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

Abstract

When ethylene/nitrogen (C2H4/N2) mixtures are used to deposit carbon films by thermal chemical vapor deposition (CVD), effects of C2H4/(C2H4 + N2) ratios on the deposition rate and microstructures of carbon films are investigated. Experimental results reveal that the deposition rate of carbon films increases with the C2H4/(C2H4 + N2) ratio, and also, raises with the residence time, deposition temperature, and working pressure. The kinetics of this thermal CVD process is discussed. The deposition rate of carbon films is proportional to the C2H4/(C2H4 + N2) ratio with a power of second order, which is resulted from the adsorption of remaining precursor gases C2H4 on the silica glass plate substrate. Few nitrogen and hydrogen atoms are incorporated into carbon films. As the partial pressure of C2H4 is smaller than a threshold pressure or the residence time is shorter than a threshold residence time, no film is formed. The activation energy (= 448 kJ/mole) of carbon deposition is related to the activation energy of C2H4 dissociation. The degree of ordering and nano-crystallite size of carbon films decrease with increasing the C2H4/(C2H4 + N2) ratio, while the sp3 carbon atoms of carbon films increase. Finally, the results of thermal CVD carbon deposition using C2H4 are compared with those using methane and acetylene.