Active matrix liquid crystal displays offer improved performance and reduced size (in terms of depth) for specialized applications in laptop computing and high-definition television. High manufacturing costs are the greatest barrier to the proliferation of this technology. To fabricate the "active matrix," display manufacturers must first deposit a thin film of amorphous or polycrystalline silicon on a glass substrate. Conventional techniques for depositing these films suffer from inefficiency, high temperatures, and consequently, high costs. Directed vapor deposition (DVD), in contrast, is a simple, potentially cost-effective deposition process. In DVD, an electron beam melts the source materials and produces a vapor. A helium gas jet passes directly over the crucible, entraining the source vapor and transporting it to the substrate. The directed vapor deposition system allows the operator to vary process variables such as substrate temperature, jet composition, and electron beam power. This research project examined the effects of these variables on the microstructure of deposited silicon films. For deposition rates of ~150-300 nanometers per minute (nm/min), the transition from an amorphous microstructure to a polycrystalline microstructure occurred between 475^oC and 515^oC. The silicon films deposited at temperatures above 300^oC exhibited rough morphology unsuitable for electronic applications. The silicon films deposited on a 70^oC substrate at a high rate (electron beam power = 600W) exhibited less surface roughness. The addition of argon to the jet also increased the film roughness. These results suggest that directed vapor deposition has the potential to excel in amorphous silicon deposition at low temperatures (< 325^oC) and high deposition rates (> ~300 nm/min) using a pure helium jet.

* Senior theses can be found at the University of Virginia's Science and Engineering Library.