In this thesis,zirconium carbide (ZrC) layers were deposited on graphite substrates using a CVD reactor at temperatures ranging from 1250 °C to 1450 °C in steps of 50 °C. The deposited layers were characterised by XRD, Raman Spectroscopy and SEM.ZrCsamples were also prepared by spark plasma sintering (SPS), at 1700, 1900 and 2100 °C at 50 MPa for 10 minutes. The phase and microstructure after the sintering process were investigated by XRD and SEM. Iridium (Ir) thin films were deposited on these ZrCsamples and annealed in vacuum at temperatures of 600 and 800 °C for 2h. The phase composition, solid-state reactions and surface morphology were investigated by GIXRD and SEM. XRD was used to identify the phases present in the as-deposited and annealed samples. It showed that Ir2Zr was the initial phase formed at 600 °C. At temperature 800 °C IrZr formed. / Thesis (PhD (Physics))--University of Pretoria, 2019. / University of Pretoria / Physics / PhD (Physics) / Unrestricted

In the past few decades, devices such as computers have become smaller, and their performance has improved beyond comparison. Semiconductors and interconnectors are used in almost all devices today and are made of thin films. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are common methods for depositing conformal films, where the film grows by being exposed to precursors either continuously as in CVD or by pulses as is pulsed CVD and ALD. It has been reported that Cu amidinate and guanidinate are precursors for depositing metallic Cu (Copper), but they tend to decompose. Precursors that are thermally stable and can be used to deposit a thin film of Cu are (1,3-di-tert-butyltriazenides) copper(I) (Cu-triazenides). This precursor has been synthesized and developed by the Pedersen Group in the Department of Physics, Chemistry, and Biology (IFM) at Linköpings University. This thesis investigates if Cu-triazenides are suitable as vapor deposition precursors using pulsed CVD and if Cu-triazenides are suitable as an ALD precursor with H2O as the second precursor. The main objective of this thesis is to focus on films deposited with ALD by finding the ALD window that gives a growth per cycle and making a saturation curve for each precursor. Si(100) and glass were used as the substrate, and SEM-EDX (Scanning electron microscopy- Energy- dispersive X-ray spectroscopy), XRD (X-ray diffraction), and XRR (X-ray reflectivity) analyzed the chemical, physical and, optical properties of the films. The Cu-triazenides were suitable as single-source precursors, as films were deposited with pulsed CVD on both Si(100) and glass. ALD deposited no film on Si(100) between the temperature 175–300 °C, and the analysis methods did not provide information on the thickness and composition of the films deposited on the glass.

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Self assembled monolayers (SAMs) are widely used for surface modification. Alkylsilane monolayers are one of the most widely deposited and studied SAMs. My work focuses on the preparation, patterning, and application of alkysilane monolayers. 3-aminopropyltriethoxysilane (APTES) is one of the most popular silanes used to make active surfaces for surface modification. To possibly improve the surface physical properties and increase options for processing this material, I prepared and studied a series of amino silane surfaces on silicon/silicon dioxide from APTES and two other related silanes by chemical vapor deposition (CVD). I also explored CVD of 3-mercaptopropyltrimethoxysilane on silicon and quartz. Several deposition conditions were investigated. Results show that properties of silane monolayers are quite consistent under different conditions. For monolayer patterning, I developed a new and extremely rapid technique, which we termed laser activation modification of semiconductor surfaces or LAMSS. This method consists of wetting a semiconductor surface with a reactive compound and then firing a highly focused nanosecond pulse of laser light through the transparent liquid onto the surface. The high peak power of the pulse at the surface activates the surface so that it reacts with the liquid with which it is in contact. I also developed a new application for monolayer patterning. I built a technologically viable platform for producing protein arrays on silicon that appears to meet all requirements for industrial application including automation, low cost, and high throughput. This method used microlens array (MA) patterning with a laser to pattern the surface, which was followed by protein deposition. Stencil lithography is a good patterning technique compatible with monolayer modification. Here, I added a new patterning method and accordingly present a simple, straightforward procedure for patterning silicon based on plasma oxidation through a stencil mask. We termed this method subsurface oxidation for micropatterning silicon (SOMS).

A modified CVD reactor was designed with a deposition chamber capable of accommodating 8" wafers, with the capacity to remotely pyrolyze two different precursors. The design was based on a previous working reactor, with the most notable improvements being a showerhead design for more even delivery of gaseous precursor and a separate heating control of the substrate holder and deposition chamber walls. The performance of the reactor was analyzed by testing the pressure gradients within and the thickness uniformity of films deposited on 8" wafers. The reactor exhibited a linear pressure gradient within, and the thickness uniformity was excellent, with a slight increase in thickness towards inlet of the showerhead. The thickness difference between the maximum and minimum thickness on an 8" wafer was 14%. Films of polyparaxylylene (PPXN), polychloroparaxylylene (PPXC), SiO₂, and PPXC/SiO₂ were deposited, with deposition rates and indices of refraction comparable to those obtained on the old reactor design. A full factorial study was performed to determine the effect of the substrate temperature, the sublimation temperature, and the pyrolysis temperature on the deposition rates of PPXC. It was determined that the substrate temperature has the greatest effect, with about 50% contribution, and deposition rates increased with decreasing substrate temperature. The sublimation temperature contributed 25%, with increasing sublimation rates leading to higher deposition rates. The pyrolysis contributes very little, with about 2%, and the variance ratio did not fall within a 90% confidence level. A low dielectric constant polymer, poly(tetrafluoro-p-xylylene) (VT-4), was synthesized by chemical vapor deposition from 4,5,7,8,12,13,15,16-octafluoro-[2.2]-paracyclophane (DVT-4). The main motivation was to find a cheaper alternative to poly( alpha, alpha , alpha ', alpha '-tetrafluoro-p-xylylene) (AF-4) with similar properties. The dielectric constant of VT-4 was measured as 2.42 at 1 MHz, and the in-plane and out-of-plane indices of refraction were 1.61 and 1.47 at 630 nm. The large negative birefringence suggests a low out-of-plane dielectric constant, which is desired for interlayer dielectrics. The VT-4 polymer was found to be stable at 460 °C by thermogravimetric analysis (TGA). Polymer/Siloxane nanocomposites were studied as an alternate path to a polymer/silica composite. This study showed that incorporation of a four-ringed liquid siloxane precursor into the parylene PPXC is not feasible. A solid precursor cube-like molecule, vinyl-T8, was incorporated with ease. Pyrolysis of vinyl-T8 at different temperatures revealed complex behavior, with the formation of polymerized vinyl-T8 (through free radical addition at the vinyl groups) as well as silica-like structures forming above 500 °C as a result of the breaking up of the cage structure of vinyl-T8. Codepositions of PPXC and vinyl-T8 were then examined as a possible path towards a polymer/silica nanocomposite. At deposition temperatures below 5 °C, precipitation of excess vinyl-T8 into cubic micron-sized crystals occurred. As this was undesirable, studies were continued at higher deposition temperatures. A Taguchi orthogonal array was set up to study the effect of the sublimation temperatures of the two precursors as well as the pyrolysis temperature and the substrate temperature on the deposition rate, the index of refraction and the weight loss after a 500 °C anneal. The deposition rate depended mostly on the sublimation temperature of the PPXC and the substrate temperature. The lowest index of refraction (and thus the lowest dielectric constant) was obtained with the lowest sublimation temperatures of 134 °C for PPXC and 195 °C for vinyl-T8 and a pyrolysis temperature of 200 °C. Each of the factors was found to have an effect on the index of refraction, with the sublimation temperature of vinyl-T8 having the most influence. The films degraded at 500 °C, indicating that post-deposition annealing of the films did not lead to a conversion of the vinyl-T8 to a SiO₂-like structure (which would be stable at that temperature). X-ray diffraction spectra of the films revealed peaks which were not present for any of the vinyl-T8 films or characteristic of PPXC. Therefore, some type of interaction between the two components occurred and affected the morphology, most likely the formation of a block copolymer. Thus, though polymer/silica films were not attained, the resulting composites had comparable properties with higher deposition rates and a cleaner process. / Master of Science

Information processing is crucial in modern society, placing a great emphasis on the performance of optoelectronic devices to match ever increasing processing and memory needs. Within these devices, MoS2 has demonstrated great potential as transistors due to its enhanced electrostatic control. As increased layer thickness of quality MoS2 films have been shown to boost the performance of its transistors, growth parameters for the synthesis of ideally uniform and large area multilayered films via chemical vapor deposition were investigated. By increasing the flow pressure in the system and the growth time, increasing levels of thickness and nucleation density was shown for MoS2 growth. Although the scale of the growth was non-uniform in nature, films containing large areas of thicker MoS2 was achieved. The thickness of the films was confirmed by Raman and photoluminescence measurements by confirming their values with exfoliated MoS2 measurements.

With the low-temperature halo-carbon epitaxial growth technique developed at MSU prior to this work, use of a halo-carbon growth precursor enabled low-temperature homoepitaxial process for 4H-SiC at temperatures below 1300 °C with good quality. Investigations of the nitrogen doping dependence are reported. It has been demonstrated that the efficiency of the nitrogen incorporation may be different for different substrate orientations, with the Cace showing the higher value of doping. The Si/C ratio is known to influence the doping during the epitaxial growth due to the site-competition mechanism. The doping on the Cace showed weak dependence on the Si/C ratio. On the Siace, the doping dependence follows the site-competition trend. At high Si/C ratio, the doping trend on Siace shows strong deviation. Both of the investigated trends are suggested for use as the main process dependencies for achieving a wide range of n type doping of SiC during the low-temperature halo-carbon homoepitaxial process.

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