bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture Toughness of Diamond Measured by Vickers Indenter Reloading Technique
Authors: Dub Sergey N.
Published: April 2011

The crack initiation sequence during Vickers indenter penetration into the (100) plane of diamond was observed. It was revealed that for <110> orientation, two median cracks are initiated during the loading half of the cycle. In unloading, the median cracks grow toward the surface and turn into half-penny cracks. It was proposed to use half-penny cracks as initials and evaluate fracture toughness in second loading from a crack-starting load for these cracks. The length of initial half-penny cracks was measured after first loading cycle from opposite side of the sample. Test results obtained by the reloading technique agree well with the data on conventional fracture toughness determination by indentation from the length of cracks after unloading.
The Unique Strength of Diamond
Authors: Gilman John J.
Published: April 2011

The features of diamond that make it unique are: 1] its efficient tetrahedral structure which is stabilized by resonance of the bonding electrons among adjacent bonds; 2] the exceptionallly high ratios of its shear moduli to its bulk modulus; 3] the large gap between the top of its valence band and the bottom of its conduction band which makes dislocation mobility very low in it; 4] its high surface energy. Although diamond is nearly elastically Isotropic, the ratio of its C44 shear constant to its bulk modulus is 1.3 which is the highest measured value for this ratio. It is quite unusual for it to be greater than unity. This high shear stiffness appears to be associated with the bimodal distribution of electrons along the lengths of the C-C bonds. Also, for centrally directed interatomic forces, the ratio C44/C12is expected to be unity. But In diamond it is 4.6, indicating that the behavior of diamond cannot be described even approximately by pair-potentials. Because of its unique strength diamond can perform exceptionally in mechanical devices such as: pressure vessels, ultracentrifuges, springs, flywheels, and cutting (or drawing) tools.
Frictional Behavior of C60 Microparticle-Coated Steel
Authors: Zhao Wei , Tang Jinke , Purl Ashok , Falster Alexander U. , Simmons William B.
Published: April 2011

The frictional behaviors of 304 stainless steel disks coated with C60 microparticles, both containing benzene and free of benzene, have been studied under different loads and sliding speeds with a pin-on-disk configuration in ambient air atmosphere at room temperature. The results indicated that the coating containing benzene, benzene-solvated C60 microparticles (C60·4C6H6), reduced friction as well as wear. The coated samples showed a 50–70% reduction in friction coefficient in comparison to uncoated samples. Neither the coated nor the uncoated sample showed significant change in friction coefficient for different sliding speeds. Under different loads, the uncoated sample had almost the same friction coefficient. However, with the increase of load, the friction coefficient of C60·4C6H6-coated disk showed a minimum value of 0.25 at 25 g load and then reached the uncoated values beyond 50 g load. The coefficient of friction of the disk coated with benzene-free C60 showed a slight increase with load, reaching the value of uncoated 304 stainless steel disk at about 40 g. The reduced friction of the solvated-C60 coated 304 stainless steel is probably due to the lowered shear strength of the hcp structure of C60·4C6H6 molecular crystal in which the benzene molecules are intercalated. The results of this study suggest the importance of the presence of second component, in addition to C60, in the coating materials in order for them to form a preferred crystal structure with low shear strength as far as using C60 as a solid lubricant is concerned.
Application of Ripple Pyrometry on Integra Rapid Thermal CVD Cluster Tools
Authors: Xing G. C. , Wang Z. H. , Schietinger C. , Wasserman Y. , Sun M. H.
Published: April 2011

This paper presents the application of ripple pyrometry on AG Associates Integra systems which are three phase powered and multi-zone controlled rapid thermal CVD cluster tools. Two types of sensor configurations were explored for optimum emissivity compensated temperature measurement performance. It was found that it is very difficult to measure temperature when a two sensor configuration is used due primarily to the chamber and reflector architecture. Good temperature measurement was obtained at high temperatures when zone ratios between the wafer and lamp sensors were aligned. It was also found that the temperature signal to noise ratio is very sensitive to ripple quality and zone ratio alignment accuracy.
Sub-Feature Speckle Interferometry: A New Approach To Temperature Measurement
Authors: Burckel D. , Zaidi S. H. , Brueck S. R. J.
Published: April 2011

A new speckle technique, sub-feature speckle interferometry, is introduced that relies on the amplitude interference of two independent speckle patterns, originating from coherent illumination, using an optical system that produces interferometric quality interference fringes on a scale comparable to the speckle correlation length. Examples are given for in-plane translation, sample tilt, and temperature measurement (strain). A temperature measurement accuracy σ = 0.92°C is realized. In contrast to traditional full-field speckle cross-correlation techniques, this technique requires only a small number of detector elements with minimal signal processing and is compatible with many real-time sensor applications. Measurements of the optical phase across a speckle feature are presented.
Realistic Three-Dimensional Modeling Of Multizone Rapid Thermal Systems
Authors: Nagabushnam R. V. , Singh R. K. , Iyer R. , Sharan S. , Sandhu G.
Published: April 2011

We have developed a methodology aimed at accurately determining the various forms of energy transfer (convective loss, radiative loss and absorption of lamp energy by the wafer)occurring in any advanced RTP system, based on basic system identification experiments and simple 3-dimensional physical model depicting the heat transfer processes. The identification experiments help in estimating the uncertain system dependent factors which characterize the various forms of energy transfer, which may be otherwise difficult to calculate on pure theoretical basis. This methodology forms the basic building block of our effort to develop a tool which can predict the temperature distribution across the wafer in a realistic way. This tool can be used both as a wafer temperature control algorithm in any advanced RTP system as well as by an end user who is equipped with a not so advanced, but multizone, RTP system( the one with the user defined power levels to various zones).
The Merits of Integrated Processing for Gate Stack Formation
Authors: Grant John M.
Published: April 2011

This work presents the results of process development in a cluster tool designed for the gate stack process of cleaning, gate oxidation, and polysilicon chemical vapor deposition. The cluster tool connects three single wafer process chambers together with a vacuum transfer chamber. The purpose of this work was to test the feasibility of the single wafer processing gate oxidation cluster tool from an electrical performance standpoint, Cleaning was performed using a gas/vapor phase process, and the results using a standard oxide indicate that gas/vapor phase cleaning is at the least comperable and possibly more effective at contamination removal than the standard RCA wet cleaining process. The oxidation was performed using rapid thermal processing, and the effect of adding nitrogen to the oxide by oxidation in an N2O containing ambient was tested. The results indicated that oxides at least at good as those grown in a conventional furnace could be produced in the cluster tool, and the nitrogen at the oxide-substrate interface improves the reliability of the oxide if the nitrogen concentration is kept below 1 atomic %.
Rapid Thermal Epitaxy for Device Applications
Authors: King C. A. , Johnson R. W. , Chiu T. Y. , Sung J. M. , Mastrapasqua M. , Pinto M. R.
Published: April 2011

Rapid thermal epitaxy (RTE) is studied for a variety of applications including transistors as well as optoelectronic devices. Two transistor applications are discussed here. First, the growth of n-type epitaxial layers over n+ buried layers for low power BiCMOS, and second, the growth and fabrication of charge injection transistors (CHINTs) from a multi-layer structure including strained Si1−xGex layers.

Scaled bipolar transistors for BiCMOS integrated circuits require low collector-substrate capacitance in order to minimize power consumption. The unintentional incorporation of dopant into a growing epitaxial layer, known as autodoping, can affect the ultimate lower limit of the collector-substrate capacitance. In this work, we studied the effects of epitaxial layer growth rate, arsenic buried layer implant dose, and pre-epitaxial bake temperature on autodoping using RTE. To begin, we experimented with the buried layer implant dose to check its affect on lateral autodoping. The amount of autodoping increased when the buried layer implant dose increased, confirming the source of the arsenic autodoping as the buried layer. Also, in contrast to data from conventional reactors, we found the peak interface concentration and integrated dose in regions adjacent to the buried layer to be linearly dependent on the growth rate (i.e. low growth rates trap less arsenic at the substrate/epi layer interface). Next, by adjusting the pre-bake temperature over a range from 800 to 1050°C without changing the growth conditions, we first observed a rise in autodoping with temperature to 950°C at which point the incorporated autodoping dose and peak concentration began to fall. Through simulation of the evaporated arsenic from the buried layer and data for arsenic desorption from the silicon surface, we explain this behavior. Finally, using the data gathered on the autodoping characteristics of RTE, we show a process using two growth rate steps and a low temperature pre-bake step which completely eliminates the lateral autodoping peak. Using this new growth process, epitaxial silicon films over arsenic doped buried layers for low power BiCMOS are possible.

Charge injection transistors and logic elements have been successfully implemented in a Si/Si0.7Ge0.3 heterostructure grown by RTE on a Si substrate. Shallow p+ source and drain ohmic contacts are obtained by a boron diffusion from a selectively deposited boron doped Ge layer. Room temperature operation of the charge injection transistor is demonstrated for the first time. High frequency measurements indicate a short circuit current gain cutoff frequency of 6 GHz.
Tisi2 Characterization of CVD-Titanium and RTP on a Cluster Platform–an Initial Investigation
Authors: Marcus Steven D. , Deutschmann Lutz
Published: April 2011

The silicidation of chemical vapor deposited (CVD) titanium has been investigated utilizing the Materials Research Corporation (MRC) PHOENIX™ cluster-tool platform which incorporated an AST elektronik GmbH cluster RTP chamber. This initial investigation focuses on C49 and C54 TiSi2 phase formation on bare silicon wafers. Equipment description, process results, comparison to classical PVD Ti silicide processing and future investigations will be presented.
Concurrent Design of an RTP Chamber and Advanced control system
Authors: Spence Paul , Schaper Charles , Kermani Ahmad
Published: April 2011

A concurrent-engineering approach is applied to the development of an axisymmetric rapidthermal- processing (RTP) reactor and its associated temperature controller. Using a detailed finite-element thermal model as a surrogate for actual hardware, we have developed and tested a multiinput multi-output (MIMO) controller. Closed-loop simulations are performed by linking the control algorithm with the finite-element code. Simulations show that good temperature uniformity is maintained on the wafer during both steady and transient conditions. A numerical study shows the effect of ramp rate, feedback gain, sensor placement, and wafer-emissivity patterns on system performance.
Mechanisms of Grain Growth in Bubble-Fence-Delineated Films
Authors: Townsend S. J. , Frost H. J. , Nichols C. S.
Published: April 2011

The strength of polycrystalline metallic films at high temperatures is limited by grain boundaries. Boundaries transverse to the film surfaces typically fail by decohesion, while boundaries parallel to the film surfaces are susceptible to sliding. In light of these facts, multilayer films are now being made that resemble stacks of columnar-grained thin films[l]. Nearly planar arrays of insoluble bubbles, called "bubble fences," maintain the integrity of the individual layers by pinning the interlayer boundaries. However, the transverse boundaries that delimit the columnar grains within an individual layer are able to move. Processing aims to produce a highly-overlapping microstructure that isolates the weak-link transverse boundaries and increases the material's time-to-failure. In potassium-doped tungsten this strategy is an extension of current lamp filament technology.

We have studied the mechanisms of grain growth within the grain layers in order to provide a basis for improving the synthesis and processing of these materials. For this type of grain growth to occur, the boundaries between grain layers must remain pinned by the bubble fences. Theory and 3D Evolver[2] simulations of a simple model provide a possible explanation for the depinning seen in recent experiments[3]. Reducing the ratio of intra-fence bubble separation to bubble diameter is predicted to eliminate the depinning. Ongoing study of a complete 3D model will further aid in tuning the synthesis and processing to create grain architectures with superior high-temperature properties.
Molecular Dynamics Simulation of Mechanical Deformation of Ultra-Thin Metal and Ceramic Films
Authors: Belak J. , Glosli J.N. , Boercker D.B. , Stowers I.F.
Published: April 2011

We present an overview of the molecular dynamics computer simulation method as employed in the study of the mechanical properties of surfaces at the nanometer scale. The embedded atom method is used to model a clean metal surface and the bond-order model is used to model ceramic surfaces. The computer experiment consists of the indentation and scraping of a hard diamond-like tool into and across the surface. Results are presented for the (111) surface of copper and silver and for the (100) surface of silicon. We explicitly demonstrate in our point indentation simulations that nanoscale plasticity in metals takes place by nondislocation mechanisms, a result suggested by recent nanoindentation experiments. We also observe the surface to accommodate nearly the entire volume of the tip and the annealing out of plastic work as the tip is removed. In our orthogonal cutting simulation, we observe an interesting phenomenon: the system dynamically reorients the grain in front of the tool tip to minimize the work performed on the shear plane (i.e. the shear plane becomes an easy slip plane). Silicon transforms into an amorphous state which then flows plastically.
Modeling and Computer Simulation of the Thermal Field Induced by Ion Beam Irradiation of Bilayers
Authors: Sebastiano Tosto
Published: April 2011

A 3D analytical model of calculation has been carried out to simulate the heat effects induced during ion beam assisted thin film deposition. The irradiation conditions enabling the growth of the film under steady conditions of temperature are discussed. Some results are presented to show the computer simulation of possible surface processing conditions.
Comparison of Damage Accumulation Models for Boron Implantation in Silicon
Authors: Simionescu A. , Hobler G.
Published: April 2011

Two models of damage accumulation during boron implantation are compared: The first one analyzes the full collision cascades and lets vacancies and interstitials recombine, if they are located within some capture radius of each other. The second one uses a constant fraction of defects surviving damage annihilation within a recoil cascade and a damage saturation density to take into account recombination with defects generated in previous cascades. While the first model is more fundamental, the second one is computationally more efficient. By comparing model predictions with 20 keV boron implantations at various doses, performed into (100) and (110) silicon with 7° and 0°, respectively, we conclude that different capture radii have to be used for damage annihilation within the recoil cascades and with defects generated in previous cascades. Moreover, we show that the two models are almost equivalent, if appropriate parameters are chosen. Recombination factors determined from simulations using a capture radius are almost independent of depth and implantation energy.
Optimization of Process Parameter and Temperature Uniformity on Wafers for Rapid Thermal Processing
Authors: Tillmann Andreas
Published: April 2011

A new strategy based algorithm to optimize process parameter uniformity (e.g. sheet resistance, oxide thickness) and temperature uniformity on wafers in a commercially available Rapid Thermal Processing (RTP) system with independent lamp control is described. The computational algorithm uses an effective strategy to minimize the standard deviation of the considered parameter distribution. It is based on simulation software which is able to calculate the temperature and resulting parameter distribution on the wafer for a given lamp correction table. A cyclical variation of the correction values of all lamps is done while minimizing the standard deviation of the considered process parameter. After the input of experimentally obtained wafer maps the optimization can be done within a few minutes. This technique is an effective tool for the process engineer to use to quickly optimize the homogeneity of the RTP tool for particular process requirements. The methodology will be shown on the basis of three typical RTP applications (Rapid Thermal Oxidation, Titanium Silicidation and Implant Annealing). The impact of variations of correction values for single lamps on the resulting process uniformity for different applications will be discussed.
Properties of Point-Defects in Si for Process Modeling
Authors: Gossmann H.-J. , Rafferty C. S. , Stolk P. A. , Eaglesham D. J. , Gilmer G. H. , Poate J. M. , Vuong H.-H. , Mogi T.K. , Thompson M. O.
Published: April 2011

The development of future Si device technologies will rely extensively on modeling, requiring truly predictive tools. Here we focus on the front-end processes, during which ion-implantation and annealing create 3-D impurity profiles that determine crucial electrical device parameters. The final configuration is the result of a complex interaction of dopant atoms with Si self-interstitials and vacancies, which themselves interact with each other as well as with the implantation-induced damage and interfaces. Predictive modeling requires for all these processes a solid understanding of the physical phenomena as well as accurate quantitative information. Si self-interstitials and vacancies are not observable directly in an experiment, but only via their interactions with some other physical quantity of the sample. We review our work employing dopant atoms in δ-doping superlattices (δ-DSL) that yield directly the time averaged depth profiles of Si native point defects during a particular processing sequence. This approach is uniquely suited for giving insights into the interplay of point defects in Si, providing crosschecks for atomistic calculations as well as parameters for process simulators. We describe experiments to extract interstitial and vacancy parameters and discuss the influence of intrinsic and extrinsic interstitial traps, as well as of the annealing environment, on the native point defect population. The latter allows to place certain bounds on the interstitial vacancy recombination coefficient as well as the ratio of interstitial and vacancy equilibrium concentrations.
Application of a Neural Manufacturing Concept to Process Modeling, Monitoring and Control
Authors: Fu Chi Yung , Petrich Loren , Law Benjamin
Published: April 2011

The cost of a fabrication line, such as one in a semiconductor house, has increased dramatically over the years, and it is possibly already past the point that some new start-up company can have sufficient capital to build a new fabrication line. Such capital-intensive manufacturing needs better utilization of resources and management of equipment to maximize its productivity. In order to maximize the return from such a capital-intensive manufacturing line, we need to work on the following: 1) increasing the yield, 2) enhancing the flexibility of the fabrication line, 3) improving quality, and finally 4) minimizing the down time of the processing equipment. Because of the significant advances now made in the fields of artificial neural networks, fuzzy logic, machine learning and genetic algorithms, we advocate the use of these new tools in manufacturing. We term the applications to manufacturing of these and other such tools that mimic human intelligence neural manufacturing. This paper describes the effort at the Lawrence Livermore National Laboratory (LLNL) [1] to use artificial neural networks to address certain semiconductor process modeling, monitoring and control questions.*
Simulation of Alkali Migration in β′′-Alumina Under Ion Bombardment
Authors: D’Ajello Paulo C.T. , Pasa André A.
Published: April 2011

Among the different effects induced by ion implantation into dielectric solids, the enhancement of the ionic mobility is the most important regarding practical applications. We simulated the Na migration in a super-ionic conductor, sodium β″-alumina, irradiated with Ar (E=200 keV) at room temperature. A theoretical model to describe the electric field originated in the bombarded region near the surface was developed. The model emphasizes the relation between the electric field and the energy deposited by the ions in the ionization process.
Point Defect-Based Modeling of Transient Diffusion of Boron Implanted in Silicon Along Random and Channeling Directions
Authors: Jäger H. U.
Published: April 2011

A point defect-based model, which has been developed to describe diffusion and electrical activation of boron in crystalline silicon during post-implantation annealing, is used to simulate the anomalous diffusion of boron implanted into silicon along the random and [100] channeling directions. The model predictions are compared to data measured by Chu et al.
A New Local Electronic Stopping Model for the Monte Carlo Simulation of Arsenic Ion Implantation into (100) Single-Crystal Silicon
Authors: Yang S.-H. , Morris S. , Tian S. , Parab K. , Tasch A. F. , Echenique P. M. , Capaz R. , Joannopoulos J.
Published: April 2011

In this paper is reported the development and implementation of a new local electronic stopping model for arsenic ion implantation into single-crystal silicon. Monte Carlo binary collision (MCBC) models are appropriate for studying channeling effects since it is possible to include the crystal structure in the simulators. One major inadequacy of existing MCBC codes is that the electronic stopping of implanted ions is not accurately and physically accounted for, although it is absolutely necessary for predicting the channeling tails of the profiles. In order to address this need, we have developed a new electronic stopping power model using a directionally dependent electronic density (to account for valence bonding) and an electronic stopping power based on the density functional approach. This new model has been implemented in the MCBC code, UT-MARLOWE The predictions of UT-MARLOWE with this new model are in very good agreement with experimentally-measured secondary ion mass spectroscopy (SIMS) profiles for both on-axis and off-axis arsenic implants in the energy range of 15-180 keV.
Conformality and Composition of Films Deposited at Low Pressures
Authors: Cale Timothy S.
Published: April 2011

Conformality limitations and film composition variations inside features for films deposited at low pressures are explained using examples of studies which combine transport and reaction simulations of deposition processes with experimental work. In the first example, the use of film profile information to decide between two kinetic models for the low pressure chemical vapor deposition (LPCVD) of SiO2 from tetraethoxysilane (TEOS) is described. In the second example, a simple but useful model for the plasma enhanced chemical vapor deposition (PECVD) of silicon dioxide from TEOS/oxygen mixtures (PETEOS) is discussed. In the third example, composition profiles in sputter deposited (PVD) Ti-W films are explained in terms of titanium re-emission. Combined simulation and experimental studies of film profiles and composition profiles in features is a valuable tool in efforts to arrive at useful kinetic and transport models.
The Influence of Strain Energy Minimization on Abnormal Grain Growth in Copper Thin Films
Authors: Zielinski E. M. , Vinci R. P. , Bravman J. C.
Published: April 2011

Sputtered Cu films on Si, Al and Cu substrates were thermally cycled to 300 °C at a rate of 6 °/min, which induced an applied thermal strain that was compressive, tensile and zero, respectively. Microstructural characterization of the annealed films revealed abnormal (100) grain growth in the films on Al and Si, but not Cu substrates. In addition, symmetric x-ray diffraction scans demonstrated that the films in which abnormal grain growth was observed were primarily (100) in orientation. In contrast, the Cu film on a Cu substrate was largely randomly oriented after cycling, with a small degree of (111) preferred orientation. These results are consistent with a strain energy driving force for abnormal grain growth, which predicts that the growth should occur in compression, as on the Si substrate, or in tension, as on the Al substrate, but not when there is no applied thermal strain, as on the Cu substrate.
Finite Element Analysis of Electromigration and Stress Induced Diffusion in Deformable Solids
Authors: Bower A.F. , Freund L.B.
Published: April 2011

With a view to analyzing failure mechanisms in interconnects, we have developed a finite element method that may be used to compute the effects of diffusion and deformation in an electrically conducting, deformable solid. The analysis accounts for large changes in the shape of the solid due to surface diffusion, grain boundary diffusion, and elastic or inelastic deformation within the grains. To illustrate the capabilities of the method, we have analyzed void migration and collapse due to current induced surface diffusion; the drift of a strip of conducting solid on a substrate; and have calculated intergranular stresses and plastic deformation induced by electromigration in a passivated, polycrystalline interconnect line.
The Effect of Cluster Interactions on Electromigration Induced Stress Evolution in Confined Metal Lines
Authors: Brown D.D. , Sanchez J.E. , Besser P.R. , Korhonen M.A. , Li C.-Y.
Published: April 2011

In near-bamboo interconnect lines used in advanced integrated circuits, electromigration flux divergences occur at the intersection between polycrystalline cluster segments (where grain boundaries offer a fast diffusion path), and bamboo segments (where there are no grain boundaries along the line length). For confined, passivated metal interconnects, these flux divergences are linked to the evolution of significant mechanical stresses in the metal. A quasisteady state stress distribution builds up relatively quickly in the cluster segments and remains unchanged until there is significant diffusion into the bamboo segments. The stress profile of a given cluster then becomes dependent on neighboring clusters as well as the diffusivity and flux in the separating bamboo segments. Previous analyses of electromigration failure in interconnect lines have focused on the distribution of cluster lengths and the stress build up in isolated cluster segments. In this paper, we show that the bamboo length distribution can strongly affect the interaction between clusters and the evolution of stresses in a near-bamboo interconnect during electromigration. We present simulation results, using a ratio of cluster to bamboo diffusivity Dc/Db=100, which show greater interactions and larger maximum stresses in cluster segments as the average bamboo segment length decreases and as the bamboo segment length distribution widens.
Study of Diffusion Barrier Performance in MOCVD TiN by Transmission Electron Microscopy
Authors: Lee Hoojeong , Sinclair Robert , Roberts Bruce , Jackson Robert
Published: April 2011

The diffusion barrier performances of MOCVD TiN films with different thicknesses and various contact layers are compared by both ex situ and in situ TEM experiments. MOCVD TiN films grown at 425°C and 10 torr without a titanium underlayer show a semi-columnar structure while films grown with a titanium layer are columnar. It is found that the former has better diffusion barrier performance for Al metallization in Si contact holes. In addition, it is found the MOCVD TiN films combined with a TiSi2 contact layer are stable up to 600°C.
Material Properties of Coherent Tin Films
Authors: Ngan Ken
Published: April 2011

In this paper, material properties of low pressure, metallic mode Coherent TiN and poison mode Coherent TiN have been examined. The material properties include resistivity, crystal orientation, stress, lattice spacing, density, texture, atomic composition, bonding, roughness, hydrogen content, and grain size. Various analytical tools have been used to analyze the TiN films.
Grain Boundary Grooving as the Mechanism of the Blech Electromigration in Interconnects
Authors: Glickman E.E. , Klinger L.M.
Published: April 2011

We present a new approach to understand the mechanism of "homogeneous", or Blech electromigration (EM). This phenomenon describes macroscopically homogeneous displacement of the up-wind edge of thin film lines in microelectronic devices and is responsible for openings at contact windows, "vias" and other sites of perfect diffusion flux divergence.

Our SEM, EPMA and EM drift velocity experiments have revealed the gradual transition from the microscopically homogeneous EM displacement to the highly nonhomogeneous mode wherein copious islands of residual material remain behind the drifting cathode edge of aluminum stripes. The transition is shown to occur due to an increase in either the current density, j, or in the stripe length, 1. The latter case suggests, that the transition results from the growth of the net grain boundary (GB) diffusion flux, I=le-Ib ,where Ie∝j and 1b∝1/1 are the EM flux and stress-gradient-driven back flux, respectively.

Based upon recent progress in the theory of GB grooving under "external" GB fluxes, with surface diffusion acting as the healing mechanism, grooves' propagation along the line and their merging is considered to be the micromechanism of the "homogeneous" EM. In terms of the simple model described, the transition from the slow receding of the cathode butt edge slightly wrinkled by shallow grooves (A-regime of EM) to the fast extension and merging of slot -like grooves (B-regime) accounts for the transition observed in EM mode, while in both regimes the EM displacement velocity, V, is presumed to represent the groove propagation rate.

The theory developed reduces to Blech formulae for V for the truly homogeneous A-regime and predicts quite different EM kinetics for the B-regime of microscopically nonhomogeneous EM. The latter is expected to dominate for films loaded by high current density with large grains and low surface diffusion.

The dependence obtained for the residual mass left behind the drifted edge vs the displacement velocity, V, for unpassivated aluminum stripes of various lengths, loaded by j=2-106 A/cm2 at 548K provides a good evidence in support of a new approach.
On the Role of Surface Diffusion in Stress Relaxation During Electromigration
Authors: Klinger L.M. , Levin L. , Glickman E.E.
Published: April 2011

We report on the role of surface diffusion involved in relaxation of electromigration (EM) induced compressive stresses in relation to hillock growth and EM behavior of interconnects. Two competing mechanisms of EM stress relaxation by material transport onto the surface are considered. The first is hillocking by threshold diffusional creep (TCH), with rather large blocks of material (grains or group of grains) involved in plastic flow. The second mechanism, atomic diffusion hillocking (ADH), is presumed to be a nonthreshold one, and represents atomic grain boundary (GB) diffusion stimulated by the hydrostatic stress gradient in the direction normal to the film surface. The latter process involves surface diffusion because GB diffusional flux onto the surface must be coupled with the flux of redistribution of the atoms over the surface. If ADH acts rapidly, this should prevent the build-up of the matter at the down-wind (anode) end of the stripe, and thus, eliminate the Blech EM threshold resulting from the stress-gradient along the stripe. The question as to whether GB diffusion capable of transporting atoms pushed by electron wind along the stripe is also effective in relieving compressive stress by GB migration of the surplus atoms in the normal direction, has remained open up to now. The problem is especially acute for short or/and narrow lines separated into short polycrystalline segments, where the Blech threshold effects are critical to EM reliability.

We derived the main features of the EM behavior in drift velocity test geometry assuming that both TCH and ADH are operative. The result can be compared with available and future experimental observations in order to reveal if and when the ADH mechanism with surface diffusion involved works.
Stress-Voiding and Electromigration in Multilevel Interconnects
Authors: Korhonen M.A. , Liu Tao , Brown D.D. , Li C.-Y.
Published: April 2011

Stress-voiding and electromigration have become urgent reliability concerns at the decrease of interconnect dimensions to submicron size. Severe stress voiding may arise in multilevel metallizations, particularly at contact and via regimes where the thermal stresses are highest. Via and contact structures with the attached refractory layers usually block entirely the electromigration flux; hence, EM voids are likely to form here. In this paper we first model the migration of atoms due to gradients in composition, stress, and electric potential. We seek a formulation in the spirit of irreversible thermodynamics, i.e. without reference to any specific micromechanisms of diffusion. We then apply the general developments to predict the stress evolution and void growth in Al based interconnect lines confined between entirely blocking Wstuds. We also analyze the effects of Cu depletion at vias, either by interfacial or grain boundary diffusion, on the stress evolution and void growth. Finally we demonstrate that the change in the line resistance due to void growth will display apparent incubation times even if the void grows linearly with time.
An Effect of Dopants on Contact Electromigration
Authors: Kim Eungsoo , Cho Kyungwon , Jang Hyungwoo , Lim Soonkwon
Published: April 2011

Recently, device reliability has been an important issue since the design rule is scaled down and complicated processing is involved. To improve the reliability, many problems should be solved. One of the problems in interconnection failure is short or open circuits at interconnection lines. Contact or via hole failure has been ignored while the metal line failure has been strongly studied by many researchers.

In this study, electromigration (EM) phenomena at the submicron size of contact hole are presented with respect to the type of dopants, boron and arsenic, implanted by high dose. In both cases, the failure mode at the contact hole, the values of the activation energy and the mean-time-to-failure (MTTF) are much different. For example the value of MTTF in boron is lower than that in As. The contact failure by EM is analyzed by SEM micrographs, FIB micrographs, EM measurement. One of the interesting results is void formation at the interface between implanted surface and silicon dioxide film, which is located between contact holes. This fact indicates that the interface migration of Si is much faster than the self-diffusion of Si because the current path is mainly formed along the interface.
Analysis of the Mechanical Failure in a Multilayered Thin Film System Tested by Microtensile Loading
Authors: Marieb T. , Ignat M. , Fujimoto H. , Flinn P.
Published: April 2011

Multilayered thin films were deposited on pure Al substrate test bars for in situ scanning electron microscope (SEM) microtensile deformation. The films consisted of a TiN layer covered by either SiO2 or W. Deformation of the samples showed that the TiN film dominated cracking events and caused cracking in the W to occur at lower critical stress values than previously reported. Crack deflections along the TiN-W interface were also seen. W film strain was measured by X-ray diffraction before and after testing to look at the effect of cracking and deformation on stress in this film.
Ligand Substitution Effect on Optical Properties in Conducting Tetraazaporphyrines
Authors: Guo Liqun , Ellis D. E. , Gubanova O. V. , Hoffman B. M.
Published: April 2011

Self-consistent Density Functional calculations have been performed on a variety of planar conjugated Ni-centered macrocycles with a basic tetraazaporphyrinic core and dithiolene groups (PZ) or fused-benzo groups (PC). Theoretical energy diagrams, charge and spin distributions and densities of states have been obtained in order to understand the electronic structure modifications due to peripheral ligand substitution. The substituents role in altering electronic properties and charge distribution of the porphyrazine macrocycles has been used to interpret the observed variations in optical absorption profiles. In the Q-band (∼ 680 nm) region, a single peak is seen for high symmetry (D4h) macrocycles and a double peak for lower symmetry (D2h and C2v) systems. Calculated intensities and band splittings are compared in detail with qualitative molecular orbital models and experiment in the visible and UV regions. Predictions are made for the infrared absorption and semiconducting band gap.
Determination of Water Content and Resistivity of Perfluorosulfonic Acid Fuel Cell Membranes
Authors: Sen. Ashish , E.Leach Kevin , D.Varjian Richard
Published: April 2011

Water uptake and resistivity have been determined for Dupont's Nafion-115®and Dow membrane 800 EW while in contact with a water-saturated nitrogen atmosphere using Fourier transform near-infrared (NIR), and AC impedance four point techniques in the temperature range of 23°C to 100°C. Results show that at room temperature there is a significant increase in water content and a corresponding decrease in the electrical resistivity as the relative humidity increases from 0% to 100%. Results also indicate that there is a substantial decrease in water uptake from water vapor at 100°C relative to that at 23°C. The water content of Dow membrane is higher than Nafion-115 under all conditions tested. The water contents of Dow PFSA 800 EW and Nafion-115 membranes at about 92% R.H. and 23°C are approximately 25 wt% and 18 wt%, respectively. The corresponding water content values at 100°C are 10 wt% and 8 wt%, respectively. The resistivity of the membranes decreases sharply with the temperature up to 60°C, reaches a minimum near 80°C then increases up to 100°C. The Dow membrane has lower resistivity than Nafion-115 over the entire range.
Nickel-Metal Hydride Electric Vehicle Batteries Through Materials Science Advances
Authors: Venkatesan S. , Fetcenko M.A. , Corrigan D.A. , Gifford P.R. , Dhar S.K. , Ovshinsky S.R.
Published: April 2011

Proprietary, multicomponent hydrogen storage materials have been developed making use of the principles of disorder by atomic engineering of the short-range and intermediate -range order. These materials form the basis for Ovonic Nickel-Metal Hydride batteries which have emerged as the leading battery technology for electric vehicle applications. Ovonic Batteries have the highest volumetric energy density available extending the practical range of electric vehicles from under 100 miles to over 200 miles.
Structural Characterization of Carbon Materials Prepared at Low Temperature
Authors: Song Xiang-Yun , Chu Xi , Kinoshita Kimio
Published: April 2011

High-capacity carbon electrodes for rechageable lithium-ion batteries were prepared by carbonization of thermosetting resins such as phenol-formaldehyde at temperatures between 500°C and 600°C. Their structures were characterized by high resolution transmission electron microscopy, in-situ transmission electron microscopy and x-ray diffraction analysis. These studies suggest that the carbons consist predominantly of disorganized (amorphous) phase. However evidence was found in carbon containing nickel cobalt oxide for the presence of organized graphite-like regions of parallel and curved layer planes. These graphitized structure usually appear as agglomerate particles which are composed of many smaller (100-nm diameter) particles. The high degree of graphitization is attributed to catalytic graphitization that occurs in the presence of the metal oxide.
Lithium Intercalation in Porous Carbon Electrodes
Authors: Tran T. D. , Feikert J. , Pekala R. W. , Miller J. , Dunn B.
Published: April 2011

Carbons derived from the phase separation of polyacrylonitrile/solvent mixtures were investigated as lithium intercalation anodes for rechargeable lithium-ion batteries. The carbon electrodes have a bulk density of 0.35-0.5 g/cm3, relatively low surface areas (< 10 m2/g), and micron-size cells. Pyrolysis temperature influences the reversible lithium intercalation and the irreversible capacity (associated with the formation of the passivating layer). Carbon electrodes pyrolyzed at 600°C have first-cycle capacity as high as 550 mAh/g as well as large irreversible capacity, 440 mAh/g. Electrodes prepared at 1050°C have reversible capacities around 270 mAh/g with relatively lower capacity losses (120 mAh/g). Doping the organic precursors with phosphoric acid, prior to pyrolysis at 1050 C, leads to carbon electrodes with reversible capacities as high as 450 mAh/g. The capacity of doped carbon increased with increasing phosphorus concentration in the samples. The doped carbon anodes exhibited good cycleability and excellent coulombic efficiency. The electrochemical performance is related to morphology, chemical composition, and local structural order.
Influence of Precursor Chemistry on Phase Evolution and Stability Range in the Potassium-Beta Alumina System
Authors: Schäfer Günter W. , de Kroon Arnoud P. , Aldinger Fritz
Published: April 2011

The beta alumina structures are known for their high ionic mobility within the lattice. This lead to the development of the Na-β”-alumina polycrystal as solid electolyte in Na/S and Na/NiCl2 batteries. The K-β”-alumina compound is a suitable precursor material to establish proton conducting materials by ion exchange. Tests with single crystal and polycrystalline samples showed the possible application in fuel cells operating between 150 - 250 °C.

One of the main problems to be solved is the correlation between composition and phase evolution of either β- or β”-phase, another problem occuring during sintering is the high vapor pressure of the alkaline oxide. This leads to the decomposition of the highly conductive β”-alumina phase into β-alumina or corundum phases and lowers significantly the ionic conductivity.

We investigated the beta alumina phase evolution using alumina raw materials with different crystallographic structure and grain size. The influence of initial alkaline content and dopant concentration on phase formation and phase stability under sintering conditions has been investigated. A refined phase diagram for Na- and K-beta aluminas will be presented.
Examination of Interact Roughening in Ion Irradiated Cu/Nb Films by Computer Simulation and by X-Ray Diffraction
Authors: Partyka P.J. , Averback R.S. , Robinson I.K. , Lee Y.S. , Flynn C.P. , Bellon P.
Published: April 2011

Interfacial roughening during ion irradiation of an immiscible system is investigated by Monte Carlo computer simulation and by an x-ray diffraction technique called crystal truncation rod (CTR) analysis. In the simulations, ion flux and sample temperature are varied, and the system is allowed to evolve under irradiation until it reaches a steady state behavior. The observed behaviors are then sought experimentally in the Cu/Nb system implanted with 2 MeV Kr+ ions at different sample temperatures. Analysis of the roughness at the Cu interface is based upon the existence of a crystal truncation rod, which contains information on exactly how the crystal is terminated, or, in other words, the interfacial roughness. Rutherford backscattering spectrometry (RBS) is also used to study the intermixing of the Cu and Nb layers.
Damage in Refractory Oxides and ion Beam Mixing at Metal-Oxide Interfaces Induced by Gev Ions and 20 Mev Cluster Beam
Authors: Thevenard P.A. , Beranger M. , Canut B. , Ramos S.M.M.
Published: April 2011

Defect creation in refractory oxides known to be unsensitive to radiolysis, was shown to take place by high level electronic excitations induced by swift heavy ions or energetic cluster bombardments. Depending on the oxide a threshold in electronic energy loss for damage production was observed : MgO 22 keV/nm, AI2O3 20 keV/nm and LiNbO3 6 keV/nm. A very strong dependence on the energy deposited for the defect production was evidenced above the threshold. In MgO, both point and extended defects were created whereas in AI2O3 only extended defects were observed and in LiNbO3 amorphization in the ion track was evidenced.

Atomic displacements due to the giant electronic excitations can be revealed at metal-oxide interfaces in the case of Na nanoprecipitates embedded in MgO single crystals.
Cantilever Beam Stress Measurements During Ion Irradiation
Authors: Van Sambeek A. I. , Averback R.S.
Published: April 2011

In-situ stress measurements on single crystal MgO and A1203 have been performed during ion irradiation. A cantilevered beam sample arrangement was used, with the stress in the implanted layer determined from the deflection of the sample as measured by the change in capacitance between the free end of the sample and a reference electrode. Point defect concentrations are obtained by dividing the volume strain by the defect relaxation volume, with saturation values of 0.8 to 1.2% obtained for 1.0 MeV Ne, Ar and Kr irradiations. Defect production is sublinear with dose, with an efficiency of less than 25% compared to Kinchin-Pease predictions. Ionization induced annealing is evaluated with 1.0 MeV He and 1.0 MeV H irradiations following heavy ion irradiation.
A Comparative Study of Radiation Damage In A12O3, FeTiO3, And MgTiO3
Authors: Mitchell Jeremy N. , Yu Ning , Sickafus Kurt E. , Nastasi Michael , Taylor Thomas N. , Mcclellan Kenneth J. , Nord Gordon L.
Published: April 2011

Oriented single crystals of synthetic alpha-alumina (α-Α12O3), geikielite (MgTiO3), and natural ilmenite (FeTiO3) were irradiated with 200 keV argon ions under cryogenic conditions (100 K) to assess their damage response. Using Rutherford backscattering spectrometry combined with ion channeling techniques, it was found that ilmenite amorphized readily at doses below 5×1014, alumina amorphized at a dose of 1-2x1015, and geikielite was amorphized at -2x1015 Ar cm-2 . The radiation damage response of the ilmenite crystal may be complicated by the presence of hematite exsolution lamellae and the experimentally induced oxidation of iron. The relative radiation-resistance of geikielite holds promise for similar behavior in other Mg-Ti oxides.