Francesco Fracassi

Plasma‐Enhanced Chemical Vapor Deposition of Organosilicon Thin Films from Tetraethoxysilane‐Oxygen Feeds

The composition of films deposited in RF glow discharges fed with tetraethoxysilane and oxygen mixtures has been investigated by means of in situ x-ray photoelectron spectroscopy and infrared spectroscopy. These results, combined with mass spectrometric investigations of the gas phase, indicate that the overall deposition consists of several concurrent heterogeneous and homogeneous reactions

Application of plasma deposited organosilicon thin films for the corrosion protection of metals

In this contribution it will be shown that plasma enhanced chemical vapor deposition (PECVD) of silicon containing organic compounds is a promising approach for the corrosion protection of metals (steel and magnesium alloys). When the deposition process is preceded by a suitable plasma treatment, which depends on the particular metal under study, a marked increase of the protective properties measured with electrochemical impedance spectroscopy (EIS) is detected. The highest impedance modulus obtained for Mg is 450 KΩ·cm2, 8000 times higher than for the bare metal. Highly protective coatings are obtained for inorganic films, free of sylanols. A marked decrease of the impedance modulus of coated substrates has been registered after immersion in electrolyte solution due to the presence of pinholes which represents defect points where localized corrosion starts.

Polymer film formation in C2F6H2 discharges

Abstract Thin fluoropolymer films deposited in an r.f. discharge fed with C 2 F 6 H 2 mixtures were studied. The effect of the electrical characteristics, the substrate temperature and the feed composition on both the chemical structure of the film and on the growth mechanism were analysed. It was found, in particular, that the structure of the film is affected by the H 2 concentration in the feed and by the discharge voltage and current values and that the polymerization rate decreases with temperature after a threshold.

Optical emission spectroscopy and actinometry in CCl4-Cl2 radiofrequency discharges

Radiofrequency discharges fed with CCl4-Cl2 mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N2 as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CClx species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.

Thin film deposition from hexamethyldisiloxane fed glow discharges

Hexamethildisiloxane-oxygen fed radiofrequency discharges have been studied under high power density and 0.05÷0.1 torr pressure, i.e., experimental conditions of high monomer fragmentation. Actinometric Optical Emission Spectroscopy of plasma phase, X-Ray Photoelectron Spectroscopy and Infrared Spectroscopy analyses of the deposited films allowed to set the basis of the first “semi-quantitative” mechanism of deposition of siloxane films which can reasonably account for both deposition rates and film compositions. A by-product of the research is the use of CH-to-Ar emission ratio as a probe of carbon content in the film, an important practical parameter for process control.

On the use of actinometric emission spectroscopy in SF6-O2 radiofrequency discharges: Theoretical and experimental analysis

A comparison of the results obtained by solving the Boltzmann equation with the experimental results from optical emissions obtained in SF6-O2 radiofrequency discharges, when N2, Ar, and He are also admitted as actinometers, has allowed us to explore the potentialities and limits of actinometry. The use of different actinometers also allowed us to monitor the evolution of the electron distribution functions as a function of the plasma parameters.

From Low-k to Ultralow-k Thin-Film Deposition by Organosilicon Glow Discharges

Continuous and modulated discharges, fed with divinyltetramethyldisiloxane mixed with oxygen and argon, were used to deposit carbon-doped silica-like (SiCOH) low-k to ultralow-k films. The effect of various process parameters on the dielectrical and thermal properties of films as well as on their chemical composition were investigated. As deposited, the SiCOH films exhibited dielectric constants from 4.45 to 2.70. Thermal annealing in the 400-450°C temperature range was found to be necessary to reach ultralow-permittivity values, but the temperature must be controlled in order to prevent an excessive collapse of the silicate matrix, which leads to poor thermal stability and mechanical properties. Lowering the oxygen content in the discharge allowed for a continuous decrease in k values down to 2.32 when low radio frequency power was used, with a limited film thickness loss upon annealing of 11%. Fourier transform infrared spectra of ultralow-k film exhibited intense absorptions from C-containing moieties, like CH x and Si(CH 3 ) x . Upon annealing at 400°C, the organic content considerably decreases, though the loss of Si(CH 3 ) x groups is quite limited. Thermogravimetric analysis coupled with mass spectrometry revealed that during thermal treatment, silicon-containing fragments were lost from the matrix along with hvdrocarbon ones.

GC-MS Investigation of Hexamethyldisiloxane-Oxygen Fed Plasmas

This paper deals with the determination of by-products formed in plasmas fed with hexamethyldisiloxane (HMDSO), oxygen, and Ar. The gas effluent has been sampled by means of a cold trap and analyzed using gas chromatography-mass spectrometry. The results indicate that under the experimental conditions utilized, HMDSO is not activated by reactions with oxygen but mainly by electron collisions. Oxygen controls the overall chemistry of the plasma since it influences the quali-quantitative distribution of by-products. Many linear and cyclic oligomers have been observed and most of them contained one or more―Me2SiO― groups. The concentration of detected by-products, except trimethylsilylformate, decreases with O2 addition.

Deposition of gold-containing siloxane thin films

Abstract Thin films containing gold clusters dispersed in a SiO x matrix have been deposited by simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane-O 2 -Ar mixtures and r.f. sputtering of a gold target. The effect of deposition conditions on film composition and on some physical properties have been investigated. The results show that the films are mainly composed of an inorganic SiO x matrix which contains gold clusters, carbon and hydrogen atoms. By changing the gold content of the film the d.c. electrical conductivity follows the trend reported in the literature for other metal-containing plasma polymers, while the optical absorption in the UV-Vis region shows some differences from published data.

Plasma and surface diagnostics in PECVD (plasma-enhanced chemical vapor deposition) from silicon containing organic monomers

Advances are presented in the study of chemical composition, properties and deposition mechanism of thin films deposited via RF glow discharges fed with oxygen and/or silicon- containing organic monomers. The effect of substrate temperature, ion-bombardment, and feed 02/monomer ratio are described. A general deposition mechanism is proposed.