Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors

Abstract

A vacuum ultraviolet single photon ionization technique has been used to probe gas-phase species important in the hot wire chemical vapor deposition (HW-CVD) of amorphous silicon carbide(a-SiC:H) films using different single-source precursors. This study focuses on monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and 1,1-dimethyl-1-silacyclobutane, and the reactions of these precursors on tungsten and rhenium filaments between 1000 and 1950°C. Silane is also considered for comparison. Si radicals are found to be major products of hot wire decomposition for all the organosilicon precursors; CH3 is also observed. C and H radicals are expected to be produced as well but are not detected at the ionization energy used in these experiments. Within the series of methylsilanes, the reaction rate on the filament is found to decrease with increasing number of methyl groups on the precursor. We propose a model in which Si–H bonds are cleaved with lower activation barriers than Si–CH3 bonds as the molecule adsorbs onto the hot metal surface. 1,1-dimethyl-1-silacyclobutane produces Si with a lower apparent activation energy than the other molecules. Coverage-dependent reaction pathways are proposed to play a role in the temperature profile of CH3 generation. Infrared spectra of films deposited by HW-CVD show that the film composition and growth rate for the different precursors correlate with the hot wire chemistry studied by single photon ionization.