Rhodium and iridium are highly electrically conductive refractory metals, which can be used as current-carrying thin-film metallizations. Their chemical inertness further enables their application at relatively high temperatures. However, due to the high elastic modulus of such metals, a residual tensile stress of 300 to 400 MPa is measured in evaporated thin films. We present novel results evidencing complete control over both the magnitude and the sign of the residual stress in such refractory thin films. The metallic layers are deposited by means of ion-beam-enhanced physical vapor deposition and both electrical resistivity and stress are controlled. Controlling the stress in this manner has enabled achieving thicker films and films with near-zero residual stress.

Characterization and quantitative analysis of stressed states of a series of W/C multilayers (10-40 periods prepared by pulsed laser deposition on Si (111) substrates of different thickness) were carried out by means of X-ray reflectometry, wide angle diffractometry and a novel laser mapping device. As the W/C multilayers were dedicated to technical applications as X-ray optics and subjected to optimization of stacking parameters (thickness and number of layers) for a long term (mechanical) stability also further investigations will be discussed. Comparison of wafer distortion as evaluated by laser scanning and strain of the W layer as deduced from X-ray diffraction let us conclude that W layers are under compressive and C layers under tensile stress. The investigation of the thermally stimulated relaxation behavior of the multilayers provided a confirmation of these results. Additional information could be obtained by comparative relaxation experiments under external mechanical constraints. Furthermore, we report on a self-organized process of structuring of the multilayers under investigation, which might be of interest also from a technical point of view. The entire surface area (diameter 2') could be converted from the smooth (as-deposited) to a structured (relaxed) state stable at room temperature. Investigations using optical and atomic force microscopy showed that the topology of the surface consists of a mountain range where the valleys are on the level of the as-deposited non-debonded surface and that long wrinkled ridges of about the same height run along arbitrary directions.

The mechanical properties of two viscoelastic thin films were measured, a polyimide and a low-k polymer dielectric. The static modulus and hardness were obtained from nanoindentation experiments using an elastic-plastic unloading model (J. Mater. Res., 13, 421 (1998)). Nanoindentation creep tests were also performed, where a value for the modulus was extracted by fitting the data to an equation based on the three-element standard linear solid model. Aside from being comparable to values reported in the literature, the moduli from creep experiments are at most 1.3 times lower than the static moduli. This decrement can be attributed to the differences in strain rate for the two methods and the effect of adhesive forces.

This study was undertaken to derive the understandings of the electro- mechanical properties of ITO films on highly elongated polymer substrates which were subjected to thermally and mechanically stresses. The substrates are polycarbonate foils with 100, 180 and 200-mm thicknesses with gas barrier layer on their bottom surface. The metallic films used in the experiments are indium- tin-oxide (ITO) and tantalum (Ta) films. Strain- gauge measurements and numerical analyses using modified Stoney formula were carried out to determine the electro-mechanics in ITO films. The numerical analyses and empirical results show the thermally and externally induced mechanical stresses in ITO films on polymer substrates are responsible for the difference in thermal expansion between the ITO films and the substrate and for substrate material and thickness, respectively. Therefore, a ramped heating processing and a buffer layer were employed to improve the electro- mechanics, and then, the effects of the buffer layer were also quantified in terms of conductivity-strain variations.

A new closed-form relation for the elastic compliance of a film-substrate system indented by a flat cylindrical punch is presented. The relation is an extension of the work of Gao at al. [1] modified to increase the applicable range of modulus mismatch between the film and substrate. The accuracy of the relation is assessed by comparison to finite element simulations, other approximate numerical solutions, and nanoindentation experiments performed on a fluorinated silicate glass (FSG) film on a silicon substrate. The benefits and limitations of the relation are discussed.

Experiments were conducted with SiGe film islands on a layer of borophosphorosilicate glass (BPSG). Initially the SiGe is under compression. Upon annealing, the glass flows and the SiGe islands relax by both inplane expansion and wrinkling. This paper provides a two-dimensional (2D) model for inplane expansion. The results from the model are compared with the experiments with small SiGe islands. The effect of winkling, which is ignored in the present model, is discussed qualitatively.

Aluminum nitride (AlN) thin films with columnar and granular structures were prepared by ion-beam assisted deposition method by changing nitrogen ion beam energy, and the effects of the film microstructure and film thickness on their microhardness were studied by using a nano-indentation system with the maximum force of 3 mN. For the columnar structure film of 600 nm in thickness, the microhardness is found to be approximately 24 GPa when the normalized penetration depth to the film thickness is about 0.1. For the granular structure film of 700 nm in thickness, the microhardness is found to be approximately 14 GPa. These results reveal that the microhardness of the AlN films strongly depends on the film microstructure, which can be controlled by regulating the nitrogen ion beam energy.

We report quantitative results on the load-deflection response of compressively prestressed square membranes under differential pressure. The membranes consist of 0.485 μm and 1.9 μm thick silicon nitride films. For these square membranes we observed a new symmetry transition of the deflection profile between a state without reflection symmetries at small loads to a state with reflection symmetries at sufficiently large loads. The load-deflection response was modeled by finite element simulations covering a wide range of prestrains e0 and pressures using various geometries. From the symmetry transition process, Young's modulus E = (150±5) GPa and the prestrain ε0 = (1.6±0.1) 10-3 of the membrane material was extracted.

Fluorinated silicon oxide (SiOF) films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD). The behavior of residual stress w as studied with water absorption. SiOF film showed compressive stress after deposition. The compressive stress increased after the exposure to room air. Fourier transformed infrared (FTI R) spectroscopy analysis was carried after the water absorption. However, the change of chemical bonding structure was not observed during the water absorption in this study. After the exposu re to room air, the films were kept in dry air. The residual stress returns to the initial value after 1 week. Considering the results of the residual stress and FTIR analysis, it is supposed that the water absorption in this study occurs entirely by physical adsorption of H2O molecules to Si-F bonds on the surface.

The rigorous formulation of the internal entropy production, and the generalized forces and conjugate fluxes associated with the virtual displacement of a triple junction are presented in multi-component systems. Extensive computer simulations are performed on the void configurational evolution during the intergranual motion; under the actions of capillary and electromigration forces in thin film metallic interconnects with bamboo structure having various grain textures. The texture studies in this work show clearly that there are two different and very distinct modes, namely: the grain boundary carving or tearing mode, and the interconnect edge cutting mode by the oblique slit formation (about 450) on the wind-side of the grain boundary.

Thin gold films with a thickness of 2mm were deposited on a silicon substrate by electron-beam evaporation. The material microstructure and internal stresses of the as-deposited gold films were characterized by scanning ion microscopy, orientation imaging microscopy, and X-ray diffraction. Microtensile tests of free-standing gold film samples were carried out to establish their intrinsic mechanical properties (in connection with a finite element analysis using crystal plasticity). Nanoindentation tests of the thin gold films attached to the silicon substrate were also carried out. Finite element analyses incorporating the crystal plasticity model were used to evaluate the effects of thin film textures, constraints due to the elastic substrate, and internal stresses on the plastic deformation behavior of the thin gold films under indentation at a direction normal to the film surfaces. Results of the combined experimental and numerical investigation indicate that the internal stresses have a strong effect on the uniaxial compression stress-strain behavior of the gold films and it may contribute to the relatively large hardness numbers obtained from the nanoindentation tests.

Effects of recovery and recrystallization on subsequent stress – strain behavior were studied in foils of non-age hardenable Al based alloy. A bulge testing device for mechanical testing of thin free standing films and foils, enabling the detection of large strains, was employed. The bulge tester was used at RT both for the predeformation of the foil in the biaxial mode and also for the study of softening after subsequent one-step annealing. Three stages of strength drop as a function of the annealing temperature were observed between RT and 590°C. The contribution of different annealing processes to the softening was established using transmission electron microscopy. It was found that below 200°C only redistribution of dislocations inside dislocation cells and refinement of the cell structure occurred. Between 200°C and 380°C the formation of a subgrain structure was observed. The softening process is terminated as partial recrystallization takes place at higher annealing temperatures. Dynamic interaction of solutes with dislocations was revealed during prestraining as well as poststraining of foils. This effect resulted in the appearance of a negative strain rate sensitivity and dynamic instabilities after appropriate prestraining and annealing conditions. The above results show that bulge testing of Al foils allows to study the successive annealing stages by measuring the most important macroscopic parameters of plastic deformation (yield stress, work hardening rate, ductility, strain rate sensitivity, etc.). These stages could be related to the microstructure evolution.

Nucleation of dislocation loops from stressed crystal surfaces is analyzed based on a variational boundary integral method in the Peierls-Nabarro framework. The stress dependent activation energies required to activate dislocation loops from their stable to unstable saddle point configurations are determined. Compared to previous analyses of this problem based on continuum elastic dislocation theory, the presented analysis provides more definitive solutions because it eliminates the uncertain core cutoff parameter by allowing for the existence of an extended dislocation core as the embryonic dislocation evolves. Moreover, the shape of the dislocation loop is solved by the variational principle instead of assumed to be semicircular as in previous analyses based on continuum elastic dislocation theory. It is noteworthy that the presented methodology can be readily used to study effects of surface inhomogeneities such as cracks and steps on dislocation nucleation.

The present work proposes a Dugdale type model to theoretically predict the multiple cracks of a residually tensile stressed thin film on a ductile substrate. The results show that there exists a critical value, Rc, of the cracking resistance number, R. When R < R, the film > c cracks and the normalized crack spacing is determined by cracking resistance number and the stress ratio of the residual stress to the yield strength of the substrate.

The thermal stress-induced delamination of 500nm polycrystalline Ta coatings on Si(100) substrates was studied via a recently developed real-time in situ imaging technique. This method used white beam synchrotron (on SSRL station 2-2) Laue transmission diffraction topography coupled with simultaneous direct radiography to record the thermomechanical failure modes of the Ta films as a function of temperature. The observations were made using a novel experimental apparatus, consisting of a 600°C hot stage and a portable CCD x-ray imaging/storage system with ~20m m resolution. The system is capable of recording 30 images/sec; hence, at moderate strain rates not only was the morphology of failure evident, but detailed study of the dynamics of delamination was also possible. The mode of failure and the adhesion strength are correlated with the physiochemical nature of the coating-substrate interface, and also with the degree of in-plane/out-of-plane texture of the Ta films. These observations should be capable of extension to the study of a variety of adhesion and cyclic failure issues in thin coatings.

Tetrahedral amorphous carbon (ta-C) contains a large percentage of sp3 carbon bonding. However, high internal stresses develop in ta-C films with a high sp3 content, which limits their applications for wear protection. In this study, Al containing ta-C films were produced using Filtered cathodic vacuum arc (FCVA) technique. The structure of films was studied using Micro-Raman spectroscopy in terms of aluminum content. The pure carbon ta-C films generally contained a relatively high residual compressive stress, which was related to its sp3 content, amorphous structure and preparation conditions. For the Al containing ta-C films, the stress reduction is significant with increase of aluminum content in the film. A decrease of the mechanical properties of the ta-C:Al nanocomposite films was noticed with the decrease of the internal stress in the films. The tribological behavior of the films was measured using ball-on-disk tribometer. The wear rate and friction coefficient were determined correspondingly. In the ball-on-disk testing, different loads are applied to the sapphire counterbody. All the tests were performed in ambient air (RH50%) and at room temperature (22°C). It was noted that the friction coefficient of ta-C:Al films increased at the beginning of the testing before reaching a peak value of about 0.25. After the peak, the friction coefficient dropped until reaching a steady state value. The original surface roughness of the counterfaces, surface smoothening due to successive wear, and wear debris produced during the testing are all responsible for the tribological behavior of ta-C:Al films.

The Point-Deflection Method is a potentially useful technique for measuring the internal stresses of freestanding thin films. By applying a small concentrated transverse load at the center of a pre-stretched film, and measuring the corresponding out-of-plane displacement at appropriate locations, the average internal stress can be readily determined. The load-deflection relationship has been derived for both circular and rectangular shapes. The method involves no additional micromachining in sample preparation and has low sensitivity to the variations in boundary constraints. Its feasibility has been further substantiated with finite element simulations from a variety of perspectives, as well as experimental correlations from the stress measurements of a photomask pellicle film.

We introduce an analytical technique for time-dependent deformation behavior of the polycrystalline films using a nano-indenter. This technique permits evaluation of structural deformation of the nanometer scale of the thin films. In this paper, good accuracy conditions were determined to measure deformation behavior of the polycrystalline films. The polycrystalline films of anatase were used to investigate the grain boundary structure. We prove that the analysis of time-dependent deformation behavior is effective to investigate the structure of the polycrystalline films.

The determination of the elastic modulus and hardness of a wide range of coating systems has been studied recently in the EC project INDICOAT. This paper describes a protocol for determining the coating properties, which has been developed and tested in that project. The procedure contains simple to implement strategies to evaluate the response of the coating and design a suitable series of indentation experiments that enable a reasonable estimation of ‘coating-only’ properties. The protocol directs how the experimental design adapts the experimental parameters to each sample. An adaptive protocol is essential to cope adequately with the different indentation responses. Indentation response depends, for example, on coating thickness and the relative properties of coating and substrate and creep response. The protocol also has to adapt itself so that it can reliably target the range of indentation depth with respect to the coating thickness necessary to obtain the coating properties from the composite indentation response. Results presented show that the parameters and approach for measurement of hard coatings are very different to those required for soft or ductile coatings. The systems studied are DLC on tool steel, Au on Ni, aluminium oxide on Ni and aluminium on optical glass (BK7).

Viscous creep behaviour of several metals and alloys was investigated at the temperatures close to one half of the absolute melting point and at very low stresses using the technique of helicoid specimens. Due to extremely high sensitivity the technique represents a unique tool for measurement of very low creep strains in reasonable time. Helicoid spring specimens were made of wires of either circular or square cross section. The stress distribution along the wire radius (caused by shear stress loading) and threshold stresses were taken into account, as well as the influence of the surface layer loaded by maximum stress.

The experimental results were interpreted as Coble diffusional creep and/or Harper-Dorn dislocation creep. Some data are in a very good agreement with Coble theory especially those obtained on some fine grained materials. For the coarse grained materials is this dependence replaced by large data scattering. Some authors dispute about the role or even the very existence of diffusional creep and offer other explanations. There are many theories trying to describe Harper-Dorn creep mechanism, but none of them is capable to explain all observed properties.

The observed effects which cannot be explained by the current theories are discussed (large scatter of creep rates obtained for coarse grain materials, creep rates much higher than those predicted by the diffusional creep theory in some materials, transition stage duration independent of stress but dependent on temperature.

Despite the problems in theoretical description, the experiment shows clearly that the viscous creep regime must be considered as an important behaviour of structural materials at conditions of engineering practice.