Kinetics of Thermal Chemical Vapor Deposition and Microstructures of Carbon Films Using Propane/Ammonia Mixtures

This study investigates the correlation between thermal chemical vapor deposition kinetics and characteristics of smooth laminar carbon films using propane/ammonia (C3H8/NH3) mixtures. During the deposition process, a residual gas analyzer is used to measure the partial pressures of residual gases. Experimental results indicate that the deposition rate raises with increasing the C3H8/(C3H8+NH3) ratio, residence time, deposition temperature, and working pressure. NH3 acts as both etcher and competing adsorber, which produces the suppressing effect. About sixteen NH3 molecules will suppress one C3H8 molecule to form the carbon film. Moreover, the pyrolysis of C3H8/NH3 mixtures is dominated by about a first order process, which is arisen from the adsorption of main product gases methane (CH4), acetylene (C2H2), and ethylene (C2H4) on the silica glass plate substrate. The activation energy of this process is 439 kJ/mol, so the dissociation of gas phase CH4 is the rate limiting step in this process. Few nitrogen and hydrogen atoms are incorporated into carbon films. The crystallinity, degree of ordering, nano-crystallite size, and sp2/(sp2+sp3) ratio of the carbon films decrease with increasing the C3H8/(C3H8+NH3) ratio. Finally, the results of thermal CVD carbon deposition using C3H8/NH3 mixtures are compared with those using CH4/NH3, C2H2/NH3, C2H4/NH3, and C3H8/N2 mixtures.