bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Water Chemistry on the Leach Resistance of Synroc C
Authors: Woolfrey J. L. , Levins D. M.
Published: March 2011

The chemical durability of SYNROC C has been measured as a function of repository conditions, namely, temperature, surface/volume ratio, groundwater pH and composition. The leach rate of SYNROC C is less dependent on temperature than borosilicate glasses; activation energies range from 15-25 kJ mol-1 compared to 33-74 kJ mol-1 for glass. The rate of release from SYNROC C is very low and independent of solution composition for the solutions studied. There is little variation in leach rate over the pH range 4-9, but at pH 2 the rate is up to 10 times higher. SYNROC C leach rate is independent of flow rate or surface/volume ratio for the mobile waste elements because of the unimportance of solution saturation effects owing to the low concentration of dissolved solids. The differential leach rate decreases rapidly with time because, after initial leaching from grain boundaries and metastable minor phases, the highly insoluble matrix protects the more leachable elements from further attack.
Static Leaching of Radioactive Glass Under Conditions Simulating a Granitic Repository for High-Level Waste: Phase 1.
Authors: Hermansson Hans-Peter , Christensen Hilbert , Clark David E , Björner Inga-Kari , Yokoyama Hayaichi , Werme Lars
Published: March 2011

A joint research project with participation from
Japan, Switzerland and Sweden is underway at Studsvik (The JSS-project). The project concerns investigations on the leaching of fully radioactive glass (containing 12 wt% fission product oxides and actinide oxides) manufactured by CEA/Marcoule.

So far the glass has been leached in doubly distilled water and in silicate water at 90°C. Some leaching experiments involved the presence of crushed Stripa granite in the same containers as the glass.

Due to strong radiation and the presence of plutonium the leaching was carried out in a specially designed lead cave using gilded stainless steel containers.

Weight losses, pH and elemental mass losses were determined together with infrared reflection spectral changes. These data are compared to those obtained from a simulated nonradioactive glass of nearly the same composition and to similar alkali borosilicate glasses previously investigated at Studsvik.
The Role of Eh in Nuclear Waste Form Dissolution
Authors: Phelps Freeborn W. , White William B.
Published: March 2011

A series of experiments was conducted to evaluate the significance of redox potential, Eh, as an independent opensystem variable in the dissolution of nuclear waste glasses and ceramics. The standard platinum electrode can be used in leach solutions. Measurements on couples with rapid kinetics such as Fe+++/Fe++ give results in agreement with thermodynamic calculations. Highly reducing leaching solutions can be obtained by passing hydrogen through the solvent in the presence of a palladium catalyst.
The Retention of Redox Sensitive Waste Elements in Compacted Bentonite
Authors: Torstenfelt B. , Allard B.
Published: March 2011

The diffusion of technetium, iodine, uranium and neptunium in compacted bentonite has been studied. The possible reduction of the transport rate of these elements (i.e. redoxsensitive elements) by mixing the clay with metallic iron (for technetium, uranium and neptunium) or by adding a chemisorbent (for iodine) to the clay is reported. Technetium has an apparent diffusivity about 5 times higher in the heptavalent state (TcO4−) than in the tetravalent state (TcO(OH)2 or TcO2), uranium and neptunium in their higher oxidation state (VI and V) have apparent diffusivities about 6 and 50 times higher, respectively, than in the tetravalent state. Iodine, as I− (or 103−), has a transport rate more than one order of magnitude lower than TcO4−.
Geohydrologic Factors and Current Concepts Relevant to Characterization of a Potential Nuclear Waste Repository Site in Columbia River Basalt, Hanford Stte, Washington
Authors: Gephart R.E. , Price S.M. , Jackson R.L. , Myers C.W.
Published: March 2011

Geologic features are identified that may affect groundwater movement near a repository located in the Columbia River basalt beneath the Hanford Site, Washington State. These include pathways through flow interiors, flow contacts, and bedrock structural discontinuities. Four concepts are considered to describe groundwater movement in basalt. Differences between concepts principally focus on the degree of vertical leakage through basalt flow interiors. The existing geohydrologic data base is preliminary and insufficient to conclusively support one groundwater-flow concept over another. However, it is proposed that available data tend to support the existence of distinct groundwater-flow systems having relatively low vertical leakage under low hydraulic-head gradients except where structural discontinuities are present. A number of geohydrologic characterization activities are underway to reduce the Present uncertainty regarding potential groundwater pathways.
Studies of Altered Vitrophyre for the Prediction of Nuclear waste Repository-Induced Thermal Alteration at Yucca Mountain, Nevada
Authors: Levy Schon S.
Published: March 2011

Nuclear waste emplacement in devitrified volcanic tuff at Yucca Mountain will raise the temperature of surrounding rock for a geologically significant period of time. This study evaluates the susceptibility of an underlying 50 ft-thick vitrophyre to thermal alteration by examining alteration that occurred in the rock as it cooled after deposition. A 10°C temperature rise should have no mineralogical effects on the vitrophyre, but an increase of 60° or more is likely to result in alteration. Expected mineralogic changes in the vitrophyre caused by this amount of thermal loading include crystallization of zeolites and smectite. Alteration will be concentrated in a thin interval near the top of the vitrophyre and along fractures. Adsorbed water and water in preexisting hydrous minerals and in glass may contribute to hydrothermal alteration of underlying vitrophyre. Bulk porosity change would be slight and local porosity increase would probably be restricted to the upper part of the vitrophyre. Although some fracture filling could occur, such a minor sealing effect would be balanced by development of secondary porosity. Zeolites and smectite, newly-crystallized along fluid flow paths below the waste repository, could provide an enhanced sorptive barrier to radionuclide migration.
Description of the Scope (Simplified Codes For Performance Evaluation) System for Use In Exploratory Analysis of Radionuclide Transporr in a Geologic Medium
Authors: Petrie Gregg M. , Sneider Steven C. , Craig Richard A.
Published: March 2011

A tool has been developed to assist investigators in exploring common problems found in radionuclide transport work. This tool consists of an integrated series of programs known as the Simplified Codes for Performance Evaluation (SCOPE) system. The heart of the system is a set of programs which make use of analytical solutions to the onedimensional solute transport for up to three-member decay chains. Longer chains are approximated by combining the results of the one-, two-, and three-member chain solutions with the effects of short lived members.

SCOPE also provides programs that allow the user to evaluate the results by integrated radionuclide releases or by dose-to-man. In the first case, the integrated release passing through the boundary of an aquifer over time is compared to a given set of criteria. The criteria normally used are those developed by EPA (Radiation Protection Program 1982) [1] for estimating hazard. To provide the user with the option of calculating dose-to-man, two existing programs (ALLDOS and PABLM) were integrated into the system.

The system is not intended to solve all classes of radionuclide transport problems. However, it can provide the user with a good “first cut” understanding of many geohydrologic systems by allowing the problem to be looked at first as one-dimensional flow in a homogeneous geology.
Characteristics of Polycrystalline Copper Films Made by CVD from Cu(HFA)2
Authors: Kim Do-Heyoung , Wentorf Robert H. , Gill William N.
Published: March 2011

Thin Copper films have been deposited on various substrates by the reduction of copper bis-hexafluoroacetylacetonate, Cu(HFA)2, with hydrogen to investigate the characteristics of the films made at 2–10 torr of total pressure, substrate temperatures of 280–400 °C and precursor temperatures of 55–90 °C. Under the conditions investigated, the highest growth rate was 650 Å/min. and the resistivity of the films was routinely near 2.0 μΩ-cm at 5000 Å or more thickness. Film growth rate depended on precursor concentration and substrate temperature. RBS and AES analysis indicate that the copper deposited at 310–400°C is highly pure. SEM photographs revealed that different structures form depending on substrate kind, the deposition conditions and the deposition time. The surface roughness of the films increased with increasing thickness. The reflectivity of the copper films depends on their thickness and decreases as the grain size increases. The grain sizes in the films were about 0.1–2.0 μm and are correlated with film thickness.
The Effect of Polysilicon Doping (Using Ion Implantation or PBr3 Diffusion or Insitu Doping) on TiSi2 Formation
Authors: Chittipeddi S. , Dziuba C. M. , Kelly M. J. , Kannan V. C. , Irwin R. B. , Kahora P. M. , Cochran W. T.
Published: March 2011

In this work we have studied the effect of polysilicon doping on titanium disilicide (TiSi2) formation using extensive physical and electrical characterization.
Quantification and Characterization of the Thermal Degradation of TiSi2 Using Thermal Wave Analysis
Authors: Fernandes M. G. , Sitaram A. R. , Kottke M. L. , Kaushik V. S. , Pintchovski F. S.
Published: March 2011

Thermal wave imaging can be used as a rapid non-destructive in-line probe to monitor defects in metals. In the study of the Ti-polysilicon system, this technique has been used to quantify the degradation of the suicide film by monitoring the formation of a second phase during BPSG annealing. The amount of second phase formed was found to vary with Ti preclean, dopant concentration and temperature of BPSG anneal on both blanket and patterned wafers. The second phase has been identified using TEM and AES to be a silicon rich phase. Digitized thermal wave images were used to obtain information regarding the size distribution of precipitates. These distributions have been correlated with resistivity changes in submicron suicide lines.
A Novel Model for Solid State Reactions in Metal-Silicon Diffusion Couples
Authors: Zhang Lin , Ivey Douglas G.
Published: March 2011

In this study, a novel model has been proposed to describe reactions in thin metal film/silicon diffusion couples. A reactive interface in a metal-Si diffusion couple is considered to be a reaction region, and a reaction process in this region is divided into three steps. Several physical quantities have been defined to describe each of these steps, i.e., the diffusion flux of moving reactant to the reaction region, J; the release rate of nonmoving reactant, r, and the formation rate of the growing phase, F. The relationship between these quantities is demonstrated by means of a reaction process plot, which is also developed in this study. A semiquantitative calculation of the reaction process plot has been done for Mn-Si and Ti-Si systems. The results show that the plots can be successfully used to predict suicide formation sequences.
The Use of Tem and Raman Spectroscopy to Determine the Absorption Coefficient and Silicidation Sequence of Cobalt Silicide
Authors: Weaver Louise , Simard-Normandin Martine , Naem Abdalla , Clark Alison
Published: March 2011

In-line thickness monitoring of CoSi2 films is usually carried out by four-point probe resistivity measurements on blanket samples. This method, however, reveals no information about the thickness variation and stoichiometry of the CoSi2 films. Transmission Electron Microscopy (TEM) can provide this information but the technique is destructive, whereas Raman spectroscopy is non-invasive and offers a technique for patterned wafers compatible with current VLSI technology.

The CoSi and Co2Si phases exhibit very characteristic Raman signatures which, with glancing angle X-ray diffraction (GA-XRD), can be used to investigate the silicidation sequence. Although CoSi2 does not produce a Raman spectrum, the silicon local mode can be easily detected through the film and is very sensitive to variations in thickness. The intensity of the silicon local mode was measured on a series of ten samples of CoSi, on silicon and the precise CoSi, film thickness subsequently determined by cross sectional TEM. From these measurements, the absorption coefficient of CoSi2 at 500nm was determined.
Interactions Between Metallization or Diffusion Layers and Doped Silicon Plugs in Deep-Submicron Contact-Holes
Authors: Drynan John M. , Hada Hiromitsu , Kunio Takemitsu
Published: March 2011

Phosphorus-doped polycrystalline silicon used to plug the high-aspect-ratio, deep-submicron contact-holes connecting suicide metallization layers and substrate diffusion or silicide/polycide layers used in prototype 64 and 256 mega-bit DRAM devices acts as a dopant source at the silicidc/plug and plug/substrate interfaces during thermal processing. This outdiffusion of phosphorus from the contact-hole plug can lead to increased contact resistance which degrades device reliability and performance. Non-doped silicon, titanium, and titanium nitride films have been investigated as phosphorus outdiffusion buffer or barrier layers which reduce or prevent interaction between the doped contact-hole plug and surrounding conduction layers. Non-doped silicon diffusion buffer layers alternately deposited with in situ-doped silicon dopant source layers have been found to be effective in reducing outdiffusion into the substrate whereas a TiN diffusion barrier layer sputter deposited between the plug and WSix metallization prevents dopant outdiffusion into the WSix layer.
A New Approach to Temperature Dependent Ideality Factors in Schottky Contacts
Authors: Horváth Zs. J.
Published: March 2011

Schottky diodes often exhibit anomalous current-vol tage characteristics at low temperatures (T) with T dependent ideality factors (IF) and apparent barrier heights (BH) evaluated for the thermionic emission. In this paper theoretical expressions are first presented for the T dependences of the IF and the apparent BH for the thermionic-field emission (TFE) including the bias dependence of BH. Model calculations are reported, which has been performed using these expressions, and their results are compared with the available experimental data. It is shown that the T dependence of the 1 Fs and apparent BHs often may be explained self consistently by the TFE with anomalously high characteristic energies Eoo.
Characterization of Rapid Thermally Nitrided Titanium Films Contacting Silicided and Non-Silicided Junctions
Authors: Chittipeddi S. , Kelly M. J. , Dziuba C. M. , Irwin R. B. , Kahora P. M. , Kaiman V. C. , Cochran W. T.
Published: March 2011

In the present work we have studied rapid thermally nitrided titanium films which contact self-aligned silicided titanium disilicide (TiSi2-salicided) and non-silicided junctions. We correlate electrical contact resistance data to SIMS results.
Oxidation of Semiconducting Iron Disilicide (β-FeSi2)
Authors: Lundberg Nils , Erlesand U. , Östling M.
Published: March 2011

Iron disilicide (β-FeSi2) has gained significant importance in recent years because of its semiconducting properties. The bandgap is reported to be direct with an energy of 0.85–0.89 eV, thus making the suicide a potential candidate for optical communications and detector applications. Compatibility with standard VLSI processing might involve a suicide thermal oxidation step. This work concerns the kinetics of both dry and wet oxidations of β-FeSi2. The oxide quality was characterized with respect to the electrical breakdown voltage. The results indicate an oxidation temperature dependence of the oxide quality and that dry oxidation yield higher breakdown voltage than wet oxidation. Structural and semiconducting suicide properties were investigated before and after oxidation. High energy implantation of xenon was used in a marker experiment to investigate a possible change of oxidation mechanism between dry and wet oxidation.
Process-Dependent Electronic Structure at Metallized GaAs Contacts
Authors: Brillson L. J. , Vitomirov I. M. , Raisanen A. , Chang S. , Viturro R. E. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: March 2011

The influence of metallization and processing on Schottky barrier formation provides the basis for one of several fruitful approaches for controlling junction electronic properties. Interface cathodo-and photoluminescence measurements reveal that electrically-active deep levels form on GaAs(100) surfaces and metal interfaces which depend on thermally-driven surface stoichiometry and reconstruction, chemical interaction, as well as surface misorientation and bulk crystal quality. These interface states are discrete and occur at multiple gap energies which can account for observed band bending. Characteristic trends in such deep level emission with interface processing provide guides for optimizing interface electronic behavior. Correspondingly, photoemission and internal photoemission spectroscopy measurements indicate self-consistent changes in barrier heights which may be heterogeneous and attributable to interface chemical reactions observed on a monolayer scale. These results highlight the multiple roles of atomic-scale structure in forming macroscopic electronic properties of compound semiconductor-metal junctions.
Pt3In7 Ohmic Contacts to n-TYPE GaAs
Authors: Swenson D. , Chang Y. A.
Published: March 2011

A thermodynamic and kinetic rationale was utilized to select Pt3In7 as an ohmic contact to n-GaAs. This analysis predicted that the contact metallurgy would be very simple and extremely uniform upon annealing. Preliminary electrical results showed that annealing samples at temperatures of 650 °C or higher led to ohmic behavior. A contact resistance of 3.4 × 10-5 Ω-cm2 was found upon annealing an uncapped contact at 750 °C for 15 s.
Chemical and Electrical Characterization of the CoGa/GaAs Interface as A Function of Temperature: A Thermally Stable Schottky Barrier up to 500°C
Authors: Alec Talin A. , Ngo Tue , Stanley Williams R.
Published: March 2011

X-ray diffraction studies and current-voltage measurements have been performed on a (100) oriented single crystal thin film of CoxGa1-x (x = 0.42) grown epitaxially on n-GaAs, from 300°C to 900°C. At this composition, CoxGa1-x, which has a broad range of homogeneity and a variable lattice parameter, is lattice matched to GaAs better than 0.5%. A Schottky barrier height of 0.68eV and an ideality factor of 1.07 have been measured up to 500°C, with significant barrier degradation at 600°C. At 700°C formation of the CoGa3 phase and a shift in CoxGa1-x stoichiometry to its bulk thermodynamically most stable composition of Co.45Ga.55 was observed with x-ray diffraction. At 800°C Co2AS formed, and at 900°C only CoGa3 and Co2As phases remained in contact with GaAs.
Metallurgical and Electrical Characteristics of MoAlx Schottky Contacts to n-GaAs
Authors: Huang T. S. , Peng J. G. , Lin C. C.
Published: March 2011

The interfacial stability, surface morphology and electrical characteristics of MoAlx contacts to n-GaAs have been investigated by using x-ray diffraction, scanning electron microscopy, sheet resistance and current-voltage measurements. The compositions of rf-cosputtered MoAlx films were x = 0.35, 2.7, and 7.0, respectively. The contacts were annealed by rapid thermal processing in the temperature range 500–1000 °C for 20 s. The interfaces of MoAl0.35/GaAs and MoAl2,7/GaAs were stable up to 900 °C, while the interfaces of MoAl7.0/GaAs were less stable and reactions occurred above 800 °C. The variations of sheet resistances and the barrier heights of the Schottky diodes as a function of annealing temperatures can be well correlated to the interfacial stability. The MoAl2.7/n-GaAs diodes exhibited the best stability and were characterized by the highest barrier height (0.98 V) and nearly unit ideality factor (1.11) after annealing at 900 °C. For all thermally stable MoAlx/n-GaAs Schottky diodes, the barrier heights increased with annealing temperature.
Ge/Pd and Si/Pd/Ge/Pd Non-Alloyed Ohmic Contacts to InP Examined by Backside Secondary Ion Mass Spectrometry
Authors: Schwarz S. A. , Sands T. , Bhat R. , Koza M. , Pudensi M. A. A. , Wang L. C. , Lau S. S.
Published: March 2011

High resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd and Si/Pd/Ge/Pd non-alloyed ohmic contacts on InP are obtained by sputter-etching from the back (semiconductor) side. The samples contain an InGaAs etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles. Detailed comparisons are made to corresponding contacts on GaAs, processed and analyzed under similar conditions. The importance of interfacial alloy formation, semiconductor regrowth, and dopant incorporation are highlighted.
Ta-Si-N and Si3N4 Encapsulants for InP
Authors: Reid J. S. , Ruiz R. P. , Kolawa E. , Chen J. S. , Madok J. , Nicolet M -A.
Published: March 2011

Thin films of sputtered, amorphous Ta36Si14N50 (a metallic conductor) and Si3N4 (an insulator) were evaluated as encapsulants for (100)-oriented InP substrates. Thicknesses of both films were approximately 100 nm. During a 15 min annealing in Ar, liberated phosphorus was gettered by a ISiO2ITa(100 nm) collector placed face-to-face on encapsulated or non-encapsulated InP. The stability of the InP with the encapsulant was characterized by backscattering spectrometry, scanning electron microscopy, and x-ray diffraction. As measured by 4He++ backscattering spectrometry, detectable amounts of phosphorus do not arise in the Ta collectors for the Ta-Si-N and Si3N4 encapsulation schemes until 650 and 700°C, respectively. Failure of the Ta36Si14N50 film is catastrophic at 700°C whereas the Si3N4 film degrades locally commencing at 600°C.
The Formation of TiN-Encapsulated Cu Interconnects
Authors: Li Jian , Strane J. W. , Russell S. W. , Chapman P. , Shacham-Diamand Y. , Mayer J. W.
Published: March 2011

A TiN(0)-encapsulated copper structure was made by annealing a Cu-10 at%Ti alloy film evaporated on a SiO2/Si(100) substrate in N2 or NH3 ambiente. During thermal cycling, the tensile stress in the nitridated films is in the range of 200 to 800 MPa. The stress relaxation depends on the cooling cycle and the presence of interlayer between film and substrate. A fast heating rate (70°C/min.) to 550°C in an NH3 ambient can effectively suppress the formation of Cu3Ti and enhance the TiNχ(0) formation near the surface of the copper film. This self-encapsulated Cu structure exhibits good adhesion to SiO2 and oxidation resistance. A fully encapsulated Cu fine line structure can be achieved by annealing a Cu-10at%Ti alloy film in an Ar ambient at 550°C and then in an NH3 ambient at 550°C to form TiOχ/Ti5Si3 adhesion layer and TiN(O) layer, respectively.
Copper Film Deposition Using H and O Atoms
Authors: Ann Halstead Judith , Locke Peter S. , Reeves Robert R.
Published: March 2011

The formation of thin copper films by H-atom reaction with Cu(FOD)2 and Cu(HFA)2 has been demonstrated at near room temperature. Oxygen atoms have now also been reacted with these β-diketonate copper complexes, producing films of copper oxide which can be readily reduced by subsequent treatment with H-atoms. The thin copper films produced are conductive and highly adherent. The oxygen atom reaction with the copper complex produces a visible chemiluminescent glow, yielding information on the nature of the reaction process.
In-situ emissivity and temperature measurement during rapid thermal processing (RTP)
Authors: Vandenabeele P. , Schreutelkamp R. J. , Maex K. , Vermeiren C. , Coppye W.
Published: March 2011

A prototype RTP system has been developed which allows for in-situ emissivity and temperature measurements. The wafer emissivity is measured by using an optical detector at a wavelength of 2.4 μm and by modulation of the lamp power. This method permits accurate temperature determination in the range from 400 to 1200°C, independent of wafer backside roughness, backside layers, and transmit tance. The feasibility of the temperature measurement technique is demonstrated by using wafers with built-in thermocouples and highly As-doped wafers with different backside roughnesses or layers. The emissivity variations during processing can also be used to study thin film reactions in-situ. This is demonstrated for Co silicidation using probing wavelengths varying from 0.6 to 3.2 μm.
Reactions of Titanium Films with thin Silicon Dioxide, Nitride, and Oxynitride Films During Rapid Thermal Annealing
Authors: Ko Sen-Hou , Devashrajee N. M. , Murarka Shyam P. , Ding Pei-Jun , Lanford William A.
Published: March 2011

The interactions of Ti with SiO2, Si3N4, and SiOiNy have been studied during rapid thermal annealing at 400 to 900 °C in Ar with 3% H2 ambient. X-ray diffraction, sheet resistance measurements, RBS, nuclear reaction technique to profile hydrogen, and microscopy have been employed in this study. The results of this investigation indicate that Si3N4 and SiOxNy are more stable with Ti than SiO2.
Quick Tests for Electromigration: Useful but not without Danger
Authors: Lloyd J. R.
Published: March 2011

Traditional electromigration life testing is a time-consuming and often painful process, consuming many expensive samples and weeks of valuable time to collect enough data for a statistically significant conclusion. Annoying, to say the least, this often causes real problems in process development when cycle times of new products can often be measured in months. Therefore, there has been a strong incentive to search for alternatives.
The Effect of Copper on the Titanium-Silicon Dioxide Rbaction and the Implications for Self-Encapsulatin G. Self-Adhering Metallization Lines
Authors: Russell Stephen W. , Li Jian , Strane Jay W. , Mayer James W.
Published: March 2011

Co-evaporated Cu-Ti films on thermally-oxidized Si substrates were annealed in vacuum at temperatures between 300 and 700°C. Reactions within the films and between film and substrate were monitored by Rutherford backscattering spectrometry, X-ray diffraction, transmission electron microscopy and sheet resistance. We found that, despite the competition from intermetallic compound formation, the Cu-Ti films react with SiO2 beginning at 400°C, with Ti migrating to the SiO2 interface to form both a suicide, Ti5Si3, and an oxide and to the free surface to form additional oxide. The reaction leaves relatively pristine Cu. Above 600°C, however, Cu begins to react with the underlying suicide. By comparison, pure Ti reacts with SiO2 only above ∼700°C.
TiN Metallization Barriers: From 1.2μ to 0.35μ Technology
Authors: Pintchovski Fabio , Travis Ed
Published: March 2011

The evolution of modern integrated circuit technology to sub micron dimensions has brought about a number of challenges, specially in the field of metallization. Decreasing junction depths have imposed stringent demands on the materials used for the electrical contacts. This is due to the potential interactions between the contact metal and silicon (or suicide in the case of salicide processes) causing junction leakage and/or shorting. The solution most commonly applied to this problem is that in which a barrier material is interposed between the metallization and the contact. The material most often selected for this purpose has been TiN. TiN can be deposited via the reactive sputtering of Ti in a N2 atmosphere or it can be also obtained by sputtering Ti and then reacting it with either N2 or NH3. Shrinking VLSI dimensions have brought about the need for improved planarization for the purposes of metal definition. It has also prevented the tapering of contacts for space saving reasons. Both of these issues resulted in deep, straight wall contacts with aspect ratios greater than 1 that cannot be metallized appropriately with conventional sputtering techniques. These requirements have driven the development of a conformai CVD TiN barrier process. This paper describes the evolution of the TiN metallization barrier from the requirements of 1.2μ to 0.35μ technologies.
Reaction Growth and Morphology of An Aluminide Compound in Al-Cu/Ti-W Bilayers
Authors: Park M. , Krause S. J. , Wilson S. R.
Published: March 2011

The effect of copper content on the reaction growth and morphology of Al12W in Al-Cu/Ti-W bilayers was studied with plan view and cross-section transmission electron microscopy. After heat treatment at 450°C for 30 minutes, a spiked growth of A112W penetrated into the grain boundaries of Al-0.5 wt.% Cu film by the reaction of Al with the Ti-W sublayer. Increasing copper addition from 0.5 to 1.5% inhibited the spiked growth of AI12W, resulting in a flat and planar layer (-150Å) of Al12W. It is suggested that increasing copper segregation in the aluminum grain boundaries during heat treatment at 450°C causes a significant change in the growth morphology of the Al12W compound.
Characterization of TiN Diffusion Barrier for Submicron Technology
Authors: Dixit G. A. , Chen F. S. , Zhang H. , Yao G. D. , Wei C. C. , Liou F. T.
Published: March 2011

The electrical properties and structure of reactively sputtered titanium nitride barrier metal films have been characterized. Junction leakages and yields for different post deposition treatments of the barrier metal layer are reported. TEM, x-ray diffraction and Auger electron spectroscopy have been used for the physical characterization of the TiN films.
A Mass Spectrometric Study of Process Steps of a Tungsten LPCVD Process
Authors: Silvestri T. A. , Guzzo G. C. , Brestovansky D. F. , Markle R. J. , Barber R.
Published: March 2011

The study of the wafer atmosphere during processing has become a key practice in understanding interactions of the process gases with the wafer, internal chamber surfaces and other process gases. For today's ULSI fabrication, Low Pressure Chemical Vapor Deposition (LPCVD) of tungsten has become common for sub-micron contact and via filling and was the chosen process for this investigation. The wafer atmosphere during key process steps of the tungsten LPCVD process has been characterized by mass spectrometry. During the tungsten LPCVD process studied, the TiN surface was first conditioned for tungsten deposition by generating active nucleation sites. This is followed by the actual deposition. After the deposition, wafer backside etch with NF3 plasma, wafer removal and an in situ chamber clean with NF3 and H2 plasmas performed. This paper discusses the mass spectral analysis of the tungsten LPCVD process during the nucleation, backside etch and in situ chamber clean process steps. Additionally, this paper describes benefits of in situ gas analysis.
Pt Reactions with Ge, SiGe, and Si/SiGe Superlattices
Authors: Wang P. J. , Chang Chin-An , Meyerson B. S. , Chu J. O. , Tejwani M. J.
Published: March 2011

Reactions between Pt and SiGe alloy have been studied by comparing several structures: Pt/Ge, Pt/SiGe, and Pt/Si-SiGe superlattices. The Ge, SiGe layers and Si-SiGe superlattices were grown on (100) Si substrates by the ultrahigh vacuum/chemical vapor deposition technique. Pt-Ge reactions start around 200 °C, forming PtzGe. This is followed by the formation of PtGe around 300 °C. The Pt-Ge reactions are thus similar to those of Pt-Si. The reactions between Pt and SiGe, however, involve a preferential Pt-Si reaction. At 200 °C, for example, while Pt2Ge is normally seen from the Pt/Ge system, only PtzSi is detected from both x-ray diffraction and Rutherford backscattering measurements. At higher temperatures, both the PtGe and PtSi phases form. This preferential Pt-Si reaction is observed in both Pt/SiGe and Pt/Si-SiGe superlattice structures.
Metallization Systems for Bonding of InP Laser Diodes to CVD-Diamond Submounts
Authors: Katz A. , Wang K-W. , Baiocchi F. A. , Dautremont-Smith W. C. , Lane E. , Lee C -H. , Wong Y- M. , Tai K. L. , Bacon D. D. , Luftman H. S. , Varma R. R.
Published: March 2011

Some metallization systems consisting of barrier metals and Au-Sn (multiple alternating layers) were studied as a bonding schemes of InP-based laser diodes to the first time used, CVD-diamond submounts. The first system to be studied, which was traditionally used in various other applications was Ti(100nm)/Pt(200nm)/Au(500nm)/Au-Sn(2.5 μm). This structure provided a molten Au-Sn layer of eutectic composition (80:20 wt%) on top of the Ti/Pt metals for about 6 sec, while heated at temperatures of 300 to 350°C, and allowed for efficient bonding of the device to the submount. Longer heating durations, however, led to reaction between Pt and Sn to consume significant amounts of Sn from the solder, thus elevating its melting temperature and resolidifying the solder. With optimum bonding conditions, a high quality bond of the InP-based laser diode to the CVD-diamond submount was observed, and a superior electrical performance of the diode was measured compared to diodes that were bonded with the standard In/BeO configurations. In order to maintain the superior performance of the InP laser diode bonded assembly but improve the thermodynamic stability of the metallurgical system and thus extending the bonding processing window, various metals such as W and Cr were studied as a replacement for the Ti/Pt barrier metals in between the CVD-diamond submount and the Au-Sn solder. While applying the W layer, a thin Ti(10nm) layer was introduced in between it and the Au-Sn to improve the solder wettability. The W layer was found to remain intact after heating at 350°C for durations as long as 5 min, and thus, due to the inert nature of the Au-Sn/W interface, the Au-Sn ratio was kept uniform at the eutectic liquid composition through a long heating duration (up to 5 min). Minimum reaction was observed, as well, at the Au-Sn/Cr interface, while executing a Ti(100nm)/Cr(200nm)/Au-Sn(1.5 μm) system, and thus allowed for an excellent bonding of the InP laser diodes to the CVD-diamond submounts.
High Temperature Performance, Reliability and Simulation of GaAs Mesfets with CVD Diamond Heat Sinks
Authors: Zhu L. , Tang Pin F. , Christou A.
Published: March 2011

An investigation of the temperature stability and high temperature characteristics of GaAs FETs on CVD diamond heat sinks was carried out by modeling the high temperature electrical characteristics for GaAs MESFETs and by experimentally measuring the elevated temperature performance. The thermal characteristics were determined experimentally using infrared microscopy techniques. The thermal measurements by infrared microscopy were correlated with results of a finite element analysis calculation of the GaAs FET thermal distribution. Reliability testing at 230°C resulted in an MTF of approximately 2000 hours.
The Kinetic Effects of Layering Sequence of Al-Ge-Ni Ohmic Contact Components on (001) GaAs
Authors: Lampert W. V. , Haas T. W. , Holloway Paul H.
Published: March 2011

Electrical characterization has demonstrated dramatic differences in the amount of heat treatment time required to convert the ohmic contact metallizations from Schottky to ohmic behavior, depending on the layering sequence of the Al, Ge, and Ni metals. Additional time differences were found to be dependent on the doping concentration of the contact layer of the GaAs and on the heat treatment temperature. For samples with Ge at the metal-semiconductor interface, the time required to convert from Schottky to ohmic behavior varies inversely with the doping concentration of the contact layer and directly with heat treatment temperature. Samples with Ni at the metal-semiconductor interface converted from Schottky to ohmic behavior much faster and had a much smaller dependence on the doping concentration and the heat treatment temperature. Models to explain these observations in terms of interdiffusion of the components and phases formed will be proposed.
The Epitaxial Growth of Al on Hydrogen Terminated Si(100) Substrates with and Without Ion Bombardment
Authors: McEachernt R. L. , Laszig Dirk , Brownt W. L.
Published: March 2011

We have demonstrated that aluminum can be grown epitaxially on H-terminated Si(100) substrates under modest vacuum conditions using thermal deposition. The effect of 1 keV to 4 keV ion bombardment during deposition was found to be either minimal or detrimental. Preliminary results from sputter-deposited Al films show very different behavior, with the films tending to relax from the epitaxial (110) texture to a (111) texture.
A Novel Wavelength Tunable Silicon Detector for Infrared Detection
Authors: Perera A. G. U. , Sherriff R. E. , Francombe M. H. , Devaty R. P.
Published: March 2011

A cryogenic extrinsic silicon detector which can detect IR photons of very low energy, i.e., down to about 5.5 meV ( 220 μm) is presented. The mechanism involves photoexcitation of carriers over low energy interfacial work function barriers at p-i or n-i interfaces in a process analogous to the classic photoelectric effect. Estimates for the responsivity and the detectivity for unoptimized commercial samples containing both p-i and n-i interfaces and a sample containing only a single p-i interface are provided by comparison with a silicon composite bolometer. The range of long wavelength thresholds (λt) observed suggests that this approach can be used to tailor detectors for different IR wavelength regions by changing the dopant impurity and the impurity concentration at levels near the metal-insulator transition. Single interface results confirm the possibility of detector optimization using multilayered structures. This should lead to a unique family of uniform monolithic IR focal plane structures with tailorable and tunable response characteristics within virtually all the IR spectral range of interest.
Photoinduced Electron Transfer Counter to the Bias Field in Coupled Quantum Wells
Authors: Stockman Mark I. , Muratov Leonid S. , Pandey Lakshmi N. , George Thomas F.
Published: March 2011

Optical excitation of electrons in an asymmetric double quantum well is theoretically examined. The well is biased to align the excited levels and permit resonant electron tunneling. Emphasis is made on the photoinduced transfer of electrons counter to the bias electric field force. A density-matrix approach is developed to describe optical excitations in the presence of an arbitrary dephasing. The excitation profiles obtained for cases of different dephasing reveal the full range of tunneling coupling between the wells from completely coherent to incoherent (stepwise).
Carrier Injection and Space Charge Effects in a-Si:H / Crystaiine Si Heterojunctions
Authors: Sanders A. , Swiatkowski C. , Grunow P. , Hirsch W. , Neitzert H. C. , Kunst M.
Published: March 2011

A study of excess carrier kinetics in a-Si:H / crystalline n-Si heterojunctions by transient photoconductivity measurements as a function of the excitation density is presented. It is observed that excess carriers can be injected from the a-Si:H in the c-Si part of the junctions, where the time associated to this injection process can be clearly resolved. The number of injected carriers increases with the number of excess carriers induced in the a-Si:H at low excitation density reaching a limit in the moderate excitation range. The driving force of the injection process is tentatively ascribed to the space charge field at the interface. The injection efficiency is estimated to be about 10%.
Influence of the photoinduced EL2 Grating on Electron and Hole Gratings Generated in GaAs
Authors: Disdier Laurent , Roosen Gerald
Published: March 2011

Dynamic gratings of free carriers are generated from optical excitation of the deep EL2 level in semi insulating gallium arsenide with nanosecond pulses. The nonlinear modification of the crystal index of refraction is evidenced by degenerate four wave mixing experiments. In regards to the sample parameters, a fair agreement is obtained between the experimental values and the theoretical predictions derived from the Drude-Lorentz model and the anharmonic motion of carriers.
Two-Wave Mixing Gain vs Intensity Dependence in Photorefractive GaAs:EL2 in Presence of Strong Electron/Hole Competition
Authors: Gravey Philippe , Wolffer Nicole , Picoli Gilbert , Renais Olivier , Viallet Jean-Emmanuel
Published: March 2011

We studied the pump intensity dependence of the 2WM gain in a photorefractive GaAs:EL2 crystal, with a 3.3 kV/cm d.c. field, at two different wavelengths. The grating period was 37 Am and the beam ratio was 4. At 1.32 μm, the characteristics exhibits a resonant behaviour (with a maximum of 0.23 cm-1). As for InP:Fe, these results can be explained by considering that thermally and optically generated carriers are of different types. The curve at 1.047 Am exhibits an original feature. At low intensities the gain as the same sign than at 1.32 μm (with a maximum of 0.12 cm-1), but the sign changes with increasing intensity and the gain tends towards an asymptotic value of -0.15 cm-1. Such behaviour may also be explained with the same model.
Non-Contact, No Wafer Preparation Deep Level Transient Spectroscopy (DlTS) Based on Surface Photovoltage (SPV)
Authors: Lagowski Jacek , Edelman Piotr , Dexter Mark
Published: March 2011

This work reports on the theoretical modeling and experimental investigation of isothermal SPV-DLTS based on the rate window concept. Experimental implementation of the technique is done using computer analysis of the SPV transients after ceasing the illumination. The transient involves two processes – a recombination of excess minority carriers and a thermal emission of carriers trapped by surface states and bulk defects. The later process is the key one for deep level defect determination.

The upper limit for the measurable deep level emission rate is provided by the recombination lifetime. This limit often exceeds, by orders of magnitude, the standard 103 s−1 limit in capacitance DLTS. The sensitivity of SPV-DLTS is of the same order as that of optical capacitance DLTS.
A New Method for Identification of Electron and Hole Traps in SI-GaAs by Modulated PITS and TSC
Authors: Zhangao Wang , Chengji Li , Hui Zhang , Yunyan Li , Lanying Lin
Published: March 2011

The electron and hole traps in semi-insulating (SI) GaAs can not be identified by common Photoinduced Current Transient Spectroscopy (PITS) and Thermally Stimulated Current (TSC) measurements because of appearing of same sign signal for electrons and holes in both experiments. Therefore, we have developed two approaches which could be used to identify the type of the traps, and the origin of the puzzling negative peaks in the PITS spectra.

The TSC and qusi-stationary Hall effect measurements have been simultaneously performed at the temperatures between 77K and 300K. The sign of Hall voltage corresponding to TSC peak shows the type of the trap.

PITS spectra with applying different bias polarity to the sample were carefully measured with below gap and above gap photoexcitation. According to the change of PITS peak's height with different bias polarity, the electron and hole traps could be readily distinguished, since a negative bias makes hole no contribution to the PITS signal whereas electron swept into the sample would fill the electron traps, and consequently results in the appearence of the electron trap peaks. On the contrary, a positive bias would cause the filling of the hole traps.

The negative PITS peaks appearing or vanishing can be understood if one takes into account the trap initial filling conditions, the carrier recapture and the high dark current etc.
Raman and Ellipsometric Studies of Delta-Doped GaAs
Authors: Yao H. , Schubert E. F. , Kopf R. F.
Published: March 2011

GaAs (100) samples with multiple δ-doped layers (N2D=∼2×1013/cm2) were studied by Raman scattering (RS) and spectroscopic ellipsometry (SE). A quasithree- dimensional (3D) plasmon-phonon coupled mode (L+), probed at λ= 514.5 nm, from a 9-layer δ-doped GaAs with layer-spacing of 100 Å, was observed at ∼895 cm−1. At similar frequency, a plasmon mode was also detected from another GaAs sample with the same δ-doping periods but doubled layer-spacing (200 Å). This provides evidence of spatial quantization of the electron distributions in δ-doped GaAs. The equivalent 3D electron concentration, estimated from the Raman plasmon mode, is ∼1.1×1019/cm3. The presence of the 3D plasmon mode from a quasi-two-dimensional (2D) electron gas is possibly contributed by the electrons in the high energy subbands in the V-shaped potential well of the δ-doped GaAs. The pseudodielectric function <ε>= <ε1>+i<ε2> of this δ-doped GaAs sample was measured by spectroscopic ellipsometry (SE), from an unoxidized surface in an ultrahigh vacuum (UHV) chamber, in the range of 1.5 to 5.0 eV. Compared with uniformly doped GaAs, our SE data indicates a reduced broadening of the optical transitions between the E1 and E1+Δ1, energies due to the δ-doping.
Influence of The Growth Temperature on The Presence of Composition Inhomogeneities in In0.52Al0.48As Layers Grown by MBE on InP Substrates
Authors: Peiro F. , Cornet A. , Hierms A. , Morante J.R. , Georgakilas A. , Halkias G.
Published: March 2011

By using Transmission Electron Microscopy we have studied the presence of composition inhomogeneities in In0.52Al0.48As layers grown on (100) InP. We have found a critical temperature equal to 550°C above which composition inhomogeneities start to appear nonuniformly distributed over the sample area. However, as the growth temperature increases they cover the whole layer. Furtermore, the density of stacking faults and threading dislocations increases for growth temperatures beyond the optimum value of 530°C.
InGaAs/GaAs Quantum Well Structures Grown by Migration-Enhanced Epitaxy
Authors: Wu J.E. , Yoo H.M. , Stoebe T.G.
Published: March 2011

GaAs/In.2Ga.8As/GaAs quantum well structures containing InGaAs layers of thickness over and under the critical thickness (hc) were studied, as grown by both conventional molecular beam epitaxy (C-MBE) and migration-enhanced epitaxy (MEE) techniques. A 6.0 monolayer per cycle (ML/cyc) growth rate, in contrast to a one or less-than-one ML/cyc growth rate used in a conventional MEE process, was used to grow In.2Ga.8As layers over hc. As-grown samples were characterized via photoluminescence, X-ray diffraction, and transmission electron microscopy (TEM). The 6.0 ML/cyc MEE-grown layers over hc show superior optical quality to MBE-grown layers with the same thickness. Both X-ray diffraction and TEM microstructure results indicate that the 6.0 ML/cyc MEE-grown In.2Ga.8As layers are still strained layers while those grown by conventional MBE method are not. The 6.0 ML/cyc MEE process seems to be advantageous for growing InGaAs layers over the critical thickness.