CONVENTIONAL AND DYNAMIC ACTINOMETRY OF DISCHARGES OF HYDROCARBON-OXYGEN-ARGON MIXTURES

Actinometric optical emission spectroscopy was used in the investigation of discharges of mixtures of C2H2, O-2, and Ar to determine relative concentrations of the species CH, OH, H, CO, and O, which all increase with increasing proportions of oxygen in the plasma feed, R(ox). The mean electron energy E and the mean electron density rho were probed using Ar and He as actinometers. Additional measurements of the ratio of the intensities of the H-alpha to H-beta lines, I(H-alpha)/I(H-beta), showed that E was not strongly dependent on R(OX). In contrast, rho was found to fall with increasing R(OX). A dynamic form of actinometry was also used to determine temporal trends in the relative concentrations of the above-mentioned species following cutting of either the O-2 or C2H2 hows. On the basis of these data it is concluded that reactions involving oxygen play a major role in the production of the species CH, H, and CO. Plasma-polymer surface reactions contribute significantly to the production of the species H, CH, CO, and OH. (C) 1995 American Vacuum Society.1352513251

OPTICAL-EMISSION STUDY OF REACTION-MECHANISMS IN THE DEPOSITION OF NITROGEN-CONTAINING AMORPHOUS HYDROGENATED CARBON-FILMS

The reaction mechanisms taking glace in a film-forming radio frequency discharge of a mixture of acetylene, nitrogen, and helium have been investigated using optical emission spectroscopy. A transient actinometric method was employed, based on the interruption of the flow of one of the feed gases (either C2H2 or N-2) ana the subsequent observation of the time-dependent changes in the discharge environment, specifically of the concentrations of CH and CN species, two possible precursors of film formation. Both N-2 and C2H2 affect the CH and CN concentrations. Nitrogen strongly enhances the rate of formation of CH, very probably via gas phase reactions between atomic nitrogen and C2H2 or other species containing carbon and hydrogen. On the other hand, the relatively high CH concentration observed in discharges without nitrogen is taken to indicate that fragmentation of the C2H2 molecules by the discharge is another important mechanism of formation of the CH species. For the CN species; gas phase reactions between carbon- and nitrogen-containing species. are expected to contribute to its appearance. However, a relatively high CN concentration could be detected even in discharges without C2H2 in the gas feed, so long as a nitrogen-containing polymer film was previously formed on the inner wall of the chamber. This is taken as evidence that interactions between the plasma and the polymer surface play an important role in the generation of the CN species. Further measurements of the CN concentration in a plasma of 100% He, produced in the chamber immediately after the formation of a nitrogen-containing polymer film, indicate that a possible reaction mechanism for the formation of the CN species is the detachment of nitrile groups (-C=N) from the poly;ner surface upon cleavage or the carbon bond Linking-the nitrile terminations to the polymerchains. (C) 1995 American Vacuum Society.1341901190

Electronic structure at InP organic polymer layer interfaces

Organic polymer layer/p-InP(100) interfaces have been investigated using surface photovoltage spectroscopy (SPS) in conjunction with ultraviolet-visible absorption spectroscopy (AS), infrared transmission spectroscopy (IRTS), time-resolved photoluminescence (PL), and x-ray photoemission spectroscopy (XPS). Prior to deposition, the etched p-InP(100) surfaces exhibited two gap states, attributed to excess surface P and adsorbed O, respectively. Postdeposition measurements show that N-containing layers suppress the former state at the interface, while the latter state is suppressed if S and F are present in the organic polymer film. A mechanism of these interfacial phenomena is suggested. (C) 1997 American Institute of Physics.70223011301

Amorphous oxygen-containing hydrogenated carbon films formed by plasma enhanced chemical vapor deposition

Films were deposited from glow discharge plasmas of acetylene-oxygen-argon mixtures in a deposition system fed with radio frequency power. The principal variable was the proportion of oxygen in the gas feed, X(ox). The chemical structure and elemental composition of the films were investigated by transmission infrared spectrophotometry and x-ray photoelectron spectroscopy. Optical properties-refractive index, absorption coefficient, and optical gap-were determined from transmission ultraviolet-visible spectroscopy data. The latter also allowed the determination of film thicknesses and hence deposition rates. It was found that the oxygen content of the films and, within limits, the refractive index are controllable by the selection of X(ox). (C) 1996 American Vacuum Society.14111812

Dynamic actinometric optical emission spectroscopy for the elucidation of plasma processes in the production of fluorinated amorphous hydrogenated carbon films from glow discharges

A dynamic form of actinometric optical emission spectroscopy in which the flow of one of the feed gases to a glow discharge deposition system is cut and the relative concentrations of species of interest in the plasma monitored as a function of time is described. The method is applied to film-depositing discharges fed with the mixtures of C6H6-SF6 and C2H2-SF6, the actinometers Ar and He also being present in small proportions. Monitoring of the temporal trends in the relative concentrations of the species CF2, F, H and CH revealed the importance of gas-phase and plasma-polymer surface processes in the production of these species. For plasmas containing SF6, the species CF2 was found to be produced mainly by the action of the discharge on material previously deposited on the inner walls of the chamber. An SF6 plasma produced gas-phase CF2 species, possibly by the release of this species from the polymer surface by plasma electrons or by the impact of F atoms on surface CHF2 groups, liberating both CF2 and HF. The species F, CH and H were also found to be produced, at least in part, by plasma-polymer surface interactions. Separate experiments revealed that the species CF2, F, H and CH can be produced even by the action of Ar or He discharges on previously deposited a-C:H,F films. Thus both gas-phase and plasma-polymer surface reactions play important roles in the plasma-enhanced chemical vapor deposition of these films. The dynamic actinometric method is both simple to implement and widely applicable to the elucidation of the deposition and ablation processes occurring in glow discharges.2774167111512

TIME EVOLUTION OF THE RESIDUAL-STRESS OF PLASMA-POLYMERIZED ACETYLENE FILMS IN VARIOUS AMBIENTS

The behavior of the residual stress with time of plasma-polymerized acetylene films in various ambients has been investigated. The plasma polymers were deposited on thin glass substrates in dc and rf discharges of acetylene. After deposition, the specimens were mounted in a chamber that could be evacuated or filled with air, oxygen, or nitrogen. Stress measurements were carried out by the bending beam method, using a He-Ne laser. A steady rise in the stress during time periods of several hours following film deposition was observed in most of the samples studied. Stress increments of more than one order of magnitude were detected in some of the films upon exposure to air. Pronounced stress increments were also observed during exposure to oxygen. Rises in the stress were detected even in a vacuum ambience. Nitrogen exposure was found to have little effect on the stress. The effect of the moisture content of air on the stress was also examined. The evolution of the stress was found to depend also on the film preparation conditions. The results strongly suggest that postplasma reactions involving active chemical species trapped in the film during deposition play an important role in the development of the stress.7094883488

RELATIONSHIPS BETWEEN THE PLASMA ENVIRONMENT AND THE COMPOSITION AND OPTICAL-PROPERTIES OF PLASMA-POLYMERIZED THIN-FILMS PRODUCED IN RF DISCHARGES OF C2H2-SF6 MIXTURES

Polymer films were grown in rf discharges containing different proportions of C2H2 and SF6. Quantitative optical emission spectrometry (actinometry) was used to follow the trends in the plasma concentrations of the species H and F, and more tentatively, of CH, CF, and CF2, as a function of the feed composition. Infrared spectroscopy revealed the density of CH and CF bonds in the deposited material. As the partial pressure of SF6 in the feed was increased, the degree of fluorination of the polymer also rose. The form of the dependency of the deposition rate on the proportion of SF6 in the feed was in good qualitative agreement with the activated growth model. From transmission ultraviolet visible spectroscopy data the refractive index and the absorption coefficient of the polymers were calculated as a function of the deposition parameters. Since the optical gap depended to some extent upon the degree of fluorination, it could, within limits, be determined by a suitable choice of the proportion of SF6 in the feed. A qualitative explanation of this relationship is given.71144845

AN ACTINOMETRIC STUDY OF C2H2 PLASMA POLYMERIZATION AND FILM PROPERTIES

Thin polymer films were grown in radio frequency discharges containing C2H2. Actinometry revealed the trend in the plasma concentration of the CH species as a function of the operating pressure. The C-H bond density in the films, revealed by infrared analysis, was found to increase with the pressure of C2H2 in a similar way to that of the concentration of the CH species in the discharge. From transmission ultraviolet-visible spectroscopy data, optical parameters of the polymers, namely, the refractive index and the optical gap, were calculated. For the range of pressure studied, the refractive index decreased from 1.73 to 1.63 and the optical gap increased from 2.4 to 3.3 eV. Finally, measurements of the residual stress of the polymer films were carried out by the bending beam method, using a He-Ne laser, yielding values from 0.05 to 0.3 GPa. (C) 1995 American Vacuum Society.1362747275

FLUORINATED POLYMER-FILMS FROM RF PLASMAS CONTAINING BENZENE AND SULFUR HEXAFLUORINE

Mixtures of C6H6 and SF6 were polymerized in an r.f. discharge. Actinometry (quantitative optical emission spectroscopy) was used to determine trends in the plasma concentrations of the species F, H and CH as a function of the proportion of SF6 in the feed. Infrared spectroscopy and electron spectroscopy for chemical analysis were employed to characterize the deposited material. Increasing proportions of SF, in the feed produced increased fragmentation of the benzene molecules and greater fluorination of the deposited material. The deposition rate, as determined by optical interferometry, was found to be enhanced about 4 times by the presence of 10-20% SF6 in the feed. At 50% SF6 in the feed, deposition rates were greater than in pure C6H6 plasmas despite the (probably large) etching effect of atomic fluorine from the discharge. Relationships between the plasma composition, electron density and temperature, film composition and growth rate are discussed

Structural and optical properties of amorphous hydrogenated fluorinated carbon films produced by PECVD

Fluorinated films were deposited from radiofrequency discharges of toluene/trifluorotoluene and toluene/sulfur hexafluoride mixtures. Actinometric optical emission spectroscopy was used to determine trends in the concentrations of the plasma species H, CH, and F as a function of the partial pressure of trifluorotoluene or sulfur hexafluoride present (expressed as a percentage of the total chamber pressure) designated R-T and R-s, respectively. Transmission infrared spectrophotometry and electron spectroscopy for chemical analysis revealed that the films contain various fluorine-containing functionalities and that the degree of fluorination increases as R-T or R-s is increased. Ultraviolet-visible spectrophotometry of films deposited at various values of R-T and of R-s allowed the determination of the absorption coefficients ct of the films. From plots of ct as a function of photon energy it was possible to calculate the optical gap (E-04). An intriguing result was a decline and subsequent rise in E-04 as R-s was increased. Molecular modelling using ZINDO/PM3 calculations provided a semi-quantitative explanation of the dependence of E-04 on R-s. (C) 1997 Elsevier Science S.A.3044167114915