Ta films were prepared in the metastable β phase using an ultra-high vacuum sputter deposition system. The stresses that arose during thermal cycles to 750°C were measured using an in situ substrate curvature measurement system, allowing oxygen content in the films to be minimized. A phase transformation from β to the stable α phase takes place in conjunction with distinct “jumps” in stress in the tensile direction during heating at approximately 400°C and 650°C. X-ray and electron backscatter diffraction (EBSD) analyses were used to determine grain sizes, along with crystal phase and orientation information. These results indicate a significant amount of grain growth accompanying the phase transformation. It is found that the measured total stress change is in reasonable agreement with that predicted by the combination of grain growth, crystal densification associated with the phase transformation, and stress relaxation.

The stability of multilayered membrane structures is a major challenge in the development of microfabricated solid oxide fuel cells (SOFC). The work presented here explores residual stress in sputter-deposited yttria stabilized zirconia (YSZ) thin films (5nm – 1000nm thickness) as a function of deposition pressure and substrate temperature. The results indicate variations in intrinsic stress from ∼0.5GPa compressive to mildly tensile (∼50 MPa). Microstructure is characterized by x-ray diffraction (XRD). The evolution of intrinsic stress with temperature is investigated by thermally cycling YSZ films deposited on silicon wafers. Observed changes of 100s of MPa in the intrinsic stress component of the film serve as indicators of possible changes in microstructure. Such changes in microstructure are subsequently characterized using x-ray diffraction of as-deposited and annealed films. Correlations with relevant mechanisms and models of residual stress evolution are discussed. Finally, use of such residual stress data in the fabrication and design of mechanically stable multilayered membranes for micro SOFC devices is discussed.

Coarsening dynamics of Ge/Si(100) nanostructures were monitored using real-time, elevated temperature scanning tunneling microscopy. Gas-source molecular beam epitaxy from digermane at 0.2 ML / min onto Si(100) at temperatures near 500 °C produced mixed hut and pyramid cluster ensembles. The width of the most elongated rectangular-based hut clusters is always less than the side length of square-based pyramid clusters for island ensembles grown using these conditions. This suggests that pyramid elongation to form hut clusters occurred at early growth stages for some smaller clusters. Growth temperature annealing revealed that pyramid clusters are more stable than narrow hut clusters with larger volumes. These larger volume huts decay by reducing their length at constant width, finally becoming small pyramids. These pyramids, which are smaller than those which never elongated to form huts, are less stable and consequently dissolve. Atomistic elastic modeling confirms that hut clusters less efficiently store elastic energy than pyramid clusters which explains our observations. Large (> 1μm diameter), low chemical potential clusters deplete the surface of Ge adatoms as evidenced by the existence of denuded zones devoid of smaller clusters. These large clusters are responsible for the decrease in total island volume in the STM field of view during the anneal.

This paper presents a microstructure-based mechanism which elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then applied to explain a series of experimental results that are related to thermal cycling of amorphous dielectric films, such as plasma-enhanced physical vapor deposited (PECVD) silicon oxide (SiOx) films, including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD SiOx films with a thickness varying from 1 to 40 m were studied, as certain demanding applications in Microelectromechanical Systems (MEMS) require such thick films serving as heat/electrical insulation layers.

Fundamental relations of surface instability for micro-scale multilayer thin film systems are derived based on the Hill and Hutchinson bifurcation theory and the volume average integral. In the present relations, a size effect is considered through generalizing the plastic hardening modulus to include the strain gradient hardening effects. By using the model, firstly, the parameter-controlled instability region is divided and analyzed, secondly, the surface instability of the multilayer thin films are analyzed. In the surface instability analysis, several kinds of failure band formations are obtained, such as the kink bands and the compressive buckling bands in vertical direction and in inclined direction. Moreover, the failure mechanism of the multilayer thin film system due to surface instability is used to interpret the microstructure features of the surface-nanocrystallization materials.

We have used a technique developed by Brochard (Macromolecules, 2004, 37, 1470) using free standing thin films to study the viscoelastic response of filled-polymer films. Transmission Electron Microscopy (TEM) experiments reported that fillers were well distributed within the films, and therefore no clustering and interfacial segregation occurred. Results from Shear Modulation Force Microscopy (SMFM) measurements revealed that the glass transition temperature of the polymer (Tg) was depressed by 10°C relative to the bulk for Au (10 nm), and bulk like for Au (3 nm). The effects of colloidal fillers on the tracer diffusion coefficient (D) were studied using secondary ion mass spectrometry (SIMS), and results found that D was increased significantly for the Au 10 nm, and constant for the Au 3 nm. Values for zero shear rate viscosity extracted from the diffusion coefficient were compared to the shear strain calculated from the hole growth measurements, and theoretical predictions. Results were attributed to an increase in excluded volume when large particles were introduced into the matrix.

Mesa structures fabricated on Si(111) surfaces have been found experimentally to develop step arrays with large spacing of the order of a micron or more after annealing at temperatures where sublimation becomes important. Ridges around the edges initially develop during annealing and form barriers to step motion before eventually breaking down. This produces an array of steps of the same sign with a few wide terraces. Computer simulations using one dimensional Burton, Cabrera and Frank (BCF) theory including attachment-detachment rates and step-step repulsion for this configuration show that the terraces evolve under different dynamics depending on the terrace widths. For large terrace widths, sublimation dominates the step dynamics and the Ehrlich-Schwoebel effect is negligible. Sinusoidal terrace width distributions result in this case. The experimentally measured step distribution has such a sinusoidal shape suggesting that the step dynamics is sublimation dominated on the mesas after ridge breakdown.

Thermal fatigue during processing of microelectronic devices is a general reliability issue of concern in the microelectronic industry. In particular, as devices continue to be downscaled, the relaxation mechanisms operating under thermal stresses are expected to change. In this study, the microstructure of 1.8 micron and 180 nm wide Cu interconnects was identified through Transmission Electron Microscopy (TEM) imaging. In addition, In-situ TEM heating, performed in both type of specimens, is used to observe the differences in dislocation dynamics under thermal stress. In-situ TEM observations show delamination and inhibited dislocation motion in 180nm Cu lines, whereas in 1.8 micron Cu lines, grain boundaries seemed to act as dislocation sources. These different deformation mechanisms are expected to have an impact on the thermal fatigue behavior of Cu interconnects as the scale of devices is brought below 100 nm.

Ag-Cu alloy nanoparticles were prepared by rapid condensation of metal flux obtained by the simultaneous evaporation of high purity Cu and Ag wires on a tungsten boat in the presence of circulating He gas. Structural properties of the samples prepared at different conditions were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area diffraction (SAD) patterns. X-ray diffraction patterns showed that particles were phase separated. The particle size obtained either from Scherer's formula or the TEM images show no systematic change on the size of either Cu or Ag particles in the evaporation temperature range between 800 and 1400 °C. By using lattice constant values and Vegard's law, the composition of the particles was calculated to be 6.6 vol% Cu in Ag. Electron diffraction images revealed that particles were softly agglomerated; these electron diffraction results were also consistent with XRD results regarding phase separation. Individual diffraction rings of the Cu and Ag were observed in the SAD patterns.

In the present study, 90 nm thick conducting tin-doped indium oxide (ITO) layers on polymer substrates are used to study the failure behaviour of brittle layers. In a two-point bending test the resistance of uniform ITO-layers and narrow ITO-lines (10 to 300 μm width) are determined as a function of the applied tensile strain. At a certain strain, the thin layer will crack and the resistance will strongly increase. This characteristic strain is analysed using a large number of samples. Early stages of crack development are studied in the fragmentation test. This paper presents the results of different failure mechanisms of thin brittle layers on the electrical conductivity of ITO-layers. When the strain in the ITO-layer increases, stable cracks of a limited length are initiated at defects in the layer (crack initiation). At the critical strain εp the crack is no longer stable and it will propagate over the whole width of the layer (crack propagation). The experiments show a wide failure strain distribution for narrow ITO-lines. The wide distribution of defects, determining the crack initiation strain, controls the failure of narrow lines. The uniform layers show a narrow failure strain distribution. This is determined by the well-defined crack propagation strain εp.

Thin films of carbon nitride deposited by ion beam assisted deposition or by magnetron sputter deposition typically contain a significant fraction of hydrogen, 1–30 atomic percent (at.%). In order to improve the thermal stability of the properties of the films, attempts have been made to minimize the hydrogen trapped during deposition. Such films typically have less than 5 at.% hydrogen. On heating these films in ultra high purity (99.999%) argon, it has been found that above 600°C they start to absorb significant amounts of hydrogen, this despite retaining their mechanical integrity. The composition of the films is determined using Rutherford Backscattering Spectroscopy in combination with Elastic Recoil Spectroscopy for detecting the hydrogen isotopes. In this paper, the possible sources of the hydrogen have been investigated by exposing the samples to deuterated water or deuterium gas during or immediately after the heat treatment.

Thin film delamination can occur when the stored elastic energy per unit area in the film due to the residual stress exceeds the interfacial toughness. Telephone cord morphology is commonly observed in delaminating thin films under compressive stresses. Here, the biaxial film stress is partially relieved by film buckling in the direction perpendicular to the telephone cord propagation, and by “secondary” blister buckling in the direction of telephone cord propagation, which results in the sinusoidal fracture patterns.

A superlayer indentation test, in which additional stress is supplied to the crack tip using a nanoindenter, can be used to measure the interfacial toughness. Estimates of the energy release rate for diamond-like carbon (DLC) films on magnetic media were obtained using the superlayer indentation test, as well as the delaminated buckling profiles. The results obtained by these two independent methods are in good agreement with each other. We find the average adhesion energy to be 6 J/m2 for DLC films on magnetic media.

Normally telephone cord blisters “run out of steam” and stop once the interfacial toughness exceeds the strain energy release rate. It is possible to make blisters propagate further by either putting mechanical energy into the system, or by introducing liquids at the crack tip, thus reducing the film interfacial toughness. Environmental species can assist cracking and contribute to thin film delamination, which is readily observed in vintage mirrors. Crack propagation rates on the order of microns per minute were measured for DLC films in different fluid environments. We identify how telephone cord buckling delamination can be used as a test vehicle for studying crack propagation rates and environmentally assisted cracking in thin films.

This paper addresses the effect of anisotropy on the organization of epitaxial islands deposited on a substrate. Focus is on in-plane anisotropies in surface stress and lattice mismatch between the film and substrate materials. Starting from a configuration where island sizes and position are random, evolution towards equilibrium through mass transport via condensation/evaporation is simulated. The effect of the degree of anisotropy is investigated. An efficient numerical method is obtained by reducing a model of square monolayer islands of finite size to point defects that interact through their elastic fields. Models for both the kinetics and energetics of the system are obtained by this reduction. It is found that the point source model is accurate for island separations larger than about 3 times the width of an island. Under isotropic conditions islands tend to form into hexagonal arrays, and as there is no preferred orientation of these arrays, defects analogous to grain boundaries in a crystalline material tend to arise. With anisotropy islands tend to align in particular directions. This is found to enhance organization in cases of modest anisotropy and cause islands to form into zigzagged lines in cases of high anisotropy.

The stability of Au nanoclusters created at defect sites on TiO2(110) surfaces is under investigation. Using Ar ion sputtering, 0 - 10% of the surface area of ideal surfaces are modified with defects at a controlled defect density. Defected surfaces are also produced using controlled vacuum heating to 1300 K for 25 minutes. Identical exposures (< 1Å) of Au were evaporated on each surface and results of propylene temperature programmed desorption (TPD) heating cycles to < 700 K are compared with ideal control surfaces. Results support the model that Au deposited on a sputtered surface is immobilized at defect sites and the clusters so formed are stable with respect to sintering. As previously observed, with increased sputtering time there is a decrease in the cluster size and increased defect density. The desorption peak of propylene from the Au-TiO2 surface is used as an in situ probe of cluster size stability. By cyclically performing TPD to 700 K for longer times and additional cycles (or higher temperature), the sintering stability can be assessed. On the sputtered TiO2 (110) surface, evaporated gold clusters sinter with only ∼25% maintaining their initial size. On the unsputtered 1300 K annealed TiO2, Au is stable with respect to sintering for many cycles of 800 K heating. This phenomenon is attributed to both the surface stability and Au affinity for the thermal defects created on the surface. This work extends our previous investigations of Au cluster formation on defected TiO2 to their stability with respect to sintering.

The purpose of the present work was to study the long term stress stability of thin films used in harsh environment sensors. A stress determination method, based on cantilevers curvatures measurements, checked by means of 3D finite element simulations, has been proposed. Stress measurements for dielectric (silicon oxide and nitride) and metallic (AlTi and TiW) thin films have been periodically performed at room temperature, after standard annealing (450°C / 30 min in a N2+H2 atmosphere) and after 4 weeks thermal aging at 150°C or 200°C.

Spontaneous surface roughening, stress relaxation and composition re-distribution are coupled fundamental processes during the growth of strained epitaxial Si1-xGex / Si (100) alloy layers. In this work, we will present both modeling and experimental approaches to investigate the inter-relationships among these mechanisms. Stress distributions in undulated layers were calculated via the Finite Element Method by assuming a sinusoidal surface geometry. They were investigated as functions of undulation wavelength and amplitude between the trough and peak regions. For example, with a 50 nm layer of × = 0.3 having undulations of 250 nm wavelength and 40 nm amplitude, the compressive stress is twice as high in the trough regions than in the peak regions even without compositional redistribution. To explore compositional redistribution in response to these laterally varying strain fields, an experimental approach has been developed to determine local germanium concentrations for such undulated alloy layers. An etchant consisting of HNO3 (70 wt %): H2O: HF (0.5 wt %), 25: 35: 5, at 28 °C etches Si1-xGex / Si (100) alloy layers at a rate of several nanometers per minute. The etching rate increases linearly with increasing Ge concentration in the alloy layer. Such etching experiments can thus be applied to etch alloy layers with compositionally varying undulations on the free surface and utilized to quantify the local germanium concentrations. For an alloy layer with × = 0.3, the Ge concentration from this analysis is estimated to be about 20 % enhanced / depleted in the peak / trough regions, respectively.

The strain driven self-assembly of faceted Ge nanocrystals during epitaxy on Si(001) to form quantum dots (QDs) is by now well known. We have also recently provided an understanding of the thermodynamic driving force for directed assembly of QDs on bulk Si (extendable to other QD systems) based on local chemical potential and curvature of the surface. Silicon-on-insulator (SOI) produces unique new phenomena. The essential thermodynamic instability of the very thin crystalline layer (called the template layer) resting on an oxide can cause this layer, under appropriate conditions, to dewet, agglomerate, and self-organize into an array of Si nanocrystals. Using low-energy electron microscopy (LEEM), we observe this process and, with the help of first-principles total-energy calculations, we provide a quantitative understanding of this pattern formation. The Si nanocrystal pattern formation can be controlled by lithographic patterning of the SOI prior to the dewetting process. The resulting patterns of electrically isolated Si nanocrystals can in turn be used as a template for growth of nanostructures, such as carbon nanotubes (CNTs). Finally we show that this growth may be controlled by the flow dynamics of the feed gas across the substrate.

Spontaneous self-assembly of nanostructures has been a problem of long-standing interest for fabricating advanced electrical and optical devices. One approach towards controlled self-assembly is epitaxial growth on topographically patterned substrates, where surface features act as preferred sites for island formation. The substrate shape addressed here is a periodic array of rectangular mesas. Strained-layer growth on such substrates has been observed to form as islands on the edge, in the center, or at a combination of those locations on the top of the mesa. The purpose of this investigation is to discern whether these morphologies are driven by energetic or kinetic mechanisms. An energetic analysis is done under the assumption that the system free energy consists of surface free energy and strain energy. Strain arises due to a lattice mismatch between the film and substrate materials. The film and substrate are treated as two-dimensional linearly elastic solids with similar elastic properties. Under the constraint of fixed volume, various island arrangements and shapes are compared to determine low energy configurations. Islands are assumed to have the shape of a circular arc, and island positions at the center of the mesa and on the mesa edges are considered for one, two, and three island systems. For symmetric configurations, depending on mismatch strain, surface energy, volume, and relative substrate dimensions, it is found that either the configuration with a single centered island or the configuration with two edge mounted islands may be favored. Allowing for asymmetry, a single island placed on one edge of the substrate mesa is generally the low energy configuration. This occurs because islands located near the edge of a raised mesa are most efficient at relaxing mismatch strain due to an increased compliance. Kinetic simulations of morphological evolution during combined deposition and surface diffusion are also conducted in order to identify possible metastable or slowly evolving non-equilibrium states.

The quality of wafer-level, gold thermocompression bonds is critically dependent on the interaction between the wafer topography, the thin film properties, the process parameters and tooling used to achieve the bonds. This study presents mechanics modeling of the effect of wafer topography. An analytical expression for the strain energy release rate associated with the elastic deformation required to overcome wafer bow is developed. Furthermore, a simple contact yielding criterion is used to examine the pressure and temperature conditions required to flatten nano-scale asperities in order to achieve bonding over the full apparent area. The analytical results combined with experimental data for the interface bond toughness obtained from four-point bend testing indicate that the overall wafer shape is a negligible contributor to bond quality. A micro-scale bond characterization based on microscopic observations and AFM measurements show that the bond yield is increased with increasing bond pressure.

Anodic aluminum oxide (AAO) has long been considered a viable material for templated growth of nanomaterials for electronic, magnetic and optical applications due to the ability to form self-organized, high aspect-ratio nanochannels. More recently these porous materials have been incorporated with silicon to create a template for nanostructured materials on a semiconducting substrate. However, there has been no investigation into how pore growth is affected by confining the pre-anodized aluminum dimensions to the nanometer scale. We have used electron beam lithography to pattern 200 nm thick aluminum structures on Si with lateral features ranging from 100 nm to several microns in size. Structures consisting of 1 – 10 individual pores 10 – 15 nm in diameter are routinely fabricated. Confinement effects in the narrowest features assist in pore ordering in the porous structures without the use of pre-patterning or a two step anodization.