Radio Frequency Inductively Coupled Plasma Research Articles

Effect of coil and chamber structure on plasma radial uniformity in radio frequency inductively coupled plasma

Enhancing plasma uniformity can be achieved by modifying coil and chamber structures in radio frequency inductively coupled plasma (ICP) to meet the demand for large-area and uniformly distributed plasma in industrial manufacturing. This study utilized a two-dimensional self-consistent fluid model to investigate how different coil configurations and chamber aspect ratios affect the radial uniformity of plasma in radio frequency ICP. The findings indicate that optimizing the radial spacing of the coil enhances plasma uniformity but with a reduction in electron density. Furthermore, optimizing the coil within the ICP reactor, using the interior point method in the Interior Point Optimizer significantly enhances plasma uniformity, elevating it from 56% to 96% within the range of the model sizes. Additionally, when the chamber aspect ratio k changes from 2.8 to 4.7, the plasma distribution changes from a center-high to a saddle-shaped distribution. Moreover, the plasma uniformity becomes worse. Finally, adjusting process parameters, such as increasing source power and gas pressure, can enhance plasma uniformity. These findings contribute to optimizing the etching process by improving plasma radial uniformity.

CO2 Conversion Synergistically Driven by Radiofrequency Inductively-Coupled Plasma and Lead-Free Halide Perovskite Photocatalyst

The conversion and utilization of carbon dioxide (CO2) driven by plasma are promising approaches to achieve the mitigation of the greenhouse effect. In this paper, for the first time, the integration of radiofrequency inductively coupled plasma (RF-ICP) and lead-free halide perovskite photocatalysts was investigated to facilitate the CO2 conversion. The photocatalyst could be modified by the plasma to improve the catalytic activity of the surface, while the photons and vibrationally excited molecules also promote the CO2 conversion in plasma. Compared with the presence of Cu, SiO2, and Cs2TeCl6@SiO2, the radiofrequency plasma filled with Cs2TeCl6@Cu exhibited the best CO2 conversion ratio of 86.5% at a specific energy of 30 eV/molecule, which is much higher than the work reported previously. This work demonstrates that the synergistic effect between RF-ICP and the photocatalyst could effectively improve the reaction efficiency, providing a new opportunity for efficient CO2 conversion in future large-scale practical application.

Thick functionally-graded W-316L composite coatings for nuclear fusion applications

Nuclear fusion is a potential pathway to finding a sustainable, carbon-free energy source. Some critical components of the fusion reactors are planned to be coated by tungsten. For the task, thermal spraying in vacuum or protective atmosphere can be employed, offering several advantages such as easy preparation of advanced feedstock for deposition of functionally graded composites. Such coatings could be a viable approach to avoid the thermal expansion coefficient mismatch between the W coating and the steel components. In this study, radio-frequency inductively-coupled plasma spray method was used to deposit W-steel composite coatings of three different W ratios, as well as a functionally graded coating consisting of the three composites and a pure W top coat. The coatings exhibited a high-quality microstructure, without intermetallic or oxide phases formation. Thermal diffusivity and conductivity of the coatings was measured at 100 °C and 600 °C, with the values falling into range between the bulk steel and plasma sprayed W. In conclusion, we have shown that the RF-ICP technology is suitable for preparation of tungsten-steel graded deposits and the outputs are now prepared for other testing and a following upscaling to the industry-relevant size.

Magnetron deposition of copper oxide coatings in a metallic mode enhanced by RF-ICP source: A role of substrate biasing

The article describes deposition of copper oxide coatings using magnetron sputtering in a metallic mode enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source. The role of substrate biasing (floating potential, −70 and −140 V) on structural properties and elemental composition of copper oxide coatings is determined using SEM with EDS, XRD and TEM. This study shows the change of coating microstructure from columnar to dense/compact and the increase in crystallinity degree of coatings, when the substrate is biased. EDS analysis reveals the presence of Ar and the increase in O content in the coating due to intensive ion bombardment. Deposition conditions are changed using substrate biasing, which suggests the contribution of ion bombardment to the coating deposition in the case of magnetron sputtering of copper oxide in the metallic mode.

The effect of gas composition on the properties of silicon oxynitride thin film prepared by low-pressure inductively coupled Ar/N2 plasma

Silicon nitride (Si3N4) has been widely used in semiconductor devices and applications, including the passivation layer in organic light-emitting diode (OLED). However, it becomes more important to adjust the refractive index value of silicon nitride layers. For example, the refractive index difference between the passivation layer and emission layer is one of the problems degrading OLED performance. Recently, silicon oxynitride (SiOxNy) thin films possessing different refractive indexes have been fabricated by varying their nitrogen and oxygen content. In this work, we control the refractive index of SiOxNy thin film by changing the N2 and Ar flow ratio in 13.56 MHz radio-frequency inductively coupled plasma (RF-ICP). To study the effects of gas composition in the plasma on the properties of thin films, nitrogen atom (N) and nitrogen molecular ion (N2+) density are investigated using actinometry and simulation via the synthetic spectrum method, respectively. We observed that when the gas ratio defined as [N2/(N2+Ar)] increases from 0.1 to 0.9, the density of N2+ increases from 4.76×1015m − 3 to 1.71×1016m − 3 and the refractive index of the thin film increases from 1.54 to 1.57. The results indicate that N2+ plays the important role in changing the properties of thin film during the plasma process.

Duplex Treatment of AISI 420 Steel by RF-ICP Nitriding and CrAlN Coating Deposition: The Role of Nitriding Duration

The duplex treatment of AISI 420 steel samples by nitriding in a radiofrequency inductively coupled plasma (RF-ICP) discharge of Ar + N2 + H2 atmosphere followed by CrAlN coating deposition was performed in this study. The influence of plasma nitriding (PN) duration (10, 20, 40, and 60 min) on the structural and functional properties of the duplex-treated samples was determined. A non-linear dependence of AISI 420 steel nitriding kinetics was found on the square root of the PN duration. The thicknesses of the compound layer (CL) and nitrogen diffusion zone (DZ) in the samples and their phase composition resulted in different critical loads of coating failures under adhesion tests. Increasing the load-bearing capacity by the PN caused coating hardening in duplex-treated samples. The role of the PN duration on the wear characteristics of the AISI 420 steel samples after the duplex treatment has been discussed. Corrosion tests of AISI 420 steel demonstrated the significant enhancement (5–67 times) of its corrosion resistance in a 3.5 wt.% NaCl solution after duplex treatment.

Magnetron Deposition of Cr Coatings with RF-ICP Assistance

The article describes a comparative analysis of chromium coatings deposited by magnetron sputtering with and without ion assistance induced by a radiofrequency inductively coupled plasma (RF-ICP) source. Four series of 2 µm-thick Cr coatings were prepared, and then their cross-sectional microstructure, crystal structure and corrosion resistance were investigated by scanning and transmission electron microscopy, X-ray diffraction and a potentiodynamic polarization method. RF-ICP assistance led to significant enhancement (almost twofold) of ion current density in a substrate. The role of RF-ICP assistance in coating properties for planetary-rotated substrates was defined in terms of ion-to-atom ratio in particle flux entering a substrate. Calculations of particle and ion flux densities revealed an increase in ion-to-atom ratio from 0.18 to 1.43 and 0.11 to 0.84 in substrate positions distant from the magnetron sputtering systems depending on their design. RF-ICP assistance is beneficial for depositing dense Cr coatings with increased corrosion resistance in a 3.5 wt.% NaCl solution. The corrosion rate of AISI 321 steel can be decreased from 6.2 × 10−6 to 4.0 × 10−8 mm/year by deposition of the dense Cr coating.

High-rate magnetron deposition of CuOx films in the metallic mode enhanced by radiofrequency inductively coupled plasma source

The article describes the high-rate deposition of CuOx films by magnetron sputtering system operated in the metallic mode and enhanced by radiofrequency inductively coupled plasma (RF-ICP) source. The role of the RF-ICP assistance on modes of Cu target sputtering in Ar + O2 atmosphere was investigated by determination of hysteresis loops and using optical emission spectroscopy. Then, the CuOx films were deposited on the unmoved substrates depending on their position in the vacuum chamber. The deposition conditions to obtain the CuOx films with some phase and elemental composition were determined. The comparison of the deposition rates of the CuO films is done for the deposition by magnetron sputtering in the metallic mode and using conventional reactive sputtering.

Hot target magnetron sputtering enhanced by RF-ICP source: Microstructure and functional properties of CrNx coatings

CrNx coatings were deposited at high rates (100–130 nm/min) using hot Cr target magnetron sputtering enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source in an Ar + N2 atmosphere. Besides separation of inert and reactive atmosphere, the RF-ICP source can be an effective tool for ion assistance in case of coating growth and to tailor film parameters. The effects of nitrogen flow rate and substrate bias potential on microstructure and functional properties of the CrNx coatings were investigated. An increase in nitrogen flow rate favored the formation of a looser microstructure of the coatings, while substrate biasing had the opposite effect. The functional properties were strongly dependent on the phase composition of the CrNx coatings. The change in coating microstructure significantly affected hardness, elastic modulus, adhesion, friction coefficients and corrosion resistance. The results indicated that ion assistance can be a key feature for regulating functional properties in the considered type of coating deposition. Cr2N and CrN compound coatings with high hardness (∼20 GPa) and low corrosion current density (icorr ∼ 3–5·10−9 A/cm2) in a 3.5 wt% NaCl solution were obtained by high-rate deposition.

Synthesis of Multiscale Ultrafine Copper Powder via Radio Frequency Induction Coupled Plasma Treatment

Nano-sized spherical copper powder has important applications in the fields of microelectronic devices, highly efficient catalysts and lubricant additives. In this study, nano-sized and micron-sized spherical copper powders were simultaneously prepared by radio frequency (RF) induction coupled plasma technology. The effects of processing parameters on the powder properties were studied. The results show that by inputting copper powder with D50 = 34.6 μm, nano-sized spherical powder with a particle size of 10–220 nm and micron-sized spherical powder with a particle size of 4.0–144.0 μm were obtained. The ratio of the nano-sized powder reached 86.4 wt.%. The optimal processing parameters are as follows: powder feed rate is 5.5 g/min, carrier gas flow rate is 5–6 L/min and reaction chamber pressure is 15 Psia. When the carrier gas flow rate is 6 L/min, in the plasma zone (>10,000 K), the powder with particle size <42.0 μm is completely vaporized, which forms nano-sized powder during cooling, while the powder with particle size >42.0 μm is melted and partially vaporized, forming a micron-sized powder. The research results provide a new way for engineering the production of copper nano-powder and some other nano-powders with low melting points, such as silver powder, tin powder and so on.

Spheroidization of lithium niobate powder by radio-frequency inductively coupled plasma

To solve the problem that lithium niobate is difficult to process into microspheres, a method of spheroidizing lithium niobate powder twice by radio-frequency inductively coupled plasma (RF-ICP) was proposed. The morphology, phase composition and particle size of primary and secondary spheroidized lithium niobate powders were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and laser particle size analysis, respectively. The results show that the powder with a larger particle size is difficult to spheroidize and easily cracks, while the powder with a smaller particle size is elliptical without cracks after primary spheroidization. Nearly all spherical lithium niobate powder can be obtained after secondary spheroidization. In addition, the crystal steps grow during the solidification of the powder. The smaller the curvature of the powder surface, the more obvious the crystal growth. Lithium niobate loses part of lithium after spheroidization, and the loss of lithium increases with the decrease of particle size.

Stripping of carbon coatings in radio-frequency inductively coupled plasma of H2/Ar

This article describes the stripping of amorphous carbon (a-C) coatings in an H 2 /Ar atmosphere using a radio-frequency inductively coupled plasma (RF-ICP) source. The power of the RF-ICP source, atmosphere composition (H 2 /Ar) and bias potential strongly affect the stripping rate (0.7–9.3 μm/h), while the operating pressure has less influence (2.7–3.2 μm/h). The selectivity of stripping of a-C and titanium coatings can be varied from 1 up to ~90 by changing the atmosphere composition. Chemical sputtering plays a key role in the productivity and selectivity of carbon stripping, it should have a higher rate compared to physical sputtering to enable high selectivity of coating stripping. Raman spectroscopy reveals the increase in graphitization degree and decreasing less ordered carbon of a-C coatings under stripping in H 2 /Ar plasma. Phase transformations of sublayer or substrate materials could occur under coating stripping in a reactive atmosphere in the example of hydride formation (TiH 2-x ) in a Ti sublayer. • Stripping of carbon coatings in RF-ICP plasma of H 2 /Ar. • Stripping selectivity of carbon coatings is regulated by H 2 /Ar flow rates. • Graphitization of a-C coatings under stripping in H 2 /Ar plasma.

Hot target magnetron sputtering enhanced by RF-ICP source for CrNx coatings deposition

This article describes hot Cr target magnetron sputtering enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source in an Ar + N2 atmosphere. Optical emission spectroscopy revealed an opportunity to perform magnetron sputtering in an inert (Ar) atmosphere, while the CrNx coating can be deposited on a substrate in a chemically reactive atmosphere formed by the RF-ICP source. High stability and repeatability of deposition process were observed, and the deposition rate of the CrNx coatings increased from 106 to 127 nm/min as N2 flow rate rose. The power of the RF-ICP source and the N2 flow rate can be used to tailor and control deposition conditions. The XRD and WDS measurements showed the effect of deposition conditions on the crystal structure and elemental composition of CrNx coatings. It was found that the change of substrate bias, RF-ICP source power and N2 flow rate result in variation of coating stoichiometry from pure Cr to CrN.

Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for the characterization of functional shape memory properties of the thick coatings was developed. The coatings exhibited cubic to monoclinic martensitic transformation and shape memory effect. The presented results prove that NiTi coatings with functional thermomechanical properties can be easily produced on structural materials by RF-ICP. Further optimization will be needed to prepare NiTi coatings with better microstructural and chemical homogeneity.

Mechanical properties and fatigue crack growth in tungsten deposited by RF-plasma

Fracture toughness and fatigue crack growth rates of free-standing thick W deposits produced in a protective atmosphere using radio frequency inductively-coupled plasma process were investigated. Stress-strain behavior of the deposits was studied using four-point bending and their fracture toughness was estimated from three-point bending following the ASTM E1820 standard. The fatigue crack growth rates were measured in symmetrical bending using a resonance approach. The results were compared with commercially available bulk tungsten prepared by powder metallurgy that served as a reference. The results showed that the deposits had significantly lower stress-strain properties: the elastic modulus and tensile strength ranged from 30% to 50% of the reference bulk values. The crack growth rate tests together with fractographic analysis suggested that a static failure by inter-granular decohesion predetermines the fatigue properties of the deposits and causes high slopes of the corresponding fatigue crack growth rate curves. Contrary to this, the reference sheet failed trans-granularly. The inter-granular failure mode of the deposits was caused by grain boundary embrittlement, a phenomenon probably related to oxides. The lowest obtained oxygen concentration in deposit was nearly by two orders of magnitude higher, than in reference sheet. The distribution of oxygen was studied by TEM and the amorphous and crystalline oxide phases were identified at splat interfaces. The presence of oxygen in the deposits produced by the inherently non-oxidizing RF technology calls for control of oxygen content in the feedstock powder. The performed characterization provided baseline data of mechanical and fatigue properties of RF plasma sprayed tungsten.

Bayesian framework for THz-TDS plasma diagnostics.

Terahertz time-domain spectroscopy (THz-TDS) is an optical diagnostic used to noninvasively measure plasma electron density and collision frequency. Conventional methods for analyzing THz-TDS plasma diagnostic data often do not account for measurement artifacts and do not quantify parameter uncertainties. We introduce a novel Bayesian framework that overcomes these deficiencies. The framework enables computation of both the density and collision frequency, compensates for artifacts produced by refraction and delay line errors, and quantifies parameter uncertainties caused by noise and imprecise knowledge of unmeasured plasma properties. We demonstrate the framework with sample measurements of a radio frequency inductively-coupled plasma discharge.

Tailoring the structure of RF-ICP tungsten coatings

Nuclear fusion is considered to be one of the future sources of sustainable energy. Prior to its widespread application, several critical issues need to be solved though. One of them is the choice of materials for the fusion reactors, in particular for plasma facing components (PFCs).At the moment, one group of candidate materials for this task are tungsten-based materials. Despite having many advantages (such as the highest melting point of all metals, high density), tungsten also possesses several drawbacks (e.g., poor machinability and weldability), making production of large-scale components particularly difficult.One of the considered production routes that could potentially overcome these problems is plasma spraying. Unfortunately, the conventional atmospheric plasma torches have critical limitations toward this task, resulting from the susceptibility of tungsten to oxidation at elevated temperatures.In this study, a radio-frequency inductively-coupled plasma (RF-ICP) torch was used. This technology enables spraying under controlled atmosphere, which helps to prevent detrimental oxidation of the metal. To examine the process window of tungsten spraying, twelve coatings were deposited on graphite substrates under two torch powers of 12 kW and 15 kW and using two feedrates. Furthermore, three different gases were used for feeding of the W powder: pure argon, a mixture of Ar/7.5%H2, and pure helium.All combinations led to production of thick coatings. It was shown that spraying using pure argon carrier gas was sensitive to the used power and feedrate, resulting in dense coatings only for a combination of the higher power and the lower feedrate. Using the Ar/H2 mixture led to an improved melting of the individual W particles where the densest microstructures were obtained for the higher torch power level only. Helium carrier gas resulted in the best coating quality, where the powder particles were properly melted in all power/feedrate combinations.

In situ XPS analysis of the electronic structure of silicon and titanium thin films exposed to low-pressure inductively-coupled RF plasma

Carbon contamination of synchrotron and free-electron lasers beamline optics continues to be a major nuisance due to the interaction of the intense photon beams with the surfaces of the optical elements in the presence of residual gases even in ultrahigh vacuum (UHV) conditions. Among the available in situ cleaning strategies, low-pressure radio frequency (RF) plasma treatment has emerged as a useful and relatively simple approach to remove such carbon contamination. However, the irreversible damage that the plasma may induce in such critical surfaces has to be carefully characterized before its general application. In this study, we focus on reducing the amount of carbon from UHV chamber inside surfaces via silicon and titanium coatings using a low-pressure inductively-coupled downstream plasma source and we characterize the surface alterations by in situ X-ray photoemission spectroscopy (XPS). The in situ mirror cleaning is simulated by means of silicon wafers. We observe upward band bending, which translates into lower binding energies of the photoemission lines, that we attribute to the generation of vacancies and trapped charges in the oxide layers.

Fast and High‐Throughput Synthesis of Medium‐ and High‐Entropy Alloys Using Radio Frequency Inductively Coupled Plasma

Multiprincipal element alloys, or medium‐ and high‐entropy alloys (MEAs and HEAs), hold great potential for numerous structural and functional applications, yet the synthesis of such alloys out of a vast composition space is a daunting task. Herein, a radio frequency inductively coupled plasma (RF‐ICP) method for preparing bulk MEAs and HEAs in a rapid and high‐throughput fashion is reported. Typical MEAs and HEAs are successfully synthesized within 40 s per alloy, thereby greatly improving the fabrication efficiency and throughput. This method provides a new opportunity to accelerate the discovery of new complex alloys for a broad range of applications.

Dynamic heating and thermal destruction conditions of quartz particles in polydisperse plasma flow of RF-ICP torch system

Numerical simulation of turbulent mixing process of polydisperse quartz particle (particle size distribution in the range of 0.1–0.4 mm) flow with Ar and Ar-H2 plasma generated by radio frequency inductively coupled plasma (RF-ICP) torch has been made. An approximate two-stage approach has been proposed to calculate the spatial–temporal distributions of temperature and resulting thermal stress in quartz particles during dynamic heating in polydisperse plasma flow. The influence of working gas compositions, particle size distributions, injection angle and flow rate of carrier gas on the thermal destruction conditions of quartz particles has been determined under different particle feed rates. It is found that all the solid quartz particles (0.1–0.4 mm) could be thermal destructed without overheating in RF-ICP torch system, when the hydrogen volume fraction in working gases is more than 1.5%–2% and particle feed rate is in a certain range. The values of the maximum and minimum feed rates have been determined under different hydrogen volume fractions. An optimal particle injection angle and flow rate of carrier gas is found around 50°–60° and 160–220 slpm, under which the value of maximum equivalent thermal stress in quartz particles is highest.