bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Stress and Elongation of Superplastic Deformation in La55Al25Ni20 Metallic Glass
Authors: Kawamura Y. , Inoue A.
Published: April 2011

We have investigated the flow stress and elongation of superplastic deformation in a La55Al25Ni20 (at%) metallic glass that has a wide supercooled liquid region of 72 K before crystallization. The superplasticity that appeared in the supercooled liquid region was generated by the Newtonian viscous flow that exhibits the m value of unity. The elongation to failure was restricted by the transition of the Newtonian flow to non-Newtonian one and the crystallization during deformation. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expressed very well by a stretched exponential function σflow=Dε exp(H*/RT) [1-exp(E/{ε exp(H**/RT)}0.82)]. Formulations describing the elongation to failure in constant-strain-rate and constant-crosshead velocity tests were, moreover, established. It was found from the simulation that the maximum elongation in the constant-strain-rate test reached more than 106% which was two orders of magnitude larger than that in the constant-crosshead-velocity test.
Analysis of Cavitation in a Near-γ Titanium Aluminide During High-Temperature/Superplastic Deformation
Authors: Lombard Carl M. , Ghosh Amit K. , Semiatin S. Lee
Published: April 2011

The superplastic flow behavior of a near-γ titanium aluminide (Ti-45.5Al-2Cr-2Nb) is determined under uniaxial tension in as-rolled or rolled-and-heat treated conditions (1177°C/4 hr or 1238°C/2 hr). Cavitation characteristics, including cavity growth rates, are established via isothermal, constant strain rate tests conducted at 10−4 to 10−2 s−1 and temperatures between 900°C and 1200°C. Differences in cavitation as a function of initial structure, strain, strain rate and temperature are noted. Cavity growth is found to be largely plasticity controlled. Experimental growth rates are compared with equations that predict rates as a function of strain rate sensitivity. Although the equations assume no coalescence and no nucleation of new cavities, which are experimentally observed, they are useful in predicting actual growth rates.
Stress-Induced Martensite in NiTi Corrugated Films
Authors: Wuttig Manfred , Slutsker J. S. , Mori Kiyotaka , Li Jiang
Published: April 2011

Films deposited on corrugated surfaces develop non-uniform stresses when cooled from the deposition temperature. A disclination model shows that the stresses have rhombohedral and tetragonal components which can preferentially stress induce the martensite variants. The deflection of NiTi/Si bimorphs caused by the formation of martensite should thus be different if the NiTi/Si interface is corrugated or not. Experimental results confirm this expectation.
Energy Absorption and Damping in Magnetostrictive Composites
Authors: Mcknight G. P. , Carman G. P.
Published: April 2011

The mechanical energy absorption characteristics of several polymer matrix Terfenol-D composites were evaluated experimentally. Magnetostrictive composites absorb energy through domain level processes that couple mechanical and magnetic energies. The testing consisted of mechanically cycling the materials at different stress amplitudes (combined compression and tension) at a single frequency. Results indicate that the magnetostrictive composites exhibit a unique combination of high damping properties in conjunction with a relatively high modulus. The measured tan delta values for the materials are functionally dependent upon the stress amplitude. In general, as the stress amplitude increased, the damping or energy absorbed during one cycle decreased. Results also indicate that damping is directionally dependent (i.e. anisotropic) and that bias magnetic fields decrease the energy absorption. The volume fraction of the composites did not play a significant role in the magnitude of damping. This effect may be related to the inherent pre-stress imparted on the particle by the resin during cure.
Dielectric Properties of Highly Oriented Lead Zirconium Titanate Thin Films Prepared by Reactive RF-Sputtering
Authors: Kalpat S. , Du X. , Abothu I.R. , Akiba A. , Goto H. , McKnistry S. Trolier , Uchino K.
Published: April 2011

Highly (100) and (111) oriented lead zirconium titanate (PZT) thin films have been grown by using reactive rf-sputtering. PZT thin films with rhombohedral composition have been grown in different orientations using selective rapid thermal annealing cycles. The polarization versus electric field curves and the resistivity of the films were measured using a standardized RT66A ferroelectric test system. The dielectric constant and the loss were determined using an impedence analyzer. The PZT(100) oriented films showed larger dielectric constant and loss than the PZT(111) films. The PZT(100) films possessed sharper square-like hysteresis loops compared to the PZT(111) films, as expected from our phenomenological calculations.
Shape Memory Alloys–Their Challenge to Contribute to Smart Structures
Authors: Boller C.
Published: April 2011

Shape memory alloys (SMA) have generated a lot of new ideas in engineering. Application is however so far limited to clamps and springs. With respect to smart structures sensing as well as control has to be included. While sensing looks to be relatively feasible control is the big challenge. This paper describes some aerospace related smart structures ideas using SMAs and discusses the challenges which need to be solved before these ideas have can be realised.
A Novel Integrated MEMS Process Using Fluorocarbon Films Deposited With a Deep Reactive Ion Etching (DRIE) Tool
Authors: Ayón A. A. , Chen D.-Z , Khanna R. , Braff R. , Sawin H. H. , Schmidt M. A.
Published: April 2011

Fluorocarbon films are useful as antistiction films for suspended structure and also for electrical isolation purposes. Furthermore, due to their low dielectric constant and ease of deposition they are useful for VLSI manufacturing applications. Thus, in the interest of building a complete database for these plasma generated fluorocarbon films, we report a designed experiment with a 4-variable matrix to fully characterize deposited films using C4F8 as the feed gas in a high density inductively coupled plasma tool. We also demonstrate the in-situ microfabrication of electrostatic actuators that exhibit the corresponding passivation film for electrical isolation. The utilization of these films as a masking material for MEMS applications and in triple nested mask arrangements is also demonstrated.
Temperature-Dependent Coefficient of Thermal Expansion of Silicon Nitride Films Used in Microelectromechanical Systems
Authors: Bargmann Melissa , Kumpel Amy , Tada Haruna , Nieva Patricia , Zavracky Paul , Miaoulis Loannis N. , Wong Peter Y.
Published: April 2011

Microelectromechanical systems (MEMS) have potential application in high temperature environments such as in thermal processing of microelectronics. The MEMS designs require an accurate knowledge of the temperature dependent thermomechanical properties of the materials. Techniques used at room temperature often cannot be used for high-temperature property measurements. MEMS test structures have been developed in conjunction with a novel imaging apparatus designed to measure either the modulus of elasticity or thermal expansion coefficient of thin films at high temperatures. The MEMS test structure is the common bi-layered cantilever beam which undergoes thermally induced deflection at high temperatures. An individual cantilever beam on the order of 100 νm long can be viewed up to approximately 800°C. With image analysis, the curvature of the beam can be determined; and then the difference in coefficient of thermal expansion between the two layers can be determined using numerical modeling. The results of studying silicon nitride films on silicon oxide are presented for a range of temperatures.
Porous Silicon as a Sacrificial Material for Microstructures Fabrication
Authors: Morel M. , Berre M. Le , Lysenko V. , Delhomme G. , Dittmar A. , Barbier D.
Published: April 2011

Porous silicon (PS) is generated by electrochemical etching in hydrofluoric acid (HF). Recently porous silicon has been applied to micromachining and micro-devices as an alternate material, this material being used as a sacrificial layer. This technology competes with conventional techniques like surface and bulk micromachining regarding its speed, simplicity and reduced costs. A wide range of microstructures and free-standing structures can be fabricated with a large freedom of design in relation to the isotropic behavior of the etching. A sacrificial layer may be realized fast over varying thickness (PS formation rate 45 μm/h compared to silicon bulk micromachining rate 20 μm/h for KOH etching).

This contribution is devoted to the materials aspects of patterning and processing: we will show how basic microstructures (trenches, polysilicon cantilevers, polysilicon free-standing membranes) may be fabricated using a very simple process based on a single photolithography. The important points are the choice of the mask, porous silicon properties as a function of its formation parameters and the choice of the solution removing the sacrificial layer. The morphology and porosity of the porous silicon layers are indeed mainly determined by the electrolyte composition and by the current density for a given substrate type. Optimized conditions (HF 15% and 80 mA/cm2) lead us to an appropriate porous silicon. Finally the applicability of this technology for various microsensors will be underlined.
The Etch Rate Variations of p+ Silicon Wafers in Aqueous KOH Solutions as a Function of Processing Conditions
Authors: Kilpinen P. , Haimi E. , Lindroos V.K.
Published: April 2011

The etching behaviour of highly boron doped (20 - 25 mω-cm) silicon wafers in aqueous KOH solutions were investigated in the present study. The etch rate of (100) crystal plane and the fastest etch plane projections (31X) and (41X), where X can be 0,1,2…, were measured as a function of processing conditions. The experimental temperatures of solutions were 65 - 75°C and the concentrations 5 - 40 wt-% KOH. The maximum etch rate of (100) crystal plane was measured to locate between 10 - 15 wt-% KOH and the maximum etch rates of fastest etch plane projections were measured to locate between 0 - 10 wt-% KOH in the whole temperature range. In lower concentrations (5 - 20 wt-% KOH) the fastest etch plane projection was determined to be (31X) crystal plane projection. In higher concentrations (25 - 40 wt-% KOH) it was determined to be (41X) crystal plane projection. The results of the present study indicate that there are differences between etch reactions of different etch planes. The difference may be connected to transferring electrons. This could explain why the different etch planes have the position of etch rate maximums as a function of KOH concentration in different places. Furthermore, this could also explain why fastest etch planes are sensitive to experimental conditions.
Structure-Property Relations in Sol-Coated PMN Ceramics: Microscopy, Dielectric and Electromechanical Response
Authors: Sehirlioglu A. , Pilgrim S.M.
Published: April 2011

Some of the most promising materials for electrostrictive response are Pb(Mg1/3, Nb2/3)O3 (PMN) - ceramics; however, the properties of a given composition are only optimum in a limited range of temperatures. In a previous study, it was found that sol coating of PMN particles modified and improved the electromechanical and/or dielectric properties of the resulting product--doubling induced strain in some cases. Understanding the origin of these changes will help to produce an optimized PMN ceramic for a given application from a single source powder. This work concentrates on the Ti and Zn coatings which gave superior properties within the concentration matrix. The relation between the structure and the enhanced electrostrictive behavior is studied. Structural characterization is done by XRD, TEM and SEM.Electrical measurements of dielectric constant, loss, polarization and strain, the property determinations needed to complete the structure-property suite.
Design, Synthesis and Characterization of Precursors for Chemical Vapor Deposition of Oxide-Based Electronic Materials
Authors: Just Oliver , Obi-Johnson Betitie , Matthews Jason , Levermore Dianne , Jones Tony , Rees William S.
Published: April 2011

Ferroelectric and other high dielectric constant metal oxides currently are sought-after for a variety of applications in the electronics industry. To meet the demand of preparation of these interesting materials in a manner compatible with traditional silicon-based fabrication procedures, chemical vapor deposition routes are desired for film growth. Compounds displaying high vapor phase stability are necessary as precursors for these applications. Additionally, in general, it is preferred to utilize compounds in a liquid state, due to the more rapid re-establishment of equilibrium at a liquid-vapor interface, compared to that present at a solid-vapor interface. This combination of desired molecular properties, in turn, presents a great challenge to the coordination chemist. Several of the metals of interest for these uses reside in groups 2–5. Common design features are emerging for the ligands best suited for attachment to these metals for subsequent utilization in the deposition of metal oxides. In order to achieve coordinative saturation of the relatively high ionic radii exhibited by most of these elements, multidentate, monoanionic ligands are relied upon. In the past, most often, homoleptic ligand sets have been employed, thereby reducing the chance for ligand scrambling to occur during the growth process. Such disproportionation processes have been credited, in previous work, with the observation of a temporal decay in vapor pressure of heteroleptic compounds. In some interesting new developments, it has been found that heteroleptic compounds possess sufficient vapor phase integrity to permit their evaluation as CVD precursors. These, and related, results are presented herein.
Monomeric Chelated Amides of Aluminum and Gallium: Volatile, Miscible Liquid Precursors for CVD
Authors: Barry Seàn T. , Gordon Roy G. , Wagner Valerie A.
Published: April 2011

New precursors were developed for the chemical vapor deposition (CVD) of aluminum nitride (AIN) and gallium nitride (GaN) at low temperatures. Synthetic methods for the new materials will be reported, along with their analyses and spectral characterization. The precursors are volatile (180 mTorr at 45-55 °C), low-viscosity (10 centipoise) liquids, so they are more convenient as vapor sources than previously available solid sources. They are thermally stable to temperatures well above their vaporization temperatures, so their vaporization is highly reproducible and leaves no residue. Unlike previously available liquid precursors, they are not pyrophoric, so they are safer to handle. AMN films formed by reaction with ammonia at around 200 °C are amorphous, transparent insulators that are good barriers to diffusion of water, oxygen, and other materials.
Metal-Organic Chemical Vapor Deposition of Zn-In-Sn-O and Ga-In-Sn-O Transparent Conducting Oxide Thin Films
Authors: Wang A. , Edleman N.L. , Babcock J.R. , Marks T.J. , Lane M.A. , Brazis P.W. , Kannewurf C.R.
Published: April 2011

The metal-organic chemical vapor deposition (MOCVD) technique has been successfully applied for growth of Sn-doped transparent, conducting Zn-In-O and Ga-In-O films using Sn(acac)2, In(dpm)3, Ga(dpm)3, and Zn(dpm)2, as volatile precursors. The 25 °C electrical conductivity of the as-grown films is as high as 1030 S/cm (n-type, carrier density N = 4.5 × 1020 cm−3, mobility µ = 14.3 cm2/V•s) for the Zn-In-O series and 700 S/cm (n-type, N = 8.1 × 1019 cm−3, µ = 55.2 cm2/V•s) for the Ga-In-O series. After Sn-doping, the Zn-In-O series exhibits 25 'C electrical conductivities as high as 2290 S/cm with a higher carrier mobility, while the Ga-InO series exhibits higher electrical conductivity (3280 S/cm at 25 °C) and much higher carrier density, but with diminished mobility. All films show broader optical transparency windows than that of commercial ITO films. Reductive annealing, carried out at 400-425 °C in a flowing gas mixture of H2(4%) and N2, results in increased carrier density and mobility as high as 64.6 cm2/V•s for films without Sn doping, but lowered carrier density for the Sn-doped films. X-ray diffraction, transmission electron microscopy, micro diffraction, and high-resolution X-ray analysis show that all films with good conductivity have cubic, homogeneously doped In2O3-like crystal structures.
Photoinduced Changes in the Charge States of Native Donors and Acceptors in ZnGeP2
Authors: Stevens K. T. , Setzler S. D. , Schunemann P. G. , Pollak T. M. , Giles N. C. , Halliburton L. E.
Published: April 2011

Bulk ZnGeP2 (ZGP) crystals grown for high-power tunable mid-infrared laser systems contain large concentrations of three native defects. Using EPR, these three defects have been identified as the Zn vacancy (an acceptor), the phosphorus vacancy (a donor), and the germanium-on-zinc antisite (also a donor). We have studied the wavelength dependence of the photoinduced changes in the EPR signal intensity of the three defect centers using 633 nm and 1064 nm light. We observe a significant increase in the EPR signal under 633 nm light. The 633-nm light also produces an increase in the defect-related 1-R.m absorption band, and we have used a spectrophotometer to measure the spectral shape of the photoinduced change in absorption in this near-IR region. The 633-nm wavelength produces paramagnetic forms of both donor centers, while 1064 nm light only produces the EPR-active center. Time decays of the photoinduced EPR signals have been measured for each of the donors.
ZnGep2 : Optical Transparency and Melt Composition
Authors: Verozubova G.A. , Gribenyukov A.I. , Vere A.W. , Flynn C. , Ivanov Y.F.
Published: April 2011

The paper presents the results of TEM and optical transparency measurements on ZnGeP2 crystals grown by the vertical Bridgman technique from melts of differing compositions. The TEM study reveals the presence of nano-dimensional precipitates of second phases: zinc and ZnxPy precipitation occurs in material grown from Zn-rich melts and GeP from the deficient melts. The precipitation is associated with cooling through the retrograde solidus at a temperature below the melting point. Elastic stress fields are also observed. The relationships between the precipitates and elastic stresses and between precipitation and optical losses are investigated
Room Temperature CW Operation of GaInAsSb/AlGaAsSb Quantum Well Lasers Emitting in the 2.2 to 2.3µm Wavelength Range
Authors: Mermelstein C. , Simanowski S. , Mayer M. , Kiefer R. , Schmitz J. , Walther M. , Wagner J.
Published: April 2011

We report on room temperature cw operation of type-I semiconductor quantum well (QW) laser diodes based on the GaInAsSb/AIGaAsSb/GaSb material system emitting beyond 2.2 µm. Lasing is observed in cw mode up to at least 320 K. A high internal quantum efficiency of 65% and a low internal loss coefficient of 5 cm1have been achieved for a single QW (SQW)large optical cavity laser at 280 K. An extrapolated threshold current density for infinite cavity length of 144 A/cm2and 55 A/cm2has been deduced for the 3 QW and SQW lasers, respectively, which scales with the number of QWs. A maximum cw light output power of 230 mW at 280 K heatsink temperature was obtained for a 3 QW large optical cavity laser with HR/AR coated mirror facets, mounted substrate-side down.
Small-Angle Neutron Scattering from Device-Quality a-Si:H and a-Si:D Prepared by PECVD and HWCVD
Authors: Williamson D.L. , Marr D.W.M. , Nelson B.P. , Iwaniczko E. , Yang J. , Yan B. , Guha S.
Published: April 2011

The heterogeneity of a-Si:H and a-Si:D films has been probed on the nano-scale by small-angle neutron scattering (SANS). Films were deposited by two techniques, plasma-enhanced chemical-vapor deposition (PECVD) and hot-wire chemical-vapor deposition (HWCVD) using conditions that yield high-quality films and devices. Four samples were examined in a light-soaked state (AM1.5, 300 h) and then re-examined after annealing (190°C, 1 h) in-situ to look for any change in SANS associated with the Staebler-Wronski effect. No changes were observed in the SANS intensity to a precision that could have readily detected the 25% change reported in 1985 (Chenevas-Paule et al). Significant differences are observed in hydrogenated and deuterated films, as well as in the PECVD versus the HWCVD materials.
A European Adventure In Amorphous Materials: From Past to Future
Authors: Solomon Ionel
Published: April 2011

The early work on amorphous silicon in Europe was dominated by the activity of the Dundee group, who demonstrated the feasibility of substitutional doping, in contradiction with previous theories which denied the possibility of doping disordered semiconductors. Also, the role of hydrogen in this new “good” disordered semiconductor was not immediately accepted, and the controversy was finally settled by the crucial experiment of post-hydrogenation by D. Kaplan. It is little known that this process of post-hydrogenation, currently used for the improvement of devices, was covered by a patent, which turned out to be quite inapplicable!

The high hopes raised by this “new” material, in particular for photovoltaic applications, rendered the field highly competitive, resulting in a surprising neglect of the basic principles of physics. A striking example is the sweeping under the rug of the effect of band bending at the surface of intrinsic a-Si:H. This effect makes the surface much more conducting than the bulk, rendering a large number of published transport measurements in planar geometry completely meaningless.

Research in Europe has been less application-oriented than research in USA and Japan, but on a small scale it was not completely absent from industrial applications to photovoltaics; a start-up adventure “a la French” is described. The problem of disordered materials is one of the timely solid-state topics, to continue to be a major subject of materials research in the near future. In that respect, amorphous silicon is an exemplary system, and the “hydrogen glass” picture, pioneered by R. A. Street et al., is an open field of research for the improvement of disordered semiconductors.
Gas-Phase and Surface Reactions of Decomposed Species In Catalytic Cvd
Authors: Honda Namiko , Masuda Atsushi , Matsumura Hideki
Published: April 2011

Gas-phase and surface reactions of transported species decomposed on the catalyzer were investigated in catalytic CVD (Cat-CVD), often called hot-wire CVD, using a specially designed reactor tube. The phenomena were comparatively studied using H2- or He-diluted SiH4. It turned out that the control of gas flow through the catalyzer between the gas showerhead and the substrate is a key factor to obtain high uniformity in not only the film thickness but also the crystallinity for Si films prepared by Cat-CVD using the gas pressure above about 10 Pa and the gas-flow velocity faster than several m/s.
Nucleation Mechanism of Microcrystalline Silicon Studied by Real Time Spectroscopic Ellipsometry and Infrared Spectroscopy
Authors: Fujiwara Hiroyuki , Toyoshima Yasutake , Kondo Michio , Matsuda Akihisa
Published: April 2011

We have characterized a-Si:H initial layers for μc-Si:H nucleation by real time spectroscopic ellipsometry (SE) and infrared attenuated total reflection spectroscopy (ATR) to investigate the μc-Si:H formation mechanism. By performing Ar plasma treatment of a-Si:H layers, we confirmed a presence of a 2 monolayer thick sub-surface in a-Si:H layers. In the a-Si:H sub-surface that leads to the μc-Si:H nucleation, an important peak at ∼1937 cm−1 assigned to the SiHn complex was found in the ATR spectra. From H2 plasma treatment experiments, we proposed that this SiHn complex is formed by H insertion into strained Si-Si bonds. The SiHn complex formed in the a-Si:H sub-surface showed a clear relationship with the μc-Si:H nucleation. From these results, we conclude that the μc-Si:H nucleation occurs by the formation of the chemically active and flexible SiHn complexes in the 2 monolayer thick a-Si:H sub-surface.
Dependence of H Diffusion in Hydrogenated Silicon on Doping and the Fermi Level
Authors: Beyer Wolfhard , Zastrow Uwe
Published: April 2011

For three types of hydrogenated silicon films, amorphous, microcrystalline and crystalline hydrogenated silicon, hydrogen diffusion was studied as a function of doping level employing depth profiling by secondary ion mass spectrometry. Hydrogen implantation was used to control the hydrogen concentration. All three materials show a similar doping dependence of H diffusion, namely a strong increase upon boron (p-type) doping and a much lesser increase for n- type (P, As) doping. In a band model of H diffusion, the effect is related to a decrease in energy of the hydrogen diffusion path. Possible explanations are a different charge state of diffusing hydrogen or an effect of the Fermi energy on the release energy of neutral hydrogen.
Fabrication of Mechanical Microstructures Using Amorphous Silicon Films on Glass Substrates
Authors: Yeh Chingwen , Boyce James B. , Ho Jackson , Lau Rachel
Published: April 2011

A new process of surface micromachining has been developed, where amorphous silicon (a-Si) and oxynitride films are used as structural and sacrificial layers on the glass substrate, respectively. Due to glass as the substrate material, the temperatures for all process steps need to be lower than 600°C. Some generic mechanical microstructures such as cantilever beams, bridges, and membranes have been fabricated. The stress changes of a-Si films with annealing temperatures are studied. It is found that the residual stress can be minimized using thermal annealing at 430°C for a few hours. In addition, some process issues such as a-Si film bubbling, the film adhesion of a-Si to the glass substrate, and stiction during structure release are discussed.
Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD at Deposition Rates up to 1 µm/minute
Authors: Nelson Brent P. , Xu Yueqin , Mahan A. Harv , Williamson D.L. , Crandal R.S.
Published: April 2011

We grow hydrogenated amorphous-silicon (a-Si:H) by the hot-wire chemical vapor deposition (HWCVD) technique. In our standard tube-reactor we use a single filament, centered 5 cm below the substrate and obtain deposition rates up to 20 Å/s. However, by adding a second filament, and decreasing the filament-to-substrate distance, we are able to grow a-Si:H at deposition rates exceeding 167 Å/s (1 µm/min). We find the deposition rate increases with increasing deposition pressure, silane flow rate, and filament current and decreasing filament-tosubstrate distance. There are significant interactions among these parameters that require optimization to grow films of optimal quality for a desired deposition rate. Using our best conditions, we are able to maintain an AM1.5 photoconductivity-to-dark-conductivity ratio of 105 at deposition rates up to 130 Å/s, beyond which the conductivity ratio decreases. Other electronic properties decrease more rapidly with increasing deposition rate, including the ambipolar diffusion length, Urbach energy, and the as-grown defect density. Measurements of void density by small-angle X-ray scattering (SAXS) reveal an increase by well over an order of magnitude when going from one to two filaments. However, both Raman and X-ray diffraction (XRD) measurements show no change in film structure with increasing deposition rates up to 144 Å/s, and atomic force microscopy (AFM) reveals little change in topology.
Defect and Tail States in Microcrystalline Silicon investigated by pulsed ESR
Authors: Kanschat P. , Mell H. , Lips K. , Fuhs W.
Published: April 2011

We report on a detailed analysis of paramagnetic states in a doping series of microcrystalline silicon, μc-Si:H, by pulsed electron spin resonance. We identify two dangling bond like structures at g = 2.0052 (db1) and g = 2.0043 (db2). Whereas db1 is evenly distributed in the gap, the db2 state is found to be localized in the lower part of the gap. The CE resonance at g ≈ 1.998 is assigned to electrons in conduction band tail states. In p-doped samples, we observe a broad structure CH at g ≈ 2.08 which we identify with holes trapped in valence band tail states. It is shown that the CH state behaves very similar on illumination as the CE resonance. In n-type samples a pair of hyperfine split lines (A ≈ 11 mT) is found which apparently does not originate from 31P-donor states. On the basis of our results we propose a qualitative model for paramagnetic states in μc-Si:H.
Low Temperature Poly-Si Layers Deposited by Hot Wire CVD Yielding a Mobility of 4.0 cm2V−1s−1 in Top Gate Thin Film Transistors
Authors: Schropp R.E.I. , Rath J.K. , Stannowski B. , Werf C.H.M. Van Der , Chen Y. , Wagner S.
Published: April 2011

Direct deposition of polycrystalline silicon (poly-Si) thin films by the Hot Wire CVD method has been used for the first time for the fabrication of poly-Si top gate Thin Film Transistors (TFTs). The TFTs have a high electron mobility in saturation of up to 4 cm2V−1s−1 as well as a remarkably large ON/OFF ratio of up to 6 × 105.
Gas Phase and Surface Kinetic Processes in Hot-Wire Chemical Vapor Deposition
Authors: Holt J. K. , Swiatek M. , Goodwin D. G. , Atwater Harry A.
Published: April 2011

One- and two-dimensional numerical simulations have been used to determine the parameters critical to high rate growth of high quality polycrystalline silicon via hot-wire chemical vapor deposition at silane partial pressures of 1-70 mTorr and a wire temperature of 2000°C. The Direct Simulation Monte Carlo method [1] was used, including gas-phase chemistry relevant for growth. Model predictions agree both qualitatively and quantitatively with experimental measurements.
Surface roughness evolution of a-Si:H growth and its relation to the growth mechanism
Authors: Smets A.H.M. , Schram D.C. , van de Sanden M.C.M.
Published: April 2011

The post-initial growth dynamic scaling exponent β, which describes the surface roughness evolution in time, is determined for a-Si:H growth using in situ single wavelength (632.8 nm) rotating compensator ellipsometry. β is measured as function of the substrate temperature for three different growth rates 2, 5 and 22 Ås-1 under conditions where SiH3 dominantly contributes to growth. β (≤ 0.5) decreases with increasing substrate temperature and does not strongly depend on the growth rate within the range of growth rates. A roughness evolution model is proposed, based upon a random generation of active growth sites and a subsequent site dependent surface diffusion process. The measured β temperature dependence can be simulated with an activated site hopping activation energy of about 1.0 eV. This activation energy is much higher than what would be expected from a model based upon the diffusion of physisorbed silyl SiH3 radical and suggests therefore another mechanism which is responsible for the surface smoothening during a-Si:H growth.
Thickness-Dependent Micro-Raman Measurement of Poly-Si Films Prepared by Metal-Induced-Crystallization using a Ni Layer
Authors: Muramatsu Shin-ichi , Minagawa Yasushi , Oka Fumihito , Yazawa Yoshiaki
Published: April 2011

Relatively thick amorphous silicon films for solar-cell applications were prepared by metal-induced-crystallization (MIC). Then, the thickness-dependent characteristics of micro-Raman spectra from a cross section of the prepared polycrystalline silicon (poly-Si) films were analyzed. It was found that Ni-induced crystallized films have a uniform composition that is 80% polycrystalline and 20% nanocrystalline. Also, the x-ray diffraction data show that a sub-mono-layer of Ni is sufficient for MIC of 6-μm-thick amorphous silicon (a-Si) films.
Probing Pore Characteristics in Low-K Thin Films Using Positronium Annihilation Lifetime Spectroscopy
Authors: Gidley D. W. , Frieze W. E. , Dull T. L. , Sun J. N. , Yee A. F.
Published: April 2011

Depth profiled positronium annihilation lifetime spectroscopy (PALS) has been used to probe the pore characteristics (size, distribution, and interconnectivity) in thin, porous films, including silica and organic-based films. The technique is sensitive to all pores (both interconnected and closed) in the size range from 0.3 nm to 300 nm, even in films buried under a diffusion barrier. PALS may be particularly useful in deducing the pore-size distribution in closed-pore systems where gas absorption methods are not available. In this technique a focussed beam of several keV positrons forms positronium (Ps, the electron-positron bound state) with a depth distribution that depends on the selected positron beam energy. Ps inherently localizes in the pores where its natural (vacuum) annihilation lifetime of 142 ns is reduced by collisions with the pore surfaces. The collisionally reduced Ps lifetime is correlated with pore size and is the key feature in transforming a Ps lifetime distribution into a pore size distribution. In thin silica films that have been made porous by a variety of methods the pores are found to be interconnected and an average pore size is determined. In a mesoporous methyl-silsesquioxane film with nominally closed pores a pore size distribution has been determined. The sensitivity of PALS to metal overlayer interdiffusion is demonstrated. PALS is a non-destructive, depth profiling technique with the only requirement that positrons can be implanted into the porous film where Ps can form.
Ultra Low k Mesoporous Silica Films: Synthesis, Film Properties and One-Level Copper Damascene Evaluation
Authors: Jin Changming , Liu J. , Li X. , Coyle C. , Birnbaum J. , Fryxell G. E. , Williford R. E. , Baskaran S.
Published: April 2011

Spin-on mesoporous silica films were prepared on eight-inch wafers at SEMATECH by condensation of a silicate network around surfactant micellar structures. Copper single-damascene one-level test structures were built using mesoporous silica as the intermetal dielectric. No major structural failures were observed after chemical mechanical planarization on both blanket films and patterned wafers, indicating relatively good mechanical integrity for a highly porous structure. A simple silane spin-coating step used at SEMATECH on the films appears to be insufficient for complete dehydroxylation and silylation. The electrical test results on the metal comb structures showed good capacitance and leakage current distributions. However, capacitance and leakage current changes were observed after each post-CMP process step, and these changes could be correlated to moisture desorption/outgassing, which was also noted during k measurement. With controlled film synthesis and dehydroxylation conditions, mesoporous silica films with k ≤2.0 and elastic modulus of 4.0 GPa have been synthesized at PNNL. The results of the Cu one-level metal screening tests at SEMATECH combined with properties obtained at PNNL indicate that mesoporous molecularly-templated silicate films hold promise as ultra low k intermetal dielectrics.
Material Properties of a SiOC Low Dielectric Constant Film with Extendibility to k < 2.7
Authors: Lopata Eugene S. , Young Lydia , Felts John T.
Published: April 2011

A plasma deposited SiOC very low k (VLK) interlayer dielectric (ILD) film has been developed which can be tuned to 2.5 = k = 3.0, demonstrates very good thermal stability, excellent adhesion properties, acceptable hardness, and an indication that it may be extendible to k < 2.5. This paper will disclose properties of this SiOC film which are important to a VLK ILD application.
Fabrication and Performance Limits of Sub-0.1 µm Cu Interconnects
Authors: Kuan T. S. , Inoki C. K. , Oehrlein G. S. , Rose K. , Zhao Y. –P. , Wang G. –C. , Rossnagel S. M. , Cabral C.
Published: April 2011

As the on-chip interconnect linewidth and film thickness shrink below 0.1 µm, the size effect on Cu resistivity becomes important, and the electrical performance deliverable by such narrow metal lines needs to be assessed critically. From the fabrication viewpoint, it is also crucial to determine how structural parameters affect resistivity in the sub-0.1 µm feature size regime. To evaluate the scaling of resistivity with thickness, we have fabricated a series of Ta/Cu/Ta/SiO2 thin film structures with Cu thickness ranging from 1 µm to 0.02 µm. These test structures revealed a far larger (∼2.3 ×) size effect than that expected from surface scattering. We have also fabricated test structures containing 50-nm-wide Cu lines wrapped in Ta-based liners and embedded in insulating SiO2 using e-beam lithography, high-density plasma etching, ionized PVD Cu deposition, and chemical-mechanical planarization processes. Direct current (16 nA) resistance measurements from these 50-nm-wide Cu lines have also shown a higher- than-expected distribution of resistivity. Cross-sectional TEM and surface AFM observations suggest that the observed extra resistivity increase can be attributed to small grain sizes in ultra- thin Cu films and to Cu/Ta interface roughness. Monte Carlo simulations are used to quantify the extra resistivity resulting from interface roughness.
Tantalum-Nitride Diffusion Barrier Studies Using the Transient-Ion-Drift Technique for Copper Detection
Authors: Heiser T. , Brochard C. , Swaanen M.
Published: April 2011

The permeability of 5 nm thick TaN, Ta and TiN diffusion barriers has been studied by monitoring the bulk copper concentration in silicon after isothermal and isochronal annealing experiments with a transient-ion-drift (TID) technique. The method estimates quantitatively the bulk copper concentration in silicon from capacitance transients of a Schottky barrier which arise when copper ions drift out of the depletion region towards the quasi-neutral region. The correlation between the copper lateral distribution and the position of the copper metal is used to distinguish between background contamination and copper originating from barrier leakage. The TID detection limit is found lower than 1012at/cm3, which makes this technique particularly well adapted for quantitative diffusion barrier studies. Isothermal and isochronal annealing experiments show that TaN fails at a higher temperature than Ta barriers. The copper concentration does not exceed the solubility limit, indicating that copper precipitates nucleate rapidly at the interface. The opposite is found in TiN covered samples where a large copper supersaturation is obtained even after short annealing times.
Study of Ta as a Diffusion Barrier in Cu/SiO2 Structure
Authors: Pan J. S. , Wee A. T. S. , Huan C. H. A. , Chai J. W. , Zhang J. H.
Published: April 2011

Tantalum (Ta) thin films of 35 nm thickness were investigated as diffusion barriers as well as adhesion-promoting layers between Cu and SiO2 using X-ray diffractometry (XRD), Scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). After annealing at 600°C for 1h in vacuum, no evidence of interdiffusion was observed. However, XPS depth profiling indicates that elemental Si appears at the Ta/SiO2 interface after annealing. In-situ XPS studies show that the Ta/SiO2 interface was stable until 500°C, but about 32% of the interfacial SiO2 was reduced to elemental Si at 600°C. Upon cooling to room temperature, some elemental Si recombined to form SiO2 again, leaving only 6.5% elemental Si. Comparative studies on the interface chemical states of Cu/SiO2 and Ta/SiO2 indicate that the stability of the Cu/Ta/SiO2/Si system may be ascribed to the strong bonding of Ta and SiO2, due to the reduction of SiO2 through Ta oxide formation.
Bonding and Cohesive Properties of Cobalt/Alumina Magnetic Tunnel Junctions
Authors: Oleinik I.I. , Tsymbal E.Yu. , Pettifor D.G.
Published: April 2011

Magnetic tunnel junctions (MTJs) are promising candidates for applications in spintronic devices such as magnetic random access memories, read heads and sensors. Previous studies have revealed the critical influence of the chemistry and structure of the ferromagnet metal/alumina interface on both sign and magnitude of the tunneling current in MTJs. We have performed a detailed first-principles study of the structure and bonding at the cobalt/alumina interface in order to understand the relationship between magnetic properties, local bonding environment and cohesion at the interface. Both Al- and 0- terminated interfaces were considered and full geometry optimization of the structure was done by selfconsistent spin-polarized calculations within density functional theory and the generalized gradient approximation. We found that the relaxed atomic structure of the 0-terminated interface is characterized by a rippling of the Co interfacial plane, the average Co-O bond length being 2.04 Å which is within 5% of that in bulk CoO and it is characterized by the covalent bonding between the 0 2p and Co 3d orbitals. The Al-terminated interface contains Co-Al bonds with an average bond length of 2.49 Å compared to 2.48 Å in bulk CoAl and it is characterized by metallic behaviour of the first aluminium layer. As a consequence of different character of bonding, the cohesion at the O-terminated interface is stronger as that at the Al-terminated interface, the work of separation being equal to 6.35 J/m2 and 3.64 J/m2 respectively.
Excimer Pulsed Laser Ablated Molecular Beam Evaporation for the Deposition of Binary Skutterudites
Authors: Durand H.-A. , Suzuki A. , Nishimoto K. , Ito K. , Kataoka I.
Published: April 2011

The family of materials bearing the skutterudite crystallographic structure have recently attracted interest because of their extra-ordinary electrical and thermal transport properties, as well as their peculiar magnetic qualities [1]. Particularly, the group of cobalt antimonide skutterudites has been referred to as electron crystals and phonon glasses. With the goal to prepare skutterudite thin films, laser ablation is unique in its capacity to transfer skutterudite target's complex composition untouched to substrates while providing an hype thermal beam that has a positive influence on thin film growth. We use a pulsed excimer laser at 193 nm to evaporate skutterudites targets in ultra-high vacuum and deposit thins films on silicon wafers and fused silica substrate. We have studied the composition and crystallographic structure of the deposits as a function of substrate temperature and target to substrate distance. Deposits are skutterudite policrystals of several hundreds nanometers. We investigated the electrical as well as the thermal transport properties of thin films having the desired phase and compare these with value reported for the bulk mono-crystals.
Strongly (111) Oriented Metallization by Ion Plating Method
Authors: Kudo T. , Sakuragi S. , Masui S. , Kinoshita K. , Makino H. , Tanaka M.
Published: April 2011

We have succeeded in the synthesis of strong Cu(111) textured films by means of the novel ion plating method(URT-IP). This URT-IP method combines the Cu deposition with the surface cleaning (self-cleaning). In the Cu film synthesis, the cations play a main role: the self-cleaning of underlying Cu seed and TaN barrier surfaces at the first stage of Cu deposition and the promotion of (111) texture. The two growth processes dependent on underlying materials cause the strong (111) orientation; the epitaxial growth on the same (111) oriented underlayer and the promotion of thermodynamically stable (111) texture on the amorphous underlayer. The in-situ Ar+ cleaning of underlayer surfaces by the URT-IP improves the (11) orientation to be much stronger. The URT-IP method is applied also to the synthesis of strong Pt(111) textured films with the same fcc system.
Surface Catalyzed Photo-Assisted Mocvd of Cobalt Thin Films for Enhanced Control of Magnetic Properties
Authors: Chioncel M.F. , Haycock P.W. , Ogrin F.Y. , Ruthven B.L. , Bull J.W.
Published: April 2011

Thin films of cobalt have been deposited by photo-assisted metal-organic chemical vapour deposition. Samples of thickness less than 60 nm, grown at 110 °C, exhibit inverse hysteresis when an external magnetic field is applied in a particular direction normal to the plane of the film. These films are a mixture of crystalline and, possibly, amorphous phases with a grain size of about 130 nm and a significant oxygen content throughout. The potential roles of the various physical characteristics, as well as that of the photolytic deposition process itself, in the origin of the inverse hysteresis are discussed, as is a possible self-limiting growth mechanism.
Thermodynamics of Paracrystalline Silicon
Authors: Voyles P. M. , Treacy M. M. J. , Gibson J. M.
Published: April 2011

Fluctuation microscopy experiments have shown that the as-deposited structure of amorphous silicon thin films is paracrystalline. A paracrystal consists of small (< 3 nm in diameter) topologically crystalline grains separated by a disordered matrix. Here we consider the thermodynamics of paracrystalline silicon as a function of the grain size and the temperature. We offer a simple model that qualitatively explains the observed metastability of the ordered structure at low temperature (300 K), the relaxation towards a more disordered structure at intermediate temperatures (600 K), and the recrystallization at high temperatures (1000 K).
Surface and Microstructural Characterization of Homoepitaxial Silicon Grown by Pulsed Laser Deposition
Authors: Pelt J.S. , Magahñ;a R. , Ramsey M.E. , Poindexter E. , Atwell S. , Zheng J.P. , Durbin S.M. , Kobayashi M.
Published: April 2011

There is a great deal of interest in thin film deposition techniques which can achieve good crystal quality at low substrate temperatures. Pulsed laser deposition (PLD), well-known as a reliable technique for fabrication of high critical temperature superconductor thin films, has a number of characteristics which may make it suitable for such applications. In particular, PLD is characterized by a relatively large average species energy, which can be controlled by the laser fluence at the target. This paper describes the growth of silicon on silicon films using PLD over substrate temperatures between 500 and 700 °C, and in-situ characterization using reflection high-energy electron diffraction (RHEED). Transmission electron microscopy confirms the growth of single crystal oriented films, and atomic force microscopy indicates smooth films with an rms surface roughness of less than 2 Å
Novel Nanocrystalline Materials by Pulsed Laser Deposition
Authors: Narayan J. , Sharma A.K. , Kvit A. , Kumar D. , Muth J.F.
Published: April 2011

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline metal, semiconductor and magnetic material thin films and composites. The size of nanocrystals was controlled by interfacial energy, number of monolayers and substrate temperature. By incorporating a few monolayers of W during PLD, the grain size of copper nanocrystals was reduced from 160nm (Cu on Si (100)) to 4nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness increased with decreasing grain size up to a certain value (7nm in the case of copper) and then decreased below this value. While the former is consistent with Hall-Petch model, the latter involves a new model based upon grain boundary sliding.

We have used the same PLD approach to form nanocrystalline metal (Ni, Co, Fe embedded in α-A12O3 and MgO) and semiconductor (Si, Ge, ZnO, GaN embedded in AIN and α-A12O3) thin films. These nanocrystalline composites exhibit novel magnetic properties and novel optoelectronic properties with quantum confinement of electrons, holes and excitons in semiconductors. We review advanced PLD processing, detailed characterization, structureproperty correlations and potential applications of these materials.