| Two aspects of chemical vapor deposition (CVD) are addressed. Both are aimed at improving existing CVD technology, by either improving film quality or by increasing the traditionally slow deposition rate. The goal was to gain a better understanding of underlying phenomena in these two areas of CVD by analyzing them theoretically. It is hoped that the theoretical models developed for this purpose will allow prediction of film properties and reactor performance, which can be used in the design and optimization of future CVD reactors. The first aspect of CVD addressed is interface evolution and the morphology of amorphous CVD films grown under high pressure (close to atmospheric) deposition. A continuum model of deposition on the microscopic scale is developed, and a detailed analysis of the influence of deposition conditions on film uniformity is presented. A linear stability analysis is presented, but the real focus is on solution of the governing equations under nonplanar growth conditions. A numerical solution procedure is developed, which allows us to follow the evolution of highly irregular morphological shapes during different CVD conditions, and from almost any initial interface shape. The process can be characterized by a Damkohler number of deposition, Da, and simulation results showed phenomena very similar to those observed experimentally. Film uniformity and step coverage decreases with increasing values of Da. We believe the solution procedure can be used for tracking interface evolution in a wide variety of Stefan-like free-boundary problems, especially those with highly irregular interface shapes.; The second part deals with an innovative CVD method, we call particle-aided chemical vapor deposition (PACVD). Application of this method was shown to increase the CVD growth rate tremendously, by seeding the gas feed with aerosol particles of a solid material. PACVD was successfully used to produce composites of SiC with {dollar}TiBsb2{dollar}, {dollar}Sisb3Nsb4{dollar} and {dollar}Bsb4C{dollar}. A theoretical analysis of PACVD is presented, where complex gas and aerosol flow phenomena in the highly non-isothermal reactor are accounted for, as well as simultaneous particle and chemical co-deposition onto the substrate. Numerical results predicted phenomena similar to those observed experimentally, and were used to determine modifications to improve uniformity of deposition. |
