Mixtures Of CF4 Research Articles

Environmentally benign processes for making useful fluorocarbons: nickel- or copper(I) iodide-catalyzed reaction of highly fluorinated epoxides with halogens in the absence of solvent and thermal addition of CF2I2 to olefins.

Highly fluorinated epoxides react with halogens in the presence of nickel powder or CuI at elevated temperatures to provide a useful and general synthesis of dihalodifluoromethanes (CF(2)X(2)) and fluoroacyl fluorides (R(F)COF) in the absence of solvent. At 185 degrees C, hexafluoropropylene oxide and halogens produce CF(2)X(2) (X = I, Br) in 68-90% isolated yields, along with small amounts of X(CF(2))(n)()X, (n = 2, 3). With interhalogens I-X (X = Cl, Br), a mixture of CF(2)I(2), CF(2)XI, and CF(2)X(2) was obtained. The fluorinated epoxides substituted with perfluorophenyl, fluorosulfonyl, and chlorofluoroalkyl groups also react cleanly with iodine to give CF(2)I(2) and the corresponding fluorinated acyl fluorides in good yields. The reaction probably involves an oxidative addition of fluorinated epoxides into metal surfaces to form an oxametallacycle, followed by rapid decomposition to difluorocarbene-metal surfaces, which alters the reactivity of the difluorocarbene carbon from electrophilic to nucleophilic. The increase of nucleophilicity of difluorocarbene facilitates the reaction with electrophilic halogens. CF(2)I(2) reacted with olefins thermally to give 1,3-diiodofluoropropane derivatives. Both fluorinated and nonfluorinated alkenes gave good yields of the adducts. Reaction with ethylene, propylene, perfluoroalkylethylene, vinylidene fluoride, and trifluoroethylene provided the corresponding adducts in 58-86% yields. With tetrafluoroethylene, a 1:1 adduct was predominantly formed along with small amounts of higher homologues. In contrast to perfluoroalkyl iodides, CF(2)I(2) also readily adds to perfluorovinyl ethers to give 1,3-diiodoperfluoro ethers.

Design and synthesis of new photoresist materials for ArF lithography

AbstractA new class of photoresist matrix polymers based on vinyl ether–maleic anhydride (VEMA) alternating copolymers was developed for ArF single‐layer lithography. These polymers were synthesized by copolymerization of alkyl vinyl ether and maleic anhydride alternating copolymers with acrylate derivatives containing bulky alicyclic acid‐labile protecting groups. The resulting polymers showed good control of polymerization and high transmittance. Also, these resists exhibited good adhesion to the substrate, high dry‐etching resistance against CF4 mixture gas (1.02 times the etching rate of deep UV resist), and high selectivity to silicon oxide etching. Using an ArF excimer laser exposure system with 0.6 NA, 120‐nm L/S patterns were resolved under conventional illumination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 165–170, 2004

Functional separation in two frequency operation of an inductively coupled plasma

Measurements of densities of excited atoms and metastables were performed in pure Ar and in mixtures of Ar and CF4 in inductively coupled plasma sustained by a high frequency (13.56 MHz) source and biased by a low frequency (500 kHz) voltage applied to the wafer supporting electrode. The measurements are made in front of the biased electrode with a goal to understand the effects of different parameters on the plasma profile and to test whether functional separation between plasma sustaining and biasing voltage is achieved. We find a very efficient separation with small or no observable effects of biasing voltage both in pure argon and in mixtures. These results have been achieved at all pressures (5–50 mTorr) and were confirmed by additional microwave measurements of electron density. The effect of flow rate, pressure, power, and distance from the biased electrode was studied from the spatial profiles of short lives excited states and metastable states of argon. We have also compared the profiles close to the biasing electrode, close to the coil and in extended processing chamber, and found a slight increase of metastable density close to the biasing electrode due to reduced electron quenching far from plasma source.

Electron field emission from fluorinated amorphous carbon nanoparticles on porous alumina

The fluorinated amorphous carbon nanoparticles (a-C:F NPs) films have been prepared on a porous alumina at a lower temperature of ∼100 °C by an ECR-CVD system with a mixture of CF 4, C 2H 2 and Ar as precursors. The morphology of a-C:F NPs films was verified by FESEM. The microstructure and chemical bonding nature of the a-C:F NPs films were investigated by Raman spectroscopy and XPS, respectively. The fluorinated samples need a lower field (∼2.25 V/μm for 10.6% F a-C:F NPs films) to emit the electron than unfluorinated ones. The excellent field-emission properties of a-C:F NPs films are due to the effect of the shape, fluorine doping and dangling bonds.

Numerical study of Ar/CF4/N2 discharges in single- and dual-frequency capacitively coupled plasma reactors

A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled (cc) radio-frequency discharges in a gas mixture of Ar, CF4, and N2. The charged species, which are followed in the model, are: Electrons and Ar+, CF3+, N2+, F−, and CF3− ions. The simulation considers electron – neutral (Ar, CF4, and N2) collisions, various kinds of collisions of ions with neutrals, positive–negative ion recombination, and electron–ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a 0.8/0.1/0.1 ratio of Ar/CF4/N2 mixture at a pressure of 30 mTorr in single (13.56 MHz) and dual frequency (2+27 MHz) cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. F− and CF3− ions are the main negative charge carriers in the single and dual frequency regime, respectively. In the presence of low-frequency (2 MHz) and a strong electric field, the light F− ions are no longer confined in the bulk plasma and they partially respond to the instantaneous electric field. The calculated electron energy probability function profiles can be approximated to a Druyvesteyn and bi-Maxwellian distribution with high-energy tails in the single- and dual-frequency regime, respectively. The ion energy distribution is narrow with one outstanding peak in the single-frequency scheme, whereas it is wide and bimodal in the dual-frequency scheme.

CF4 decomposition by thermal plasma processing

Decomposition of CF4 was investigated by thermal plasma method. Thermal plasma processes applied to environmental problems have the features of high temperature, high activity and rapid decomposition rate, so it can perfectly decompose non-decomposed materials like CF4 to a high degree. Before the experiment, thermodynamic equilibrium calculations were performed from 300 K to 5,000 K at atmospheric pressure. Based on the thermodynamic equilibrium calculations, the trends in decomposition and recombination of CF4 were studied. Decomposition was carried out by injecting mixtures of CF4 bubbled by Ar, with some addition gases, such as H2 and O2, at atmospheric pressure. Experiments were performed to determine the effects of additive gas identity, additive gas dilution, input power, etc. on the decomposition of CF4. Plasma input power has a slight effect on CF4 decomposition, and the injection of reacting gas through a torch increased CF4 decomposition. Supply of H2 and O2 as addition gases increased the CF4 decomposition to 99% for experimental conditions tested.

Particle-in-cell/Monte Carlo simulation of a capacitively coupled radio frequency Ar/CF4 discharge: Effect of gas composition

A one-dimensional particle-in-cell/Monte Carlo model is developed to study a capacitively coupled radio frequency discharge in a gas mixture of argon and CF4. The simulation takes into account the following charged particles: electrons, two kinds of positive ions (Ar+, CF3+), and two kinds of negative ions (F−, CF3−). The model considers electron–Ar collisions, electron−CF4 collisions, various kinds of collisions of CF3+, F−, CF3−, or Ar+ with Ar or CF4, and positive–negative ion recombination. The probability for the positive–negative ion recombination is determined from a recombination rate constant. The ion–neutral elastic and reactive collisions are simulated by an ion–molecule collision model for endothermic reactions. The typical results of this model are electron and ion densities, fluxes and energy distributions, collision rates, and electric field and potential distributions. The simulation is performed for 0.1/0.9, 0.5/0.5, and 0.9/0.1 ratios of a Ar/CF4 mixture, as well as for pure Ar and pure CF4 discharges at a pressure of 200 mTorr. It is observed that at high CF4 concentration the discharge behaves as a typical electronegative discharge and that CF3+ is the major positive ion. At low CF4 concentration, keeping the other operating parameters the same, the double layer structure and the electron density maxima at the bulk–sheath interface, which are representative for an electronegative discharge, disappear and the Ar+ density exceeds the CF3+ density by more than 1 order of magnitude. The results show that the F− ions are the dominant negatively charged species for all Ar/CF4 ratios investigated.

Surface characterization of nickel alloy plasma-treated by O2/CF4 mixture

The micro- or nano-structured mold used for polymer embossing typically must be coated with an anti-adhesion material to reduce its interaction with the embossing. The mold is typically made by nickel sulphamate electroforming. For the anti-adhesion coating to adhere to the mold, the nickel mold surface must be clean and preferably unoxidized or possess reactive groups suitable for covalent bonding with the anti-adhesion coating. The effectiveness of plasma cleaning using mixtures of oxygen (O2) and tetrafluoromethane (CF4) with varying ratios versus liquid-only cleaning was investigated. To simulate the nickel mold, Ni200 alloy was used. Plasma treatment using mixtures of O2 and CF4 was found to be more effective in cleaning the Ni200 surface than liquid-only cleaning or pure O2 or pure CF4 plasma treatment. Using a 1 : 1 O2 /CF4 mixture plasma, the contact angles of water, glycerol and diiodomethane on Ni200 were the lowest and the calculated surface energy was the highest among the investigated treatments. From X-ray photoelectron spectroscopy (XPS), the amount of organic contamination on Ni200 was significantly reduced with plasma treatment. For liquid-only cleaned samples, metallic nickel, NiO and Ni(OH)2 are present on the surface. With pure O2 or pure CF4 or 1 : 1 O2 /CF4 mixture plasma, both oxidation and fluorination occur and the surface contains combinations of NiF2, Ni(OH)2, Ni(OH)F, Ni2O3 and NiO15F instead (without metallic nickel and NiO). The proportions of these different compounds vary according to the O2/CF4 ratio; O/Ni ratio is highest for pure O2 plasma treatment, whilst F/Ni is highest for pure CF4 plasma treatment.

Systematic study of amorphous hydrogenated and fluorinated carbon films

Amorphous fluorinated carbon films were grown from CF4 and C2H2 mixtures, using a Plasma Assisted Chemical Vapour Deposition (PACVD) apparatus. Two sets of films were deposited, changing in a systematic way the CF4 flux and the bias voltage (Vb). Film composition and structure were analysed by secondary ion mass spectroscopy (SIMS), infrared (IR) and Raman spectroscopies. Film hardness was obtained by micro-indentation measurements. On increasing fluorine content in films, hardness decreases and a fluorescence background in Raman spectra appears at high fluorine content, showing a diamond- to polymer-like structural transition. Infrared spectra indicate the presence of CFx, CCHF and CCF2 groups in the films. Our data are compared with previous results in the literature and the mechanisms involved in film formation are discussed, especially regarding fluorine substitution for hydrogen.

Ion flux composition in HBr/Cl2/O2 and HBr/Cl2/O2/CF4 chemistries during silicon etching in industrial high-density plasmas

Anisotropic etching of silicon gates is a key step in today’s integrated circuit fabrication. For sub-100 nm gate dimensions, one of the main issues is to precisely control the shape of the etched feature. This requires a detailed knowledge of the various physicochemical mechanisms involved in anisotropic plasma etching. Since silicon etching in high-density plasmas is strongly ion assisted, the identities of the ions bombarding the wafer is a key parameter that governs the etch rates and the etched profiles. In the present article, mass spectrometry has been used to investigate the chemical composition of the ion flux bombarding the reactor walls of an industrial inductively coupled plasma used for 200-mm-diam silicon wafer processing. The plasma chemistries investigated are HBr/Cl2/O2 and HBr/Cl2/O2/CF4 mixtures optimized for sub-100 nm gate processes. Quantitative ion mass spectra show that under those conditions the ion flux contains up to 50% of SiClXBrY+ (X,Y=0–2) ions, although Cl+, Cl2+, and Br+ ions were expected to be the predominant species. This observation can be explained by the combination of two well-accepted phenomena that are discussed in detail. The impact of the surprisingly large amount of ionized silicon-based etch products on silicon etching mechanisms are discussed.

Plasma etching of cesium iodide

Thick films of cesium iodide (CsI) are often used to convert x-ray images into visible light. Spreading of the visible light within CsI, however, reduces the resolution of the resulting image. Anisotropic etching of the CsI film into an array of micropixels can improve the image resolution by confining light within each pixel. The etching process uses a high-density inductively coupled plasma to pattern CsI samples held by a heated, rf-biased chuck. Fluorine-containing gases such as CF4 are found to enhance the etch rate by an order of magnitude compared to Ar+ sputtering alone. Without inert-gas ion bombardment, however, the CF4 etch becomes self-limited within a few microns of depth due to the blanket deposition of a passivation layer. Using CF4+Ar continuously removes this layer from the lateral surfaces, but the formation of a thick passivation layer on the unbombarded sidewalls of etched features is observed by scanning electron microscopy. At a substrate temperature of 220 °C, the minimum ion-bombardment energy for etching is Ei∼50 eV, and the rate depends on Ei1/2 above 65 eV. In dilute mixtures of CF4 and Ar, the etch rate is proportional to the gas-phase density of atomic fluorine. Above 50% CF4, however, the rate decreases, indicating the onset of net surface polymer deposition. These observations suggest that anisotropy is obtained through the ion-enhanced inhibitor etching mechanism. Etching exhibits an Arrhenius-type behavior in which the etch rate increases from ∼40 nm/min at 40 °C to 380 nm/min at 330 °C. The temperature dependence corresponds to an activation energy of 0.13±0.01 eV. This activation energy is consistent with the electronic sputtering mechanism for alkali halides.

Measurements of the electron energy distribution function in an Ar/CF4 inductively coupled plasma

Measurements of the electron energy distribution function (eedf) of a low-pressure inductively coupled plasma operated in a mixture of Ar and CF4 are reported. The measurement method was laser Thomson scattering. Extensive test were performed in order to verify that any perturbations caused by the laser did not affect the measurements. The eedf was measured for different concentrations of CF4 gas, and the results indicated that it was non-Maxwellian when even small amounts of CF4 gas were present. This dependence was attributed partially to the effect of electron-molecule vibrational excitation collisions.

Predicting membrane flux of CH4 and CF4 mixtures in Faujasite from molecular simulations

AbstractThe Fickian transport diffusivities of binary mixtures of methane and CF4 in the zeolite faujasite were investigated as a function of composition and loading. Using equilibrium molecular dynamics simulations, transport diffusivities of the mixtures were calculated from linear response theory. At low loadings, the diffusive cross terms are an order of magnitude smaller than the diffusive main terms, but at higher loadings they are on the same order of magnitude. The main term diffusivities are weak functions of concentration. The transport diffusivities were fitted as a function of adsorbate concentrations and used in the Fickian flux equations to predict codiffusion, counterdiffusion, and osmotic diffusion through a perfectly crystalline faujasite membrane. The osmotic and counterdiffusion cases show that it is critical to include both the cross term and main term diffusivities to predict the correct behavior. The permeances of methane and CF4 through the faujasite membrane are reported.

High-transmittance surface textures formed by plasma etching of metallophthalocyanine films

The effect of rf-induced plasma etching on thermally evaporated metallophthalocyanine films is investigated. Etching by a gas mixture of nitrogen and CF4 results in a transparent microstructuring residue with a grain size in the 100 nm range. The residue-covered surface increases visible transmittance up to 3%–4% over the glass substrate. The high-transmittance effect, which is nearly insensitive to wavelength, is characterized by modeling a gradient refractive-index profile bounded on discrete interfaces with surrounding media.

Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

Abstract Results of a systematic investigation on the effects of some deposition parameters (partial pressure of CF4 and self-bias voltage) on the microstructure, mechanical and tribological properties of a-C:H:F films are presented. The films were deposited by r.f.-PECVD using CH4–CF4 mixtures. The film composition was measured by ion beam analysis and, combining these results with the film thickness, the film density was determined. The structural arrangement was probed by Raman spectroscopy and the chemical bonding was investigated by infrared absorption and X-ray photoelectron spectroscopies. The hardness was measured by microindentation and the internal stress was determined by measuring the changing of the substrate curvature after the film deposition. The friction coefficient was measured by lateral force microscopy. The results indicate that the properties of a-C:H:F films are controlled by the ionic bombarding during the film growth. For a fixed self-bias, the increase of the CF4 partial pressure leads to a transition from diamond-like to a polymer-like structure, to a higher fluorine incorporation and to a decrease of both hardness and internal stress. The friction coefficient decreases too. The fluorine incorporation also increases with the increase of the self-bias and was associated to higher plasma decomposition. Fluorine-poor polymer-like films were deposited at low self-bias (−50 V). In both situations, fluorine incorporation occurs at the expenses of the hydrogen content and the reduction of the energy of the bombarding species results in less dense and soft films with a polymer-like structure.

Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

The etching characteristics of a LiNbO3 single crystal have been investigated using plasma reactive ion etching (RIE) with a mixture of CF4/Ar/H2. The etching rate of LiNbO3 with the mixture of CF4/Ar/H2 gases was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy methods. The rate-determining process of RIE is the supply of F radicals in RIE. The surface morphology of the etched LiNbO3 changed with the increase in the H2 gas flow ratio. The surface profile became flat, on optimizing the etching conditions, similar to the surface of non-etched LiNbO3. The X-ray diffraction peakfor etched LiNbO3 using the mixture of CF4 and Ar gases did not appear, because a non-crystalline layer was formed. It was found that the crystallinity of the surface is dependent on both, the flow rate of H2 gas and the etching time. F atoms exist in the contamination layer of the sample etched, using the mixture of CF4, Ar and H2 gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, were determined.

Iododifluoromethyl alkenes [ICF 2CHCHR]: a labile system generated from 1,1-difluoro-1,3-diiodoalkanes and its trapping with nucleophiles

Treatment of 1,1-difluoro-1,3-diiodoalkanes (ICF 2CH 2CHIR 1, 1) with NEt 3 in various solvents or with KF/Al 2O 3/CH 3CN gave no alkenes (ICF 2CHCHR 1, 2), whereas with NaOH afforded α,β-unsaturated carboxylic acids, although a signal of 2 in 19 F NMR spectroscopy could be observed momentarily sometimes. However, the labile 2 can be trapped either with thiolate or phenoxide ions. The former reaction gives a mixture of CF 2CHCH(SR)R 1 and RSCF 2CHCHR 1, whereas the latter affords only ArOCF 2CHCHR 1. The nucleophilic substitution of the bromoanalogues, BrCF 2CH 2CHBrR 1 and BrCF 2CHCHR 1, has also been investigated. A mechanism involving S N2′ and an allene intermediate is proposed.

Studies of CF2 radical and O atom in oxygen/fluorocarbon plasmas by laser-induced fluorescence

Laser-induced fluorescence 0LIF) has been used to examine behaviors of the CF2 radicals and O atoms in oxygen/fluorocarbon plasmas by utilizing a magnetic neutral loop discharge 0NLD), which is characterized by the efficient plasma production around the neutral loop, ‘NL region'. It was found that, in a pure CF4 plasma, the radial profile of CF2 density near the NL region changes from convex to concave with increasing rf power. This implies that the NL region is a source for CF2 at low rf powers and changes into a net sink at high rf powers, probablydue to the excess dissociation of CF2. In contrast, the O atom density in a pure O2 plasma was found to be very high and increases steadily against the rf power, corresponding to the dissociation degree of more than 20%. These features, emphasized by the high dissociation efficiency of the NLD, demonstrate different behaviors of both speciesrelated with the production and loss mechanisms. In plasmas of O2/ CF4 mixtures, it was found that the variation of O density as a function of gas composition is mostly linear, depending on the dilution factor, while thatofCF2 is nonlinear. This fact straightforwardly indicates that CF2 is mainly lost through reaction with O2 and that O is generated by the dissociation of residual O2. The change in the CF2 radial profile by O2 addition suggested that CF2 and O2 react in gas-phase and that the NL region fundamentally acts as a source for CF2. The results for O2/C4F8 plasmaswere also presented and understood with the same description as in O2/CF4 plasmas taking into account the compositional balance of C/O2 and the slow surface-loss process.

Reactive ion etching of diamond in CF4, O2, O2 and Ar-based mixtures

The reactive ion etching of diamond in O2, CF4/O2, CHF3/O2, O2/Ar discharges has been examined as a function of bias voltage, flow rate and composition of the gas mixtures. Etching in O2 and O2/Ar plasmas (with flow ratio of O2/Ar ≥ 25%) was characterised by a high etch rate (∼35 nm/min) and an increase in surface roughness with rising bias voltage. The CF4/O2 plasmas also produced a high etch rate (∼50 nm/min) but with only minor dependence of roughness on bias voltage. In comparison, the O2/Ar (with O2/Ar flow ratio <25%) and CHF3/O2 plasmas resulted in a low etch rate (7–10 nm/min). The high and low rate regimes were identified as ionenhanced chemical etching and physical sputtering respectively. Etching in the O2/Ar plasmas has been attributed to a combination of the two processes dependent on the O2 content.

High temperature gas and plasma transport properties of F2 and CF4 mixtures

Transport properties of chemical equilibrium mixtures F2, CF2, CF4 are investigated numerically. Influence of dissociation and ionization processes on viscosity and thermal conductivity is demonstrated. Free fluorine atom fraction in mixtures causes increase in values with a factor of 2–3.