bluuebunny/crossref_metadata_2025 huggingface dataset:
High Temperature Studies with Co2 Laser Heated Sapphire: Reactivity and Surface Structures
Authors: Abrevaya Hayim , Nordine Paul C.
Published: March 2011

CO2 Laser heating of c-axis sapphire filaments was used in a low pressure flow reactor in order to study evaporation and chlorination of single crystal and liquid aluminas. Reacted specimens were examined by scanning electron microscopy (SEM) to monitor the evolution of facets and other surface structures with reaction conditions.

An increase of the incident energy on a laser heated sapphire filament at the melting point does not result in complete melting, because the semi-transparent melt layer that forms has a higher effective emittance than the solid. This technique allows simultaneous reactivity study of liquid and single crystal aluminas at the melting point, as well as study of reactions of single crystal alumina at lower temperatures.

Sapphire specimens develop a hexagonal prism shape after reaction with chlorine containing gases whereas evaporation does not change the initially cylindrical specimen shape.

The primary structural characteristic of the 0.025 cm as-received sapphire specimens from Tyco is the presence of ∼1μm voids that are produced during the growth of the crystal. These voids form conical arrays 20–30μm apart along the filament axis. Specimens reacted with chlorine containing gases below ∼1900K exhibit surface structures which form arrays with the same size and pattern as the voids in the as-received specimens.
Characterization of Sputter Deposited Al-Nitride And Al-Oxide by X-Ray Photoelectron Loss Spectroscopy
Authors: Kubiak Charlene J.G. , Aita Carolyn Rubin , Tran Ngoc C. , Barr Tery L.
Published: March 2011

The results of an x-ray photoelectron loss spectroscopy (XPLS) study of several wide band gap aluminum compounds are presented here. XPLS is a new application of x-ray photoelectron spectroscopy involving the determination of the energy separation, ΔE, between a particular core photoelectron peak and its principal loss peak. The materials investigated here are sputter deposited thin film Al-nitride and oxide, and bulk single crystal α-alumina. It is not possible to distinguish between these materials on the basis of the chemical shift in the binding energy of the A12p and A12s photoelectrons (Siegbahn shift). The results show that XPLS can be used to distinguish between these materials. ΔE in Al-oxides and nitride differs by several eV and is independent of sample charging. Comparison with ΔE calculated using a free electron gas model is made and related to the plasmon nature of ΔE.
Electrodiffusion of Ions in Alpha-Quartz
Authors: Lopez Augusto R. , West J. D. , Martin J. J.
Published: March 2011

Electrodiffusion (sweeping) is a post-growth treatment which allows the selective exchange of charge compensating intersititial ions in quartz. This technique is employed commercially to enhance the radiation hardness of the material used for precision oscillator crystals. Most as-grown quartz contains substitutional Al3+ with an interstitial alkali providing the charge compensation. Additional unidentified sites also trap protons to form the OH--growth defects responsible for several IR absorption bands. When thermally released from their trapping sites, the intersitials can migrate along the large c-axis channels. Therefore, if the sample is heated with an electric field applied along the c-axis, the ions can be swept out and replaced either by protons from the surrounding atmoshpere or by the desired alkal i from a salt electrode. In order to better understand the electrodiffusion, we are systematically investigating various aspects of the process. The apparent ionic conductivity data taken as the swept sample is cooled usually shows a curved log( T) vs 1000/T plot. The conductivity of H+ in is much less than that of the lithium or sodium. The activation energies at high temperatures tend to be lower than those found from the low temperature data. The exponential prefactors are considerably larger than the values predicted for a given aluminum content and reasonable estimates of the attack frequency and jump distance. It seems likely that an additional source of mobile ions is present. The peak or plateau observed during the warm-up period for air or hydrogen sweeping appears to be caused by the transition from conduction primari1y by a1ka1i s to conduction by protons.
Inhomogeneous Sintering: Stresses, Distortion and Damage
Authors: Evans A.G.
Published: March 2011

Heterogeneities in a sintering compact constitute a source of stress and distortion. Procedures for calculating the stresses and the distortion are described. Specific trends in the stress with initial differentials in density or particle size and with temperature are then discussed. Some effects of non-sinterable heterogeneites (hard agglomerates or whiskers) on sintering retardation are also analyzed. Finally, some remarks concerning sintering damage are presented.
Strain Rate Effects on the Tensile Strength of Concrete as Predicted by Thermodynamic and Fracture Mechanics Models
Authors: Reinhardt Hans W.
Published: March 2011

Models are presented and discussed which predict the influence of stress rate or strain rate on the tensile strength of concrete. Three of them are based on linear fracture mechanics and two on thermodynamics. It is shown that four models are appropriate and useful in the low to medium stress rate whereas two can predict realistic values at high stress rates. Finally a proposal is made how to apply the knowledge to engineering practice.
Compressive Strain Rate Effects of Concrete
Authors: Bischoff P. H. , Perry S. H.
Published: March 2011

Since good constitutive laws are required to model correctly the behaviour of concrete under impact loading, it is necessary to determine the complete stress-strain response of concrete at varying strain rates. Conflicting evidence emerges about whether the critical compressive strain (defined as the strain observed at maximum stress) increases or decreases with an increasing strain rate. In this paper, a comprehensive description is given of the brittle fracture process for plain concrete under static and impact loading. The strain rate dependance of tensile microcrack growth is used to explain both the increase in strength and the increase in critical compressive strain that can occur at high strain rates. More extensive experimental results are required to determine the fundamental changes in behaviour that occur as the loading rate is increased and, thus, facilitate the development of a more precise failure model for concrete.
Concrete and Fiber Reinforced Concrete Subjected to Impact Loading
Authors: Shah Surendra P.
Published: March 2011

Despite its extensive use, low tensile strength has been recognized as one of the major drawbacks of concrete. Although one has learned to avoid exposing concrete structures to adverse static tensile load, these cannot be shielded from short duration dynamic tensile stresses. Such loads originate from sources such as impact from missiles and projectiles, wind gusts, earthquakes and machine vibrations. The need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the mechanical properties of the component materials at high rates of straining.

One method to improve the resistance of concrete when subjected to impact and/or impulsive loading is by the incorporation of randomly distributed short fibers. Concrete (or Mortar) so reinforced is termed fiber reinforced concrete (FRC). Moderate increase in tensile strength and significant increases in energy absorption (toughness or impact-resistance) have been reported by several investigators in static tests on concrete reinforced with randomly distributed short steel fibers. A theoretical model to predict fracture toughness of FRC is proposed. This model is based on the concept of nonlinear elastic fracture mechanics.

As yet no standard test methods are available to quantify the impact resistance of such composites, although several investigators have employed a variety of tests including drop weight, swinging pendulums and the detonation of explosives. These tests though useful in ascertaining the relative merits of different composites do not yield basic material characteristics which can be used for design.

The author has recently developed an instrumented Charpy type of impact test to obtain basic information such as load-deflection relationship, fracture toughness, crack velocity and load-strain history during an impact event. From this information, a damage based constitutive model was proposed. Relative improvements in performance due to the addition of fibers as observed in the instrumented tests are also compared with other conventional methods.
The Fracture of Reinforced Concrete under Impact Loading
Authors: Bentur Arnon , Mindess Sidney , Banthia N.
Published: March 2011

The behaviour under impact loading of concrete beams, reinforced with both smooth and deformed steel reinforcing bars, was studied. Tests were carried out using an instrumented drop-weight impact apparatus, with a 345 kg mass hammer, and drop heights of up to 2.36 m. It was found that, under certain circumstances, the steel reinforcement itself fractured. This behaviour is discussed with reference to the drop height, the type of reinforcement, and the strength of the concrete matrix.
Continuum Damage Mechanics Studies on the Dynamic Fracture of Concrete
Authors: Chen E. P.
Published: March 2011

The dynamic fracture of concrete in tension is studied by applying a continuum damage model developed by the author and his coworkers [1–3]. In this model, the degree of damage in concrete corresponds to the fraction of concrete volume that has been tension relieved, and tensile microcracking has been taken as the damage mechanism. In compression, the concrete is assumed to respond in an elastic/perfectly plastic manner. Strain-rate effects have been explicitly included in the model. Accumulation of damage in the material is reflected by the progressive weakening of the material stiffness. Examples involving center- and edge-cracked plate specimens subjected to the action of step and ramp loads are used to demonstrate the material responses predicted by the model. The bulk pressure versus strain relationships at locations close to the crack tip clearly show strainsoftening behavior. The damage tends to localize around the crack and its extent in the specimen is dependent upon both the crack geometry and the loading type. These results are presented and their implications are discussed.
Elliptical Surface Representation of Continuum Vectorial Damage
Authors: Galloway Rodney G.
Published: March 2011

This paper focuses on the establishment of a simple damage surface that allows the use of a vector representation of damage to be applied in a two or three dimensional framework. Specifically for contrast to some types of tensor representations [1], the surface is developed in such a manner to allow maximum damage to occur in planes adjacent to the plane of maximum tensile strain. The limitations of this surface then are pointed out. Comparison of this postulate with recent data from Jan van Mier [2] is also presented.
Tensile Strength of Concrete at Different Strain Rates
Authors: Soroushian Parviz , Choi Ki-Bong , Fu Gung
Published: March 2011

Results of dynamic tensile strength tests of concrete, produced by the authors and other investigators, were used to study the effects of strain rate on the tensile strength of concrete. The influence of moisture content and compressive strength of concrete, and type of test (splitting tension, flexure, or direct tension) on the strain rate-sensitivity of the tensile strength were evaluated. An empirically developed expression is presented for the dynamic-to-static ratio of concrete tensile strength in terms of the rate of straining.
Effect of the Loading rate on the Tensile strength of Concrete
Authors: Glinicki Michal A.
Published: March 2011

The knowledge of the loading rate influence on the tensile strength of concrete is of considerable importance in engineering practice. The safety of several concrete structures subjected to impact and impulsive loads is often controlled by the tensile strength and stress-strain behaviour because these properties greatly influence the cracking of concrete, bond properties of reinforcing steel and behaviour under shear forces.
A Procedure for the Interpretation of Fly Ash Particle Size Data
Authors: Diamond Sidney , Kilgour Carol L.
Published: March 2011

A procedure has been developed for organizing and displaying the results of particle size distribution determinations on fly ash so as to promote simple and useful comparisons. The procedure involves comparative plots of histograms displayed on a logarithmic size basis, and is illustrated by selected data drawn from a larger suite of analyses of Indiana fly ashes.
Fly Ash Beneficiation and Utilization in Theory and in Practice
Authors: Butler W. Barry , Mearing Marc A.
Published: March 2011

Over the years there have been hundreds of papers written on benefication of fly ash to extract alumina, magnetite, activated carbon, cenospheres, etc., and to enhance the properties of the fly ash itself for concrete making purposes. Several of the processes have been patented. Few of them have been exploited commercially. We examine some of the more popular processes, the history of their success or failure, and current achievements with fly ash beneficated for use in Portland cement concrete.
Identification of Chemical Compounds in Fly Ash by X-Ray Absorption Spectroscopy and Proton-Induced X-Ray and Gamma-Ray Emission Analyses
Authors: Lytle N. W. , Eatough D. J. , Hansen L. D. , Hill M. W. , Mangelson N. F. , Lytle F. W. , Greegor R. B.
Published: March 2011

Proton-induced X-ray emmision and proton-induced gamma-ray emission analyses have been used to determine the elemental content of four oil fly ash samples collected from the flue line of an oil-fired power plant. X-ray absorption spectroscopy was used to characterize the vanadium and nickel compounds present in the fly ash. Vanadium was present primarily as VOSO4·3H2O and nickel was present as a mixture of NiSO4 and NiO.
Surface Characterization of the Mechanism for Decreased Boiler Slagging via Fly Ash Surface Modification
Authors: Macey Christopher J.
Published: March 2011

Slagging difficulties encountered in large, pulverized coal-fired utility boilers can be alleviated by using recently developed chemical conditioners designed to inhibit the agglomeration of molten fly ash particles. Slagging results from the impaction and accretion on the boiler interior surfaces of molten ash particles in the flue gas resulting from the combustion of coal. Electron Spectroscopy for chemical Analysis (ESCA) and ion sputtering depth profiling were utilized to examine the mechanism whereby a fuel conditioner containing copper oxychloride effectively reduced slag deposition rates during a pilot-scale, pulverized coal combustion experiment.
Carbonation Effects in Hardened Fly Ash Cements
Authors: Meland Inger
Published: March 2011

Carbonation in hardened pastes of fly ash cements, stored in a CO2 atmosphere and exposed to different relative humidities, has been investigated in order to study its effects upon different properties of cement pastes. Thermogravimetry (TG), x-ray diffractometry, SEM, and mercury porosimetry (MIP) have been used to characterize the carbonation phenomenon. The results indicate that different relative humidities in the storage chambers lead to carbonation of different solid phases in the hydrated pastes. This effect is discussed in terms of TG- and x-ray analysis. Changes in pore size distribution due to carbonation have been analyzed by MIP and SEM.
Diffusion and Pore Structure in Portland Cement Pastes Blended with Low Calcium Fly Ash
Authors: Kumar Amitabha , Roy Della M.
Published: March 2011

Effective coefficients for the diffusion of Cs+ and Cl− ions accross hardened plates of Portland cement and Portland cement-fly ash blend pastes were measured at 27°, 38° and 60° for samples cured up to 28 d. The porosity and pore size distributions of the same hardened plates were also determined. The fly ash blends show lower anion and cation diffusion rates at higher temperatures, although the porosity is not significantly different from the neat paste. The finer pore size is considered responsible for the slower diffusion in the blends. The electronegative nature of the pore surfaces also contributes to the slower cation diffusion.
A Strength Model for Concretes Containing Fly Ash, Blast-Furnace Slag and Silica Fume
Authors: Dunstan Edwin R.
Published: March 2011

This paper describes preliminary a model for the strength of concretes containing industrial by-products such as fly ash, blast-furnace slag, and silica fume. A formula that describes the various strength production mechanisms of these by-products is developed. These materials produce strength by pozzolanic reaction, by latently hydraulic reactions and by self-cementing reactions similar to Portland cement. A method of separating the effect of each mechanism is proposed. A parameter for each of these strength producing mechanisms can be determined from concrete strength data.
Scientific Basis for Effective Fly Ash Disposal
Authors: Murarka Ishwar P.
Published: March 2011

Disposal of fly ash in landfills and surface impoundments continues to be the most cost-effective and common practice in the electric utility industry. Fly ash, like most solid residues from industrial processes, contains water soluble constituents. The composition of fly ash however varies from plant to plant with the type of fuel being used, the method of firing, and the way in which the ash is collected. Even though data on the bulk chemical composition of fly ash are now generally available, it is not known how this information can be used to predict the dissolution and migration of ash constituents in natural waters. Concerns for groundwater protection have raised issues which may alter the practice of land disposal for fly ash and make it more costly than necessary. Regulatory actions to date indicate that stricter engineering requirements may be placed on disposal practices in order to protect groundwater from contamination. Natural and artificial liners seem to be the most commonly required engineering solutions - an apparent over-reaction.
Leaching Behavior of Fixed-Bed Gasification Ash Derived from North Dakota Lignite
Authors: Hassett D. J. , Henke K. R. , McCarthy G. J.
Published: March 2011

three different fixed-bed gasifiers have been leached using: (1) the EPA-EP leaching test; (2) a similar test that starts with a synthetic North Dakota groundwater; (3) the ASTM D3987–81 method; (4) a long-term (120 day) leaching experiment. The gasification ashes were highly alkaline and produced pH's in the range 10–13 during tests 2 through 4. Compositions of major, minor and trace elements were determined by AAS and ICAP analyses of leachates. None of the EPA-EP test leachates from any of the ashes exceeded the EP Trigger values that define a hazardous waste according to the RCRA criteria. The long-term leaching experiments provided insights into the rates of extraction of elements from ash and could be useful in modeling selected failure scenarios in an ash disposal pit. At various times during the long-term leaching experiments, substantial fractions of the Na, K, Al, S, As, Mo, Se and V in the ash were extracted. Liquid to solid (l:s) ratios were important in determining the quantities of elements extracted and in controlling solution pH; during most of the 120 day experiments, pH's were near 13 in a 2:1 ratio experiment and just below 10 in a 20:1 ratio experiment. X-ray diffraction analysis of the leaching residue indicated that only a portion of the ash reacted with the leaching solutions. The reaction products were largely noncrystalline, but minor amounts of zeolites, calcite and gibbsite were identified. The formation of such secondary solid phases appears to be important in controlling leachant concentrations.
Thermal Properties of Fly Ash-Slag Cement Waste forms for Disposal of Savannah River Plant Salt Waste
Authors: Kaushal S. , Roy D. M. , Licastro P. H. , Langton C. A.
Published: March 2011

Waste processing at the Savannah River Plant will involve reconstitution of the salts (NaNO3, NaNO2, Na2 SO4 and NaOH) into a concentrated solution followed by solidification in a cement-based waste form. Phase stability and mechanical durability of this material will depend to a considerable extent on the thermal properties of the waste form. Fly ash has been used to moderate the hydration and setting processes so as to avoid high temperatures which could cause thermal stresses. Both high-calcium (Class C) and low-calcium (Class F) fly ashes were studied. Other constituents of the mixes include granulated blast furnace slag and finely crushed lime-stone. The adiabatic temperature increases and thermal conductivities were measured and related to matrix mineralogy and microstructure as determined by x-ray diffraction and scanning electron microscopy, respectively.
A Survey of Ash Sources for Mineral Recovery
Authors: Watson J. S.
Published: March 2011

Twenty-two ash samples from utility companies across the country were studied to determine their potential use for mineral recovery. Most tests were limited to chemical analyses and determination of leachable metal values in the ashes, but samples from two utilities were examined in more detail. The more detailed analyses included physical as well as chemical properties. This work was part of a broad-based effort supported by the Electric Power Research Institute (EPRI), and the results from this study were used in economic assessments of mineral recovery from fly ash made by Kaiser Engineers in another part of the EPRI program. Although the compositions and properties of the ash samples varied considerably, only two of the 22 ash samples studied appeared to be unsuitable for mineral recovery. These results indicate that large portions of the ash produced in this country are suitable for potential resource recovery, but further work to evaluate potential upgrade of the leached ash residue is recommended.
Characterization of the Inorganic Constituents in Coal
Authors: Finkelman R. B.
Published: March 2011

Anticipating the environmental effects of utilization or disposal of coal combustion and conversion by-products requires proper characterization of the inorganic constituents in coal. Inorganic constituents include minerals as well as the organically associated inorganic elements. Characterization of these constituents should not be limited to the types and abundances of the minerals and elements, but should also include their modes of occurrence (Table I and Figures 1–4). Information on modes of occurrence should include the textural relationships of the minerals and the chemical form of the elements (i.e. organic/inorganic associations). This will enable us to predict better how the inorganic constituents will behave upon cleaning, combustion, conversion, or leaching of the coal. For example, chalocophile elements (As, Bi, Cd, Cu, Hg, Pb, Se, Sb, Tl, Zn) associated with secondary cleat (vertical breaks in the coal) or with vein filling sulfides will likely be removed during coal cleaning. In contrast, these elements, when associated with dispersed accessory sulfides and selenides [sphalerite (ZnS), clausthalite (PbSe), chalcopyrite (CuFeS2), galena (PbS)] are commonly concentrated in the cleaned coal. Calcium present in coal as a carbonate would respond to technological processes in a different way than calcium present in organic association or as calcium sulfate, phosphate or silicate.
Monolithic Integration of Si and GaAs Devices
Authors: Choi H. K. , Turner G. W. , Tsaur B-Y. , Windhorn T. H.
Published: March 2011

Integration of Si MOSFETs with GaAs MESFETs and with GaAs/AlGaAs double-heterostructure LEDs on monolithic GaAs/Si substrates is reported. Both Si MOSFETs and GaAs MESFETs show characteristics comparable to those for devices fabricated on separate Si and GaAs substrates. In LED/MOSFET integration, the cathode of each LED is connected with the drain of a MOSFET. This is the first time that Si and GaAs devices have been monolithically interconnected. LED modulation rates up to 27 Mbps have been achieved by applying a stream of voltage pulses to the MOSFET gate.
High Volume Production Growth of GaAs on Silicon Substrates
Authors: Ito Chris R. , Feng M. , Eu V. K. , Kim H. B.
Published: March 2011

A high-volume epitaxial reactor has been used to investigate the feasibility for the production growth of GaAs on silicon substrates. The reactor is a customized system which has a maximum capacity of 39 three-inch diameter wafers and can accommodate substrates as large as eight inches in diameter. The MOCVD material growth technique was used to grow GaAs directly on p-type, (100) silicon substrates, three and five inches in diameter. The GaAs surfaces were textured with antiphase boundaries. Double-cyrstal rocking curve measurements showed single-cyrstal GaAs with an average FWHMof 520 arc seconds measured at four points over the wafer surface. Within-wafer thickness uniformity was ± 4% with a wafer-to-wafer uniformity of ± 2%. Photoluminescence spectra showed Tour peaks at 1.500, 1.483, 1.464, and 1.440 ev. Schottky diodes were fabricated on the GaAs on silicon material.
Photoluminescence and Photoluminescence Excitation Spectra of GaAs Grown Directly on Si
Authors: Zemon S. , Shastry S. K. , Norris P. , Jagannath C. , Lambert G.
Published: March 2011

The photoluminescence of GaAs/Si grown by OMCVD has been analyzed as a function of temperature and the dominant high temperature line identified as a conduction-band-to-valence-band transition. Photoluminescence excitation spectra indicate that the transition is excitonic at 4.2 K. A second line, also identified as intrinsic, dominates the spectra below 100 K. A biaxial tensile strain is proposed to account for the two intrinsic lines through a splitting of the valence band degeneracy.
MBE Growth of Low Dislocation and High Mobility GaAs-on-Si
Authors: Lee Jhang Woo
Published: March 2011

Data is presented on the optimization of several molecular beam epitaxial growth processes to provide low dislocation density and high mobility GaAs single crystals on (100) Si wafers. The substrate tilt angle, the growth temperature, and the first buffer layer structure, were investigated Tor this purpose. Using Hall measurements the GaAs layers grown on 2 or 3-degree tilt (100) Si showed consistently high mobilities which are equivalent to the homoepitaxial GaAs mobility. Transmission electron microscopy (TEM) revealed that on tilted (100) Si substrates most of the misfit dislocations were confined within the first 50 Å GaAs layer by forming a type of edge dislocation at the Si surface step edges. Also low temperature grown buffer layers always gave better morphologies and lower etch pit densities while keeping the high mobilities on overgrown GaAs layers.
Microstructure of thin layers of MBE-grown GaAs on Si substrates
Authors: Rosner S. J. , Koch S. M. , Harris J. S. , Laderman S.
Published: March 2011

The ability to grow high quality epitaxial GaAs films directly on Si substrates has recently been demonstrated by Molecular Beam Epitaxy. Many of the most successful growth techniques include initial growth at low temperatures and slow growth rate to nucleate the compound on the elemental semiconductor with subsequent normal growth under conditions used for homoepitaxial GaAs MBE. The mechanisms for the success of this method are still poorly understood. This work focusses on a study of the structural evolution of this low temperature initial layer and conventionally grown overlayer. Thin films in the 5 to 300 nm range were used to evaluate the effect of the temperature and thickness on the growth process. Thicker films, described elsewhere, were used to evaluate the crystalline and optical quality of potential device layers.

The structure of the thin buffer layers was studied as a function of both temperature and thickness. The crystalline quality of these layers was found to be quite poor, with substantial disorder at the GaAs/Si interface. The quality improved slowly as a function of thickness. The effect of the conventional overgrowth on this initil layer was also investigated. It was found that the quality of the low tumperature layer improved as normal overgrowth continued, as measured by ion channeling aligned yields. After 200 nm of overgrowth, ion channeling aligned yields from the material at the interface had declined substantially. This indicates that substantial regrowth and annealing of defects occurs as growth continues. These observations are further confirmed by TEM.
Characteristics of Thin Layers of SiO2 Fabricated by Rapid Thermal Oxidation
Authors: Prasad S. , Haase J. , Früchtnicht R. , Ferretti R. , Haack D.
Published: March 2011

Thin layers of SiO2 (60-300 Å) were fabricated by rapid thermal oxidation (RTO). Growth rate on (100) and (111) Si was determined. Two different high-temperature anneal cycles were used to reduce the interface state density. Work function difference between metal and semiconductor depends upon technology and can be attributed to the changes in Si-SiO2 barrier height.
A Comparison of RTO and Furnace Oxides
Authors: Burnham Marie E. , Legge Ronald N. , Jaim Nulman Jaim Nulman , Fejes Peter L. , Brown James F.
Published: March 2011

The original intent of this study was to compare rapid thermal, thin (80-100Å) gate oxides with standard, furnace-grown, thin gate oxides for endurance. Wafer processing before gate oxide growth was chosen to duplicate processing used ina typical non-volatile memory product. In particular, care was taken to duplipate pre- and post- gate growth processing of field oxide isolated polysilicon capacitors for all wafers in order to eliminate the previous difficulties in comparing oxides when different cleans and processing steps are used.[1] Substrate defects, atypical to this process, were presumably introduced during the initial wafer cleaning and scattered the time-to-breakdown (TTB) values during a constant current stress of these oxides to the point where statistical comparison of TTB averages was dubious. However, for unannealed wafers and for post polysilicon definition heat treatments of 900°C, RTO oxides grown with HCL had the same oxide trapping rate as the furnace oxides grown with TCA and RTO oxides grown in pure O2 had a faster trapping rate. Higher temperature post polysilicon definition heat treatments had different effects. RTO oxides exhibited better yield than the furnace oxides. These results illustrate the differences between RTO and furnace oxidation in the presence of non-ideal wafer substrates.
Rapid Thermal Nitridation of Thin Oxides
Authors: Shih D.K. , Lee S.K. , Ku Y.H. , Kwong D.L. , Lee S.
Published: March 2011

In this paper the kinetics of initial nitridation of thermal oxides is studied by using rapid thermal nitridation of thin oxides. FTIR and AES were used to investigate the chemical properties of nitrided oxide films. The amount of the nitrogenincorporated in and the oxygen escaped from 100Å oxides has been characterized quantitatively as a function of RTN conditions. Results show that RTN at 1100° for 120s incorporates about 85% and 12% of the maximum nitrogen concentration value at oxide surface and bulk, respectively. The nitrogen pile up peak at interface can be seen after RTN at 1100°C with the time as short as 5 s. Study of the effects of the nitridation temperature and the original oxide film thickness indicates that the reaction species has permeated through oxides before effective replacement reaction takes place. The diffusion coefficient of the permeating species is estimated of the value larger than 40−13cm2/s.
Comparison of the Growth Kinetics of Oxides Grown in Tungsten-Halogen and Water Cooled Arc Lamp Systems
Authors: Paz de Araujo C.A. , Gelpey J.C. , Huang Y.P. , Kwor R.
Published: March 2011

Rapid thermal oxidation of silicon has been performed in a tungsten-halogen system (AG-410) and a water-wall arc lamp system (Eaton ROA-400). Growth kinetics of the oxides are studied with particular attention to ramp-up ambient conditions, dwell time, maximum wafer temperature and difference in activation energies. These parameters are characterized using ellipsometry in order to measure system bias with respect to growth rate and breakdown. Experiments were designed to identify the differences in the initial enhanced growth conditions, and their effect on growth kinetics during the dwell cycle.
In-Situ Processing of Silicon Dielectrics by Rapid Thermal Processing: Cleaning, Growth, and Annealing
Authors: Nulman J.
Published: March 2011

The in-situ processing of silicon dielectrics by rapid thermal processing (RTP) is described. RTP includes here three basic sequentially performed processes: wafer cleaning, oxidation and annealing. The insitu cleaning allows for reduction of chemical and native oxides and silicon surface chemical polish, resulting in interface density of states as low as 5×l09 cm-2eV-1. Kinetics of oxide growth indicates an activation energy of 1.4 eV for the initial linear oxidation rate.
Resistivity Differences in C49 Tisi2 Films Formeid by Rapid Thermal Processing
Authors: Reader A.H. , Van Ommen A.H. , Van Houium H.J.W.
Published: March 2011

TiSi2 films produced from co-sputtered Ti/Si mixtures by rapid thermal processing at temperatures around 630°C were found to have a higher resistivity than films formed by the solid state reaction of deposited Ti with (100) silicon during asimilar anneal. Diffraction studies indicated the films comprised of the C49 phase only. It is argued that the resistivity difference arises from the extremely high (3106cm−1) stacking fault density in the annealed co-sputtered layers.
High Purity Titanium Silicide Films Formed by Sputter Deposition and Rapid Thermal Annealing
Authors: Brat T. , Wei J.C.S. , Poole J. , Hodul D. , Parikh N. , Wickersham C.
Published: March 2011

We have investigated the formation of titanium silicide films sputter deposited from a high purity (99.995%) composite TiSi2.2 target. The films, sputtered at a rate of 3.7 nm/sec, were deposited on Si(100), Si02 , and N+ Poly-Si substrates at temperatures ranging from room temperature to 425°C. Room temperature depositions produced amorphous films, while heated substrate depositions formed crystalline films with a metastable C49 TiSi2 structure. Rapid thermal processing of these films at temperatures higher than 700°C resulted in the formation of a stable C54 TiSi2 structure. Stoichiometry of the deposited films over a 10 cm diameter wafer was found to be independent of the substrate temperature. Stress in the films was measured as a function of deposition and annealing parameters. The amorphous films showed a tensile stress of about 0.1 GPa, while films deposited on substrates at 425°C had an order of magnitude higher tensile stress level.The resistivity measured on the 400°C deposited films was about half of that obtained with the films deposited at roomtemperature. A comparison between films deposited on a hot substrate and those which were rapid thermal processed is presented.
omparisons of Silicide Formation by Rapid Thermal Annealing and Conventional Furnace Annealing
Authors: Ma E. , Natan M. , Lim B.S. , Nicolet M-A.
Published: March 2011

Silicide formation induced by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) in bilayers of sequentially deposited films of amorphous silicon and polycrystalline Co or Ni is studied with RBS, X-ray diffraction and TEM. Particular attention is paid to the reliability of the RTA temperature measurements in the study of the growth kinetics of the first interfacial compound, Co2Si and Ni2Si, for both RTA and CFA. It is found that the same diffusion-controlled kinetics applies for the silicide formation by RTA in argon and CFA in vacuum with a common activation energy of 2.1+0.2eV for Co2Si and 1.3+0.2eV for Ni Si. Co and Ni atoms are the dominant diffusing species; during silicide formation by both RTA and CFA. The microstructures of the Ni-silicide formed by the two annealing techniques, however, differs considerably from each other, as revealed by cross-sectional TEM studies.
Application of RTA To Bipolar Ic'S
Authors: Reuss Robert H. , Bushey Thomas P.
Published: March 2011

RTA has been investigated for a variety of applications including implant anneal and modification of poly silicon. However, little has been reported on the integration of RTA into actual process flows. We describe here results for bipolar IC's with RTA for the fabrication of shallower junctions and lower sheet resistance (Rs) poly electrodes. For a successful bipolar IC, not only are good diode characteristics and related transistor parameters important, but also, resistor behavior, uniformity, and yield are critical. An AG Heatpulse system was used to successfully anneal the emitter implant of 2.0 um design rule bipolar IC's. The yield and variation in gate delay were comparable to furnace annealed counterparts. These results are especially encouraging since both transistor performance and resistor matching are critical for the circuits tested. However, significant improvement in gate delay was not observed.
Control of Bipolar Junction Transistor Current Grain Using Rapid Thermal Processing.
Authors: Kermani A. , Van Gieson F. , Litwin S. , Sullivan R. , DeBolske T. J. , Crowley J.L.
Published: March 2011

The activation of ion implanted emitters for two types of NPN bipolar junction transistors ( BJT ) by rapid thermal processing (RTP) was evaluated. The dopant profiles and the resultant junction depths were measured for various thermal cycles, using spreading resistance profile technique. The electrical characteristics of the transistors were then determined and compared to the standard furnace processes. The common emitter current gain values, hFE, for arsenic emitters were low and phosphorous emitters exhibited improved or comparable betas. The breakdown voltages in common emitter configuration, BV,CEO, BVcEs and BVEBO were comparable or better than the furnace annealed samples and no evidence of transistor leakage was observed.
The Effect of Rapid Thermal Processing on the Electrical Characteristics of Polysilicon Gate Mos Capacitors
Authors: Felch Susan B. , Hodul David T. , Mak Salimian Mak Salimian
Published: March 2011

Rapid thermal processing has previously been observed to affect the dielectric integrity of thin oxides.' In order to study this phenomenon in more detail, we have fabricated a set of wafers with 290 Å thick gate oxide and patterned pads of 2000 Å thick doped polysilicon. Some of the pads were patterned with a wet etch, while others were dry etched in a commercial reactive ion etcher (RIE), which is suspected to be a damaging process. To simulate a self-aligned MOS process, some of the patterned wafers were also ion implanted with 70 keV, 2E15 As+/cm2 . Subsequently, all of the wafers were rapidly annealed in a Varian RTP-800 lamp annealer under a variety of conditions (lO00-1100°C, 10-30 sec), and the breakdown characteristics of the MOS capacitors were measured. A few control samples were annealed in a furnace. It was found that the rapid annealing cycle without ion implantation or dry etching caused no deterioration of the oxide quality. However, rapid annealing after either RIE or implantation does result in oxide breakdowns at lower voltages, with those capacitors having higher perimeter-toarea ratios affected to a greater degree. The effect of capacitor shape and annealing conditions on breakdown statistics and uniformity will be presented and discussed in light of possible ion bombardment damage during RIE and oxide charging during ion implantation. Several mechanisms explaining the breakdown properties will be discussed.
Silicon Temperature and Thermal Gradients Measurements in a Rapid Thermal Processor Operating at Atmospheric Pressure or in Vacuum
Authors: Dilhac J-M. , Ganibal C. , Martinez A.
Published: March 2011

Temperature-time profiles obtained by an optical pyrometer and a mechanically contacted thermocouple are first presented it appears that the thermocouple response is sensitive to the pressure in the processing chamber. The authors suggest that, in vacuum, the thermocouple is thermally isolated from the wafer, until the temperature is high enough for thermal radiation exchanges to occur. Experimental evidence of the influence of thermal history, and of gas pressure and flow, on temperature drop at periphery of the wafer is then given.
A Method for Rapid Thermal Annealing of Compound Semiconductors by Cw CO2 Laser Irradiation
Authors: Neta U. , Richter V. , Kalish R.
Published: March 2011

A new Rapid Thermal Processing technique based on heating by irradiation from CO2 laser is presented. It is particularly suitable for thermal treatment of low melting temperature materials such as annealing implantation induced damage in compound semiconductors.

Short time heating of the sample is achieved by its contact with a quartz plate heated by photons from a CW CO2 laser. The quartz serves both as an absorbing medium for the radiation and as a proximity cap. Steady state temperature can be obtained by the simultaneous heating of the sample by the laser and its cooling by a jet of N2 gas.

The present technique, when applied to ion implanted InSb (TA<450°C, t=10 seconds), leads to removal of the implantation damage which is comparable to that obtained by furnace or flash lamp (Heatpulse™)annealing.
Rapid Thermal Processing: How Well is it Doing and Where is it Going?
Authors: Sedgwick T.O.
Published: March 2011

The use of Rapid Thermal Processing (RTP) as a processing tool in semiconductor technology is still increasing and and becoming more diverse. The use of RTP in a reactive mode for film growth and deposition is an important new direction. The strong interest in III-V compound annealing studies represents one of the most important application areas. Although RTP is predominantly exploratory and developmental in nature it is slowly being introduced into the manufacture of Si devices. The technological necessity for the greater use of RTP in routine production will depend on either demonstrated productivity/cost advantages or on some intrinsic advantage of RTP. The intrinsic advantages of RTP are due to the single wafer processing nature of the operation or due to the possibility of selectively enhancing one desired process over another undesired reaction in a partically fabricated structure. Although significant impovements in commercially available reactors have been made in the last several years, better temperature measurement and control and particularly temperature uniformity of the wafer are still sorely needed.
Properties of Gallium Implanted Furnace and Rapidly Annealed Polycrystalline Silicon
Authors: Harrison H.B. , Pogany A.P. , Komem Y.
Published: March 2011

Polycrystalline silicon films have been amorphized by implantation with 100keV Ga ions of doses 0.3 and 6×1015cm−2. These films were subsequently recrystallized using either a furnace for longer times lower temperature (∼30 mins, 600° C) or rapid thermal processing (RTP) for shorter times higher temperatures ( ≤ 30 sec, 800° C, 900° C) in an endeavour to suppress any long range movement of the Ga during the anneal phase. It is found that for both the furnace and RTP for temperatures ≤ 800°C no significant movement is observed and that the lower temperature anneal for the highest dose produces the highest electrical conductivity. By contrast however, annealing at 900° C, even though the initial conductivity is higher than for any other anneal we observe a significant reduction with time and extremely rapid movement of the dopant species throughout the original poly layer. An initial rationale for this behaviour is proposed in terms of a liquid phase transformation during annealing.
Secondary Grain Growth During Rapid Thermal Annealing of Doped Polysilicon Films
Authors: Cammarata R. C. , Thompson C. V. , Garrison S. M.
Published: March 2011

Recently there has been a great deal of interest in the use of thin (≤0.1µm) heavily doped polysilicon films as diffusion sources for shallow junctions in silicon substrates. It has been reported that grain growth and solid phase epitaxy occur during annealing of such films and that the apparent rates of both are much greater during rapid thermal annealing. We report similar grain growth behavior for rapid thermal annealed thin polysilicon films deposited onto amorphous SiO2. Based on these experimental results we propose that solid phase homoepitaxy in polysilicon films occurs via secondary grain growth. This process proceeds rapidly at first but slows down due to grain boundary drag. Rapid thermal annealing of polysilicon films provides a method for selectively utilizing the kinetic process that dominates for short times.
Electrical Properties of n- and p-type In0.53Ga0.47As Layers Formed by Ion Implantation and Rapid Thermal(Flash)Anneal
Authors: Liu S.G. , Narayan S.Y. , Magee C.W. , Wu C.P. , Kolondra F. , Paczkowski J. , Capewell D.
Published: March 2011

Rapid thermal annealing (4−7s) of 28Si and 9Be implants in VPE-grown In0.53Ga0.47As has produced n- and p-type active layers with controlled doping levels between 1017 and 3×1018 cm−3. The multiple-implant schedules were based on Rp and ΔR data derived from SIMS measurements on single-energy implants. The activated n- and p-type layers have a good surface morphology and 300 K mobilities of 3000–7000 and 100–200 cm2 /V−s, respectively. Data on implant schedules, electrical characteristics, carrier concentration profiles, and Rp /ΔRp information are presented.
Thermal Stability of Tasix-Gaas Schottky Barriers
Authors: Haynes T. E. , Han C. C. , Lau S. S. , Picraux S. T. , Chu W. K.
Published: March 2011

Sputtered TaSix films on GaAs have been examined as potential refractory Schottky barrier contacts suitable for self-aligned gate fabrication of GaAs MESFETs. The thermal stability of electrical and physical characteristics has been studied following furnace annealing or rapid thermal processing of contacts with compositions near Ta5Si3 (x=06). The electrical characteristics, interface interdiffusion, and evaporation loss of Ga and As through the contact have been examined. The barrier heights of 30-min furnaceannealed contacts were found to increase with temperature over the range 600 to 900°C. The Schottky barrier heights after rapid thermal processing (RTP) of the contacts were fixed at 0.78 eV for temperatures in the range 700 to 900°C. A major finding of this work is that the Schottky barrier contact maintains its integrity even though the equivalent of at least 5 monolayers of Ga and As have decomposed and evaporated through the contact.
Rapid Thermal Processing for High-Speed III-V Compound Devices
Authors: Kuzuhara M.
Published: March 2011

Recent activities in rapid thermal processing on III-V compound materials are reviewed with primary focus on its application to high-speed GaAs integrated circuits. Advantages of the rapid thermal processing are discussed, from the viewpoint of doping characteristics obtained both for n-type channel implants and for high dose n-type contact implants. Enhanced electrical activation is demonstrated by optimizing the encapsulating material employed for annealing high-dose Si implants. Not only these advantages, but also several problems, which should be solved before this technology can be fully utilized in industrial applications, are discussed. Special attention is devoted to improvement in the activation uniformity over a complete 2 inch diameter GaAs wafer.
The Redistribution of Impurities Under RTP for Polysilicon Capped Silicon
Authors: Hockett R. S.
Published: March 2011

Rapid Thermal Processing is being evaluated in the IC industry as a way to meet the thermal budget requirements of reduced scaling in high performance Si IC's. As scaling is reduced and alternative processing is used, the study of low level interfacial impurities is expected to become more important. An example is presented here for the redistribution of interfacial impurities under RTP for polysilicon capped silicon similar to that proposed for shallow junction bipolar transistors.