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Remote hydrogen and remote oxygen plasma chemical vapor depositions (RHP−CVD and ROP−CVD, respectively) of amorphous hydrogenated silicon−carbon (a-Si:C:H) and amorphous silica (a-SiO2) films, respectively, from organosilicon source compounds were selected as model processes for the mechanistic study. Hexamethyldisilane (HMDS) and trimethylsilane (TrMS) source compounds were used for RHP−CVD, whereas tetraethoxysilane (TEOS) was a source compound for ROP−CVD. The reactivity of HMDS and TrMS with atomic hydrogen and TEOS with atomic oxygen was characterized by determining the rate constants of RHP−CVD and ROP−CVD, respectively. On the basis of the values of the rate constants, the identified low-molecular-weight and oligomeric products collected from the gas phase, and the chemistry involved in their formation, the mechanisms of the precursors formation step are proposed. The results provide strong evidence for the gas-phase conversion of HMDS and TrMS to 1,1-dimethylsilene, Me2SiCH2, and TEOS to diethoxysilanone, (EtO)2SiO, transient intermediates as major precursors to the a-Si:C:H and a-SiO2 films, respectively. Owing to the high-reactivity π-bonds in the silene (>SiC<) and silanone (>SiO) units, the precursors may readily undergo polymerization. A hypothetical mechanism of the polymerization and cross-linking steps contributing to the growth of the a-Si:C:H and a-SiO2 films are discussed.

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The remote hydrogen plasma chemical vapor deposition (CVD) using tetrakis(trimethylsilyl)silane (TMSS) as a source compound has been examined in terms of the mechanism of the activation step. The deposition experiments performed for different configurations of the afterglow tube (straight, with a light trap, and with a hydrogen-radical annihilator) prove that the TMSS molecules are exclusively activated by the reactions with the hydrogen radicals. The determined temperature dependence of the film deposition rate suggests that the examined remote hydrogen plasma CVD is a nonthermally activated process. Susceptibility of particular bonds in TMSS molecule to the activation step has been characterized using suitable model source compounds. Mechanisms of the most important elementary reactions contributing to the activation step have been proposed.

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