Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 167-178). Available also in a digital version from Dissertation Abstracts.

Made available in DSpace on 2014-07-29T15:07:53Z (GMT). No. of bitstreams: 1 Dissertacao Tatiane Martins.pdf: 647656 bytes, checksum: b344932502d967c35cd933892c12768c (MD5) Previous issue date: 2008-07-24 / Foi conduzido um experimento utilizando-se 630 pintos com um dia de idade com o objetivo de avaliar os efeitos de ácidos orgânicos, frente à inoculação experimental de Salmonella Typhimurium sobre a saúde intestinal, desempenho, bacteriologia de órgãos e função hepática. As aves foram distribuídas em delineamento inteiramente ao acaso com seis tratamentos e sete repetições com 15 pintos cada. O desafio experimental com a bactéria ocorreu por duas vias de administração: via inglúvio, ao primeiro dia após eclosão, e via ração durante o período de sete a 14 dias de idade. Estes grupos foram tratados ou não com ácidos orgânicos, definindo-se desta forma, um esquema fatorial de 3x2 (agente versus ácidos orgânicos). Os pintos dos tratamentos preconizados para inoculação no primeiro dia de vida receberam via inglúvio, a dose de 5,0 x 102 /0,5mL unidades formadoras de colônias (UFC) de Salmonella Typhimurium. Os tratamentos com contaminação via ração, receberam o desafio na dosagem de 5,0 x 102 UFC de Salmonella Typhimurium/ kg de ração. O teste de Tukey (5%) foi utilizado para análises das variáveis. Os grupos tratados com ácidos orgânicos apresentaram melhores de ganho de peso, peso médio e conversão alimentar (p<0,05) aos 14, 21 e de ganho de peso e peso médio (p<0,05) aos 28 dias de idade. Os grupos inoculados com Salmonella Typhimurium apresentaram piores índices de desempenho (p<0,05) aos sete, 14 e 28 dias. O peso do intestino delgado foi maior (p<0,05) para os grupos inoculados quando comparado ao grupo controle, entretanto com comprimento menor para o mesmo fragmento intestinal. O tratamento inoculado via inglúvio e tratado com ácidos orgânicos apresentou menores valores (p<0,05) de unidades formadoras de colônia/g de Escherichia coli em excretas do que os grupos que foi comparado. O pH do conteúdo do conteúdo cecal e do intestino delgado não foi afetado (p>0,05) pela adição de ácido, enquanto o pH do intestino delgado dos grupos inoculados foi menor (p<0,05) quando comparado ao grupo controle negativo durante todo o período experimental. Também foi verificado menor peso (p<0,05) de fígado para os grupos controle negativo aos 21 e 28 dias. Os grupos tratados com ácido, independente da via de administração com Salmonella Typhimurium, obtiveram menores freqüências de isolamento em todos os órgãos analisados. Foram também observadas alterações (p<0,05) na bioquímica sérica hepática e na análise histopatológica do fígado pela atuação da Salmonella. Pode-se concluir que o ácido utilizado na dosagem de 0,4% potencializou o desempenho, foi eficaz no controle de Salmonella Typhimurium e não promoveu lesões hepáticas, quando da inoculação experimental de Salmonella Typhimurium ácido nalidíxico resistente.

The demand for high performance electronic devices is ever increasing in today's world with advent of digital technology in every field. In order to support this fast paced growth and incursion of digital technology in society, smarter, smaller integrated circuits are required at a lower cost. This primary requirement drives semiconductor industries towards the integration of larger number of smaller transistors on a given circuit area. The past decades have seen a rapid evolution of material processing and fabrication techniques, as focus shifts from submicron to sub-nanometer length scales in device configuration. As the functional feature size of an integrated circuit decreases, the threshold of defect causing impurities rises drastically. Huge amount of resources are spent in downstream and upstream processing in order to restore system from contamination upsets and in the upkeep of Ultra-High-Purity (UHP) process streams to meet these stringent requirements. Contamination once introduced into the system also drastically reduces process yield and throughput resulting in huge losses in revenue. Regular UHP fluid distribution system maintenance as well as restorative operations involve a purging operation typically known as Steady State Purge (SSP). This purge operation involves large amount of expensive UHP gas and time. Depending on the scale of the system and type of process involved this results in significant tool, process downtimes and can have a wide range of environment, health and safety (ESH) ramifications. A novel purge process, referred to as Pressure Cyclic Purge (PCP) was studied for establishing gas phase contamination control in UHP applications. In understanding the basic mechanism of this technique and to analyze its extent of application in aiding purging operations, a coupled approach involving experimental investigation and computational process modelling was used. Representative and generic distribution sections such as main supply lines and sections with laterals were contaminated with a known amount of moisture as impurity. The dynamics of the impurity transport through the system from purging with SSP as well as PCP was captured by a highly sensitive analyzer. The surface interactions between the moisture and EPSS were characterized in terms of adsorption and desorption rate constants and surface site density. A computational process model trained using experimental data was then validated and used to study the steady and cyclic purge mechanisms and predict complex purge scenarios. Industrially relevant and applicable boundary conditions and system definitions were used to increases the utility of the computational tool. Although SSP compared closely with PCP on simple systems without laterals, a drastic difference in dry-down efficiency was noticed in systems with dead volumes in the form of capped laterals. Studies on system design parameters revealed that the disparity in performance was observed to increase with larger number and surface area of dead volumes, opening a path to critical understanding of the differences in process mechanisms. Beneficial transient pressure gradient induced convective flow in the dead volumes during cyclic purge was identified to be the main factor driving the enhanced dry down rate. Similar trends were observed on using surface concentration as the purge metric. Hybrid purge schemes involving a combination of SSP and PCP were found to yield higher benefit in terms of efficient use of purge gas. Removal of strongly interacting contaminant species showed a higher benefit from use of controlled PCP scheme. Although, parametric analysis carried out on the operating factors of cyclic purge suggested that the enhancement in dry down increased with higher pressure range, it was highly conditional towards configurational factors in design and operation such as system dimensions, holding time, cycling pattern, valve loss coefficients and the complex inter coupling between them. The robustness of the process simulator allows the development of optimal purge scenarios for a given set of system parameters in order to perform a controlled purge. The benefit of using a hybrid PCP scheme was evaluated in terms of UHP purge gas and process time as a function of purity baseline required. Apart from UHP gas distribution systems, process vessels, chambers and components along the process stream are also prone to molecular contamination and pose a threat to product integrity. The dead volumes acting as areas of contaminant accumulation represent cavities or dead spaces in flow control elements such as mass flow controllers (MFCs), gauges, valves or dead spaces in process chambers. Steady purge has very little effect in cleanup of such areas and more efficient methods are necessitated to raise purge efficiency. The analysis of application of PCP is extended to such components through the development of a robust and comprehensive process simulator. The computational model applies a three dimensional physical model to analyze purge scenarios with steady and cyclic purge. The results presented pertain to any generic gas phase contaminant and electronic grade steel surfaces. Close investigation of the purge process helped elaborate the cleaning mechanism. Critical steps driving the purge process were identified as - dilution of chamber by introduction of fresh gas during re-pressurization and chamber venting during depressurization. Surface and gas phase purging of chambers with dead spaces using steady and cyclic purge were studied and compared. Cyclic purge exhibited a higher rate of dry down. The effect of system, design and purge operating parameters on surface cleaning were studied. Although higher frequency cycles and larger operating pressure ranges optimized for a given geometry are found to deliver better pressure cyclic purge (PCP) performances, the benefit is found to be contingent to a strong interplay between system parameters. PCP is found to be advantageous than steady state purge (SSP) in terms of purge gas usage and operation time in reaching a certain purity baseline. Specialty process gases supplied to the fabrication facility are typically stored in the form of liquids in enormous tanks outside the fab. Ammonia is a widely used in UHP concentrations for a variety of process including epitaxial growth, MOCVD, etching and wet processes in the semiconductor industry. The recent development in LED research has risen the demand and supply for Ammonia based compounds. Stringent baselines are maintained for the impurities associated with the manufacturing of such gases (e.g. Moisture in Ammonia). Apart from the difference in the rates of evaporation of the individual species from the storage cylinder causing accumulation of slower evaporating species, external temperature fluctuations also generate unsteady flux of desired species. When concentrations rise above this threshold additional purification or in most cases discarding large volumes of unused gas is warranted, causing loss of resources and causing ESH issues. Bulk gases are usually delivered over long lengths of large diameter pipes which produce large density of adsorption sites for contaminants to accumulate and eventually release into the gas stream. In order to establish contamination control in the gas delivery system, the surface interactions of the multispecies system with the delivery line surface was characterized. Desired concentrations of moisture in ammonia and UHP nitrogen mixtures were produced in a gas mixing section capable of delivering controlled mass flow rates to an EPSS test bed. Transient moisture profiles during adsorption and desorption tests at various test bed temperatures, mass flow rates and moisture concentration were captured by a highly sensitive analyzer. A mathematical model for single and multi-species adsorption was used in conjunction with experimental data to determinate kinetics parameters for moisture, ammonia system in EPSS surface. The results indicate competitive site binding on EPSS between ammonia and water molecules. Also, the concentration distribution of each species between surface, gas phase is interdependent and in accordance to the kinetic parameters evaluated. Back diffusion of impurity is a major source of contaminant introduction into UHP streams. Back diffusion refers to the transport of contaminants against the flow of bulk process stream. Molecular species can back diffuse from dead volumes, during mixing operations etc., simply when there is a gradient of concentration. A steady state approach was used to analyze the mechanism and effects of various geometrical and operational parameters on back diffusion. High sensitivity moisture detectors were used to capture the dynamics of contamination in a section of a generic distribution system. Results showed that back diffusion can occur through VCR fittings, joints and valves under constant purge. General trends on the effect of design parameters on back diffusion were derived from studies on various orifice sizes, system dimensions, flow rates and test moisture concentrations. Coupled parametric studies helped identify critical variable groups to perform dimensionless analysis on back diffusion of moisture. Crucial points where back diffusion can be minimized or completely eliminated are identified to help set up guidelines for cyclic and steady purge parameters without excessive use of expensive UHP gas or installation of unnecessarily large factors of safety. Wet cleaning of micro/nano sized features is a highly frequent process step in the semiconductor industry. The operation is a huge consumer of ultra-pure water and one of the main areas where process time minimization is focused. Comprehensive process model is developed to simulate the mechanism and capture the dynamics of rinsing high aspect ratio Silicon features in the nanometer scale. Rinsing of model trench, post etch contaminated with ammonium residue is studied. Mass transport mechanisms such as convection, diffusion are coupled with surface processes like adsorption and desorption. The effect of charged species on the trench surface and in the bulk, the resultant induced electric field on the rinse dynamics and decay of surface species concentration is studied. General rinsing trends and critical points in change in mechanisms were identified with critical groups such as mass transfer coefficient and desorption coefficient. The model is useful in evaluating process efficiency in terms of rinse time and DI water consumption under varying process temperature, contaminant concentration, and rinse fluid flow rate. The generic build of the model allows extension of its functionality to other impurity-substrate material couples.

Particle contamination control is a critical issue for the semiconductor industry. In the near future, this industry will be concerned with the chemical identities of contaminant particles as small as 0.01 pm in size. Therefore, analytical techniques with both high chemical sensitivity and spatial resolution are required. Transmission electron microscopy (TEM) provides excellent spatial resolution and yields structural and compositional information. It is rarely used, however, due to the difficulty of sample preparation. The goals of this research are to promote the use of TEM as an ultrafine particle analysis tool by developing new sample preparation methods, and to exploit the new TEM techniques for analysis of particles in semiconductor processing fluids. A TEM methodology for the analysis of particulate contaminants in fluids with an elemental detectability limit as low as 0.1 part per trillion (ppt), and a particle concentration detectability limit as low as 1 particle/ml for particles greater than 0.2 pm was developed and successfully applied to the analysis of particles in HF, H202, de-ionized (DI) water, and on the surface of an electronic device. HF samples from three manufacturers were examined. For HF (B), the maximum particle concentration was 8.3 x 103 particles/ml. Both a viscous material and lath-shaped particles were observed. The Sb concentration was less than 0.6 part per billion (ppb). HF (C) was the cleanest. CaF2 and TiO2 particles were identified in HF (D). For H2 02, iron and tin oxides and hydroxides were identified. The maximum particle concentration was 990 particles/ml. The Sn and Fe concentrations were less than 0.3 ppb. Spherical and dendritic particles were observed. For DI water, spherical and dendritic particles (<2 particles/ml), and particles containing Fe or Si with concentrations less than 0.1 ppt were observed. Contaminants on an electronic device surface were also analyzed. Clusters of small particles were determined to be a mixture of aluminum oxides and aluminum silicates.

Na odontologia, o biofilme formado nas linhas d\'água de equipos odontológicos pode disseminar a contaminação microbiana na água. O objetivo desta pesquisa foi investigar a contaminação microbiana da água de abastecimento e de equipos odontológicos antes e após a implementação de um protocolo para melhoria e manutenção da qualidade microbiológica da água de equipos odontológicos, bem como desenvolver produtos antibiofilme com possível aplicabilidade nas linhas d\'água. A carga microbiana da água de 27 torneiras e equipos (reservatórios, seringas tríplice e alta rotação) de uma clínica odontológica foi avaliada por meio do sistema Petrifilm(TM) (bactérias aeróbias totais e fungos) e meios de cultura convencionais (enterobactérias e Legionella spp.) em duas etapas distintas, sendo a segunda análise realizada após a implementação de um protocolo para melhoria e manutenção da qualidade microbiológica da água dos equipos. Ainda, as atividades antibacteriana (concentração inibitória mínima - hipoclorito de sódio, ácido cítrico, bicarbonato de sódio, cloreto de sódio, dodecil sulfato de sódio, peróxido de hidrogênio, polissorbato 20 e quitosana) e antibiofilme (biomassa total e viabilidade celular) foram determinadas in vitro a partir de substâncias e produtos com possível aplicabilidade na desinfecção de linhas d\'água de equipos. As amostras de água das torneiras apresentaram carga bacteriana dentro do parâmetro estabelecido pela legislação brasileira, no entanto, as seringas tríplices e os alta rotação não. A implementação do protocolo para manutenção da qualidade microbiológica da água dos equipos demonstrou uma redução nas cargas bacteriana e fúngica apenas nos alta rotação. Enterobactérias e Legionella spp. não foram isoladas das amostras de água das torneiras e dos equipos. De acordo com a concentração inibitória mínima, o ácido cítrico, bicarbonato de sódio, cloreto de sódio, hipoclorito de sódio e peróxido de hidrogênio demonstraram as melhores atividades antibacterianas. As melhores atividades antibiofilme (biomassa total) foram do peróxido de hidrogênio a 5% (E. coli e P. aeruginosa), ácido cítrico a 30% (P. aeruginosa) e bicarbonato de sódio a 30% (S. aureus). Os produtos (Wanitox A e Wanitox B) desenvolvidos apresentaram atividade antibiofilme (viabilidade celular) contra a E. coli e S. aureus. Assim, os produtos desenvolvidos nesta pesquisa apresentaram possível aplicabilidade no enfrentamento do biofilme nas linhas d\'água de equipos odontológicos, que permanece como um dos grandes desafios na odontologia. Ainda, pesquisas adicionais são necessárias para o aperfeiçoamento e aplicabilidade destes produtos. / In dentistry, biofilm formed on dental unit waterlines can disseminate microbial contamination in water. The objective of this research was to determine the microbial contamination of water from supplies and dental units before and after the implementation of a protocol for improvement and maintenance of microbiological water quality of water from dental units as well as to develop antibiofilm products with possible applicability in waterlines. The microbial load of water from 27 taps and dental units (reservoirs, air-water syringes and high-speed turbines) in a dental clinic was evaluated through a Petrifilm(TM) system (total aerobic bacteria and fungi) and conventional culture mediums (enterobacteria and Legionella spp.) in two distinct stages, being the second analysis performed after the implementation of a protocol for improvement and maintenance of microbiological water quality of water from dental units. Moreover, the antibacterial (minimum inhibitory concentration - sodium hypochlorite, citric acid, sodium bicarbonate, sodium chloride, sodium dodecyl sulfate, hydrogen peroxide, polysorbate 20 and chitosan) and antibiofilm (total biomass and cell viability) activities were determined in vitro from substances and products with possible applicability in disinfection of dental unit waterlines. The water samples from taps presented bacterial load within the parameter established by Brazilian legislation; however, air-water syringes and high-speed turbines did not. The protocol implementation for maintenance of microbiological water quality of water from dental units showed a decrease on bacterial and fungal loads only on high-speed turbines. Enterobacteria and Legionella spp. were not isolated from water samples from taps and dental units. According to minimum inhibitory concentration, citric acid, sodium bicarbonate, sodium chloride, sodium hypochlorite and hydrogen peroxide showed the best antibacterial activities. The best antibiofilm activities (total biomass) were from 5% hydrogen peroxide (E. coli and P. aeruginosa), 30% citric acid (P. aeruginosa) and 30% sodium bicarbonate (S. aureus). The developed products (Wanitox A and Wanitox B) showed antibiofilm activity (cell viability) against E. coli and S. aureus. Thus, the products developed in this research presented a possible applicability in confrontation with biofilm on dental unit waterlines, and this remains as a major challenge in dentistry. Besides, additional researches are necessary for enhancement and applicability of these products.