bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical-Vapor-Deposited Tungsten for Vertical Wiring
Authors: Ohba Takayuki 
Published: August 2016

As the feature size of ULSI (ultralarge-scale integration) circuit devices shrinks, interconnects need to be scaled to maximize the wiring density and wire ability. This increased density leads to smaller contacts or via holes connecting the wires. The reduction in size increases the aspect ratio of these features for the same dielectric thickness. Conventional physical vapor deposition (PVD) techniques such as sputtering are unable to fill high aspect-ratio contacts/vias with aluminum conformally, as shown in Figure 1. This poor conformity is attributed to the shadowing effect by already-deposited nondirectional sputtering atoms and leads to void formation and open failures. Chemical vapor deposition (CVD) is a solution for achieving conformal filling.This is a prime reason why CVD has been investigated since the 1980s and why a large number of metals have been proposed. Above all, because tungsten as a refractory metal has high resistance to electromigration (EM) failures and tungsten hexafluoride (WF6) as a source gas has some advantages in manufacturing, for example, high vapor pressure (boiling point = 17.4°C) and purity, W-CVD with WF6 based on H2 or SiH4 reduction has been widely studied. Blanket W-CVD has been used for actual via-hole filling for 0.5-μm devices. Figure 2 shows a cross-sectional view of five-level interconnects using W plugs in 0.35-μm devices. Another advantage of W-CVD is that W deposits selectively into via holes if a low flow-rate ratio of reductants to WF6 is used.
Aluminum Reflow Sputtering
Authors: Kikuta Kuniko 
Published: August 2016

The scaling of integrated-circuit device dimensions in the horizontal direction has caused an increase in aspect ratios of contact holes and vias without a corresponding scaledown in vertical dimensions. Conventional sputtering has become unreliable for handling higher aspect-ratio via/contact holes because of its poor step coverage. Several studies have attempted to overcome this problem by using W-CVD and reflow technology. The W-CVD is used for practical device fabrications. However, this technique has several problems such as poor adhesion to SiO2, poor W surface morphology, greater resistivity than Al, and the need of an etch-back process.Al reflow technology using a conventional DC magnetron sputtering system can simplify device-fabrication processes and achieve high reliability without Al/W interfaces. In particular, the Al reflow technology is profitable for multi-level interconnections in combination with a damascene process by using Al chemical mechanical polishing (CMP). These interconnections are necessary for miniaturized and high-speed devices because they provide lower resistivity than W and simplify fabrication processes, resulting in lower cost.This article describes recent Al reflow sputtering technologies as well as application of via and interconnect metallization.
Chemical-Mechanical Planarization of Aluminum-Based Alloys for Multilevel Metallization
Authors: Fury M.A. , Scherber D.L. , Stell M.A. 
Published: August 2016

As recently as 1993, the prevailing presumption among the semiconductor technical community was that then-current development efforts associated with aluminum lines and tungsten damascene vias needed to shift rapidly to copper multilevel interconnect schemes. This is exemplified by the June 1993 issue of the MRS Bulletin, which featured copper metallization as its theme. In the intervening years, however, that same technical community revised the Semiconductor Industry Association (SIA) roadmap and placed renewed emphasis on the use of an all-aluminum interconnect scheme. This was done largely in deference to the costs associated with converting existing semiconductor lines to copper-compatible facilities. In addition to tooling costs, there is a learning curve for copper systems that remains to be established for device reliability, field failures, yield learning, and process maturation. On the other hand, existing fabs are already compatible with aluminum metallurgies, and there is a rich history of reliability and yield data.This change in direction creates two immediate needs: (1) the need to fill small-diameter vertical interconnects (vias) with void-free aluminum and (2) the need to remove the top surface aluminum resulting from its blanket deposition (overburden) following the metal fill. In addition, for high circuit-density applications, it may be desirable, if not necessary, to form the metal lines using the same damascene fill method as is used for the vias. This process strategy replaces metal etching and insulator gap fill with insulator (usually silicon oxide) etching and metal gap fill.
Design of High-Strength, High-Conductivity Alloys
Authors: Miyake J. , Ghosh G. , Fine M.E. 
Published: August 2016

Computer-aided design of alloys is becoming increasingly useful, replacing the completely experimental approach. The computer-aided approach significantly reduces the cost of alloy design and more easily leads to optimum properties by reducing the amount of experimentation. Design of high-strength, high-conductivity alloys is a good example of the efficacy of using the computer to design experimental alloys.Alloys that have both high strength and high electrical conductivity are needed for many applications such as lead frames, connectors, conducting springs, and sliding contacts. Figure 1 shows the strength and conductivity of some commercially available copper-based alloys. Since dissolved solutes in an otherwise pure metal rapidly reduce the electrical conductivity (as well as the thermal conductivity), solid solution strengthening is not suitable for designing this class of alloys. Such alloys must be designed on the basis of precipitation or dispersion hardening. The theory of the yield stress of alloys with precipitates or dispersed phases has been well-formulated and may be used for alloy design. The solubility of the hardening phase in the matrix must be very small. Otherwise the conductivity will be degraded too much. Nordheim's rule relates conductivity to dissolved solute in alloys and is also available for alloy design. Decreasing the dissolved solute increases the conductivity and strength due to an increase in the volume fraction of the precipitate.
Interatomic Potentials for Atomistic Simulations
Authors: Voter Arthur F. 
Published: August 2016

Atomistic simulations are playing an increasingly prominent role in materials science. From relatively conventional studies of point and planar defects to large-scale simulations of fracture and machining, atomistic simulations offer a microscopic view of the physics that cannot be obtained from experiment. Predictions resulting from this atomic-level understanding are proving increasingly accurate and useful. Consequently, the field of atomistic simulation is gaining ground as an indispensable partner in materials research, a trend that can only continue. Each year, computers gain roughly a factor of two in speed. With the same effort one can then simulate a system with twice as many atoms or integrate a molecular-dynamics trajectory for twice as long. Perhaps even more important, however, are the theoretical advances occurring in the description of the atomic interactions, the so-called “interatomic potential” function.The interatomic potential underpins any atomistic simulation. The accuracy of the potential dictates the quality of the simulation results, and its functional complexity determines the amount of computer time required. Recent developments that fit more physics into a compact potential form are increasing the accuracy available per simulation dollar.This issue of MRS Bulletin offers an introductory survey of interatomic potentials in use today, as well as the types of problems to which they can be applied. This is by no means a comprehensive review. It would be impractical here to attempt to present all the potentials that have been developed in recent years. Rather, this collection of articles focuses on a few important forms of potential spanning the major classes of materials bonding: covalent, metallic, and ionic.
Biology and Materials? Part I
Authors: Alper Mark 
Published: August 2016

Poets and philosophers have, through the ages, viewed organisms as the embodiment of the mysterious “Vital Force,” a unique non-earthly element required for the functioning of life processes.Biologists have seen, in living organisms, an adaptive, self-reproducing, evolving collection of molecules acting solely according to the laws of chemistry and physics.Historians speak of the iron or bronze ages and, more recently of the plastics (polymers) and the silicon ages. Materials science departments speak of metals, alloys, ceramics, and perhaps polymers—but not of genes.The “common man” has, it must be admitted, seen living organisms as a source of useful and important materials—wood for building; cotton, silk, and other fibers for textiles; horn, shell, and bone for tools and weapons; fats for lubricants; fur for clothingBut, in fact, few of us now think of materials when we think of living things. Neither do we think of DNA, protein, and carbohydrates when we think of materials.No, biologists have not been blackballed by materials scientists, chemists, and physicists. Until recently, they neither understood the processes by which life produces its materials nor even conceived of manipulating those processes to tailor the properties of the materials to our needs. Only within the past few years has the “biological revolution” expanded our understanding of the molecular basis for biological phenomena and our ability to control them. It is only now, for the first time, that one can point to a legitimate field of science based on mimicking, adapting, and controlling biological systems with the goal of producing novel materials with important, unique, and useful properties.
Eggshell Mineralization: A Case Study of a Bioprocessing Strategy
Authors: Fink David J. , Caplan Arnold I. , Heuer Arthur H. 
Published: August 2016

Product Concept: Fluid packaging device.Description: A package is required to contain approximately 50 ml (55–60 grams) of a viscous, 2-phase, thermally labile, aqueous medium containing proteins, carbohydrates, salts, nucleic acids and fats. A seamless ellipsoidal container is anticipated having a maximum radial dimension of 45 mm and a maximum axial dimension of 60 mm. The container wall must be permeable to respiratory gases and water vapor. External surface texture must be minimal. White coloration is acceptable, but the ability to incorporate solid or patterned surface coloration is desirable. The package wall must weigh approximately 5 g, the material must contain at least 0.3 g of bioavailable calcium, and it must be recyclable and biodegradable. The container must withstand 400-g drop test impacts.Processing: All materials must be maintained and the container fabricated by aseptic processing in neutral-pH, aqueous medium at less than 40°C and with a unit production time of less than 24 hours.Unit cost: Filled unit containers must be produced for approximately $4.00/100 units, with approximately $1.00/100 units allocated to container components and assembly.Laboratory Solution: Not achievable in the laboratory.Biological Solution: The eggshell.In its composition, architecture, and function, the eggshell is an elegant solution to the design problem posed above—a multilayered bioceramic composite, consisting of a mineral phase (primarily calcite, CaCO3) deposited on and within a complex organic phase (the matrix). The eggshell provides a unique microenvironment for housing embryonic development. It protects the embryo, regulates respiratory gases, water and ions, and provides calcium for embryonic skeletal development.
Genetic Production of Synthetic Protein Polymers
Authors: Cappello Joseph 
Published: August 2016

A goal of polymer chemistry is to control the final properties of a processed material by controlling the chemistry and physics of the polymer chain. Since the final formulated materials' properties are a complex function of chemical and physical interactions at both the micro and macro scales, it would be desirable to influence those interactions at the level of the molecular chemistry of the chain. However, in order to affect those macromolecular associations that occur via chemical functionalities separated over long distances, a chemistry is needed that can specify not only variability in chemical composition along the chain but can also specify the positions at which this chemical variability must occur over the entire length of the chain—several hundred nanometers.Protein-based materials in nature are formulated from protein chains which have evolved chemical compositions that through the specific sequence of their amino acid monomer constituents can result in diverse materials such as ultrahigh strength fibers, silks and collagens, and soft, ultradurable elastomers, elastin. As described in the article by Kaplan in this issue, the fundamental six amino acid repeat of the crystalline fraction of Bombyx mori silk fibroin is composed of essentially three amino acids, glycine (G), alanine (A), and serine (S), in a 3:2:1 ratio. The strength of the fiber is derived from these crystallized peptide blocks. They are positioned to a great extent as tandem repeats of the sequence GAGAGS.
Quantitative Structural and Chemical Analysis of Thin Films Part I
Authors: Bruynseraede Y. , Schuller Ivan K. 
Published: August 2016

Thin-film materials are playing an ever-increasing role in basic and applied research and are the basis for a large number of devices. In many cases, thin films are used in multilayered configurations so that the interfaces between different materials play a key role in their properties. The thicknesses of thin films being investigated approach interatomic spacing, so interfacial structure and chemistry become dominant. The field is now at a stage where it is no longer sufficient to only obtain qualitative information; it is also necessary to understand the structure and chemistry quantitatively and to determine limits on the accuracy of the various characterization tools. The present and next issues of the MRS Bulletin bring together a number of experts in the most commonly used characterization tools. To highlight and encourage international collaboration, the articles presented here are jointly written by scientific groups in the United States and Europe.The first issue of this series is dedicated to the most commonly used techniques: electron microscopy, x-ray diffraction, and surface analysis. The article on electron diffraction by Ourmazd, Scheffler, Heinemann, and Rouviere presents studies of atomic resolution microscopy and their limitations. Aspects highlighted are the importance of comparing simulations to the images obtained in the electron microscope, and the importance of theoretical studies to obtain quantitative information. The article by Fullerton, Bruynseraede, and Schuller describes recent developments in the field of x-ray diffraction. This article focuses on a refinement technique capable of quantitative determination of interfacial roughness, interdiffusion, and crystal structure changes in a variety of novel multilayer configurations.
Quantitative X-Ray Diffraction From Superlattices
Authors: Fullerton Eric E. , Schuller Ivan K. , Bruynseraede Y. 
Published: August 2016

The physical properties of superlattices have been the subject of considerable interest because a wide range of phenomena associated with very thin films, interfaces, and coupling effects can be studied. Recent areas of activity in metallic superlattices include antiferromagnetic coupling of ferromagnetic layers across nonmagnetic spacer layers, giant magnetoresistance, magnetic surface anisotropy, low-dimensional superconductivity, and anomalous mechanical properties. All of these phenomena are strongly affected by the chemical and physical properties of the individual layers and by the superlattice structure. Therefore, a detailed understanding of the properties of superlattices requires a nondestructive, quantitative determination of the superlattice structure.Because superlattices are not in thermodynamic equilibrium, their structure is sensitive to preparation methods and growth conditions. A dramatic example of superlattice structural dependence on growth conditions is shown in Figure 1, for sputtered Nb/Si superlattices. Increasing the Ar pressure during sputtering decreases the kinetic energy of the deposited atoms, thereby changing their surface mobility, and thus altering growth dynamics. Figure 1 shows the low-angle x-ray diffraction and cross-sectional transmission electron microscopy (TEM) images of [Nb(35 Å)/Si(25 Å)]40, superlattices sputtered in, respectively, 3 and 15 mTorr of Ar. The TEM image of the 3 mTorr superlattice clearly shows the smooth and continuous layering across the entire cross section of the image (≈5 μm). This is characteristic of sputtered metal/semiconductor superlattices used for x-ray optics.
Tribological Investigations Using Friction Force Microscopy
Authors: Overney R. , Meyer E. 
Published: August 2016

Many attempts have been made in recent centuries to investigate friction, adhesion, lubrication, and wear. Most of the experimental approaches and theories were based on macroscopic experiments, such as tensile and indentation tests. For a long time, only the bulk properties of the materials were considered.Late in this century a new term was created combining all of the above-mentioned properties which deal with the science of interacting material interfaces in relative motion: tribology. The state of the art of science today reveals that processing in nature depends strongly on interfaces that cannot be described only by bulk properties. Tribologists realize they must study the sliding surfaces by analytical surface-science tools. With the surface force apparatus developed by J.N. Israelachvili and D. Tabor, we have a surface analysis tool that provides new insight into the field of macroscopic sliding contact of lubricated systems.After Amontons' laws were established as a first attempt to describe sliding friction analytically, theories were advanced over the course of this century. A classic discipline was developed: contact mechanics. More quantitative treatments of friction were developed by various authors. The energy dissipation in most processes in tribology induced the theorists to consider the sliding bodies as spring models creating phonon-phonon interactions. And with modern computer facilities, they started to perform computational experiments whenever classical experiments could not provide information on the submicron scale.
Interfacial Junctions and Cavitation
Authors: Landman Uzi , Luedtke W.D. 
Published: August 2016

Understanding the atomistic mechanisms, energetics, structure, and dynamics underlying the interactions and physical processes that occur when two materials are brought together, separated, or rub against each other (hence the term tribology, from the Greektribos, meaning to rub) is fundamentally important to many basic and applied problems. Examples include adhesion, capillarity, contact formation, surface deformation, elastic and plastic response characteristics, hardness, micro- and nanoindentation, friction, lubrication, wear, fracture, atomic-scale probing, and modifications and manipulations of materials surfaces. These considerations have for over a century motivated extensive theoretical and experimental research into the above phenomena and their technological consequences.Explorations of materials systems and phenomena in the nanoscale regime often require experimental probes and theoretical and computational methods that allow investigations with refined spatial, as well as temporal, resolution. Consequently, until recently most theoretical approaches to the above issues, with a few exceptions, have been anchored in continuum elasticity and contact mechanics. Experimental observations and measurements of surface forces and the consequent materials response to such interactions have been macroscopic in nature.
Simulation of Nanometer-Scale Deformation of Metallic and Ceramic Surfaces
Authors: Belak James , Boercker David B. , Stowers Irving F. 
Published: August 2016

The precision machining of metal surfaces and the ductile-regime grinding of ceramic surfaces are examples of fundamental cutting processes used in fabricating high-tolerance parts. Components with dimensional tolerances of a few tens of nanometers are currently being produced by direct machining with single-point diamond tools. Despite the ability to fabricate these parts, little is understood of the basic deformation mechanisms that determine how material is removed and deformed, how a tool-tip interacts with a workpiece, how induced surface and subsurface damage occurs, and how cutting tools wear.The key to solving these problems is a fundamental understanding of basic tribological processes such as surface indentation and scraping. Indentation experiments measure the mechanical response of a surface, the onset of plastic deformation, and material hardness. Macroscopic hardness measurements have been shown to correlate well with observed tensile yield strengths. Microscopic indentation studies, where the indentation size is smaller than the material grain size, show new and interesting phenomena. In the pioneering work of Gane and Bowden, no permanent penetration occurred until a critical load was achieved. They related this critical yielding to the theoretical shear strength in the metal, the strength required to create dislocations. Yielding of this sort has since been observed by many investigators.
Electroless Cu for VLSI
Authors: Cho James S.H. , Kang Ho-Kyu , Wong S. Simon , Shacham-Diamand Yosi 
Published: August 2016

Interconnection technology is a key factor in the continual advancement of integrated systems. The rapid increase in device density and circuit complexity through scaling demands a similar increase in the interconnection density. Traditionally, this is achieved by reducing the metal pitch as well as gradually increasing the number of interconnection levels. As the width and spacing of interconnections are scaled down to submicron dimensions at the chip level and micron dimensions at the board level, signal delay, crosstalk, electromigration, and stress-induced migration become important concerns.Cu holds promise as an alternative metallization material to Al alloy due to its low resistivity and ability to reliably carry high-current densities. Cu has a bulk resistivity of 1.68 μΩ-cm, whereas Al has a bulk resistivity of 2.65 μΩ-cm. The only metal with a resistivity lower than Cu is Ag. Since Cu has a melting point and atomic weight both higher than Al, it is expected to have better resistance to electromigration, although properties such as grain structure and resistance to corrosion at high temperatures may also affect electromigration characteristics.