With the decrease in feature size in semiconductor manufacturing, molecular contamination problems are increased significantly. In order to optimize the yields in wafer fabrication units there is a need for process modeling that addresses the details of wafer contamination. Wafer contamination and cleaning is a complex process that covers various length and time scale events and phenomena. At the largest scales, there is the availability and transport of specific species within the fabrication unit and subsequent contamination of the wafer surface either through processing steps or through simple ambient transport processes. To limit wafer contaminant levels and/or to decontaminate them, wafers in the semiconductor fabrication unit are often cleaned and transported in a closed enclosure called Front Opening Unified Pod (FOUP) and purged with an inert gas like nitrogen. For the FOUP geometry, I analyze the large scale process modeling approaches to cleaning wafers. At smaller scales, the specific molecular configuration of the contaminant species impacts the kinetic chemical-physical cleaning mechanisms. To determine, from a fundamental perspective, the mechanisms contributing to wafer cleaning requires different scale tools from transport tools aimed at characterizing equipment scale (e.g., FOUP) contamination issues. I use molecular dynamics models and optimization techniques to infer physicochemical rates for molecular desorption on wafer surfaces. This dissertation considers these problems from a common perspective. The objective of this study has been to characterize the multi-scale problem of wafer cleaning with the objective of developing appropriate tools and models at different scales to best predict the dynamics of contaminant removal from wafer surfaces. A standardized method has been presented to extract kinetic rate parameters using molecular dynamics simulation (smaller-scale) and optimization for use in a larger-scale model of wafer decontamination using computational fluid dynamics (CFD). Also, by using available experimental data and CFD analysis an optimized FOUP purging recipe for better decontamination is presented and the relative magnitude of the time scales associated with surface kinetics and FOUP purging have been estimated. / text

<p> Solar cells were made by diffusing impurities into the rough or backside of commercially available silicon wafers to form a junction. The properties of these solar cells were compared to solar cells made by diffusing impurities into the polished surface of similar silicon wafers. The processing steps involved in preparing each type of solar cell were identical. </p> / Thesis / Master of Engineering (MEngr)

<p> Solar Cells of at least 10% conversion efficiency were fabricated from silicon wafers of one inch diameter and the same processing procedure was applied to wafers of three inch diameter. Four of the three inch diameter solar cells were affixed to a galvanized steel plate and hooked in a parallel configuration to make a solar cell panel. A piece of special plastic was placed over the solar cells on the panel and hermetically sealed to protect the solar cells from the environment which in time would degrade the performance of the solar cells. </p> / Thesis / Master of Engineering (MEngr)

Non-destructive monitoring of residual elastic stress in silicon wafers is a matter of strong concern for modern photovoltaic industry. The excess stress can generate cracks within the crystalline structure, which further may lead to wafer breakage. Cracks diagnostics and reduction in multicrystalline silicon, for example, are ones of the most important issues in photovoltaics now. The industry is intent to improve the yield of solar cells fabrication. There is a number of techniques to measure residual stress in semiconductor materials today. They include Raman spectroscopy, X-ray diffraction and infrared polariscopy. None of these methods are applicable for in-line diagnostics of residual elastic stress in silicon wafers for solar cells. Moreover, the method has to be fast enough to fit in solar cell sequential production line.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Zhijian Pei / Silicon is the primary semiconductor material used to fabricate integrated circuits (ICs). The quality of integrated circuits depends directly on the quality of silicon wafers. A series of processes are required to manufacture the high-quality silicon wafers. Chemical mechanical polishing is currently used to manufacture the silicon wafers as the final material removal process to meet the ever-increasing demand for flatter wafers and lower prices. A finite element analysis has been conducted to study the effects of influencing factors (including Young's modulus and Poisson's ratio of the polishing pad, thickness of the pad, and polishing pressure) on the wafer flatness. In addition, an experimental study was carried out on the effects of process variables (including wafer rotation speed, pad rotation speed, the temperature of the cooling wafer in polishing table, polishing pressure, and the slurry flow rate) on material removal rate (MRR) in polishing of silicon wafers. The results from this study show that the polishing pressure and the pad speed are the most significant factors affecting the MRR. The polishing pad is one of the most critical factors in planarizing the wafer surface. It transports the slurry and interacts with the wafer surface. When the number of polished wafers increases, the pad is glazed and degraded and hence the polishing quality is decreased. The pad properties are changed during the process. The measuring methods for the pad properties including pad thickness monitoring, elastic properties and hardness are reviewed. Elasticity of two types of pads are measured and compared. The poor flatness problems such as tapering, edge effect, concave or convex wafer shape were investigated. Finite element models were developed to illustrate the effects of polishing pad and carrier film properties on the stress and contact pressure distribution on the wafer surface. Moreover, the material removal unevenness is studied. A grinding-based manufacturing method has been investigated experimentally to demonstrate its potential to manufacture flat silicon wafers at a lower cost. It has been demonstrated that the site flatness on the ground wafers (except for a few sites at the wafer center) could meet the stringent specifications for future silicon wafers. One of the problems is the poor flatness at the wafer center: central dimples on ground wafers. A finite element model is developed to illustrate the generation mechanisms of central dimples. Then, effects of influencing factors (including Young's modulus and Poisson's ratio of the grinding wheel segment, dimensions of the wheel segment, grinding force, and chuck shape) on the central dimple sizes are studied. Pilot experimental results are presented to substantiate the predicted results from the finite element model. This provides practical guidance to eliminate or reduce central dimples on ground wafers. The study in this thesis is to understand the mechanism of CMP and grinding of silicon wafers. Improving the processes and the quality of silicon wafers are the final goals.

The development of a chip-based sensor array composed of individually addressable polystyrene-polyethylene glycol and agarose microspheres has been demonstrated. The microspheres are selectively arranged in micromachined cavities localized on silicon wafers. These cavities are created with an anisotropic etch and serve as miniaturized reaction vessels and analysis chambers. The cavities possess pyramidal pit shapes with trans-wafer openings that allow for both fluid flow through the microreactors/analysis chambers as well optical access to the chemically sensitive microspheres. Identification and quantification of analytes occurs via colorimetric and fluorescence changes to receptor and indicator molecules that are covalently attached to termination sites on the polymeric microspheres. Spectral data is extracted from the array efficiently using a charge-coupled device (CCD) allowing for the near-real-time digital analysis of complex fluids. The power and utility of this new microbead array detection methodology is demonstrated here for the analysis of complex fluids containing a variety of important classes of analytes including acids, bases, metal cations, sugars and antibody reagents. The application of artificial neural network analyses to the microbead array is demonstrated in the context of pH measurements. To assess the utility of the analysis and gain an understanding of the molecular level design of the sensor, parameters such as the choice of the indicator dyes, array size, data pre-processing techniques, as well as different network types and architectures were evaluated. Additionally, the development of miniaturized chromatographic systems localized within individual polymer microspheres and their incorporation into an array is reported. The integrated chromatographic and detection concept is based on the creation of distinct functional layers within the microspheres. Such beads have been incorporated into the array platform and used for speciation and concentration determination of aqueous metal cation solutions. / text

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-04-24T14:42:28Z No. of bitstreams: 1 Dissertacao Taila Final.pdf: 2384346 bytes, checksum: 8e3d52f21033cdc04d8f1c3449453ceb (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-05-08T19:50:29Z (GMT) No. of bitstreams: 1 Dissertacao Taila Final.pdf: 2384346 bytes, checksum: 8e3d52f21033cdc04d8f1c3449453ceb (MD5) / Made available in DSpace on 2018-05-08T20:07:12Z (GMT). No. of bitstreams: 1 Dissertacao Taila Final.pdf: 2384346 bytes, checksum: 8e3d52f21033cdc04d8f1c3449453ceb (MD5) Previous issue date: 2018-02-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The solar cells manufactured in n-type silicon, doped with phosphorus, do not present light induced degradation and they have the potential of achieving high efficiency due to the larger minority charge carrier lifetime. Besides, they are less susceptible to contamination by metal impurities. The aim of this work was to analyze different dopants to obtain the p+ region in n+np+ solar cells manufactured in Czochralski silicon wafers, solar grade, n-type, 120 ?m thick. The acceptor impurities used were B, Al, Ga, GaB and AlGa, deposited by spin-on and diffused at high temperature. The temperature, time and gases used in the process of diffusion were ranged. The sheet resistances (R?) of the diffused regions and the impurity concentration profiles were measured. We concluded that the B and GaB can be diffused at 970? C for 20 min to obtain p+ emitters with values of R? suitable to the production of solar cells with screenprinted metal grid. The Ga and AlGa require high temperatures (greater than 1100? C) and long times to produce doping profiles compatible with the production of solar cells. The Al did not produce low sheet resistance regions, even at temperatures of 1100? C. The use of argon gas instead of the nitrogen did not lead to the decreasing of the sheet resistance. The GaB is the only one doping material analyzed that can be a viable replacement for the B in the production of p+ emitter in n-type solar cells.The GaB was the only one doping material analyzed that allowed the manufacture of solar cells with the maximum efficiency of 13.5%, with the diffusion performed at 1020? C for 20 min. The FF was the main parameter that reduced the efficiency of solar cells doped with GaB when compared to the boron doped cells due to a lower shunt resistance. The n+np+ solar cell, 120 ?m thick, that achieved the highest efficiency was doped with boron and reached 14.9%, a value higher than the previously obtained in studies in the NT-Solar with thin silicon wafers. / As c?lulas solares fabricadas em l?minas de sil?cio tipo n, dopadas com f?sforo, n?o apresentam degrada??o por ilumina??o e t?m potencial de obten??o de maior efici?ncia devido ao maior valor do tempo de vida dos portadores de carga minorit?rios. Adicionalmente, s?o menos suscept?veis ? contamina??o por impurezas met?licas. O objetivo deste trabalho foi realizar uma an?lise de diferentes dopantes para obten??o da regi?o p+ em c?lulas solares n+np+fabricadas em l?minas de sil?cio Czochralski, grau solar, tipo n, com espessura de 120 ?m. Os elementos aceitadores utilizados foram o B, Al, Ga, GaB e AlGa, depositados por spin-on e difundidos em alta temperatura. Foram variadas as temperaturas, os tempos e os gases utilizados no processo de difus?o. Foi medida a resist?ncia de folha (R?) das regi?es difundidas e o perfil de concentra??o de impurezas em fun??o da profundidade. Foram desenvolvidas c?lulas solares com B, Ga, GaB e Al. Verificou-se que o B e GaB podem ser difundidos em temperatura de 970 ?C e por 20 min para obten??o de emissores com valores de R? compat?veis com a produ??o de c?lulas solares metalizadas por serigrafia. O Ga e AlGa necessitam de altas temperaturas (maiores que 1100 ?C) e tempos elevados para produzir perfis de dopantes compat?veis. O Al n?o produziu regi?es p+ de baixa R?, mesmo com a difus?o a 1100 ?C. O uso de Ar para substituir o N2 n?o acarretou em diminui??o da resist?ncia de folha. O GaB foi o ?nico dopante analisado que permitiu a fabrica??o de c?lulas solares com efici?ncia m?xima de 13,5 %, com difus?o a 1020 ?C por 20 min. O fator de forma foi o principal par?metro que reduziu a efici?ncia dos dispositivos com GaB quando comparado ao valor obtido com B devido a menor resist?ncia em paralelo. A c?lula solar n+np+ de 120 ?m de maior efici?ncia produzida neste trabalho foi dopada com boro e atingiu a efici?ncia de 14,9 %, sendo maior que as anteriormente obtidas em trabalhos realizados no NT-Solar com l?minas finas.

La connaissance des interactions interfaciales et l'énergie de surface est nécessaire pour étudier et modéliser les processus qui se déroulent dans le mouillage, l'adhésion ou la diffusion. Tels phénomènes sont rencontrés dans la préparation des suspensions, des émulsions et les peintures. Dans ce contexte, l'énergie de surface représente un paramètre important dans l'étude des propriétés interfaciales solide/liquide où plusieurs applications sont impliquées. Nous avons étudié l'effet de la modification chimique sur l'énergie de surface de deux silices choisies selon deux différentes échelles: l'OX qui présente un substrat nanométrique et les wafers de silicium qui est un substrat millimétrique. Pour la silice OX 50, La modification chimique de la surface a été réalisée avec l'hexadecyltrichlosilane (HTS) à caractère hydrophobe. L'infrarouge en transmission et la quantification de carbone organique ont été efficaces pour estimer les quantités croissantes d'HTS greffées à la surface de la silice. Deux isothermes d'adsorption ont été tracées. Ensuite, la volumétrie d'adsorption continue d'argon et d'azote a été utilisée pour étudier l'évolution de l'hétérogénéité énergétique. Ceci a été achevé en faisant recours à une stratégie d'analyse de volume adsorbée à la monocouche (Vm) d'azote et d'argon. Les résultats obtenus ont servi pour tracer une troisième isotherme d'adsorption. La quantification de l'énergie de surface a été réalisée avec la montée capillaire (technique macroscopique) et la chromatographie gazeuse en phase inverse (CGI) (technique moléculaire). Pour les wafers de silicium, deux types de surfaces ont été élaborées durant cette étude. Le premier hydrophile (traitement Piranha, formations des groupements OH). Cette surface a été obtenue par oxydation de ces wafers (traitement Piranha). La deuxième a été obtenue par le greffage d'HTS (greffons CH3). La quantification de l'énergie de surface a été réalisée avec la mouillabilité (technique macroscopique) et la microscopie à force atomique (AFM) (technique nanoscopique). Enfin, les différentes valeurs d?énergie de surface de la silice vierge OX 50 ont été comparées avec celles de la surface plane hydrophile (OH). Pour les surfaces hydrophobes, on a comparé les valeurs d?énergie de surface de la silice OX 50 modifiée d'une quantité maximale d?HTS avec le wafer de silicium à greffons CH3 / The knowledge about interfacial free energy interactions and surface energy is necessary for understanding and modeling many surface and interface processes. The investigation of the surface properties of solids is very important in several applications such as wetting, spreading and adhesion processes. Such processes occur during the preparation of suspensions, emulsions, painting, printing and corrosion protection. Knowledge about surface free energy of solids appears as a very important parameter determining the interfacial properties in solid/liquid and solid/gas interfaces where many implementations are involved. We have studied the effect of the chemical modification on surface energy for two types of silica: Aerosil OX 50 is chosen as a nanometric substrate and the wafers of silicium chosen as micrometric substrate. For silica OX 50, the chemical modification was carried out using the hydrophobic hexadecyltrichlorosilane (HTS). Transmission infrared and the quantification of organic carbon were helpful in the estimation of increasing quantities of HTS grafted to the surface. Two adsorption isotherms were drawn. Then, continuous adsorption isotherm of argon and nitrogen was used to study the evolution of energetic heterogeneity in the course of the chemical reaction. This was achieved by applying an analysis strategy of the monolayer volume (Vm) of adsorbed argon and nitrogen. Results enabled the drawing of a third adsorption isotherm. The quantification of surface energy for various samples was realize using capillary rise (macroscopic technique) and inverse gas chromatography (IGC) (molecular technique). For silicon wafers, two types of surfaces were elaborated in this study. The first hydrophilic (OH grafting), was obtained by oxidation of silicon wafers (Piranha treatment), the second hydrophobic (CH3 grafting), was obtained by grafting HTS molecules to the surface. The quantification of the surface free energy was achieved using the wettability (macroscopic technique) and the atomic force microscopy (AFM) (nanoscopic technique). Finally the different values of surface free energy obtained for native silica are compared to those of hydrophilic (OH) flat surfaces. As for hydrophobic surfaces, the silica OX 50 modified with maximum quantity of HTS is compared to Hydrophobic (CH3) flat surfaces

Nano scale processing of IC chips has become the prime production technique as the microelectronic industry aims towards scaling down product dimensions while increasing accuracy and performance. Accurate control of temperature and a good monitoring mechanism for thickness of the deposition layers during epitaxial growth are critical parameters influencing a good yield. The two-fold objective of this thesis is to establish the feasibility of an alternative to the current pyrometric and ellipsometric techniques to simultaneously measure temperature and thickness during wafer processing. TAP-NDE is a non-contact, non-invasive, laser-based ultrasound technique that is employed in this study to contemporarily profile the thermal and spatial characteristics of the wafer. The Gabor wavelet transform allows the wave dispersion to be unraveled and the group velocity of individual frequency components to be extracted from the experimentally acquired time waveform. The thesis illustrates the formulation of a theoretical model that is used to identify the frequencies sensitive to temperature and thickness changes. The group velocity of the corresponding frequency components is determined and their corresponding changes with respect to temperature for different thickness are analytically modeled. TAP-NDE is then used to perform an experimental analysis on Silicon wafers of different thickness to determine the maximum possible resolution of TAP-NDE towards temperature sensitivity, and to demonstrate the ability to differentiate between wafers of different deposition layer thickness at temperatures up to 600?C. Temperature resolution is demonstrated for ?10?C resolution and for ?5?C resolution; while thickness differentiation is carried out with wafers carrying 4000? and 8000? of aluminum deposition layer. The experimental group velocities of a set of selected frequency components extracted using the Gabor Wavelet time-frequency analysis as compared to their corresponding theoretical group velocities show satisfactory agreement. As a result of this work, it is seen that TAP-NDE is a suitable tool to identify and characterize thickness and temperature changes simultaneously during thermal annealing that can replace the current need for separate characterization of these two important parameters in semiconductor manufacturing.

Nano scale processing of IC chips has become the prime production technique as the microelectronic industry aims towards scaling down product dimensions while increasing accuracy and performance. Accurate control of temperature and a good monitoring mechanism for thickness of the deposition layers during epitaxial growth are critical parameters influencing a good yield. The two-fold objective of this thesis is to establish the feasibility of an alternative to the current pyrometric and ellipsometric techniques to simultaneously measure temperature and thickness during wafer processing. TAP-NDE is a non-contact, non-invasive, laser-based ultrasound technique that is employed in this study to contemporarily profile the thermal and spatial characteristics of the wafer. The Gabor wavelet transform allows the wave dispersion to be unraveled and the group velocity of individual frequency components to be extracted from the experimentally acquired time waveform. The thesis illustrates the formulation of a theoretical model that is used to identify the frequencies sensitive to temperature and thickness changes. The group velocity of the corresponding frequency components is determined and their corresponding changes with respect to temperature for different thickness are analytically modeled. TAP-NDE is then used to perform an experimental analysis on Silicon wafers of different thickness to determine the maximum possible resolution of TAP-NDE towards temperature sensitivity, and to demonstrate the ability to differentiate between wafers of different deposition layer thickness at temperatures up to 600?C. Temperature resolution is demonstrated for ?10?C resolution and for ?5?C resolution; while thickness differentiation is carried out with wafers carrying 4000? and 8000? of aluminum deposition layer. The experimental group velocities of a set of selected frequency components extracted using the Gabor Wavelet time-frequency analysis as compared to their corresponding theoretical group velocities show satisfactory agreement. As a result of this work, it is seen that TAP-NDE is a suitable tool to identify and characterize thickness and temperature changes simultaneously during thermal annealing that can replace the current need for separate characterization of these two important parameters in semiconductor manufacturing.