The Effects of Chloromethane on Diamond Nucleation and Growth in a Hot-filament Chemical Vapor Deposition Reactor
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The effects of chloromethane on diamond nucleation and growth in a hot-filament chemical vapor deposition reactor Jih-Jen Wu and Franklin Chau-Nan Honga),
b)
Department of Chemical Engineering, National Cheng-Kung University, Tainan, Taiwan 701, Republic of China (Received 17 January 1997; accepted 16 December 1997)
The effects of chloromethane on diamond nucleation and growth were studied by employing laser reflective interferometry. Chloromethane enhances the film-growth rate only slightly compared to methane. However, chloromethane greatly enhances the nucleation density and shortens the film-forming stage, more significantly at a lower temperature. Thus, chloromethane facilitates the low temperature growth mainly through the enhancement of nucleation. Nucleation density is strongly dependent on the compositions of H atoms and carbon species prior to diamond growth. The residual diamond seeds by diamond-grit scratching are suggested to be the major nucleation sites. Chloromethane can enhance diamond nucleation by protecting the residual seeds from being etched by H atoms.
I. INTRODUCTION
Because of their tremendous industrial applications, diamond films have been studied extensively recently. They can be grown from most gaseous carbon sources by various chemical vapor deposition (CVD) methods employing all kinds of high energy sources to generate high concentrations of atomic hydrogen.1 Atomic hydrogen is the most essential factor in growing diamond crystallites. The carbon sources can be any kind of hydrocarbon, including oxygen- or halogen-containing hydrocarbons. Oxygen, halogen, or nitrogen can also be added to enhance the gas and surface reactions. The improvement of diamond deposition technology remains crucial in order to realize many application prospects. For example, heteroepitaxial and low temperature growths are still being pursued. There has been much interest in studying the diamond deposition using halocarbon sources or halogencontaining molecules.2–18 Cl-related chemistry is of particular interest to several groups. Hong et al.3–5,8,12 found that chloromethane was more efficient than methane to grow diamond at low temperatures in the hot-filament and dc plasma CVD reactors. Bai et al.6 also showed that the chlorocarbon radical was a more effective growth species than the methyl radical. Komplin et al.7 further observed that the addition of HCl in CH4yH2 reactants could enhance the growth rate significantly at a low substrate temperature. Tsang et al.13 and Rego et al.14 employed molecular beam mass spectrometry to measure the composition of gas-phase species for chloromethaneyH2 or CH4yCl2yH2 mixtures,
and suggested that chlorine atoms were involved in the gas-surface reactions which produced active growth sites on the diamond surface. Kotaki et al.15 employed an AryH2 dc plasma jet to compare the diamond growth using dichlorobenzene with that using benzene. They concluded that the abstraction of surface-adsorbed hydrogen by the Cl atom plays a d
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