Addition Of CF4 Research Articles

Effect of CF4 concentration on the discharge dynamics and reactive species distribution of atmospheric nanosecond pulsed He plasma jet

Based on a two dimensional self-consistent model, the effect of different CF4 concentrations on the discharge dynamics characteristics, F-containing species distribution and the distribution of the axial and radial ionization rates of He atmospheric pressure plasma jet (APPJ) has been investigated. In addition, the accuracy of the simulation is verified by comparing the experimental results. The ionization rate of He APPJ enhances with the increase of CF4 from 0% to 2% because of the Penning ionization of CF4 with metastable He while decreases in the case of 3% CF4 owing to the electronegativity and the electron excitation energy loss of CF4. The increase of CF4 concentration and the decrease of the electron density leads to the decrease of CF4 + density at 3% CF4. CF3 + density is determined by the Penning ionization rate of CF4 and the reaction rate of He+ + CF4 → CF3 + + F + He. As CF4 concentration increases from 2% to 3%, the decrease of metastable He and He+ concentration results in the significant decrease of CF3 + density. The densities of CF3 − and F− keep increasing from 1% to 3% CF4 due to the effect of the electron attachment reaction of CF4. With the addition of CF4, the ionization reaction of CF4 is gradually playing the major role in the streamer head, the Penning ionization of CF4 is the main source of electron ionization inside the jet and dominates in the formation of ionization wave tail. As the concentration of CF4 increases from 0% to 2%, the electron impact ionization rates of He and CF4 near the axis increase, resulting in the more uniform radial ionization rate distribution of He + 2% CF4 APPJ.

Effect of CF4 additive on dynamic surface charge deposited on dielectric by helium atmospheric pressure plasma jet

Abstract The addition of active trace components to non-thermal plasmas effectively enhances their chemical activity and has attracted considerable academic attention in the plasma community. It is essential to quantitatively estimate the effect of active addition on the properties of the plasma–surface interaction (PSI). In this study, we focus on the fundamental properties of dynamic surface charge deposited by a He-atmospheric pressure plasma jet (APPJ) with 0%–2% CF4 additive. The charge distribution is measured by a reflective optical measurement platform based on linear electro-optic effect, and is calculated with surface charge density inversion algorithm. Results show that a higher CF4 concentration can shrink the region of surface charge accumulation. Polarity effect is observed in aspects of maximum charge density when the CF4 concentration gradually rises. The negative charge deposition is suppressed by the addition of CF4, nearly disappearing at 2% concentration. While the maximum density of positive charge rises to ∼25 nC cm−2 at 0.5% CF4 before it decreases to ∼10 nC cm−2. The dispersions of total surface charge at 0.5% and 1.5% additives indicate the unstable periodic bombardment of ionization waves in He/CF4 APPJ. The double effect of CF4 additive on the surface charges by He-APPJ is also discussed. These results provide fresh and deep insights into the interaction between dielectric surface modification and ionization waves that occurs in other plasmas processing fed with composite gases.

Jet morphology analysis of microwave‐generated plasma for microfabrication of optics

AbstractThe jet morphology of the fluorine‐containing plasma is important for the accuracy and efficiency of nondestructive optical fabrication. This paper investigated changes in the jet size and active radicals of microwave plasma. Results show that little addition of CF4 and O2 in Ar could promote the ionization process, but excessive addition of them would inhibit the production of active radicals and limit the jet size. Both optimizing the proportion of CF4 and O2 and the applied power can greatly improve the jet morphology. The regulation principle of the plasma jet morphology was interpreted as the balance between the ionization resistance of the working gas and the applied power, which ensures a high etch rate and process resolution.

Effect of small amount of CF4 addition on He and Ar atmospheric pressure plasma jet and influence of relative permittivity of downstream material on plasma–surface interaction

CF4 is an important source of fluorine groups in atmospheric pressure plasma jet (APPJ). In order to obtain reactive fluorine species under atmospheric pressure, noble gas (Ar or He) and CF4 are usually mixed and used as the working gas of APPJ. In this paper, the differences in the discharge dynamics on He/CF4 APPJ and Ar/CF4 APPJ are investigated experimentally. Meanwhile, combined with simulation, the effects of downstream targets with different relative permittivity on the radial propagation range of the plasma plume and the distribution of F-containing reactive species are studied. It is discovered that the addition of a small amount of CF4 (20 sccm) will increase the intensity of He/CF4 APPJ due to the contribution of Penning ionization of metastable He with CF4. Differently, the addition of CF4 will continuously lead to a significant decrease in the intensity of Ar/CF4 APPJ. The radial propagation range of He/CF4 APPJ on the target surface decreases with the increase in the relative permittivity of the downstream target. The smaller relative permittivity inhibits the axial propagation speed of APPJ, but it increases the radial propagation range of reactive species. The larger relative permittivity promotes the production of F-containing reactive species and their flux intensity on the target surface.

Effect of CF4 ratio on the interaction of atmospheric nanosecond pulsed He plasma jet with a dielectric material

In this paper, a two dimensional (2D) axisymmetric fluid model is built to study the effect of the ratio of CF4 admixture on the plasma dynamics and F-containing species concentration in He atmospheric pressure plasma jet. The steady mole fraction distribution of He and CF4 is first studied, which presents that the mole fractions of CF4 show peaks at 5 mm from the symmetry axis on the dielectric surface due to the dual influences of the boundary layer effect and air mixing. The CF4 admixture enhances the propagation speed of ionization wave, and the axial velocity reaches the peak value in the case of He + 1.5% CF4. The conversion from the ring-shaped plasma–surface interaction to a solid-disk one results from the addition of CF4. The Penning ionization of CF4 accelerates the plasma jet propagation within 1.5% CF4. However, the excitation energy loss and electron attachment caused by the addition of CF4 also quench the propagation of plasma jet, which become obvious in the case of 2% CF4. F-containing groups (CF4+, CF3+, CF3−, F−, CF3, and F), mainly produced by the Penning ionization reaction, electron attachment reaction, and He+ + CF4 → He + CF3+ + F, also show peaks for He + 1.5% CF4. On the dielectric surface, as the radial distance increases, the ratio of F-containing neutral species (CF3 and F) to O atom at 200 ns decreases due to the increase of O atom concentration and then increases at the streamer head because the surface flux of CF3 reaches the maximum value. The maximum surface flux radial distribution distance for ratio of F-containing species to O atom, CF3 and F appear in the case of 1.5% CF4.

Surface morphology evolution of a polycrystalline diamond by inductively coupled plasma reactive ion etching (ICP-RIE)

The needle-like surface morphology evolution in oxygen plasma in combination with a secondary gas (Cl2, CHF3 or CF4) by inductively coupled plasma reactive ion etching (ICP-RIE) on a free-standing polycrystalline diamond was investigated. The addition of CF4 can produce trans-polyacetylene (t-PA), which is similar to the result when the pure O2 etching takes place, and generate compact needle-tip particles. However, the t-PA disappears with the introduction of Cl or H ions. The optimised etching parameters for the needle-like structure formation are as following: Cl2/O2 ratio 20% and RF-power (RFP) 100 W, where more compact and even nano-needles are realised with an average etching rate of 2 μm/min. The Cl2/O2 plasma etching results indicate that the time-dependent etching mechanism of diamond nano-needles results from (1 1 1) crystal plane selective etching and preferential graphitisation at the twin-plane boundary and dislocation area.

Effect of CF4 Addition to Cl2/Ar Plasma on the Etching of ZrO2 Thin Films

Effect of CF₄ Addition to Cl₂/Ar Plasma on the Etching of ZrO₂ Thin Films

InAs-based metal-oxide-semiconductor structure formation in low-energy Townsend discharge

We developed and applied a method of InAs passivation in the low-energy plasma of Townsend discharge. The controlled interface oxidation in the Ar:O2:CF4 gas mixture under visualization of gas discharge plasma allowed growing thin homogeneous films in the range of 5–15 nm thickness. Oxidation with the addition of CF4 in gas-discharge plasma led to the formation of In and As oxyfluorides with a wide insulating gap and isostructural interface with unpinned Fermi level behavior. The metal-oxide-semiconductor structure showed excellent capacitance-voltage characteristics: small frequency dispersion (<15 mV), density of interface states (Dit) in the gap below 5 × 1010 eV–1cm−2, and fixed charge (Qfix) below 5 × 1011 cm−2.

An investigation of Ar metastable state density in low pressure dual-frequency capacitively coupled argon and argon-diluted plasmas

An tunable diode laser absorption spectroscopy has been used to determine the Ar*(3P2) and Ar*(3P0) metastable atoms densities in dual-frequency capacitively coupled plasmas. The effects of different control parameters, such as high-frequency power, gas pressure and content of Ar, on the densities of two metastable atoms and electron density were discussed in single-frequency and dual-frequency Ar discharges, respectively. Particularly, the effects of the pressure on the axial profile of the electron and Ar metastable state densities were also discussed. Furthermore, a simple rate model was employed and its results were compared with experiments to analyze the main production and loss processes of Ar metastable states. It is found that Ar metastable state is mainly produced by electron impact excitation from the ground state, and decayed by diffusion and collision quenching with electrons and neutral molecules. Besides, the addition of CF4 was found to significantly increase the metastable destruction rate by the CF4 quenching, especially for large CF4 content and high pressure, it becomes the dominant depopulation process.

Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault

Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (Cre; ∼30 fmol kg−1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1–9 times Cre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10–980 times Cre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20–100 km) suggests that the SAFS potentially emits (0.3–1)×10−1 kg CF4 yr−1 to the Earth's surface. For comparison, the chemical weathering of ∼7.5×104 km2 of granitic rock in California is estimated to release (0.019–3.2)×10−1 kg CF4 yr−1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial–interglacial transitions.

Chemistry studies of SF6/CF4, SF6/O2 and CF4/O2 gas phase during hollow cathode reactive ion etching plasma

In this work, mass spectrometry and optical emission spectroscopy techniques were used to monitor the molecular and atomic neutral species during SF6/CF4, SF6/O2 and CF4/O2 plasmas generated in a radio-frequency Hollow Cathode Reactive Ion Etching (HCRIE) reactor keeping constant the following operational conditions: total gas flow rate, gas pressure, and discharge power. The investigations were aimed to understand the chemistry behavior of plasmas generated with SF6 and CF4 mixtures or mixed separately with O2. The neutral mass spectrometry analysis showed a high concentration of gas species namely SF5+ (parent specie = SF6), SF3+ (SF4), CF3+ (CF4) and HF+ (HF) in SF6/CF4 plasmas, SF5+, SF3+, O2+ (O2), F+ (F) and HF+ in SF6/O2 plasmas and CF3+, O2+, CO2+ (CO2) and HF+ in CF4/O2 plasmas. The presence of other species was observed in quantities lower than 1% of total gas pressure. It was used the actinometry method to monitor the atomic fluorine (F) concentration during discharge operation. Higher density of F was observed in all experiments, varying from (2.8–9.5) × 1019 m−3 in SF6/CF4 plasmas, (0.2–1.7) × 1020 m−3 in SF6/O2 plasmas and (0.06–1.17) × 1020 m−3 in CF4/O2 plasmas. The addition of CF4 in SF6 plasma reduces monotonically the F concentration when compared with the SF6/O2 and CF4/O2 plasmas that promotes an increase of F for low O2 concentrations. This effect shows the importance of oxygen species in the dissociative processes of the fluorine-based plasma also for this type of plasma reactor. Moreover, it is highlighted the higher concentrations of HF in gas phase that promotes reactions paths that decrease the F species in gas/plasma phase.

Low-temperature plasma-assisted growth of germanium nanorods

Plasma-assisted growth of germanium nanorods (Ge-NRs) was performed in electron cyclotron resonance (ECR) plasma with a GeH4–H2–CF4 system using indium nanocrystals as seed particles via the vapor–liquid–solid mechanism. The addition of CF4 was found to be a key factor facilitating low temperature growth of Ge-NRs as it promoted efficient etching of competing surface deposition of Ge, which would lead to the formation of Ge crusts on the surface of indium droplets and thus retard nanorod growth. The effective growth of crystalline Ge-NRs at temperatures as low as 170 °C has been achieved. A systematic study of the diameter dependence of the nanorod growth rate is presented. The growth rate increases with increasing Ge-NR diameter. The results suggest that the direct impingement of growth species on indium liquid droplets is the dominant factor for nanorod growth, indicating that the growth rate is governed by the Gibbs–Thomson effect.

Investigation on critical breakdown electric field of hot sulfur hexafluoride/carbon tetrafluoride mixtures for high voltage circuit breaker applications

Sulfur hexafluoride (SF6) gas, widely used in high-voltage circuit breakers, has a high global warming potential and hence substitutes are being sought. The use of a mixture of carbon tetrafluoride (CF4) and SF6 is examined here. It is known that this reduces the breakdown voltage at room temperature. However, the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown depends on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF6/CF4 mixtures corresponding to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300 K to 3500 K. The equilibrium compositions of hot SF6/CF4 mixtures under different mixing fractions were determined based on Gibbs free energy minimization. Full sets of improved cross sections for interactions between electrons and the species present are presented. The critical reduced electric field strength of these mixtures was obtained by balancing electron generation and loss mechanisms. These were evaluated using the electron energy distribution function derived from the Boltzmann transport equation under the two-term approximation. The result indicates that critical electric field strength decreases with increasing heavy-particle temperature from 1500 to 3500 K. Good agreement was found between calculations for pure hot SF6 and pure hot CF4 and experimental results and previous calculations. The addition of CF4 to SF6 was found to increase the critical reduced electric field strength for temperatures above 1500 K, indicating the potential of replacing SF6 by SF6/CF4 mixtures in high-voltage circuit breakers.

Vibrational Relaxation of O2(X3Σg–, v = 6–8) by Collisions with O2(X3Σg–, v = 0): Solution of the Problems in the Integrated Profiles Method

The linear kinetic analysis called the integrated profiles method (IPM) makes it simple to analyze the multistep relaxation processes of vibrational manifold. The problem that plots for linear regression in the IPM analysis cannot be made, however, has been found in the study of self relaxation of O2(X3Σ(-)g, v = 6-8). The cause of the problem is the identical time-dependence of the populations of the adjacent vibrational levels. An addition of CF4 into the system made a difference in the time profiles and enabled us to make IPM analysis and determine the rate coefficients. In the experiments, a gaseous mixture of O3/O2/CF4 in an Ar carrier at 298 K was irradiated at 266 nm, and the direct photoproduct O2(X3Σ(-)g, v = 6-9) from O3 was detected by laser-induced fluorescence (LIF)in the B3Σu-X3Σ(-)g transition. Time-resolved LIF intensities of O2(X3Σ(-)g, v) at various pressures of O2 and fixed pressure of CF4 were recorded. The resulting rate coefficients for v = 6−8 correlate smoothly with those for v ≤ 5 and v ≥ 8 reported previously.The vibrational-level dependence (v = 2-13) of the rate coefficients for relaxation of O2(X3Σ(-)g, v) by O2 is accounted for by the balance between the harmonic transition probabilities and the energy defect in the V-V energy-transfer mechanism.

Fast Etching of Molding Compound by an Ar/O2/CF4 Plasma and Process Improvements for Semiconductor Package Decapsulation

Decapsulation of a SOT23 semiconductor package with 23 um copper wire bonds is conducted with an especially designed microwave induced plasma system. It is found that a 30%-60% CF4 addition in the O2/CF4 etchant gas results in high molding compound etching rate. Si3N4 overetching which is encountered in plasma decapsulation is solved by an improved etching process. Critical processing parameters are investigated and 350 um thick molding compound on top of the die is removed selectively by pure plasma etching for 6 minutes, which is at least 10 times faster than conventional plasma etchers.

Background reduction and spin-dependent limits using DRIFT - a directionally sensitive dark matter detector

The DRIFT (Directional Recoil Identification From Tracks) collaboration operates a 1m3 low pressure gaseous negative ion time projection chamber (NI-TPC) WIMP dark matter search experiment in the Boulby Underground Laboratory. Recent progress from the DRIFT collaboration is presented that includes a series of background reduction work and the addition of CF4 to the target volume. A preliminary limit on the spin-dependent WIMP-proton interaction cross-section is presented from a non-blind analysis of 47.2 days live time with a 0.8 m3 30 Torr CS2 - 10Torr CF4 target. The preliminary limit has a minimum of 1.1 pb for a 100 GeV WIMP.

Hydrophobic treatment of organics against glass employing nonequilibrium atmospheric pressure pulsed plasmas with a mixture of CF4 and N2 gases

A hydrophobic organics surface selectively against glass was realized by employing nonequilibrium atmospheric-pressure pulsed plasmas with a mixture of CF4 and N2 gases. The organic surface was drastically altered to have a high hydrophobicity, while the glass surface itself remained hydrophilic after the plasma treatment with the addition of a small amount of CF4 to the N2 gas. After 100 CF4/N2 plasma treatments, no thin film deposition was observed on the organic material. To investigate the characteristics of the CF4/N2 plasma, the exhaust gas from the plasma was measured by using ion attachment mass spectroscopy (IAMS). The IAMS spectrum indicated that the amounts of CF3 and F radicals were increased drastically with increasing addition of CF4. A mechanism of the selective surface modification was clarified on a result of surface chemical bonding with the gas phase.

Plasma etching of SiO2 using remote-type pin-to-plate dielectric barrier discharge

Atmospheric pressure plasma etching of SiO2 was examined using a modified remote-type dielectric barrier discharge (DBD), called “pin-to-plate DBD.” The effect of adding four gases CF4, C4F8, O2, and Ar to the base gas mixture containing N2 (60 slm) (slm denotes standard liters per minute)/NF3 (600 SCCM) (SCCM denotes cubic centimeter per minute at STP) on the SiO2 etch characteristics was investigated. The results showed that the SiO2 etch rate decreased continuously with increasing C4F8 (200–800 SCCM) addition, whereas the SiO2 etch rate increased with increasing CF4 (1–10 slm) addition up to 7 slm CF4. This increase in the SiO2 etch rate up to 7 slm CF4 was attributed to the effective removal of Si in SiO2 by F atoms through the removal of oxygen in SiO2 by carbon in the CFX in the plasma. However, the decrease in SiO2 etch rate with further increases in CF4 flow rate above 7 slm was attributed to the formation of a thick C–F polymer layer on the SiO2 surface. A SiO2 etch rate of approximately 243 nm/min was obtained with a gas mixture of N2 (60 slm)/NF3 (600 SCCM)/CF4 (7 slm), and an input voltage and operating frequency to the source of 10 kV and 30 kHz, respectively. The addition of 200 SCCM Ar to the above gas mixture increased the SiO2 etch rate to approximately 263 nm/min. This is possibly due to the increased ionization and dissociation of reactive species through penning ionization of Ar.

Inductively coupled plasma etching of poly-SiC in SF6 chemistries

A study was made to find a low-cost and robust etching solution for silicon carbide (SiC) using a commercially available inductively coupled plasma etching tool. Sulfur hexafluoride (SF6) was selected because of its high degree of F dissociation and nonhazardous nature. A parametric study of the etching characteristics of poly-SiC in inductively coupled plasma (ICP) SF6 chemistries was performed. Etch chemistry was found to greatly affect etch rate, selectivity, and the postetch surface condition. Etch rates as high as 5884Å∕min were achieved with high SiC∕Cr selectivity (36) using a SF6∕CF4∕He gas mixture, but the etched surface was relatively rough (134 Å rms). He addition was found to increase the SiC etch rate, and this effect is believed to be caused by increased ionization of SF6 in the plasma and the resulting increases in the SF3+ and fluorine (F) radical concentrations. The formation of pillar-like structures and sidewall deposition was observed on the etched SiC surfaces under some conditions. These unwanted etch byproducts exhibited a high concentration of chromium (Cr) and fluorine. However, an argon (Ar) plasma preclean of the substrate, high ICP, and/or bias powers, and CF4 addition reduced the pillar formation significantly.

Characterization and preparation of SiO2 and SiOF films using an RF PECVD technique from TEOS/O2 and TEOS/O2/CF4 precursors

Preparation of high quality SiO2 and SiOF films has been attempted from tetraethoxysilane (TEOS)/O2 and TEOS/O2/CF4 precursors by modifying deposition variables. The deposited films were fully characterized by various analytical tools, such as FT-IR, UV-VIS-NIR spectrophotometry, XPS, ex situ ellipsometry and SEM. From the characterization of SiO2 films, it was demonstrated that the TEOS/O2 flow ratio is a critical parameter that controls the film quality and, when the TEOS/O2 flow ratio is low enough to prevent the physical adsorption of TEOS on the film surface during growth, good quality SiO2 films can be deposited at a high growth rate, even at low temperatures of 100°C. It is also noted that the addition of CF4 ranging from 0 to 70 sccm to the TEOS/O2 mixture can induce a lowering of the refractive index by replacing the highly polarizable Si–OH and OH bonds with less polarizable Si–F bonds and result in the formation of an SiOF film having good optical and structural characteristics without disadvantages such as a porous structure and hygroscopicity.