The morphological stability and strength retention following elevated temperature exposure or thermal cycling will be crucial in exploiting the extremely high strengths of nanolayered materials in advanced engineering applications. The effects of elevated temperature (≤800°C) vacuum annealing on the morphological stability and mechanical properties of sputter deposited Cu-Nb multilayers with 75 nm bilayer period are reported here. Even after 800°C/ 1 hour anneal, the continuity of the layered structure is maintained and the bilayer periods are unchanged. The in-plane grain sizes in both Cu and Nb coarsened but were anchored at grooved boundaries preventing further growth. For a constant bilayer period, the effect of increasing the in-plane grain size on the multilayer hardness is found to be insignificant. After annealing, the layers are observed to be offset by shear along a vertical plane at the triple point junctions that have equilibrium groove angles aligned in a zig-zag pattern. A new mechanism is proposed for the evolution of this “anchored” structure that is resistant to further morphological instability.

We have investigated the aluminum nitride microtubes made of aluminum nitride thin film. Aluminum nitride thin film deposited on aluminum foil forms microtubes of itself at room temperature when the aluminum foil is dissolved in hydrochloric acid solution. The aluminum nitride microtubes exhibit a large bending stress of 1100 94 megapascals. The bending stress is more than three times larger than the bending strength of aluminum nitride bulk. The diameter of the microtubes is proportional to the film thickness. The bending stress is independent of the film thickness and is fixed.

A rigorous analysis of a multilayered polysilicon laminated system, constructed by alternating deposition of low-pressure chemical vapor deposition (LPCVD) polysilicon at two different temperatures is presented. Different residual deformation fields are generated in these polysilicon thin films as a function of fabrication temperatures, due to different crystallization behavior at the two temperatures. The combination of the two layers, however, enables precise control of the radius of curvature of released structures, provided the material properties are well defined. We describe a new method, which combines experimental and numerical procedures, to define the material properties, which are responsible for the residual stresses as a function of layer thickness, as well as a procedure to design the desired curvature of a multilayered Micro-optical-electromechanical system (MOEMS) device. A linear deformation field is assumed. It is shown that precise design of the thicknesses of the individual layer is a prerequisite for controlled curvature. The procedure we have developed predicts the curvature of multilayered polysilicon systems with good precision.

Low temperature silicon dioxide thin films have been prepared by plasma-enhanced chemical vapor deposition (PECVD) using tetramethylsilane (TMS) as the silicon precursor at 100- 200°C in the pressure range of 2- 8 Torr. PECVD TMS oxide thin films deposited at these temperatures and pressures exhibit adjustable stress. The type of stress, including tensile stress, zero stress, and compressive stress, as well as the stress level can be tailored as desired by changing the deposition conditions and film thickness. In addition, the conformality of PECVD TMS oxide thin films varies significantly with the deposition conditions. It improves when the deposition pressure is raised and the substrate temperature is reduced. The mechanisms for the variations of stress and conformality with respect to deposition conditions are discussed in this study. The adjustable stress and conformality of the PECVD TMS oxide make it a promising material for many low temperature applications, such as inter-level dielectric, micro-electro-mechanical systems (MEMs), microfabrication, and large area electronics.

Stresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) wereevaluated at each stage of fabrication. The individual layers of the Si/SiO2/Poly-Si/WSi2/Poly-Si multilayer structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were capped with a 25nm thermal oxide and the strain in the WSi2 film was also analyzed by XRD. The change in strain of the WSi2 layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The layers of the multilayered film affect the stress in the WSi2. A poly-Si layer on top of WSi2 reduces its stress, since it introduces a compressive component, which further decreases upon annealing. It also maintains a Si supply at the poly- Si/SiO2 interface, thus, eliminating Si outdiffusion during heat treatment in an oxygen containingambient. Capping the system by a thin oxide layer modifies the stress pattern of the WSi2, which becomes compressive.

As films heteroepitaxially grow on substrates, lattice mismatch strain at the interfaces causes stresses in the films and substrates. These stresses can have deleterious effects on film quality. To facilitate an understanding of defect production and control during growth of films on compliant substrates, transient finite element models were developed to simulate the complete mechanical stress and strain fields. Effects of constraints between the template and handle wafer on the film stresses were examined. The investigation showed that different types of constraints caused stress variations over a large range. Other factors affecting the stresses, such as lattice mismatch strain, wafer radius, film and template thickness, were also assessed.

We present a study demonstrating the capability for controlled shape memory thin film growth using molecular beam epitaxy. Here, NiTiCu alloy films were grown which are known to exhibit the martensitic transformation well above room temperature. Remarkably, the microstructure of these films was found to be very different compared to conventionally sputtered polycrystalline films: here, the crystallites are highly oriented within 3° along the film plane normal. Moreover, a splitting of the martensite orientation is detected indicating the selection of only two specific martensite variants. Mechanical stress measurements reveal a high ratio of recoverable stress even for films below 500 nm thickness. These results open up the possibility for tailoring microstructure and crystallographic orientation of shape memory thin films and thus suggest promising characteristics, especially in regard to their superelastic behavior.

Nanoindentation testing of hard film – soft substrate systems can exhibit permanent deformation prior to a yield excursion, indicating that the occurrence of this sudden discontinuity is predominantly controlled by the hard film cracking rather than dislocation nucleation and multiplication. In a previous paper, a model was developed to predict the mechanical response prior to hard film fracture. In the current study a this model, which superimposes large deflection of the hard film and plastic deformation of the substrate the model, is further refined by testing a variety of materials with different film formation conditions. The tested materials include anodic titanium oxide on titanium, thermal aluminum oxide on aluminum and sputtered tungsten films on aluminum. The film fracture strength of titanium oxides on titanium is estimated as 15 GPa and that of aluminum oxides on aluminum is around 10 GPa. In the case of vacuum sputtered tungsten film on aluminum, the tungsten layer is likely plastically deformed. The strain at film fracture is roughly estimated to be 3.4%.

Low-k material integration issues that plague the microelectronics industry include the compromise in mechanical properties that one incurs in abandoning fully dense silica dieletrics. Typical elastic moduli of OSG low-k dieletric films are 2-10 GPa with corresponding hardnesses of 0.5 to 1.5 GPa. In the present study, the hardness and elastic modulus properties measured by nanoindentation of porous silica based low-k films are correlated with in initial estimates of density using a novel technique of spectroscopic ellispsometry. Transmission electron microscopy and X-ray photoelectron spectroscopy show the structural and chemical similarity of the films. Nanoindentation and spectroscopic ellipsometry results reflect significant deviations in material behavior from that expected from a simple model of silica (SiO2) with included voids or porosity, suggesting that the methyl groups are actively participating in the mechanical and optical properties of the material.

The structure of TiAlN and other thin films depends on the coating method, parameter variation and an eventual treatment of the coating after deposition. Concerning the coating process, reactive sputter and evaporation parameters influence structure formation as well as plasma driven chemical reaction on the substrate surface. Besides, crystal formation and agglomeration depends on energetic level and flow rates in the coating system, the kind and number of reactive partners, temperature and specific parameters of the coating plant.

Post-deposition treatments on the other hand may influence the formation of residual stresses but not the crystallization of different phases within the complete coating. Besides, mechanical treatment may change the coating's morphology which may be important depending on the application since sometimes a columnar structure is to be optimized in size, amount and location. Thus a homogeneous coating is not always the optimum solution. In the experiments presented here we investigated the wear properties of thin TiAlN films. They were post-treated by sandblasting and heating in order to reduce frictional forces between the contacting bodies or analyze the effects of elevated temperatures respectively. These wear properties were evaluated by turning of 42CrMo4V at low cutting speed.

Tin oxide thin films on glass are used in a variety of applications ranging from transparent conductors to coupling layers to wear resistant coatings. The mechanical properties and wear resistance are crucial to most applications of tin oxide films. In the present study, ultrathin tin oxide films were sputter-deposited on the two different glass substrates. Nanoindentation, nanoscratch and nanowear experiments were performed on the tin oxide films with different thickness using a Hysitron TriboScope at different loads. Hardness and Young's modulus of elasticity were determined from the depth sensing load-displacement data. A lower friction coefficient was observed on the thinner film using the ramping load scratch test. Critical loads were determined by the ramping load scratch test and multi-slide nanowear tests on the tin oxide film deposited on the alkali contained commercial float glass (LOF-P16) glass. Discussion on the effect of surface chemistry on the mechanical properties was made.

The residual stress induced in a Pt-aluminide bond coat formed on a single-crystal superalloy has been measured. The stresses arise because of the thermal expansion misfit with the substrate on cooling from the manufacturing temperature. Since the lattice parameters are unknown, the interpretation of diffraction measurements is problematic, and the “wafer” curvature method has been applied. This method required that the substrate thickness be systematically reduced by mechanical thinning. It was also required that curvature measurements be made with the bond coat present as well as after it had been removed by thinning. This approach revealed that the bond coat is in residual tension, 140MPa, consistent with its thermal expansion coefficient, relative to that for the substrate.

A refractory metallization of Au/Nb is proposed for use in first level metallization of GaAs devices. The diffusion and reaction kinetics are explored using sheet resistance measurements, along with X-ray diffraction and Auger electron spectroscopy depth profiling. The interdiffusion coefficients are reported. Diodes are fabricated using Nb/Au metallization and characterized

The stress distribution in silicon substrates under a silicon dioxide thin film edge, long oxide thin film stripes and long oxide window structures have been studied using the infrared photoelastic (IRPE) method. The experimental IRPE stress fringe patterns were compared with the simulated patterns based on an analytic solution we obtained recently for the stress distribution under a thin film edge in isotropic substrates. Dependence of the stress distribution in these structures on the geometrical parameters such as the stripe width, window width, and substrate thickness were also studied. The implication of a slight discrepancy between the experimental and simulated IRPE patterns on the singular behavior of stress field in the substrate at the film edge and the concentrated force assumption are discussed.

Contact mechanics for indentation testing with spherical indenter is very attractive. Numerous projects have established equations to define strain and stress distribution in order to obtain stress-strain relationship from a single indentation experiment. Also a large number of studies have focused on metallic materials with the objective of estimating the yield point.

The subject of this work is to analyze the behavior of various polymeric materials during spherical indentation testing at various temperature in order to observe the relationship between the indentation behavior and compression stress-strain behavior of the same materials as a function of temperature. Thermal effects on the indentation data are used to understand the actual effects of the mechanical properties on the indentation behavior. In addition to the load, displacement, and frequency specific stiffness information, topographic analysis of the residual indentation print is used to accurately estimate the contact area, therefore, validate the indentation models for contact depth calculations using spherical indentation. Results presented in this article include spherical indentation data obtained on PMMA and Polycarbonate over a range of temperature from 5°C to l00°C.

Thin film electroluminescent devices employing zinc sulfide doped with manganese are extensively used for applications in which the weight, brightness and mechanical robustness requirements preclude the use of other types of displays such as cathode ray tubes or liquid crystal displays. The physical, optical and electrical properties of phosphors such as ZnS:Mn can often depend strongly on microstructure, which in turn depends on the growth and processing of the film. For this study, ZnS:Mn layers were fabricated by metalorganic chemical vapor deposition (MOCVD) in the 250°-500°C range on an Al2TiO/ In2SnO5 /glass stack. Selected samples were then subjected to a post-deposition anneal in H2S/Ar at 700°C for up to 4 hours. The microstructure of the ZnS:Mn films was examined by Transmission Electron Microscopy (TEM). For all growth and annealing conditions, the films consisted of columnar grains whose column axis was parallel to the growth direction, and which widened laterally through the thickness of the films. For the as-deposited films, the crystal structure was found to be predominantly 2H structure, with the 8H polytype being identified in the low-temperature ZnS:Mn films. The 700°C post-deposition annealing was found to initiate a solid state transformation to the cubic (3C) ZnS crystal structure. All films contained high densities of stacking faults and microtwins, whose role in the 2H-3C transformation is discussed. Also discussed are initial Ultrasonic Force Microscopy (UFM) results which suggest a correlation between the defect microstructure and the elastic response of the material.

Adhesion in multi-layer thin film structures was measured using the four-point bend technique. The investigation primarily focused on layers found in the backside metalization processes of Power MOSFETs (typically in a DMOSFET or U-MOSFET structure). Variation in metal layer and substrate condition produced changes in the adhesion behavior of the systems of interest. Pt, Cu, and Ti metals were applied to Si and SiO2 surfaces with various roughnesses in order to establish the relative contributions of surface chemistry and roughness variation. G values ranging from 2 – 100 J/m2 were measured and it was found that variation in surface chemistry has a larger impact than roughness on the adhesion strength of the systems investigated. The four-point bend adhesion test was determined to be adequate for the measurement of weak to intermediate adhesion of metals on Si wafers with RMS roughness values on the order of the metal film thickness.

Hardness measurements on thin films have to face the problem of the effect of the substrate hardness on the obtained result. Also the method of hardness measurement exerts a considerable influence on the experimental data. Some models, which take such effects into account, are presented. We describe experimental results of hardness measurements made with the Vickers 5g probe. Nitride layers (CrN, TiN, NbN), superlattices composed of these nitrides and thin metal films deposited either on the monocrystalline Si or metallic substrates such as steel or copper have been investigated.

We also present measurements of the magnetoresistivity (MR) effect. on superlattices, which consist of the multilayers TiN/NbN deposited on Si substrates. Layers of different thickness of TiN and NbN obtained by the reactive sputtering method with different superlattice period values (L) and number have been studied. The composite hardness of the structures (superlattice on Si) was found to reach 80 GPa and MR value in the best probes was ~80% (for fields from some Gs to kGs). When the supporting thin metallic layer was present, then its influence on the composite hardness was also observed.

Experiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.

Quasicrystalline films were formed by RF sputtering from a powder composite target onto Inconel substrates, which produces a polymorphic nanoquasicrystalline grain structure, ~2.5 - 10 nm. Subsequent annealing at 500°C for 4 hours, at base pressures of below 5*10-5 Torr, and with Ar flow to 5 - 10 mT, fully develops the quasicrystalline structure with decagonal phase predominating, except near the termination surface. Analysis by XPS indicated extensive oxygen incorporation and limited aluminum enrichment at the termination surface. These results are correlated with structure and strain analysis via synchrotron grazing incidence x-ray scattering (GIXS). By varying the incident angle, hence the x-ray penetration depth, the evolution of an amorphous and crystalline crystalline secondary phases at the surface of the film has been detected. Residual strain analysis shows that this second phase induces a compressive residual strain of 0.10% as measured from the displacement of the major quasicrystalline peaks in the surface layers of the film.