A. Granier

A comparative study of oxygen/organosilicon plasmas and thin SiOxCyHz films deposited in a helicon reactor

Thin SiOxCyHz films have been prepared by plasma enhanced chemical vapor deposition (PECVD) on silicon substrates at low pressure (2 mTorr) and 300 W rf power, using tetraethoxysilane (TEOS) or hexamethyldisiloxane (HMDSO) as a monomer and oxygen as a reactive gas. The plasma composition, the structure and properties of the deposited films are studied as a function of the organosilicon fraction (Xorg). Optical emission spectroscopy is carried out in order to identify the species in the plasma. The layers are characterized by in situ spectroscopic ellipsometry and by several ex situ diagnostics including infra-red spectroscopy, X-ray photoelectron spectroscopy, gravimetry and chemical etching. At low values of Xorg, the structure and properties of the films and optical emission spectra are very similar whatever the organosilicon precursor. At high values of Xorg, the structure and properties of the deposited films and emitting species significantly depend on the organosilicon precursor.

Diagnostics in helicon plasmas for deposition

and helicon plasmas used for plasma enhanced chemical vapour deposition of 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 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 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 plasma (5 mTorr, 300 W) the fluxes of oxygen positive ions and atoms impinging onto a floating substrate are estimated to be and respectively. Under these plasma conditions, near-stoichiometric 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 plasma at two rf powers confirms the major role of oxygen atoms.

Inorganic to organic crossover in thin films deposited from O2/TEOS plasmas

The structure of thin films prepared from O2/TEOS plasmas in an rf helicon reactor has been investigated using in situ UV-visible spectroscopic ellipsometry and ex situ X-ray, reflectivity, Fourier transform infrared, photoelectron and Rutherford backscattering spectroscopy. It is shown how the structure of the films evolves from an inorganic silica-like structure towards an organic SiOxCyHz framework when the relative proportion of TEOS in the plasma increases. On the one hand, the structure and properties of the silica-like films are shown to be very close to those of a thermal oxide. On the other hand, the organic films have larger refractive index and extinction coeAcient but are less dense than the SiO2-like films. It is shown that the increase in the refractive index and extinction coeAcient is correlated to the carbon incorporation into the film. It is further established that the O/Si content ratio is enhanced from about 2 to 2.5 with increasing TEOS volume fraction. This evolution is explained by the increasing number of Si‐O‐H and Si‐O‐CxHy bonds in the material at the cost of the number of ‐Si‐O‐Si‐ bonds. It is furthermore shown that the abrupt character of the transition between silica-like and organic films is likely to be correlated to the depletion in oxygen atoms in the plasma. ” 2000 Elsevier Science B.V. All rights reserved.

Room temperature synthesis of carbon nanofibers containing nitrogen by plasma-enhanced chemical vapor deposition

This letter reports low-pressure, room-temperature growth of carbon nanofibers containing nitrogen by plasma chemical vapor deposition arrangement. By alternating pure acetylene plasma and afterglow pure nitrogen high dense plasma, a fine control of the fibers growth kinetic is obtained. This layer-by-layer deposition technique takes advantage of nitrogen chemical etching effects during the growth of nitrogen-doped carbon nanofibers.

Optical spectroscopic analyses of OH incorporation into SiO2 films deposited from O2/tetraethoxysilane plasmas

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 ...

Silicon dioxide deposition in a microwave plasma reactor

Abstract SiO x C y H z films were deposited using hexamethyldisiloxane (HMDSO) in a 2.45 GHz microwave plasma reactor. The plasma was characterised by optical emission spectroscopy as a function of the HMDSO-to-oxygen ratio. The emission of species resulting from the dissociation and recombination of the monomer was identified. The film structure was investigated by means of FTIR spectroscopy and ellipsometry was used to determine the thickness and refractive index of the layer. The infrared spectrum and the deposition rate are strongly dependent on the HMDSO-to-O 2 ratio, whereas the refractive index is quite constant and lower than expected.

Optical emission spectra of TEOS and HMDSO derived plasmas used for thin film deposition

This paper is devoted to the optical emission spectra (OES) of low pressure (1 mTorr–1 Torr) plasmas created in tetraethoxysilane (TEOS) and hexamethyldisiloxane (HMDSO) used pure or mixed with oxygen. The UV-visible emission spectra are recorded at low resolution (0.3 nm) using a 46 cm focal length monochromator and at high resolution (0.3 cm−1) using a Fourier transform spectrometer. Since almost all the atomic and molecular emissions have been identified, the spectra displayed here can be used as reference emission spectra for TEOS, HMDSO and O2/TEOS(HMDSO) plasmas. The OES of O2/TEOS and O2/HMDSO plasmas are very close and are dominated by CO, OH, H2 and H emissions. In contrast, the OES of TEOS and HMDSO plasmas are quite different: the emissions of excited Si, SiO and SiH are characteristics of HMDSO plasma, while those of OH, CO, CO+, CO2+ are characteristics of TEOS plasmas. On the basis of these spectra and the data reported in the literature, it is finally concluded that the CO and OH molecules detected in TEOS plasmas are very likely created at the reactor walls by desorption from the growing film.

Carbon nanowalls as material for electrochemical transducers

The electrochemical reactivity of a carbon nanowalls electrode was highlighted. The carbon nanowalls were synthesized at 520 °C in an acetylene/ammonia electron cyclotronic resonance plasma without any metal catalyst. The electrode surface was characterized by scanning and transmission electron microscopy. Its electrochemical reactivity was studied by both cyclic voltammetry and electrochemical impedance spectroscopy. After the carbon nanowalls deposition, the electronic transfer rate constant and the electroactive surface area were found to be increased by a factor of 7 and 3, respectively.

Analysis of Low-k Organosilicon and Low-Density Silica Films Deposited in HMDSO Plasmas

Low-dielectric constant (low-k) films have been prepared by plasma-enhanced chemical vapor deposition from hexamethyldisiloxane (HMDSO). The films are analyzed by ellipsometry, infrared absorption spectroscopy while their electrical properties are deduced from C–V and I–V measurements performed on metal/insulator/silicon structures. First, it is shown that the carbon-containing silicon oxide films deposited in HMDSO and HMDSO/Ar plasmas have a dielectric constant equal to 3.0 ± 0.1 and are thermally stable at 400°C. The leakage current densities measured for an electric field of 1 MV/cm are less than 10−9 A/cm2 and the breakdown fields are in the range of 6–7 MV/cm. Then, a low-density silica film was obtained by exposing a film deposited in an HMDSO plasma to an O2 plasma. The dielectric constant of this low-density silica film is 3.5 and its breakdown field is close to 6 MV/cm.

In situ ellipsometry and infrared analysis of PECVD SiO2 films deposited in an O2/TEOS helicon reactor

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Silicon dioxide thin films have been deposited at room temperature on silicon substrates in oxygen/tetraethoxysilane (O 2 /TEOS) helicon diffusion plasmas at low pressure (5 mTorr) and 300 W rf power. The properties of the films have been measured by in and ex situ ellipsometry, ex situ infrared spectroscopy, and chemical etching (p-etch) as a function of the TEOS flow rate (Q TEOS ). The growth rate (V d ) is determined in situ using an ultra violet-visible phase modulated spectroscopic ellipsometer (1.5 to 5 eV). Two different kinetic regimes appear: at low TEOS flow rate (Q TEOS <5 sccm) V d increases linearly and no carbon species are detected while the OH content rises strongly. For higher values of Q TEOS , V d saturates at 11 nm. The change in the kinetics corresponds to the appearance of carbon impurities. The increase in the deposition rate is accompanied by a decrease in the refractive index and an increase in the p-etch rate. The Bruggeman effective medium approximation (BEMA) is used to determine the fraction of voids incorporated in the layer. It is shown that porous films incorporate water when exposed to the atmosphere. Based on this result, an explanation is proposed for the insensitivity of the stretching peak of Si-O-Si to the deposition conditions. Good quality SiO 2 films with optical properties close to that of a thermal oxide can be obtained at low deposition rates (V d <5 nm/min).