The mechanical properties of hydrogen-free tetrahedral amorphous diamond-like carbon have been investigated in connection with its elastic and failure properties. Micro-tension specimens of gage thickness of 1.2–1.8 μm and widths of 10 μm or 50 μm have been fabricated by the Sandia National Laboratories (SNL). The mechanical characterization has been conducted via in situ AFM measurements and Digital Image Correlation (DIC) data strain analysis and the local deformation fields of (a) uniform and (b) internally notched tension specimens with acute notches (K=27) have been experimentally obtained. Young's modulus and Poisson's ratio were measured for the first time directly from such small specimens and averaged 750 GPa and v=0.16 respectively, while the tensile strength was found to be very consistent averaging 7.1 GPa. Stressed material domains with smaller dimensions in the vicinity of micronotches exhibited even higher failure strengths reaching 11.5 GPa with limited data scatter. AFM images of in situ tested specimens have indicated sp3 to sp2 phase transformations on the film surface that was subject to ultra-high tensile stresses (>6 GPa). This is the first time these phase transformations are observed during tensile tests of brittle materials.

The thermo-mechanical behavior of plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films are investigated during thermal cycling and annealing. It is well known that PECVD films have a large amount of incorporated hydrogen that evolves on heating. This reduction in hydrogen is shown to be directly responsible, via constrained volume decrease, for irreversible increases in tensile stress. It is demonstrated that no stress equilibrium is attained during very long time anneals. The thermal cycling behavior of PECVD films can be modeled by chemical reaction theory, with the irreversible development of film stress a mechanical consequence. The model assumes first-order reaction kinetics of Si-H and N-H bonds, which react to form molecular hydrogen and reformed network bonds. The activation energy of reaction is not single-valued, indicative of the strong influence that the local bonding environment has on bond energies. If the incorporated hydrogen reactant pairs are assumed to be normally distributed with activation energy, irreversible stress development is well modeled, and the mean activation energy ranges from 2.44 to 2.93 eV for 150 to 300 °C deposited films.

Based on the bending model, three double-parameter criteria characterizing thin film peeling process are introduced and analyzed in detail. Three double-parameter criteria include: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the interfacial crack tip slope angle of thin film, and (3) the interfacial fracture toughness and the critical von Mises effective strain of thin film at crack tip. Based on the three double-parameter criteria, the thin film nonlinear peeling problems are solved analytically for each case. The results show that the solutions of thin film nonlinear peeling based on the bending model are very sensitive to the model parameter selections. Through analyses and comparisons for different solutions, a connection between solutions based on the bending models and based on the two-dimensional elastic-plastic finite element analysis is obtained.

YBa2Cu3O7-x (YBCO) films grown by pulsed laser deposition (PLD) on (100) LaAlO3 (LAO) substrates show a strong thickness dependence on the electrical properties. For example, for films in excess of 0.3 μm, the critical current density decreases with increasing thickness. In contrast, nano-composite films consisting of a series of multiple layers of YBa2Cu3O7-x and (Ba0.05, Sr0.95)TiO3 (BSTO) thin films having a total thickness of 5 μm show improved electrical properties. In order to understand this phenomenon, a detailed microstructural characterization has been undertaken. Transmission electron microscopy (TEM) observations show that cracks, stacking faults, c-║ crystals and secondary phase precipitates are present on the single-layer films, while a high-quality microstructure is observed for the nanocomposite multiple-layer films although defects at YBCO/BSTO interface are still present. In addition, nanocomposite films have a reduced surface roughness. In this complex microstructure, the YBCO/BSTO interfaces and the lattice mismatch strain play a crucial role in controlling the nature of the defects and stability of phases. In order to understand the role of the BSTO layer has on the microstructure, the interfacial mismatch strain and defects are analyzed by high-resolution transmission electron microscopy (HRTEM) in combination with the Moiré fringe technique.

A quasi-static model is proposed to describe wafer deformation due to stress build up in the Si epitaxy process. The analysis takes into account temporal stress variations as the wafer sags into the dish-shaped pocket of the susceptor at a deposition temperature above 1100 °C. It is shown that the magnitude of the negative bending moment at the wafer supporting edge decreases over time. As a result, the maximum deflection at the wafer center and the tensile stress at the wafer supporting edge also decrease over time. The generation of slip defects near the wafer edge as the wafer responds the thermal, gravitational and contact stress is explored. A new test methodology is developed to track the time-varying wafer deflection. It allows for the measurement of quality of the susceptor and its fitness for use in the reactor system.

The indentation fracture test was used to evaluate residual stress in ZnO thin films deposited on silicon wafers. Using the calibrated constants involved in a simple semi-empirical formula, which was developed based on fracture analysis and experimental results, we estimated the residual stress in the ZnO thin films by measuring the indentation-induced crack length as a function of the indentation load.

Selective etching of a SiGe layer for Si/SiGe/Si stacked layers was investigated for device applications. The SiGe layer is selectively and laterally etched by a HF:HNO3:H2O solution after patterning the layers. The selective etching rate of the SiGe layer increased as the Ge ratio increased. The etching rate of a SiGe layer annealed at 800°C did not change from an as-grown sample, and the Ge diffusion into Si was very small. However, the etching rate of a layer annealed at 1000°C was found to have decreased, and Ge diffused into Si in large amounts. This indicates that annealing at less than 800°C is suitable for device applications.

Thin film multilayers of Al2O3 / ZrO2 have been deposited on quartz and AISI 440C steel substrates at room temperature by sol-gel dip coating technique followed by annealing at different temperatures ranging from 200°C to 800°C for 5h. Prior to annealing the deposited films have been exposed 10 min to ultraviolet radiation (248 nm wavelength) and microwave (2.45 MHz at 800 W power) respectively. Unlike conventional annealing methods, microwave heating is generally quite faster, simpler, and very energy efficient. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwave on solid phase diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyser techniques have been employed to characterize structural, morphological and elemental composition of the thin films. Adhesion strength failure measurements on films have shown critical loads up to 35 N. Nanohardness indentation tests of the films exposed to microwave have shown hardness of 10 GPa with elastic modulus of 85 GPa compared to the annealed films hardness of 4.5 GPa with elastic modulus 57 GPa.

During the chemical ordering of the high anisotropy FePt L10 phase a fcc-→fct structural distortion in the unit cell occurs. Monitoring the stress relaxation time dependencies during isothermal annealing cycles may lead to a better understanding of the L10 ordering kinetics thickness dependencies in thin FePt films. During the isothermal portion of the anneal cycle all films showed an exponentially decaying stress relaxation with time to lower compressive stress states for all temperatures and thickness. The stress relaxation rate increased significantly with an increase in Fe51Pt49 film thickness and annealing temperature. Stress relaxation activation energies of 2.21 eV, 2.40 eV, and 2.96 eV for the 50nm, 25nm, and 10nm Fe51Pt49 films, respectively, were extracted. This correlated well with the observed trends in the post annealed film coercivity, increase of the (001) superlattice L10 peak, and the shifting of the (111) peak position, all indicators of L10 chemical ordering transformation.

Accurate mechanical properties of thin films are essential for viable design and fabrication of semiconductor devices and microelectromechanical systems. Relevant properties of thin films such as intrinsic stress, biaxial modulus, and fracture strength can be significantly different than their corresponding bulk values, and much more difficult to measure. However, such data can be obtained from the pressure-deflection response of clamped freestanding membranes, i.e., the so-called pressure-bulge test. Experimental challenges include membrane leakage prevention, ensuring proper structural boundary conditions, and accurately measuring applied pressure and transverse displacements simultaneously. In addition to these issues, most previously-developed pressure-bulge instruments rely on vacuum pump loadings. Such tools are limited by the one-atmosphere differential pressure over the membrane, which is inadequate for burst testing of high-strength films. Consequently, an enhanced pressure-bulge tool has been developed and will be described in this paper. It incorporates positive pressure to overcome the one-atmosphere load limitation, improved edge constraints, and the ability to test an array of membrane windows across a single substrate.

Internal stresses and thermal stability of strongly (111) oriented Cu thin films, which are one of promising interconnect materials in advanced ULSI devices, have been studied comparing with those of non-oriented Cu films. Their internal stresses parallel to a film surface were measured by a conventional X-ray diffraction technique (d-spacing vs. sin2ψ method), while the strain distribution with depth by a grazing incidence X-ray scattering (GIXS) methods. Large stress relaxation in strongly (111) oriented Cu films takes place at 200°C without showing any significant grain growth and formation of thermal defects like hillocks. The residual internal stresses of highly oriented (111) Cu films increase almost linearly throughout the thickness up to the substrates. The feature of stress distribution in film depth does not change on annealing. The changes of the residual stresses at each depth are nearly the same as stresses parallel to film surface measured.

Nanoindentation experiments have been used to investigate mechanical properties of polymeric thin films. In this paper, the problem is modeled as normal indentation of a viscoelastic half-space by a rigid smooth frictionless axisymmetric polynomial indenter. An analytical solution, which relates the indentation load to the penetration depth, is presented. The solution is valid as long as the contact region is simply connected and the indenter is in complete contact with the half-space. It shows that a similar fundamental relation exists in Laplace space.

We present the use of x-ray scattering from Si1-XGeX/Si1-YGeY superlattices as a tool for measuring the concentration dependence of interdiffusivity in Si/SiGe epitaxial thin films. Although x-ray scattering from compositionally modulated films is an ultra-high-sensitivity technique for measuring interdiffusion in a variety of systems, the concentration dependence of Si/SiGe interdiffusion complicates its interpretation. We show that these complications can be avoided using Si1-XGeX/Si1-YGeY superlattices with a small compositional modulation. This strategy is assessed using numerical simulations of both interdiffusion and dynamical x-ray diffraction. We demonstrate its effectiveness by measuring the activation enthalpy and exponential prefactor for interdiffusion in compressively strained Si0.925Ge0.075. The results are 4.38 ± 0.05 eV and 36 ± 9 cm2/s respectively.

The nanoindentation technique has great promise in evaluating mechanical properties such as nanohardness and elastic modulus at micrometer or nanometer scales, since sample preparation and testing procedures are very easy. However, the nanohardness and elastic modulus cannot be directly related to basic material flow properties. Here a novel and simple experimental/computational method is proposed to extract stress-strain curves based on finite-element modeling (FEM) of nanoindentation. This method was verified for bulk Al by comparing the stress-strain curves extracted with those obtained from tensile testing, and was applied to Al thin films (0.5 μm and 1 μm) deposited on a Si substrate.

We have investigated the influence of process parameters in electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) of silicon nitride, on the intrinsic stress of thin SiN films and on their composition, in order to obtain SiNx films suitable to micromechanical applications. The silane to nitrogen gas flow ratio, along with addition of helium to gas mixture, was found to be a critical parameter for the tuning of the intrinsic stress in ECR-PECVD SiNx films, from compressive to tensile stress, with a maximum related to the largest Si-N bond density in the film.

A previous dislocation model analysis predicts that nano-scale contacts of surface steps induce nucleation of dislocations leading to pro-load and anti-load dislocation segregation near the contact surface. Such dislocation segregation generates a sub-layer of tensile residual stress in a much thicker layer of compressive residual stress near the surface. The sub-layer thickness is expected to be about 50 to 100 times the step height. In order to verify the predictions of the model analysis, experiments are carried out on polycrystalline aluminum surface to determine the existence of the tensile sub-layer. The variation of the residual stress along the thickness direction is measured using a newly developed high sensitivity curvature-measurement interferometer. The interferometer measures the curvature change of the back surface of a plate specimen of about 1.9 mm thickness while the contact-loaded front surface is chemically etched. The residual stress distribution measured with sub-nanometer spatial resolution is compared with analytical predictions.

Thin stripes of gold deposited onto elastomeric substrates can be stretched reversibly by more than 20 % while remaining electrically conducting. We are developing such stripes to serve as electrical interconnects on stretchable electronic skins. The gold layers are 25-nm to 500-nm thick. We observe two different film morphologies: the stripe is either buckled and continuous, or flat and contains micrometer-long cracks. Stretchability is correlated with the thickness and initial topography of the gold layer. Stripes thicker than 100-nm fail electrically at tensile strain of ∼ 1 %, while thinner stripes remain conducting up to much larger strain. Upon stretching the buckled stripes flatten and break into islands of 1 to 100 micrometers on a side, while the initially microcracked stripes retain their micrometer scale structure. The electrical resistance of the buckled stripes is the lowest but the micro-textured stripes can be stretched more.

This paper studies the effects of bilayer thickness and chromium content on the microstructure and mechanical properties of nanolayered TiAlN/CrN thin films. By rotation of samples holder and control of targets activity, a variety of multilayers and chemically modulated thin films were grown on WC-Co substrates using cathodic arc PVD. Conventional and high resolution TEM showed that aluminum contributes to refinement of structure while chromium favors the formation of coarse columnar morphology. Consequently, TiAlN layers periodically interrupt the formation of columns in CrN layers in multilayer films, while in chemically modulated samples the columns are not interrupted leading thus to the formation of strongly columnar films. Both Cr content and bilayer thickness contribute to hardness enhancement. Effect of Cr arises from the formation of hard fcc-(CrAl)N phase to the detriment of softer wurtzite-like hcp-AlN. The contribution of bilayer thickness is explained by the grain refinement based on Hall-Petch effect and the formation of highly stressed columnar structures with (111) preferred orientation. Such structural modifications strongly influence crack modes and morphologies as observed using AFM and FIB cross-section of indents. Thin bilayer films exhibit well-organized straight cracks parallel to the contact edge between indenter and film, while large bilayer films show a network of discontinuous irregular mud cracks attributed to grain boundary sliding. Refinement of structure favours crack meandering and branching that prevents the propagation of large cracks with more dramatic effects.

Hard CrNx coatings of various composition were deposited on hot work tool steel by means of reactive sputter deposition in an industrial PVD reactor. All deposited coatings (thickness 3–4 micron) were under compressive stress. The coatings were subjected to scratch testing with a diamond stylus. Two critical loads were determined. The first critical load, Lc1, indicates the onset of chipping and/or spalling. The second critical load, Lc2, indicates complete coating removal inside the track. Micrographs showing the coating failure are presented. Stoichiomeric CrN coatings outperform understoichiometric CrN0.6 coatings in scratch tests. It was found that for all specimens the coating-to-substrate adhesion is very good, independent on composition. Although the values of Lc1 and Lc2 are distinctly different, their dependence on composition is similar.

Various low-k materials are being pursued as dielectric materials for future interconnects. However, poor thermo-mechanical properties of low-k materials cause tremendous reliability concerns, thus the proper materials for integration with Cu are not suggested yet. In this study, the line width and spacing dependence of damascene Cu lines embedded by TEOS and low-k materials (CORAL) was analyzed using x-ray diffraction. Generally, the hydrostatic stress of Cu/TEOS was greater than that of Cu/CORAL, while the opposite for von-Mises stress. Using a three-dimensional finite analysis (FEA), the effect of low-k materials on the stress and its distribution in via-line structures of dual damascene Cu interconnects was studied. In the case of Cu/TEOS, the hydrostatic stress was concentrated at the via and on the top of the lines, where it was suspected that the void would nucleate. On the other hand, in the via-line structures integrated with organic low-k materials, large von-Mises stress was maintained in the via. Therefore, the deformation of via, rather than voiding, may be the main failure mode in the interconnects with low-k materials.