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O 2 and O 2 /TEOS helicon plasmas used for plasma enhanced chemical vapour deposition of SiO x films are investigated in the 1-10 mTorr pressure and 0-800 W rf power ranges. The positive oxygen ions are analysed by energy selective mass spectrometry and Langmuir probes. The oxygen atom concentration is monitored by actinometry and ionization threshold mass spectrometry. In oxygen plasmas it is shown that O + 2 is the major positive ion, and that the oxygen molecules are far from being completely dissociated, due to a very high oxygen atom recombination frequency on the reactor walls. The dissociation degree increases with the rf power reaching 10% at 500 W. In O 2 /TEOS plasmas, the plasma density and electron temperature decrease as the TEOS fraction increases. In contrast, the degree of oxygen dissociation increases sharply with the addition of a few per cent TEOS, is maximum for about 5% TEOS and decreases as TEOS fraction is further increased. In a 95:5 O 2 /TEOS plasma (5 mTorr, 300 W) the fluxes of oxygen positive ions and atoms impinging onto a floating substrate are estimated to be 4 × 10 15 cm −2 and 10 18 cm −2 s −1 respectively. Under these plasma conditions, near-stoichiometric SiO 2 films, with low OH content, are deposited at ambient temperature. The corresponding atom to ion flux ratio is about 250, which suggests the dominant role of oxygen atoms in the deposition kinetics. The comparison of the compositions of layers grown in a 5 mTorr 95:5 O 2 /TEOS plasma at two rf powers confirms the major role of oxygen atoms.

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Silicon dioxide films have been deposited at low pressure (a few millitorr) and low substrate temperature (<200 °C) by oxygen/silane helicon diffusion radio frequency plasmas. High deposition rates (20–80 nm/min) are achieved at 800 W rf source power. The effect of the oxygen/silane flow rate ratio (R) on the film properties has been investigated: characterization of the deposited films has been carried out by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy, Rutherford backscattering, x-ray photoelectron spectroscopy (XPS), and chemical etch rate measurements (P etch) and the results have been compared to thermally grown oxide. The deposition kinetics has a great effect on the internal film structure: for films presenting a good stoichiometry ([O]/[Si]≥1.95 for R≥3), a decrease in the deposition rate is accompanied by a decrease of the refractive index, P-etch rate and XPS line width and by an increase of the Si–O stretching peak frequency toward the thermal oxide respective values. A sufficient oxygen/silane flow rate ratio (R=10) leads to stoichiometric films which exhibit good optical properties. Small differences in the P-etch rate, XPS linewidth, and infrared stretching peak frequency are still observed between our stoichiometric plasma deposited film and a thermally grown oxide film.

TiO2 nanoparticles (NPs), 3 nm in size, were injected inside a very-low-pressure O2 plasma reactor using a liquid injector and following an iterative injection sequence.Simultaneously, hexamethyldisiloxane (HMDSO) vapor precursor was added to create a SiO2 matrix and a TiO2-SiO2 nanocomposite (NC) thin film. Both the liquid injection and vapor precursor parameters were established to address the main challenges observed when creating NCs. In contrast to most aerosol-assisted plasma deposition processes, Scanning/Transmission Electron Microscopy (S/TEM) indicated isolated (i.e. non-agglomerated) NPs distributed in a rather uniform way in the matrix. The fraction of the TiO2 NPs inside the SiO2 matrix was estimated by SEM, Spectroscopic Ellipsometry (SE), and X-ray Photoelectron Spectroscopy.All techniques provided coherent values, with percentages between 12 and 19%. Despite the presence of TiO2 NPs, SE measurements confirmed that the plasma-deposited SiO2 matrix was dense with an optical quality similar to the one of thermal silica. Finally, the percentage of TiO2 NPs inside the SiO2 matrix and the effective refractive index of the NCs can be tuned through judicious control of the injection sequence.

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Silicon dioxide thin films are deposited on (100) silicon substrates at low pressure (5 mTorr), from O2/tetraethoxysilane (TEOS) helicon plasmas. The reactor is operated at 300 W radio frequency power without any intentional heating or biasing of the substrate. The samples are characterized using infrared spectroscopy, ultraviolet-visible ellipsometry, and complementary density measurements. Changes in film properties are observed varying the TEOS fraction in the gas mixture. Good quality SiO2 films, insensitive to postdeposition exposure to atmospheric water, are deposited for low TEOS fractions (<5%) in the mixture. As the O2 flow rate decreases, porous SiO2 and polymeric SiOxCyHz samples are successively obtained. Aging over 5 months of intentionally produced porous films has been investigated using Fourier-transform infrared spectroscopy. The 2900–3800 cm−1 OH absorption stretching band is quantitatively analyzed with three deconvolution bands. These films are hygroscopic and they show changes in the infrared spectra indicating an incorporation of additional highly associated hydroxyl groups. In addition, the development of the 935 cm−1 Si–OH stretching band and the evolution of the Si–O–Si stretching peak are due to interactions between the airborne absorbed water and silica network. On the other hand, isolated silanol species are rather insensitive to the postdeposition exposure to the atmospheric water. The respective contribution of growth induced and after growth ex situ incorporated Si–OH groups is established. Using the Bruggeman effective medium approximation, we found that water molecules account well for the dielectric properties of these highly associated SiOH groups mainly originating from postdeposition silica hydrolysis.