of a buffer layer. A dominant fourfold anisotropy with a uniaxial contribution is observed in 10 nm Co electrodeposited films on GaAs. An easy axis is observed in the [001] GaAs direction with two hard axes of differing coercivities parallel to the [011] and [011] directions. For thicker films the easy axes in the [001] direction becomes less pronounced and the fourfold anisotropy becomes less dominant. Co films of similar thicknesses deposited onto an electrodeposited Cu buffer layer were nearly isotropic. From X-ray diffraction 21 nm Co layers on GaAs were found to be hcp with the c-axis tending to be in the plane of the film. The anisotropy is ascribed to the Co/GaAs interface and is held responsible for the unique spin-valve properties seen recently in electrodeposited Co/Cu films.
Characterization of Slurry System and Suppression of Oxide Erosion in Aluminum CMP (Chemical-Mechanical Planarization)
Authors: Zhong Lei , Yang Jerry , Holland Karey , Grillaert Joost , Devriend Katia , Heylen Nancy , Meuris Marc
Published: April 2011

In this work, we investigated the dependence of the removal rate upon the oxidizer (peroxide) addition into commercially available slurries for a variety of films such as aluminum, titanium, titanium nitride and oxide. We found that the barrier layer materials were extremely sensitive to the peroxide addition while the removal rate varied only slightly for aluminum and oxide. The selectivity to titanium and titanium nitride drops from as high as 1000 to almost close to 1 as the mixture ratio (peroxide : slurry) increases. We proposed that the barrier layer be used to protect the oxide from being over-exposed and suppress the erosion eventually. This can be easily realized by dividing the process into two steps with each step being run at a specific peroxide mixture ratio. The experimental result unambiguously proved, for the first time, the effectiveness of this approach.
Pattern Dependent Modeling for CMP Optimization and Control
Authors: Boning D. , Lee B. , Oji C. , Ouma D. , Park T. , Smith T. , Tugbawa T.
Published: April 2011

In previous work, we have formalized the notions of “planarization length” and “planarization response function” as key parameters that characterize a given CMP consumable set and process. Once extracted through experiments using carefully designed characterization mask sets, these parameters can be used to predict polish performance in CMP for arbitrary product layouts. The methodology has proven effective at predicting oxide interlevel dielectric planarization results.

In this work, we discuss extensions of layout pattern dependent CMP modeling. These improvements include integrated up and down area polish modeling; this is needed to account for both density dependent effects, and step height limits or step height perturbations on the density model. Second, we discuss applications of the model to process optimization, process control (e.g. feedback compensation of equipment drifts), and shallow trench isolation (STI) polish. Third, we propose a framework for the modeling of pattern dependent effects in copper CMP. The framework includes “removal rate diagrams” which concisely capture dishing height and step height dependencies in dual material polish processes.
PCA Characterization of Residual Subsurface Damage After Silicon Wafer Mirror Polishing and its Removal
Authors: Ogita Y. , Kobayashi K. , Daio H.
Published: April 2011

Residual subsurface damages introduced by mirror polishing into Si CZ wafers degrade GOI in ULSI MOS devices. A removal of the damage throughout 9 times SC1 cleaning was systematically characterized as correlated between PCA signals measured by noncontact UV/mmwave technique, GOI at 10MV/cm for MOS diodes with a thin gate-oxide thickness of 10nm, surface microroughness Ra measured by AFM. The same characterization was carried out for epitaxial wafers, as reference. Degraded GOI and PCA signal were recovered throughout 3 times SC1 cleaning and did not depend on Ra of 0.1–0.2 nm, which led to that the damage causes the degradation of GOI, but it can be removed by 3 times SC1 cleaning, and the damage depth was about 21nm. Further, the PCA signal well reflects to removal of the damage and degradation of GOI so that it can be a monitor for characterizing the removal and GOI. Direct observation of the damage using OSDA was carried out for the epitaxial wafer polished and SC1 cleaned. The OSDA indicated an image involving straight lines which disappeared after 3 times SC1 cleaning. This gave a direct evidence for catching up it by PCA and existence of residual subsurface damages.
Tribological Experiments Applied to Tungsten Chemical Mechanical Polishing
Authors: Bielmann Marc , Mahajan Uday , Singh Rajiv K. , Agarwal Pankaj , Mischler Stefano , Rosset Eric , Landolt Dieter
Published: April 2011

Tungsten CMP involves a synergistic interaction of electrochemical and tribological (wear) phenomena. So far, numerous studies have been conducted using static electrochemical measurements as well as some polishing experiments. In this study, we present some results obtained from carrying out potentiodynamic measurements and tribological experiments in a reciprocating sphere-on-plate tribometer, which allowed a precise control of mechanical and electrochemical conditions. In addition, anodic current-time transient measurements were also used to characterize the kinetics of tungsten passivation reaction. These results indicate that the presence of an passive film is essential for wear of tungsten to take place.
Long Range Order in Ultra-Thin SiO2 Grown on Ordered Si(100)
Authors: Hurst Q.B. , Herbots N. , Shaw J.M. , Floyd M.M. , Smith D.J. , Culbertson R.J. , Grams M.P. , Bradley J.D. , Zimmerman P , Atluri V.
Published: April 2011

In this paper, we investigate the correlation of electrical properties and structure of 1-4 nm thick SiO2 grown on H-passivated Si(100) for ultra-thin gate applications. Ordered (1×1) Si(100) stable in ambient air is obtained at room temperature by wet chemical cleaning. Ion Beam Analysis using a combination of ion channeling and 16O(α,α)16O nuclear resonance yields Si areal densities lower than that of a bulk-terminated Si crystal as calculated by Monte-Carlo simulations. This result indicates shadowing of Si substrate atoms by Si atoms in the thermally grown oxide. Detection of order by ion channeling is supported by Reflection High Energy Electron Diffraction (RHEED). C-V and I-V measurements are generally inconclusive for ultra-thin (1-2 nm) oxides because of leakage and breakdown. Surface charge analysis enables a comparison between ordered oxides and conventional oxides. The results are promising.
Atomic Scale Modeling of the Silicon (100) Thermal Oxidation, A Kinetic Monte Carlo Approach
Authors: Esteve A. , Rouhani M. Djafari , Faurous Ph. , Esteve D.
Published: April 2011

In this paper, we propose an original approach of the silicon (100) dry thermal oxidation modeling that is capable to reproduce the oxidation dynamics at the atomic level and at a large scale comparing with ab initio methods. This approach is based on the use of a Monte Carlo procedure to manage the temporal aspect. In conjunction with experimental literature data, first principle calculations have been carried out with the objective of isolating some elementary oxidation mechanisms, i.e. basic atomic movements and their corresponding energies. This preliminary list of mechanisms is discussed in detail. A growth mechanism allowing the oxide defect generation is proposed. Finally, we present Monte Carlo calculations with the implemented mechanisms where at least three silicon layers are oxidized.
Measuring Interface State Distributions in Ultra-Thin Mos Capacitors with Direct Tunnel Current Leakage
Authors: Song H. , Farmer K. R.
Published: April 2011

Using a leakage-compensated charge (LCCV) technique to obtain static capacitance-voltage (C-V) curves, we extend the standard high-low C-V method for determining the interface state level density, Dit as a function of energy in the silicon band gap to metal-oxide-silicon capacitors in the direct tunneling regime (oxide thickness ∼<3.5 nm). The LCCV technique yields true static C-V curves for oxides at least as thin as 2.8 nm, where the tunnel leakage current is so high that the usual quasistatic C-V measurement is not possible. As applications of this method, Dit is compared for fresh oxides of different tunnel thickness, and Dit is measured before and after constant voltage stress of a 3.5-nm oxide. The stress results indicate, as in other work on thicker oxides, that interface traps are created during the stress, with peak densities both below and above midgap. This approach is expected to be useful for evaluating both ultra-thin oxides and leaky alternate gate dielectrics.
Remote Plasma Enhanced-Metal Organic Chemical Vapor Deposition of Zirconium Oxide/Silicon Oxide Alloy, (ZrO2)1-(SiO2)1−x (x:≤0.5), Thin Films for Advanced High-K Gate Dielectrics
Authors: Wolfe D. , Flock K. , Therrien R. , Johnson R. , Rayner B. , Günther L. , Brown N. , Claflin B. , Lucovsky G.
Published: April 2011

A remote plasma enhanced-metal organic chemical vapor deposition (RPE-MOCVD) process was developed for the preparation of non-crystalline (ZrO2)x-(SiO2)1−x (x ≤ 0.5) alloys, targeting the compound composition ZrSiO4with k ∼ 12.5. Shifts in Si LVV and Zr LMM AES energies with respect to elemental values showed that the deposited film was a fully-oxidized zirconium/silicon alloy. FTIR results were consistent with AES, and a Zr-O-Si bonding mode was identified in the spectra. The films were amorphous before and after RTA at 900°C for 30 sec, as monitored via RHEED. Optical absorption measurements indicated the onset of band-to-band transitions at an energy of approximately 6 eV. Finally, C-V testing showed that the films were insulating.
Fabrication of Ta2O5 Thin Films by Anodic Oxidation of Tantalum Nitride and Tantalum Silicide: Growing Mechanisms, Electrical Characterization and ULSI M-I-M Capacitor Performances
Authors: Dueñas S. , Castán H. , Barbolla J. , Kola R.R. , Sullivan P.A.
Published: April 2011

In this work we report on tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide to be used as the dielectric of Metal-Insulator-Metal (MIM) capacitors. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Several counter and bottom electrodes have been used and compared. The effects of the different processing conditions (top-electrode metals, annealing conditions, bottom electrode stoichiometry and precursor) on the capacitor performances are extensively discussed throughout this work. The electrical behavior of the resulting high-density MIM capacitors has been extensively characterized. Finally, we propose a set of selection guides to select the more appropriate process parameter values and electrode materials for a given application of these capacitors.
H8Si8O12 Clusters on Si(100)-2×l and Gold: A Comparative Infrared Spectroscopic Study
Authors: Nicholson Kenneth T. , Biscotto Mark A. , Holl Mark M. Banaszak
Published: April 2011

Reflection-absorption infrared data are presented for H8Si8O12 clusters chemisorbed to Si(100)-2×1 and evaporated gold surfaces. Peak assignments and the implications of the local symmetry imposed upon the cluster by the surface are discussed.
On the Influence of Boron-Interstitial Complexes on Transient Enhanced Diffusion
Authors: Stiebel D. , Pichler P. , Ryssel H.
Published: April 2011

We present new experimental results on the transient enhanced diffusion (TED) of boron after ion implantation. The investigation is focussed on effects that influence TED of shallow profiles in the absence of {311}-defects. Under these conditions, TED is mainly determined by the formation of boron-interstitial complexes (BIC). In addition, effects from the proximity of the surface become more and more important. Insight into the behavior of the dopant atoms is obtained by the comparison with simulations.
Non Destructive Profile Measurements of Annealed Shallow Implants
Authors: Borden Peter , Niimeiier Regina , Lingel Karen
Published: April 2011

Controlling the profile of shallow doped layers is critical for obtaining desired performance from deep sub-micron devices. An especially difficult challenge is measuring depth uniformity of the activated implant over the full area of a wafer.

This paper demonstrates the capabilities of a new rapid, non-contact optical technique for measuring active doping depth of shallow implants. Employing a 2 Pim spot size, it provides a measurement of fine-scale spatial uniformity in dimensions approaching those of individual devices. By measuring multiple sites, it can rapidly characterize uniformity over large areas and edge-to-edge, without an edge exclusion zone.

Data will be presented showing performance on layers varying in depth from 200 to 1200 Å. Edge-to-edge diameter scans on 8” wafers with le15, B11 implants at energies in the range of 200 to 2,000 eV and various RTA temperatures show radially symmetric uniformity patterns of depth and edge effects in the outermost centimeter. Measurements are validated based on correlation to spreading resistance profiles for a number of samples.
Temperature- and Time-Dependence of Boron-Enhanced Diffusion From Evaporated- and Ultra-Low Energy Ion-Implanted Layers
Authors: Agarwal Aditya , Gossmann H.-J. , Eaglesham D. J.
Published: April 2011

Silicon layers containing B in excess of a few atomic percent create a supersaturation of Si self-interstitials in the underlying Si, resulting in enhanced diffusion of B in the substrate (boron-enhanced diffusion, BED). The temperature- and time-dependence of BED is investigated here. Evaporated-boron as well as ultra-low energy 0.5-keV B-implanted layers were annealed at temperatures from 1100 to 800°C for times ranging from 3 to 3000s. Isochronal 10s anneals reveal that the BED effect increases with increasing temperature up to 1050°C and then decreases. In contrast, a simulation of interstitial generation via the kick-out mechanism predicts a decreasing dependence on increasing temperature leading to the conclusion that the kick-out mechanism is not the dominant source of excess interstitials responsible for BED. The diffusivity enhancements from the combined effects of BED and TED (transient-enhanced diffusion), measured in 2×105cm−2, 0.5-keV B-implanted samples, show a similar temperature dependence as seen for evaporated B, except that the maximum enhancement occurs at 1000°C. The temperature-dependent behavior of BED supports the hypothesis that the source of excess interstitials is the formation of a silicon boride phase in the high B concentration silicon layer.
Sub-30 nm abrupt P+ junction formation with Ge preamorphization and high energy Si Co-implantation
Authors: Lee K. L. , Zabel Ted , Kozlowski Paul M. , Viswanathan Raman , Chen Kai
Published: April 2011

Experiments have been caried out to form ultra-shallow (Xj <50nm) and abrupt (Xjs < 5nm/decade) P'junction for sub-50 nm CMOS devices using a combination of shallow implant, Ge preamorphization and high energy Si implant as an interstitial getter layer. Experimentally, it was observed that the Si getter layer, not only stopped the TED at the boron tail but also promoted enhanced diffusion close to the surface boron peak. These unique features have enabled the shallowest and sharpest box-like boron junction yet achieved by implant. With I kV BF2, Xj ∼ 23 nm, Xjs ∼ 48 A/decade, no Ge end of range damages and good dopant activation at the same time.The sheet resistance ρ − 1 kohm/sq is comparable to shallow BF2 + Ge and is better than the shallow BF 2 alone (ρ ∼ 2.38 kΩ/sq) or the shallow BF2 + Si implants (ρ ∼ 1.5 kohm/sq). Tests with device leakage test structures show that there is no additional junction leakage introduced by the Si getter layer.
In-Situ High Temperature Optical Microscopic Observations of Crystallization Mechanism in NdBa2Cu3Ox
Authors: Aswal D.K. , Shinmura M. , Hayakawa Y , Kumagawa M.
Published: April 2011

The pseudo-binary NdBa2Cu3O-Ba3Cu10O13phase diagrams and the crystallization of NdBa2Cu3Ox have been in-situ observed using high-temperature optical microscopy in air and under three different reduced oxygen atmospheres namely, 1%, 0.1% and 0.0097% oxygen in argon. The liquidus line was found to become narrower both in composition and temperature with reducing oxygen content in the atmosphere. These results suggested that while in air NdBa2Cu3Ox can be crystallized from both high-temperature solution and peritectic melt; under reduced oxygen atmospheres the crystallization of NdBa2Cu3Ox is only possible from a peritectic melt. The in-situ observations of crystallization of NdBa2Cu3Ox from high-temperature solutions revealed that the growth mechanism changes from 3D via 2D layer-by-layer to continuos dendritic growth with increasing cooling rate. On the other hand, the NdBa2Cu3Ox crystallization from a peritectic melt involved two distinct steps (i) conversion of Nd4Ba2Cu2Ox into NdBa2Cu3Ox and (ii) nucleation and growth of NdBa2Cu3Ox The growth morphology in this case was independent of the cooling rate. This result and the direct observation of the dissolution of Nd4Ba2Cu2Ox into the liquid suggested that the solute diffusion is the rate-limiting factor.
In Situ Design of Experiments for A Reactive Ion Etching Process
Authors: Galarza Cecilia G. , Klimecky Pete , Khargonekar Pramod P. , Terry Fred L.
Published: April 2011

We introduce a new procedure to perform a design of experiments (DOE) for plasma etching processes. In particular, we use in situ etch rate estimations to maximize the number of observable setpoints during a single run of the etching process. This procedure is applied to characterize the spatial uniformity of a plasma chamber used in the manufacturing of flat panel displays.
Real-Time Spectroscopic Ellipsometry Study of the Thermal Cleaning Process for Silicon Epitaxial Growth by UHV-CVD
Authors: Nozawa K. , Katayama K. , Kanzawa Y. , Sugahara Q. , Saitoh T. , Kubo M.
Published: April 2011

Real-time spectroscopic ellipsometry (RTSE) method was applied to study thermal cleaning process of silicon surfaces for epitaxial growth by ultra-high vacuum chemical vapor deposition (UHV-CVD). For the first time, in-situ observation of oxide decomposition process under Si2H6 ambience was carried out. The substrates with thin oxide formed by wet chemical treatment were heated up by infrared heater under UHV or under Si2H6 ambience in an UHV-CVD chamber and the oxide decomposition processes were observed by RTSE. Ellipsometric parameters Psi and Delta increase with the progress of oxide decomposition process and become constant with the completion of the decomposition. It was found that the oxide decomposition process consists of two phases and rate-determing processes are different in each phase. It was also found that Si2H6 lowers the activation energies of oxide decomposition process in each phase.
In-Situ Spectroscopic Ellipsometry and Optical Emission Studies of CF4/O2 Plasma Etching of Silicon Nitride
Authors: Parent T. , Tie J. , Madhukar A.
Published: April 2011

Electron cyclotron resonance (ECR) CF4/ 02 plasma etching of silicon nitride (SixNy) deposited by plasma enhanced chemical vapor deposition (PECVD) has been examined in-situ by means of spectroscopic ellipsometry (SE) and optical emission (OE). The observed real-time etchrate and the relative intensity of emission of atomic fluorine at 703.7 nm are measured simultaneously and both are found to change with time during the etch in a reproducible manner. The evolution of the real-time etch rate and the fluorine emission intensity depends on the machine input settings and the extent to which the chamber has been exposed to CF4/ 02 plasma prior to sample introduction. In general the initial 10 to 40 seconds of etching reveal a rapid increase in the etch rate, the remainder of the etch exhibiting an etch rate which typically increases gradually until the etch is stopped. This variation in etch behavior with time during the etch process complicates the task of precisely and reliably etching ultrathin (< 50 nm) films, necessitating real-time control based upon in-situ sensors, the end objective of this work. The dependence of the evolution of the SixNy etch rate on microwave power, chamber pressure, and gas in-flow rate is presented and the implications of these dependencies on the implementation of real-time feedback control are discussed.
Atomic Interdiffusion in Amorphous Silicon and Germanium
Authors: Persans P. D. , Ruppert A. F.
Published: April 2011

We present measurements of interdiffusion in amorphous silicon/amorphous germanium compositional multilayer structures using Raman scattering and optical absorption spectroscopies. We find that interdiffusion coefficient D* can be described by D* = Do exp (−ED/kT) with ED = 3.3 eV and Do = 104 cm2s−1. The high value of ED suggests that the diffusion process is substitutional.
Diffusion, Migration and the Atomic Structure of some Grain Boundaries
Authors: Krakow W. , Smith D. A.
Published: April 2011

The atomic structure of representative tilt boundaries in gold has been determined by high resolution transmission electron microscopy. Characteristic and varying regions of decreased density and coordination have been identified and related to mechanisms of grain boundary diffusion and migration
Undercooling of Liquid Germanium
Authors: Devaud G. , Turnbull D.
Published: April 2011

Small liquid germanium (ℓ-Ge) droplets (0.3–0.5mm diameter) have been undercooled in a B2O3 flux a maximum of 415 ± 20°C below Tm before recalescence. Although the droplets undercooled to temperatures well below the temperature expected for metastable equilibrium with amorphous Ge, Taℓ, the solidified structures were always polycrystalline. There was no evidence of a continuous liquid-to-amorphous transition at or below Taℓ. The nucleation frequency was calculated to be ˜8 × 106 /cm 3-sec at the maximum undercooling. This should be an upper limit to the homogeneous nucleation frequency of the crystal phase since we did not establish that the nucleation was homogeneous in our experiments. However, this limiting I for Ge indicates that homogeneous nucleation of the crystal or amorphous phase would not become appreciable in nsec laser pulsing experiments until ℓ-Ge is undercooled to well below Taℓ. The structure of solidified Ge and Ge/Sn alloy droplets indicates that dendritic growth does not occur in Ge until the liquid is undercooled at least 300°C, and in Ge/Sn until the liquid is undercooled at least 250°C. Greater undercoolings lead to increased dendritic breakup, which results in grain refinement in the final structure.
Theoretical Studies of Dark Current of Quantum Dots
Authors: Chang Yia-Chung , Kuo David M. T.
Published: April 2011

A time evolution method is used to compute the electron escape time and dark current of a quantum dot under electric field. We found that for quantum dots with just one bound state, the ground state wave function can be well described by the product of a 2D confined wave function in the x, y plane and a 1D confined wave function in the z direction with an effective quantum well potential. A comparison of phase-shift analysis and the full time-dependent calculation is presented. Good agreement between the two in the large time scale is found, but discrepancy exists in the small time scale. Our study shows that the electron escape rate (which determines dark current) of quantum dots is much lower than that of quantum wells with the same bound-to-continuum transition energy.
Optical Phonons in CdS Nanocrystals: Effects of Size, Shape and Packing Density
Authors: Rolo A.G. , Vasilevskiy M.I. , Gomes M.J.M. , Vikhrova O.V. , Rakovich Yu.P. , Artemyev M.V.
Published: April 2011

Optical vibrations confined in CdS nanocrystals (embedded in a glass film or forming a close-packed film with some organic-molecule links between them) have been studied experimentally, by means of FIR and Raman spectroscopies, and theoretically. The asymmetric Raman lineshape can be modelled considering resonant and non-resonant scattering on spherical modes with 1=0 (those with n>l are responsible for the low-frequency wing). A phonon-related dielectric response of the nanocrystal composites has been studied by measuring FIR reflectivity and transmission spectra. The theoretical consideration consists of the (i) calculation of the single-particle polarisability due to the confined 1=1 modes and (ii) including the dipole-dipole interaction between the particles. We show that, for the smallest particles, the FIR response has a bimodal structure, which disappears as the nanocrystal size increases. However, the experimentally observed bulk-CdS-like reflection band at 230–300 cm−1 is too broad and can not be explained by the model. Only making further assumptions, namely, of a fractal structure of the nanocrystal composites, enables us to fit well the experimental FIR spectra.
Line Shape in Resonance Raman Scattering from Silicon Quantum Dots
Authors: Soni R.K. , Fonseca L.F. , Resto O. , Weisz S.Z. , Tripathy S.
Published: April 2011

We have carried out a resonance Raman study of line-shape in silicon quantum dots synthesized on a quartz substrate by co-sputtering bulk Si and Si02. Optical transmission measurements are used to evaluate dot size distribution. The size distribution shows peaks around 1.0 and 1.4 nm. The Si dots exhibit photoluminescence in the visible region, which shifts to higher energy with decreasing size. The size dependence of Raman scattering shows phonon softening and increasing asymmetrical broadening for small dots (< 2nm). The observed spectra are compared with calculations considering electron-hole interactions at a quasi-direct gap of a spherical quantum dot.
Wafer Bonding Involving Complex Oxides
Authors: Alexe M. , Kopperschmidt P. , Gösele U. , Tong Qin-Yi , Huang Li-Juan
Published: April 2011

The present paper proposes a simple method which may be able to provide true single-crystal films of complex oxides on large substrates including semiconductors like silicon or gallium arsenide. The method describes a layer transfer process using layer splitting by hydrogen implantation and direct wafer bonding (DWB) to obtain single-crystal oxide films on different substrates. Alternatively, a fabrication process of ferroelectric-semiconductor heterostructures based on direct wafer bonding and layer transfer is also described. This process is an alternative method to the direct deposition of oxides films (ferroelectric, high-k) on silicon and allows fabrication of metal oxide-silicon heterostructures with an interface having a good structural quality as well as a low trap density.
Characterization of Retention Phenomena of Micron-Size Electrical Domains in Pzt Thin Films
Authors: Hong Seungbum , Shin Hyunjung , Pak Y. Eugene , No Kwangsoo
Published: April 2011

The retention phenomena of purposely aligned micron-size domains (defined as “bits”) in Pb(Zr,Ti)O3 thin films were characterized by atomic force microscopy (AFM) combined with a lock-in amplifier. It is found that the retention loss occurs by “region by region” showing local variation of the rate of the loss. Furthermore, the total retention loss can be successfully described by an extended exponential decay, which implies a narrow distribution of the relaxation times of the domains. This probably comes from the fact that the micron-size bits consist a few hundreds of domains. Along with the characterization, the effects of the bit size and the poling time per unit area on the retention characteristics were investigated. Based on our observations, it is concluded that the retention time is proportional to both the poling time per unit area and the bit size. This trend is successfully explained by a kinetic model developed by our group.