Microsensors are measurement devices fabricated using planar integrated circuit technology together with enhancements generically called “micromachining”. It is well known that the thin-film materials used in microelectronics can have properties which differ from their bulk counterparts. In addition, thin-film materials exhibit residual stress, which is known to be strongly process dependent. The sensor designer must understand how the detailed process used to fabricate a particular device impacts the specific mechanical properties, hence, the expected mechanical device performance. This paper illustrates the problem of process-dependent material properties using examples of residual stress of several materials, and then presents an object-oriented material-property database which is being developed as part of a CAD system for microelectromechan-ical systems (MEMCAD).

Characterization of undoped polycrystalline silicon films indicates that correlations exist between stress and microstructure. Films of thickness between 0.5–3.6 μm were deposited onto SiO2-covered single crystal silicon wafers between 605 and 700°C using low pressure chemical vapor deposition (LPCVD). The average in-plane film stress and the stress gradient through the film thickness were determined from wafer curvature measurements, and film microstructure was studied with cross-sectional TEM. Films deposited near 605°C exhibit overall tensile stresses that result from an amorphous to crystalline phase change. At deposition temperatures exceeding 630°C, a columnar grain structure evolves out of a transition region of small grains at the SiO2 interface. The columnar films are compressive, with the source of compression linked to the region of small grains. Stress is modeled using a closed form solution ihat considers a linearly elastic contracting ellipsoidal inclusion near the surface of a half space. Several applications of the stress model are discussed.

Cu/Zr-type multilayers prepared by cold-rolling have been subjected to cold and hot pressing until the onset of crystallization. It is found that application of a uniaxial stress perpendicular to the plane of the layer interfaces accelerates both the growth rate of amorphous interlayers and the onset of subsequent crystallization. These effects have been attributed to stress-induced flow parallel to the interfaces that helps relax diffusion-induced internal stresses and increases interfacial reaction constants controlling crystalline layer formation at the amorphous/Zr layer interfaces.

In this paper the results of experiments are summarized in which the internal stress (i.e. force per unit width) of thin films was measured in situ under UHV conditions with a bending beam apparatus. It is demonstrated that characteristic types of stress vs. thickness curves can be correlated with different growth modes (i.e. columnar grain growth and island growth) caused by differences in the adatom mobility of the deposited material. With a selection of thin film systems it is then shown that stress measurements can be used to study the effect of gas incorporation, of gas diffusion from the substrate, of reaction with the substrate and of the substrate temperature on the growth and structure of a thin film. Finally it will be demonstrated that stress measurements can even be used to study gas adsorption on vapor deposited films.

Wafer bending measurements have been used to study the glass transition temperature, Tg, of thin coatings of polystyrene and polycarbonate on Si wafers. The observed values of Tg agree with DSC and TMA measurements on bulk samples. The evolution of the substrate curvature has been used to examine the behavior of Tg in thin epoxy films and coatings derived from divinylsiloxane bisbenzocyclobutene, mixed stereo and positional isomers of 1, 3-bis(2-bicyclo[4.2.0]octa-1, 3, 5-trien-3-ylethenyl)-1, 1, 3, 3-tetramethyl disitoxane (CAS 117732–87–3). The dependence of the Tg of the epoxide coatings is studied as a function of the cross-linking. The evolution of the Tg in the benzocyclobutene coating is found to be a monotonie function of the level of conversion of the polymer network.

The effect of deposition parameters on the properties of sputtered Be films has been studied. The parameters have been optimized to obtain stress free films. Nitrogen pulsing has been used to improve the film microstructure by suppressing the columnar grain growth.

We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized <100> silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

Stress and structure evolution in thin films of sputtered Mo on Si(100) substrates has been studied, as a function of microstructure, by x-ray diffraction, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). Double crystal x-ray diffraction topography (DCDT) has been employed to determine film stress as a function of thickness. High compressive stress, about 1000 MPa, is found for the thinnest Mo film. With increasing film thickness a minimal residual stress level is reached. Low incidence angle x-ray diffraction patterns indicated that crystalline Mo is present even in the thinnest films. Line broadening of the Mo(l10) diffraction peak has shown that the grain dimension is comparable to the film thickness over the range studied. Plan view TEM observations of films less than 20nm demonstrated the presence of continuous film with grain dimensions on the order of film thickness, in good agreement with the x-ray results.

Co-Cr alloy thin films are considered as an applicable perpendicular magnetic recording medium, and their mechanical properties such as internal stress can not be neglected. In this experiment, Co-Cr films are deposited on glass substrates by D. C planar magnetron sputtering, and the effects of film thickness, Ni-Fe underlayer as well as substrate temperature on the stress are studied respectively. The stresses are all tensile in all cases, and the stress existing at the film-substrate interface is very small. According to the above experimental results and the structure analysis of the films, the atomic peening effect produced by the rebounded working gas atoms can be negligible, and the stress is thought to originate from the film growth process but not from the inter-facial effect. Therefore, the structural defect elimination model is proposed (here the defects mainly include vacancies and grain boundaries). With this model, the origin of the tensile stress as well as the relations between the stress and the deposition conditions are explained qualitatively.

As device dimensions decrease in silicon integrated-circuits, conventional LOCOS (local-oxidation of silicon) isolation becomes inadequate to meet dimensional demands. Variations on LOCOS are therefore being explored for further miniaturization of devices. One such variation involves poly-buffered LOCOS + trench-isolation (PBLT). In this study, PBLT structures were characterized using TEM. Wright-etched cross-section SEM micrographs showed etch-pits associated with a combination of high-dose (> 5E14 cm-2) phosphorous implants and PBLT isolation. TEM characterization showed that dislocations were formed in the structures for a combination of high-dose (1E15 cm-2) phosphorous implants (followed by an anneal) and PBLT isolation. Structures exposed to lower-dose (1E14 cm-2) implants showed no defects and neither did 1E15 implanted structures prior to annealing. The results are modelled in terms of the stress configurations present in the structures, and in terms of dislocation-sources resulting from implantation-related dislocation-loops. The dislocation-sources operate in the presence of stresses associated with the isolation-trenches. Glide-loops form, which then grow in response to stresses in the structures and dislocations result on glide planes.

An ionized cluster beam (ICB) source was used to deposit Pd onto oxidized silicon substrates. The ICB source was operated in both the neutral mode (no ionization and no acceleration) and in the ICB mode with ionization and acceleration voltages at 3 kV and 6 k.V. Also, substrate temperatures were varied between 100°C and 400°C. The Pd film thicknesses were generally between 1, 200Å and 1, 800Å, with one film thickness about 500Å. The films were examined by transmission electron microscopy (TEM), transmission electron diffraction (TED), and x-ray diffraction (XRD). Grain size measurements by TEM and XRD showed that ionization and acceleration of Pd resulted in a slight increase in grain size compared to films deposited without ionization or acceleration at any substrate temperature. However, the grain size increased significantly as the substrate temperature rose. XRD showed that all ICB deposited Pd films have significant (111) texturing as determined by comparison to XRD data for Pd powder. For Pd films deposited at 400°C, almost all grains were oriented with the (111) planes parallel to the substrate surface. The electrical conductivity of all Pd films was comparable to that of bulk Pd.

We have investigated the influence of strain on the rate of thermal oxidation of crystalline Si. This was carried out by performing the oxidation in two steps at 850°C with an intermediate annealing step. It was observed that an anneal at 1050°C increased the oxidation rate 20% compared with an anneal at 850°C. At the same time, the films annealed at higher temperatures exhibited lower levels of strain, as determined by infrared spectroscopy, in the oxide layer grown before the anneal. These results have been interpreted in terms of a strain dependent diffusion model for the thermal oxidation process.

The present study describes the measurement of microcrystalline grain dimensions and crystallite strain for polycrystalline silicon (poly-Si) and titanium suicide, using grazing incidence X-ray diffraction (GIXRD). A variety of poly-Si sample configurations were synthesized by different low pressure chemical vapor deposition (LPCVD) processing techniques. Selected samples were subsequently processed by phosphorous diffusion doping and reaction with thin titanium layers. Characterization with GIXRD reveals differing crystallite grain dimensions, ranging from =80Å to =900Å. Crystal strain was measured in direction perpendicular to (111) lattice planes. Phosphorous diffusion doping is shown to remove this (111) strain, in addition to increasing crystallite grain dimensions. The GIXRD characterization, which measures a specific fraction of the sample crystal texture, indicates that deposition rate modulated poly-Si LPCVD reduces (111) microscopic strain in poly-Si films two-fold, compared to conventional poly-Si deposition. The crystallite dimensions of conventional poly-Si, are found to peak approximately in direction perpendicular to (110) planes. The same trend is observable for deposition rate modulated poly-Si, where grain dimensions, measured in [110] direction, are reduced by =30%. Larger crystallite dimensions were measured in direction perpendicular to (110) planes, for both cubic poly-Si and orthorhombic Ti-silicide layers, suggesting the presence of preferred crystallite growth directions, resulting in anisotropie crystallite grain dimensions.

The microstructure, of unannealed and annealed polysilicon films was studied using TEM and XRD. The LPCVD films were grown at 600°C and 620°C with 320 mTorr of silane, and at 580°C with 220 mTorr of silane. The substrates were [001] Si with a thin oxide film. The stress state of the films changed from compressive at 580°C and 620°C, to tensile in a narrow region around 600°C. The same materials were annealed at 1100°C. The unannealed films vary from partially amorphous at 580°C, where the slowest growth rate was observed, to randomly oriented and equiaxed at 600°C, to columnar and highly oriented at 620°C. The grains in the 620°C material have a high stacking fault and polytype density, and it was proposed that these occurred on growth, and not from dislocation motion. The grain size increased from 40–250run to 100–300 nm in the 600°C samples when annealed at 1100°C, and the density of twins and stacking faults was reduced. The hexagonal phase was observed only in unannealed materials in SAED and as broad “wings” at the base of the llld.c (diamond cubic) peak in XRD. Within the limits of SAED, no change in lattice parameter of the hexagonal phase was observed.

Thin films of Cu and Cu on Ti were prepared by sputtering films onto SiO2 substrates. The films were annealed at temperatures between 350 and 400°C in vacuum and hydrogen ambiente. The stress was measured in-situ during the anneals. The stress in vacuum initially was compressive, then became tensile and remained so. The stress in hydrogen started in compression and remained so throughout the anneal. The origin of these stresses is explained as a result of compound formation. In vacuum anneals, TiCu forms during the compressive stage with an activation energy of 1.7 eV, then TiCu3 forms during the tensile stage with an activation energy of 2.5 eV. In hydrogen, a single compound, TiH2, forms under the Cu with an activation energy of 0.93 eV.

Studies on the Cu films indicate that hydrogen reduces the incremental stress formed in the films during annealing. A possible explanation is presented for the stress change in that hydrogen has been shown to assist in annealing dislocations. Experimental evidence of an instantaneous change in the stress state upon the introduction of a new ambient is also presented.

Thermal oxidation of different crystallographic surface orientations of Si reveals a complex rate behavior not only in the initial stage but also in sequential two step oxidation with high temperature annealing where enhanced oxidation is observed as well. These phenomena are explained by the reduction of oxygen solubility in SiO2 due to stress in the SiO2 film, which has been confirmed by isotope labeling oxidation with SIMS analysis.

Stress generated by thermal annealing of thick parylene-n (PA-n) films (4–7 μm) has been studied. We examined the behavior of stress for as-deposited films and rapidly thermally annealed films. The annealing was done in vacuum and the stress measured after the anneal. In another experiment the stress was also studied in-situ with thermal annealing. The as-deposited films are under compressive stress of about 18 MPa. When the backside film was removed by plasma etching, the stress changed from compressive to tensile. As the films are annealed, the stress decreases and then becomes tensile, peaking at about 60 MPa. The film crystallinity and stress are correlated for PA-n films. It was observed that stress is reduced during the crystal phase transformations at around 220°C and 270°C. This property can be used to relieve stress in multilevel structures. It was also found that slower heating and cooling led to lowered stress. The stress has been compared to reported values from other sources. Stress in PA-c (chlorinated) and co-polymerized PA-n and -e (esterfied) films has also been reported.

The biaxial elastic constants and viscosity between 100 and 300 °C of amorphous PdSi/PdSiFe multilayered thin films with repeat lengths between 2.0 and 4.9 nm have been determined using substrate curvature measurements. No dependence on repeat length has been seen for either property. Linear increases of the multilayer viscosities with time are observed. An analysis of the viscous flow of multilayers shows that in the present case this regime is reached after a very short transient period.

We have measured stress variations with temperature as a function of film thickness and a given grain size in pure Al and AI-0.5%Cu films on Si substrates. The variation in thickness for a given grain size is brought about by using the same film and the repeated controlled growth and dissolution of a barrier anodic oxide which can be grown uniformly on the film. Stress measurements were made as a function of temperature by measuring wafer curvature after successively removing each 0. Iμm of Al film. The components of strengthening due to the film thickness and the presence of grain boundaries were separated by assuming that the flow stress of the film is simply the sum of these two components. The observations are consistent with results obtained using lascr-rcflowed films in an earlier work. The variations of these two components with temperature, and under tension and compression is discussed.

Tensile superplastic deformation was studied using ceramic specimens that had a cross section of approximately 1 μm × 10–50 μm, and a length of 4 mm. These fibers were prepared by physical vapor deposition of oxides on a predefined pattern made by lithography.

Experiments with Y2O3 stabilized ZrO2 fibers and spinel fibers showed two characteristic features of flow behavior: serrations and a threshold stress. The serrations were explained by a flow model based on discrete sliding events distributed in time and space throughout the polycrystal. These fluctuations in flow stress were detected in our microfiber specimens due to relatively few grains in the gage section. Experimental results of the effect of sample size, grain size and strain rate on the serration behavior are discussed in the frame of the new model.