<p> Substantial development of silicon-based technology is required to continue to improve product reliability and production yield of silicon-based IC devices. Defects play a key role in process technology and research is required into their properties and interactions with host and impurity atoms. Cavities formed by ion implantation of helium into a silicon substrate are known to be efficient gettering sites for mobile interstitials and metallic impurities. In addition, the existence of a buried void layer drastically reduces the unintentional parasitic transistor gain in power devices by introducing mid-gap energy levels in the substrate. Utilizing slow positron annihilation spectroscopy (PAS), void formation by implanted He+ at a dose of lxl016/cm2 and energy of 60 keV subsequently subjected to various annealing conditions, i.e. different temperatures, times, ramp rate and ambients, is reported. Quantitative measurement of cavity sizes shows that the annealing temperature largely influences helium out-diffusion from the implanted region. Consequently, different void evolution processes associated with specific annealing temperatures are found. Furthermore, larger voids are formed in oxygen ambient leading us to suggest that the supersaturation of interstitials enhances bubble migration and coalescence during the stage when a large fraction of He atoms remains in the cavities. </p> <p> In recent years, SiGe pseudomorphic alloys have become attractive for heterostructure devices due to their higher mobility, lower noise and lower power consumption, as compared with traditional Si devices. More importantly, SiGe is highly compatible with Si processing technologies. With the continuous improvement of SiGe technology, it has been coupled with complementary metal oxide semiconductor (CMOS) technology and has the potential to replace III-V compound semiconductor devices in the near future. However, many unknowns remain in this material system. The study of point defect injection during various thermal treatments is important in itself, and would also allow additional tools for the study of dopant diffusion in the material under different conditions. With preexistent voids in the buried substrate, we performed furnace wet oxidation on a Si0.98Geo.08 sample at 900 °C for half an hour. A small shrinkage of the voids, as compared to complete annihilation in the case of inert annealing, signifies vacancy injection during the oxidation process. Possible defect generation mechanisms and difference in growth rate enhancement in dry and wet oxidation are discussed. Based on a literature review of Si and SiGe oxidation, we suggest that stress relaxation and the Si replacement mechanism are responsible for the catalytic effect of the oxide growth and the change of point defect generation. </p> / Thesis / Master of Applied Science (MASc)

The raceway in the ironmaking blast furnace is a void in front of the hot blast tuyeres where coke and supplementary fuel burn to supply heat to the ironmaking process. The air velocity through the tuyeres is high (around 200 m/s) and this causes the coke particles to circulate in a rotating flow field inside the raceway. The size and shape of the raceway determine the gas flow dstribution, the reactions that occur, and the temperature profiles in the lower part of the blast furnace. It is for these reasons that the raceway has been extensively researched in the past. . Literature review revealed that forming and breaking of the raceway has not been yet studied. So, in the present study, we have concentrated our effort to study the formation and breaking of the raceway for different blast and bed parameters. The experiments have been performed in two-dimensional glass models. An attempt has been made to develop a correlation for each case. The formation of the void has been studied with change in parameters like density and size of the particles, bed height. The theory of the void formation has been derived from the fundamental principles. The formation of raceway, has been studied with the change in blast parameters like particle density and diameter, bed height and model width. It was found that when raceway is formed there is a sudden increment in pressure drop. The condition for breaking of the raceway, has been studied with change in blast and bed parameters like particle size and density, bed height and model width. It was observed that during the breaking of raceway, pressure decreases continuously. New semi-empirical correlations have been developed using dimensional analysis for formation of void, formation of raceway, and breaking of the raceway. The raceway growth also characterized with change in model width, flow rate, particle diameter, density of the particles and bed height. A few experimental results have been compared with published data. New semi-empirical correlation have been developed using dimensional analysis for the growth of raceway. Velocity of the gas exiting from top of the bed has been measured with the help of hot wire anemometer. It was observed that the velocity leaving from the bed is more on top of the raceway compared to the velocity leaving from the other parts of the bed. High velocity was observed near the wall of the model. Coefficient of wall-friction and angle of internal friction in presence and absence of gas were studied to explain the effect of bed height on formation of the void and raceway. It was observed that in presence of gas, coefficient of friction between the particles and wall and angle of internal friction between particles decreased, compared to the values in absence of gas. To study the effect of mixed particles, on the formation and breaking of the raceway, different sized particles in fixed proportion were taken. It was found that the experiments were more reproducible in case of uniform sized particles compared to mixed particles. It was also observed that for the same average particle diameter, mixture particles requires more velocity to form the void and raceway. New semi-empirical correlations have been developed using dimensional analysis for the formation of void, formation of raceway, growth of the raceway, and breaking of the raceway. Finally, an attempt has been made to quantify the various forces (pressure, bed weight & frictional forces) present in the raceway. Results show that further investigation is required in quantifying these forces properly.

Within the high-performance composite manufacturing industry, there exists a need to improve the reliability of LCM (Liquid Composite Molding) manufacturing processes in producing composite parts that better approach the quality and consistency of pre-impregnated composite tapes that are cured in autoclaves with cost being a driving factor of this need. One obstacle to that end is the phenomenon of void formation during the LCM infusion processes. The formation of these voids through different mechanisms leads to composite parts with lower mechanical properties and consistency than their pre-impregnated autoclave cure counterparts. The objective of this research is to investigate the different mechanisms through which voids form during LCM processes as well as potential actions that can be taken to reduce the total percent volume of voids that form during the infusion. This research also aims to investigate the correlation of the void content observed at the tool-ply interface compared to the void content through the thickness of composite laminates. Finally, this research investigates the effect that chemical modification of the wettability of carbon fiber fabrics has on void formation during infusions.

Fiber-reinforced composites (FRCs) offer a stronger and lighter weight alternative to traditional materials used in engineering components such as wind turbine blades and rotorcraft structures. Composites for these applications are often fabricated using liquid molding techniques, such as injection molding or resin transfer molding. One significant issue during these processing methods is void formation due to incomplete wet-out of the resin within the fiber preform, resulting in discontinuous material properties and localized failure zones in the material. A fundamental understanding of the resin evolution during processing is essential to designing processing conditions for void-free filling, which is the first objective of the dissertation. Secondly, FRCs used in rotorcraft experience severe vibrational loads during service, and improved damping characteristics of the composite structure are desirable. To this end, a second goal is to explore the use of matrix-embedded nanoscale reinforcements to augment the inherent damping capabilities in FRCs. The first objective is addressed through a computational modeling and simulation of the infiltrating dual-scale resin flow through the micro-architectures of woven fibrous preforms, accounting for the capillary effects within the fiber bundles. An analytical model is developed for the longitudinal permeability of flow through fibrous bundles and applied to simulations which provide detailed predictions of local air entrapment locations as the resin permeates the preform. Generalized design plots are presented for predicting the void content and processing time in terms of the Capillary and Reynolds Numbers governing the molding process. The second portion of the research investigates the damping enhancement provided to FRC's in static and rotational configurations by different types and weight fractions of matrix-embedded carbon nanotubes (CNTs) in high fiber volume fraction composites. The damping is measured using dynamic mechanical analysis (DMA) and modal analysis techniques, and the results show that the addition of CNTs can increase the material damping by up to 130%. Numerical simulations are conducted to explore the CNT vibration damping effects in rotating composite structures, and demonstrate that the vibration settling times and the maximum displacement amplitudes of the different structures may be reduced by up to 72% and 50%, respectively, with the addition of CNTs. / Ph. D.

No description available.

To meet the requirements of miniaturization and multifunction in microelectronics, understanding of their reliability and performance has become an important research subject in order to characterise electronics served under various loadings. Along with the demands of the increasing miniaturization of electronic devices, various properties and the relevant thermo-mechanical-electrical response of the lead-free solder joints to thermal cycling and electro-migration become the critical factors, which affect the service life of microelectronics in different applications. However, due to the size and structure of solder interconnects in microelectronics, traditional methods based on experiments are not applicable in the evaluation of their reliability under complex joint loadings. This thesis presents an investigation, which is based on finite-element method, into the performance of lead-free solder interconnects under thermal fatigue and electro-migration, specifically in the areas as follows: (1) the investigation of thermal-mechanical performance and fatigue-life prediction of flip-chip package under different sizes to achieve a further understanding of IMC layer and size effects of a flip chip package under thermal cycling; (2) the establishment of a numerical method, simulating void-formation/crack-propagation based on the results of finite-element analysis, to allow the prediction of crack evolution and failure time for electro-migration reliability of solder bumps; (3) the establishment of a flow-based algorithm for combination effects of thermal-mechanical and electro-migration that was subsequent implemented in to an FE model to evaluate the reliability assessment of service lives associated with a flip chip package.

Resin infusion of composite parts has continually been reaching to achieve laminate quality equal to, or exceeding, the quality produced with prepreg in an autoclave. In order for this to occur, developers must understand the key process variables that go in to producing a laminate with minimal void content. The purpose of this research is to continue efforts in understanding 1) the effect of process conditions on the resultant void content, with a focus on resin infusion flow rate, 2) applying statistical metrics to the formation, location and size of voids formed, and 3) correlate these metrics with the local mechanical properties of the composite laminate. The variation in dispersion and formation of micro-voids and macro-voids varied greatly between the rates of flow the infusion occurred, especially in the non-crimp carbon fiber samples. Higher flow rates led to lower volumes of micro-voids in the beginning section of the carbon fiber laminates with macro-voids being introduced approximately half-way through infusion. This was determined to have occurred decreasing pressure gradient as the flow front moved away from the inlet. This variation in void content per location on the laminate was more evident in the carbon fiber samples than the fiberglass samples. Micro-voids follow void formation modeling especially when coupled with a pressure threshold model. Macro-void formation was also demonstrated to correlate strongly to void formation models when united with void mobility theories and pressure thresholds. There is a quick decrease in mechanical properties after the first 1-2% of voids signaling strength is mostly sensitive to the first 0-2% void content. A slight decrease in SBS was noticed in fiberglass laminates, A-F as v0 increased but not as drastically as represented in the NCF laminates, G and H. The lower clarity in the exponential trend could be due to the lack of samples with v0 greater than 0% but less than 1%. Strength is not well correlated to void content above 2% and could possibly be related to void morphololgy.

This dissertation constitutes two major sections. In the first major section, a kinetic analysis was established to investigate the electromigration (EM), enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints to Cu under bump metallization (UBM). The model takes into account the interfacial intermetallic reaction, Cu-Sn interdiffusion, and current stressing. A new approach was developed to derive atomic diffusivities and effective charge numbers based on Simulated Annealing (SA) in conjunction with the kinetic model. The finite difference (FD) kinetic model based on this approach accurately predicted the intermetallic compound growth when compared to empirical observation. The ultimate electromigration failure of the solder joints was caused by extensive void formation at the intermetallic interface. The void formation mechanism was analyzed by modeling the vacancy transport under electromigration. The effects of current density and Cu diffusivity in Sn solder were also investigated with the kinetic model. The second major section describes the integration of Step and Flash Imprint Lithography (S-FIL®) into an industry standard Cu/low-k dual damascene process. The yield on a Back End Of the Line (BEOL) test vehicle that contains standard test structures such as via chains with 120 nm vias was established by electrical tests. S-FIL shows promise as a cost effective solution to patterning sub 45 nm features and is capable of simultaneously patterning two levels of interconnect structures, which provides a low cost BEOL process. The critical processing step in the integration is the reactive ion etching (RIE) process that transfers the multilevel patterns to the inter-level dielectrics (ILD). An in-situ, multistep etch process was developed that gives excellent pattern structures in two industry standard Chemical Vapor Deposited (CVD) low-k dielectrics. The etch process showed excellent pattern fidelity and a wide process window. Electrical testing was conducted on the test vehicle to show that this process renders high yield and consistent via resistance. Discussions of the failure behaviors that are characteristic to the use of S-FIL are provided. / text

Global competition is pushing the composites industry to advance and become more cost effective. Liquid Composite Molding or LCM is a family of processes that has shown significant promise in its potential to reduce process times and cost while maintaining high levels of part quality. However, the majority of research and information on composite processes have been related to prepreg-autoclave processing which is significantly different than LCM. In order for LCM processes to gain large scale implementation, significant research is required in order to model and simulate the unique nature of the resin infusion process. The purpose of this research is to aid in the development of in situ void measurement and characterization during LCM processing, particularly for carbon fiber composites. This will allow for the gathering of important empirical data for the validation of models and simulations that aid in the understanding of void formation and movement during LCM. For such data to be useful, it needs to include details on the formation, mobility and evolution of the void over time during infusion. This was accomplished by creating a methodology that allowed for in situ images of voids to be captured during the infusion process. A clear mold was used to visually monitor infusions during RTM with UV dye and lighting to enhance contrast. Consecutive images were acquired through the use of macro lens photography. This method proved capable of yielding high quality images of a variety of in situ voids during infusions with carbon fiber composites. This is believed to be the first instance where this was accomplished. A second methodology was then developed for the analysis of the collected images. This was done by using ImageJ software to analyze and process the acquired images in order to identify and characterize the voids. Success was found in quantifying the size and circularity of a wide range of micro and macrovoids in both a satin weave and double bias NCF woven fabrics. To facilitate the burden of collecting large amounts of data, this process was made to be automated. A user generated macro script could be applied to large sets of images for rapid processing and analysis. This automated method was then evaluated against manually processed images to determine its overall effectiveness and accuracy as tool for validating void theory.

No description available.