Generation Of High-density Plasma Research Articles

Generation of high-density plasma via transparent electrode in capacitively coupled plasma

Generation of high-density plasma via transparent electrode in capacitively coupled plasma

Experimental studies and COMSOL 1-D simulation in Ar capacitively coupled plasmas

This work systematically studies a capacitively coupled plasma (CCP) source using experiments and 1-D COMSOL simulations relevant to Ar plasmas. Two radio frequency compensated Langmuir probes (LPs) and optical emission spectroscopy (OES) were purposefully used to measure the plasma parameters, and the experimental results were compared with those of simulations. We studied the axial variation of plasma parameters using an axial LP between the power and ground electrodes of the CCP at various operating pressures ranging from 10 to 150 mTorr. The electron density showed a gradual increase in its value with rising pressures. In addition, we employed a radial LP at the axial location L = 4 cm from the surface of the power electrode to measure the plasma parameters and compare these data with those of the axial LP and simulations. The variations of plasma potential measured by the radial LP showed an opposite trend of variation to those of simulations and the axial LP at pressures 10–60 mTorr, which is attributed to the plasma diffusion at low pressures. LP and OES measurements and simulation data suggest stochastic heating that generates high electron temperatures at low pressures. In addition, data revealed that the high-density plasma generation at high pressures could be due to the effects of both collisional heating and stochastic heating. Analysis showed that electrons could gain energy from the strong field regime of the sheath closed to the electrodes, which has a similar variation to electron temperature. The results of simulations have shown excellent agreement with experiments, and this work has the basis for plasma applications like plasma-enhanced chemical vapor deposition.

Effects of combined coils on the uniformity of RF ion source

The radio frequency (RF) ion source is significant in the industry because of its advantages of easy control and maintenance, low gas consumption, high energy and high-density plasma generation abilities. Unfortunately, the problem of high-density plasma uniformity limits its applications. RF coils, as the most important part of the ion source, play a critical role on plasma density and distribution. In this paper, we performed simulations of the combined coils magnetic field and plasma with power distribution and conducted process experiments with the RF ion source to obtain its etching uniformity by the characterization of a step profiler. The results show that the application of the same direction and a suitable coil current is beneficial to extend the uniformity range. The uniformity is improved by applying reversed coil currents. The results of process experiments are consistent with the simulation conclusions. This paper provides informative suggestions for the optimization of coil structures in the RF ion source.

Development of plasma sources and diagnostics for the simulation of fusion edge plasmas

Although the research on divertors and scrape-off layers (SOLs) has been not as focused on as the recent success of the Korean fusion program, a few linear plasma devices have been developed for simulating divertor and SOL plasmas: (1) diversified plasma simulator (DiPS), a versatile linear machine, has been developed for simulations of divertor and space plasmas with various electric probes, such as single, triple, and Mach Probes and gridded energy analyzer. DiPS consists of two major parts: a divertor plasma simulator with a \(\hbox {LaB}_6\) DC plasma source and a space plasma simulator with a helicon RF plasma source, (2) divertor plasma simulator-1 (DiPS-1) is a part of DiPS with only a \(\hbox {LaB}_6\) cathode, where a low-power laser-induced fluorescence (LIF) is added and more electric probe diagnostics are augmented; it is dedicated only for fusion edge and divertor plasmas, (3) Divertor Plasma Simulator-2 (DiPS-2) has been modified from the DiPS-1 by adding a magnetic nozzle with a limiter structure and by removing the helicon source and space chamber. DiPS-2 is a linear plasma device with a 4-inch \(\hbox {LaB}_6\) cathode, the same as DiPS-1, and it is focused on the development of various diagnostics, such as those used for LIF and laser Thomson scattering (LTS) along with various electric probes, on the divertor and scrape-off plasmas and on the plasma-material interaction (PMI) research, such as that of tungsten and graphite as plasma-facing components (PFCs), (4) A Multi-Purpose Plasma (\(\hbox {MP}^2\)) device is a renovation of the Hanbit mirror device [Kwon et al., Nucl. Fusion 43, 686 (2003)] with the installation of two plasma sources: \(\hbox {LaB}_6\) (DC) and helicon (RF) plasma sources. A honeycomb-like large-area \(\hbox {LaB}_6\) (HLA-\(\hbox {LaB}_6\)) cathode has been developed for the divertor plasma simulation to improve the resistance against the thermal shock fragility for large (8-inch) and high density plasma generation, (5) DiPS-2 has been augmented by adding another cylindrical device, called the Dust interaction with Surfaces Chamber (DiSC) for the generation and diagnostics of dusts. This combined system (DiPS-2+DiSC) has added two more diagnostics: Laser Photo-Detachment (LPD) for dust density and laser Mie Scattering (LMS) for dust size. Moreover, dusts or negative ions have been analyzed by using electric probes and capacitive diagram gauges in Transport and Removal of Dusts (TReD) device.

The Effects of Magnetic Field on the Properties of Diamond-Like Carbon Films Produced by High-Density Helicon Wave Plasma

Diamond-like carbon (DLC) films were grown on Si substrates by high-density helicon wave plasma (HWP) generated under low pressure, with the help of CH4 as an important single-source precursor. The influence of magnetic field ( ${B}_{0}$ : 1200–2400 Gs) on the film structure, morphology, composition, and mechanical properties has been studied. The high deposition rate of the films exhibits a maximum of 800 nm/min, which is contributed by the high-density plasma generation of HWP. By the X-ray photoelectron spectroscopy (XPS) analysis, the as-deposited DLC film is composed mainly of sp2 C-C. The DLC film deposited at ${B}_{0} =2400$ Gs exhibits that the friction coefficient reaches its minimum value of $5 \times 10^{-3}$ , with small surface roughness (root mean square (RMS) ~ 10 nm). Considering that ${B}_{0}$ can be easily controlled, this article opens up a new approach to achieve ultralow friction coefficient DLC films with a high deposited rate at room temperature.

High-rate synthesis of SiCN films using single-source silicon precursor with high-density helicon plasma

A novel type of compound, namely Si-guanidinate, where the Si center of alkylsilyl is linked with pyrrolyl-guanidinate ligand, has been synthesized as potential chemical vapor deposition (CVD) precursor and characterized by 1H, 13C, EI-MS, and elemental analysis. The thermal properties of the Si-guanidinate, including vapor pressure and thermal stabilities which were investigated by simultaneous thermal analyses (STA) exhibit a promising precursor in CVD process. The Si-guanidinate was used as a single-source liquid organosilicone precursor to deposit silicon carbon nitride (SiCN) films with the helicon plasma-enhanced chemical vapor deposition (HWP-CVD) method. The effect of the substrate pules negative bias voltage (-Vs) on the microstructure, morphology, composition and optical properties (including refractive index) of the SiCN films has been studied. The deposition rate of the films exhibits a maximum of 15.3 μm/min, which is contributed by the high-density plasma generation of HWP. By X-ray photoelectron spectroscopy (XPS) analysis, the film is mainly composed of Si–C–N. The SiCN films deposited at -VS of 1500 V appear to be high N content of 30.0% (k = 1.83) materials with quite small surface roughness (Root mean square (RMS)~0.7 nm).

Enhancement of surface discharge in catalyst pores in dielectric barrier discharges

The generation of high-density plasmas on the surface of porous catalysts is very important for plasma catalysis, as it determines the active surface of the catalyst that is available for the reaction. In this work, we investigate the mechanism of surface and volume plasma streamer formation and propagation near micro-sized pores in dielectric barrier discharges operating in air at atmospheric pressure. A two-dimensional particle-in-cell/Monte Carlo collision model is used to model the individual kinetic behavior of plasma species. Our calculations indicate that the surface discharge is enhanced on the surface of the catalyst pores compared with the microdischarge inside the catalyst pores. The reason is that the surface ionization wave induces surface charging along the catalyst pore sidewalls, leading to a strong electric field along the pore sidewalls, which in turn further enhances the surface discharge. Therefore, highly concentrated reactive species occur on the surfaces of the catalyst pores, indicating high-density plasmas on the surface of porous catalysts. Indeed, the maximum electron impact excitation and ionization rates occur on the pore surface, indicating the more pronounced production of excited state and electron-ion pairs on the pore surface than inside the pore, which may profoundly affect the plasma catalytic process.

Comparison of plasma properties in normal and multiple holes hollow cathode RF PECVD and their utility in a-SiNx:H thin film deposition

Conventional and multiple-hole hollow cathode (MHHC) showerhead electrodes of an RF capacitively coupled plasma (CCP) source were experimentally studied to investigate their capability of plasma generation and suitability of plasma application like PECVD. The plasma characteristics of the CCPs were critically examined for the PECVD plasmas produced by various showerhead configurations. The optimum performance in terms of high-density plasma generation and high emission intensity of excited species was observed for the operation using MHHC discharge. The MHHC discharge is characterized by an anode glow and a strong low-frequency fluctuation in the range of ∼ a few kHz that is measured by the Langmuir probe (LP). The LP measurements in a broad pressure range revealed the scenario of hollow cathode discharge characterized by the enhanced electron temperature and the highest plasma density around 120 mTorr. It is realized that the bulk plasma intrusion inside the hole of the electrodes of the showerhead and the enhanced ionization in the plasma sheath regions of each hole facilitated the generation of high-density plasmas when the hole diameter is slightly bigger than twice or thrice the sheath length. The effectiveness of MHHC PECVD for high rate and low-temperature deposition of a-SiNx:H thin films is realized.

The effect of power balance on the heating mode transition in micro-dielectric barrier helium glow discharges

A particle-in-cell simulation has been adapted to analyze the helium discharge characteristics of a planar micro-dielectric barrier discharge with a gap distance less than 100 µm for variation of driving frequency from 10 to 500 MHz. Two scaling laws for the breakdown voltage were obtained with the change in heating mechanism from the γ- to the α-mode with increasing frequency. The optimal condition for the efficient generation of high-density plasmas with minimized power is obtained when the ratio of ion transit time to the RF period is about 1/4, so that the secondary electrons emitted by ion bombardment on the dielectric-gap boundary are accelerated in phase with the sheath potential. Under this condition, the plasma density as well as the ion current is maximum, the displacement current and the electron current are almost the same, and the ratio of the power delivered to the plasma is 50% of the total power. At high frequencies, the collisional electron heating increases by the induced bulk electric field, enhancing excitation and elastic collisions, and thus ionization efficiency decreases while excitation efficiency increases.

High-density microwave plasma source using negative-permeability metamaterial with tuned wave attenuation

High-density plasma generated by waves with efficient wave power consumption is suitable for various dry processes. However, when we use microwaves as power sources, the electron density in a conventional microwave plasma source is limited within the range in which the permittivity of the plasma is positive. To overcome this drawback, a negative refractive index phenomenon is applicable, in which the permittivity and permeability are both negative and microwaves can propagate even in a negative-permittivity space with high electron density. In this report, we demonstrate a promising scheme for the efficient generation of high-density plasma by propagating microwaves in a negative-permeability space, and show the experimental observation of the enhancement of plasma generation using the lower imaginary part of the permeability.

Study on the ion-beam etching process to remove the oxide layer in the cold-rolled steel production process

Cold-rolled steel (CRS) has been used worldwide in several industrial fields such as automobiles, electric/electronic appliances, etc. Recently, steel companies requested a higher performance coating layer, such as Zn-Mg or Al-Mg, due to its corrosion resistance. If a coating process is to be applied removal of the oxide layer from the CRS surface is necessary to improve adhesion, which is the main problem with using a coating. If the oxide layer is to be removed in a mass production process, the etching rate needs to be over 10 nm/sec (as a Si standard) because the production-line speed is 100–200 m/min. Therefore, our research developed a high-current, large-area ion-beam source to apply a high-rate etching process to the CRS before the coating process. To develop the high-rate etching source, we considered the high-density plasma generation, a high-current, large-area extraction system, and the lifetime of the ion source. The current density of the ion beam and the ion beam’s distribution over a wide range were measured by using a single-directional, electric-type Faraday cup. The high-rate ion-beam etching process depends on the ion beam’s current density and the distance from the target to the source (T.S.). We carried out a high-rate etching process of over 10 nm/sec at a T.S. distance of 300 mm.

A New High-Performance Ion Source Based on Magnetically Neutral Loop Discharge

We have developed a new high-performance ion source on the basis of the high-density plasma formation method known as magnetically neutral loop discharge (NLD). The ion source consists of three separate electromagnetic coils, an ion extraction electrode, and a quartz vessel plasma chamber with a one-turn RF antenna coil, which is the main component of conventional RF ion sources. The three electromagnetic coils are located around the periphery of the plasma chamber. The current in the middle coil flows opposite to the currents in the top and bottom coils. With this configuration, our source produces a high plasma density of 1011 cm-3, which is about ten times higher than that of a conventional source under a low gas pressure of 0.1 Pa. In addition, it is possible to control both the ring like plasma diameter and the high-density plasma generation position in the plasma chamber. As a result, we achieved a high ion current density of up to 1 mA/cm2 at 50 V of ion extraction voltage, which is almost five times higher than the conventional source. Furthermore, we also obtained a high ion current uniformity of ±5% over a 6-in.-diameter wafer using the source's plasma space controllability. A processing system that uses this ion source will contribute to faster processing, high-quality processing, and excellent-uniformity processing for ion beam etching, ion beam deposition, and ion beam sputter deposition. Many other applications are also expected.

Effective design of multiple hollow cathode electrode to enhance the density of rf capacitively coupled plasma

Multiple-hole electrode rf capacitively coupled plasma is experimentally studied to determine the optimum condition for high-density plasma discharge. The plasma density was measured at various pressures, hole diameters, rf currents, and gas species conditions. The bulk plasma intrusion in the hole and the ionization avalanche in the sheath region facilitated high-density plasma generation when the diameter of the hole is slightly wider than triple the sheath length. The analytic design of the efficient multihole electrode for high-density rf capacitively coupled plasma discharge will be discussed.

Influence of space debris impact on solar array under power generation

Recently solar array has become higher in potential and larger in capacitance. Therefore, possibility of collision between space debris and enlarged solar array has been pointed out. Many debris and dust impacts were confirmed on fuselage of the retrieved satellite Space Flyer Unit (SFU) and solar array paddle of satellite Eureca. If space debris collides with the solar array of an orbiting satellite, it may cause generation of high-density plasma by debris impact induced dielectric breakdown of satellite component and the phenomenon called sustained arc. By the short circuits on the solar array, current will not flow into a pay load of the satellite. And the worst event by this discharge is operational end of the satellite. However, any events of discharge phenomenon by debris impact cannot be yet confirmed. But we cannot ignore such possibility of discharge by debris impact. The purpose of this paper is to investigate discharge condition due to debris impact which yields us reduction of electric power of solar array, and to reduce influence of the impact on satellite missions. In this study, a solar array coupon was tested under hypervelocity impact in which a projectile was launched by a two-stage light gas gun installed in Kyushu Institute of Technology (KIT).

Honeycomblike large area LaB6 plasma source for Multi-Purpose Plasma facility

A Multi-Purpose Plasma (MP(2)) facility has been renovated from Hanbit mirror device [Kwon et al., Nucl. Fusion 43, 686 (2003)] by adopting the same philosophy of diversified plasma simulator (DiPS) [Chung et al., Contrib. Plasma Phys. 46, 354 (2006)] by installing two plasma sources: LaB(6) (dc) and helicon (rf) plasma sources; and making three distinct simulators: divertor plasma simulator, space propulsion simulator, and astrophysics simulator. During the first renovation stage, a honeycomblike large area LaB(6) (HLA-LaB(6)) cathode was developed for the divertor plasma simulator to improve the resistance against the thermal shock fragility for large and high density plasma generation. A HLA-LaB(6) cathode is composed of the one inner cathode with 4 in. diameter and the six outer cathodes with 2 in. diameter along with separate graphite heaters. The first plasma is generated with Ar gas and its properties are measured by the electric probes with various discharge currents and magnetic field configurations. Plasma density at the middle of central cell reaches up to 2.6 x 10(12) cm(-3), while the electron temperature remains around 3-3.5 eV at the low discharge current of less than 45 A, and the magnetic field intensity of 870 G. Unique features of electric property of heaters, plasma density profiles, is explained comparing with those of single LaB(6) cathode with 4 in. diameter in DiPS.

High density plasma generation by RF ohmic discharge in toroidal divertor simulator NAGDIS-T

A new toroidal divertor plasma simulator, NAGDIS-T (NAGoya DIvertor plasma Simulator with Toroidal magnetic configuration) has been constructed, in which the toroidal plasma is generated by RF Joule and/or DC discharge. In order to obtain high density deuterium plasmas relevant to divertor conditions in fusion devices, the optimum condition of RF ohmic discharge was investigated by varying gas pressure, driving frequency and RF transformer turn ratio. The experimental result was compared with the simple numerical modeling.

Preliminary study on sustained arc due to plasma excited by hypervelocity impact of space debris on the solar array coupon

Recently, solar array has become higher in potential and larger in capacitance. Therefore, possibility of collision between space debris and enlarged solar array has been pointed out. Many debris and dust impacts were confirmed on fuselage of the retrieved satellite space flyer unit (SFU) and solar array paddle of satellite Eureca. If space debris collides with the solar array of an orbiting satellite, it may cause generation of high-density plasma by debris impact-induced dielectric breakdown of satellite component and the phenomenon called discharge. This discharge short circuits the solar array and current will not flow into pay load of the satellite. And the very worst event by this discharge is the operational end of the satellite. However, any events of discharge phenomenon by debris impact cannot be yet confirmed. But we cannot ignore such possibility of discharge by debris impact. The purpose of the present paper is to investigate discharge condition due to debris impact which yields us reduction of electric power of solar array, and to reduce influence of the impact on satellite missions. In this study, a solar array coupon was tested under hypervelocity impact in which a projectile was launched by a two-stage light gas gun installed in Kyushu Institute of Technology (KIT). As a result, we verified discharge event in the hypervelocity impact ground test.

Numerical Analysis on Generation of High Density Plasmas in the Toroidal Device NAGDIS-T for SOL and Divertor Simulation Studies

Toroidal simulator for boundary plasma studies may have a substantial potential in plasma and impurity transport under an open magnetic field configuration and plasma-surface interactions under a grazing incident magnetic field line to the wall of the plasma-facing component in fusion devices. NAGDIS-T is the toroidal version in NAGDIS-series plasma simulator with RF Joule heating for toroidal plasma generation. A simple numerical analysis was employed to predict the plasma parameters in this new machine, considering the particle and energy balance equations. It was found that the gas pressure dependence of the plasma density is very similar to that obtained in the preliminary experiment with moderate RF power. The analysis predicts a plasma density exceeding 1019 m–3 by injecting the RF power of more than 10 kW which will be available soon. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Inductively coupled plasmas: Optimizing the inductive-coupling efficiency for large-area source design

An inductively coupled plasma (ICP) source enabling high-density plasma generation was developed for large area processing. Technological difficulties related to the scaling up of the coil antenna, dielectric vacuum window, and gas distribution have been addressed. The proposed solution consists in using a magnetic core to concentrate the magnetic field produced by the antenna. Both are placed within the plasma chamber, and the gas injection is done through the magnetic pole. A 75×72-cm2 plasma source has been designed based on this solution. First, the electrical operation and coil geometries were optimized. The results show that the use of a low excitation frequency (2MHz) increases the electrical efficiency of the magnetic core, enabling a higher plasma-density generation than at the classical radio frequency of 13.56MHz. The antenna configuration providing the better uniformity is composed of three loops connected in parallel. Some tuning inductances in series with each loop were added to balance the rf power, i.e., the plasma density over the reactor area. Deviation from plasma uniformities better than 12% over 60×60cm2 were achieved. Preliminary SiO2 etching experiments with CF4 gas show that the etching uniformity deviation reaches 7% over 60×60cm2 with etching rates larger than 150nm∕min. These results are very promising and open the way to the successful scale-up of ICP sources to large areas.

Generation of high-density plasma in the polar cap observed by the Akebono satellite

The polar cap ionosphere is known as a comparatively low-density (<10 3 cm −3 above 3000 km) plasma region and less active than the cusp or auroral region in terms of particle precipitation. Because of the low density, very limited information on the thermal plasma in the high-altitude polar cap is available in the literature. On very rare occasions, the Akebono satellite encounters regions of unusually high-density plasma above 4000 km altitude, in which both the electron temperature (<3000 K) and parallel ion drift velocity (<1 km s −1) are distinctively low. The ion drift meter observations on the DMSP satellite show that the plasma convection in the polar cap is predominantly directed from the dayside to nightside on such occasions, suggesting that anti-sunward convection is a necessary condition. The low electron temperature and ion velocity accompanied by the high plasma density may suggest that a small-amplitude ambipolar electric field is also another necessary condition for increasing the plasma density.