Scattering and Chemical Investigations of Semiconductor Surfaces.
This two-part thesis describes: (i) the design of an ion scattering system to examine the surface and near-surface region of semiconductors, and (ii) the chemical reaction channels of unsaturated hydrocarbons on the silicon (100) surface. Details on the design and construction of an ultrahigh vacuum, high-energy ion scattering system are presented. The use of MeV ion scattering to investigate surface and near -surface regions of materials is described and the combination of ion scattering with complimentary surface science techniques is stressed. The thermal activation of chemical bonds of the adsorbed unsaturated hydrocarbon molecules ethylene, propylene, and acetylene is investigated on the Si(100)-(2 times 11) surface with a goal of understanding the surface chemistry of Si-C formation. The use of precision dosing techniques, Low Energy Electron Diffraction, Auger Electron Spectroscopy, and Temperature Programmed Desorption in the investigation of the remaining carbonaceous species is described. Comparisons of the adsorption and desorption behavior of these molecules is made in terms of the carbon -carbon double and triple bonds (ethylene to acetylene) and the methyl functional group (ethylene to propylene). We find that the monolayer saturation coverage of these hydrocarbons is in very good agreement with the number of dimer sites on the surface estimated from scanning-tunneling microscopy, which suggests that the bonding of these hydrocarbons to the Si(100) surface is similar. It is also found that ethylene, in particular, does not provide an efficient Si-C reaction channel upon thermal activation, with nearly 100% of the ethylene molecules desorbing. In contrast, acetylene is found to be very efficient in SiC formation: >=q90% of the adsorbed acetylene thermally dissociates and eventually leads to SiC formation. Propylene has an efficiency of roughly 70% upon heating. Evidence for the diffusion of carbon into the bulk is seen at >=q850 K for propylene and acetylene.
- Pub Date:
- December 1988
- Physics: Condensed Matter