Showing papers in "Materials Science & Engineering R-reports in 1993"

Thin anodic oxide layers on aluminium and other valve metals: high field regime

Abstract: The formation kinetics and electric properties of anodic barrier oxides on Al, Hf, Nb, Ta, Ti, and Zr depend on the migration of ions, controlled by an electric field strength of up to 107 V cm−1. The high field model, based on ideas of Guntherschulze, Betz, Verwey, Mott, and Cabrera, explains only parts of the experiments. Contradictory models and investigations of the last 60 years are compared with new results, which enable a more detailed understanding of many aspects of the high field model, e.g. the shape of experimental transients, the time and field dependent concentration of mobile ions, the nature of the mobile species and the interaction of anion and cation transport, and the location of the rate determining step.

Superplasticity in advanced materials

Abstract: The ability to achieve a high tensile ductility in a polycrystalline material is of interest both from a scientific point of view and also because of potential applications in the materials forming industry. The superplasticity of conventional metallic alloys is now well-documented and understood reasonably well. However, the field of superplasticity has expanded recently beyond the traditional metallic alloys to include evidence of superplastic-like behavior in a very wide range of new and advanced materials. To date, superplasticity has been reported in mechanically alloyed metals, metal matrix composites, ceramics, ceramic matrix composites and intermetallic compounds. This review presents an overview of these new developments using the established behavior of conventional metallic alloys as a standard for comparison with the mechanical properties of these new materials. As well be demonstrated, the new materials often exhibit significant differences in their flow characteristics in comparison with the traditional superplastic metallic alloys. The successful utilization of superplastic materials in forming applications requires an understanding of the failure processes occurring in the materials in terms of both the localization of external flow and the accumulation of internal damage through the nucleation and growth of cavities. These problems are also addressed in this review.

Modulation spectroscopy of semiconductors: bulk/thin film, microstructures, surfaces/interfaces and devices

Abstract: Modulation spectroscopy is a powerful method for the study and characterization of a large number of semiconductor configurations, including bulk/thin film, microstructures (heterojunctions, quantum wells, superlattices, quantum dots), surfaces/interfaces and actual device structures in addition to semiconductor growth/processing. Furthermore, the influence of external perturbations such as temperature, electric fields, hydrostatic pressure, uniaxial stress, etc. can be investigated. This optical technique utilizes a very general principle of experimental physics, in which a periodically applied perturbation (either to the sample or probe) leads to sharp, derivative-like spectral features in the optical response of the system. Because of the richness of the derivative-like spectra, the information in the lineshape fits, room temperature performance and relative simplicity of operation this method is becoming increasingly more important as a tool to study these materials and structures. This article will review developments in the field during the last decade.

Silicides for integrated circuits: TiSi2 CoSi2

Abstract: Silicides have been a topic of intensive research for more than a decade. The driving force for these investigations has certainly been the interesting materials aspects of the silicides and their applications in integrated circuits. The advantages of easy formability and low resistivity for both CoSi2 and TiSi2 have led to an intensive use of these silicides in self-aligned processes for simultaneous silicidation of source, drain and gate. The fundamental investigations of these silicides include thermodynamic and kinetic aspects of phase formation, interactions with doped Si and related defect generation, and the interaction with oxide and metals. Specific issues related to the technological implementation of silicides in a full process will be discussed in view of the trend to scale the silicided area both in the vertical and in the lateral dimensions.

Stress-induced void formation in metallization for integrated circuits

Abstract: The term “stress migration” in Al lines in ICs is used in a broad sense to described thermally induced void formation and resulting failures, i.e. open circuits and increases in resistance, which occur in high-temperature processes, such as insulating film deposition on Al lines in IC fabrication, and during storage tests at elevated temperatures for evaluating the reliability of fabricated ICs. Stress migration degrades the IC production yield and reliability. The problem becomes more serious as the linewidth decreases. This paper reviews stress migration-induced void formation and resulting failures in Al lines, and is intended to clarify current experimental and theoretical knowledge of their characteristics. The main topics discussed are classification and characteristics of stress migration, accelerated life test results and failure prediction, Al line stress, void formation models and countermeasures for reducing failures.

Phonon-mediated particle detectors: physics and materials

Abstract: This review starts with a short introduction on the physical motivations for a new class of elementary particle detectors, known as bolometers, in which the detection is mediated by the production of phonons in a dielectric or superconductive material. Successively, the basic principles of these devices are exposed. In the next section the thermalization dynamics of the energy released in the absorber is analysed; the physics of the most common phonon sensors, doped semiconductors working in the variable range hopping conduction regime, is then discussed in depth. The last section is an outlook on the most important experimental results obtained with bolometers. Special attention is devoted to the materials (and to the related physical implications) chosen to realize the energy absorbers of the detectors.

MBE growth of artificially-layered magnetic-metal structures on semiconductors and insulators

Abstract: This review considers recent developments in MBE growth of artificially-layered magnetic-metal structures on both semiconductors and insulating substrates. It is seen that the ability to seed specific orientations of such structures and to probe their structural and chemical properties with a variety of in situ probes is a key advantage of MBE over more conventional deposition techniques. In particular, interface formation can be probed during growth. This is helpful in developing a realistic picture of interfaces in such structures and in relating magnetic properties to interface structural and chemical properties. Furthermore, the growth of epitaxial structures permits the detailed characterization of atomic and interface structure with X-ray diffraction and electron microscopy.