The technique of ellipsometry was applied to the study of nonuniform anodic oxide films resulting from electrolyte incorporation into the oxide on growth. Ellipsometry results obtained in air and in situ on oxides formed on Ta in phosphoric acid are consistent with the results of tracer studies in which the oxide consists of two layers which grow simultaneously due to metal and oxygen ion transport during anodization, and further that electrolyte incorporation into the outer layer on growth modifies its properties with respect to the inner layer. The ellipsometry results were not consistent with a single homogeneous layer film or with a film possessing an index of refraction changing linearly with thickness. Thus ellipsometry provides a new, nondestructive method of determining ion transport numbers. The index of refraction and thickness of each layer were obtained by curve fitting ellipsometry results obtained as a function of increasing oxide thickness. Computer methods for solving the ellipsometry equation and curve fitting are given. Computed results are given and discussed for cases of one and two layer films growing on a metal. Finally, an error analysis of ellipsometry is made. Ellipsometry results were obtained and curve-fitted for oxides grown in various solutions, at different rates and for anodization in a sequence of electrolytes. The major findings of this part of the study are as follows: Electrolyte incorporation decreases ionic conductivity, dielectric constant and index of refraction. At constant current formation, the fraction of oxide made up by the outer layer increases with current density, and electrolyte concentration, and depends on previous formation of the oxide. The log J-E characteristics at constant voltage in dilute phosphoric acid are curved and occur at higher fields than those for dilute sulphuric acid. Analysis of the above results indicates that: a) the conduction process is bulk controlled b) ionic conduction and dielectric properties arise from the same process and c) that electrolyte incorporation is responsible for part if not all the curvature in the logJ-E characteristics of ionic conduction. Photo-stimulated growth at low electric fields was investigated by ellipsometry. The effect of radiation is to first modify the properties of the existing oxide after which photo-stimulated growth occurs accompanied by a build up of secondary current. The secondary photocurrent is ionic in nature and the radiation rather than the applied field is responsible for the generation of ions to sustain this current. The photo-grown oxide consists of two layer with the outer layer having a much lower index of refraction than normally grown oxide. The thermal recrystallization of stripped anodic oxide films was studied using transmission electron microscopy. Various diffraction patterns were obtained and analyzed. The major result in terms of ionic conduction is that electrolyte incorporation inhibits recrystallization, again, consistent with a decreased ionic mobility with incroporation. A critical test has been devised and applied to a recently proposed theory of ionic conduction, the dielectric polarization theory. This theory postulates that the autocatalytic build up of ionic current on applying a constant high field to the oxide is due to an internal field controlled process and that the rate of build up of polarization (P) towards its equilibrium value (P₀) is enhanced by the passage of current, J, given by dp/dt = AJ(P₀-P). It is shown that this theory predicts an increase in small signal capacitance during the passage of the transient. However, measurements indicate that the capacitance decreases. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The dependence of flow stress of body centered cubic metals on variables such as strain rate, temperature, strain and microstructural is a research area of continued interest. Recently, there has been renewed interest in deformation of fine grained BCC metals, which display characteristics that are different from their coarse-grained counterparts. Deformation mechanisms, strain-rate and temperature dependence, and strain hardening characteristics of fine-grained BCC metals are not well understood. The aim of this thesis is to understand the effect of strain-rate, temperature, strain and microstructure (i.e., grain size) on the mechanical response of poly¬crystalline tantalum. Among the topics addressed were constitutive modeling of flow stress, understanding the microstructural origins of strain hardening, and characterizing the effect of severe plastic deformation (SPD) on microstructure and mechanical properties. Rolling and equal-channel angular pressing (ECAP) were among the processing techniques employed. Mechanical testing was conducted over a range of temperatures and strain rates, and this was supported by a slew of microscopic characterization methods. It was found that the strain hardening response depends on microstructural evolution at different strain rates. Results indicate that the same thermally activated mechanisms operate in both as-received and processed material and this was found to be the overcoming of Peierls barriers via a double-kink mechanism. Lastly, it was found that the low strain rate sensitivity of SPD processed material was not due to fine grain size, but instead due to high internals stresses.

No description available.

Tantalum capacitors are electronic components that are widely used in many types of devices. They are particularly valued for their exceptionally high capacitance and volumetric efficiency. One of the most vital performance parameters for this type of capacitor is the ability to handle unwanted AC ripple, since high levels of ripple can lead to overheating and capacitor failure. Yet the actual ripple limit for a capacitor has been historically difficult to quantify, and has been previously provided to customers only in the form of heavily padded estimates. Throughout the capacitor industry there has been significant demand for more realistic ripple ratings. The discussion here describes a new test system that has been designed to meet this demand for ripple characterization of wet tantalum capacitors.

The metallurgy and superconductivity of the Nb-Ti-Ta ternary alloy system were studied. The Nb-Ti, and Ta-Ti binary samples, and Nb-Ti-Ta ternary samples were precipitation heat treated under different schedules. After the precipitating heat treatment, the samples were characterized by X-Ray Diffraction (XRD) techniques. Equilibrium binary and ternary phase diagrams based on the different alloy compositions and heat treatment temperatures were developed. The Ta-Ti binary phase diagram is very close to the ASM standard phase diagram. The ��-phase boundary of Nb-Ti binary phase diagram developed here is at a higher temperature relative to the ASM standard one. A working ternary equilibrium phase diagram for the Nb-Ti-Ta system has been developed that is based on the experimental measurements and quantitative thermodynamic calculations. Measurements of superconducting critical temperature, Tc, show a good agreement with previous measurements of Tc in the ternary alloys. / Graduation date: 2002

Electrochemical Mechanical Polishing (ECMP) has become increasingly important due to the continuous decrease of the device size in integrated circuit (IC) fabrication. Tantalum (Ta) is a promising material as a substitute for copper in ICs. This dissertation studies the tribology and electrochemistry of Ta ECMP. The present research uses experimental combined analysis approaches. A specially designed experimental setup assembling a tribometer and a potentiostat was used to carry out Ta ECMP. The friction force and electrochemical reactions were measured simultaneously. Using this setup, we found the factors which affected the frictional behaviors of Ta during ECMP. The technique of single frequency electrochemical impedance spectroscopy (EIS) was employed to investigate the material removal mechanisms in Ta ECMP. The results presented the competing mechanisms of removal and formation of a surface oxide layer of Ta. In order to further the investigation in a nanoscale, the atomic force microscope (AFM) was used to measure the material removal rate. The Preston equation for the Ta ECMP was established. A new methodology was developed to study the oxidation state and process of Ta during ECMP. Through comparing the material removal rate measured by using the AFM and the calculated one via the Faraday’s law, the distribution of the Ta suboxides and pentoxide, as well as the oxidation process, was revealed. The oxidation process was strongly dependent of the applied anodic potential, thickness of the oxide layer, mechanical forces, and surface orientation. A polymer environmental cell was designed and produced. Using this cell and AFM, it was found that the material removal in the nanometer scale was a function of the surface orientations. This research is beneficial for optimization of the Ta ECMP process. This dissertation includes six chapters. After Introduction and Motivation and Objectives, the material, setup, and testing conditions are discussed in Chapter III. Chapter IV discusses the tribology and material removal mechanisms in Ta ECMP, while Chapter V the oxidation of Ta during ECMP, followed by Conclusions and Future Work.

Thesis (Ph. D.)--School of Physics, Georgia Institute of Technology, 2004. Directed by Walter A. de Heer. / Vita. Includes bibliographical references (leaves 84-90).

Electro-Chemical Mechanical Planarization (ECMP) is a new and highly promising technology just reaching industrial application; investigation of chemistries, consumables, and tool/control approaches are needed to overcome technological limitations. Development of chemical formulations for ECMP presents several challenges. Unlike conventional CMP, formulations for ECMP may not need an oxidant. Organic additives, especially inhibitors used to control planarity (i.e. to protect recessed regions), need to be stable under applied anodic potential. To have a high current efficiency, the applied current should not induce decomposition of the formulations. In addition, to enable clearing of the copper film, the interactions between multiple exposed materials (barrier material as well as copper) must be considered. Development of a full sequence ECMP process would require the removal of the barrier layer as well. Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP. The main goal of this research is to investigate the chemistries suitable for ECMP of copper and tantalum films. Copper was electroplated onto the gold electrode of quartz crystals, and its dissolution/passivation behavior in hydroxylamine solutions was studied at different applied potential values. The dissolution rate of copper is pH dependent and exhibits a maximum in the vicinity of pH 6. Copper dissolution increases with respect to overpotential (η) and dissolution rates as high as 6000 Å/min have been obtained at overpotential of 750mV. While both benzotriazole (BTA) and salicylhydroxamic acid (SHA) serve as good inhibitors at lower overpotentials, their effectiveness decreases at higher overpotentials. A fundamental study was undertaken to evaluate the usefulness of a sulfonic acid based chemical system for the removal of tantalum under ECMP conditions. Tantalum as well as copper samples were polished at low pressures (~0.5 psi) under galvanostatic conditions in dihydroxy benzene sulfonic acid (DBSA) solutions maintained at different pH values. At a current density of 0.5 mA/cm² and a pH of 10, tantalum removal rate of 200 Å/min with a 1:1 selectivity to copper was obtained in 0.3M DBSA solutions containing 1.2M H₂O₂. The presence of a small amount (~ 0.1%) of colloidal silica particles was required to obtain good removal rates. A comparison of DBSA and methane sulfonic acid (MSA) based chemical system was studied for the removal of tantalum. The performance of DBSA is better than that of MSA. Additionally, DBSA solution has been used for tantalum nitride removal under ECMP conditions. However, DBSA is not as effective for tantalum nitride as it is for tantalum. Polishing of the patterned test structure in optimized solution containing 0.01M BTA results in complete removal of barrier layer and surface planarity is achieved.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 55-57).

Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Speyer, Robert; Committee Co-Chair: Sanders, Thomas; Committee Member: Gerhardt, Rosario; Committee Member: Sandhage, Kenneth; Committee Member: Snyder, Robert; Committee Member: Zhang, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.