Effects of Propane/Nitrogen Mixtures on Thermal Chemical Vapor Deposition Rates and Microstructures of Carbon Films

Abstract

When propane/nitrogen (C3H8/N2) mixtures are used to deposit carbon films by thermal chemical vapor deposition (CVD), effects of C3H8/(C3H8+N2) ratios on the deposition rate and microstructures of carbon films are investigated. Experimental results show that as the C3H8/(C3H8+N2) ratio increases from 20 to 100%, the deposition rate increases from 23.7 to 127 nm/min. Alternatively, if the residence time, deposition temperature, and working pressure raise, the deposition rate of carbon films also increases. The kinetics of this thermal CVD process is discussed. The activation energy obtained in this work is 234 kJ/mole. Furthermore, this CVD reaction is controlled by a process of about first order, which is resulted from the adsorption of main product gases, acetylene (C2H2) and ethylene (C2H4), on the silica glass plate substrate. Few nitrogen and hydrogen atoms are incorporated into carbon films. The crystallinity, ordering degree, and nano-crystallite size of carbon films decrease with increasing the C3H8/(C3H8+N2) ratio. Meanwhile, as the C3H8/(C3H8+N2) ratio increases from 20 to 100%, the sp2/(sp2+sp3) ratio of carbon films decreases from 92 to 61%. Finally, the results of thermal CVD carbon deposition using C3H8/N2 mixtures are compared with those using methane/nitrogen (CH4/N2), C2H2/N2, and C2H4/N2 mixtures.