The stresses in sputter-deposited, NiMn- and PtMn-pinned top spin valve multilayers were measured using a laser-based wafer curvature technique. As-deposited stresses were 150 to 180 MPa in compression for NiMn- and 970 to 1020 MPa in compression for PtMn-pinned spin valves. Following deposition and stress measurement, these films were annealed in an applied magnetic field of 250 Oe for 2 hours at 300°C. This anneal causes the antiferromagnetic layer to undergo a phase transformation from the face-centered cubic (fcc) to the face-centered tetragonal (fct) crystal structure. This phase transformation increases the average stresses in the spin valves to 740–800 MPa in tension for the NiMn-pinned spin valves and to 475–580 MPa for the PtMnpinned spin valves. Stress changes during the antiferromagnetic phase transformation were also observed as a function of annealing temperature and time during substrate heating, annealing, and cooling. The stress varied nearly linearly with temperature during the heating and cooling of the substrate, indicating that the bulk of the phase transformation occurs during the isothermal portion of the anneal. By monitoring stress vs time during the isothermal anneal, the progression of the antiferromagnetic phase transformation was observed. Final stress data obtained from the wafers annealed in the wafer curvature system (no applied magnetic field) are within 10% of those obtained using the magnetic annealing process.

TiN/NbN multilayers and TiN monolithic films have been grown by UHV reactive magnetron sputter deposition on MgO single crystals. The hardness has been measured by nanoindentation and the as-deposited and deformed structures studied in cross-section using transmission electron microscopy. It has been found that initially the multilayers grow epitaxially with the substrate. However, once the overall film thickness has reached ∼300 nm, epitaxial growth ceases. No increase in hardness with respect to monolithic films of the multilayer components is observed in these multilayers. Experiments on monolithic films of TiN show that the same loss of epitaxy occurs, leading to a reduction in the hardness of the films, and that this change in growth morphology is triggered by the internal stresses induced within the films during deposition.

The hypothesis that a thin nanometer-scale multilayered surface film could delay crack initiation and extend fatigue lives was evaluated by electrodepositing a Cu-Ni multilayer on Cu fatigue samples. A significant improvement in fatigue lives resulted and this improvement is attributed to properties of the multilayer coating.

The Ni-Ni3Al system is the basis of a large number of Ni-based superalloys used extensively in the aerospace industry. The mechanical properties of bulk superalloys, which primarily consist of a Ni-based fcc matrix reinforced with cubic precipitates of Ni3Al, have been extensively researched. The goal of the present study is to investigate the mechanical properties of multilayered Ni / Ni3Al nanocomposites in the thin film form. These multilayers have been processed using UHV magnetron sputtering by alternate deposition of pure elemental Ni and Ni-25at%Al layers in the range of 20 nm – 120 nm. By varying the substrate material and processing parameters such as deposition temperature, multilayers with two types of interfacial orientations. (111) Ni //(111) Ni3Al and (002) Ni //(002) Ni3Al have been fabricated. Microstructural and phase characterization of the multilayers in both plan-view as well as cross-section geometries have been carried out using x-ray diffraction, SEM and TEM and the results of these will be discussed. Both orientations exhibited a high density of twins lying on the {111} planes. The loss of coherency in these multilayers as a function of the layer thickness will also be discussed. The cross-section fracture behavior of these multilayers has been studied by SEM fractography. Failure mode for fracture was a result of the application of tensile stresses. Interesting effects of the interfacial orientation and the layer thickness on the fracture surface of these multilayers will be discussed.

Nanoindentation studies were preformed on amorphous metal, multilayered thin films containing alternating layers of Fe50Ti50 and Cu35Nb65 in order to investigate the mechanism for plastic deformation in metallic glass. Films with a total thickness of 1μm and bilayer repeat lengths ranging from 2 to 50 nm were magnetron sputter-deposited onto sapphire substrates. In contrast to many crystalline multilayered systems, where large hardness enhancements have been observed when the bilayer repeat length is reduced below about 10 nm, no significant hardness enhancement as a function of bilayer repeat length was observed in the Fe50Ti50/ Cu35Nb65 amorphous metal system. This result suggests that a dislocation–like mechanism for plastic deformation may not be appropriate for these amorphous metals.

This work describes a methodology developed to predict the thermal shock behaviour of thin bi-material ceramic systems. An experimental procedure based on controlled air cooling has been devised to simulate the flow of a gas stream over the surface of a thin two-layer ceramic system. Results of microstructural and fractographic investigations conducted on tested samples, including representative fracture patterns and crack initiation sites, are presented. A probabilistic-deterministic approach to predict the thermal shock behaviour of bi-material ceramic systems is proposed. Failure diagrams are constructed from a combination of the experimental and analytical studies. Critical thermal transient conditions typical of start-up and shut-down operation in solid oxide fuel cell are determined.

We determined that self implantation of pseudomorphically strained silicon epitaxial layers greatly attenuates strain relaxation. We employed highly boron doped 150 mm diameter silicon with a nominally un-doped, 2.5 μm thick epitaxial layer (p/p+). The compressively strained layer (mismatch ≈ 1.5 × 10−4) showed inhomogeneous relaxation after epitaxial growth, with misfits forming only near the wafer periphery. High temperature rapid thermal annealing was employed after ion implantation to study misfit dislocation nucleation and glide. Our results suggest that low dose ion implantation has a potential to reduce misfit dislocation propagation and nucleation in epitaxial thin films.

Al-Ti multilayered films were deposited by magnetron sputtering of Al and Ti targets on to Si (100) or NaCl substrates. The bi-layer thickness was 16 nm with Ti constituting 12% of the total thickness. The films were subsequently annealed in vacuum at 400°C for periods between 2 and 24 h. In the course of the annealing, interdiffusion and chemical reaction between Al and Ti layers led to the precipitation of Al3Ti particles. Plan view and cross-section TEM examination of as-deposited and annealed films were performed to study the microstructural evolution, and to estimate the Al grain and AI3Ti particle size distributions. Cross-section TEM and X-ray diffraction showed a well-defined layered structure in the as-deposited films. The microstructure was found to be metastable in the first 6 h of annealing, with Al-Ti multilayers being gradually replaced by an AI-AI3Ti composite structure. The Al3Ti particles were uniformly distributed throughout the film. X-ray and electron diffraction analyses showed that Al3Ti possessed the ordered DO22 structure. The hardness of the Al-Ti films in as-deposited and annealed conditions was determined using a nanoindenter and the data have been correlated with the microstructural changes with annealing.

The effects of film thickness and passivation on plasticity of thin metal films on substrates have been studied using gold films as a model system. Wafer curvature/thermal cycling measurements were used to study plasticity in films ranging in thickness from 0.2 to 2.5 micrometers. We were able to describe these stress-temperature curves using a simple phenomenological model for linear kinematic hardening. The yield stresses revealed by the modeling were inversely proportional to the film thickness for thicknesses greater than about one micrometer. This relationship is expected from a dislocation model of plasticity. However, the residual stresses in thinner films are substantially lower than this relationship would predict and on unloading, these films show stress-temperature plots not predicted by the model. Stress-temperature curves were also measured after a tungsten passivation was deposited on the gold surface. Films thinner than one micrometer were substantially strengthened by this passivation and could then be described by the linear kinematic model. The observed stresses are only minimally affected for films thicker than about a micrometer. This strengthening effect on thinner films is consistent with the complete blocking of grain boundary diffusion near the free surface of the film.

The low temperature (T < 100 °C) inelasticity of polycrystalline Ag thin films on thick substrates has been studied. In-situ Transmission Electron Microscopy and stress-relaxation experiments indicate that thermally-activated glide of dislocations through forest-dislocation obstacles is the dominant inelastic mechanism. Values of the activation volume for inelastic deformation obtained with both experiments are reported. The mean distance between obstacles along the length of moving dislocations was found to be significantly smaller than the thickness of the film and the average grain size, which explains why current models for dislocationmediated plasticity underestimate the strength of thin films. Results from these experiments on Ag are expected to be representative of other metallic thin films (e.g. Cu and Au) on substrates.

It is well known that the mechanical properties of thin films depend critically on film thickness However, the contributions from film thickness and grain size are difficult to separate, because they typically scale with each other. In one study by Venkatraman and Bravman, Al films, which were thinned using anodic oxidation to reduce film thickness without changing grain size, showed a clear increase in yield stress with decreasing film thickness.

We have performed a similar study on both electroplated and sputtered Cu films by using chemical-mechanical polishing (CMP) to reduce the film thickness without changing the grain size. Stress-temperature curves were measured for both the electroplated and sputtered Cu films with thicknesses between 0.1 and 1.8 microns using a laser scanning wafer curvature technique. The yield stress at room temperature was found to increase with decreasing film thickness for both sets of samples. The sputtered films, however, showed higher yield stresses in comparison to the electroplated films. Most of these differences can be attributed to the different microstructures of the films, which were determined by focused ion beam (FIB) microscopy and x-ray diffraction.

Very fine-grained Ni and Cu films were formed using pulsed laser deposition onto fused silica substrates. The grain sizes in the films were characterized by electron microscopy, and the mechanical properties were determined by ultra-low load indentation, with finite-element modeling used to evaluate the properties of the layers separately from those of the substrate. Some Ni films were also examined after annealing to 350 and 450°C to enlarge the grain sizes. These preliminary results show that the observed hardnesses are consistent with a simple extension of the Hall-Petch relationship to grain sizes as small as 11 nm for Ni and 32 nm for Cu.

The mechanical behavior of a thin film that is clamped to an elastically hard substrate can be compared to a bulk metal by studying the absorption of hydrogen. Since hydrogen is dissolved in interstitial sites and exerts force on neighboring metal atoms, the in-plane stresses increase with increasing hydrogen concentration. In the case of Nb-films covered with a thin Pd layer, stresses of several GPa were measured. Nb and Pd films prepared by evaporation were loaded with hydrogen. Out-of-plane strain and in-plane stresses during electrolytic loading with hydrogen were determined by performing x-ray diffraction and substrate curvature measurements. At low H-concentrations the developing stresses correspond to a clamped film expanding elastically out-of-plane only. Above a critical H-concentration the films deform plastically. In some cases the critical hydrogen concentration corresponds to the terminal H-solubility, above which the hydride precipitates by emission of extrinsic dislocation loops. For the remaining cases a critical stress is reached before passing the phase boundary, which leads to the formation of misfit dislocations at the interface between film and substrate. The concomitant slip lines were observed on the surface of a Gd (0001) film using Scanning Tunneling Microscopy. An additional surface pattern that can be correlated with emitted dislocation loops was observed.

Plastic deformation in thin Cu films was studied by stress measurements with the wafercurvature technique during thermal cycling and in combination with four-point bending. The results from 0.5 ¼m and 1 ¼m thick Cu films are compared. In thermal cycling experiments, strengthening during cooling and a Bauschinger-like effect during reheating were observed. The stress-strain behavior investigated by four-point bending showed to be asymmetric regarding tension and compression at lower temperatures. These phenomenons are explained by a dislocation arrangement at the film-substrate interface which has formed during a previous thermal cycle.

The relaxation of strained layers frequently occurs by the glide of threading dislocations. From very early on in the relaxation process, gliding dislocations will be forced to intersect a number of prior dislocations with almost-perpendicular line directions and their progress may be blocked. This effect has been widely reported in semiconductor films, and there is some experimental evidence that it is reduced when layers are grown on vicinal substrates. This implies that the blocking is sensitively dependent on the dislocation configuration and in particular on the dislocation line directions.

In this paper the interactions between gliding threading dislocations and the perpendicular or nearly-perpendicular dislocation in their path are modelled quantitatively. The differences arising from different initial dislocation configurations and different predominant line directions are found to be small. Strain relaxation, at least in its early stages, should be virtually independent of the initial dislocation configuration.

X-ray diffraction has been used to measure the stress in thin nickel films. In addition to the stress value, information is obtained about the elastic interaction between grains. Various models exist to calculate the stress from the strain. A model that uses the mechanical elastic constants has been used. From this model it can be concluded that the model by Hill is applicable for the layers analyzed. Annealing experiments between 300 and 500 K show that the initially present growth stress reduces to zero at 500 K. The microstrain inside the grains is obtained from the broadening of the diffraction lines measured. During annealing the diffraction lines narrow. This is caused by two effects: grain growth and reduction of the dislocation density.

Iridium and rhodium thin films have been formed by e-gun physical vapor deposition on thin-chromium-coated, thermally-oxidized, silicon substrates. Cr, Ir and Rh deposition rates and substrate temperature during deposition were measured and controlled. The effects of the latter deposition parameters on the sheet resistance and stress of the Ir and Rh films are presented and it is demonstrated that both stress and sheet resistance can be desirably minimized by proper choice of the process conditions. The resistivity of these Rh and Ir thin films has been measured at room temperature. Rh can be formed in a wider process window than Ir. Rh films with Rsh = 0.1 Ω/square have been obtained at a thickness of 0.6 ¼m.

A novel process of pulse-heating copper films under high pressure has been developed for filling high-aspect-ratio vias and contact holes with copper. A copper film is sputter-deposited on to an oxidised silicon substrate containing an array of via holes with varied aspect ratios. The film, which is thick enough to bridge over the via holes, is then subjected to laser pulse heating under selected pressures of inert gas. Via filling has been achieved, up to an aspect ratio of 6 for 0.35 μm diameter holes. The microstructure of the pulse-heated copper films has been investigated by X-ray diffraction, and by focused ion beam microscopy (FIB) including sectioning. The FIB images of the film over a via pattern show a ‘chequer-board’ pattern of grains corresponding to the square pattern of via holes underneath. This pattern can be explained by transient melting of the film under pulse-heating and subsequent solidification in which each via hole acts as a nucleation site and has a crystal associated with it. Even though the as-deposited films are fine-grained and have (111) texture, the treated films can show (111) or (100) texture, depending on processing conditions. The origins of the final film texture and the possibilities for microstructural control are discussed.

The influence of Cu on the response of Al-Cu thin films to thermally induced stress is studied. The copper concentration is varied between 0 and 1.15 at. %. It is proposed that copper atoms which have not formed precipitates, largely affect the mechanical behaviour. This idea is supported by the following observations. An isothermal hold results in temporary strengthening of the films. The extent of this strengthening increases with copper concentration, increases with decreasing isothermal hold temperature and saturates with increasing isothermal hold period. Based on these observations the large tensile stress increase below 200 °C is ascribed to the formation of Cottrell atmospheres.

In situ transmission electron microscopy (150 kV) has been employed to study the evolution of dislocation microstructures during relatively rapid thermal cycling of a 200 nm Al thin film on Si substrate. After a few thermal cycles between 150 and 500°C, nearly stable Al columnar grain structure is established with average grain less than a μm. On rapid cooling (3–30+ °C/s) from 500°C, dislocations first appear at a nominal temperature of 360–380°C, quickly multiplying and forming planar glide plane arrays on further cooling. From a large number of such experiments we have attempted to deduce the dislocation evolution during thermal cycling in these polycrystalline Al films and to account qualitatively for the results on a simple dislocation model.