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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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Atomic oxygen-induced chemical vapor deposition (AOCVD), using tetraethoxysilane (TEOS) as single-source compound, was investigated t o get insight into the mechanism o f silica film growth. In particular, an effort was made t o elucidate the chemical nature o f silica film-formin precursors. AOCVD, selected as a model process suitable for mechanistic study, has been examined i n terms o f the egects o f atomic oxygen concentration, o f the contents o f the ground and excited state oxygen atoms i n atomic oxygen fraction, and o f thermal activation. The growth rate o f silica film does not depend on the composition o f the atomic oxygen fraction, but is proportional t o the total concentration o f atomic oxygen fed into the CVD reactor. In the light o f the apparent activation energy (E,) values calculated from the Arrhenius plots o f the substrate temperature dependencies o f film growth rate, the mechanism o f AOCVD is related t o the concentration o f atomic oxygen. The near zero E, value found at low concentration o f atomic oxygen (1.5 X 1014 implies that AOCVD is not a thermally activated process; diffusion o f the precursors from the gas phase t o the substrate seems t o be the ratelimiting factor o f AOCVD under these conditions. Apparently negative E, values observed for high concentrations o f atomic oxygen ( 29.7 x 1014 indicate that the adsorption o f the precursors onto the growth surface is the main factor controlling the rate o f AOCVD. Reaction products o f the gas-phase conversion o f TEOS, investigated b y high-resolution gas chromatography/mass spectrometry, revealed the presence o f linear and cyclic siloxane oligomers, containing the -(EtO),SiO-repeating unit. The structure o f identified oligomers, results o f the study o f TEOS reactions with atomic oxygen, the structure o f the deposited film, chemiluminescence spectra o f the gas-phase products i n the CVD reactor, and the results o f step coverage tests, point t o diethoxysilanone (a high reactivity intermediate) and hexaethoxydisiloxane (a high surface mobility, low reactivity intermediate) as the major precursors o f silica film growth.

The wall recombination coefficient (γ) of atomic oxygen on a pyrex surface and O(1D) concentration in the downstream flow were measured in a radio-frequency (13.56 MHz) oxygen discharge in the applied power region of 200 W-2500 W. The NO2 * continuum intensity was used to monitor the atomic oxygen. The γ varies from 1.1×10-4 to 6.1×10-5, having a minimum value of 5.1×10-5 at 700 W, at which point the glow discharge plasma changes to an arclike plasma. The mechanism of the transition of glow discharge plasma to arclike plasma and possible reasons for the inconstant γ are discussed in light of electron density, O(1D) concentration in the downstream flow, and the gas temperature.

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