Radio Frequency Oxygen Plasma Research Articles

Plasmaoxidative Degradation of Polymers Studied by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

Different low molecular mass model polymers, such as poly(ethylene terephthalate), poly(methylmethacrylate), poly(ethylene glycol) and aliphatic poly(carbonate) were exposed to an oxygen radio frequency plasma for different times. The change of the molecular weight distribution and the formation of different functionalized fragments of these low molecular mass polymers were investigated by matrix-assisted laser desorption/ionization mass spectrometry. The majority of the polymers show the expected strong decrease of the molecular masses in the spectra of their soluble fraction indicating a degradation of the polymers. Simultaneously, different types of degradation products were found, which can give detailed information on the chain scission processes occuring in an oxygen plasma.

Negative ions in a radio-frequency oxygen plasma.

A systematic study of a low pressure (5--200 mTorr) oxygen discharge is presented. Measurements of the electron and negative ion densities in the 13.56 MHz capacitively coupled plasma are performed by means of a microwave resonance technique in combination with photodetachment. A kinetic model is developed, incorporating volume and wall reactions of ions as well as neutral species. It is shown, by matching the experimental results with the model, that the dominant ion is ${\mathrm{O}}^{\mathrm{\ensuremath{-}}}$ whereas the ${\mathrm{O}}_{2}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{O}}_{3}^{\mathrm{\ensuremath{-}}}$ densities reach 10 to 20 % of the total negative ion density. The ratio of negative ion to electron density varies between 5 and 10 and decreases with pressure and rf power. The total negative ion density is about 5\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$, it increases with gas flow, is independent of the rf input power, and has a maximum at a pressure of 30 mTorr. The agreement between the measurements and the model is within the experimental error for a wide range of conditions. Deviations are explained by changes in the gas and wall temperatures. From the known ion density the effective ionization rate has been determined and related to the electron temperature. The ionization temperature obtained in this way varies between 2 and 4 eV and decreases with increasing gas pressure and power, as expected for the bulk electron temperature in this type of discharge.

Cleaning of metal parts in oxygen radio frequency plasma: Process study*

The removal of different lubricants (oils and greases) from metal surfaces by use of a capacitively coupled 13.56 MHz low-pressure oxygen discharge has been examined. Stainless steel, tool steel, brass, aluminum, and copper were used as a substrate materials. The ion bombardment and chemical reactions occurring at the metal surfaces in such a discharge allow for high cleaning speed. A hollow-cathode discharge has been used to increase the plasma density in contrast to a plane cathode discharge configuration. The cleaning process was characterized by use of emission spectroscopy and mass spectroscopy. Influence of rf power (up to 1 kW), pressure (from 0.01 to 1 mbar), and magnetic field (up to 20 mT) on the process duration and surface cleanliness has been investigated. The criteria for detection of the process end point are formulated and checked. The spectral information is useful for end point detection only in restricted regions of the process conditions. Results indicate a strong influence of the lubricant temperature on the process duration. The removal rate of N62 oil at 140 °C is twice as high as that at 50 °C. For temperatures higher than 140 °C the creation of a hardly removable solid residue occurs. The influence of the initial lubricant area and lubricant thickness on the process duration has been investigated. The increase of the lubricant area results in an increase of the process time (loading effect for cleaning process). The increase of the lubricant film thickness results in a proportional increase of the process time.

Multitechnique study of hexatriacontane surfaces modified by argon and oxygen RF plasmas: effect of treatment time and functionalization, and comparison with HDPE

Hexatriacontane (C36H74) has been used as a model molecule for the study of the surface modifications of high-density polyethylene (HDPE) in argon and oxygen radio-frequency (RF) plasmas. The combination of static secondary ion mass spectrometry (SIMS), ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements has constituted a powerful method for the investigation of the surface modifications induced by the plasma treatments. The surface degradation and functionalization are shown to depend on both the nature of the treated material and the nature of the plasma atmosphere. The SSIMS results obtained on plasma-modified hexatriacontane and HDPE are compared in order to identify the nature of the functionalities present at the plasma-treated surfaces. Finally, plasma treatment 18O atmosphere was performed on HDPE, C36H74, and polystyrene (PS). In that case, the isotopic specificity of both ISS and SIMS allowed the determination of the relative concentrations of 16O and 18O in relation to the probed depth and plasma atmosphere.

SiO2 thin film deposition by radio frequency oxygen plasma enhanced laser ablation from Si

A novel process of room temperature deposition of thin SiO2 film by laser ablation from a c-Si target in a low pressure (<5 mTorr) rf oxygen magnetron plasma background was developed. The gas phase reactions which usually dominate in other high pressure reactive ablation processes are suppressed and the energetic particles from the target have good transport to the substrate in the low pressure background. The surface reactions are continuously enhanced after the arrival of Si particles by the high fluxes of oxygen radicals and ions from the steady state magnetron discharge. The deposition of stoichiometric, less disorder, dense, and water free films are demonstrated.

Radio-frequency (RF) plasma etching of graphite with oxygen: a scanning tunnelling microscope study

The surface topography of highly oriented pyrolytic graphite (HOPG) after exposure to a radio-frequency (RF) oxygen plasma has been studied using scanning tunnelling microscopy (STM) in ambient air. The STM images obtained show that the HOPG surface after etching in an oxygen RF plasma is remarkably different from that of the freshly cleaved material. The resultant topographical features are found to be strongly dependent on the etching conditions used. The layer-by-layer etching of graphite by an oxygen RF plasma revealed in the high resolution STM images obtained is attributed to the structural characteristics of graphite and to the synergistic effects of oxygen ion bombardment and atomic oxygen reactions.

Radio-frequency (RF) plasma etching of graphite with oxygen: a scanning tunnelling microscope study

The surface topography of highly oriented pyrolytic graphite (HOPG) after exposure to a radio-frequency (RF) oxygen plasma has been studied using scanning tunnelling microscopy (STM) in ambient air. The STM images obtained show that the HOPG surface after etching in an oxygen RF plasma is remarkably different from that of the freshly cleaved material. The resultant topographical features are found to be strongly dependent on the etching conditions used. The layer-by-layer etching of graphite by an oxygen RF plasma revealed in the high resolution STM images obtained is attributed to the structural characteristics of graphite and to the synergistic effects of oxygen ion bombardment and atomic oxygen reactions.

Surface characterization of highly oriented pyrolytic graphite modified by oxygen radio-frequency plasmas

STM study, combined with initial XPS results, of surface modification of the highly oriented pyrolytic graphite (HOPG) surface when exposed to oxygen r.f. plasmas. Images show the dramatic modification of the HOPG surface topography and surface chemical activities produced by the oxygen r.f. plasma.

Growth of silicon oxide on silicon in the thin film region in an oxygen plasma

The time dependence of silicon oxide growth in a radio frequency oxygen plasma is studied by using in situ rapid ellipsometry. An extremum in the change of the ellipsometric parameter Δ versus discharge time is observed in the thin films region and is explained by a change in the refractive index value accompanying the oxide film growth.

Pattern transfer onto carbon films on silicon using radio frequency oxygen plasma etching

Pattern transfer onto semiconducting carbon films with diamondlike properties using optical lithography and radio frequency oxygen plasma etching is reported. Titanium, aluminium, and gold were used as masking materials during oxygen etching. It was found that the titanium mask was most suitable for this process because of better resistance to the oxygen plasma. The microstructures observed were very uniform and well defined.

Interactions of Cold Radiofrequency Plasma with Solid Wood I. Nitrogen Permeability along the Grain

Abstract Exposure of 1.5 cm diameter × 1.2 cm long white fir and Douglas-fir heart-and sapwood samples to the action of cold radiofrequency oxygen, nitrogen, and helium plasmas strongly increased wood permeability to nitrogen flow along the grain. Oxygen was most effective, followed by nitrogen and helium. While an increase in radiofrequency energy level increased the effect, the opposite was true for an increase in reactant gas flow rate. With white fir the rate of permeability increase was higher at the beginning of the plasma treatment. This was attributed to differing ablation rates of cellulose, hemicelluloses, and lignin. No significant time difference in the rate of permeability increase was observed with Douglas-fir. Extractives suppressed the plasmainduced permeability increase; thus extraction with water and ethanol, followed by oxygen plasma treatment increased permeability of Douglas-fir heartwood 32 times, while plasma treatment of the unextracted Douglas-fir increased permeability only 8 tim...

ESCA study of several fluorocarbon polymers exposed to atomic oxygen in low Earth orbit or within or downstream from a radio-frequency oxygen plasma

The ESCA (electron spectroscopy for chemical analysis) spectra of films of poly(vinyl fluoride) (Tedlar), tetrafluoroethylene-hexafluoropropylene copolymer (in the form of a Teflon FEP coating on Kapton H, i.e. Kapton F) and polytetrafluoroethylene (Teflon or Teflon TFE) exposed to atomic oxygen (O( 3P)) - either in low Earth orbit (LEO) on the STS-8 Space Shuttle or within or downstream from a radio-frequency oxygen plasma - were compared. The major difference in surface chemistry of Tedlar induced by the various exposures to O( 3P) was a much larger uptake of oxygen when etched either in or out of the glow of an O 2 plasma than when etched in LEO. In contrast, Kapton F exhibited very little surface oxidation during any of the three different exposures to O( 3P), while Teflon was scarcely oxidized.

Some aspects of the surface chemistry of coal, kerogen and bitumen as revealed by ESCA

The application of ESCA (electron spectroscopy for chemical applications) to the study of the structure, bonding and reactivity of coals, kerogens and bitumen samples has been examined, with particular reference to torbanite, vitrinite, kimmeridge kerogen, brown coal and Gilsonite pitch. The ESCA valence band spectra and C l s band profiles of a rank rangeof coal samples are discussed. Differences in C l s signal between naturally occurring heat altered coal and the unaltered coal are reported. The surface sensitivity of the ESCA experiment reveals enriched silicon and aluminium concentrations on the cleaved surfaces of grahamite bitumen, relative to bulk ESCA analyses. Surface oxidation of anthracite through atmospheric weathering is found to be amenable to study by ESCA and substantial oxidation of the coal occurs after an exposure period of one week. Artificially induced oxidation by means of low power radiofrequency oxygen plasma treatments have been performed. In the case of Gilsonite pitch the distribution of oxidized carbon functionality is found to differ from that reported during the irradiation of Gilsonite in u.v. light (254 nm) in air.

Thermal studies of carbonaceous electrode materials chemically modified with cyanuric chloride

A thermoanalytical investigation of chemically modified graphite and activated carbon is presented. Evaluation of thermal curves shows that radio-frequency oxygen plasma treatment is superior to electrochemical oxidation for increasing surface functional group concentrations, which when chemically reduced, can be used for cyanuric chloride binding. The amount of cyanuric chloride bound to the carbonaceous surface is determined by both potentiometric titration of hydrolyzed chloride and magnitude of weight loss at 275–290°C. The species evolved in this temperature range is identified by temperature-programmed mass spectrometry as cyanuric acid.

Use of chemically modified activated carbon as a support for immobilized enzymes

Loading and activity assays of the enzymes alpha-chymotrypsin, alpha-chymotrypsinogen, and glucose oxidase covalently bound to an activated carbon support are presented. The activated carbon support material was pretreated using either a radio-frequency oxygen plasma or an electrochemical oxidation to maximize the enzyme attachment. Cyanuric chloride or water-soluble carbodiimide linking reactions were used to covalently attach the enzymes to the carbon support. Discussion of the relative merits of each reaction scheme is presented.

Radiofrequency oxygen plasma treatment of pyrolytic graphite electrode surfaces

Radiofrequency oxygen plasma treatment of pyrolytic graphite electrode surfaces

Simple Optical Devices for Detection of Radiofrequency Oxygen Plasma Stripping of Photoresists

In an earlier paper, a spectroscopic technique was presented for studying the removal of negative photoresists from silicon wafers using a radiofrequency (RF) oxygen plasma. The potential application of the technique to a wide variety of manufacturing situations became quite evident especially for monitoring and controlling various stripping and etching operations induced by highly energetic plasma. It was also evident that if the technique was to enjoy wide usage in the manufacture of various integrated circuits, for example, a much more compact detection system would be necessary. Two rather versatile devices satisfying this need are described briefly here.