Plasma-enhanced chemical vapor deposition of hydrogenated silicon carbide films from novel precursors

The influences of precursor molecular structure and electronic properties on the molecular structure, stoichiometry, and optical properties of a-SiC:H alloy films prepared through plasma enhanced chemical vapor deposition were investigated using infrared spectroscopy, ultraviolet-visible absorption spectroscopy, and sputtered neutral atom mass spectrometry (SNMS). Members of the homologous series tetramethylsilane (TeMS), trimethylsilane (TrMS), and dimethylsilane (DMS) as well as methane-silane (MS) were characterized as a-SiC:H precursors. Film structure, optical properties, and stoichiometry were studied as a function of precursor structure and deposition conditions, with deposition pressure serving as the manipulated variable.The infrared spectra of films prepared from the alkylsilane precursors revealed a strong dependence of the film structure on the deposition pressure, with high pressures ($>$0.1 torr) producing linear, polymeric films, and low pressures ($<$0.1 torr) producing amorphous, crosslinked films. The structure of the polymeric films was dominated by carbon atoms incorporated as chain terminating methyl groups. The crosslinked films contained fewer methyl groups and proportionately more bridging methylene and methylidyne groups. Similar film structures were obtained from all of the alkylsilane precursors.SNMS measurements revealed that the carbon-to-silicon ratio was inversely dependent on deposition pressure, with carbon content increasing as deposition pressures decrease Carbon content was also dependent on the precursor stoichiometry, with films prepared from TeMS exhibiting the highest carbon content (55-68 atomic percent) and films prepared from DMS exhibiting the lowest carbon content (35-52 atomic percent).UV-visible absorption measurements indicated that the optical properties of the films were strongly dependent on the deposition pressure, particularly at deposition pressures below 0.1 torr, and were only weakly dependent on the precursor structure. Films deposited from alkylsilane monomers exhibited larger optical gaps at higher deposition pressures. Observed gaps ranged from 2.1 eV to 3.6 eV, with TrMS producing materials with consistently larger optical gap energies.From these results, a phenomenological film structure evolution model is postulated, stressing the decomposition pathways of the methyl substituents as the primary determinant of the film structure.U of I OnlyETDs are only available to UIUC Users without author permissio