Copper interconnects for semiconductor devices

Copper/low-k dielectric materials have been rapidly replacing conventional aluminum-alloy/SiO₂-based interconnects in today’s semiconductor devices. This paper reviews the advantages of transitioning to copper/low-k interconnects. Materials and process challenges during the fabrication of devices with copper/low-k interconnects are discussed. Reliability concerns associated with such devices are highlighted. For more information, contact S.M. Merchant, Agere Systems, Orlando, Florida 32819; (407) 371-7538; agere.com.     

Recent progress in large-grain REBCO melt texturing

Melt texturing large-grain yttriumbarium-copper-oxide materials has evolved in the last few years into a technology capable of producing large quantities of high-perfor-mance superconducting bulk materials. Such materials are used for developing novel engineering devices, such as energy-storage systems and motors. This article gives an overview of the principles of large-grain growth, various processing strategies for these materials, and the limitations of present processing techniques. On the basis of this overview, some directions for further improving superconducting properties and the processing techniques of these materials are discussed. For more information, contact W. Lo, University of Houston, Texas Center for Superconductivity and Department of Mechanical Engineering, Calhoun Road, Houston, Texas 77204; (713) 743-4530; fax (713) 743-4503.     

The X-ray characterization of InGaN and AiGaN heterostructures for blue-light emitters

III–V compound semiconductors in the InAlGaN system are being developed for commercial applications in both electronic and optoelectronic devices. For example, the growth and characterization of quantum-well heterostructures is of increasing interest for visible (especially blue and green) light-emitting diodes and injection lasers. The crystallographic and optical properties of these materials are of critical importance in these applications. In this article, the results of x-ray diffraction studies of the structural characteristics of InGaN and AlGaN heterostructures grown by low-pressure metalorganic chemical vapor deposition on (0001) oriented sapphire substrates are discussed. C. Eiting earned his M.S. in electrical engineering from the University of Texas at Austin in 1996. He is currently a graduate research assistant at the University of Texas at Austin. P. Grudowski earned his M.S. in electrical engineering from the University of Texas at Austin in 1995. He is currently a graduate student at the University of Texas at Austin. R.D. Dupuis earned his Ph.D. in electrical engineering from the University of Illinois Urbana—Champaign in 1973. He is currently a professor at the University of Texas at Austin.     

Key methods for developing single-wall nanotube composites

Single-wall nanotubes (SWNTs), one of the newest of reinforcements for composite materials development, are heralded as having the highest strength features of any reinforcement. The development of composite materials is seen as a good first step toward taking advantage of the structural, electrical, and thermal properties of SWNTs, but processing SWNTs with polymers, metals, and ceramics pose new challenges because of their nanometer size and features. Recently, advances have been made toward developing their mechanical and electrical properties, and initial concerns of composite processing in polymers have been overcome. The potential for conducting polymers is at hand, and the strength features of these new composites are increasing with each new process development. This paper identifies some of the key methods for developing single-wall nanotubereinforced polymer composites for a range of applications and focuses on producing nearterm multifunctional materials for structural and electrical applications. For more information, contact E.V. Barrera, Rice University, Department of Mechanical Engineering and Materials Science, P.O. Box 1892, Houston, Texas 77005-1892; (713) 348-6242; fax (713) 348-5423; e-mail ebarrera@rice.edu.     

Colloidal stability by surface modification

The study of colloids is important in the design of materials for uses ranging from pot making to petroleum refining. This review presents the reasons for instability and different methods for attaining stability in various systems of interest. in this context, both steric and electrostatic stabilization are discussed. Also discussed are surface modification in core-shell technology and the importance of surfactants in emulsions. For more information, contact Sudipta Seal, University of Central Florida, Advanced Materials Processing and Analysis Center, Mechanical, Materials and Aerospace Engineering, Nanotechnology Science and Technology Center, Eng. 381, Orlando, FI 32816; (407) 882-1119; fax (407) 823-5277; e-mail: sseal@mail.ucf.edu.     

Fundamentals of nondestructive materials characterization

An attempt is made to outline the term ‘materials characterization’. On the basis of the structure-to-property-relationships, a philosophy is proposed, adapted to systematical development of methods for nondestructive materials characterization. The state of the art reached for metals is reviewed and typical applications of macroscopic physical properties for nondestructive materials characterization are given. The materials characterization of ball bearing steel and cast iron by multiparameter materials characterization is discussed in detail.     

Carbon nanotubes and other fullerene-related nanocrystals in the environment: A TEM study

Carbon nanotubes and other fullerene-related nanocrystals are ubiquitous in the atmospheric environment—both indoor and outdoor. In fact, these nanostructures have been observed even in a 10,000 year-old ice core sample, indicating their natural existence in antiquity, probably as natural gas/methane combustion products. Similar carbon nanotubes and complex carbon nanocrystal aggregates are observed to be emitted from contemporary combustion sources such as kitchen stoves (natural gas and propane), water heater and furnace exhaust vents, natural gas-burning (electric) power plants, and industrial furnace operations, among others. These observations have been made by collecting nanoparticulates and nanocrystal aggregates on carbon/formvar and silicon monoxide/formvarcoated 3 mm grids that were examined with a transmission-electron microscope. This study begins to establish an environmental context for considering the potential impact of future nanostructured particles on human health. For more information, contact L.E. Murr, the University of Texas at El Paso, Department of Metallurgical and Materials Engineering, El Paso, Texas 79968; (915) 747-6929; fax (915) 747-8036; e-mail fekberg@utep.edu.     

Vapor-grown carbon-fiber composites: Processing and electrostatic dissipative applications

In recent years, the demand for composite materials has grown in many directions. Although polymer composites have long been classified as structural materials for purposes such as mechanical enhancement and weight savings, the need for conducting polymer composites is growing. Vapor-grown carbon nanofibers (VGCFs), used as reinforcements for thermoplastic matrices, have potential application as conducting polymers, enhancing both stiffness and thermal stability.^1–4 This article discusses the processing of VGCFs from the perspective of their electrical and thermal properties, availability, and application in the electrostatic dissipative market. For more information, contact K. Lozano, University of Texas Pan American, Department of Engineering, Edinburg, Texas, 78539 USA; (956) 316-7020; fax (956) 381-3527; e-mail lozanok@panam.edu.     

Powder metallurgy Ti-6Al-4V-xB alloys: Processing,microstructure, and properties

This article describes processing of Ti-6Al-4V-xB alloys via pre-alloyed and blended elemental powder metallurgy techniques. The influence of processing on the microstructural evolution and mechanical properties of the alloys produced by these two routes is summarized, and the thermo-mechanical response and optimization of processing parameters to produce defect-free engineering shapes in these alloys is also discussed. Potential applications and issues involved in the development of these materials for damage-critical components are highlighted. For more information, contact S. Tamirisakandala, Air Force Research Laboratory, AFRL/MLLMD, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433-7817; (937) 904-4333; fax (937) 255-3007; e-mail sesh.tamirisa@fnnet.wpafbml.org     

From Grain Boundaries to Single Defects: A Review of Coherent Methods for Materials Imaging in the X-ray Sciences

This review summarizes the literature describing recent advances in the coherent x-ray sciences for the high-resolution characterization of materials. The principles and some of the main experimental techniques as well as their applications are discussed. The advantages of x-ray methods for characterizing 3D microstructures as well as for characterizing plasticity in the bulk become clear from the examples presented. Materials that exhibit size effects within the 0.1–10-μm range benefit enormously from these techniques, and development of the relevant x-ray methods will add to our fundamental understanding of these phenomena. Many of the ideas that have developed in the coherent x-ray science literature have been enabled through advances in x-ray source and detection technology, which has occurred over the past 10 years or so. It is a topic of considerable importance to consider how these techniques, which have matured rapidly, may be best applied to materials imaging in order to meet the growing needs of the community. As coherent x-ray methods for characterizing materials at multiple length scales have developed, several key applications for these techniques have emerged. The key breakthroughs that have been enabled by these new methods are discussed throughout this review, together with an examination of some of the problems that will be addressed by these techniques within the next few years.     

Processing nanostructured materials: An overview

This article reviews a variety of processing techniques for preparing nanostructured materials. A bulk nanostructured material can be produced in two-step processes by preparing nanostructured powders with subsequent consolidation, or directly in one-step processes such as electrodeposition and crystallization of amorphous solids. Principles, characteristics, and potential of both one-step and two-step processes are discussed in this paper. Although those processes have been used to produce full-density samples with little or no grain growth, further improvements are required in order to produce parts large enough for most engineering applications. Leon L. Shaw, University of Connecticut, Department of Metallurgy and Materials Engineering, Storrs, CT 06269; (860) 486-2592; fax (860) 486-4745; e-mail Ishaw@mail.ims.uconn.edu.     

A new approach to online thickness measurement of thermal spray coatings

In the past 10 years, significant progress has been made in the field of advanced sensors for particle and spray plume characterization. However, there are very few commercially available technologies for the online characterization of the as-deposited coatings. In particular, coating thickness is one of the most important parameters to monitor and control. Current methods such as destructive tests or direct mechanical measurements can cause significant production downtime. This article presents a novel approach that enables online, real-time, and noncontact measurement of individual spray pass thickness during deposition. Micron-level resolution was achieved on various coatings and substrate materials. The precision has been shown to be independent of surface roughness or thermal expansion. Results obtained on typical high-velocity oxyfuel and plasma-sprayed coatings are presented. Finally, current fields of application, technical limitations, and future developments are discussed. This article was originally published inBuilding on 100 Years of Success: Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Carbonate fuel cell materials

This article reviews the current status and discusses future opportunities for major direct fuel cell (DFC) materials. Major progress on DFC materials development (e.g., electrode, electrolyte, matrix, catalyst, cell hardware, and stack/power plant hardware) at fuel cell energy is discussed. Long-term (i.e., ∼18,000 h) field testing results are reported. These results confirm at least a five year operational life for selected key stack materials. Cost reduction is the current main focus. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

Inert anodes for the Hall-Héroult cell: The ultimate materials challenge

Inert anodes have been considered for years to be the future of aluminum production. Research is continuing on materials that would best serve that purpose. Results of studies on three possible materials are presented in this paper: ceramics, cermets, and metals. At this time, metals appear to be the most suitable material for inert anodes. For more information, contact D.R. Sadoway, Massachusetts Institute of Technology, Department of Materials Science and Engineering, 77 Massachusetts Avenue, Room 8-109, Cambridge, Massachusetts 02139-4307; (617) 253-3487; fax (617) 253-5418; email dsadoway@MIT.EDU.     

The fundamentals of nanostructured materials processed by severe plastic deformation

Nanostructured materials produced by severe plastic deformation (SPD) are 100% dense, contamination-free, and sufficiently large for use in real commercial structural applications. These materials are found to have high strength, good ductility, superior superplasticity, a low friction coefficient, high wear resistance, enhanced high-cycle fatigue life, and good corrosion resistance. This article reviews the structures and properties of nanostructured materials produced by SPD and reports recent progress in determining the deformation mechanisms that lead to these superior mechanical properties. For more information, contact Yuntian T. Zhu, Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, NM 87545; (505) 667-4029; fax (505) 667-2264; e-mail yzhu@lanl.gov.     

Determination of Young's modulus and yield stress of porous low-k materials by nanoindentation

In the present study, the concept of the ‘effectively shaped indenter’ was used to analyse nanoindentation data of rather soft films on hard substrates. This approach was introduced for monolithic materials by Pharr and co-workers some years ago [G.M. Pharr, A. Bolshakov: J. Mater. Res. 17 (2002) 2660, A. Bolshakov, W.C. Oliver, G.M. Pharr, MRS Symp. Proc 356 (1995) 675]. Substrate to layer moduli ratios range from nearly 60 to 160. With such soft and brittle materials (Young's modulus nearly 3 GPa or smaller, yield strength around 100 MPa), no completely elastic measurements can be performed even at low loads. Hence, an established method for the determination of yield stresses by means of nanoindentation, namely that of loading-partial-unloading [N. Schwarzer: ASME J. Tribology 122 (2000) 672, T. Chudoba, N. Schwarzer, F. Richter: Thin Solid Films 355-356 (1999) 284, T. Chudoba, N. Schwarzer, F. Richter: Surf. Coat. Technol. 127 (2000) 9] was not applicable. However, the ‘effectively shaped indenter concept’ allows one to separate the elastic stresses due to the penetration from the residual stresses caused by the inelastic deformation, assuming that their influence on the elastic stress field is small. Thus, by using this approach critical yield stresses of soft porous materials have been obtained. Additionally, the Young's modulus of these materials has also been determined by means of laser-generated surface acoustic wave (LSAW) measurements and the Oliver and Pharr method. In the latter case, a special extrapolation method for the indentation modulus had to be applied to correct for the substrate influence. The results by the different methods are compared and their deviations are discussed. As there is no complete solution available for the correction of the substrate influence on Young's modulus of the film when plastic deformation occurs during indentation, the authors are searching for an approach to approximate the elastic properties of a soft film on a hard substrate. It seems that the determination of the Young's modulus of very soft films cannot be separated from the determination of the yield stress. As an example for a low-k material actually of interest, porous silica xerogel films on silicon with porosities of 38 up to 51 vol.% were investigated.     

The rare earths: Enablers of modern living

Rare earth-containing materials are increasingly being selected for a host of markets for their unique application properties and because they are environmentally benign. The recent development of products for the rechar geable battery, automotive catalyst, and permanent magnet markets is highlighted to demonstrate the breadth of processing techniques being adopted to achieve specific performance properties. Editor’s Note: This article is a distillation of the author’s presentation at the Extraction & Processing Division’s luncheon during the 1998 TMS Annual Meeting in San Antonio, Texas. For more information, contact Rhodia Rare Earths and Gallium, CN 7500, Prospect Plains Road, Cranbury, New Jersey 08512; (609) 860-4549; fax (609)860-0207.     

Key technologies for manufacturing and processing sheet materials: A global perspective

Modern industrial technologies continue to seek new materials and processes to produce products that meet design and functional requirements. Sheet materials made from ferrous and non-ferrous metals, laminates, composites, and reinforced plastics constitute a large percentage of today’s products, components, and systems. Major manufacturers of sheet products include automotive, aerospace, appliance, and food-packaging industries. The Second Global Symposium on Innovations in Materials Processing & Manufacturing: Sheet Materials is organized to provide a forum for presenting advances in sheet processing and manufacturing by worldwide researchers and engineers from industrial, research, and academic centers. The symposium, sponsored by the TMS Materials Processing & Manufacturing Division (MPMD), was planned for the 2001 TMS Annual Meeting, New Orleans, Louisiana, February 11–15, 2001. This article is a review of key papers submitted for publication in the concurrent volume. The selected papers present significant developments in the rapidly expanding areas of advanced sheet materials, innovative forming methods, industrial applications, primary and secondary processing, composite processing, and numerical modeling of manufacturing processes. For more information, contact M.Y. Demeri, Ford Motor Company, 20000 Rotunda Drive, MD 3135, Dearborn, Michigan 48121-2053; (313) 845-6092; fax (313) 390-0514; e-mail mdemeri@ford.com.     

Future materials requirements for the high-energy-intensity production of aluminum

Like all metallurgical industries, aluminum smelting has been under pressure from two fronts—to give maximum return on investment to the shareholders and to comply with environmental regulations by reducing greenhouse emissions. The smelting process has advanced by improving efficiency and productivity while continuing to seek new ways to extend the cell life. Materials selection (particularly the use of more graphitized cathodic electrodes) has enabled lower energy consumption, while optimization of the process and controlling in a narrow band has enabled increases in productivity and operations at higher current densities. These changes have, in turn, severely stressed the materials used for cell construction, and new problems are emerging that are resulting in a reduction of cell life. The target for aluminum electro-winning has been to develop an oxygen-evolving electrode, rather than one that evolves substantial amounts of carbon dioxide. Such an electrode, when combined with suitable wettable cathode material developments, would reduce operating costs by eliminating the need for frequent electrode change and would enable more productive cell designs and reduce plant size. The materials specifications for developing these are, however, an extreme challenge. Those specifications include minimized corrosion rate of any electrode into the electrolyte, maintaining an electronically conducting oxidized surface that is of low electrical resistance, meeting the metal purity targets, and enabling variable operating current densities. Although the materials specifications can readily be written, the processing and production of the materials is the challenge. Editor’s Note: This was an invited plenary lecture for the symposium Processing Materials for Properties II, which was held in San Francisco, California, November 5–8, 2000. For more information, contact B.J. Welch, University of Auckland, High Temperature Materials and Processes Group, School of Engineering, Private Bag 92019, Auckland, New Zealand; +649-373-7515; fax +649-521-9142; e-mail barry@barry.co.nz.     

The mechanical properties of nanostructured materials

In this paper, the state-of-the-art progress in research on novel mechanical properties of nanocrystalline materials and carbon nanotubes is reviewed. There is evidence that the relation between the strength of nanocrystalline materials and grain size does not observe the classic Hall-Petch plot. Lowtemperature and high-strain rate superplasticity have been found in some nanocrystalline materials. Theoretical prediction and experimental data indicate that carbon nanotubes are materials with high stiffness, high strength, great toughness, and low density. There are already some application examples for novel mechanical properties of nanocrystalline materials and carbon nanotubes. For more information, contact P.K. Liaw, University of Tennessee at Knoxville, Materials Science and Engineering Department, 427-B Dougherty Engineering Building, Knoxville, Tennessee 37996; (865) 974-6356; fax (865) 974-4115; e-mail pliaw@utk.edu.