Chemical vapor deposition of diamond

• Main Author: Doty, Fred Patrick
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1991
• Subjects: Chemical engineering; Electrical engineering; Materials science
• ISBN: 9798641332871

Low pressure formation of diamond is now a well known phenomenon, although the formation mechanism remains unknown. Much experimental work has recently been reported by those developing chemical vapor deposition (CVD) techniques to exploit the unique properties of diamond for diverse applications, such as wear resistant coatings, heat sinks and semiconductor devices, and a number of models have been proposed for chemical and physical processes causing conditions under which carbonaceous gas mixtures deposit diamond rather than graphite, the thermodynamically favored structure at low pressure. The prevailing theories rely on species including hydrocarbon molecules and free radicals, which are generated by homogeneous gas-phase chemistry, and provide a kinetically favorable route to the diamond structure. For example, one model relies on a free radical initiation step followed by addition of acetylene to the diamond surface. Another proposed model invokes positive ions to initiate the process. Thus conflicting theories have been proposed, and little experimental work specifically addressed to qualifying these theories has been reported. This work was undertaken to test the proposed growth mechanisms, and to identify the dominant physical and chemical processes occurring during the deposition process. A modified CVD reactor was used, which enabled growth experiments to be carried out under unique and well controlled conditions. None of the proposed growth mechanisms is supported by the results of these growth experiments, and it was found that a negatively charged species strongly affects the CVD process. Since charged species in the CVD reactor are important, the electrical behavior of the reactor was thoroughly investigated. The results support surface catalyzed reactions for generating the species participating in the diamond growth process, and show that electric fields can be used to improve the CVD process and reactor design.