bluuebunny/crossref_metadata_2025 huggingface dataset:
Gamma Radiolysis Effects on Grande Ronde Basalt Groundwater
Authors: Gray W.J.
Published: March 2011

Gamma radiolysis of reference Grande Ronde Basalt groundwater containing 700 mg/L methane produces a milky liquid that is a suspension of fine particles of organic polymers similar to polyethylene. The amount and nature of these polymers does not vary much over the range of conditions tested. Differences in the radiolytic products that are formed may occur when host rock and engineered-barrier materials are present. This possibility is currently being investigated as is the potential for interactions between radionuclides and the products of radiolysis.
Numerical Analysis of Radionuclide Migration Through Engineered Barriers
Authors: Cheung S.C.H. , Chan T. , Lopez R.S.
Published: March 2011

A finite-element simulation has been performed to study the effects on the radionuclide flux, of the failure characteristics of a nuclear fuel disposal waste container, the buffer configuration, and the backfill properties, assuming an intact borehole rock wall. The results show that the total integrated flux from a failed container, through the buffer to a backfill with a diffusion coefficient and hydraulic conductivity higher than that of the buffer, increases as the radial buffer thickness increases, and the vertical buffer thickness decreases. The total flux can be estimated by a one-dimensional diffusion equation. If the backfill has the same diffusion coefficient and hydraulic conductivity as the buffer, the total flux will be reduced by approximately 30% compared with the situation when crushed rock or sand is used as backfill. For localized failure of the waste container, the total flux is mainly dependent on the failure location regardless of the area of the failed surface.
Diffusion in the Matrix of Granitic Rock Field Test in the Stripa Mine Part 2.
Authors: Birgersson Lars , Neretnieks Ivars
Published: March 2011

A migration experiment in the rock matrix is presented. The experiment has been carried out in “undisturbed” rock, that is in rock under its natural stress environment. Since the experiment was performed at the 360 m-level (in the Stripa mine), the rock was subject to nearly the same conditions as the rock surrounding a nuclear waste repository as proposed in the Swedish concept (KBS).

The results show that all three tracers (Cr-EDTA, Uranine and 1-) have passed the zone disturbed by the presence of the injection hole and migrated some distance into “undisturbed” rock.

These results indicate the existence of a connected micro fissure system in undisturbed rock, in which tracers (and therefore radionuclides) can migrate. Diffusivities obtained in this experiment are comparable to those obtained in laboratory experiments.
Mineralogy-Petrology and Groundwater Geochemistry of Yucca Mountain Tuffs
Authors: Bish David L. , Ogard Allen E. , Vaniman David T.
Published: March 2011

Research at Yucca Mountain in southern Nevada (Fig. 1), is being supported by the US Department of Energy to evaluate this site as a possible high-level radioactive waste repository. Yucca Mountain is underlain by a thick sequence of ash-flow and bedded tuffs, with a few silicic lavas.Variations in mode of tuff emplacement and postemplacement alterations have given rise to pyroclastic rocks of quite variable character, ranging from nonwelded to densely welded, vitric to devitrified, and nonzeolitized to completely zeolitized. The proposed repository horizon is in the lower portion of the thick, densely welded Topopah Spring Member of the Paintbrush Tuff in the unsaturated zone. Within the Topopah Spring Member and in the rocks beneath the proposed repository horizon, there are significant variations in mineralogy [1]. Such changes in mineralogy include the localized occurrence of such potentially reactive phases as cristobalite,tridymite, smectite, and volcanic glass. The important sorptive minerals clinoptilolite and mordenite also occur in discrete horizons, and their distribution changes horizontally and vertically. We have undertaken a study of the mineralogy in Yucca Mountain as a function of depth and lateral position to predict the horizontal and vertical distribution of these important potentially reactive and sorptive minerals. This knowledge has aided in locating the repository horizon and will help to put bounds on mineralogic variability within the repository horizon. In addition, studies of the distribution of minerals in Yucca Mountain allow us to deduce the factors that have controlled mineral distributions and to predict mineral assemblages along transport pathways [1,2]. In addition, we are investigating the groundwater chemistry because it and mineralogy are used as input to codes for calculating the transport rate of waste elements from the repository to the accessible environment.
Corrosion Test Plan to Guide Canister Material Selection and Design for a Tuff Repository.
Authors: McCright R. D. , Van Konynenburg R. A. , Ballou L. B.
Published: March 2011

Corrosion rates and the mode of corrosion attack form a most important basis for selection of canister materials and design of a nuclear waste package. Type 304L stainless steel was selected as the reference material for canister fabrication because of its generally excellent corrosion resistance in water, steam and air. However, 304L may be susceptible to localized and stress-assisted forms of corrosion under certain conditions. Alternative alloys are also investigated; these alloys were chosen because of their improved resistance to these forms of corrosion. The fabrication and welding processes, as well as the glass pouring operation for defense and commercial high-level wastes, may influence the susceptibility of the canister to localized and stress forms of corrosion.
Relationship of Engineering Geology to Conceptual Repository Design in the Gibson Dome Area, Utah.
Authors: Helgerson Ronald , Henderson Norman , Memorial Battelle
Published: March 2011

The Paradox Basin in Southeastern Utah is being investigated as a potential site for development of a high-level nuclear waste repository. Geologic considerations are key areas of concern and influence repository design from a number of aspects: depth to the host rock, thickness of the host rock, and hydrologic conditions surrounding the proposed repository are of primary concern. Surface and subsurface investigations have provided data on these key geologic factors for input to the repository design.

A repository design concept, based on the surface and subsurface geologic investigations conducted at Gibson Dome, was synthesized to provide needed information on technical feasibility and cost for repository siting decision purposes. Significant features of the surface and subsurface repository facilities are presented.
Performance Analysis of Conceptual Waste Package Designs in Salt Repositories
Authors: Jansen George , Raines Gilbert E. , Kircher John F.
Published: March 2011

A performance analysis of commercial high-level waste and spent fuel conceptual package designs in reference repositories in three salt formations was conducted with the WAPPA waste package code. Expected conditions for temperature, stress, brine composition, radiation level, and brine flow rate were used as boundary conditions to compute expected corrosion of a thick-walled overpack of 1025 wrought steel. In all salt formations corrosion by low Mg salt-dissolution brines typical of intrusion scenarios was too slow to cause the package to fail for thousands of years after burial. In high Mg brines judged typical of thermally migrating brines in bedded salt formations, corrosion rates which would otherwise have caused the packages to fail within a few hundred years were limited by brine availability. All of the brine reaching the package was consumed by reaction with the iron in the overpack, thus preventing further corrosion. Uniform brine distribution over the package surface was an important factor in predicting long package lifetimes for the high Mg brines.
Very Rough Preliminary Estimate of the Colloidal Sodium Induced in Rock Salt by Radioactive Waste Canister Radiation
Authors: Levy P. W. , Kierstead J. A.
Published: March 2011

Very rough estimates have been made of the total amount, the formation rate and spatial distribution of the Na metal colloid particles induced in rock salt adjacent to four types of radioactive waste canisters. A number of extrapolations were required. Salt immediately adjacent to a lightly shielded, 2.16 kW, high level waste canister could be converted entirely to colloidal Na (and presumably chlorine gas) in 200-400 years. The total Na metal formed will be 250-300 kg. A heavily shielded, 3.3 kW, spent fuel canister will convert roughly 0.3 percent of the salt at the canister surface to colloidal Na and the total sodium metal will be roughly 0.5 kg. Even at the lowest colloid levels the Na metal formed should greatly influence interactions between canisters and the surrounding salt, particularly if brine enters.
Selection of Barrier Metals for a Waste Package in Tuff
Authors: yyRussell E. W. , McCright R. D. , O'Neal W. C.
Published: March 2011

The Nevada Nuclear Waste Storage Investigations (NNWSI) project under the Civilian Radioactive Waste Management Program is planning a repository at Yucca Mountain at the Nevada Test Site for isolation of high-level nuclear waste. Lawrence Livermore National Laboratory is developing designs for an engineered barrier system containing several barriers such as the waste form, a canister and/or an overpack, packing, and near field host rock. In this paper we address the selection of metal containment barriers.
Leaching Behavior of Simulated Radioactive Waste Glass by Neutron Activation Method
Authors: Sato Seichi , Furuya Hirotaka , Ohta Kazuaki , Sugisaki Masayasu , Tanai Tadaharu
Published: March 2011

Simulated radioactive waste glass was irradiated in a nuclear reactor and radiation damage was induced by 10B(n,0)7Li reaction up to 0.14 displacement per atom. Static leach tests of the activated waste glass were carried out at 40°C, up to 38 days. Concentration of elements in leachate was determined by gamma-spectrometry. The leach test of non-irradiated glass was also performed at 40°C up to 82 days in which the solution concentration of elements was determined by an atomic absorption analysis. Leach results are given in terms of normalized elemental mass loss for the seven elements Na, K, Cs, Ca, Zn, La and Ce. Normalized elemental mass loss of alkali ions was proportional to square root of time and then, was proportional to time. Normalized elemental mass loss of alkali earth ions did not show such a simple tendency. Build up of zinc on the waste glass surface was observed following its initial leaching. It was also found that theleach rate of Cs, Zn and Ce decreased with increase of irradiation exposure of waste glass.
Radiatio Damaae Growth Models for the Interpretation of Radiation Effects on Nuclear Waste Form Leaching
Authors: Ougouag A. M. , Machiels A. J.
Published: March 2011

Two approaches for modeling radiation damage growth are presented and evaluated in the light of existing data. It results that purely geometric and statistical considerations about the distribution and overlap of damage are insufficient for accounting for the differences observed in leaching data from ion implantation and actinide doping experiments. It is shown, however, that the incorporation of effects such as those induced by the proximity of a free surface and the directionality of the irradiation into the kinetics of radiation damage ingrowth has the capability for accounting for the differences.
Conclusions from an Nea Workshop: The Role of Phenomenological Sorption Modelling in Performance Assessment of RadioactiveWaste Disposal Systems
Authors: Muller A.B. , Langmuir D. , Neretnieks I.
Published: March 2011

To give due credit to the barrier of the far field geologic environment in many host media it is necessary to account for sorption processes. The ultimate impact of sorption modelling will be in helping to define the degree of confidence that may be placed on geochemical retardation occurring in this barrier. For those involved in site characterisation, systems' design, design implementation and regulation, this confidence is best derived from a combination of a fundamental phenomenological understanding of the sorption process with empirical observations of sorption in natural environments. Neither alone is adequate. By performing a few additional measurements during classical Ko experiments, the data necessary for the more fundamental models, such as that of double-layer or surface ionization and complexation, may also be provided. The basis of these models and their integration into broader performance analysis are outlined in the context of how this maximises confidence in the geologic barrier of critically concerned groups.
Verification and Validation of the Swift Model
Authors: Ward David S. , Reeves Mark , Duda Leonard E.
Published: March 2011

A number of tests have been performed, under controlled conditions, with the SWIFT model in order to complete its quality-assurance records. Some of these tests verify the numerical algorithms employed by the code implementation through comparison with analytical data. Other tests validate the processes addressed by the model through comparison with field data. These tests show good agreement between SWIFT and the reference data. In this paper several of the tests are highlighted.
Kinetics of Chemical Vapor Deposition of Copper from (β-diketonate)CuL Precursors
Authors: Jain Ajay , Chi K. M. , Kodas T. T. , Hampden-Smith M. J.
Published: March 2011

The reaction kinetics of (hfac)CuL were examined in a warm-wall differential reactor. The data are consistent with neutral ligand L dissociation as rate limiting for (hfac)CuVTMS. A strong dependence of film resistivity on (hfac)CuVTMS pressure was observed. Selectivity for tungsten (W) surfaces in the presence of PECVD SiO2 was not observed for (hfac)CuVTMS under the conditions employed.
Interactions and Stability of Cu on CoSi2
Authors: Shy Y. -T. , Murarka S. P. , Sitaram A. R. , Ding P.-J. , Lanford W. A.
Published: March 2011

Copper is being investigated for application as multi-level interconnection metal in silicon ultra-large-scale integration (ULSI). On the other hand, COSi2 is being tested for application as contacts in sub-half micron ULSI circuits. Copper will thus be used on COSi2 to bring the electrical connection to the outside world. In this investigation we have therefore studied the interactions of copper with CoSi2 employing sheet resistance measurements (four-point probe), Rutherford back scattering (RBS), and X-ray diffraction (XRD). In addition the stability of the Schottky diodes, n-Si/CoS2/Cu, has been investigated as a function of the heat treatment in the range of room temperature to 600° C in argon-3% hydrogen mixture gas ambient. Both the measurements of the analytical and electrical characteristics show that Cu on n-Si/CoSi2 is stable at least up to a 30 minutes anneal at 600°C in argon-3% hydrogen medium. These results will be presented and discussed.
Thermal Stability of Cobalt Disilicide for Self-Aligned Silicide Applications
Authors: Chen W. , Lin J. , Banerjee S. , Lee J.
Published: March 2011

The thermal stability of COSi2 for thermal budgets suitable for a self-aligned P+ gate MOSFET process using rapid thermal processing was studied. The substrate underlying the suicide has a major impact on suicide degradation. Suicides formed on as-deposited amorphous silicon films and on single crystal Si were found to be stable at least up to 1000°C, whereas suicides formed on as-deposited polysilicon (i.e. conventional polycide) began to degrade at annealing temperatures greater than 800°C. BF2-implant dosages of 1×1015 cm-2 to 2×1016 cm-2 at 20keV in the suicide were found to affect the conventional polycide significantly. With higher implant dosages, the degradation of the conventional polycide is retarded for a 900°C anneal. However, for thermally stable suicides i.e., suicides formed on as-deposited amorphous Si and on single crystal Si, a high dose 2×1016 cm-2 implant increases the sheet resistance slightly from 1.4 Ω/square to 1.6 Ω/square for suicides on as-deposited amorphous Si substrate, and from 1.3 Ω/square to 1.6 Ω/square for suicides on single crystal substrates. A model which involves spheroidization of the suicide, silicon incursion, and indiffusion of Co into polysilicon is proposed to explain the degradation behavior.
Nucleation and Morphology of TiSi2 on Si
Authors: Nemanich R. J. , Jeon Hyeongtag , Sukow C. A. , Honeycutt J. W. , Rozgonyi G. A.
Published: March 2011

This study explores the nucleation and surface and interface morphology of TiSi2 films formed on Si (100) and (111) surfaces. Titanium suicide films were formed on atomically clean Si(111) and (100) surfaces by UHV deposition of Ti followed by in situ anneals. The TiSi2 formation process was characterized is itu using AES and LEED, and the interface structure was determined post preparation by HRTEM. The metastable C49 and stable C54 TiSi2 phases have been identified from Raman spectroscopy measurements. The islands were partially recessed into the substrate, and the shape and degree of recession was different for the islands on (111) and (100) substrates. On (111) substrates epitaxial islands were observed which exhibited different interface structures and epitaxial alignments. The contact angles of the islands were measured and the surface and interface energies of the different configurations were deduced. The mechanisms pertaining to island formation and interface morphology are described in terms of the wetting properties of a liquid-liquid system, with the effects of interface structures causing deviations from the model.
The Ideality of Spatially Inhomogeneous Schottky Contacts
Authors: Rau Uwe , Güttler Herbert H. , Werner Jürgen H.
Published: March 2011

We present a new analytical theory of electronic transport for inhomogeneous Schottky contacts. Our model combines a novel method to solve Poisson's equation for the space charge region of an inhomogeneous contact with thermionic emission theory. We explain quantitatively the temperature and voltage dependences of the ideality factor n of current/voltage characteristics, and we are able to extract from experimental data information on the characteristic size of the inhomogeneities. Our measurements on polycrystalline and epitaxial Schottky contacts yield values in the range of 200–500nm as the typical size of inhomogeneities, covering a fraction of 0.1–1% of the total interface area.
Comparison of the Interface and Surface Morphologies of Zirconium and Titanium Silicides on Silicon
Authors: Sukow C. A. , Nemanich R. J.
Published: March 2011

The morphology of zirconium suicide grown on Si(111) is investigated and compared to that of titanium suicide on Si(111) and (100). Zirconium was deposited on atomically clean silicon in UHV, and the suicide was formed by postdeposition annealing. ZrSi2 films formed from ≤100 Å of Zr deposited on Si(111) remained continuous for anneals of 400°C to 700°C. A film formed from 50 Å of Zr on Si(111) remained continuous for anneals up to 800°C, at which point the reappearance of a partial 7×7 LEED pattern indicated island formation. The interfaces of the films, studied by TME, show roughening after suicide formation. These results are compared and contrasted with the islanding behavior of titanium suicides, and analyzed in terms of a liquid-liquid model previously used with TiSi2.
Ion Beam Treatment of Ohmic Contacts to n-TYPE Hg1-xCdxTe
Authors: Leech Patrick W. , Reeves Geoffrey K. , Li Yuan H.
Published: March 2011

The application of ion beam mixing and ion implantation techniques in the formation of ohmic contacts to n-Hg1-xCdxTe (x = 0.6, 0.7) has been investigated. For experiments in ion beam mixing, an indium layer (15nm thick) on Hg1-xCdxTe wasbombarded with 45keV Te+ ions at doses ranging from 1 × 1013 to 1 × 1016 cm2. Minimum values of specific contact resistance, pc, of 4 × 10-4Ωcm-2 were measured for a dose of 1 × 1016 cm-2 after 200°C annealing; pc was independent of dose in this range. Analysis of the interfaces by Auger depth profile and Rutherford backscattering spectrometry has shown that ion beam mixing produced an enhanced indiffusion of indium. In comparison, samples which were ion implanted with In+ at 50keV prior to metalisation showed a reduction in pc which was strongly dependent on dosage.
A Photoemission Investigation of the Interfacial Electronic Properties of Mo and Ni Schottky Barriers to CuInSe2(112)
Authors: Niles David W. , Nelson Art J. , Richard Schwerdtfeger C. , Höchst Hartmut , Rioux Dennis
Published: March 2011

We studied Mo and Ni contacts to p-type CuInSe2(112) with angular-resolved synchrotron radiation ultraviolet photoemission spectroscopy in the range 40 eV hv < 120 eV. By varying the photon energy, we determined that emission from the CuInSe2 Г-point in the Brillouin zone occurs for hv = 60 eV, and identified emission from the valence band maximum. After depositing Ni and Mo, we found that the conduction band minimum of the CuInSe2 very nearly aligned to the Fermi edges of both metals, giving Schottky barriers Vsb = 1.05 ±0.1 eV. The interfaces are not atomically abrupt, as seen by the outdiffusion of Se into the refractory metal overlayers and the formation of In-Mo and In-Ni alloys.
Manufacturing and Technology Requirements for Submicron Multilevel Metal
Authors: Seidel T. E.
Published: March 2011

Multilevel Metal (MLM) technology has been driven by the need for ever faster switching speed. In the simplest considerations, this need has been described by the RC time constant applied to the metal interconnect runner embedded in a dielectric medium:
Barrier Inhomogeneities Dominating Low-Frequency Excess Noise of Schottky Contacts
Authors: Rau Uwe , Güttler Herbert H. , Werner Jürgen H.
Published: March 2011

We introduce a new quantitative description for electronic noise at Schottky contacts. The model combines spatially inhomogeneous current transport across the interface with the modulation of the local barrier height due to trapping dynamics of charged states located at or close to the interface. The experimentally observed increase of noise power with decreasing temperature is explained by the inhomogeneity of the interface. Our model fits experimental data obtained from different silicide/silicon Schottky contacts and the detailed analysis of measured noise spectra yields information about the interfacial potential fluctuations.
Au-GaAs Reaction Kinetics: Its Role in Fabrication of Ohmic Contacts
Authors: Barcz Adam J.
Published: March 2011

Annealing of Au/GaAs leads to vaporization of As species and migration of Ga atoms into Au. These processes are simultaneous only on a macro-scale. A simple kinetic model is developed in which they are treated sequential by introducing specific fluxes F(Ga) and F(As). F(Ga) is calculated assuming linear flow at the phase boundary. F(As) is set constant for a given external pressure of arsenic. The model accurately describes the observed reaction rate in both capped and open configuration. It is shown that instantaneous composition of GaAs surface adjacent to the metal evolves from initially As-rich to Ga-rich when Au becomes saturated with Ga. The model is consistent with common observation that short-time heating of Au(dopant)/GaAs activates dopant species preferentially on Ga vacant sites. To activate dopants in As sublattice longer times and/or higher temperatures are needed.
Estimating Local Deposition Conditions and Kinetic Parameters Using Film Profiles
Authors: Cale T. S. , Chaara M. B. , Hasper A.
Published: March 2011

EVREST, a program which uses film profile data in features obtained from low pressure chemical vapor deposition (LPCVD) processes to estimate the local partial pressures, temperature, and kinetic parameters is demonstrated for blanket tungsten deposition by the hydrogen reduction of tungsten hexafluoride. EVREST uses EVOLVE, a physically based process simulator for ballistic transport and heterogeneous reactions in features on patterned wafers, to compute film profiles for a given set of deposition conditions and kinetic parameters. Calculated film profiles are compared with the experimental film profile and the free parameters are adjusted to minimize the sum of squared differences between points on the calculated and experimental profiles. EVREST uses Marquardt's method to determine the set of deposition parameters which provide the best calculated profile. Simulated and experimental profiles are in very good agreement.
Formation of Nickel Silicides on Ion-Amorphized Silicon
Authors: Mohadjeri B. , Linnros J. , Svensson B. G. , ÖStling M. , Johanssons S. , D'Heurle F. M.
Published: March 2011

The formation of NiSi and NiSi2 upon annealing of an ion-amorphized Ni/Si structure has been studied by various surface analytical techniques to characterize the morphology, stoichiometry and interface sharpness of the NiSi2 layer. In comparison with reactions of nickel on crystalline silicon (c-Si), sharpening 0ofthe NiSi2/C-Si interface is obtained for appropriate amorphization depths. Moreover, the surface roughness of the NiSi2 films is significantly reduced by implantation. The NiSi2 formation temperature is, however, not reduced as observed for structures with nickel deposited on amorphous silicon prepared by evaporation. This dissimilarity can be explained by an unexpected low crystallization temperature or the ion-amorphized structure, where Ni-ennanced solid phase epitaxy occurs at a temperature as low as 425°C.
Recent Progress of Alloyed Ohmic Contacts to GaAs Compound Semiconductors
Authors: Murakami Masanori , Otsuki A. , Tanahashi K. , Tarata H. J. , Callegari A. , Lustig N.
Published: March 2011

Low resistance, alloyed AuGeNi Ohmic contacts have been extensively used in the current manufacturing GaAs devices. However, extension of usage of these devices to Very Large Scale Integration levels requires the contacts with excellent thermal stability, shallow diffusion depth, and smooth contact surface in addition to low contact resistance. In the present paper recent studies for development of “non-gold” Ohmic contacts which improve the poor contact properties of the alloyed Ohmic contacts are rev i ewed.
Low Au Content Ohmic Contacts to n-GaAs Incorporating Sputtered Tungsten Oxide
Authors: Lustig Naftali , Schad R. G. , Fleischman A.
Published: March 2011

Electron-beam (e-beam) evaporated low Au content NiGe(Au)W ohmic contacts with a contact resistance (Rc) as low as 0.15 Ω-mra have been reported. Due to the high melting point of W it is desirable to deposit this layer by means other than e-beam evaporation. However, the use of nearly oxygen-free sputtered W, yields contact resistances in excess of 0.7 Ω-mm. By replacing the sputtered W by a reactively sputtered metallic W oxide, containing ∼25 at. % oxygen, the low contact resistance (Rc < 0.15 Ω-mm) is restored. Contacts employing a reactively sputtered W nitride in place of W oxide also yield high Rc's (∼0.75 Ω-mm). Auger depth profiles of the reacted contacts show a significant outdiffusion of Ga from the GaAs substrate in the presence the oxygenated W but not in the low oxygen and the W nitride contacts. These results and the fact that our previously reported e-beam evaporated W contacts also contain ∼25 at. % oxygen, suggest an oxygen assisted ohmic contact formation mechanism.
Ti/Pt Based Contacts to Heterojunction Bipolar Transistors
Authors: Kalkur T. S. , Wright P. D. , Ko S. K. , Lu Y. C. , Casas L. , Jones K. A.
Published: March 2011

Ti/Pt metallization was used to form contacts on both n+-InAs emitter cap and p+ base layers of heterojunction bipolar transistors (HBTs). The as-deposited contacts were found to be ohmic for both the base and emitter cap layers. Rapid thermal processing of the contact metallizations was performed in the temperature range of 3 00–500 C for 30 seconds. Minimum contact resistivities of l×10-6 ohm-cm2 for the base and 3×l0-7 ohm-cm2 for the emitter layer were achieved. The influence of heat treatment on contact morphology was also examined.
Thermal Stability of Reactively Sputtered TiN on InP as a Diffusion Barrier
Authors: Pang Zhengda , Boumerzoug Mohamed , Kruzelecky Roman V. , Mascher Peter , Simmons John G.
Published: March 2011

The stability of rcactively sputtered TiN films on InP for application as a diffusion barrier has been examined using electrical measurements, Auger profiling and scanning electron microscopy (SEM). The samples were subjected to rapid-thermal-annealing (RTA) in a N2 atmosphere at temperatures between 400°C and 900°C. The SEM pictures of “as deposited” and RTA stoichiometric films show that the morphology is smooth, fine-grained and stable until 800°C. Auger depth profiling shows little interdiffusion between TiN and InP for RTA below 800°C. Annealing at temperatures of about 700°C reduces the sheet resistance of TiN relative to the “as-deposited” films by about 50%. Annealing at temperatures above 800°C results in a large sheet resistance. This may be associated with the deterioration of the TiN/InP morphology at high anneal temperatures as observed by SEM.
Hillock Formation in Platinum Films
Authors: Hren Philip D. , Al-Shareef H. , Rou S. H. , Kingon A. I. , Buaud P. , Irene E. A.
Published: March 2011

Hillocks, surface protrusions from thin metal films, have been observed in Al, Al/Cu, Pb, and other materials. Platinum films are widely used as substrates for the deposition of ferroelectric thin films because of their superior oxidation resistance. However, hillock formation in platinum films has not been reported in the literature. In this work, we report the appearance of hillocks in platinum in Pt/Ti bilayers on oxidized silicon wafers. Platinum films 250 to 300 nra were deposited by ion beam sputter deposition at 25°C and 300°C onto a 70 nm Ti film on oxidized Si wafers. The wafers were then heated in flowing argon to 600°C, held 1 hr at 600°C, and cooled to room temperature while the wafer curvature (and hence the film stress) was measured with a laser beam deflection technique. At 600°C, compressive stresses of 0.1 to 0.4 GPa, due to thermal expansion mismatch, developed in the metal films. The platinum surface, initially flat, showed strong hillocking after the anneal. Cross-sectional TEM revealed that severe Ti/Pt interdiffusion occurred, in one case leading to a Ti layer on the top surface.
Fermi Level Inhomogeneities on GaAs(110) Surface Imaged with a Photoelectron Microscope
Authors: Kim Changyoung , King Paul L. , Pianetta Piero
Published: March 2011

A photoelectron microscope operating with a retarding field analyzer has been used to exploit core level energy shifts due to band bending in order to directly image Fermi level variations on n- and p-type cleaved GaAs(110) surfaces. Fermi level maps resolved to better than 10 um indicate lateral variations in the surface Fermi level which are often quite abrupt. In agreement with earlier, lower resolution work [1], Fermi level topography is found to be highly correlated with surface roughness as characterized by SEM, optical microscope and stylus profi lometer. The largest defect derived pinnings encountered to date resut in the Fermi level lying 0.5 eV above the VBM for both n- and p-type GaAs. Low coverage In evaporations have the. effect of reducing Fermi level contrast as Fermi levels in formerly unpinned regions move into the gap.
Construction of Band Profiles for Semiconductor Heterojunctions and Layered Structures
Authors: Garland J. W. , Kassel L. , Yang D. , Zhang Z. , Raccah P. M.
Published: March 2011

Band profiles specify the position of all band edges as a function of distance from a sample surface or interface. They largely determine the electrical and optoelectronic properties of semiconductor heterostructures. Neither theory nor standard transport measurements alone have been able to give reliable values for band offsets, much less entire band profiles. However, the use of electroreflectance, which reveals crossover transitions between localized states or band edges present on opposite sides of an interface, and which allows us to measure accurately built-in fields, has allowed us to determine accurate band profiles for several types of semiconductor heterostructures. The procedure used to find the band profile is elucidated in detail for two technologically important cases.
W and Related Alloys Deposited onto InP by RT-LPCVD
Authors: Katz A. , Feingold A. , Pearton S. J. , Lane E. , Nakahara S. , Geva M.
Published: March 2011

Tungsten (W) films were deposited onto InP in a cold wall, rapid thermal low-pressure chemical vapor deposition (RT-LPCVD) reactor, from a tungsten hexafluoride (WF6) gas reduced by hydrogran (H2). W films of thickness 50 to 450 nm were deposited in the temperature range of 350° to 550°C, pressure range of 0.5 to 4.5 Torr and deposition rates up to 4 nm/sec with an apparent activation energy of about 1.12 eV. The film stress varied depending upon the deposition pressure, from low compressive for deposition at 0.5 Torr to moderate tensile for deposition at about 4.5 Torr. The films were aged at temperatures as high as 300°C for about 800 hr and exhibited an excellent mechanical stability. Post-deposition sintering of the W films at temperatures up to 600°C led to reduction of the resistivity with a minimum value of about 55μΩ-crn as a result of heating at 500°C. Conditions for both selective and blanket deposition were defined, and a dry etching process for further geometrical definitions of the films was developed, providing etch rates of 40 to 50 nm·sec-1. This report reflects the first attempt to deposit W films onto III-V semiconductor at a very high rate by means of RT-LPCVD.
Interfacial Reactions of the Pt/Ti/Si Structures
Authors: Tseng Bae-Heng , Lee Chong-Kuang , Tseng Ming-Feng
Published: March 2011

A 15rm-thick Ti-layer incorporated between Pt and Si was found to be effective in improving the structures of PtSi/Si interface. The roles of Ti-layer were to react with native oxides on the Si substrate and to form Ti-O solid solutions instead of Ti oxides which act as diffusion barrier and inhibit the reactions between Pt and Si. Auger depth profiling gave evidence that Ti and O moved outward as platinum suicides were formed. A smooth PtSi/Si interface was revealed by the transmission electron microscope.
Nonconformal Al Via-Hole Filling by Electron Beam Evaporation
Authors: Cho C.-C.
Published: March 2011

Using electron beam evaporation, we have deposited Al on patterned SiO2 films grown on various Si(100)-based substrates and characterized the Al films by scanning electron microscopy, x-ray diffraction and transmission electron microscopy. The growth mode of Al in the via holes of the SiO2 films is found to depend on the base materials of the holes. For via holes based on Si(100) and TiSi2, Al fills the holes nonconformally, showing little Al on the side walls. The nonconformal growth of Al is useful for submicron via-hole filling because it prevents void formation caused by shadowing effect. In contrast, for holes of AlCu bases, Al grows conformally. For the Al grown in the via holes of Si(100) bases, single crystal Al with Al(110)//Si(100) epitaxial relation can be grown in the holes at a substrate temperature of 300°C.
Comparative Electrical Study of Epitaxial and Polycrystalline GdSi2/(100)p-Si Schottky Barriers
Authors: Kovács B. , Horváth Zs. J. , Mojzes I. , Molnár G. , Petó G. , Andrási M.
Published: March 2011

The electrical and interface parameters of epitaxial orthorombic, textured orthorombic, polycrystalline orthorombic, and polycrystalline hexagonal structures with different initial thickness of the evaporated Gd layer are compared. The Schottky barrier height, the ideality factor, the series resistance, the breakdown voltage, the relative interfacial layer thickness, the energy distribution spectra of interface states, and the equilibrium interface charge have been evaluated from the current-voltage and capacitance-voltage measurements. The obtained results indicate that the initial thickness of the Gd layer influences much more stronger the obtained parameters through the perfection of the epitaxial layer than the crystal structure.
Planarized Copper Interconnects by Selective Electroless Plating
Authors: Kiang M. H. , Tao J. , Namgoong W. , Hu C. , Lieberman M. , Cheung N. W. , Kang H. -K. , Wong S. S.
Published: March 2011

Electroless deposition of planarized copper in SiO2 trenches has been carried out using Pd/Si plasma immersion ion implantation (PIII) or Pd2Si deposition to form a seed layer at the bottom of trenches. Electrical resistivity of the plated Cu is < 2 μΩ-cm for both types of seeding layers. For the PHI seeding method, we found a threshold Pd dose of 2 ×l014/cm2 is required to initiate Cu plating, and RBS analysis confirms intermixing of Pd, Si, and SiO2 improves the adhesion of the plated Cu to SiO2. Electromigration tests show both void and hillock formation under accelerated current stress testing, with an activation energy of 0.8 eV for interconnect open failure. The DC and pulse-DC median-time-to-failure (MTF) of plated Cu are found to be about two orders of magnitude longer than that of Al-2%Si at 275°C, and about four orders of magnitude longer than that of Al-2%Si when extrapolated to room temperature. Pulsed DC electromigration stressing exhibits a transition from low to high frequency behavior around 900 kHz, indicating a vacancy relaxation time much shorter than that of Al. For bipolar AC stressing, the ratio MTFAC / MTFDC of Cu is much smaller than that of Al-2%Si, indicating a different void recovery mechanism for Cu.
Reliability, Properties and Microstructure of W80Ti20 Diffusion Barriers Between Al-Based Metallizations and Si.
Authors: Dirks A. G. , Wolters R. A. M. , De Veirman A. E. M.
Published: March 2011

Tungsten-rich W-Ti (or W-Ti-N) alloy films are known for their applicability as diffusion barriers in advanced silicon technology, especially in the case of aluminium-based metallizations. For a wide variety of deposition conditions and post-deposition anneal treatments these refractory-metal barriers show a columnar microstructure. In contact with aluminium the W-Ti films do not form absolute barriers, because of mutual diffusion resulting in compound formation. The reactivity of the W-Ti barriers with the Al99Si1 interconnect has been studied by in-situ resistance measurements in vacuum at temperatures of approximately 450 °C (for W-Ti alloy films) and 475 °C (for W-Ti-N alloy films). In this paper new results dealing with the relationship between deposition conditions, microstructure and barrier properties will be discussed. Furthermore, it will be shown that the actual distribution of the titanium atoms in the tungsten matrix has a substantial influence on the reactivity of the barrier film with the Al99Si1 interconnect.
Plasma Diagnostics and Modeling of TI/TIN Reactive Sputtering
Authors: Tsai W. , Fair J. , Hoddl D. , Ginzton Edward L.
Published: March 2011

In situ optical emission spectroscopy studies of Ti/TiN reactive sputtering were carried out in a Varian M2000 cluster tool. Deposition rates of Ti/TiN films at 4.3 mTorr are directly proportional to ratio of Ti(365)/Ar(435) emission lines. Measurement of the ratio of the N(655)/Ar(435) emission lines indicates an incubative dependence on.nitrogen flow due to nitridation of the target. TiN reactive sputtering is accurately described by a mathematical model based on the nitrogen flux balance on target and wall/shield at steady state.
Competitive Reactions in Unicomponent/Bicomponent Contact Systems
Authors: Eizenberg M.
Published: March 2011

The advance of microelectronic devices has emphasized the important role of contact metallization. Contacts have become more and more complex in their structure. In this review we present some of our work on three different types of contact systems consisting of a unicomponent/bicomponent interface. The systems are: 1) alloy films (codeposited two metals) on Si, 2) a metal on Si1-xGex epilayers, and 3) a metal on a compound semiconductor (GaAs). Due to applied heat-treatments, competitive interfacial reactions take place between the various constituents of the contacts. These interfacial reactions can affects the properties of the contacts and their stability and reliability.
MOCVD-TiN Barrier Layers for ULSI Applications
Authors: Raaijmakers Ivo J. , Vrtis Raymond N. , Yang Jack , Ramaswami Seshadri , Lagendijk Andre , Roberts David A. , Broadbent Eliot K.
Published: March 2011

Material properties are reported of high quality TiN thin films, deposited by a low temperature (400 – 450 C) and low pressure (10 Torr) metalorganic chemical vapor deposition process using tetrakis(diethylamino)Ti and ammonia. Layer resistivities of less than 200 μΩ cm are achieved in 300 to 500 A thick films. The carbon and oxygen content in the films is found to be low (<3% C, <0.5% O). Conformality of the films in small contact holes is sufficient for the films to be applicable as diffusion barrier and adhesion layers in integrated circuit manufacturing at the 0.25 μΩgeneration.

Integration of the MOCVD-TiN films in a Ti/TiN/Al-alloy metallization scheme is also reported. The diffusion barrier performance of the MOCVD-TiN layers is found to exceed that of PVD-TiN layers.
Optically Controlled Space Charge Fields under the Electrode Region in Cadmium Telluride
Authors: Ziari Mehrdad , Steier William H.
Published: March 2011

We report an optically controlled and space-charge related formation and erasure of large electric fields in the electrode region of CdTe:In. The measurement of the field distribution under different illumination conditions can be explained by a simple model. This nonlinearity has been used in optically controlled switching devices and spatial light modulators.
A Novel Technique for Characterization of Amorphous Silicon Thin Films
Authors: Malhotra V. , Weling M.
Published: March 2011

A novel technique for characterizing the variation of depletion width versus reverse bias voltage, the absorption coefficient, and the defect density in amorphous silicon thin films has been developed. The technique utilizes the fact that the rate of change of dc photocurrent with reverse voltage in a photodiode is strongly dependent upon the wavelength of light.
Photo-Hall, Pr, Pl and Photoconductivity Study On Native Defects in CuInS2
Authors: Ueng H. Y. , Cheng Y. H. , Hwang H. L.
Published: March 2011

By correlating the results of photoreflectance, photoconductivity, photoluminescence, and differential-Hall and photo-Hall measurements with the stoichiometry, for a number of undoped single crystal samples, we could conclude two donor levels (35 meV, 70 meV) and three acceptor levels (100 meV, 155 meV, 170 meV) distributed in the forbidden ga.p for undoped CuInS2 samples.
Integration of Heterojunction Bipolar Transistors and Shallow Quantum Well Modulators for Smart Pixel Fabrication
Authors: Goossen K. W. , Cunningham J. E. , Jan W. Y. , Walker J. A.
Published: March 2011

Using the recently developed SESHL (for Single Epitaxy Supporting HBT and Low-barrier modulator) process, we present a monolithic single-stage common-emitter amplifier with photodiode input and modulator output (or HBT-SEED), one of the simplest forms of smart pixels.
New Theoretical Treatment of Electroreflectance from Surfaces and Interfaces Having Large Built-in Fields
Authors: Garland J. W. , Zhang Z. , Kim C. , Yang D. , Raccah P. M.
Published: March 2011

We have constructed a completely quantum-mechanical theoretical treatment of the modification of the local dielectric function by intense electric fields. It includes the numerical calculation of depletion-region bound-state energies and wavefunctions as well as band wavefunctions. We use this treatment to construct electroreflectance (ER) lineshapes. Our numerical results differ significantly from those of previously proposed ER lineshapes for GaAs with Nd >> 1016. They yield excellent fits to ER data and allow the accurate determination of doping levels and band bendings from ER data.
Terahertz Beams: Generation and Spectroscopy
Authors: Ralph Stephen E. , Grischkowsky D.
Published: March 2011

TeraHertz beams of ultrafast pulses of far infrared (λ=40–1000μm, v = 0.3x1012− 7.5×1012Hz) radiation generated via the induced dipole of photogenerated charge within a strong electric field in semiconductors are an emerging spectroscopic technique which incorporates ultrafast optical pulse generation, optoelectronics, and far infrared techniques. Recent results obtained using the trap enhanced field (TEF)[1] effect in the generation of THz beams demonstrate the extended frequency range of these sources and show their importance to time resolved infrared spectroscopy.

The generation of collimated THz radiation within semi-insulating materials is dramatically improved by the extremely large field enhancement near the anode of an electrically biased metal/semi-insulator/metal structure. Our experimental results for semiinsulating GaAs establish an operational regime in which the applied potential is confined to a small region near the anode resulting from a space charge region which exists due to a dramatic change in the number of ionized EL2 traps. The effect, contrary to that observed in trap free or doped materials, is enhanced by optical injection of carriers near the anode, and can be exploited for the efficient generation of ultrafast THz radiation.

Spectroscopy using THz beams allows both the static and dynamic properties, including refractive index, absorption, and photoconductivity, of materials and structures to be accurately measured. The energy range and time resolution of freely propagating subpsec THz pulses have not been previously available.
Rowth of Y-CUT LiNbO3 Layers on (1102) Al2O3
Authors: Robinson H. , Milledge H.J. , Pitf C.W.
Published: March 2011

It has been found that y-cut LiNbO3 heteroepitaxial layers of good quality (as determined from X-ray diffraction patterns) can be obtained by radio frequency sputtering on noncrystallographic (vicinal) substrate surfaces approximating (1102) of Al2O3, in accord with the results concerning (100) Si growth on A12O3.

Such material may find application in optical modulators monolithically integrated on to silicon-on-sapphire (SOS) circuits.
LOW-Temperature Epitaxial Growth of GaAs on Si Substrates by MBE
Authors: Chiang Ting-Yen , Liu En-Huery , Yiin Der-Hwa , Yew Tri-Rung
Published: March 2011

This paper presents results of the low—temperature epitaxial growth of GaAs on Si substrates with orientation 1°—4° off (100) by molecular beam epitaxy (MBE). The epitaxial growth ·is carried out on Si wafers subjected to HF solution treatment by “spin-etch” technique before the wafer is transferred to the entry chamber of MBE system. Methods used for reducing defect density in the epitaxial layers are proposed. The characterization techniques include cross-sectional transmission electron microscopy (XTEM), plan-view transmission electron microscopy, scanning electron microscopy (S EM), and double crystal X-ray diffraction (DCXRD). Epitaxial films with a full width at half—maximum (FWHM) of about 310 arcsec measured by DCXRD are obtained without annealing.-
Initial Stage of Solid Phase Epitaxial Growth of GaAs Films on Vicinal Si (001) Substrate
Authors: Choo W.K. , Kim I. , Lee J.Y. , Cho K.I. , Lee J.-L. , Kim Y.J.
Published: March 2011

The initial stage of solid phase epitaxial (SPE) growth of GaAs films on the vicinal Si (001) substrate was investigated by high resolution transmission electron microscopy (H-RTEM). Cross-sectional [110] and [110] HRTEM images show that the SPE growth of crystalline GaAs islands from the amorphous phase proceeds via the formation of three-dimensional islands at the initial stage and islands' size and spacing are not critically dependent on the substrate tilt direction. The average vertical and lateral dimensions of islands were found to be 9 nm and 14 nm respectively, and the average island spacing was 10 nm. Moreover, many internal stacking faults (and/or microtwins) and a few dislocations have been already formed at this initial stage of growth. In addition, the critical thickness for misfit dislocation formation is found to depend upon the islands' lateral dimensions as well as the heights.