COMPOSITIONAL AND STRUCTURAL-PROPERTIES OF HYDROGENATED AMORPHOUS SILICON-CARBON FILMS PREPARED BY ULTRA-HIGH-VACUUM PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION WITH DIFFERENT CARBON-SOURCES

Hydrogenated amorphous silicon-carbon films were deposited by ultra-hi gh-vacuum plasma-enhanced chemical vapour deposition in silane + metha ne and silane + acetylene gas mixtures. Both types of film were compar ed with respect to their Compositional, optical and structural propert ies. They have an optical gap in the range 2.3-3.3 eV for [C]/[C + Si] between 0.2 and 0.7 and possess high uniformity. The deposition rate of C2H2-based films is 4-5 Angstrom s(-1), one order of magnitude high er than CH4-based films having large bandgap. By infrared (IR) spectro scopy, marked differences in carbon and hydrogen incorporation have be en found for the films grown using the two different carbon sources. A nalysis of the IR spectra reveals, among the most important structural characteristics, that the films grown from the SiH4 + CH4 plasma have a higher concentration of Si-C bonds than those grown from SiH4 + C2H 2, and that C2H2-based alloys allow the formation of carbon clusters d uring the growth of the films. Considerations of the average coordinat ion number, the chemical bonding and the degree of chemical order are also reported and discussed.