Capacitively Coupled Radio Frequency Plasma Research Articles

Effect of Addition of Nitrogen to a Capacitively Radio-Frequency Hydrogen Discharge

A hybrid PIC/MC model is developed in this work for H2-xN2 capacitively coupled radio-frequency (CCRF) discharges in which we take into account 43 kinds of collisions reaction processes between charged particles (e−, H+3, H+2, H+, N+2, N+) and ground-state molecules (H2, N2). In addition, the mean energies and densities of electrons and ions (H+3, H+2, H+), and electric field distributions in the H2-N2 CCRF discharge are simulated by this model. Furthermore, the effects of addition of a variable percentage of nitrogen (0–30%) into the H2 discharge on the plasma processes and discharge characteristics are studied. It is shown that by increasing the percentage of nitrogen added to the system, the RF sheath thickness will narrow, the sheath electric field will be enhanced, and the mean energy of hydrogen ions impacting the electrodes will be increased. Because the electron impact ionization and dissociative ionization rates increase when N2 is added to the system, the electron mean density will increase while the electron mean energy and hydrogen ion density near the electrodes will decrease. This work aims to provide a theoretical basis for experimental studies and technological developments with regard to H2-N2 CCRF plasmas.

Study of high radio frequency plasma discharge effects on carbon fiber using Raman spectroscopy

The goal of this research is to evaluate the potential of single and dual high RF reactors for the treatment of carbon fiber by Raman and FT-IR spectroscopies. Unsized poly-acrylonitrile (PAN) carbon fiber was treated with single high frequency (40.68MHz) and double radio frequency capacitively coupled plasma (RF-CCP) discharge reactor (40.68/2.1MHz) using pure nitrogen gas. The changes in the structure of the carbon fiber surfaces due to the variations of the D and G band intensity ratio (ID/IG), crystallite size (La) and Full-Width-at-Half-Maximum with plasma power, gas pressure, and treatment-time were described. It was found that the disorder of carbon fiber increases (the ID/IG ratio increased) with increasing high RF power and the process time. In contrast, the degree of the order (La) increases with increasing the gas pressure. It was also observed that the degree of graphitization accrued due to the shift of the D and G bands to the lower wave number. And, from FT-IR result, it was found that the CC bond disappeared, and only carbon to nitrogen double and triple bonds are available by increasing pressure and RF power. In dual RF reactor, at high pressure and long process time, the disorder values (ID/IG) decrease with the increase of low frequency power. Furthermore, this mode has faster effects on the surface of carbon fiber than single RF mode.

Transition of water adhesion on superhydrophobic surface during aging of polypropylene modified by oxygen capacitively coupled radio frequency plasma

Polypropylene (PP) was modified by an oxygen capacitively coupled radio frequency plasma (CCP) under a radio frequency (RF) power of 200W for an exposure time of 20min. The aging process of the plasma-modified PP was studied at temperatures of 20°C, 60°C, and 90°C for 5h. The post-aged PP surface with bundles of nanowires showed the as-modified surface morphology with a gradual decrease of the polar oxygen-containing groups. A hydrophobic over-recovery from the superhydrophilic state to the superhydrophobic state was observed on the post-aged PP surface. The as-modified superhydrophilic PP surface turned into the hydrophilic state at 20°C and then the superhydrophobic state with the high water adhesion at 60°C. The superhydrophobic state with the low water adhesion was achieved at 90°C. Under the imposed pressure of 202Pa to water droplet, the superhydrophobic surface with the high water adhesion shifted to the hydrophilic state and the superhydrophobic surface with the low water adhesion showed a good stability. The conversion from the superhydrophilic state to the superhydrophobic state on the post-aged PP surface by the plasma nanotexturing was ascribed to the change of the surface compositions under the acceleration of increased aging temperature. The change of contact geometry and the decrease of adhesive force of the liquid–solid interface in the TCL due to more intense surface restructuring under the stimulus of higher aging temperature aroused the transition of the water adhesion on the post-aged superhydrophobic PP surface by the plasma nanotexturing.

Electron and Negative Ion Analysis in Oxygen Capacitively Coupled Radio Frequency Plasma

AbstractLow pressure capacitively coupled radio frequency plasmas (cc‐rf plasmas) were investigated by minimalinvasive 160 GHz Gaussian beam microwave interferometry. The interferometer is a frequency stabilized (PLL) heterodyne system which immediately provides the line integrated electron density at spatial (axial) resolution of about 10 mm and temporal resolution of 200 ns. The line integrated electron density was measured in dependence on the processing parameters rf power (10 … 100 W) and total pressure (10 … 100 Pa) in comparison between argon and oxygen. Thereby, the changed distance between the fixed microwave beam axis as well as the sheath edge is taken into consideration using an analytical collision‐dominated sheath model and results from optical emission spectroscopy. Microwave, interferometry and simultaneous laser photodetachment in oxygen plasma additionally permits the measurement of the negative atomic oxygen ion density. Dynamic and transient phenomena in oxygen plasmas are discussed such as mode transitions, afterglow behaviour in pulsed rf plasma, and electron density fluctuations due to attachment‐induced ionization instabilities (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrophobic over-recovery during aging of polyethylene modified by oxygen capacitively coupled radio frequency plasma: A new approach for stable superhydrophobic surface with high water adhesion

In this work, a new approach for the stable superhydrophobic surface with a high water adhesion has been found from an aging process at a high aging temperature of 90°C during an aging time up to 24h for the low density polyethylene (LDPE) modified by the oxygen capacitively coupled radio frequency plasma (CCP) under a radio frequency (RF) power of 200W for an exposure time of 5min. The plasma nanotexturing produced the nanofibrils array on the LDPE surface showing the contact angle of approximately 0°. During the aging process, the as-modified superhydrophilic LDPE surface underwent a hydrophobic over-recovery into the superhydrophobicity with a pinned water droplet showing the contact angle higher than 150°. A time-dependent contact angle model on the nanotextured surface was developed from the Cassie's equation for the heterogeneous surface containing different wetting patches, to describe the hydrophobic over-recovery due to the surface restructuring on the nanofibrils array. The stable superhydrophobicity with the high water adhesion was attributed to the CCP modified LDPE surface with the nanofibrils composed of the heterogeneous chemical compositions of polar and nonpolar chains/groups after the aging process.

Controllable wettability of poly(ethylene terephthlate) film modified by oxygen combined inductively and capacitively coupled radio-frequency plasma

Poly(ethylene terephthalate) (PET) film was modified by using oxygen combined inductively coupled radio-frequency plasma (ICP) and capacitively coupled radio-frequency plasma (CCP) at the radio-frequency (RF) power of 200 W and 100 W, respectively, for a treatment time up to 300 s. The RF plasma modification under the combined ICP and CCP mode with the controllable oxygen plasma density and oxygen ion-flux energy significantly improved the wettability of PET film, due to the creation of the polar functional groups containing oxygen, such as C–O and O–C O, and the increase of the surface roughness. At a low surface roughness, the polar functional groups on the PET film affected both the advancing contact angles and receding contact angles. When the surface roughness increased over a threshold, the advancing contact angles mainly depended on the polar functional groups, and the receding contact angles were particularly dependent on the surface roughness. Therefore, the controllable advancing contact angles and receding contact angles on the plasma-modified PET film were independently determined by plasma functionalization and plasma etching under the combined ICP and CCP mode.

The gain and loss of energy by electrons in the RF-CCP sheath

The exact mechanism for the heating of electrons in the sheath of radio frequency capacitively coupled plasma (RF-CCP) discharges is poorly understood. A hybrid one-dimensional model of a RF-CCP discharge is used to study this problem by tracking electron trajectories and electron energy change in the RF-CCP sheath. This study shows that the Ohmic electric field, the field due to conduction current, can have an effect on electron heating in the plasma sheath. Both the ambipolar and the Ohmic electric field can repel low energy electrons and reduce their interaction with the changing electric field in the sheath region. A comparison is made between the more realistic Brinkmann fluid sheath model and a hard wall approximation. For energetic electrons, the hard wall approximation accurately models electron heating. However, the hard wall approximation does not accurately model the heating of lower energy electrons or allow for electron losses to the electrode. A comparison is also made between the electron energy probability function calculated using a Monte Carlo simulation with and without the effects of the sheath.

Spatial and Phase-Resolved Optical Emission Patterns in Capacitively Coupled Radio-Frequency Plasmas

Phase-resolved optical emission spectroscopy is a powerful tool to investigate the excitation mechanisms within the radio-frequency (RF) cycle of capacitively coupled RF plasmas. In this paper, the optical emission of oxygen, hydrogen, and argon atoms is investigated over a wide range of process parameters. The spatially (axial) and temporally resolved spectroscopy reveals four prominent emission patterns.

Estimation of the Methane Conversion in a Capacitively Coupled Radio-Frequency Plasma.

Methane decomposition was investigated experimentally with the capacitively coupled rf discharge. Glow discharge was generated from the low temperature capacitively coupled radio frequency (rf) plasma and was used for activating methane to make free radicals without catalysts. Operating variables in the experiment were reaction pressure, feed flow rate, and total input power. The gaseous reaction products were mainly hydrogen, ethane, propane and ethylene. When the input power increased, the density of hydrogen increased and the unsaturated groups of C2 and C3 began to form. The surface-phase polymerization reactions occurred inside the discharge tube wall. A mathematical model was derived using collision theory and diffusion effect of reaction products. From the result of the mathematical modeling, the simple mathematical relation of the methane conversion was obtained, and it was the function of specific input energy only. As the results of sensitivity analysis, the conversion of methane could be determined from the input flow rate and the electrical input power without measuring reaction temperature.

Ultraviolet cavity ring-down spectroscopy of free radicals in etching plasmas

Many reactive species of interest in technological plasmas absorb light in the UV spectral region (200–300 nm). Measurement of these weak absorbances (typically 10 −2–10 −4 for a single pass) allows us to determine their absolute concentration. Low-resolution absorption spectra of these systems have previously been obtained by broad-band absorption spectroscopy. Here we present spectra obtained using laser cavity ring-down spectroscopy, which has much higher spectral resolution, and potentially higher sensitivity. Spectra were obtained for CF, CF 2, AlF and SiF 2 radicals in capacitively-coupled radio-frequency plasmas in fluorocarbon gases. This technique offers the possibility of real-time (1 s) absolute concentration measurements during wafer processing.

容量結合型高周波プラズマ中の電子エネルギー分布関数とイオン衝撃2次電子の観測

容量結合型高周波プラズマ中の電子エネルギー分布関数とイオン衝撃2次電子の観測

A Novel Sustaining Mechanism in Capacitively Coupled Radio Frequency Plasma in Oxygen

A Novel Sustaining Mechanism in Capacitively Coupled Radio Frequency Plasma in Oxygen