We have investigated regional variations of elastic properties using a magnetic force controlled AFM. A piece of small magnet was fixed at the end of the backside of the AFM cantilever so as to apply forces directly to the tip through the external magnetic field of an electromagnet. By modulating the applied forces to the tip and measuring the resulting amplitude of oscillation, a sensitive measurement of the local contact stiffness can be made. We have applied this technique to phase-separated films of polystyrene/polymethylmethacrylate (PS-PMMA) which have almost identical Young's moduli.

The deformation of film/substrate systems due to a through-the-thickness distribution of mismatch strain is discussed for cases when the layers are thin, compliant and freestanding. The connection between substrate curvature and mismatch strain is reviewed within the framework of small strains and small deflections. These results are applied to determine the second-order correction to the Stoney formula and to note the connection between mismatch strain distribution and curvature history. Then, for small strains but large deflections, it is observed that a symmetric system with equi-biaxial mismatch strain can undergo a bifurcation in deformation mode. It is also shown that the bifurcation response is sensitive to system imperfections. Finally, the critical condition for introduction of an interface misfit dislocation in an epitaxial system is established, thereby extending the Matthews-Blakeslee criterion to the case of free-standing compliant systems.

Nucleation of voids due to vacancy condensation in passivated aluminum lines is analyzed within the context of classical nucleation theory. A discussion of sources of hydrostatic tensile stress in such lines provides a reasonable upper limit of 2 GPa. The void nucleation rate is then calculated at various sites within the line. Results suggest that nucleation rates are far too low to account for observed rates of voiding. Void nucleation at a flaw at the line/passivation interface is then considered as an alternative nucleation mechanism. Such flaws may be created by contaminants introduced during fabrication of the line. In this case, nucleation is feasible at greatly reduced stresses, well within the observed values. Furthermore, a simple model of void growth indicates that a fast atomic transport path, such as a grain boundary, must intersect the void for an appreciable growth rate. These results suggest that void nucleation in aluminum interconnect lines occurs at flaws at the sidewall of the line and that stress-induced and electromigration-induced voiding can be controlled by eliminating interfacial contamination.

We have modeled the effects of grain aspect ratio on strain energy density in (100)-oriented grains in a (111)-textured Cu film on a Si substrate. Minimization of surface energy, interface energy, and strain energy density (SED) drives preferential growth of grains of certain crystallographic orientations in thin films. Under conditions in which the SED driving force exceeds the surface- and interface-energy driving forces, Cu films develop abnormally large (100) oriented grains during annealing. In the elastic regime the SED differences between the (100) grains and the film average arise from elastic anisotropy. Previous analyses indicate that several factors (e.g. elimination of grain boundaries during grain growth) may alter the magnitude of the SED driving force. We demonstrate, using finite element modeling of a single columnar (100) grain in a (111) film, that changes in grain aspect ratio can significantly affect the SED driving force. A minimum SED driving force is found for (100) Cu grains with diameters on the order of the film thickness. In the absence of other stagnation mechanisms, such behavior could cause small grains to grow abnormally and then stagnate while large grains continue to grow. This would lead to a bimodal grain size distribution in the (100) grains preferred by the SED minimization.

We have developed a technique for measuring thin film stress during growth by monitoring the wafer curvature. By measuring the deflection of multiple parallel laser beams with a CCD detector, the sensitivity to vibration is reduced and a radius of curvature limit of 4 km has been obtained in situ. This technique also enables us to obtain a 2-dimensional profile of the surface curvature from the simultaneous reflection of a rectangular array of beams. Results from the growth of SiGe alloy films are presented to demonstrate the unique information that can be obtained during growth.

Void and hillock formation during annealing was studied depending on the deposition conditions. Aluminum films were deposited onto oxidized silicon substrates by the self-ion assisted technique. The bias 0 or 6 kV was applied to the substrate during deposition. The films were then annealed in vacuum for 1 hour in the temperature range from 150° to 550°C. The structure of the films was investigated by transmission electron microscopy. The void and hillock formation was studied with optical and scanning electron microscopes.

It was found that recrystallization and void and hillock formation in the films depend on the bias during deposition. Normal grain growth occurred in the films deposited without bias. Abnormal grain growth was observed in the 6 kV-films. It was also found that the mechanism of stress relaxation during thermal cycling depends on the self-ion bombardment. In the films prepared without bias, stress relaxation proceeds by diffusion creep. In the films deposited at the 6 kV bias, stress relaxation proceeds by plastic deformation.

Passivated metal lines, commonly used in integrated circuits, show thermally induced stresses due to the difference of the thermal expansion coefficients of the lines and their surroundings. These stresses cause voidage and plastic flow of the lines. Aim of the analysis was to derive equations connecting experimentally measured strains or stresses by the X-ray diffraction and wafer curvature techniques with the magnitude of voidage and plastic shear deformation of the lines.

Using the concepts of linear elasticity the volume averaged stresses of an array of parallel interconnects embedded in a passivation layer on a flat substrate are analysed. Equations are derived connecting the volume averaged stresses in the metal and in the passivation with the “Heigen-strains” of the metal which characterize the true (stress free) thermal strains and plastic deformation strains of the metal. The coefficients entering these equations are determined from (elastic) finite element method (FEM) calculations performed for various geometries and aspect ratios of the metal lines. Choosing the proper values of the coefficients allows the eigen- strains to be determined from the experimental data.

By comparison of the evaluated eigen-strains with the purely elastic eigen-strains ΔαΔT the extent of voidage and/or plastic shear deformation of passivated metal lines caused by thermally induced stresses can be determined model independently.

The evolution of stresses due to the patterning and thermal loading of thin lines on Si wafers, and the consequent changes in the overall curvature of the wafer are studied theoretically and experimentally. The analysis involves finite element simulations within the context of generalized plane strain models. The analysis is capable of predicting the wafer curvature in directions parallel and perpendicular to the lines. These predictions compare reasonably well with experimental measurements of curvature made on model systems. The thickness, width and spacing of the patterned lines have been varied systematically, and the associated changes in the evolution of stresses and curvature have been determined. The non-uniform stress field within the fine lines is also analyzed.

Mechanical stress and its relaxation in aluminum metallization in integrated circuits (IC) are a major concern for the reliability of the material. It is known that adding Cu improves the reliability but complicates plasma etching and increases corrosion sensitivity. The mechanical behavior of AlVPd, AlCu and Al blanket films is investigated by wafer curvature measurements. During thermal cycling between 50°C and 400°C the highest tensile stress is found in AlVPd. In a subsequent experiment, the cooling was interrupted at several temperatures to investigate the stress behavior during an eight hour isothermal treatment. Isothermal stress relaxation has been observed in the three types of films and is discussed.

800 nm thick and 1μm wide Al-1wt.%Si-0.5wt.% Cu parallel lines with 1 μm spacing were passivated with PECVD oxide, oxynitride or nitride. Substrate curvature measurements as a function of temperature and XRD-measurements at room temperature were used to characterize macroscopic samples of these parallel Al-Si-Cu-lines. By using both techniques the average inplane stresses for the Al-Si-Cu lines as well as for the covering passivation material can be determined as a function of temperature. The highest and lowest stresses in the Al-Si-Cu are observed for lines with nitride and oxide passivations, respectively. Also the number of voids in the lines after a storage test at 250 °C is clearly highest for a nitride passivation and lowest for an oxide passivation.

The stress in the passivation itself and its temperature dependence is found to be very different from the stress in a blanket passivation film.

Al and Al- alloys are commonly used as interconnect materials in integrated electronic devices. Stress induced voiding and degradation of metal lines by electromigration are closely related to the stresses in the lines.

We have studied the strain and stress evolution during thermal cycling, isothermal relaxation and due to electromigration in passivated Al and AlSi(l%)Cu(0.5%) lines by X-Ray diffraction with variation of experimental parameters such as the aspect ratio and the electrical current density. Furthermore the extent of voiding and plastic shear deformation has been determined from the experimental metal strains with the help of finite element calculations.

Main results are: 1) During thermal cycling the voiding is less than 2 ·10−3. The extent of plastic shear deformation increases with increasing line width and with decreasing flowstress. 2) During isothermal relaxation void growth occurs but no significant change in the plastic shear deformation. 3) An electric current in the lines causes no measurable additional change of the volume averaged stresses up to line failure.

Stress, giant magnetoresistance (GMR), structure, and magnetic properties of sputtered (Co90Fe10X Å/Ag Y Å)×20 multilayer films have been investigated at room temperature where X ranges from 7.5 to 25 Å and Y from 10 to 60 Å. These films exhibit distinct GMR behaviors dependent on individual layer thicknesses, including layered granular-type GMR in CoFe 7.5 Å samples and ‘discontinuous’ GMR (DGMR) in CoFe 15 and 25 Å samples with Ag thicknesses over 30 Å. No antiferromagnetic coupling was observed. CoFe 10 Å samples act as a transition between GMR behaviors. Compressive stress decreases with increasing Ag thickness in the CoFe 7.5 Å samples. In the CoFe 15 and 25 Å samples the stress fluctuates similarly depending on Ag thickness. The difference in stress and MR behavior between the CoFe 7.5 Å and the 15 and 25 Å samples is thought to be due to incomplete CoFe layering in the CoFe 7.5 Å samples. In the CoFe 15 Å DGMR samples, high temperature annealing resulted in tensile stresses large enough to cause film detachment. X-ray diffraction reveals a strong (111) growth texture as well as satellite peaks from coherent layering. This (111) texture is also evidenced by patterns with hexagonal symmetry formed by the detached films.

The electrical properties of vacuum sublimed thin films of TTF-TCNQ and its derivatives mainly are determined by electron barriers at grain boundaries. The electrical conductivity is thermal activated and exhibits a significant dependence on a force acting perpenticularly to the film plane. The sample resistance R decreases continiously with increasing force F. TCNQ thin films on steel show a similar R-F relation. The effect has been observed already at forces of 1 N, but also up to about 60 kN. An explanation of these phenomena is given by a grain boundary limited hopping mechanism with pressure dependent potential barrier width and height. Morphology investigations by SEM support the model.

We have grown and characterized epitaxial NbxTi1-xO2 on TiO2(110) and (100) for the purpose of investigating the role of chemically-inequivalent metal atoms on the thermal and photocatalytic properties of TiO2. Our goal is to introduce, in a highly controlled fashion, a Group VA transition metal into the lattice of a Group IVA transition metal oxide without altering the crystallographic structure. So doing would alter the electronic structure in interesting and potentially useful ways by the addition of one valence electron per substituted metal atom. However, strain builds in the film as more Nb is added at a rate which depends on the crystallographic orientation of the growth direction. Films grown along (110) can accommodate Nb mole fractions as high as ˜0.3 without forming misfit dislocations, whereas those grown along (100) are limited to ˜10 at. % Nb. Nb-O bond lengths in NbxTil−xO2 are the same as Ti-O bond lengths in pure TiO2 prior to the onset of dislocation formation. The extra 4d valence electron per Nb atom forms a nonbonding band which is degenerate with bonding states in the valence band region.

Heteroepitaxial Si1-xGex. thin films deposited on silicon substrates exhibit surface roughening via surface diffusion under the effect of a compressive stress which is caused by a lattice mismatch. In these films, surface roughening can take place in the form of ridges which can be aligned along <100> or <110> directions, depending on the film thickness. In this paper, we investigate this anisotropic dependence of surface roughening and present an analysis of it. We have studied the surface roughening behaviour of 18% Ge and 22% Ge thin films subjected to controlled annealing experiments. Transmission electron microscopy and atomic force microscopy have been used to study the morphology and microstructure of the surface ridges and the dislocations that form during annealing.

Strained islands grown coherently on a relatively thick substrate with similar elastic properties are considered within the framework of continuum mechanics. The condition of uniform surface chemical potential is imposed to calculate two-dimensional equilibrium island shapes. The stress distribution in the equilibrium islands is shown to be highly nonhomogeneous. The effects of introducing a single misfit dislocation at the island-substrate interface are considered. It is found that there is critical island volume above which a dislocation decreases the total free energy of the system. The dislocation alters the stress distribution in the island, causing the island to relax via mass transport to an equilibrium shape with a lower height-to-width aspect ratio and a smaller surface chemical potential than the island prior to the introduction of the dislocation.

AlxGa1-xP layers (0 ≤ x ≤ 0.7), with thicknesses of ≤ 1 μm were grown on Si (100) wafers by metal-organic molecular beam epitaxy (MOMBE) at 450 °C. Transmission electron micrographs of the single crystal films revealed that the microstructure contains stacking faults and microtwins especially near the interface as well as both threading and misfit dislocations. Hardness and elastic modulus were measured using a Nanotest 500 indenter, which can probe the film properties without influence from the substrate.

The hardness H varies linearly according to (11.8 - 2.3x) GPa. The absence of alloy hardening is due to the fact that there is no difference in atomic size of Al and Ga. The indentation modulus E/(1-v 2) decreases monotonically from 136 GPa for GaP to 129 GPa for Al0.7Ga0.3P and bows only slightly (about 2 %) below the straight line of linear interpolation.

Both the sign and magnitude of residual stress can vary with the thickness of sputter deposited films. The origins of this behavior are not well understood. In this work, we consider the correlation between the residual stress behavior and the depth dependence of impurities in thin (2.5 nm - 150 nm) sputtered Mo and Ta films. We also consider the effects of phase transformations and microstructural changes on the stress behavior. Films were deposited onto Si substrates with native oxide. The residual stress observed in the Mo films varied from highly compressive at 2.5 nm film thickness to ∼ 0 ˜ 10 nm thickness. Ta films also exhibited a high compressive stress, which relaxed from highly compressive to tensile between 10 nm and 50 nm film thickness. Impurities in the films may originate from the sputtering targets, the background gases, and the substrate surfaces. Auger Electron Spectroscopy (AES) results showed the presence of O and C contamination near the film/Si interface; these impurities contributed to the compressive stresses in the thinner films. As anticipated, both Mo and Ta films exhibited grain growth as a function of film thickness, which may have contributed to the relaxation in the compressive stress. The Mo films were entirely bcc. The Ta films showed a transformation from the amorphous phase to the β crystalline phase between 2.5 nm and 20 nm film thickness, which contributed to the relaxation in stress observed in that thickness regime.

By exploiting the strain dependence of the ruby luminescence line, we have measured the strain in alumina scales thermally grown on Fe-Cr-Al alloys. Results are compared, and found to be reasonably consistent with strains determined using x-rays. Oxidation studies were carried out on alloys with compositions Fe - 5 Cr - 28 Al and Fe - 18 Cr - 10 Al (at. %, bal. Fe). Significantly different levels of strain buildup were observed in scales on these alloys. Results on similar alloys containing a “reactive element” (Zr or Hf) in dilute quantity are also presented. Scales on alloys containing a reactive element (RE) can support significantly higher strains than scales on RE-free alloys. With the luminescence technique, strain relief associated with spallation thresholds is readily observed.

A model is developed to understand the morphological stability of a SiC film on a Si substrate during carbonization where the Si substrate is exposed to a carbon precursor. The morphological stability is determined by considering the surface evolution along a slightly wavy film surface and film-substrate interface. The morphological evolution along the film surface is dominated by surface diffusion and along the interface by a chemical reaction. The kinetic analysis shows the stability is controlled by the film surface energy, the interface energy, the diffusion-reaction process of the carbon precursor, and the strain energy. At small wavelengths of the surface profiles, the two types of surface energy dominate, which results in stable morphology. The diffusion-reaction process dictates the surface stability at large wavelengths. The strain energy may cause the surfaces to become unstable at moderate wavelengths; the instability can be completely suppressed by the diffusion-reaction process and the film surface energy, while it is enhanced by a large value of interface energy.