bluuebunny/crossref_metadata_2025 huggingface dataset:
The Waste Package Materials Field Test in S.E. New Mexico Salt
Authors: Molecke Martin A. , Torres Teresa M.
Published: March 2011

A six-part, waste package materials field test was conducted in a halite horizon of a potash mine in southeastern New Mexico. The primary purposes of this test were to evaluate the thermophysical and geochemical performance of candidate HLW-package backfill materials emplaced in rock salt and the corrosion behavior of candidate waste canister or overpack alloys. This field test series also served as a precursor to forthcoming Waste Isolation Pilot Plant (WIPP) in situ waste package performance experiments on simulated defense high-level waste packages, serving to develop applicable testing, instrumentation, and sampling techniques. The backfill materials tested (individually, in one- to five-month tests) were: low-density bentonite clay; low-density bentonite (70 wt.%)-silica sand (30 wt.%) mixtures, both dry and brine-injected; high-density bentonite-sand annular compacts; trapped air; and finely-crushed WIPP salt. The in situ measured thermal conductivities (at a maximum canister-heater surface temperature of 150° or 250°C) for the backfills ranged from 0.25 W/mK for pure bentonite to about 1.25 W/mK for the high-density bentonite-sand. No significant backfill material degradation products were detected in post-test analyses. No appreciable corrosion of the titanium-, nickel-, or iron-based alloys embedded in the hot backfill was found; potentially significant pitting corrosion of 2 1/4 Cr-1 Mo steel and copper was detected.
Activity Diagrams for Calcium/Hydrogen, Sodium/Hydrogen, and Potassium/Hydrogen, and H4SiO4and Their Relation to Reactions in Systems Containing Radioactive Waste Forms, Cement, and Rock in the Presence of Water
Authors: Barnes Mary W. , Roy Della M.
Published: March 2011

In order to identify reactions which can occur in systems containing nuclear waste forms, cement, and repository rock in the presence of water, activity diagrams were calculated from free energies for aluminosilicates and calcium silicates. Log (calcium activity)/(hydrogen activity)2was plotted against log (H4SiO4activity) for reactions among calcium aluminum silicates for which free energies are available in the literature. Similar diagrams were made for sodium/hydrogen activity, and potassium/hydrogen activity. For calcium an activity diagram was constructed for the silicates.

Groundwater compositions from candidate repository sites in the Palo Duro Basin of Texas, the Delaware Basin of New Mexico, and the Nevada Test Site were plotted on these diagrams. Essentially all of these are shown to be in the calcium zeolite field as shown on the diagram for calcium in the absence of other cations. When considerable Mg and Fe are present in the water, other phases may replace the calcium zeolite in the pertinent region of the diagram. Chlorite is shown to be stable in this region at the Mg and pH level of the Ogallala if the chlorite is high in iron, and at the Mg and pH level of the Wolfcamp low- or high-Fe chlorites are stable. Potassium and sodium mineralrelationships fall in two categories, dilute waters and saline waters. Of the dilute waters, that from the Ogallala aquifer in the Palo Duro Basin, and most of the Nevada Test Site waters, including that from the proposed radwaste repository horizon, are in equilibrium with Na-beidellite and kaolinite. Boreholes at Yucca Flat and Mercury Valley at the Nevada Test Site, and shallow ground water from the Rolling Plains north and east of the Palo Duro Basin are in equilibrium with kaolinite. Of the saline waters, that from the Castile (deep in the Delaware Basin) is a kaolinite water. The brines from the Salado and Rustler formations are in equilibrium with kaolinite and possibly also with sodium-potassium zeolite and illite.

Leachates of cement and water, and cement, waste, and water were plotted on the calcium silicate activity diagram. These solutions are in equilibrium with calcium silicate hydrate hydrolysis reactions, with grossular and possibly with Ca-zeolites. Among the calcium silicates, calciumsilicate-hydrate gel (C-S-H gel) and tobermorite are the most likely candidates, but the thermodynamic data are not adequate to distinguish all the possibilities. The underlying assumptions are discussed.
Stability of Radioactive Waste Glasses Assessed from Hydration Thermodynamics
Authors: John Plodinec M. , Jantzen Carol M. , Wicks George G.
Published: March 2011

Assessment of the geologic performance of radioactive waste glasses requires extrapolation of finite tests to very long times. Hydration thermodynamics provides a means to compare the stability of waste glasses to natural analogues and to ancient synthetic glasses. The glass composition is separated into structural components of known free energy of hydration. These are then summed to provide a discrete measure of the stability of a given glass to aqueous attack. Hydration thermodynamics can be used to extend the results of laboratory tests of Savannah River waste glass to the repository environment.
Kinetics of the Adsorption of Radionuclides on Tuff From Yucca Mountain
Authors: Rundberg R. S.
Published: March 2011

The sorption of simple cations in tuff is dominated by adsorption on aluminosilicates that have charged surfaces, suc as zeolites and clays. The most significant sorbing minerals present in Nevada tuff are clinoptilolite, heulandite, mordenite, and montmorillonite. The kinetics of sorption on tuffs containing the minerals clinoptilolite and montmorillonite has been determined by studying the uptake of strontium, cesium, and barium on thin tuff wafers. The rate constants for uptake of these elements on tuff are consistent with a model of sorption that is diffusion limited but where diffusion occurs in two stages. First the cations diffuse into the rock through the water-filled pore space. Next, the cations must diffuse into the much narrower channels within the aluminosilicate crystals. After they are within the zeolite framework o between the clay planes, the cations may rapidly sorb on the negatively charged surfaces. The actinide elements have a time constant for the apparent sorption that is inconsistent with this model and may have a radically different mechanism o removal from solution.
A Natural Analogue Study of Radionuclide Migration in Clays
Authors: Mckinley Ian G. , Mackenzie Angus B. , West Julia M. , Scott R. D.
Published: March 2011

The use of sediment laid down in a Scottish loch during the Flandrian marine transgression as a source term for a “natural analogue” study of elemental migration in clays over a timescale of 103 − 104 y has been investigated. Depth profiles of over 20 elements have been measured which illustrate varying post depositional behaviour ranging from effectively total immobility to complete redistribution throughout the sediment profile. These results are contrasted with laboratory batch sorption data for a range of nuclides on samples of this sediment.
Disproportionation and Polymerization of Plutonium(IV) in Dilute Aqueous Solutions
Authors: Newton T. W. , Rundberg V. L.
Published: March 2011

The rates of polymerization and disproportionation of Pu(IV) have been studied using low concentrations: (1.7 − 10) × 10−6M Pu, (0.8 − 12) × 10−4M HCI and 0.01M ionic strength. Osmium(II) complexes such as the tris−4,41−2,21−bipyridine complex were found to react rapidly with Pu(IV) but very slowly, if at all, with Pu(IV) polymer, Pu(lll), or Pu(V). Thus, it is possible to determine unreacted Pu(IV) in the presence of reaction products by using Os(II) complexes. Disproportionation reaction products, Pu(IlI) and Pu(V), were determined using their reactions with Ce(IV) sulfate. We find −d[Pu(IV)]/dt = k'[Pu(IV)]2 at constant pH. Log k1 varies from about 4.25 at pH 3 to about 7.0 at pH 4.1 (units for k1 are M−1min−1). The [H+] dependence varies from about −2 to −3 over the pH range studied. The measured rate is the sum of those for polymerization and disproportionation; the latter reaction amounts to about 75% of the total at pH 3 and 20% at pH 4. The second-order rate constants for disproportionation are very much larger than expected on the basis of extrapolation from 0.2 to 1.OM HClO, solutions. The products of the reaction do not affect the rate, but U(VI), aged Pu(IV) polymer, and CO2 increase the rate.
Permeability and Pore-Fluid Chemistry of the Topopah Spring Member of the Paintbrush Tuff, Nevada Test Site, in a Temperature Gradient – Application to Nuclear Waste Storage
Authors: Morrow C. A. , Moore D. E. , Byerlee J. D.
Published: March 2011

The Topopah Spring Member of the Paintbrush Tuff from the Nevada Test Site is being investigated by the Nevada Nuclear Waste Storage Investigations project (NNWSI) as a possible nuclear waste repository host rock. Changes with time of the permeability and fluid chemistry of the Topopah Spring Member have been measured in samples subjected to a temperature gradient. Maximum temperatures of the imposed gradients ranged from 90° to 250°C; minimum temperatures were 36° to 83°C. Confining and pore pressures simulated a depth of about 1.2 km, which is greater than the proposed repository depth, but chosen for comparison with previous studies at these pressures. Pore fluid used in the experiments was groundwater from the Nevada Test Site; the direction of pore-fluid flow was from the high- to the low-temperature side of the tuffs.

Initial permeabilities of the tuff samples ranged from 3 to 65 μdarcys, the wide range in values resulting from differences in the void and fracture geometries of the samples. Heating the tuffs produced no change in permeability in tne lowest temperature experiment and only small changes at higher temperatures. The fluids discharged from the tuffs were dilute waters of nearneutral pH that differed only slightly from the original groundwater composition.

Since proposed burial in the Topopah Spring Member would be in the unsaturated zone, the high initial permeabilities and the absence of permeability change with heating may be desirable, because downward-percolating waters would be able to drain into deeper formations and not collect at the repository level. in addition, any fluids that may come in contact with waste canisters wlll not have acquired any potentially corrosive characteristics through interaction with the tuff.
The Use of Natural Radionuclides to Predict the Behavior of Radwaste Radionuclides In Far-Field Aquifers
Authors: Hubbard N. , Laul J. C. , Perkins R. W.
Published: March 2011

In appropriate aquifers the natural radionuclides of the U and Th decay series are important sources of information about the behavior of radwaste radionuclides in far-field aquifers. The Wolfcamp Carbonate, Pennsylvanian Carbonate and Granite Wash aquifers in the Palo Duro Basin of the Texas Panhandle are prime examples of such aquifers. Sampling and analysis for key radionuclides in the ground waters of these aquifers are quite feasible and have been accomplished. Key early results are: (1) Ra does not appear to be retarded by sorption, (2) Th appears to be strongly sorbed, (3) kinetics seem to be different on time scales of days to months than on ones of hundreds of thousands of years, and (4) U and Th behave similarily when the time scales (half-lives) are similar, leading to the suggestion that uranium is in the +4 valence state in these aquifers.
Mechanisms for the Interaction of Americium(III) and Neptunium(V) with Geologic Media
Authors: Allard B.
Published: March 2011

The sorption of americium(III) and neptunium(V) on geologic media has been measured under oxic conditions. The aqueous phase was generally a synthetic groundwater. The solid phase was a pure mineral, representative of crystalline granitic rocks. Altogether 40 minerals and rocks were used. The effects of parameters such as pH and ionic strength of the aqueous phase as well as cation exchange capacity and surface/mass ratio of the solid sorbent are discussed. The sorption mechanism in the environmental pH-range can be denoted as physical adsorption process, which is largely governed by pH and the speciation in the aqueous phase and to a less extent by the exchange capacity of the solid.
The Basalt/Water System: Considerations for a Nuclear Waste Repository
Authors: Lane D.L. , Apted M.J. , Allen C.C. , Myers J.
Published: March 2011

High-level nuclear Waste emplaced in a repository in basalt will lead to elevated temperatures and chemical reactions between the basalt and repository groundwater. The resultant changes in groundwater chemistry and the formation of secondary minerals will affect radionuclide release rates from the repository. In this study, Grande Ronde Basalt and synthetic groundwater were reacted at temperatures of 100°, 150°, and 300°C at a pressure of 30 MPa. Dickson-type sampling autoclaves were used to follow solution composition changes with time. Solution PH remained weakly alkaline, while steady state concentrations of F-, Cl-, SO4-2, and total Carbon were similar to or lower than initial values. Alteration assemblages at 300°C included silica, zeolites, potassium feldspar, and iron smectite. These assemblages are metastable, and prediction of alteration in the basalt and packing material depends on “accelerated” tests results and must be supplemented by study of metastable assemblages in natural analog systems and by tests in open systems with varying flow rates. Experimental data are consistent with rapid adjustment of Eh to reducing values; however, more work on reaction rates and buffering capacity is in progress.
Chemical Migration by Contact Metamorphism between Pegmatite and Country Rocks: Natural Analogs for Radionuclide Migration
Authors: Laul J. C. , Walker R. J. , Shearer C. K. , Papike J. J. , Simon S. B.
Published: March 2011

Comparison of trace element signatures of country rocks as a function of distance from the contact with two pegmatites, Tin Mountain and Etta, in the Black Hills of South Dakota, suggests that some elements such as K, Li, Rb, Cs, As, Sb, Zn and Pb, have migrated to distances of 4 to 40 meters during contact metamorphism. The relative degree of migration varies depending on the element. On the other hand, there is virtually no migration of rare earth elements (REE), Al, Sc, Cr, Hf, U, and Th. Biotite and muscovite are effective trace element traps for Li, Rb and Cs. Biotite has a greater affinity for Rb, Cs and Li than muscovite.
CVD and Characterization of Al-Cu Metallization Thin Films
Authors: Houlding V. H. , Maxwell H. , Crochiere S. M. , Farrington D. L. , Rai R. S. , Tartaglia J. M.
Published: March 2011

The chemical vapor deposition of Al-Cu thin films on Si, SiO2, and TiN substrates was examined in a vertical low pressure cold wall reactor using trimethylamine alane (TMAA1) at 20 C as the Al source. The Cu sources bis-(hexafluoroacetylacetonato)copper(H)(CuHFA), (cyclopentadienyl)copper(I) triethylphosphine (CpCuPEt3), and (hexafluoroacetylacetonato)copper(I) trimethylphosphine (HfaCuPMe3), were compared. The Cu content of the films was controlled up to“5 wt% by simply varying the temperature of the Cu source. Codeposited Al-Cu films with excellent conductivity, purity, and adhesion properties were obtained with all Cu sources. Optimal film smoothness was achieved at∼350 C. The compounds differed in the ease of control over the %Cu in the films. CuHFA exhibited a massive parasitic reaction which made control very difficult. The Cu(I) complexes showed very minor parasitic reactions. Analysis of films with high Cu content by SEM-EDS showed clear segregation of Cu and Al, consistent with the low solubility of Cu in Al. Films with >2% Cu appeared homogeneous on a μm scale by both SEM-EDS and SIMS depth profiling. TEM of film cross sections revealed a polycrystalline Al film with small (20–100 Å) Cu-rich particles dispersed throughout the Al grains. These particles exhibited bright field-dark field contrast characteristic of crystalline material.
Detection of Titanium Silicide Formation and Phase Transformation by Picosecond Ultrasonics
Authors: Lin H. -N. , Stoner R. J. , Maris H. J. , Harper J. M. E. , Cabral C. , Halbout J. -M. , Rubloff G. W.
Published: March 2011

Picosecond ultrasonics is employed to study the titanium silicide formation sequence for evaporated Ti films on silicon substrates annealed at temperatures between 300 and 800 °C. The measurements show significant differences in the ultrasonic echo pattern before and after the structural phases C49 and C54 are formed, thus indicating that picosecond ultrasonics is a sensitive non-destructive probe of silicide formation. The longitudinal sound velocity has been found to be (8.3 ± 0.2) × 105 cm/sec for C49 TiSi2, and about 5% lower for the C54 phase.
The Influence of a TiN Cap Layer on a Titanium-S Alici de Process: Titanium vs Titanium Nitride/Titanium
Authors: Zhang S. -L. , Kaplan W. , Östling M. , Norström H. , Lindberg A.
Published: March 2011

To minimize the bridging problem In the self-aligned titanium slllcide (SALICI DE) processes, a titanium nitride (TiN) cap has been suggested. The objective of this work was to study the impact of such a TiN cap layer on a Ti-based SALICI DE process. The slllcide formation was carried out by Rapid Thermal Annealing (RTA). The Ti-Si Interaction, the dopant loss during silicide formation, the contact resistance between the formed TiSi2 and SI substrates, the leakage current, and the lateral diffusion of SI atoms over the spacers of MOS devices were investigated with and without a TiN layer on top of Tl films. The dependence of these factors on the annealing temperature was also investigated. The results showed that: a) An increased dopant loss was a direct result of more silicide formation, due to a larger SI substrate consumption. This was observed both with and without TiN cap. b) The specific contact resistance increased with annealing temperature, regardless the TiN cap. c) Sheet resistance, specific contact resistance and leakage current were not sensitive to the selective etch procedure. And d) A lower yield for bridging test structures was found where a TiN cap was employed, Indicating that the TiN layer did not suppress the Si lateral diffusion.
Air-Bridge Electron-Beam Lithography for Coplanar Millimeter Wave Circuits
Authors: Haydl William H. , Bojko R. J. , Eastman L. F.
Published: March 2011

In the development of air bridges for low capacitance crossovers, resists of 3–6μm thickness a e needed, which calls for special alignment techniques. A technique has been developed for an air bridge tec nology, which is realized entirely by electron beam lithography. Such an all-electron-beam technique for sub-micron devices and ultrahigh frequency circuits, results in a fast turn-around-time in the development of integrated circuits.

Gold plated air bridges with 20 to 120 pm span, 5–60 μm width, 2.6 pm height, and 2–4 μm thickness, were realized on GaAs and InP.
Assessing Ohmic Contacts
Authors: Barry Harrison H , Reeves Geoffery K
Published: March 2011

This paper reviews specific contact resistivity pc values obtained theoretically and experimently for a range of semiconducting materials. Techniques of obtaining pc values in terms of measurement, accuracy and reproducibility are then considered and matched to the semiconducting materials previously covered.
Barrier Inhomogeneities at Schottky Contacts: Curved Richardson Plots, Idealities, and Flat Band Barriers
Authors: Werner Jürgen H. , Güttler Herbert H. , Rau Uwe
Published: March 2011

Evaluating either curved Richardson plots or temperature-dependent ideality data allows for a quantitative characterization of spatial inhomogeneities at Schottky contacts. Applying the two independent methods to PtSi/Si diodes we obtain a standard deviation around 70mV for the barrier fluctuations. These results agree with those from the comparison of temperature-dependent current and capacitance barriers. We discuss also flat band barrier heights which should be used if one investigates the temperature dependence of fundamental Schottky barrier heights. Their temperature coefficients depend on metallization. For epitaxial NiSi2/Si contacts on (100) oriented Si we find a strong influence of interface crystallography on the temperature coefficients.
The Properties of a Plasma Deposited Candidate Insulator for Future Multilevel Interconnects Technology.
Authors: Gelatos A. V. , Mogab C. J. , Saha N. C. , Parikh N.
Published: March 2011

Results are reported from an investigation of the properties of boron nitride thin films. The BN films were deposited by the method of plasma enhanced chemical vapor deposition (PECVD) from mixtures of ammonia and diborane. The deposition variables were RF power, pressure, ammonia partial pressure, diborane partial pressure, diluent type (nitrogen or argon), and temperature. The films were characterized for their stoichiometry, hydrogen content, stress, refractive index, and especially for their dielectric properties. It was observed that the main parameters affecting the dielectric constant were the ratio of ammonia to diborane flow, and the deposition temperature. The dielectric constant decreased with increasing ammonia to diborane ratio, while it increased with decreasing deposition temperature. The lowest dielectric constant value achieved was 4.0 ·, 0.1. Nitrogen dilution allowed the deposition of boron nitride films with the lowest dielectric constant value at ammonia to diborane ratios smaller than those required under argon dilution, which suggests some incorporation of nitrogen into the boron nitride matrix from the diluent.
Doping and beyond: towards a common model for the ohmic contact formation mechanism in the Au/Te/Au/-, AuGe/-, and Ge/Pd/n-GaAs systems
Authors: Wuyts K. , Watté J. , Silverans R. E. , MüNder H. , Berger M. G. , Luth H. , Van Hove M. , Van Rossum M.
Published: March 2011

The results of our recent research on the ohmic contact formation mechanism in furnace alloyed Au/Te/Au/GaAs contacts are summarized, and preliminary Raman measurements on annealed Ge/Pd/GaAs structures are presented. The data and those reported in literature on the AuGe- and Ge/Pd- GaAs systems are argued to be more in agreement with the graded crystalline heterojunction concept (the formation of n+-Ge/GaAs, n+Ga2Te3/GaAs junctions) than with the doping model (the formation of n+-GaAs).
Lognormal Lateral Distribution of Barrier Height in Au/n-GaAs Schottky Junctions?
Authors: Horváth ZS. J.
Published: March 2011

Experimental capacitance-voltage (C-V) characteristics are presented for Au/n-GaAs Schottky contacts. The deviation of the obtained C-V characteristics from the theoretical one including the linear regions of the 1/Ca-V plot may be explained by either the normal or the lognormal lateral distribution of the barrier height. It is concluded that from physical point of view the lognormal lateral distribution of the Schottky barrier height proposed first in this work, is more likely than the normal distribution.
Fabrication of Hollow High Aspect Ratio Metal Microstructure Arrays
Authors: Calvert J. M. , Georger J. H. , Rebbert M. L , Anderson M. A. , Park D. , Hickman J. J. , Dulcey C. S. , Peckerar M. C.
Published: March 2011

A process has been developed to produce regular arrays of hollow metal microstructures on substrates of choice. Optical lithography was used to define high aspect ratio structures in photoresist. The resist structures were selectively metallized by electroless (EL) deposition such that metal was deposited only on the sidewalls of the resist and on the surface of the substrate. Dissolution of the polymeric photoresist resulted in regular arrays of hollow metal cylinders and cones with geometries and structure spacings determined by the original resist structures. Characterization of metallized microstructures using surface analytical techniques and SEM is presented. Arrays of microstructures with 500–1000 Å thick EL Ni walls and aspect ratios (height/tip diameter) of 8:1 are shown.
Stability of Nanoscale Cobalt Silicide Film Formation on Polysilicon
Authors: Pramanick S. , Erokhin Yu. N. , Patnaik B. K. , Rozgonyi G. A. , Gambino J. P.
Published: March 2011

We have extended the recent work1,2 on grain boundary grooving, agglomeration and islanding during the reaction of thin Co films on single crystal Si<100> substrates (source/drain contacts) to the case of poly silicon substrates3 (gate contact and local interconnects). The stability of 27 to 50 nm CoSi2 films formed via rapid thermal annealing on polysilicon substrates with and without P+ or Ge+ implantation was examined using XTEM, RBS, XRD, and Four-probe measurements. For an undoped polysilicon, partial agglomeration of a 30 nm CoSi2 film has been observed, similar to that seen on a single crystal Si substrate.2For heavily Phosphorus doped polysilicon, a transition from low resistance, stoichiometric cobalt disilicide films (700 °C, 10 sec RTA) to high resistance films at 700 °C, 30 sec RTA (600–1000 Ω per square and discontinuous suicide grain growth) has been observed. Concurrent suicide formation on preamorphized polysilicon (Ge+ I/I and no anneal) has been found to suppress agglomeration of nanoscale cobalt suicide layers, since small grain size and low grain boundary energy are favorable for improving thermal stability4. These continuous layers also exhibited the lowest sheet resistance corresponding to a resistivity of ≤ 21 μΩ-cm.
Effect of Near-Interface Concentration Change on Barrier Height in Ion-Bombarded and Heat-Treated GaAs Schottky Contacts
Authors: Horváth ZS. J.
Published: March 2011

The change of the doping concentration (including type) near the metal-semiconductor interface influences the Schottky barrier height (BH). In many cases this phenomenon is apparently spontaneous, or it is a side effect of the technology. The goal of this paper is to summarize the effect of the near-interface concentration change on the apparent and real Schottky BHs, and to demonstrate its importance with experimental results obtained in GaAs Schottky contacts. The question of the definition of the real BH for some of these structures is also treated.
Optimizing n+ Ohmic Contacts on GaAs for HemtS
Authors: Harris H. M. , Farley J. R.
Published: March 2011

Low ohmic contact resistance is essential for high performance microwave and millimeter wave transistors. Rapid thermal processing (RTP) has been used to optimize the ohmic contact resistance of gold - germanium / nickel / gold metallizations on gallium arsenide (GaAs) layers for high electron mobility transistor (HEMT) applications. A HEMT layer structure consisting of a 9000Å buffer layer grown on a semi-insulating substrate followed by a 20Å undoped AlGaAs spacer layer, a 700Å Al0.22Ga0.78 As layer doped at 1.0 × 1018cm-3and a 500Å GaAs cap layer doped at 1.5 × 1018 cm°C to 450°C. Time at temperature was varied from 10 seconds to 1 minute. Optimum conditions for our equipment and layer structure were found to be 365°C for 30 seconds. These conditions produced contact resistances of 0.08 ohm-mm (approximately 2.0 times better than the standard furnace alloy process).
The Ternary Phase Diagram for Au-Ga-As Using the Flow Chart Technique
Authors: Mueller C. H. , Holloway P. H. , Connell R. G.
Published: March 2011

Degradation of the Au/GaAs interface during heating is a problem which limits device reliability. The “flow chart” method was used to construct the ternary Au-Ga-As phase diagram and determine the equilibrium reactions which are responsible for interfacial degradation. Interfacial degradation was correlated with the removal of Asx from the interface, which lowered the liquidus temperature and enhanced the dissolution of GaAs. The dissolution proceeds by a series of class II reactions within the Au-AuGa-GaAs ternary system and results in the incorporation of Ga into the Au phase, and growth of several AuxGay phases. However, when the processing is accomplished in a manner which prevents the interface from being depleted in As, no interfacial degradation is expected.
Metallurgical Behavior of the Metal-IN-P Systems: Implications for the Design of Contacts to Inp
Authors: Mohney Suzanne E. , Austin Chang Y.
Published: March 2011

Phase equilibria in the M-In-P (M = transition metal) ternary systems is determined through a combination of thermodynamic calculation and experimentation. Palladium is identified as a particularly attractive metal for contacts to InP. One useful feature of this system for contact design is the occurance of PdχInP ternary phases. Additionally, Pdln is found to be in equilibrium with InP and is identified as a promising contact material to InP because of its high melting point, low resistivity, and favorable properties for processing. Progress in the development of Pdln-based contacts to InP is briefly discussed.
Au/Ge/Pd Ohmic Contacts to n-TYPE InP
Authors: Jian Ping , Ivey Douglas G. , Bruce Robert , Knight Gordon
Published: March 2011

Ohmic contact formation and thermal stability in a Au/Ge/Pd metallization to n-type InP, doped to a level of 1017 cm-3, have been investigated. Contact resistance was measured using a transmission line method, while microstructural changes were examined by means of TEM, EDX, CBED and SAD. Contacts became ohmic after annealing at temperatures ranging from 300°C to 375°C. A minimum contact resistance of 2.5×l0-6 Ω-cm2 was obtained after annealing at 350°C for 320s. The drop in resistance to ohmic behavior corresponded to the decomposition of an epitaxial quaternary phase (Au-Ge-Pd-P). Annealing at 400°C and above resulted in Au10In3 spiking into InP and a break down of contact lateral uniformity, which increased contact resistance.
The Achievement of Low Contact Resistance to Indium Phosphide: the Roles of Ni, Au, Ge, and Combinations Thereof
Authors: Fatemi Navid S. , Weizer Victor G.
Published: March 2011

We have investigated the electrical and metallurgical behavior of Ni, Au-Ni, and Au-Ge-Ni contacts on n-InP. We have found that very low values of contact resistivity (pc) in the E-7 Ω-cm2 range are obtained with Ni-only contacts. We show that the addition of Au to Ni contact metallization effects an additional order of magnitude reduction in pc. Ultra-low contact resistivities in the E-8 Ω-cm2 range are obtained with both the Au-Ni and the Au-Ge-Ni systems, effectively eliminating the need for the presence of Ge in the Au-Ge-Ni system. The formation of various nickel phosphides at the metal-InP interface is shown to be responsible for the observed pc values in the Ni and the Au-Ni systems. We show, finally, that the order in which the constituents of Au-Ni and Au-Ge-Ni contacts are deposited has a significant bearing on the composition of the reaction products formed at the metal-InP interface and therefore on the contact resistivity at that interface.
Physical AMD Electrical Properties of Iridium Thin Films
Authors: Elliman R. G. , Lawn M. A. , Reeves G. K. , Jagadish C.
Published: March 2011

Thin Ir films were deposited onto clean (111) Si surfaces. The films were analysed by Rutherford backscattering and transmission electron microscopy and were shown to be continuous for film thicknesses as small as 0.5nm. The films contained internal stress as deposited and coiled up when the substrate was removed chemically.

A four point probe was employed to measure the resistivity of the films as a function of film thickness. The resistivity increased with decreasing film thickness, from ∼35 micro-Ohm. cm for 160nm thick films to -190 micro-Ohm. cm for 0.5nm thick films. This increase in resistivity is shown to be consistent with theories of carrier transport in thin films.
Advanced Planarized Aluminum Metallization Process
Authors: Chen F. S. , Durit G. A. , Staman J. W. , Wei C. C. , Liou F. T.
Published: March 2011

Sputtered aluminum has been used for interconnection in integrated circuits because of its low resistivity. However conventional sputtered aluminum has two important drawbacks, poor step coverage and poor planarization, which make it unsuitable for eubmicron multi-level interconnect process. CVD tungsten is an attractive option for forming plugs and interconnects but suffers several drawbacks. It is therefore preferable to use aluminum for both plugs and interconnections due to its simplicity and established prior history. We have developed a fully planarieed aluminum metallization process which produces void free contact plugs.

In order to verify the filling of the contact plugs, we have carried out extensive SEM analysis using secondary electron and backscattered electron imaging methods with various SEM sample preparation methods, i.e. chemical etching to extract the metal plug without inducing any damage to the metal, SEM cross section prepared with some oxide (about 1000Å) left in front of the metal plug and standard SEM cross section through the metal plug. Complementary secondary and backscattered imaging has proven to be a reliable method for ascessing the filling of the contact holes. Wafer and package level reliability data for the planarized aluminum metallization used on a megabit device will also be presented.
The Volatile Component Loss and the Surface Morphology of the Gold-Palladium Metallizations to the Compound Semiconductor Structures
Authors: Dobos L. , Kovács B. , Mojzes I. , Malina V. , Pécz B. , Karányi J.
Published: March 2011

Palladium based metal systems can be used to make ohmic contacts to AIIIBV compound semiconductors. A covering layer of gold is advantageous even from the point of view of bonding. Gold, palladium, Au/Pd layers were studied on InP and GaAs substrates. The samples were annealed in the vacuum chamber of the scanning electron microscope (SEM) and the volatile component losses (arsenic or phosphorus) were monitored by a quadrupole mass spectrometer. The changes of the surface morphology were studied using the SEM images. In the case of Pd/AIIIBV samples a single characteristic peak due to the interaction taking place between the palladium and the substrate was observed on the volatile component loss vs. temperature curve. In the case of Au/Pd/AIIIBv samples a second peak appeared on the evaporation vs. temperature curve due to the interaction between gold and AIIIBV substrate. The temperature of that second peak is about 50–60°C higher than in the case of a single gold layer on AIIIBV substrates because gold had to diffuse through the palladium layer, what hindered the reaction of gold with AIIIBV materials.
Interconnection Challenges of the 1990'8
Authors: Fury Michael A.
Published: March 2011

Silicon device performance has improved dramatically over the past two decades. During that time, the portion of total circuit delay attributable to interconnect wiring has increased to nearly half. Changes in the use of aluminum wiring and silicon oxide insulators must be considered to further improve performance.

The generation of ULSI circuitry now under development in the industry depends heavily on innovations in materials and processes to achieve significant improvements in wiring density and circuit performance. The subsequent generation places even greater demands on materials improvements for lower resistivity wiring and a lower dielectric constant insulator. Integrating materials and methods compatible with semiconductor processing while ensuring device reliability will create a significant financial challenge in addition to the technical challenge.

This presentation enumerates the interconnection challenges facing the materials scientist and the circuit designer. The ultimate limits in materials improvements are predictable and finite. Further improvements will be derived from design innovations such as treating interconnects as active rather than passive devices. Accurate physical modelling of MLM structures will complement even more complex electrical modelling. Manufacturing sciences will grow in sophistication if implementation is to succeed. The financial burden of these technical challenges will foster collaborations among semiconductor manufacturers, equipment vendors, and research universities.
Experimental Design Study of Coincident Titanium Nitride/Titanium Silicide Formation from Rapid Thermal Processing
Authors: O'Meara D. L. , Spero J. C.
Published: March 2011

An experimental design method was used to define the process behavior of the two barrier metal properties most applicable to semiconductor device fabrication: contact resistance and contact junction current leakage. Instead of using basic research-level evaluations such as sfoichiomefry and film composition, we attempt to optimize titanium nitride (TiN) barrier metal properties to obtain both low contact resistance and low contact junction current leakage. The optimization was based on TiN films made using a rapid thermal process (RTF).

Our study focussed on TiN barriers formed on arsenic-doped n-type contacts. A two-step thermal process was used with temperature and duration of each step and the initial titanium thickness chosen as process variables. Response surface modeling of the contact resistance and contact junction leakage current reveals response variations that suggest three regions of film formation. The model defines an optimum barrier metal process to minimize both contact resistance and current leakage for the arsenic-doped contacts used for this study.
Enhanced Pteos and O3-Teos CVD Processes for Improved Step Coverage and Gap-Filling
Authors: Ghosh Sumanta K. , Bourgeois Mark A. , Ramkumar K. , Saxena Arjun N.
Published: March 2011

The step-coverage and gap-filling characteristics of SiO2 films deposited by TEOS based plasma CVD and Thermal CVD processes on AlX and Cu/X metallizations were studied. It was found that the conformality of the films, in the case of plasma CVD, is influenced by the relative flow rates of TEOS to oxygen. The suitability of the two types of SiO2 films for filling gaps of different aspect ratios on AlX and Cu/X metallizations with different aspect ratios was examined. The results are discussed and correlated with the other important characteristics of these SiO2 films.
Selective Metallization of CVD Diamond Films
Authors: Calvert J. M. , Pehrsson P. E. , Dulcey C. S. , Peckerar M. C.
Published: March 2011

A process has been developed for the deposition of patterned adherent metal on diamond substrates using low temperature processing conditions. CVD diamond films on Si wafers were oxidized with an RFO2 plasma and subsequently functionalized by attachment of self-assembled ultrathin films (UTFs) to the oxidized diamond surface. The UTFs were exposed to patterned deep UV radiation, and selectively metallized by electroless (EL) deposition. EL Ni and Co patterns, with feature sizes to 20 μm linewidth have been produced. Oxidized and UTF-modified surfaces were characterized by surface spectroscopie and wettability techniques. The EL metal deposits on the diamond substrate passed the Scotch tape adhesion peel test.
Thermal Studies of Au-Ti Thin Films Deposited on Oxide Substrates
Authors: Strane J. W. , Russell S. W. , Li Jian , Mayer J. W.
Published: March 2011

Co-evaporated Au-Ti thin films deposited onto sapphire and silicon dioxide substrates were thermally treated over a temperature range of 300–900°C in both vacuum and reactive amb ients. Vacuum annealing produced negligible reaction between the oxide substrate and film, the Au-Ti, however, reacted to form intermetallic compounds with little net elemental redistribution in the film. Heat treating in oxygen resulted in segregation of titanium to the surface where it formed both rutile and anatase structures. In addition, the high interfacial energy between the gold and the oxide phases led to the formation of large (5 micron diameter) gold particles on the film surface or voids at the titania-gold interface. Annealing in Ammomia produced an oxynitride surface in addition to the Ti-Au separation, Au particulate formation, and/or interfacial voiding already observed. The extent of surface degradation observed during these reactive ambient anneals varied with Ti concentration and temperature. The film did not react with SiO2 under any circumstances, however, at temperatures above 650°C in reactive ambients the titanium accumulated at the Al2,O3 interface. These results were obtained by RBS, X-ray diffraction, TEM and SEM.
Kinetics of Intermetallic Formation in Free Standing Cu/Mg Multilayer Thin Films
Authors: Arcof B. , Clevenger L. A. , Murarka S. P. , Harper J. M. E. , Cabrai C.
Published: March 2011

Differential scanning calorimetry (DSC) has been used to study the temperatures, kinetics and phase formation mechanisms in Cu/Mg multilayer thin films. When the Cu:Mg layer thickness ratio was 1:4, CuMg2 was the only phase that formed. Cu/Mg films with a layer thickness ratio of 1:1 first form CuMg2 at 215°C with an activation energy of 1.0 ± 0.04 eV and then Cu2Mg at 380°C with an activation energy of 0.73 ± 0.04 eV. The temperatures at which the two phases form decrease as the layer thicknesses decrease due to the shorter reaction times needed in thinner films. The constant scan rate DSC data from films with a layer thickness ratio of 1:1 show three exothermic peaks. The first peak is extremely sharp and results from the formation of isolated nuclei of CuMg2 at the Cu/Mg interface. The formation of CuMg2 is thus shown to be nucleation controlled. The second peak is a growth peak due to the heat released during the growth of CuMg2. The third peak corresponds to the formation and growth of Cu2Mg.
Space Charge Effects Due to Near Contact Non-Uniform Electric Fields in Semi-Insulating GaAs
Authors: Derhacobian Narbeh , Haegel Nancy M.
Published: March 2011

Variable length semi-insulating GaAs p+-υ-n+ diodes are used to investigate the influence of near contact electric field non-uniformities on the injection of minority carriers. The results show that despite the presence of highly linear IV characteristics, significant nonuniformities in the electric field dominate the device response. The current density through the device is shown to depend on the device length with a power law J ∞ (L)1.0 at a constant bias. The experimental results are compared, with good agreement, to a theoretical model which treats semi-insulating GaAs as a trap-dominated relaxation semiconductor. Electroabsorption measurements are used to observe the slow transients associated with the appearance of near contact field nonuniformities.
Evidence of Electrical Interactions between Photo-Induced Charge Carriers and Moving Dislocations in Red Mercuric Iodide
Authors: Marschall Jochen , Milstein Frederick
Published: March 2011

Variations in both the hole and the electron photocurrents in single crystals of mercuric iodide (HgI2) are measured during plastic deformation by shearing over (001) planes. The results demonstrate the presence of electrical interactions between moving “easy glide” dislocations and photo-induced charge carriers in HgI2. It is found that both hole and electron photocurrents are decreased during dislocation motion and that the extent of this effect (and the subsequent recovery after deformation ceases) depends on the applied bias.
Direct In-Situ Observation of Charge Carrier Separation During Formation of an Amorphous Silicon / Crystalline Silicon Heterojunction
Authors: Neitzert H. C. , Hirsch W. , Kunst M.
Published: March 2011

The signal of the Transient Microwave Detected Photoconductivity after laser pulse illumination is followed during the PECVD growth of intrinsic amorphous silicon on top of crystalline silicon (c-Si) substrates. Depending on the thickness of the amorphous layer the observed phototransients can be assigned to the excess charge carriers in different regions of the so grown heterojunction. For thin a-Si:H layers the signal amplitude decreases exponentially with deposition time. In the case of thick amorphous silicon the signal reflects only the properties of the amorphous silicon and the signal amplitude is constant. In an intermediate range a large contribution of charge carriers absorbed in the a-Si:H and subsequently transported to the crystalline part of the heterostructure to the measured signal can be observed. Due to their much higher mobility in the crystalline layer these excess charge carriers become visible only after reaching the crystalline silicon. This leads to the observed delay of the TRMC signal amplitude relative to the exciting laser pulse. The experiments show, however, that this charge carrier transfer takes place only in the case of a low defect a-Si:H layer to a measurable extent and is suppressed by the low carrier mobility in highly defective a-Si:H deposited at lower substrate temperatures.
Large Modulation Effects on Photorefractive Grating Formations with Moving Gratings
Authors: Brost George A.
Published: March 2011

A finite difference technique was used to model photorefractive grating formations under conditions of moving gratings and large modulation. These results were generalized through analytical expressions which approximate the numerical solutions.
Photoinduced Space-Charge Gratings in Semi-Insulating Multiple Quantum Wells
Authors: Wang Q. , Brubaker R. M. , Nolte D. D. , Melloch M. R.
Published: March 2011

High-order spatial harmonics of photo-induced space-charge gratings are observed in semi-insulating photorefractive quantum wells. Two-wave mixing combined with four-wave mixing in holographic thin films can provide a versatile probe of absorption and photorefractive gratings.
New Concept of Multilayer Photorefractive Device
Authors: Viallet Jean Emmanuel , Picoli Gilbert , Gravey Philippe
Published: March 2011

We propose a multilayer photorefractive device based on the association of two classes of materials respectively designed for transport and electro-optic properties. This device consists in repeated elementary cells, each of them made with an electro-optic material layer embedded between two different photoconductive layers. In these layers (respectively hole and electron dominated) deep levels allow to build-in a space charge field distribution under periodic illumination, giving rise in the electro-optic layer to a perpendicular electric field component, yielding to a diffraction grating. Its efficiency can be increased by the repetition of these cells. InGaAsP/InP MQW can be used as electro-optic material and semi-insulating InP:Ti and InP:Fe as respectively electrons and holes dominated photoconductors. We present simulation results of the behaviour of this device under electric bias and of the coupling effects between adjacent layers which yield space charge field modulation well over the usual diffusion limit.
Surface Charge Imaging in Semiconductor Wafers by Surface Photovoltage (SPV)
Authors: Edelman Piotr , Lagowski Jacek , Jastrzebski Lubek
Published: March 2011

We present fast, wafer-scale imaging of the surface charge achieved via non-contact measurement of the surface potential barrier by surface photovoltage (SPV) under high excitation levels. The approach is capable of resolving surface charge differences as small as 108 q/cm2. Fundamentals of surface charge imaging are discussed, and the method is compared with standard SPV contamination mapping. Examples include problems relevant to silicon IC fabrication and surface charge maps of GaAs and InP.
Electro-Optical Studies of Vanadium in GaP by Space Charge Spectroscopies
Authors: Bremond Georges , Guillot G. , Roura P. , Ulrici W.
Published: March 2011

A complete understanding of the electrical and optical properties of the Vanadium related donor level (VGa3+/VGa4+) in GaP is deduced from a number of different characterization techniques (deep level transient and deep level optical spectroscopies, optical absorption) performed on p-type V doped GaP. The VGa3+/VGa4+ donor level is located at Ev+0.25eV. This assignment is based on the correlation of optical absorption spectra and the photoneutralization cross-section σp°(hv) curve obtained by deep level optical spectroscopy confirming that this technique is very unique for deep level identification in semiconductor materials.