Mechanical properties of thin films

The mechanical properties of thin films on substrates are described and studied. It is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur. It is argued that the approaches that have proven useful in the study of bulk structural materials can be used to understand the mechanical behavior of thin film materials. Understanding the mechanical properties of thin films on substrates requires an understanding of the stresses in thin film structures as well as a knowledge of the mechanisms by which thin films deform. The fundamentals of these processes are reviewed. For a crystalline film on a nondeformable substrate, a key problem involves the movement of dislocations in the film. An analysis of this problem provides insight into both the formation of misfit dislocations in epitaxial thin films and the high strengths of thin metal films on substrates. It is demonstrated that the kinetics of dislocation motion at high temperatures are expecially important to the understanding of the formation of misfit dislocations in heteroepitaxial structures. The experimental study of mechanical properties of thin films requires the development and use of nontraditional mechanical testing techniques. Some of the techniques that have been developed recently are described. The measurement of substrate curvature by laser scanning is shown to be an effective way of measuring the biaxial stresses in thin films and studying the biaxial deformation properties at elevated temperatures. Submicron indentation testing techniques, which make use of the Nanoindenter, are also reviewed. The mechanical properties that can be studied using this instrument are described, including hardness, elastic modulus, and time-dependent deformation properties. Finally, a new testing technique involving the deflection of microbeam samples of thin film materials made by integrated circuit manufacturing methods is described. It is shown that both elastic and plastic properties of thin film materials can be measured using this technique. The Institute of Metals Lecture was established in 1921, at which time the Institute of Metals Division was the only professional division within the American Institute of Mining and Metallurgical Engineers Society. It has been given annually since 1922 by distinguished men from this country and abroad. Beginning in 1973 and thereafter, the person selected to deliver the lecture will be known as the “Institute of Metals Division Lecturer and R.F. Mehl Medalist” for that year. WILLIAM D. NIX, Professor, obtained his B.S. degree in Metallurgical Engineering from San Jose State University, San Jose, CA, and his M.S. and Ph.D. degrees in Metallurgical Engineering and Materials Science, respectively, from Stanford University, Stanford, CA. He joined the faculty at Stanford in 1963 and was appointed Professor in 1972. In 1964, Professor Nix received the Western Electric Fund Award for Excellence in Engineering Instruction and, in 1970, the Bradley Stoughton Teaching Award of ASM. He received the 1979 Champion Herbert Mathewson Award and, in 1988, was the Institute of Metals Lecturer and recipient of the Robert Franklin Mehl Award of TMS-AIME. He was elected Fellow of the American Society for Metals in 1978 and elected Fellow of TMS-AIME in 1988. He also received a Distinguished Alumnus Award from San Jose State University in 1980, and he served as Chairman of the 1985 Gordon Conference on Physical Metallurgy. In 1987, he was elected to the National Academy of Engineering. In 1966, he participated in the Ford Foundation's “Residence in Engineering Practice” program as Assistant to the Director of Technology at the Stellite Division of Union Carbide Corporation. From 1968 to 1970, Professor Nix was Director of Stanford's Center for Materials Research. Professor Nix is engaged in research on the mechanical properties of solids. He is principally concerned with the relation between structure and mechanical properties of materials in both thin film and bulk form. He is coauthor of about 190 publications in these and related fields. Professor Nix teaches courses on dislocation theory and mechanical properties of materials. He is coauthor of “The Principles of Engineering Materials,” published in 1973 by Prentice-Hall, Incorporated, Englewood Cliffs, NJ.     

Edge-to-edge matching in thin films

A peculiar type of preferential orientation was recently observed in polycrystalline films that are formed by a solid-state reaction on a single crystal substrate. This texture, for which the term axiotaxy was proposed, is characterized by the preferred alignment of a low-index plane in the film to a low-index plane with the same d-spacing in the substrate. The alignment of lattice planes with nearly identical d-spacings across the interface results in a periodic structure along one direction in the plane of the interface. As a consequence of the constraint that a set of planes in the film is preferentially parallel to a set of planes in the substrate, the texture manifests itself as an off-normal fiber texture. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee.     

Edge-to-edge matching in thin films

A peculiar type of preferential orientation was recently observed in polycrystalline films that are formed by a solid-state reaction on a single crystal substrate. This texture, for which the term axiotaxy was proposed, is characterized by the preferred alignment of a low-index plane in the film to a low-index plane with the same d-spacing in the substrate. The alignment of lattice planes with nearly identical d-spacings across the interface results in a periodic structure along one direction in the plane of the interface. As a consequence of the constraint that a set of planes in the film is preferentially parallel to a set of planes in the substrate, the texture manifests itself as an off-normal fiber texture. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Grwoth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee.     

Edge-to-edge matching in thin films

A peculiar type of preferential orientation was recently observed in polycrystalline films that are formed by a solid-state reaction on a single crystal substrate. This texture, for which the term axiotaxy was proposed, is characterized by the preferred alignment of a low-index plane in the film to a low-index plane with the same d-spacing in the substrate. The alignment of lattice planes with nearly identical d-spacings across the interface results in a periodic structure along one direction in the plane of the interface. As a consequence of the constraint that a set of planes in the film is preferentially parallel to a set of planes in the substrate, the texture manifests itself as an off-normal fiber texture. This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Grwoth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee.     

Photoelectrochemical effects in the electrolyte-pigment-metal system. I. Metal-free phthalocyanine film description of short-circuit photocurrents for thin films of pigment

Short-circuit photocurrents produced by a semitransparent metallic electrode covered with multilayers of chlorophyll and immersed in an electrolyte have been studied. The action spectrum of maximum photocurrent is identical to the absorption spectrum of the film of pigment. The kinetics of rise of the photocurrent are photoindependent for thin multilayers but dependent on thickness. Comparison of efficiency of light energy conversion on the basis of short-circuit photocurrent seems to show that the stack of Chl a monolayers is the more efficient chlorophyll solid system. Introduction for the same number of Chl a molecules of vitamin K1 and Phytol shows that vitamin K1 acts probably like an excitation quencher as in monolayers at the water-air interface.