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Adherence/Diffusion Barrier Layers for Copper Metallization: Amorphous Carbon:Silicon Polymerized Films

Description: Semiconductor circuitry feature miniaturization continues in response to Moore 's Law pushing the limits of aluminum and forcing the transition to Cu due to its lower resistivity and electromigration. Copper diffuses into silicon dioxide under thermal and electrical stresses, requiring the use of barriers to inhibit diffusion, adding to the insulator thickness and delay time, or replacement of SiO2 with new insulator materials that can inhibit diffusion while enabling Cu wetting. This study proposes modified amorphous silicon carbon hydrogen (a-Si:C:H) films as possible diffusion barriers and replacements for SiO2 between metal levels, interlevel dielectric (ILD), or between metal lines (IMD), based upon the diffusion inhibition of previous a-Si:C:H species expected lower dielectric constants, acceptable thermal conductivity. Vinyltrimethylsilane (VTMS) precursor was condensed on a titanium substrate at 90 K and bombarded with electron beams to induce crosslinking and form polymerized a-Si:C:H films. Modifications of the films with hydroxyl and nitrogen was accomplished by dosing the condensed VTMS with water or ammonia before electron bombardment producing a-Si:C:H/OH and a-Si:C:H/N and a-Si:C:H/OH/N polymerized films in expectation of developing films that would inhibit copper diffusion and promote Cu adherence, wetting, on the film surface. X-ray Photoelectron Spectroscopy was used to characterize Cu metallization of these a-Si:C:H films. XPS revealed substantial Cu wetting of a-Si:C:H/OH and a-Si:C:H/OH/N films and some wetting of a-Si:C:H/N films, and similar Cu diffusion inhibition to 800 K by all of the a-:S:C:H films. These findings suggest the possible use of a-Si:C:H films as ILD and IMD materials, with the possibility of further tailoring a-Si:C:H films to meet future device requirements.
Date: May 2004
Creator: Pritchett, Merry
Partner: UNT Libraries

Analysis of PAH and PCB Emissions from the Combustion of dRDF and the Nondestructive Analysis of Stamp Adhesives

Description: This work includes two unrelated areas of research. The first portion of this work involved combusting densified refuse derived fuel (dRDF) with coal and studying the effect that Ca(0H)2 binder had on reducing polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) emissions. The second area of work was directed at developing nondestructive infrared techniques in order to aid in the analysis of postage stamp adhesives. With Americans generating 150-200 million tons a year of Municipal Solid Waste (MSW) and disposing of nearly ninety percent of it in landfills, it is easy to understand why American landfills are approaching capacity. One alternative to landfilling is to process the MSW into RDF. There are technical and environmental problems associated with RDF. This work provides some answers concerning the amount of PAH and PCB emissions generated via the combustion of RDF with coal. It was found that the Ca(OH)2 binder greatly reduced both the PAH and the PCB emissions. In fact, PAH emissions at the ten-percent level were reduced more by using the binder than by the pollution control equipment. If the Ca(0H)2 binder can reduce not only PAH and PCB emissions, but also other noxious emissions, such as acid gases or dioxin, RDF technology could soon be the answer to the current landfill problems. The second portion of this work focused on developing a method to analyze stamp adhesives nondestructively. Using this method, it was fairly easy to differentiate among the three different types of adhesives that have been used by the United States Postal Service: gum arabic, dextrin, and polyvinyl alcohol. Differences caused by changes in chemicals added to the adhesives were also detected. Also, forgeries were detected with as much success, if not more, than by conventional methods. This work also led to the construction of equipment that allows large ...
Date: May 1989
Creator: Poslusny, Matthew
Partner: UNT Libraries

The Analysis of PCDD and PCDF Emissions from the Cofiring of Densified Refuse Derived Fuel and Coal

Description: The United States leads the world in per capita production of Municipal Solid Waste (MSW), generating approximately 200 million tons per year. By 2000 A.D. the US EPA predicts a 20% rise in these numbers. Currently the major strategies of MSW disposal are (i) landfill and (ii) incineration. The amount of landfill space in the US is on a rapid decline. There are -10,000 landfill sites in the country, of which only 65-70% are still in use. The Office of Technology Assessment (OTA) predicts an 80% landfill closure rate in the next 20 years. The development of a viable energy resource from MSW, in the form of densified Refuse Derived Fuel (dRDF), provides solutions to the problems of MSW generation and fossil fuel depletions. Every 2 tons of MSW yields approximately 1 ton of dRDF. Each ton of dRDF has an energy equivalent of more than two barrels of oil. At current production rates the US is "throwing away" over 200,000,000 barrels of oil a year. In order to be considered a truly viable product dRDF must be extensively studied; in terms of it's cost of production, it's combustion properties, and it's potential for environmental pollution. In 1987 a research team from the University of North Texas, in conjunction with the US DOE and Argonne National Laboratory (ANL), cofired over 550 tons of dRDF and bdRDF with a high sulfur Kentucky coal in a boiler at ANL. This work examines the emission rates of polychlorinated dioxins (PCDDs) and furans (PCDFs) during the combustion of the dRDF, bdRDF, and coal. Even at levels of 50% by Btu content of dRDF in the fuel feedstock, emission rates of PCDDs and PCDFs were below detection limits. The dRDF is shown to be an environmentally acceptable product, which could help resolve one of the ...
Date: August 1990
Creator: Moore, Paul, 1962-
Partner: UNT Libraries

Brainstem Lipids' Relationship to Death

Description: Previous work relating postmortem findings with cause of death have focused on the vitreous portion of the body. This research investigated the link between phospholipids in the brainstem and cause of death. The lipids were extracted by the Folch extraction method and then separated by High Performance Thin Layer Chromatography. These techniques gave excellent separation and resolution. Results showed no link between cause of death and the type of lipids found in the brainstem after death.
Date: December 1982
Creator: Schrynemeeckers, Patrick J.
Partner: UNT Libraries

Calcium Silicates: Glass Content and Hydration Behavior

Description: Pure, MgO doped and B2C3 doped monocalcium, dicalcium, and tricalcium silicates were prepared with different glass contents. Characterization of the anhydrous materials was carried out using optical microscopy, infrared absorption spectroscopy, and X-ray powder diffraction. The hydration of these compounds was studied as a function of the glass contents. The hydration studies were conducted at 25°C. Water/solid ratios of 0.5, 1, 10, and 16 were used for the various experiments. The hydration behavior was monitored through calorimetry, conductometry, pH measurements, morphological developments by scanning electron microscopy, phase development by X-ray powder diffraction, and percent combined water by thermogravimetry. A highly sensitive ten cell pseudo-adiabatic microcalorimeter was designed and constructed for early hydration studies. Conductometry was found to be of great utility in monitoring the hydration of monocalcium silicate and the borate doped dicalcium silicates.
Date: August 1987
Creator: Zgambo, Thomas P. (Thomas Patrick)
Partner: UNT Libraries

Chemical and Electronic Structure of Aromatic/Carborane Composite Films by PECVD for Neutron Detection

Description: Boron carbide-aromatic composites, formed by plasma-enhanced co-deposition of carboranes and aromatic precursors, present enhanced electron-hole separation as neutron detector. This is achieved by aromatic coordination to the carborane icosahedra and results in improved neutron detection efficiency. Photoemission (XPS) and FTIR suggest that chemical bonding between B atoms in icosahedra and aromatic contents with preservation of π system during plasma process. XPS, UPS, density functional theory (DFT) calculations, and variable angle spectroscopic ellipsometery (VASE) demonstrate that for orthocarborane/pyridine and orthocarborane/aniline films, states near the valence band maximum are aromatic in character, while states near the conduction band minimum include those of either carborane or aromatic character. Thus, excitation across the band gap results in electrons and holes on carboranes and aromatics, respectively. Further such aromatic-carborane interaction dramatically shrinks the indirect band gap from 3 eV (PECVD orthocarborane) to ~ 1.6 eV (PECVD orthocarborane/pyridine) to ~1.0 eV (PECVD orthocarborane/aniline), with little variation in such properties with aromatic/orthocarborane stoichiometry. The narrowed band gap indicate the potential for greatly enhanced charge generation relative to PECVD orthocarborane films, as confirmed by zero-bias neutron voltaic studies. The results indicate that the enhanced electron-hole separation and band gap narrowing observed for aromatic/orthocarborane films relative to PECVD orthocarborane, has significant potential for a range of applications, including neutron detection, photovoltaics, and photocatalysis. Acknowledgements: This work was supported by the Defense Threat Reduction Agency (Grant No.HDTRA1-14-1-0041). James Hilfiker is also gratefully acknowledged for stimulating discussions.
Date: December 2016
Creator: Dong, Bin
Partner: UNT Libraries

Chemistry, Detection, and Control of Metals during Silicon Processing

Description: This dissertation focuses on the chemistry, detection, and control of metals and metal contaminants during manufacturing of integrated circuits (ICs) on silicon wafers. Chapter 1 begins with an overview of IC manufacturing, including discussion of the common aqueous cleaning solutions, metallization processes, and analytical techniques that will be investigated in subsequent chapters. Chapter 2 covers initial investigations into the chemistry of the SC2 clean - a mixture of HCl, H2O2, and DI water - especially on the behavior of H2O2 in this solution and the impact of HCl concentration on metal removal from particle addition to silicon oxide surfaces. Chapter 3 includes a more generalized investigation of the chemistry of metal ions in solution and how they react with the silicon oxide surfaces they are brought into contact with, concluding with illumination of the fundamental chemical principles that govern their behavior. Chapter 4 shows how metal contaminants behave on silicon wafers when subjected to the high temperature (≥ 800 °C) thermal cycles that are encountered in IC manufacturing. It demonstrates that knowledge of some fundamental thermodynamic properties of the metals allow accurate prediction of what will happen to a metal during these processes. Chapter 5 covers a very different but related aspect of metal contamination control, which is the effectiveness of metal diffusion barriers (e.g. Ru) in holding a metal of interest, (e.g. Cu), where it is wanted while preventing it from migrating to places where it is not wanted on the silicon wafer. Chapter 6 concludes with an overview of the general chemical principles that have been found to govern the behavior of metals during IC manufacturing processes.
Date: May 2005
Creator: Hurd, Trace Q.
Partner: UNT Libraries

Copper Electrodeposition on Iridium, Ruthenium and Its Conductive Oxide Substrate

Description: The aim of this thesis was to investigate the physical and electrochemical properties of sub monolayer and monolayer of copper deposition on the polycrystalline iridium, ruthenium and its conductive oxide. The electrochemical methods cyclic voltammetry (CV) and chronocoulometry were used to study the under potential deposition. The electrochemical methods to oxidize the ruthenium metal are presented, and the electrochemical properties of the oxide ruthenium are studied. The full range of CV is presented in this thesis, and the distances between the stripping bulk peak and stripping UPD peak in various concentration of CuSO4 on iridium, ruthenium and its conductive oxide are shown, which yields thermodynamic data on relative difference of bonding strength between Cu-Ru/Ir atoms and Cu-Cu atoms. The monolayer of UPD on ruthenium is about 0.5mL, and on oxidized ruthenium is around 0.9mL to 1.0mL. The conductive oxide ruthenium presents the similar properties of ruthenium metal. The pH effect of stripping bulk peak and stripping UPD peak of copper deposition on ruthenium and oxide ruthenium was investigated. The stripping UPD peak and stripping bulk peak disappeared after the pH ≥ 3 on oxidized ruthenium electrode, and a new peak appeared, which means the condition of pH is very important. The results show that the Cl- , SO42- , Br- will affect the position of stripping bulk peak and stripping UPD peak: the stripping bulk peak will shift and decrease if the concentration of halide ions is increasing, and the monolayer of UPD will increase at the same time.
Date: December 2003
Creator: Huang, Long
Partner: UNT Libraries

Determination of Solute Descriptors for Illicit Drugs Using Gas Chromatographic Retention Data and Abraham Solvation Model

Description: In this experiment, more than one hundred volatile organic compounds were analyzed with the gas chromatograph. Six capillary columns ZB wax plus, ZB 35, TR1MS, TR5, TG5MS and TG1301MS with different polarities have been used for separation of compounds and illicit drugs. The Abraham solvation model has five solute descriptors. The solute descriptors are E, S, A, B, L (or V). Based on the six stationary phases, six equations were constructed as a training set for each of the six columns. The six equations served to calculate the solute descriptors for a set of illicit drugs. Drugs studied are nicotine (S= 0.870, A= 0.000, B= 1.073), oxycodone(S= 2.564. A= 0.286, B= 1.706), methamphetamine (S= 0.297, A= 1.570, B= 1.009), heroin (S=2.224, A= 0.000, B= 2.136) and ketamine (S= 1.005, A= 0.000, B= 1.126). The solute property of Abraham solvation model is represented as a logarithm of retention time, thus the logarithm of experimental and calculated retention times is compared.
Date: August 2015
Creator: Mitheo, Yannick K.
Partner: UNT Libraries

Direct Atomic Level Controlled Growth and Characterization of h-BN and Graphene Heterostructures on Magnetic Substrates for Spintronic Applications

Description: Epitaxial multilayer h-BN(0001) heterostructures and graphene/h-BN heterostructures have many potential applications in spintronics. The use of h-BN and graphene require atomically precise control and azimuthal alignment of the individual layers in the structure. These in turn require fabrication of devices by direct scalable methods rather than physical transfer of BN and graphene flakes, and such scalable methods are also critical for industrially compatible development of 2D devices. The growth of h-BN(0001) multilayers on Co and Ni, and graphene/h-BN(0001) heterostructures on Co have been studied which meet these criteria. Atomic Layer Epitaxy (ALE) of BN was carried out resulting in the formation of macroscopically continuous h-BN(0001) multilayers using BCl3 and NH3 as precursors. X-ray photoemission spectra (XPS) show that the films are stoichiometric with an average film thickness linearly proportional to the number of BCl3/NH3 cycles. Molecular beam epitaxy (MBE) of C yielded few layer graphene in azimuthal registry with BN/Co(0001) substrate. Low energy electron diffraction (LEED) measurements indicate azimuthally oriented growth of both BN and graphene layers in registry with the substrate lattice. Photoemission data indicate B:N atomic ratios of 1:1. Direct growth temperatures of 600 K for BN and 800 to 900 K for graphene MBE indicate multiple integration schemes for applications in spintronics.
Date: August 2016
Creator: Beatty, John D.
Partner: UNT Libraries

Direct Inject Mass Spectrometry for Illicit Chemistry Detection and Characterization

Description: The field of direct inject mass spectrometry includes a massive host of ambient ionization techniques that are especially useful for forensic analysts. Whether the sample is trace amounts of drugs or explosives or bulk amounts of synthetic drugs from a clandestine laboratory, the analysis of forensic evidence requires minimal sample preparation, evidence preservation, and high sensitivity. Direct inject mass spectrometry techniques can rarely provide all of these. Direct analyte-probed nanoextraction coupled to nanospray ionization mass spectrometry, however, is certainly capable of achieving these goals. As a multifaceted tool developed in the Verbeck laboratory, many forensic applications have since been investigated (trace drug and explosives analysis). Direct inject mass spectrometry can also be easily coupled to assays to obtain additional information about the analytes in question. By performing a parallel artificial membrane assay or a cell membrane stationary phase extraction prior to direct infusion of the sample, membrane permeability data and receptor activity data can be obtained in addition to the mass spectral data that was already being collected. This is particularly useful for characterizing illicit drugs and their analogues for a biologically relevant way to schedule new psychoactive substances.
Date: May 2016
Creator: Williams, Kristina
Partner: UNT Libraries

Electrodeposition of Copper on Ruthenium Oxides and Bimetallic Corrosion of Copper/Ruthenium in Polyphenolic Antioxidants

Description: Copper (Cu) electrodeposition on ruthenium (Ru) oxides was studied due to important implications in semiconductor industry. Ruthenium, proposed as the copper diffusion barrier/liner material, has higher oxygen affinity to form different oxides. Three different oxides (the native oxide, reversible oxide, and irreversible oxide) were studied. Native oxide can be formed on exposing Ru in atmosphere. The reversible and irreversible oxides can be formed by applying electrochemical potential. Investigation of Cu under potential deposition on these oxides indicates the similarity between native and reversible oxides by its nature of inhibiting Cu deposition. Irreversible oxide formed on Ru surface is rather conductive and interfacial binding between Cu and Ru is greatly enhanced. After deposition, bimetallic corrosion of Cu/Ru in different polyphenols was studied. Polyphenols are widely used as antioxidants in post chemical mechanical planarization (CMP). For this purpose, different trihydroxyl substituted benzenes were used as antioxidants. Ru, with its noble nature enhances bimetallic corrosion of Cu. Gallic acid (3,4,5 - trihydroxybenzoic acid) was chosen as model compound. A mechanism has been proposed and validity of the mechanism was checked with other antioxidants. Results show that understanding the chemical structure of antioxidants is necessary during its course of reaction with Cu.
Date: August 2007
Creator: Venkataraman, Shyam S.
Partner: UNT Libraries

Electrodeposition of Diamond-like Carbon Films

Description: Electrodeposition of diamond-like carbon (DLC) films was studied on different substrates using two different electrochemical methods. The first electrochemical method using a three-electrode system was studied to successfully deposit hydrogenated DLC films on Nickel, Copper and Brass substrates. The as-deposited films were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV). A variety of experimental parameters were shown to affect the deposition process. The second electrochemical method was developed for the first time to deposit hydrogen free DLC films on Ni substrates through a two-electrode system. The as-deposited films were characterized by Raman spectroscopy and FTIR. According to Raman spectra, a high fraction of diamond nanocrystals were found to form in the films. Several possible mechanisms were discussed for each deposition method. An electrochemical method was proposed to deposit boron-doped diamond films for future work.
Date: August 2002
Creator: Chen, Minhua
Partner: UNT Libraries

Experimental Determination of L, Ostwald Solubility Solute Descriptor for Illegal Drugs By Gas Chromatography and Analysis By the Abraham Model

Description: The experiment successfully established the mathematical correlations between the logarithm of retention time of illegal drugs with GC system and the solute descriptor L from the Abraham model. the experiment used the method of Gas Chromatography to analyze the samples of illegal drugs and obtain the retention time of each one. Using the Abraham model to calculate and analyze the sorption coefficient of illegal drugs is an effective way to estimate the drugs. Comparison of the experimental data and calculated data shows that the Abraham linear free energy relationship (LFER) model predicts retention behavior reasonably well for most compounds. It can calculate the solute descriptors of illegal drugs from the retention time of GC system. However, the illegal drugs chosen for this experiment were not all ideal for GC analysis. HPLC is the optimal instrument and will be used for future work. HPLC analysis of the illegal drug compounds will allow for the determination of all the solute descriptors allowing one to predict the illegal drugs behavior in various Abraham biological and medical equations. the results can be applied to predict the properties in biological and medical research which the data is difficult to measure. the Abraham model will predict more accurate results by increasing the samples with effective functional groups.
Date: May 2012
Creator: Wang, Zhouxing
Partner: UNT Libraries

Fabrication and light scattering study of multi-responsive nanostructured hydrogels and water-soluble polymers.

Description: Monodispersed microgels composed of poly-acrylic acid (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) interpenetrating networks were synthesized by 2-step method with first preparing PNIPAM microgel and then polymerizing acrylic acid that interpenetrates into the PNIPAM network. The semi-dilute aqueous solutions of the PNIPAM-PAAc IPN microgels exhibit an inverse thermo-reversible gelation. Furthermore, IPN microgels undergo the reversible volume phase transitions in response to both pH and temperature changes associated to PAAc and PNIPAM, respectively. Three applications based on this novel hydrogel system are presented: a rich phase diagram that opens a door for fundamental study of phase behavior of colloidal systems, a thermally induced viscosity change, and in situ hydrogel formation for controlled drug release. Clay-polymer hydrogel composites have been synthesized based on PNIPAM gels containing 0.25 to 4 wt% of the expandable smectic clay Na-montmorillonite layered silicates (Na-MLS). For Na-MLS concentrations ranging from 2.0 to 3.2 wt%, the composite gels have larger swelling ratio and stronger mechanical strength than those for a pure PNIPAM. The presence of Na-MLS does not affect the value of the lower critical solution temperature (LCST) of the PNIPAM. Surfactant-free hydroxypropyl cellulose (HPC) microgels have been synthesized in salt solution. In a narrow sodium chloride concentration range from 1.3 to 1.4 M, HPC chains can self-associate into colloidal particles at room temperature. The microgel particles were then obtained in situ by bonding self-associated HPC chains at 23 0C using divinyl sulfone as a cross-linker. The volume phase transition of the resultant HPC microgels has been studied as a function of temperature at various salt concentrations. A theoretical model based on Flory-Huggins free energy consideration has been used to explain the experimental results. Self-association behavior and conformation variation of long chain branched (LCB) poly (2-ethyloxazoline) (PEOx) with a CH3-(CH2)17 (C18) modified surface are investigated using light scattering techniques in various ...
Date: December 2003
Creator: Xia, Xiaohu
Partner: UNT Libraries

FTIR-ATR Characterization of Hydrogel, Polymer Films, Protein Immobilization and Benzotriazole Adsorption on Copper Surface

Description: Plasma polymerization techniques were used to synthesize and deposit hydrogel on silicon (Si) substrate. Hydrogel is a network of polymer chains that are water-insoluble and has a high degree of flexibility. The various fields of applications of hydrogel include drug release, biosensors and tissue engineering etc. Hydrogel synthesized from different monomers possess a common property of moisture absorption. In this work two monomers were used namely 1-amino-2-propanol (1A2P) and 2(ethylamino)ethanol (2EAE) to produce polymer films deposited on Si ATR crystal. Their moisture uptake property was tested using FTIR-ATR technique. This was evident by the decrease in -OH band in increasing N2 purging time of the films. Secondly, two monomer compounds namely vinyl acetic acid and glycidyl methacrylate which have both amine and carboxylic groups are used as solid surface for the immobilization of bovine serum albumin (BSA). Pulsed plasma polymerization was used to polymerize these monomers with different duty cycles. Initial works in this field were all about protein surface adsorption. But more recently, the emphasis is on covalent bonding of protein on to the surface. This immobilization of protein on solid surface has a lot of applications in the field of biochemical studies. The polymerization of vinyl acetic acid and glycidyl methacrylate were shown as successful method to attach protein on them. Chemical mechanical polishing (CMP) of Cu is one of the processes in the integrated chips manufacturing industry. Benzotriazole is one of the constituents of this CMP slurry used as corrosion inhibitor for Cu. Benzotriazole (C6H5N3) is a nitrogen heterocyclic derivative having three nitrogen atoms, each with an unshared pair of electrons, forming five-membered ring structure. This molecule coordinates with Cu atoms by loosing a proton from one of its nitrogen atom and thereby forming a film which is polymeric in nature that prevents further oxidation of Cu. ...
Date: December 2007
Creator: Pillai, Karthikeyan
Partner: UNT Libraries

Hydraulic Activity in Synthetic and Commercial Slags

Description: Slag, by itself, shows very little hydraulic activity. However, hydration is greatly accelerated by incorporation of the slag with Portland cement. This phenomenon is due to the activating role of calcium hydroxide released from the hydration of Portland cement. This study was aimed at finding other activators that will increase hydration in both synthetic and commercial slags. The effects of chemical composition and the aggregation state of the slag on the hydration process were also investigated. For the synthetic slags, the aggregation state was altered by different quenching techniques. The chemical composition was varied by synthesizing a series of slags. The degree of hydration was studied by developing a thermogravimetric analysis technique and the glass content was determined using microscopy. Minerals were determined using powder x-ray diffraction analysis.
Date: May 1982
Creator: Saad, Bahruddin bin
Partner: UNT Libraries

Hydrogen terminated silicon surfaces: Development of sensors to detect metallic contaminants and stability studies under different environments

Description: Hydrogen terminated silicon surfaces have been utilized to develop sensors for semiconductor and environmental applications. The interaction of these surfaces with different environments has also been studied in detail. The sensor assembly relevant to the semiconductor industry utilizes a silicon-based sensor to detect trace levels of metallic contaminants in hydrofluoric acid. The sensor performance with respect to two non-contaminating reference electrode systems was evaluated. In the first case, conductive diamond was used as a reference electrode. In the second case, a dual silicon electrode system was used with one of the silicon-based electrodes protected with an anion permeable membrane behaving as the quasi reference electrode. Though both systems could function well as a suitable reference system, the dual silicon electrode design showed greater compatibility for the on-line detection of metallic impurities in HF etching baths. The silicon-based sensor assembly was able to detect parts- per-trillion to parts-per-billion levels of metal ion impurities in HF. The sensor assembly developed for the environmental application makes use of a novel method for the detection of Ni2+using attenuated total reflection (ATR) technique. The nickel infrared sensor was prepared on a silicon ATR crystal uniformly coated by a 1.5 micron Nafion film embedded with dimethylglyoxime (DMG) probe molecules. The detection of Ni2+ was based on the appearance of a unique infrared absorption peak at 1572 cm-1 that corresponds to the C=N stretching mode in the nickel dimethylglyoximate, Ni(DMG)2, complex. The suitable operational pH range for the nickel infrared sensor is between 6-8. The detection limit of the nickel infrared sensor is 1 ppm in the sample solution of pH=8. ATR - FTIR spectroscopy was used to study the changes that the hydride mode underwent when subjected to different environments. The presence of trace amounts of Cu2+ in HF solutions was found to roughen the silicon ...
Date: August 2002
Creator: Ponnuswamy, Thomas Anand
Partner: UNT Libraries

Interfacial Electrochemistry and Surface Characterization: Hydrogen Terminated Silicon, Electrolessly Deposited Palladium & Platinum on Pyrolyzed Photoresist Films and Electrodeposited Copper on Iridium

Description: Hydrogen terminated silicon surfaces play an important role in the integrated circuit (IC) industry. Ultra-pure water is extensively used for the cleaning and surface preparation of silicon surfaces. This work studies the effects of ultra-pure water on hydrogen passivated silicon surfaces in a short time frame of 120 minutes using fourier transform infrared spectroscopy – attenuated total reflection techniques. Varying conditions of ultra-pure water are used. This includes dissolved oxygen poor media after nitrogen bubbling and equilibration under nitrogen atmosphere, as well as metal contaminated solutions. Both microscopically rough and ideal monohydride terminated surfaces are examined. Hydrogen terminated silicon is also used as the sensing electrode for a potentiometric sensor for ultra-trace amounts of metal contaminants. Previous studies show the use of this potentiometric electrode sensor in hydrofluoric acid solution. This work is able to shows sensor function in ultra-pure water media without the need for further addition of hydrofluoric acid. This is considered a boon for the sensor due to the hazardous nature of hydrofluoric acid. Thin carbon films can be formed by spin coating photoresist onto silicon substrates and pyrolyzing at 1000 degrees C under reducing conditions. This work also shows that the electroless deposition of palladium and platinum may be accomplished in hydrofluoric acid solutions to attain palladium and platinum nanoparticles on a this film carbon surface for use as an electrode. Catalysis of these substrates is studied using hydrogen evolution in acidic media, cyclic voltammetry, and catalysis of formaldehyde. X-ray diffractometry (XRD) is used to ensure that there is little strain on palladium and platinum particles. Iridium is thought to be a prime candidate for investigation as a new generation copper diffusion barrier for the IC industry. Copper electrodeposition on iridium is studied to address the potential of iridium as a copper diffusion barrier. Copper electrodeposition ...
Date: December 2003
Creator: Chan, Raymond
Partner: UNT Libraries

Interfacial Study of Copper Electrodeposition with the Electrochemical Quartz Crystal Microbalance (EQCM)

Description: The electrochemical quartz crystal microbalance (EQCM) has been proven an effective mean of monitoring up to nano-scale mass changes related to electrode potential variations at its surface. The principles of operation are based on the converse piezoelectric response of quartz crystals to mass variations on the crystal surface. In this work, principles and operations of the EQCM and piezo-electrodes are discussed. A conductive oxide, ruthenium oxide (RuO2) is a promising material to be used as a diffusion barrier for metal interconnects. Characterization of copper underpotential deposition (UPD) on ruthenium and RuO2 electrodes by means of electrochemical methods and other spectroscopic methods is presented. Copper electrodeposition in platinum and ruthenium substrates is investigated at pH values higher than zero. In pH=5 solutions, the rise in local pH caused by the reduction of oxygen leads to the formation of a precipitate, characterized as posnjakite or basic copper sulfate by means of X-ray electron spectroscopy and X-ray diffraction. The mechanism of formation is studied by means of the EQCM, presenting this technique as a powerful in-situ sensing device.
Date: May 2005
Creator: Ojeda Mota, Oscar Ulises
Partner: UNT Libraries

Metal Oxide Reactions in Complex Environments: High Electric Fields and Pressures above Ultrahigh Vacuum

Description: Metal oxide reactions at metal oxide surfaces or at metal-metal oxide interfaces are of exceptional significance in areas such as catalysis, micro- and nanoelectronics, chemical sensors, and catalysis. Such reactions are frequently complicated by the presence of high electric fields and/or H2O-containing environments. The focus of this research was to understand (1) the iron oxide growth mechanism on Fe(111) at 300 K and 500 K together with the effect of high electric fields on these iron oxide films, and (2) the growth of alumina films on two faces of Ni3Al single crystal and the interaction of the resulting films with water vapor under non-UHV conditions. These studies were conducted with AES, LEED, and STM. XPS was also employed in the second study. Oxidation of Fe(111) at 300 K resulted in the formation of Fe2O3 and Fe3O4. The substrate is uniformly covered with an oxide film with relatively small oxide islands, i.e. 5-15 nm in width. At 500 K, Fe3O4 is the predominant oxide phase formed, and the growth of oxide is not uniform, but occurs as large islands (100 - 300 nm in width) interspersed with patches of uncovered substrate. Under the stress of STM induced high electric fields, dielectric breakdown of the iron oxide films formed at 300 K occurs at a critical bias voltage of 3.8 ± 0.5 V at varying field strengths. No reproducible result was obtained from the high field stress studies of the iron oxide formed at 500 K. Ni3Al(110) and Ni3Al(111) were oxidized at 900 K and 300 K, respectively. Annealing at 1100 K was required to order the alumina films in both cases. The results demonstrate that the structure of the 7 Å alumina films on Ni3Al(110) is k-like, which is in good agreement with the DFT calculations. Al2O3/Ni3Al(111) (γ'-phase) and Al2O3/Ni3Al(110) (κ-phase) ...
Date: August 2005
Creator: Qin, Feili
Partner: UNT Libraries

Methods Development for Simultaneous Determination of Anions and Cations by Ion Chromatography

Description: The problem with which this research is concerned is the determination of inorganic anions and cations with single injection ion chromatography. Direct detection of the separated analyte ions occurs after the analyte ions have passed through ion-exchange resins where they are separated according to their affinity for the ion-exchange resin active sites. The techniques involve the use of essentially a non-suppressed ion chromatographic system followed by a suppressed ion chromatographic system. With this system it is possible to accomplish both qualitative and quantitative determinations.
Date: May 1987
Creator: Jones, Vonda K. (Vonda Kaye)
Partner: UNT Libraries

Model Development for the Catalytic Calcination of Calcium Carbonate

Description: Lime is one of the largest manufactured chemicals in the United States. The conversion of calcium carbonate into calcium oxide is an endothermic reaction and requires approximately two to four times the theoretical quantity of energy predicted from thermodynamic analysis. With the skyrocketing costs of fossil fuels, how to decrease the energy consumption in the calcination process has become a very important problem in the lime industry. In the present study, many chemicals including lithium carbonate, sodium carbonate, potassium carbonate, lithium chloride, magnesium chloride, and calcium chloride have been proved to be the catalysts to enhance the calcination rate of calcium carbonate. By mixing these chemicals with pure calcium carbonate, these additives can increase the calcination rate of calcium carbonate at constant temperatures; also, they can complete the calcination of calcium carbonate at relatively low temperatures. As a result, the energy required for the calcination of calcium carbonate can be decreased. The present study has aimed at developing a physical model, which is called the extended shell model, to explain the results of the catalytic calcination. In this model, heat transfer and mass transfer are two main factors used to predict the calcination rate of calcium carbonate. By using the extended shell model, not only the catalytic calcination but also the inhibitive calcination of calcium carbonate have been explained.
Date: December 1987
Creator: Huang, Jin-Mo
Partner: UNT Libraries

Process Evaluation and Characterization of Tungsten Nitride as a Diffusion Barrier for Copper Interconnect Technology

Description: The integration of copper (Cu) and dielectric materials has been outlined in the International Technology Roadmap for Semiconductors (ITRS) as a critical goal for future microelectronic devices. A necessity toward achieving this goal is the development of diffusion barriers that resolve the Cu and dielectric incompatibility. The focus of this research examines the potential use of tungsten nitride as a diffusion barrier by characterizing the interfacial properties with Cu and evaluating its process capability for industrial use. Tungsten nitride (β-W2N) development has been carried out using a plasma enhanced chemical vapor deposition (PECVD) technique that utilizes tungsten hexafluoride (WF6), nitrogen (N2), hydrogen (H2), and argon (Ar). Two design of experiments (DOE) were performed to optimize the process with respect to film stoichiometry, resistivity and uniformity across a 200 mm diameter Si wafer. Auger depth profiling showed a 2:1 W:N ratio. X-ray diffraction (XRD) showed a broad peak centered on the β-W2N phase. Film resistivity was 270 mohm-cm and film uniformity < 3 %. The step coverage (film thickness variance) across a structured etched dielectric (SiO2, 0.35 mm, 3:1 aspect ratio) was > 44 %. Secondary ion mass spectroscopy (SIMS) measurements showed good barrier performance for W2N between Cu and SiO2 with no intermixing of the Cu and silicon when annealed to 390o C for 3 hours. Cu nucleation behavior and thermal stability on clean and nitrided tungsten foil (WxN = δ-WN and β-W2N phases) have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, the Auger intensity ratio vs. time plots demonstrates layer by layer Cu growth for the clean tungsten (W) surface and three-dimensional nucleation for the nitride overlayer. Auger intensity ratio vs. temperature measurements for the Cu/W system indicates a stable interface up to 1000 ...
Date: August 2005
Creator: Ekstrom, Bradley Mitsuharu
Partner: UNT Libraries