Studies of halogens in diamond chemical vapor deposition
Komplin, Norma Jean
Margrave, John L.
Doctor of Philosophy
Presently there is a need for low pressure diamond chemical vapor deposition (CVD) at lower temperatures to decrease thermal stress and permit coatings on low melting materials such as plastics. A novel thermal assisted fluorine CVD process has been proven to deposit diamond at temperatures between 650$\sp\circ$C and 250$\sp\circ$C using fluorine and hydrocarbons. The reactions were carried out in a flow tube system operating at ambient pressures where the reactant gases were passed through a resistively heated reaction chamber. Typically the reaction gases were composed of carbon, hydrogen, fluorine and oxygen. Reactant gases were sampled both preceding and following the hot thermal activation zone for further analysis with matrix isolation Fourier transform infrared spectroscopy (MI-FTIR) and mass spectroscopy. MI-FTIR was also employed in an effort to gain mechanistic information concerning fluorine assisted CVD by studying the reactions of fluorine and methane with and without activation by photolysis. Information obtained on reaction intermediates involved in the fluorine-assisted CVD method has the potential to lead to a better understanding of the reaction pathways, thereby improving our ability to control and direct diamond deposition with this technique. Quantitative growth rates have been measured on diamond (110) faces in a hot filament CVD reactor. It was found that the addition of HCl to typical methane-hydrogen mixtures produced significantly higher growth rates at low substrate temperatures than just methane-hydrogen mixtures. The dependence of the diamond growth rate on the concentration of HCl in the above system was studied. The abstraction of hydrogen by atomic chlorine is estimated to be approximately 60 times faster than the abstraction of hydrogen by hydrogen at 670$\sp\circ$C for the experimental conditions. It is believed that chlorine abstraction of surface adsorbed hydrogen plays a dominant role in activating the diamond surface at low substrate temperatures, thus giving rise to higher diamond deposition rates at these low substrate temperatures.
Physical chemistry; Inorganic chemistry