An environmentally friendly, and contamination free process for etching and cleaning semiconductors is critical to future of the IC industry. Under the right conditions, water has the ability to meet these requirements. Water becomes more reactive as a function of temperature in part because the number of hydronium and hydroxyl ions increase. As water approaches its boiling point, the concentration of these species increases over seven times their concentrations at room temperature. At 150 °C, when the liquid state is maintained, these concentrations increase 15 times over room temperature. Due to its enhanced reactivity, high temperature water (HTW) has been studied as an etch and clean of thermally grown SiO2, Si3N4, and low-k films. High temperature deuterium oxide (HT-D2O) behaves similarly to HTW; however, it dissociates an order of magnitude less than HTW resulting in an equivalent reduction in reactive species. This allowed for the effects of reactive specie concentration on etch rate to be studied, providing valuable insight into how HTW compares to other high temperature wet etching processes such as hot phosphoric acid (HPA). Characterization was conducted using Fourier transform infrared spectroscopy (FTIR) to determine chemical changes due to etching, spectroscopic ellipsometry to determine film thickness, profilometry to measure thickness change across the samples, scanning electron microscopy (SEM), contact angle to measure changes in wetting behavior, and UV-Vis spectroscopy to measure dissolved silica in post etch water. HTW has demonstrated the ability to effective etch both SiO2 and Si3N4, HT-D2O also showed similar etch rates of Si3N4 indicating that a threshold reactive specie concentration is needed to maximize etch rate at a given temperature and additional reactive species do not further increase the etch rate. Because HTW has no hazardous byproducts, high temperature water could become a more environmentally friendly etchant of SiO2 and Si3N4 thin films.

In this thesis, bulk and local scale spectroscopic and microscopic tools have been applied to investigate the purified raw material of SWCNT and synthesized MWBNNT, BN-nanocapsules, B-doped SWCNT and SiC nanostructures. Using bulk scale sensitive techniques, including optical absorption spectroscopy, Raman spectroscopy, high-resolution electron energy-loss spectroscopy, the average response of the whole sample is obtained. On the other hand, on a local scale transmission and scanning electron microscopy as well as TEM-electron energy-loss spectroscopy provide information on single tubes or other nanostructures. First, diverse chemical and oxidation methods for the purification of as-produced SWCNT were presented. Purified samples were investigated using TEM and OAS. The analysis of the optical absorption spectra in the UV-Vis energy range revealed that some of the chemical treatments are harmful to nanotubes. In contrast to the chemical treatments an oxygen burning procedure was used on the raw material in high vacuum and a temperature range 450?650oC. The purification processes of SWCNT by HNO3 and oxygen burning procedures resulted in SWCNT comprised of selected diameters and a reduced diameter distribution. Both HNO3 and oxygen burning treatments can be used to selectively remove SWCNT with smaller diameters from the samples. In addition, an adapted substitution reaction was used for the synthesis of multiwall boron nitride nanotubes. It was shown that the IR-response of MWBNNT can be used as a fingerprint to analyse MWBNNT. As in h-BN for the analysis one has to be aware of the sample texture and the LO-TO splitting of the IR-active modes. TEM images and B1s and N 1s excitation edges of the grown material reveal the presence of multiwall BN nanotubes with an inner diameter of 3.1 nm and with a larger interplanar distance than in h-BN. The electronic properties of the multiwall BN nanotubes as derived from the q-dependent dielectric function e(w,q) are dominated by the band structure of the hexagonal-like BN sheets, as revealed by the large degree of momentum dispersion observed for the p and s+p plasmons, in agreement with that previously reported for different graphitic allotropic forms. Moreover, a fast and highly efficient synthesis route to produce BN nanocapsules with a narrow size distribution was developed. This was achieved by an adapted substitution process using SWCNT as templates followed by a rapid cooling treatment. The IR responses reveal the strong dipole active fingerprint lines of h-BN with distinct differences, which are due to texturing effects and which highlight the BN nanocapsules potential application as a reference source when deriving the sp2 to sp3 ratio in BN species due to their random orientation Furthermore, the idea of substitution was used for the systematic studies of B-doped SWCNT. The experiments carried out have resulted in 1, 5, 10, and 15 % boron incorporated into the single wall carbon nanotubes. Core level excitation spectroscopy of the B1s and C1s edges revealed that the boron atoms substitute carbon atoms in the tube lattice keeping an sp2-like bond with their nearest C neighbour atoms. Our results show that a simple rigid band model as has been applied previously to intercalated SWCNT is not sufficient to explain the changes in the electronic properties of highly doped B-SWCNT and a new type of a highly defective BC3 SWNT with new electronic properties is obtained. Finally, different silicon carbide nanostructures were produced. The spectroscopic and microscopic data led to a good understanding of the formation process. NH3 acts as a source of hydrogen that plays a key role in the formation of the structures through its ability to decompose SiC at high temperature such that along with the stacking faults that arise from the many polytypes of SiC the produced SiC nanorods become porous then hollow and eventually are completely decomposed.

No description available.

No description available.

Recognizing the dual ability of the nitride ligand to react as a nucleophile or an electrophile – depending on the metal and other supporting ligands – is a key to their broad-range reactivity; thus, three DFT studies were initiated to investigate these two factors effects (the metal and supporting ligands) for tuning nitride ligand reactivity for C-H and N-H bond activation/functionalization. We focused on studying these factors effects from both a kinetic and thermodynamic perspective in order to delineate new principles that explain the outcomes of TMN reactions. Chapter 2 reports a kinetic study of C–H amination of toluene to produce a new Csp3–N (benzylamine) or Csp2–N (para-toluidine) bond activated by diruthenium nitride intermediate. Studying three different mechanisms highlighted the excellent ability of diruthenium nitride to transform a C-H bond to a new C-N bond. These results also revealed that nitride basicity played an important role in determining C–H bond activating ability. Chapter 3 thus reports a thermodynamic study to map basicity trends of more than a one hundred TMN complexes of the 3d and 4d metals. TMN pKb(N) values were calculated in acetonitrile. Basicity trends decreased from left to right across the 3d and 4d rows and increases from 3d metals to their 4d congeners. Metal and supporting ligands effects were evaluated to determine their impacts on TMNs basicity. In Chapter 4 we sought correlations among basicity, nucleophilicity and enhanced reactivity for N–H bond activation. Three different mechanisms for ammonia decomposition reaction (ADR) were tested: 1,2-addition, nitridyl insertion and hydrogen atom transfer (HAT). Evaluating nitride reactivity for the aforementioned mechanisms revealed factors related to the metal and its attached ligands on TMNs for tuning nitride basicity and ammonia N–H activation barriers.

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The sublimation recondensation crystal growth of aluminum nitride, titanium nitride, and yttrium nitride were explored experimentally and theoretically. Single crystals of these nitrides are potentially suitable as substrates for AlGaInN epitaxial layers, which are employed in ultraviolet optoelectronics including UV light-emitting diodes and laser diodes, and high power high frequency electronic device applications. A thermodynamic analysis was applied to the sublimation crystal growth of aluminum nitride to predict impurities transport (oxygen, carbon, and hydrogen) and to study the aspects of impurities incorporation for different growth conditions. A source purification procedure was established to minimize the impurity concentration and avoid degradation of the crystal’s properties. More than 98% of the oxygen, 99.9% of hydrogen and 90% of carbon originally in the source was removed. The AlN crystal growth process was explored in two ways: self-seeded growth with spontaneous nucleation directly on the crucible lid or foil, and seeded growth on SiC and AlN. The oxygen concentration was 2 ~ 4 x 1018cm-3, as measured by secondary ion mass spectroscopy in the crystals produced by self-seeded growth. Crystals grown from AlN seeds have visible grain size expansion. The initial AlN growth on SiC at a low temperature range (1400°C ~1600°C) was examined to understand the factors controlling nucleation. Crystals were obtained from c-plane on-axis and off-axis, Si-face and C-face, as well as m-plane SiC seeds. In all cases, crystal growth was fastest perpendicular to the c-axis. The growth rate dependence on temperature and pressure was determined for TiN and YN crystals, and their activation energies were 775.8±29.8kJ/mol and 467.1±21.7kJ/mol respectively. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45o angle between TiN [100] and W [100], was seen for TiN crystals deposited on both (001) textured tungsten and randomly orientated tungsten. Xray diffraction confirmed that the YN crystals were rock-salt structure, with a lattice constant of 4.88Å. Cubic yttria was detected in YN sample from the oxidation upon its exposed to air for limited time by XRD, while non-cubic yttria was detected in YN sample for exposures more than one hour by Raman spectra.

Master of Science / Department of Electrical and Computer Engineering / Andrew Rys / It is important in semiconductor manufacturing to understand the physical and electrical characteristics of new proposed semiconductors to determine their usefulness. Many tests are used in order to achieve this goal, such as x-ray diffraction, Hall effect measurements, and the scanning electron microscope. With these tests, the usefulness of the semiconductor can be determined, leading to more possibilities for growth in industry. The purpose of the present study was to look at the semiconductor scandium nitride (ScN), grown using the hydride vapor phase epitaxy (HVPE) method on various substrates, and determine the physical and electrical properties of the sample. This study also sought to answer the following questions: 1) Can any trends be found from the results?, and 2) What possible application could scandium nitride be used for in the future? A sample set of scandium nitride samples was selected. Each one of these samples was checked for contaminants from the growth procedure, such as chlorine, under the scanning electron microscope and checked for good conduction of current needed for the Hall effect measurements. The thickness of the scandium nitride layer was computed using the scanning electron microscope. Using the thickness of the scandium nitride, Hall effect measurement values were computed. The plane the samples lie on was checked using x-ray diffraction. The test results shed light on many trends in the scandium nitride. Many of the samples were determined to have an aluminum nitride (AlN) contamination. This contamination led to a much higher resistivity and a much lower mobility no matter what thickness the scandium nitride was. The data from the samples was then used to offer suggestions on how to improve the growth process.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy