We have studied the possibilities of reducing the threading dislocation (TD) density in GaAs on Si using free side wall growth on patterned Si substrates and/or using a soft ZnSe interlayer in combination with post growth annealing procedures. TD densities were accurately determined using large area plan view TEM and were found to be unaffected by proximity to free side walls and by the ZnSe interlayer. Post growth heat treatments led to a factor of ∼2 reduction in TD density and to bunching of dislocations throughout the thickness of the film.

GaAs epitaxial layers were successfully grown on Si/Sapphire substrates using Molecular Beam Epitaxy(MBE). Residual compressive strain was found in GaAs films on Si/Sapphire. By Photoluminescence, the magnitude of residual strain in GaAs on Si/Sapphire was estimated to be 5×10-4 which is about one order smaller than that of GaAs on Si.

As an effort to achieve further reduction in the residual strain, Indium- doped GaAs films were used as buffer layers in order to compensate compressive thermal strain by tensile misfit strain in the GaAs layer. Using this method, strain- free GaAs layers could be grown with thickness up to 0.4 μm on Si/Sapphire.

The stresses in a silicon wafer which has undergone diffusion by a high concentration of boron are partially relaxed by the generation of dislocations in the boron-diffused regions of Si. It is found that these dislocations nucleate at the Si surface as dissociated half-loops lying on {111} planes inclined to the surface. Expansion of the half-loops to the diffused/virgin Si interface produce segments of misfit dislocations which are of the dissociated 60º type. These misfit dislocations move deeper into the crystal as the diffusion front moves further in the wafer and often intersect other misfit dislocations on intersecting glide planes. In this paper, the misfit dislocations and the reactions between them are characterized and discussed.

We have discovered a surface instability in In.25GaAs.75/GaAs (100) grown by molecular beam epitaxy (MBE) by direct comparison of atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) investigations. While slipline spacings measured by AFM correspond fairly well with those measured by TEM and SEM, the height displacement measured by AFM was seven times greater than that inferred from dislocations observed with TEM; the number of dislocations are insufficient to produce such dramatic heights. The difference in height measured by AFM with respect to the theoretical height calculated by strain relaxation and TEM dislocation number measurement can be attributed to a surface instability.

In this work, the directions of the secondary beams which are scattered by each mosaic block within an epitaxial layer allow to explain the position and profile of the LS hybrid multiple diffraction peak in the substrate Renninger Scan (RS). Furthermore, by choosing a secondary beam diffracted almost parallel to the interface, the LS peak is able to provide information even for thin (500Å) layers. The position of the LS peak in the substrate RS of the GaAs layers grown by VCE on Si(001) provides the a║ values necessary to analize the layer stress state. As an external bending moment is applied on the sample to compensate the stress steming from the difference in thermal expansion coefficients a split of both epilayer and buffer layer LS peaks can be observed. This split also indicates the degree of cohesion between these two layers.

In this paper we have investigated the carrier contribution to elastic constants in very thin films of stressed small gap compounds within the domain of theory. It is found, taking stressed ultrathin films Hg1-xCdxTe and In1-xGaxAsyP1-y lattice matched to InP as examples, that the elastic constants increase with increasing electron concentration and decreasing film thickness respectively in oscillatory manners. Besides the stress enhances the numerical values of such contribution to the elastic constants. In addition, the theoretical formulation is in agreement with the suggested experimental method of determining such constants in materials having arbitary dispersion laws.

The mechanical stress of epitaxial SrF2 and CaF2 films on Si(111) substrates has been measured as a function of temperature by the substrate curvature technique. The temperature dependence of the stress in the SrF2 film is interpreted in terms of an energy barrier to dislocation motion. When the strain energy is smaller than the value needed to overcome the barrier, the change in stress is due mainly to elastic deformation. As the temperature change increases, the strain energy becomes large enough to overcome the barrier, at which point plastic deformation initiates. Unlike SrF2, the stress behavior of the CaF2 film for increasing temperature is quite different from its behavior for decreasing temperature. This unusual behavior is not understood at this time.

n-type PbTe(Ga) films were grown by the laser deposition and the hot wall techniques on BaF2 substrates in <111> orientation. Doping results in the appearance of a high-ohmic state with nearly intrinsic free carrier concentration at low temperatures and activation character of conductivity at T∼300 K. Persistent photoconductivity has been observed at T < 100 K. In the hot wall-grown layers a new effect of bistability during the cooling-heating-cooling cycles has been found. On the first stage of the cycle a rapid decrease of resistivity (∼3 orders of magnitude) is observed at To∼50 K. The value of To changes by ± 15 K depending on the cooling rate. After a brief heating up to 80 K the subsequent cooling results in the high-ohmic state of the layer at the low temperatures. This state seems to be unstable. Relaxation to the low ohmic state can be accelerated by the application of electric field. The effect may be understood in terms of bistability of the Ga impurity charge state under the action of strain between the film and the substrate during the cooling-down process.

The ZnSe-ZnTe combination is a potential candidate for the realisation of visible light-emitting devices. The lattice mismatch between bulk ZnSe and bulk ZnTe is important (∼ 8%). Therefore, their hetero-structures are strained and high quality superlattices will only be grown if having small periods. This prescription can be fulfilled in the case of metal organic vapour phase epitaxy (MOVPE) growth by combining triethylamine dimethyl zinc adduct with di-isopropyl telluride as precursors for the growth of the ZnTe layers. The growth of high quality ZnTe can then be performed at a temperature of 300ºC , close to the best MOVPE-growth temperature for ZnSe (280ºC). Lowering the growth temperature of ZnTe to this value, we could thus obtain sharp interfaces. This work reports on ZnSe-ZnTe superlattices grown on ZnSe and ZnTe buffers deposited on GaAs substrates. We demonstrate that the stokes-shift between the reflectance and photoluminescence features ( ∼ 40 meV ) measured when the thickness of ZnSe layers does not exceed 20 Å, drastically increases for layer thicknesses beyond this critical value. This, we interpret in terms of the onset of plastic relaxation which favours tellurium diffusion in the ZnSe slices. Then photoluminescence spectra broaden ( contributions of trapped-excitons dominate), and observation of free excitons in reflectance become impossible. We have studied in detail the optical properties of the superlattices and compared our findings with the predictions of a multiband envelope function calculation. We show that both zone centre excitons as well as excitons associated with the miniband dispersions (saddle-point excitons) are observed in these superlattices.

We have performed a constant temperature classical molecular dynamics simulation of the epitaxial growth of a C60 monolayer film deposited on the dimerized Si(100) surface. Our simulation, based on non-central many-body inter-atomic potentials, is capable of predicting the structural stability of the C60 film and the Si substrate and provides a theoretical basis for the results of a recently-performed STM- based experiment for this system.

Three-dimensional geometries have been generated on computer and used for the animation of the simulation runs.

The influence of processing conditions on the structure and properties in spin coated polyimide films prepared from flexible, semi-rigid and rigid chemistries was investigated. While the relationship between processing, structure and properties is different for each chemistry, some general trends were observed. Curing above the glass transition in the flexible polyimide BTDA//ODA/MPD, that is incapable of crystallizing and has very little in-plane orientation, has virtually no effect on the structure or properties compared to curing below the glass transition. Curing at temperatures above the glass transition in cry stall izable stiff polyimides such as BPDA//PPD and PMDA//ODA results in an increase in birefringence, in-plane CTE and biaxial stress. In BPDA//PPD, the increase in birefringence is attributed to an increase in polarizability and possibly, an increase in the overall in-plane alignment of the imide ring as evidenced by IR analysis. The increase in in-plane CTE is attributed to a loss in chain axis orientation caused by relaxation effects. The increase in stress is attributed to the increase in the in-plane CTE and also from shrinkage forces arising from crystallization. Rapid heating during cure in the flexible amorphous BTDA//ODA/MPD has essentially no effect on structure or properties compared to slow heating. In the semi-crystalline polyimides, rapid heating during cure leads to higher levels of crystallinity and significantly higher stresses. The increase in stresses is attributed to a loss in chain axis orientation in the plane of the film and shrinkage forces arising from additional crystallization. The directional dependence of the coefficient of thermal expansion, an important functional property, is extremely sensitive to molecular anisotropy. BTDA//ODA/MPD, which is almost isotropic, has an out-of-plane CTE that is approximately 20 percent higher than the in-plane CTE. In contrast, the out-of-plane CTE for the most anisotropic polyimide in this study, BPDA//PPD, is 25 times larger than the in-plane CTE. This sensitivity of the CTE to molecular orientation must be taken into account when modeling stress in, or designing, electronic devices.

A finite element model was employed to analyze the microindentation test with a spherical indenter on gelatin films. The deficiency of using elastic-plastic constitutive law to describe indentation response of gelatin film was recognized and a viscoelastic model was proposed for the first time to analyze indentation experiments on polymeric materials. Based on viscoelastic analysis, it was found that gelatin is nonlinear viscoelastic. In addition, modulus in the thickness direction of a gelatin film was determined to be 2.5–2.9 GPa as compared with its tensile modulus of 4.6 GPa in the transverse direction.

Indentation creep testing was done on cross-linked glassy polymers based on polystyrene, specifically poly(styrene-co-divinylbenzene) (PS-DVB) and poly(divinylbenzene) (PDVB). The continuous depth-sensing capabilities of the Nano-Indenter II were used to measure the time-dependent response to indentation at constant applied load. The raw creep data in terms of indentation depth vs time showed that PDVB was about 20% more resistant to penetration than PS-DVB. A data analysis program was developed that converted the raw data to stress σ and plastic strain rate ε and generated the plastic flow curve that was observed to follow the power law . The stress exponent a for PS-DVB increased with applied loads between 1 and 27 mN and was generally larger in magnitude than the exponent for PDVB. When compared at equivalent stress and indentation depth, the plastic strain rate for PDVB was observed to be about 100 times slower than for PS-DVB. This was attributed to the higher degree of cross-linking increasing the characteristic relaxation time governing creep flow in these polymers.

We discuss here the complete determination of the elastic properties of a polyimide film using two experimental techniques. One technique employs the polymer film as a vibrating membrane and allows a direct determination of the ’macroscopic’ biaxial modulus. Brillouin scattering, which measures the elastic properties on a ∼ 100 μ scale, allows for a complete characterization of the elastic behavior. The results obtained by the two techniques are in agreement within the reported error bars.

By studying the topography of crazes and shear deformation zones in polymer films with the Atomic Force Microscope (AFM), it was found that crazes and shear deformation zones grew by a micro-necking process. This discovery indicates that when a glassy polymer undergoes local deformations, the material drawn into the deformation zones continues to be deformed until a much later time than that previously understood. Details of the craze micro-necking mechanism and its important implications will be discussed. Based on the necking mechanics, it was shown that craze initiation and growth can be examined using a modified Considere construction, and the stress distribution within a micro-deformation zone was investigated by assuming the Bridgman's theory. The results of the stress analysis are in excellent agreement with the breakdown behavior of crazes observed experimentally. The Young's moduli of the crazed and sheared polymers within the tiny deformation zones were also measured using a simple new AFM technique. Evidence of strain softening was clearly observed in that both the Young's moduli of crazes and shear deformation zones were very low compared to that in the bulk.

This work examines the planarization of polymer thin film coatings derived from Cyclotene™ 3022 prepolymer resins. Cyclotene™ 3022 is a divinyl siloxane bis-benzocyclobutene prepolymer (DVS-BCB, CAS 117732-87-3). It is used primarily as a dielectric in microelectronics applications.

Using profilometry, planarization measurements have been made on thin films spun over features consisting of lines and trenches. Feature widths have been varied from 2 to 1000 μm and the feature depths and film thickness have been varied from 1 to 16 μm. Effects of the processing procedure, resin concentration and resin additives have been explored. Local (versus global) planarization will be discussed.

Planarization has been found to depend on all feature dimensions and the polymer film thickness. Lines or other structures having a width of 100 μm or less can be planarized to 90% or better with standard commercial formulations of Cyclotene™ 3022, provided that the mean film thickness is twice the line-height or feature-depth. Metals such as Al, Cu, Cr and Ti can all be planarized to this degree; however, surface preparations may influence the result.

The trend towards higher density and smaller feature sizes in today's devices, and the increasing costs associated with designing and manufacturing these devices, has placed a greater emphasis on obtaining an a priori understanding of how various materials will perform in a device. A number of manufacturers have turned to computer modeling, utilizing finite element analysis to aid in the design of new devices and reduce the costs associated with preparing prototypes. The use of computer modeling requires a constitutive equation relating the response of a material to an applied load. Polymer behavior is complex and writing an equation or a series of equations that describe the behavior of the polymer over the entire range of possible temperatures and deformations is nontrivial. Instead, series of equations that describe ideal material behavior are used in an attempt to describe the behavior of real materials over a narrow range of temperatures and deformations. For solids, the ideal material response that is generally used to describe real polymer behavior is linear elasticity.

We propose a new test to measure the adhesion of thin polymeric coatings used in microelectronic applications. Similar to previous tests [1-3], the edge delamination test (EDT) takes advantage of the thermal residual stress present in the coating to induce delamination. However, in the EDT, we take advantage of lithography to fabricate test geometries that probe a complete range of debond energies. As a result, nearly a hundred adhesion tests can be performed on a single wafer. In this report, we apply finite element analysis to assess the debond energy generated at the coating/substrate interface to determine the feasibility of the test. The analysis also quantifies the effect of various geometries and boundary conditions. We apply the EDT to study the adhesion of Cyclotene™ 3022 polymer to silicon coated with evaporated aluminum. The critical mode I strain energy release rate for the Cyclotene/Aluminum interface with no adhesion promoter is 10.5±0.2 J/m2.

Continuous microindentation tests on electropolished, single crystal Fe(3wt%Si) and Ni surfaces with thin passivation layers exhibit sharp discontinuities in the load-displacement behavior. At the discontinuity, which occurs at a load of 1.8 mN for Fe(3wt%Si) and 0.1 mN for Ni, stresses below the indenter were close to the theoretical strength of the corresponding metal. Microindentation tests performed to loads less than the discontinuity point showed an elastic load-unload behavior. On removing the passive film with a NaCl or HC1 solution, strengths are one to two orders of magnitude smaller in the presence of the chloride ions. On evaporation of the liquid, the load at the discontinuity returned to its initial value due to repassivation, indicative of a passivation oxide layer with varying thickness. This conclusion was verified by ellipsometry. Even though the elastic load-unload behavior on the passivated surface suggests elastic behavior, both elastic finite element and non-linear, elastic perfectly plastic finite element solutions strongly suggest that this might not be the case. Several suggestions as to the reasons for the deviation from continuum theory are presented.

Excimer laser processing enables both thermally-driven transformations and the incorporation of solutes into the surface of materials through melting and diffusional mixing. We have examined the effect of excimer laser processing on the microstructure and surface mechanical properties of titanium alloys. Changes in the surface hardness due to laser processing were studied using a Nanoindenter™. Alloying experiments using both mixing of evaporated surface layers of boron and laser gas alloying in air and in nitrogen all result in changes in the surface hardness of the material. Alloying with boron results in an amorphous surface which is somewhat harder than the as polished surface. Laser processing in air and pure nitrogen results in incorporation of oxygen and nitrogen and the development of fine precipitates of TiO and TiN respectively. Substantial increases in surface hardness result due to solution and precipitation mechanisms. Nanoindenter™ data from several depths in the material are correlated with microstructure and solute concentration to illuminate the strengthening mechanisms involved.