Hot Wire Chemical Vapor Deposition Chemistry in the Gas Phase and on Surfaces

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The proposed research focuses on the gas-phase reaction chemistry and kinetics involved in the growth of silicon carbide and nitride thin films using hot wire chemical vapor deposition (HWCVD), and involves characterizing the structural and energetic properties of radical intermediates, and understanding the chemical processes taking place on the metal wire and substrate surfaces. HWCVD has been widely used to produce Si-based thin films, diamond coatings, nanoparticles and organic polymer coatings. Silicon carbides are excellent candidates for blue light-emitting diodes (LEDs) and wide bandgap window materials in solar cells, while silicon nitrides can be used as passivation layers in thin film transistors, anti-reflection coatings and diffusion barriers in solar cells. In the proposed research, laser ionization mass spectrometry, equipped with complimentary "soft" single photon vacuum UV laser ionization and efficient laser-induced electron ionization methods, will be used as a powerful diagnostic tool for the detection of gas-phase chemical species. These approaches, supported by isotope labeling, chemical trapping and ab initio calculations, will help unravel the complex reaction chemistry in the gas phase that is responsible for the formation of gas-phase thin film growth precursors. The structures and energetic properties of important radical species will be investigated using resonance enhanced multiphoton ionization (REMPI) spectroscopy combined with the techniques of high-voltage pulsed electric discharge and pulsed laser ablation. Highly sensitive and selective detection methods for the hard-to-isolate radical species will be developed from these studies. Our studies of the surface chemistry in HWCVD will be centered on metal alloy formation on the hot filament and Si-based thin film production on the substrate. Metal filaments are essential in HWCVD as they serve as catalysts to decompose source gases to form reactive species which initiates the gas-phase reaction chemistry. Exposure of metal filaments to the gas-phase reactive species leads to the formation of metal silicides and carbides. These resultant alloys cause the filament to age and affects the deposited film properties. We will systematically study the silicide and carbide formation on the metal wire upon exposure to various organosilicon source gases important for silicon carbide and nitride film growth. This will help solve the problem of filament aging and allow the deposition process to be controlled. Finally, characterization of the structural and optical properties of the ultimate Si-based thin film materials produced under various growth conditions will be correlated to the scientific findings from the gas-phase reaction chemistry and filament alloying. Overall, the proposed research will advance our current understanding of HWCVD chemistry and contribute to a rational improvement of the HWCVD process that will lead to superior-quality thin films for industrial applications. It will benefit greatly the industrial areas of semiconductors, alternative energy sources and microelectronics in Canada.