bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Structures of Native Oxides Formed During Wet Chemical Treatments on NH4F Treated Si(111) Surfaces
Authors: Hattori Takeo , Ogawa Hiroki
Published: March 2011

Chemical structures of native oxides formed during wet chemical treatments on NH4F treated Si(111) surfaces were investigated using X-ray Photoelectron Spectroscopy (XPS) and Fourier Transformed Infrared Attenuated Total Reflection(FT-IR-ATR). It was found that the amounts of Si-H bonds in native oxides and those at native oxide/silicon interface are negligibly small in the case of native oxides formed in H2SO4-H2O2-H2O solution. Based on this discovery, it was confirmed that native oxides can be characterized by the amount of Si-H bonds in native oxides. Furthermore, it was found that the combination of various wet chemical treatments with the treatment in NH4OH-H2O2-H2O solution results in the drastic decrease in the amount of Si-H bonds in native oxides.
Surface Contamination Level of GaAs Wafers Treated with Solutions of Organic Base Measured by Total Reflection X-Ray Fluorescence (TXRF)
Authors: Shibaya H. , Kondo H. , Tomizawa K.
Published: March 2011

Contamination level of chemically cleaned (100) GaAs wafer surfaces were measured by Total reflection X-Ray Fluorescence (TXRF). Cu and Zn were detected as major metallic Impurities on GaAs surfaces. The Cu contamination level was in the range of 1011 atoms/cm2 on wafers treated with NH4 OH/H2O2 /H2O (80:1:400) mixture. On the other hand, Cu could be reduced to less than 5×1010 atoms/cm2 and Zn could be controlled below the detection limit by treating with a choline/H2O2 /H20/Na5P3O10 or SEMICO-CLEAN 23/H2O2 /Na5P3O10 solution. Surface cleanliness depended on the H2O2 concentration and whether or not Na5P3O10 was present in the organic base solutions.
Interaction of Metallic Impurities Adsorbed on Si Wafers in SC1 Solution
Authors: Okuda Hitoshi , Ryuta Jiro , Morita Eturo , Shimanuki Yasushi
Published: March 2011

Changes in the surface concentration of Fe, Ni, Cu and Zn on Si wafers processed in a NH 4OH / H2O2 / H2O (SC1) solution was investigated. The adsorption of Fe or Zn on Si wafers was not affected by the other impurities in the SC1 solution. However, the adsorption of Ni or Cu on Si wafers was obstructed by Fe, and was not obstructed by Zn.
A Photoemission Study of Electrochemically Etched Light Emitting Silicon
Authors: Terry Jeff , Liu H. , Cao R. , Woicik J. C. , Pianetta P. , Yang X. , Wu J. , Richter M. , Maluf N. , Pease F. , Dillon A. , Robinson M. , George S.
Published: March 2011

The valence band and the Si 2p core level of electrochemically etched light emitting porous silicon samples prepared with different etching parameters and upon thermal annealing have been studied. The core level shows appreciable broadening as chemical etching time increases. Upon annealing, the core level linewidth decreases and the valence band develops spectral features. The photoluminescence intensity, also, decreases upon annealing. However, impurity species are found to be present only in trace amounts. Our data is consistent with a photoluminescence mechanism involving a silicon species that degrades, decomposes, or desorbs upon annealing.
Characterization of HF Treated (100) Si Surfaces by Surface Charge Analysis (SCA)
Authors: Fitch Jon T.
Published: March 2011

Surface Charge Analysis (SCA), and ellipsometry have been used to study the stability over time of HF treated (100) silicon surfaces as a function of the post-HF rinse time. Using SCA, the electrical properties of the chemical terminating layer of these silicon surfaces were measured. The surfaces which remained native oxide free the longest (−10 hours) had very low Qox and Dit values on the order of 1.0 × 1011/cm2 and 5.0 × 1010 eV−lcm−2, respectively. A good correlation was found between Dit and the native oxide thickness measured by ellipsometry. This and other results are discussed in terms of the chemical bonding on the silicon surfaces.
Use of Dilute, Aqueous HF for Selective Etching
Authors: Gow Catherine J. , Martin Dale W. , Albaugh Kevin B.
Published: March 2011

Hot, dilute aqueous solutions of hydrofluoric acid (HF) are used to etch silicon nitride films selectively relative to thermally grown silicon dioxide films. Etching is performed in a batch, immersion reactor. The wafers are then rinsed in deionized water and dried with isopropanol vapor. A maximum selectivity of 10.9 to 1 for a 1000:1 HF:H2O dilution at 70 °C is observed. Wafers are etched in hot, dilute HF and cleaned using standard techniques [1]. A thin (12 nm) oxide is then grown and dielectric properties are measured to determine optimum process conditions. For very dilute solutions at lower temperatures, relatively low dielectric strengths (5-6 MV/cm) for the grown oxide are observed, which indicates roughening of the silicon surface. Although the parameter space for exploiting the selective etch process is constrained, a significant range of process conditions exist where selectivity is present and no electrical properties are degraded.
Room-Temperature HF Vapour-Phase Cleaning for LPCVD EPI of Si and SiGe
Authors: Kuiper A.E.T. , Lathouwers E.G.C.
Published: March 2011

Silicon dioxide films can be etched in a mixture of HF and H2O vapour. This process can be performed at reduced pressure, which has allowed us to develop a highvacuum compatible etch facility. Channelling-RBS analysis demonstrates the feasibility of epitaxial LPCVD of Si and SiGe layers at 600°C on Si(100) substrates that previously have been vapour-etched in situ at room temperature. With RBS also kinetic information about these deposition reactions can be derived.
Selectivity Mechanisms in Low Temperature (<950°C) Selective Silicon Epitaxy
Authors: Fitch J.T. , Denning D.J.
Published: March 2011

Low temperature selective silicon epitaxy was studied over a range of process pressures and HCI flows using a SiH2Cl2/HCl/H2based chemistry. Thermodynamic modelling was carried out with the aid of the SOLGAS program to investigate the effect of process pressure, HCI flow rate, and leaks on the distribution of gas phase species. Selectivity results are interpreted in terms of the defect microchemistry on SiO2surfaces.
A New Two-Step Plasma-Assisted Surface Cleaningoxidation and Film-Deposition Process Sequence for The Formation of Si(100)/SiO2 Interfaces with Low Densities of Interfacial Traps
Authors: Ma Y. , Yasuda T. , Habermehl S. , He S.S. , Stephens D.J. , Lucovsky G.
Published: March 2011

Device quality SiO2 films have been deposited by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD). The substrate surface cleaning, both ex-situ and insitu, influence the density of trapping states at the Si/SiO2 interface. Pre-deposition exposure to plasma-generated atomic-H significantly reduces hydrocarbon and 0 contamination, but damages the Si surface leading to high interface trap densities (Dit) in the Si band-gap. Pre-deposition exposure to plasma generated O-atoms, removes the residual hydrocarbons, and oxidizes the Si substrate while maintaining an atomically smooth interface. Metal Oxide Semiconductor (MOS) structure fabricated by RPECVD have midgap Dit values of ∼1-3×1010cm−2eV−1 for 0-plasma cleaned surface. Final rinse after RCA cleaning in HF solutions with different pH values affects surface morphology; however surface roughening by atomic-H is always the determinant contributor to high values of Dit.
Effects of Hydrogen Coverage on Silicon Surface Reactivity
Authors: Dillon A.C. , Robinson M.B. , George S.M. , Gupta P.
Published: March 2011

Hydrogen passivation of silicon surfaces plays an important role in silicon surface cleaning and preparation. To measure the effect of hydrogen passivation on silicon surface reactivity, Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the oxidation of silicon surfaces versus hydrogen coverage. Experiments were performed insitu in an ultrahigh vacuum (UHV) chamber using high surface area poroussilicon samples. Si-H stretching and bending vibrations and Si-O-Si stretching vibrations were employed to monitor the silicon surface species. Oxidation studies with O2 conducted versus various initial hydrogen coverages revealed that oxidation rates and apparent oxygen saturation levels on porous silicon decreased as a function of initial surface hydrogen coverage. Exceptional surface stability was observed when the porous silicon surface was passivated by both monohydride and dihydride surface species. In addition, new blue-shifted Si-H stretching and bending features were observed following the oxidation of partially hydrogen-passivated porous silicon which indicated the presence of Ox SiH species. Thermal annealing studies revealed that the thermal stability of these OxSiH species increased with increasing oxidation of the silicon surface. These results have important implications for silicon growth and surface cleaning because they indicate that hydrogen removal is more difficult when the silicon surface is contaminated with oxygen. These FTIR results have also been compared with earlier results of oxidation versus hydrogen coverage on Si(111) 7×7.
Transport of 14C and Uranium in the Carrizo Aquifer of South Texas, a Natural Analog of Radionuclide Migration
Authors: Andrews Robert W. , Pearson F. J.
Published: March 2011

Ground-water flow and transport were modeled along a one-dimensional, vertical cross-section of the Carrizo aquifer from its outcrop down gradient for 100 km. Using a constant flux of 14C at the recharge boundary, the 14C mass fraction distribution downgradient was simulated until steady-state was attained. The match between the observed data and simulated results is excellent for a porosity of 35% and a KD of zero. The transport of both 234U and 238U was simulated with varying retardation coefficients. The best fit occurred with a RD of about 30, which corresponds to a KD of 6. The results indicate that modeling may be reliably conducted over time periods and distances of interest in radionuclide transport performance assessments and that regionally averaged hydrologic properties can provide appropriate values for predicting ground-water flow and nuclide transport.
The Behavior of 99Tc in Doped-Glass/Basalt Hydrothermal Interaction Tests
Authors: Coles D.G. , Apted M. J.
Published: March 2011

The release of polyvalent radionuclides from a nuclear waste repository located in basalt may be sensitively related to the redox potential (Eh) imposed by the basalt. A series of tests are reported here evaluating the effect of basalt on the concentrations of 99Tc released into solution from a borosilicate glass waste form. Crushed PNL 76-68 glass, doped with 0.7 mg 9 99Tc/g glass, was reacted with reference basalt groundwater under oxic hydrothermal conditions in a sampling autoclave, both alone and in the presence of crushed basalt. The steady state fluid concentrations of 99Tc and various stable species were determined from samples obtained at the test conditions of 200 °C, 30 MPa, and a initial solution to solid mass ratio of 10 for both tests.

In the glass + groundwater test, the 99Tc concentration rose rapidly to about 50 mg/L after only 200 hr of run time and remained at a value between 50 and 60 mg/L throughout the duration of the test. For the basalt + glass + groundwater test, the 99Tc concentration rose to an initial value of about 2.5 mg/L. At about 700 hr, the 99Tc concentration began to drop rapidly until a value near the analytical detection limit (approximately 0.005 mg/L) was reached after a test duration of 1,400 hr. It is concluded that the presence of basalt in these hydrothermal experimtents reduces the concentration of 99Tc in solution by nearly four orders of magnitude, probably by control of solution Eh and subsequent precipitation of a solid containing a reduced form of technetium. Reaction mechanisms are discussed that can account for these observations.
Laboratory Investigations on Radiolysis Effects on Rock Salt With Regard to the Disposal of High-Level Radioactive Wastes
Authors: Jockwer Norbert
Published: March 2011

As a result of the heat producing high-level radioactive waste, volatile components which are in the host rock will be liberated and further gases will be generated by thermal cracking and radiolysis.
The Source Term for the Release of Nuclides From a Radioactive Waste Repository – 1. Vitrified waste in granite
Authors: Ewart F.T. , Morris J.B. , Severn J. , Sharpe B.M. , Thomason H.P.
Published: March 2011

Samples of simulated vitrified radioactive waste have been prepared containing, separately, neptunium, plutonium and technetium. These glasses have been leached in static granite groundwater for 150 days. The resulting solutions have been characterised with respect to both the ionic and colloidal species: these solutions have then been contacted with concrete and granite to produce initial measurements of the source term from a typical repository. The results show that (a) the colloidal species arise from detached particles of the so-called gel layer on the surface of the glass, (b) e solution activities were 590 Bq.ml-1 in the case of 99Tc and 20 Bq.ml-1 for 237Np, and (c) the sorption coefficients wIre 1.4 and > 300 ml.g for concrete and 0.4 and 8.3 ml.g-1 for granite respectively. The technetium was only weakly sorbed and the neptunium strongly sorbed in each case.
Uranium Migration at Some Hydrothermal Veins Near Marysvale, Utah: A Natural Analog For Waste Isolation.
Authors: Shea Micheal
Published: March 2011

The fission track method was used to map 235Udistribution in thin sections made from twenty-one rock samples. Uranium locations within the studied samples include: veins and veinlets, microcracks, secondary minerals sealing microcracks, rock matrix, grain boundaries and cleavages, and accessory minerals. Two traverses show evidence for nuclide movement by diffusion (−5 and −1 cm, respectively) away from a vein and a veinlet and two other traverses show limited movement along a few microcracks. Three traverses show evidence for no uranium movement. One shows a complex combination of perhaps both bulk diffusion and microcrack transport. Apparent diffusivity (Da) values derived for the rock matrix (10-19to 10-16[m2/sec]) are several orders of magnitude less, and distribution constant (Kd) values (1 to 102[m3/kg]) are several orders of magnitude greater than predicted by laboratory experiments. Values for chlorite phases within the rock matrix were Da= 10-22to 10-19[m2/sec] and Kd= 101to 104[m3/kg].
The Corrosion Resistance of Alloys to Salt Brine Attack
Authors: Mirschinka V. , Odoj R.
Published: March 2011

Six metal alloys were subjected to surface and creeprupture stress corrosion tests using NaCl- and Q-brines. Low-allou materials do not seem to be suitable as a barrier against salt brine attack due to the high surface corrosion rate. Creep-rupture strength corrosion was insignificant for the tested materials. Hastelloy C 4 showed no corrosion attack by salt brines in autoclaves at 200°C and 100 bar during 8 months of testing. Bentonite was shown to reduce the corrosion attack considerably.
Investigations of Hydraulic Properties in Crystalline Rock.
Authors: Carlssn Leif , Winberg Anders , Rosander Björn
Published: March 2011

Hydraulic properties of crystalline rock from four potential repository sites in Sweden were analysed. The hydraulic conductivity of the bedrock was established by means of transient water-injection tests with constant head conducted in 25 m sections. The bedrock at the sites was divided into different hydraulic units. An effective hydraulic conductivity was calculated for the rock mass at each site. This was done on the basis of the frequency distribution of all measured values within this unit. A log-nornal distribution was found to fit the data reasonably well. Regression analysis of hydraulic conductivity as a function of depth indicated similar relationships between the four sites. At a depth of 500 m the effective hydraulic conductivity for three-dimensional flow was about 5.10-11 m/s.

The fracture frequency of the sites was established from existing core-logs. At depths of about 500 m the mean fracture frequency of the rock mass at the four sites was 1.8-2.5 fractures per meter. Of this total fracture frequency only a a certain proportion is considered to be hydraulically conductive. This proportion was established from results of hydraulic tests perforned in 2 or 3 m sections. Results obtained indicated a frequency of hydraulically conductive fractures of 0.1-0.3 fractures per meter in the rock mass at depths below 300 m.
NNWSI Performance Assessment Considerations
Authors: Tyler L. D. , Peters R. R. , Hayden N. K. , Johnstone J. K. , Sinnock S.
Published: March 2011

The Nevada Nuclear Waste Storage Investigations (NNWSI) project includes a Performance Assessment task to evaluate the containment and isolation potential for a nuclear waste repository at Yucca Mountain in southern Nevada. This task includes calculations of the rates and concentrations at which radionuclides might be released and transported from the repository and will predict their consequences if they enter the human environment. Among the major tasks required for these calculations will be the development of models for water flow and nuclide transport under unsaturated conditions and in fractured hard rock. The program must also quantify the uncertainties associated with the results of the calculations. The performance assessment will provide evaluations needed for making major decisions as the U. S. Department of Energy seeks a site for a repository. An evaluation will be part of the environmental assessments prepared to accompany the potential nomination of the site. If the Yucca mountain site is selected for characterization and development as a repository, the assessments will be required for an environmental impact statement, a safety analysis report, and other documents.

This program has been divided into five tasks. Collectively they will provide the performance assessments needed for the NNWSI Project.
Migration of Radionuclides: Experiments Within the Site Investigation Program at Gorleben
Authors: Warnecke Ernst , Hollmann Almut , Stier-Friedland Gerhard
Published: March 2011

Experiments concerning the sorption of radionuclides carried out on the site-specific unconsolidated sediments have been in progress in 6 laboratories since 1981 as part of the Gorleben site investigation program for the most relevant radionuclides. Sorption data are being determined for the site-specific conditions, and the influence of parameters, such as e.g. pH, Eh, complexing agents and NaCl concentrations is investicated. The data are necessary for the safety assessment of the repository. As the investigations have not yet been terminated, the results represent a preliminary state.
The Expected Environment for Waste Packages in a Salt Repository
Authors: Pederson L. R. , Clark D. E. , Hodges F. N. , Mcvpy G. L. , Rai D.
Published: March 2011

This paper discusses results of recent efforts to define the very near-field (within approximately 2m) environmental conditions to which waste packages will be exposed in a salt repository. These conditions must be considered in the experimental design for waste package materials testing, which includes corrosion of barrier materials and leaching of waste forms. Site-specific brine compositions have been determined, and “standard” brine compositions have been selected for testing purposes. Actual brine compositions will vary depending on origin, temperature, irradiation history, and contact with irradiated rock salt. Results of irradiating rock salt, synthetic brines, rock salt/brine mixtures, and reactions of irradiated rock salt with brine solutions are reported.
Evaluation of Iron-Base Materials for Waste Package Containers in a Salt Repository
Authors: Westerman R. E. , Nelson J. L. , Pitman S. G. , Kuhn W. L. , Basham S. J. , Moak D. P.
Published: March 2011

Design studies for high-level nuclear waste packages for salt repositories have identified low-carbon steel as a candidate material for containers. Among the requirements are strength, corrosion resistance, and fabricability. The studies of the corrosion resistance and structural stability of iron-base materials (particularly lowcarbon steel) are treated in this paper. The materials have been exposed in brines that are characteristic of the potential sites for salt repositories. The effects of temperature, radiation level, oxygen level and other parameters are under investigation. The initial development of corrosion models for these environments is presented with discussion of the key mechanisms under consideration.
Evaluation of Spent Fuel as a Waste Form In a Salt Repository
Authors: GRAY Walter J. , McVay Gary L. , Barner John. O. , Shade John W. , Cote Roger W.
Published: March 2011

Leach tests have been performed on spent fuel in synthetic Permian Basin salt brine at 25 and 75°C. Complementary tests on unirradiated UO2 pellets have been conducted in both salt brine and deionized water in the range 25 to 150°C. Iron and/or oxidized zircaloy coupons were included in some of the tests. Uranium release from spent fuel was more than 100 times greater than from U02. In brine, iron had no significant effect on the total uranium release but substantially reduced the amount in solution by causing the uranium to plate out on the iron coupon and container walls and to precipitate as filterable particles.
Immobilization of HLW in Synroc-E
Authors: Kesson S.E. , Ringwood A.E.
Published: March 2011

SYNROC-E is a new TiO2- rich formulation designed to immobilize ≤7% HLW. It comprises hollandite, zirconolite, perovskite, pyrochlore and alloy (totalling ˜20%) in a continuous matrix of fully densified rutile, and utilizes the principle of “synthetic rutile microencapsulation” in its microstructure. Short-term (%100 day) tests at 95°C reveal that the leach-rates for Cs,Ca,Sr and Ba lie within about an order of magnitude of one another and fall by %2 orders of magnitude over this time period. Leach-rates for U,Ce,Nd,Ti and Zr are initially extremely low and rapidly fall below ICP detection capabilities. On longer timescales, when SYNROC phases exposed at the surface of the wasteform have been leached away, the very low solubility of the protective rutile matrix should greatly inhibit further leaching. SYNROC-E is particularly suitable for burial in salt or in deep ocean sediments as a consequence of its thermal output, microstructure and its capacity to achieve public acceptability.
Polyphase Ceramic and Glass-Ceramic forms for Immobilizing ICPP High-Level Nuclear Waste
Authors: Harker Alan B. , Flintoff John F.
Published: March 2011

Polyphase ceramic and glass-ceramic forms have been consolidated from simulated Idaho Chemical Processing Plant wastes by hot isostatic pressing calcined waste and chemical additives at 1000°C or less. The ceramic forms can contain over 70 wt% waste with densities ranging from 3.5 to 3.85 g/cm3, depending upon the formulation. Major phases are CaF2, CaZrTi2O7, CaTiO3, monoclinic ZrO2, and amorphous intergranular material. The relative fraction of the phases is a function of the chemical additives (TiO2, CaO, and Si02) and consolidation temperature. Zirconolite, the major actinide host, makes the ceramic forms extremely leach resistant for the actinide simulant U238. The amorphous phase controls the leach performance for Sr and Cs which is improved by the addition of SiO2. Glass-ceramic forms were also consolidated by HIP at waste loadings of 30 to 70 wt% with densities of 2.73 to 3.1 g/cm3 using Exxon 127 borosilicate glass frit. The glass-ceramic forms contain crystalline CaF2, Al2O3, and ZrSiO4 (zircon) in a glass matrix. Natural mineral zircon is a stable host for 4+ valent actinides.
Partitioning of High-Level Waste as Pretreatment in Waste Management
Authors: Kubota M. , Yamaguchi I. , Okada K. , Morita Y. , Nakano K. , Nakamura H.
Published: March 2011

Removal of the long-lived radionuclides from high-level waste (HLW) is a potential means not only for making wastes more acceptable in terms of long term hazards, but also for alleviating storage requirement. From these points, the authors are developing a method of partitioning actinides, Sr-90 and Cs-137 from HLW. A chemical flow-sheet has been constructed and experiments with actual HLW were initiated in 1982. Through the partitioning, active elements in HLW can be fractionated into 3 groups. Total volume of the solid materials of the 3 groups was calculated and found to be reduced to less than one-third of the volume of the vitrified material containing 10 wt% of fission products as oxide. Such volume reduction seems to facilitate the long term storage or the deep geological disposal of HLW.
GEL Adsorption Processing for Waste Solidification in 'NZP' Ceramics
Authors: Yang L.J. , Komarneni S. , Roy R.
Published: March 2011

Simulated PW-4b waste solution along with Na additive was mixed with Zr-P-O gel, dried and then fired to form the desired sodium zirconium phosphate, NaZr2 (PO4) 3 [NZP] ceramic. NZP and monazite were the only phases produced upon firing at 900°C with 10 to 40% of PW-4b mixed with the gel. CsZr2(PO4) 3 which is isostructural with NZP was also identified when fired under reducing conditions. The -200 mesh powders of these waste forms prepared under reducing conditions showed excellent leach resistance under hydrothermal conditions.

Alternatively, PW-4b and Three Mile Island (TMI) wastes were adsorbed on Zr-P-O gel in a column. The gel was dried, pelletized and fired to form the desired [NZP] ceramic. Cesium was found to be selective on the Zr-P-O gel because no breakthrough of Cs was detected up to 38 column volumes of TMI waste. Thus, it is possible to use a tailored gel to sorb Cs and/or Sr from accident waste water and then fired the bed to form the [NZP] ceramic below 1000°C. The main advantages of the gel adsorption process are its simplicity and its enormous compositional flexibility.
Radionuclide Transport Modeling of Diffusion Cell Experiments Specific to a Backfill Barrier in a Salt Repository
Authors: Anderson Harold M. , Pietz John M. , Smith Douglas M.
Published: March 2011

Experimental radionuclide migration diffusion cell data have been collected as part of the WIPP Waste Package Performance Program. This data was collected under conditions approximating geologic isolation of a backfill barrier in a salt repository. The experiments are designed to aid in the evaluation of engineered backfill barriers.

This paper describes a radionuclide transport model designed to aid interpreting experimental diffusion cell migration data and eventually to simulate the long-term effectiveness of the backfill barrier in a salt repository. The model is designed to test a variety of expressions representative of potential mechanisms for retardation within the backfill for the best-fit with experimental data. From the comparison, the aim is to select the appropriate mechanism from the host of potential mechanisms for retardation. The model employs a novel integral equation approach to the solution of the transport equation with nonlinear retardation terms. The solution technique used in this model is a semi-analytical, iterative method for the general nonlinear problem. It is felt the technique offers improved computational efficiency over comparable finite difference methods.

Comparisons between experimental migration diffusion cell data and the model predictions are presented in this paper. Tentative conclusions concerning the importance of the retardation mechanism to radionuclide transport in the backfill barrier will be drawn.
Factors Influencing Mass Diffusion in Bentonite and Mixtures of Bentonite and Sand
Authors: Cheung S.C.H. , Oscarson D.W. , Lopez R.S.
Published: March 2011

A model, based on the relative volumes of surface and interstitial water in soil, has been developed to study the effective mass diffusion coefficient in bentonite and mixtures of bentonite and sand. The results show that, when the surface water layer is fully developed to a thickness of 0.25 nm, the theoretical effective mass diffusion coefficient decreases with increasing dry density andbentonite content in a mixture of bentonite and sand. The development of surface water depends on the initial water content, the conversion of interstitial water to surface water, and the dry density. When the surface water layer is not fully developed, the effective mass diffusion coefficientdoes not necessarily decrease as the dry density increases.

Considering the magnitude of measured mass diffusion coefficients in bentonite compacted to a dry density of 1.75 Mg/m], the model indicates that in this system there is significant conversion of interstitial to surface water. This suggests that mass diffusion coefficients in compacted bentonite are mainly influenced by the relative volumes of interstitial and surface water.
Porosities of and Diffusivities in Crystalline Rock and Fissure Coating Materials
Authors: Skagius Kristina , Neretnieks Ivars
Published: March 2011

The diffusion of non-sorbing species in different rock materials and fissure coating materials have been studied. The results show that the effective diffusivity of iodide in granites with fissure coating materials is of the same magnitude or higher as the effective diffusivity for iodide in granites without fissure coating material. Also the porosities of the granites with fissure coating material were higher. The effective diffusivity for iodide in rock materials without fissure coating material was determined to be from 1.i0-14 m2/s to about 7.10-13 m2/s.To simulate the stress that exists in the bedrock at large depths diffusion experiments with iodide in rock materials under mechanical stress, and electrical resistivity measurements in salt-water-saturated rock cores under stress have been started. Electrical resistivity measurements is an indirect method to determine the diffusivity.Results from some initial measurements show that the effective diffusivity is reduced to about 40 % of the value for unstressed samples at pressures of 230-280 bar. This is the expected stress at repository depths.
Rock Properties Input to the Site Screening Process
Authors: Bauer Arthur A. , Ratigan Joe E.
Published: March 2011

The site-screening process is designed to provide information on rock formations that will serve as the basis for recoximnding potentially suitable sites for locating a nuclear waste repository. While the application of criteria to extrinsic characteristics of the host rock, such as minimum depth and areal extent, are based on requiremnts associated with repository design and waste isolation, the significance of intrinsic characteristics (e.g., thermal conductivity, heat capacity, Young's modulus) is less firmly based. This is of particular importance with crystalline or grantitic-type rocks since they exhibit a wide range of canpositions and properties.

The range of crystalline rock property variations has been defined and results describing the impact of these variations on repository thermal, mechanical, chemical, and hydrological performance constraints obtained. Results also are presented for various repository design options (emplacement mode, thermal loading, package power/pitch). For the analysis, rock properties and repository design elements are treated as stochastic parameters by statistical methods. The output range of a performance parameter is determined with respect to the range of stochastic parameters to establish their importance in site selection.
A Natural Analogue Approach for Estimating the Health Risks from Release and Migration of Radionuclides from Radioactive Waste.
Authors: Gilbert Thomas L.
Published: March 2011

The health risks from radioactive waste may be expressed as a sum of products of transfer factors that characterize the causal chain of events between disposal of radionuclides in a waste field and the consequent health effects. “Model” estimates for the transfer factors are commonly obtained by modeling transport and other mechanisms in the subsystems that form the links in the causal chain. “Natural” estimates of some transfer factors for naturally occurring radionuclides can be obtained from data on the concentrations of naturally occurring radionuclides in soil, food, and the human body. These “model” and “natural” estimates can be used with scaling procedures to estimate the uncertainties and to obtain better estimates of the transfer factors. The scaling procedures take into account the differences in the source characteristics for radionuclides in a waste field of limited size and for radionuclides generally distributed in the natural environment. The ratios of the natural estimates to the model estimates for several transfer factors and several radionuclides belonging to the U-238 decay series have been determined. These ratios range from 1/8 to 4/1 for food-concentration/sourceconcentration transfer factors for the food pathways and from 1 to 77 for dose-rate/source-concentration transfer factors for the internal radiation dose pathways to various organs.
Prediction of Waste Performance in a Geologic Repository
Authors: Chambre' Paul L. , Pigford Thomas H.
Published: March 2011

The rate of dissolution of low-solubility species from waste forms in a geologic repository can be calculated from a theoretical analysis of the time-dependent rate of mass transfer by diffusion and convection Into the groundwater surrounding the waste, assuming a concentration at the waste-form surface eanal to the solubility of the radioelement. The analytical solutions for time-dependent mass transfer are reduced to asymptotic steady-state approximations valid over specified ranges of repository conditions. The predicted steady-state dissolution rates are considerably below those observed in laboratory leaching experiments with borosilicate glass and with other waste forms, indicating that the solid-liquid chemical reaction rates measured in the laboratory experiments are greater than the rates of diffusive-convective mass transfer in the concentration boundary layer surrounding the waste form in a geologic repository. It is shown that the time to reach steady-state dissolution can be as short as a few years, if convective mass transfer in the concentration boundary layer is important, to many thousands of years, If mass transfer is mainly by diffusion in the groundwater. The steady-state mass transfer rate can be Increased, and the time to reach steady state decreased, by sufficiently short half lives of the dissolving species. The theory has been extended to Include the effect of backfill on the steady-state mass transfer from the waste-form surface into moving groundwater.

The mass-transfer theory has been extended to include the effect of time-dependent solubilities, diffusion coefficients, and retardation coefficients, which provides a means of calculating the time-dependent dissolution of lowsolubility species from waste exDosed to groundwater during the Period of repository heating. The effects of timetemperature transient dissolution on far-field concentrations and cumulative release are calculated.

The transient and steady-state diffusion of radionuclides through a finite backfill layer separating a finite waste solid and porous rock has been analyzed, Including the effects of radioactive decay. Previous backfill analyses have neglected radioactive decay and have assumed an infinite amount of backfill. The results show that the break-through time and rate of radionuclide release depend on properties of the backfill and surrounding rock and on the waste form dimensions.

Laboratory tests have been designed to validate these theoretical analyses of diffusive-convective mass transfer with solubility-limit boundary conditions. Preliminary tests are now underway at the Battelle Northwest Laboratory.

Peak far-field concentrations of more soluble radionuclides such as cesium-135, with suitably long
radionuclide transport times and sufficiently large axial dispersion, are shown to he insensitive to dissolution rate. Equivalent phenomena occur in fracture-flow radionuclide transport.
Boron Redistribution During Formation of Cobalt Silicides
Authors: Zaring C. , Svensson B. G. , ÖStling M.
Published: March 2011

Redistribution of boron during the formation of the cobalt suicides Co2Si, CoSi and CoSi2 has been studied. The suicides were formed by solid state reactions of cobalt deposited on boron implanted silicon. The suicide formation was determined by Rutherford backseat tering spectrometry (RBS), and the resulting redistribution of boron was studied using secondary ion mass spectrometry (SIMS). The study shows that the atoms participating in the suicide formation diffuse in the growing suicide without any mutual interference. Boron atoms in the consumed silicon layer redistribute within the formed suicide layer and accumulate at the surface, while boron in the underlying unconsumed silicon is unaltered, and no accumulation due to snowplowing occurs at the silicide/silicon interface.
Composition Dependence of Crystallization of Co-Si Alloys
Authors: Hong Q. Z. , Barmak K. , Clevenger L. A.
Published: March 2011

The composition dependence of crystallization of amorphous Co-Si alloys has been investigated. Crystallization temperature decreased slowly from 400°C for a Co0.42Si0.58 alloy to 300°C for a CO0.2Si0.8 alloy. However, abrupt decrease in the crystallization temperature was observed for alloys with the monosilicide and disilicide compositions. The crystallization of alloys compositionally close to the disilicide was a one-step process with an activation energy of about 1.3 eV. The heat release and the volume contraction during crystallization of the stoichiometric Co0.33Si0.67 alloy were measured to be 0.118 eV/atom and 0.6%, respectively. In the case of the CO0.2Si0.8 alloy, complete crystallization was achieved in two steps with an activation energy of 2.1 eV for the primary crystallization.
The Effect of Silicide Formation on the Electrical Properties of Gate Oxides
Authors: Gambino J. P. , Cunningham B. , Buchanan D. A.
Published: March 2011

CoSi2, or TiSi2 formation on gate polysilicon can degrade the current-voltage and capacitance-voltage characteristics of MOS capacitors. Degradation of the gate oxide breakdown field is much more severe for capacitors with TiSi2 than for those with COSi2 TEM reveals evidence for a reaction at the interface between TiSi2 and SiO2, whereas there is no observable reaction between COSi2 and SiO2- The low breakdown fields for devices with TiSi2 may be due to thinning of the gate oxide by the interfacial reaction or mechanical deformation. A high density of electron traps and a small reduction in the breakdown field is observed when COSi2 contacts the gate, possibly due to a compressive stress in the oxide exerted by the suicide. In addition, an increase in the interface state density at the Si-SiO2 interface is seen for all samples exposed to a rapid thermal anneal (RTA) at 800°C, possibly due to the release of H from dangling bonds.
Reactions at the Titanium-Silicon Interface Studied Using Hot-Stage Tem
Authors: Kirtikar Amol , Sinclair Robert
Published: March 2011

The interaction of titanium thin films sputter-deposited onto single crystal silicon was studied by in situ heating experiments within the TEM. Reactions at the Ti-Si interface including amorphization, crystallization, allotropie phase transformations and agglomeration have been observed in real time and recorded on videotape. Interpretation of these recordings can yield a wealth of information on the silicidation process.
Determination of the Optical & Materials Properties of βFeSi2 Layers Fabricated Using Ion Beam Synthesis
Authors: Hunt T. D. , Reeson K. J. , Gwilliam R. M. , Homewood K. P. , Wilson R. J. , Spraggs R. S. , Sealy B. J. , Meekison C. D. , Booker G. R. , Oberschachtsiek P.
Published: March 2011

IBS of buried α and β iron suicide layers was achieved by the implantation of 2 MeV 56Fe+ ions into (100) single crystal silicon substrates over a dose range of 3 × 1017 to 1 × 1018 cm“-2followed by a high temperature anneal. No photoluminescence was observed from the as-implanted samples which contained a discontinuous layer of βFeSi2 precipitates approximately 1.5 μm below the silicon surface. Upon annealing at 700°C, a 200 nm polycrystalline βFeSi2 layer was formed which gave a PL signal centred at 1.55 μm. After a 900°C anneal, the layer transformed to αFeSix with a resistivity of approximately 280μΩcm.
Improved Planarization for a Sog Etchback Process by Modifying the PECVD Oxide Film
Authors: Weling Milind , Jain Vivek
Published: March 2011

In this study we have shown, for the first time, that Inter-Metal Oxide (IMO) planarization using a spin-on-glass (SOG) etchback process can be significantly improved by changing the composition of the deposited PECVD oxide film. Earlier studies have emphasized the importance of lowering the SOG to PECVD oxide etch selectivity below unity to compensate for micro-loading effects and thereby achieve good planarization. However, we have shown that a range of selectivities could be obtained by merely changing the silicon-richness of the PECVD oxide film. It was observed that for a given etch selectivity, planarization after SOG etchback was better with a silicon-rich oxide than with a stoichiometric oxide and particularly so for tight spacings that are characteristic of sub-micron technologies. We believe that increasing the silicon-richness of the PECVD oxide suppresses the micro-loading effects and consequently enables operation at selectivities closer to unity while maintaining good planarization. This feature has an important advantage of significantly widening the process window for a SOG etchback application.
Improved Detection of Deep Voids in Al Metalization Using Phase-Optimized Thermal Wave Imaging
Authors: Welles C. G. , Bivas Albert , Smith Lee
Published: March 2011

The importance of minimizing stress-induced voiding for reliable VLSI metalization is now well appreciated. For detection of subsurface voids in a nondestructive manner, thermal wave modulated reflectance (TW) imaging is increasingly utilized.

Although the TW response is vectorial (with components that are in-phaSfi. and 90 degrees out-of-phase with the laser modulation), heretofore only the magnitude of this signal was utilized in this application. For optimum imaging of deep voids, it is desirable to selectively display a signal that responds to both phase-delay and magnitude information simultaneously. The phase delay originates from the round-trip propagation time of the thermal wave from the surface to the void.

In this paper, we demonstrate the use of this technique to (a) improve the detection (i.e. signal-to-noise ratio) of subsurface voids (b) distinguish between near-surface artifacts and deep voids, and (c) demonstrate the general utility of this technique by exhibiting improved S/N in crystalline silicon defects.
The Influence of Substrate Doping on Silicide Formation with Tungsten Deposited From Tungsten Hexafluoride
Authors: Zhang S. -L. , ÖStling M. , Buchta R. , Smith U. , Linnros J. , Gong S. -F.
Published: March 2011

The influence of substrate doping on the WSiz formation is investigated. Ion implantation was used to dope Si wafers with either B, Al, P, As or Sb. Implanted doses were in the range from 1 × 1013 to 5 × 1016at./cm2. Dopant activation was always performed before tungsten deposition in a hot wall LPCVD system. The sillcidation was monitored by means of Rutherford backscattering spectrometry (RBS), and the dopant redistribution was analyzed by secondary ion mass spectroscopy (SIMS). The suicide formation on p-type substrates was retarded at high doping levels, whereas that on the n-type substrates showed a more complex behavior. In the latter cases, the silicidation could be either retarded or unaffected, depending on the dopant concentration. Sb doped wafers exhibited a slightly increased silicidation rate with doping level, while P and As doped wafers showed a peak, reaction rate for intermediate doping levels. SIMS analysis revealed a segregation of B and P into the suicide during formation, while Al, As and Sb were snowplowed and accumulated at the WSi2/Si interface. Binary and ternary compounds of Al, P and As with W and Si were found by X-ray diffraction for the highest doping levels.
Ungated Vacuum Field Emission from Ordered Arrays of Microlithographically Defined Cylinders
Authors: Hickman James J. , Georger J. H. , Anderson M. , Bergeron G. L. , Kirkpatrick D. A.
Published: March 2011

A new process has been developed which allows electroless metal deposition on ordered arrays of resist structures with high aspect ratios (10–25 μm tall x 0.5–13 μm diameter). The fabricated structures have demonstrated ungated vacuum field emission at fields of 80–300 kV/cm in background pressures of 5 × 10-6 torr. The surface composition and Interface contamination relate directly to cathode performance. Cathode performance can be optimized by controlling the chemistry at these interfaces. X-ray Photoelectron Spectroscopy depth profiles, Scanning Auger Electron Spectroscopy, and Scanning Electron Microscopy have been used to characterize this system. These structures have potential vacuum microelectronics applications such as addressable electron emitters for flat panel displays.
A Combined Thermodynamic and Kinetic Approach to the Metallization of GaAs
Authors: Austin Chang Y.
Published: March 2011

A combined thermodynamic/kinetic methodology was presented to give a rational approach to the metallization of n-GaAs when a reciprocal system of GaAs-MδsGa-MsM'-MAs exists. Fortunately, for many quaternary systems consisting of Ga-M-M'-As, such a reciprocal system does exist. This methodology may be used either for Schottky enhancement or ohmic contacts to n-GaAs. Two examples were used to illustrate the approach and preliminary results were given.
Chemical Mechanical Polishing of Interlevel Dielectrics: Models for Removal Rate and Planarity
Authors: Sivaram S. , Tolles R. , Bath H. , Lee E. , Leggett R.
Published: March 2011

This paper reviews some of the problems limiting broad manufacturing implementation of chemical mechanical polishing (CMP) as a planarization process for interlevel dielectrics. We examine the mechanism whereby polish rates tend to decrease as the polish pad ages, and propose an explanation based on slurry transport. We review a simple theory which provides an understanding in terms of basic mechanical principles of how CMP produces its planarizing effect. Finally, we demonstrate a method capable of providing a quantitative measure of planarity.
A Comparison of AFM, SEM, and TEM Analysis of AL/SI/CU Thin Films
Authors: Westra K. L. , Thomson D. J.
Published: March 2011

Atomic Force microscopy, scanning electron microscopy, and transmission electron microscopy was used to study Al/Si/Cu films sputter deposited at 2 and 45 mTorr. AFM and SEM analysis shows the films to consist of columnar structures commonly seen in PVD deposited thin films, while the TEM analysis showed the films be polycrystalline. Comparing the columnar structures seen in the AFM and SEM study to the grains found in the TEM study, we conclude that the columns consist of single grains. Thus for these films AFM or SEM analysis can be used to determine the grain size. Finally, an AFM scan of a Al/Si/Cu deposited via was performed. The AFM image clearly shows the high resolution of the AFM, while it also illustrates the problems caused by the finite size of the AFM tip.