Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Bibliography: 211-229.

Thesis (M.S.)--Ohio University, August, 1995. / Title from PDF t.p.

No description available.

Metallic films are important in various applications, such as electric devices where it can act as contacts. In electrical devices, the substrate typically consists of silicon dioxide (SiO2) which is a temperature-sensitive substrate. Therefore, plasma enhanced chemical vapor deposition (PECVD) are better suited than thermally activated chemical vapor deposition (CVD). Depositing metallic films with PECVD demands co-reactants that act as reducing agents. However, these are not well-studied and do not always have the power enough to perform the reduction reaction for metals. Recently it has been concluded that electrons can act as reducing agents in the deposition of first row transition metallic films in a PECVD process. By supplying a positive bias to the substrate, the electrons got attracted to the surface of the substrate, which facilitated metal growth. The study concluded that metal growth only occurred at conductive -and semiconductive substrates and that the substrate bias and plasma power affected the metal growth. The process is however not well understood, which causes a knowledge gap, signifying that studies of the surface chemistry are needed. Here a new modified analytical method to study the surface chemistry in the newly developed process mentioned above is presented. The analytical method consists of an electrically modified quartz crystal microbalance (QCM) with gold electrodes as a conductive substrate. This allows the electron current to run through the QCM during the measurement. By supplying a DC-voltage to the front electrode it gets readily biased (negative and positive) and by placing a capacitor in the circuit, it connects the AC-circuit (oscillator circuit) and the DC-circuit (DC-voltage bias circuit). At the same time, it blocks the DC-current from going back to the oscillator but allows the high-frequency signal to pass from the QCM. The results in this thesis concluded that the QCM can be electrically modified to allow an electron flux to the QCM while using it as a substrate when electrons are used as reducing agents. Scanning electron microscopy (SEM) of a QCM crystal revealed that a 2 µm film had been deposited while SEM coupled with energy dispersive X-ray spectroscopy (EDS) showed that the film indeed contained iron. Further analysis was made by high-resolution X-ray photoelectron spectroscopy (HR-XPS) to find the elemental composition of the film, which revealed that the thin film contained 41 at.% iron. In addition, this study investigated if the QCM could be used to study CVD processes where electrons were used as reducing agents. The results indeed revealed that it is possible to study the surface chemistry where electrons are used as reducing agents with the electrically modified QCM to gain knowledge concerning film deposition. Initial results of the QCM showed that film growth could be studied when varying the plasma power between 5 W to 15 W and the QCM bias between -40 V to +40 V. The method generated easily accessible data concerning the process where electrons are used as reducing agents, which gained insight to the method that never has been disclosed before.

No description available.

[Truncated abstract] This study investigates the thermal stability of Plasma Enhanced Chemical Vapor Deposited (PECVD) silicon nitride thin films. Effects of heat-treatment in air on the chemical composition, atomic bonding structure, crystallinity, mechanical properties, morphological and physical integrity are investigated. The chemical composition, bonding structures and crystallinity are studied by means of X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) Spectroscopy and Transmission Electron Microscopy (TEM). The mechanical properties, such as hardness and Young’s modulus, are determined by means of nanoindentation. The morphological and physical integrity are analyzed using Scanning Electron Microscopy (SEM) . . . The Young’s modulus (E) and hardness (H) of the film deposited at 448 K were measured to have E=121±1.8 GPa and H=11.7±0.25 GPa. The film deposited at 573 K has E=150±3.6 GPa and H=14.7±0.6 GPa. For the film deposited at 573 K, the Young’s modulus is not affected by heating up to 1148 K. Heating at 1373 K caused significant increase in Young’s modulus to 180∼199 GPa. This is attributed to the crystallization of the film. For the film deposited at 448 K, the Young’s modulus showed a moderate increase, by ∼10%, after heating to above 673 K. This is consistent with the much lower level of crystallization in this film as compared to the film deposited at 573 K. In summary, low temperature deposited PECVD SiNx films are chemically and structurally unstable when heated in air to above 673 K. The main changes include oxidation to SiO2, crystallization of Si3N4 and physical cracking. The film deposited at 573 K is more stable and damage and oxidation resistant than the film deposited at 448 K.

This dissertation proposed the idea of “plasma-enhanced chemical vapor deposition on living substrates (PECVD on living substrates)” to bridge the gap between the thin film deposition technology and the biological and living substrates. This study focuses on the establishment of the knowledge and techniques necessary to perform “PECVD on living substrates” and contains three main aspects: development, characterization, and biological applications. First, a PECVD tool which can operate in ambient air and at low temperature was developed using a helium dielectric barrier discharge jet (DBD jet). It was demonstrated that various materials, such as polymeric, metallic, and composite films, can be readily synthesized through this technique. Second, the PMMA and copper films deposited using DBD jets were characterized. High-rate (22 nm/s), low-temperature (39 ºC) PMMA deposition was achieved and the film surface morphology can be tailored by altering the discharge power. Conductive copper films with an electrical resistivity lower than 1×10-7 ohm-m were obtained through hydrogen reduction. Both PMMA and copper films can be grown on temperature-sensitive substrates, such as plastics, pork skin, and even fingernail. The electrical, optical, and imaging characterization of the DBD jets was also conducted and several new findings were reported. Multiple short-duration current pulses instead of only one broad pulse per half voltage cycle were observed when a dielectric substrate was employed. Each short-duration current pulse is induced by a leading ionization wave followed by the formation of a plasma channel. Precursor addition further changed the temporal sequence of the pulses. An increase in the power led to a mode change from a diffuse DBD jet to a concentrated one. This mode change showed significant dependence on the precursor type, tube size, and electrode configuration. These findings regarding the discharge characteristics can thus facilitate the development of DBD-jet operation strategies to improve the deposition efficacy. Finally, this technique was used to grow PMMA films onto agar to demonstrate one of its potential biological applications: sterile bandage deposition. The DBD jet with the film depositing ability enabled the surface to be not only efficiently sanitized but also protected by a coating from being reached by bacteria.

The structure and the energy band gap of hydrogenated amorphous silicon carbide are theoretically revised. In the light of defect pool model, density of states distribution is investigated for various regions of mobility gap. The films are deposited by plasma enhanced chemical vapor deposition system with various gas concentrations at two different, lower (30 mW/cm2) and higher (90 mW/cm2), radio frequency power densities. The elemental composition of hydrogenated amorphous silicon carbide films and relative composition of existing bond types are analyzed by x-ray photoelectron spectroscopy measurements. The thicknesses, deposition rates, refractive indices and optical band gaps of the films are determined by ultraviolet visible transmittance measurements. Uniformity of the deposited films is analyzed along the radial direction of the bottom electrode of the plasma enhanced chemical vapor deposition reactor. The molecular vibration characteristics of the films are reviewed and analyzed by Fourier transform infrared spectroscopy measurements. Electrical characteristics of the films are analyzed by dc conductivity measurements. Conduction mechanisms, such as extended state, nearest neighbor and variable range hopping in tail states are revised. The hopping conductivities are analyzed by considering the density of states distribution in various regions of mobility gap. The experimentally measured activation energies for the films of high carbon content are too low to be interpreted as the difference between Fermi level and relevant band edge. This anomaly has been successfully removed by introducing hopping conduction across localized tail states of the relevant band. In other words, the second contribution lowers the mobility edge towards the Fermi level.

The instability under bias voltage stress and low mobility of hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT), produced by plasma enhanced chemical vapor deposition (PECVD) technique, are the main problems impeding the implementation of active matrix arrays for light emitting diode display panels and their peripheral circuitry. Replacing a-Si:H by hydrogenated nanocrystalline silicon film (nc-Si:H) seems a solution due to its higher mobility and better stability. Therefore nc-Si:H TFT was produced and investigated in this thesis. All TFT layers (doped nc-Si:H, intrinsic nc-Si:H and insulator films) were produced separately, characterized by optical (UV-visible and FTIR spectroscopies, XRD) and electrical (current-voltage, I-V) methods, and optimized for TFT application. Afterwards the non self-aligned bottom-gate TFT structure was fabricated by the photolithographic method using 2-mask set. The n+ nc-Si:H films, used for TFT drain/source ohmic contacts, were produced at high H2 dilution and at several RF power densities (PRF). The change of their lateral resistivity (rho) was measured by reducing the film thickness via reactive ion etching. The rho values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The optimum PRF for the lowest incubation layer was determined. Among the deposition parameters only increased NH3/SiH4 flow rate ratio improved the insulating properties of the amorphous silicon nitride (a-SiNx:H) films, chosen as the TFT gate dielectric. The electrical characteristics of two TFTs with a-SiNx:H having low leakage current, fabricated at different NH3/SiH4 ratios (~19 and ~28) were compared and discussed. The properties (such as crystallinity, large area uniformity, etc.) of the nc-Si:H film as TFT channel layer, were found to depend on PRF. For the films deposited at the center of the PECVD electrode the change from an amorphous dominant structure to a nanocrystalline phase took place with increasing PRF, whereas those at the edge had always nanocrystalline nature, independent of PRF. The two different TFTs produced at the center of the electrode with a-Si:H and nc-Si:H grown at low and high PRF, respectively, were compared through their I-V characteristics and electrical stability under the gate bias voltage stress. Finally, nc-Si:H TFT structure, produced and optimized in this work, was analyzed through gate-insulator-drain/source capacitor by capacitance-voltage (C-V) measurements within 106-10-2 Hz frequency (F) range. The inversion regime was detected at low F without any external charge injection. Besides, ac hopping conductivity in the nc-Si:H bulk was extracted from the fitting results of the C-F curves.

The significance of the radioxenon memory effect in the context of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty is introduced as motivation for the project. Existing work regarding xenon memory effect reduction and thin film diffusion barriers is surveyed. Experimental techniques for radioxenon production and exposure, as well as for thin film deposition on plastic by plasma enhanced chemical vapor deposition (PECVD), are detailed. A deposition rate of 76.5 nm min⁻¹ of SiO₂ is measured for specific PECVD parameters. Relative activity calculations show agreement within 5% between identically exposed samples counted on parallel detectors. Memory effect reductions of up to 59±1.8% for 900 nm SiO₂ films produced by plasma enhanced chemical vapor deposition and of up to 77±3.7% for 50 nm Al₂O₃ films produced by atomic layer deposition are shown. Future work is suggested for production of more effective diffusion barriers and expansion to testing in operational monitoring stations. / text