ABSTRACT
Chemical vapour deposition is a process by which gaseous molecular precursors are converted to solid-state materials, usually in the form of a thin film, on a heated surface [1, 2]. In figure 2.2.1 some of the fundamental processes accessible to the precursor molecules are illustrated. The gaseous molecules are introduced into the chamber. Some gas-phase reactions may occur. Normally this leads to more reactive daughter products. These daughter products, along with unreacted precursor molecules, are transported to the vicinity of the wafer where they may adsorb onto the surface. In many cases, the fluence of these unreacted species is higher due to their higher concentrations in the gas phase; however, due to their lower reactivity, they are less likely to adhere on the surface of the wafer. It is also typically true that the daughter by-products are more easily transported to the wafer surface due to their lighter mass (and therefore higher diffusivity). On the substrate surface the adsorbed precursor molecules and daughter molecules may: (1) desorb from the surface and re-enter the transport flow, (2) diffuse along the substrate surface, and/or (3) react to form a solid deposit. Once reaction has occurred, the by-products desorb from the surface and are removed from the reaction chamber via the transport flow.
