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

本研究的重点是利用热丝化学气相沉积（HWCVD）技术制备碳化硅和氮化硅薄膜的气相化学反应和动力学，包括表征自由基中间体的结构和能量特性，以及了解发生在金属丝和衬底表面的化学过程。HWCVD已广泛应用于硅基薄膜、金刚石涂层、纳米颗粒和有机聚合物涂层的生产。碳化硅是太阳能电池中蓝色发光二极管（led）和宽禁带窗材料的优秀候选者，而氮化硅则可以用作薄膜晶体管的钝化层、太阳能电池中的增透涂层和扩散屏障。在本研究中，激光电离质谱法将作为一种检测气相化学物质的强有力的诊断工具，配备了互补的“软”单光子真空紫外激光电离和高效的激光诱导电子电离方法。这些方法在同位素标记、化学捕获和从头计算的支持下，将有助于揭示气相中复杂的化学反应，这是气相薄膜生长前体形成的原因。利用共振增强多光子电离（REMPI）光谱技术，结合高压脉冲放电和脉冲激光烧蚀技术，研究了重要自由基的结构和能量性质。在这些研究的基础上，将开发出对难以分离的自由基具有高灵敏度和选择性的检测方法。我们对HWCVD表面化学的研究将集中在热丝上金属合金的形成和基板上硅基薄膜的生产上。金属细丝在HWCVD中是必不可少的，因为它们作为催化剂分解源气体形成反应物质，从而启动气相反应化学。金属细丝暴露在气相反应物质中会形成金属硅化物和碳化物。这些合成的合金使长丝老化并影响沉积薄膜的性能。我们将系统地研究暴露于对碳化硅和氮化硅薄膜生长重要的各种有机硅源气体时金属丝上的硅化物和碳化物的形成。这将有助于解决长丝老化问题，并使沉积过程得到控制。最后，在不同生长条件下制备的最终硅基薄膜材料的结构和光学性质的表征将与气相反应化学和长丝合金化的科学发现相关联。总的来说，所提出的研究将促进我们目前对HWCVD化学的理解，并有助于HWCVD工艺的合理改进，从而为工业应用带来高质量的薄膜。它将大大有利于加拿大的半导体、替代能源和微电子工业领域。

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.