Thermal hillocks in sputter-deposited Al films have been studied as a part of a broad study of stress-induced diffusional processes in Al. Trace amounts of the impurities Ti, W, and O were incorporated into the films during deposition, causing them to be much stronger than most sputter deposited Al films. Stress measurement during thermal cycling, using the wafer curvature method, showed that these Al films are very strong; this finding was corroborated by hardness measurements. Microstructural studies using TEM and FIB showed that the hillocks start to form at the Al/SiO2 interface and grow under the original Al film, with its columnar grain structure. In some cases, the film fails as hillocks grow completely through the original film. The Al film on top of the hillocks appears to inhibit hillock growth by creating a back pressure associated with power law creep of the film. We modeled this form of hillock formation by modifying the boundary conditions in Chaudhari's hillock model [1]. Our model describes hillock formation by diffusion of Al atoms from the surrounding area into isolated hillocks, assuming that the original Al film on top of hillocks deforms following power law creep. Our model can be applied to many different situations by using different creep laws for the top Al film.

Free-standing rectangular Al thin films have been fabricated using sputter deposition and standard micromachining techniques. Mechanical properties and residual stresses of both asdeposited and annealed Al films were measured by bulge testing. The films were loaded into the plastic deformation regime, and then unloaded and reloaded several times. The pressure and deflection of the thin films were recorded and used to generate stress-strain curves. The planestrain elastic modulus, flow stress and plastic behavior of the Al thin films were used to characterize the mechanical response of these films. The Al films were measured to have a plane-strain modulus that is slightly lower than the literature values for a {111} textured film. The Von-Mises equivalent yield stress was measured to be higher in the annealed films but much more significant strain hardening was observed in the as-deposited films. A plastic hysteresis was observed on unloading and reloading stress-strain curves of the as-deposited Al films but not the annealed films.

In this paper, a detailed analysis of silicide induced stress is presented. Micro-Raman spectroscopy measurements of the silicide induced stress in the silicon substrate are combined with simulations by Finite Element Modeling down to 0.1 μm MOS technologies. It is shown that the scaling possibilities of TiSi2 and of CoSi2 are both hampered by the increasing silicide stress, which can even result in the generation of dislocations in the silicon substrate. Because of the difference in material properties between TiSi2 and CoSi2, TiSi2 induces a higher stress in the silicon substrate than CoSi2. It is also proven that the silicide induced stress affects the performance of transistors and diodes. Therefore, the mechanical characteristics related to the silicide formation become a critical parameter in the optimization of the silicide for sub-0.25μm MOS technologies.

It has been long recognized that excess point defects are generated when a metal silicide is formed on silicon. Since the common dopants diffuse in Si with the aid of both self-interstials and vacancies, these point defect perturbations will influence motion of diffusions that are in the adjacent vicinity. TiSi2 is known to enhance the concentration of vacancies and several mechanisms have been proposed for this effect. Recent literature has dealt with and rejected many of these ideas; however, some of the remaining few like film strain and lattice contraction upon silicidation have been the subject of state of the art experiments which has led to their rejection.

It is the contention of this paper that by using the experimental data from this recent work and reinterpreting it, the model of volume contraction of the silicides as the cause for vacancy injection, still represents the most physically satisfying cause and therefore, was mistakenly rejected.

Mismatch stress relaxation mechanisms in bilayer films of (In, Al)As on InAs on GaP have been examined. Initial edge (90°) misfit dislocations at the InAs/GaP interface appear to be introduced directly at island edges during initial stages of growth. The incomplete mismatch compensation is taken up by later introduction of glissile (60°) dislocations, usually in pairs which combine to form edge dislocations. The edge dislocations in the interface then move laterally to equalize their spacings. The upper (In, Al)As capping layer, which is tensile strained to match the relaxed InAs, exhibits a different mechanism of misfit dislocation introduction. Threading dislocations move by climb, directly introducing sessile edge dislocations at the buried interface. It is believed this is the first time that this mechanism has been observed.

This study explores stress relaxation of epitaxial SiGe layers grown on Si substrates with unique orientations. The crystallographic orientations of the Si substrates used were off-axis from the (001) plane towards the (111) plane by angles, θ = 0, 10, and 22 degrees. We have grown 100nm thick Si(1−x) Ge(x) epitaxial layers with x=0.3 on the Si substrates to examine the relaxation process. The as-deposited films are metastable to the formation of strain relaxing misfit dislocations, and thermal annealing is used to obtain highly relaxed films for comparison. Raman spectroscopy has been used to measure the strain relaxation, and atomic force microscopy has been used to explore the development of surface morphology. The Raman scattering indicated that the strain in the as-deposited films is dependent on the substrate orientation with strained layers grown on Si with 0 and 22 degree orientations while highly relaxed films were grown on the 10 degree substrate. The surface morphology also differed for the substrate orientations. The 10 degree surface is relatively smooth with hut shaped structures oriented at predicted angles relative to the step edges.

The relaxation for large lattice mismatch systems such as GaSb/GaAs and GaAs/InP has been studied by numerical analysis of HREM images. The GaSb/GaAs epitaxial system can be obtained with an interface constituted by a perfect square array of Lomer dislocations. GaSb appears to be coherently and homogeneously relaxed. For GaAs/InP grown at 450°C the GaAs layer becomes well relaxed at some distances from the interface by a network of randomly distributed partial and 60° dislocation segments with a limited length. At low temperature, the plastic relaxation appears directly at the growth front when the individual adatoms take a position different from the ideal pseudomorphic one. In this case, the relaxation mechanism is incoherent.

We summarize here the results of recent experimental and analytical investigations into stress effects in planar SiO2 thin films. Experimentally, we examine the effects of a constant superposed in-plane stress upon the growth of thin oxide films in the 100 Å range. In contradiction to a widely accepted model of stress effects upon SiO2 film growth, we find that both compressive and tensile in-plane stresses tend to retard oxide growth by a roughly equal amount. Analytically, we investigate the effects of the small component of strain induced parallel to the oxidation interface by the large volume expansion inherent in the oxidation of silicon. Depending upon the circumstances, this strain component, dubbed the “intrinsic strain”, can have a non-negligible effect upon the growth of planar oxide layers.

We have investigated nano-structured multiphase coatings consisting of mixed carbide components. Two ternary carbide systems, Ti-Mo-C and Ti-Si-C, were examined. Coatings were fabricated by co-sputtering from carbide targets, thereby allowing a complete range of film compositions to be obtained in each system. Films were deposited on Si and sapphire substrates at temperatures ranging from room temperature to 650°C. Film compositions were determined using XPS, and x-ray diffraction and TEM analysis were used to examine the films for texture, grain size, phase stability and the potential for creating nano-structured multiphase films. Mo was found to be soluble in TiC up to about 80% Mo, and between 85–95% Mo a multiphase structure was obtained. The hardness of these films generally did not improve due to the Mo additions. For the Ti-Si-C films, X-ray diffraction results were consistent with the formation of cubic SiC and TiC phases. In these films, the hardness was found to improve with SiC additions optimally giving hardness values of about twice that of TiC alone.

X-ray double- and triple-axis diffractometries were employed to characterize the strain status and structural deformation in Si0.7Ge0.3 alloy layers grown on Si (001) substrates. We show that, at low levels of strain relaxation, x-ray peaks of the Si0.7Ge0.3 alloy layers contain two components, a narrow one superimposed on a broad one. Such a peak profile corresponds to a layer structure consisting of mosaic regions laterally separated by more perfect regions. With the increase in the degree of strain relaxation and consequently in the dislocation density, the narrow component of the x-ray peak gradually disappears as a result of expansion of the mosaic regions and shrinkage or even vanishing of the perfect regions in the layer. Moreover, our results indicate that the conventional method of estimating dislocation density from the x-ray rocking curve width fails in our case.

Biaxial modulus and residual stress of silicon-rich silicon nitride (Si3 + xN4−x) films on silicon substrates were measured at multiple discrete locations across wafer surfaces using a versatile bulge testing method. An array of 0.2 μm thick silicon nitride membranes were fabricated across the surface of 100 mm diameter wafers. The membranes were 1 mm square. Material properties of the film were extracted by measuring the deflection of the silicon nitride membranes under controlled pressure loading conditions. Pressures from 0 to 12 psi were applied across the membranes, while their deflected shapes were measured with a white light interferometer. Numerical analysis of the measured pressure-deflection behavior of the membranes enabled the biaxial modulus and residual stress of the film to be mapped over the wafer surface. These initial results indicated that the technique was able to determine biaxial modulus to within ±1 % and residual stress within ±4 %. Furthermore, the technique can be applied to composite membranes, enabling the determination of biaxial modulus and residual stress of an additional film subsequently deposited upon the membrane film.

The fatigue behavior of bilayer microbeams consisting of thin Ag films on an SiO2 substrate was investigated. The beams were cyclically deflected using a commercial nanoindentation instrument, which is capable of precise positioning of indentations. The dynamic beam stiffness is monitored continuously throughout the whole experiment. Silver was chosen as a model material for fcc metals. For large strains and/or strain amplitudes the beam stiffness decreased significantly during the fatigue tests, which is related to damage formation, as cracks and extrusions were found after the experiment. In fatigue tests at lower strains and the same number of cycles no significant stiffness change was observed. In this case only extrusions but no cracks occurred.

A micro instrument is developed to apply force on free standing cantilever samples with suborm thickness. The objective is to study the effect of small thickness on the strength of materials when subjected to bending. The instrument consists of a MEMS actuator, 2mm × 3mm in size, and 20μm deep. It is employed to study an annealed Al cantilever sample, 110nm thick, 2μm wide and 15μm long, fabricated by evaporation. The sample yields at 841M Pa during the first cycle of loading. It is then unloaded and reloaded, when yielding occurs at 1200M Pa. To the best of our knowledge, this is the first reported experiment on free standing submicron metal film subjected to bending.

The performance of microelectromechanical systems (MEMS) switches is highly dependent on the switches' constituent materials. The switch material must be able to provide both structural integrity and high electrical conductivity. Cantilever beams, doubly clamped beams, and membranes are typical MEMS structures used in microwave/millimeter wave applications. In this study, cantilever and doubly clamped beam microswitches were fabricated on GaAs substrates using evaporated bilayers of titanium and gold metallization in which the total thickness was held constant at 1.5 μm while the gold thickness varied from 0.5 μm to 1.5 μm. The lengths of the cantilevers varied from 300 to 500 μm and the doubly clamped beams varied from 600 to 800 μm. An upward deflection of the gold dominated cantilever beams indicated an increasing tensile stress gradient. Results of microwave characterization demonstrated higher switch isolation (off-resistance) for shorter beam switches at the expense of higher insertion loss (on-resistance) and actuation voltage. A discussion of the observed released microswitch structure within the context of the measured film stresses and electrical performance will be presented.

Pure cobalt shows a martensitic transformation from a face-centered-cubic to an hexagonal-close-packed phase. In this work it is chosen as a model-system to investigate the influence of film thickness, film stress and microstructure on the martensitic transformation in thin films.

Co films of 0.2 μm to 3.0 μm thickness were sputter-deposited on Si substrates. This paper presents wafer curvature measurements during temperature cycles of these films and results obtained by focused ion beam microscopy. Upon repeated thermocycling, the martensitic transformation was repeatedly observed in 3 μm thick films, whereas it was not found in 0.2 μm Co films. A stress drop on heating as well as on cooling accompanied the martensitic transformation. It was observed that the stress level at which the transformation occurs can be changed by varying the film thickness or maximum temperature of the temperature cycles. As a result, the martensitic start temperature decreases with increasing stress. It is concluded that the film stress is a critical parameter which strongly affects the martensitic transformation.

Piezoelectric films are attractive materials for use in microelectromechanical systems (MEMS) due to their ability to act as both sensors and actuators. One of the primary modes of deformation is the deflection of lead zirconate titantate (PZT) beams and membranes, where the adhesion of the film is critical for the reliability of the device. Thin films of PZT between 250 and 750 nm have been grown via solution deposition routes onto platinized silicon substrates. The films have been tested using nanoindentation techniques. Two failure mechanism in these films have been observed Indentation induced delamination at the PZT-Pt interface occurs after the indenter tip is removed from the film when loads between 1 and 10 mN are applied to the sample, and at large loads (>75 mN) failure can be generated between the underlying oxide film and the silicon substrate while the tip is still engaged with the sample. Since each of these failure modes has a different mechanics solution, the results are compared to determine adhesion energy of the films. Fracture around the delaminated regions has been examined using scanning probe and electron microscopy. Freestanding PZT membranes above micromachined cavities have been mechanically deformed to examine the mechanical response and failure modes in these structures. The adhesion of the PZT improves with increased percent crystallization due to the introduction of residual tensile stresses. Processing, mechanical properties, and failure modes in these devices will be discussed.

The magnitude and origin of residual stresses in thin polysilicon MEMS structures are discussed in this article. The curvature of polysilicon beams were determined at different temperatures. An accurate method of analysis that avoids the thick substrate approximation is described. The polysilicon beams without an Au layer exhibited temperature-independent curvatures, indicating that their residual stresses were largely process related. Beams with an Au top-coat exhibited a strong temperaturedependent effect, and allowed derivation of a stress-free temperature of 143°C. The technique allowed an independent estimate of the thermal expansion coefficient of polysilicon, namely 2.5×10−6 to 3.1×10−6/°C.

Residual stresses in thin films play an important role in the mechanical behaviour of MEMS. In this paper we present a study of the stress and its relaxation for the PZT films, and associated electrodes, deposited on oxidized silicon substrates. The stresses were calculated from the bending plate method and the Stoney's equation. The radius of curvature were measured by optical profilometry before and after films deposition. The substrates (180 μm Si + 0.66 μm thermal SiO2) were coated with sputtered Ti (20 nm) and Pt (200 nm) used as bottom electrode. The global stress in the Ti/Pt layer was found compressive (−1.29 GPa) after deposition and tensile (465 MPa) after annealing (400°C, 30s, Ar). A 0.55 μm thick PZT layer was RF-magnetron sputtered and crystallized by a RTA (700°, 30s, Air). The as-deposited PZT films exhibited a little tensile stress of 43 MPa. After annealing, a tensile stress value of 363 MPa was found. Finally, we observed that the stress of the whole multilayer showed a decrease as a function of time. In order to explain this phenomenon, depth profile of each component of the PZT layer were obtained by Secondary Ion Mass Spectrometry (SIMS). This time-dependent stress relaxation was then correlated to a lead and oxygen migration across the PZT layer.

Humidity and temperature control accessories for Hysitron Triboscope have been developed to study the environmental influence on in situ properties of drying coatings. Mechanical properties of drying poly (vinyl alcohol) (PVOH) and poly (vinyl pyrrolidone) (PVP) coatings on silicon wafer were measured under different humidities. The modulus results were compared with outputs of elastic, plastic and viscoelastic theories of indentation testing.

Dynamic properties of polymer surfaces affect their ability to withstand abrasive actions. Kinetic conditions, like velocity, penetration depth and shape of the abrasive particles, change the abrasion mechanisms and the morphology of the abraded surface. Using the scratch technique, along with profilometry measurement across the scratches, we have been able to completely characterize the residual scratch morphology. Pile-up deformation and visco-plastic relaxation are key phenomena that characterize the importance of ductility in the scratch resistance of polymer surfaces. Cross profilometry aids in studying the relaxation of the scratch morphology for different time and temperature history after the scratch is made. The effect of scratch velocity, penetration depth and indenter geometry on the contact pressure and friction coefficient estimated during a scratch test can also be analyzed. Following Eyring's law, a good correlation, was found between normal indentation and scratch testing in the evolution of the contact pressure with the applied strain rate. This work results in a better understanding of the stresses and the strains applied by an abrasive particle, and especially relates the dynamic mechanical properties of viscous materials, like stress exponent, to their scratch behavior. The method presented can provide for the measurement of dynamic properties of polymer surfaces or thin films under a very large range of strain rates.