Ion Energy Analyzer Research Articles

Characterization of water propellant in an electron cyclotron resonance thruster

A coaxial electron cyclotron resonance thruster operating on water vapor propellant is investigated to determine the influence of molecular propellant chemistry on thruster performance. The performance is characterized at different mass flow rates (0.1–0.4 mg/s) and powers (20–200 W) using a thrust stand, ion energy analyzer, and spectrometer. Experimental data are compared to the results from a theoretical model that includes non-equilibrium chemical kinetics. The thruster is observed to transition from a state where power deposition favors propellant dissociation and ionization into a state where it favors electron heating and ion acceleration. The results suggest that the majority of plasma heating occurs in a core region that surrounds the thruster antenna and that propellant flow outside this region is not efficiently utilized for propulsion.

Investigation of an electrode-driven hydrogen plasma method for in situ cleaning of tin-based contamination

To prolong the service life of optics, the feasibility of in situ cleaning of the multilayer mirror (MLM) of tin and its oxidized contamination was investigated using hydrogen plasma at different power levels. Granular tin-based contamination consisting of micro- and macroparticles was deposited on silicon via physical vapor deposition (PVD). The electrode-driven hydrogen plasma at different power levels was systematically diagnosed using a Langmuir probe and a retarding field ion energy analyzer (RFEA). Moreover, the magnitude of the self-biasing voltage was measured at different power levels, and the peak ion energy was corrected for the difference between the RFEA measurements and the self-biasing voltage ( ). XPS analysis of O 1s and Sn 3d peaks demonstrated the chemical reduction process after 1 W cleaning. Analysis of surface and cross-section morphology revealed that holes emerged on the upper part of the macroparticles while its bottom remained smooth. Hills and folds appeared on the upper part of the microparticles, confirming the top-down cleaning mode with hydrogen plasma. This study provides an in situ electrode-driven hydrogen plasma etching process for tin-based contamination and will provide meaningful guidance for understanding the chemical mechanism of reduction and etching.

SiC plasma characterization produced by 3 ns pulse laser at 1010 W/cm2 intensity

A silicon carbide (SiC) plasma has been produced by a Q-switched laser at 1064 nm, 3 ns pulse and 1010 W/cm2 intensity, in high vacuum to investigate the fundamental mechanisms of laser-semiconductor interaction. Although the high hardness and chemical stability restrain the SiC micromachining, it is a valuable semiconductor for devices working under extreme conditions. The plasma has been characterized by using time-of-flight (TOF) measurements of ions detected by an ion collector ring (ICR) and an ion energy analyzer (IEA). Fast CCD camera, quadrupole mass spectroscopy (QMS) and surface profiler have been employed to provide deep insights into the laser-SiC interaction mechanisms. Ion kinetic energies, charge states, plasma expansion velocity, ablation yield per laser pulse, plasma temperature and density have been measured. Applications of the laser-generated plasma are presented and discussed.

Fullerene C20 carbon nucleation induced by IR ns pulsed laser-generated plasma

Intense laser pulses can be employed to generate plasma, carbon aggregates, and nanoparticles. The plasma produced by ns laser pulses impinging on carbon targets in a vacuum generates carbon vapors, atoms nucleation and growth of nano aggregates. Mass quadrupole spectrometry has permitted to analyze the mass of the carbon atoms and molecules produced in a vacuum by laser-generated plasma, discovering that the fullerene C20 and other small carbon aggregates have a high probability of being produced. In this paper, the conditions of C20 aggregate synthetization are presented, and their yield generation is approximately evaluated. It also calculated the process ablation yield, the maximum carbon energy acquired in the plasma, the plasma temperature and density, the adiabatic plasma expansion velocity, and the carbon ion charge state distributions. To this, measurements of time-of-flight (TOF) of ions have been performed using suitable ion collectors and ion energy analyzers.

In-situ non-destructive removal of tin particles by low-energy plasma for imitation of EUV optical mirrors self-cleaning

In this study, the feasibility was explored of realizing in-situ and non-destructive self-cleaning of the multilayers mirror (MLM) by utilizing hydrogen plasma at low input power (<10 W). The hydrogen plasma generated by the electrode at low power was comprehensively diagnosed using the Langmuir probe and the retarding field ion energy analyzer (RFEA). Meanwhile, the ion concentration ratios and atomic density in hydrogen plasma were calculated by constructing a zero-dimensional plasma chemical model. These experimental results show that the plasma distribution at 1 W is more uniform than that at 10 W, and the peak ion energy at 1 W is lower than 22 eV. Cleaning rates of 0.3–0.75 nm min−1 are achieved to remove discontinuous tin particles at different powers. According to the experiment and calculation results, the chemical etching of ions (breaking the Sn–Sn bond) occurred at 1 W. The etching yield is 0.23–0.87 Sn/ion for 10–40 eV. The analysis of surface morphology and cross-sectional morphology shows that the removal of tin particles is realized by top-down cleaning with hydrogen plasma at low power. This study is of great significance for understanding the detailed mechanism of MLM self-discharge cleaning tin pollutants at low power. It has made a comprehensive calculation and diagnosis of plasma parameters.

Measurements of ion fluxes in extreme ultraviolet-induced plasma of new EUV-beam-line 2 nanolithography research machine and their applications for optical component tests

In modern extreme ultraviolet (EUV) lithography machines, sensitive optical components, such as multilayer mirrors and photomasks, may be affected by plasma interactions. The new 13.5 nm EUV-beam-line 2, designed to provide accelerated tests for next generation lithography, is used to investigate EUV-induced plasma phenomena. First systematic measurements of ion fluxes produced in EUV-induced hydrogen plasma are reported, with operating conditions including 5 and 20 Pa gas pressure, 3 kHz EUV pulse repetition rate, and 4.2 W total EUV beam power produced in a 10–15 ns EUV pulse. Space- and time-resolved distributions of ion fluxes and ion energies were measured using a retarding-field ion energy analyzer mounted next to the EUV beam. Typical ion energies were in the range of 1–8 eV and typical ion fluxes were in the range of 2–8 × 1017 ions m−2 s−1. The obtained ion fluxes are applied in a photomask lifetime test to understand the material effects after an EUV exposure.

Charge state and Energy distribution of carbon ions and protons emitted from laser-produced graphite plasma

The energy and charge state distribution of atomic carbon ions, carbon cluster ions, and protons emitted during Q-switched Nd:YAG laser (1064 nm/6 ns) laser irradiation of high purity graphite target was investigated by employing a time of flight ion energy analyzer (TOF-IEA). Laser fluence on the target surface was varied from 2 to 26 J cm−2. At the lower fluence range (2–6 J cm−2), multiply charged low mass odd numbered cluster ions with n = 3, 5, 7 and charge state up to 5 + and carbon atomic ions up to the charge state of 3 + were detected. For the fluence greater than 6.4 J cm−2, carbon atomic ions up to a charge state of 6 + and protons were observed. The energy distribution of various carbon ions and protons was measured at the fluence of 5.1 and 25.5 J cm−2. At 5.1 J cm−2, the measured energy range for carbon cluster ions and carbon was 0.2–3.1 keV and 0.2–1.2 keV, respectively. At 25.5 J cm−2, the energy of carbon ions (q = 2–4) was in the range of 0.4–3.8 keV. Surprisingly, energetic protons with maximum energy of 1.5 keV and considerable intensity were detected at 25.5 J cm−2. The bi-component structure of ion energy distribution suggested a complex ion accelerating mechanism, which is discussed within the framework of the electrostatic model.

Influence of axial magnetic field on angular distribution of charge and energy of laser produced slow and fast tungsten ion groups

Here effect of magnetic field on the angular distribution of laser produced tungsten (W) ions is reported. Plasma plume was generated by irradiating surface of W target, placed inside a vacuum chamber under magnetic field of 0.23 T, by nanosecond pulsed laser beam. Angular distribution of W ion flux was measured with the help of an ion collector (IC) and explained under the framework of Anisimov model. Magnetic field clearly split the ion signals temporally into comparable fast and slow ion components and enhanced the intensity of fast ion group significantly. Enhancement of ion charge state with B was confirmed by Ion energy analyser (IEA). Theoretical fitting of bimodal ion signal suggested the existence of thermal and non-thermal component of nanosecond laser produced plasma. With magnetic field, a two fold increase in total charge of the fast ion component was observed. Magnetic field effect on ion energy was also investigated. The optical emission spectrum of W plasma was also recorded, and plasma parameters were measured in both the absence and presence of magnetic field. The rise of electron temperature and number density in presence of B confirmed the heating of W plasma by magnetic field.

Compact retarding potential analyzers enabled by glass-ceramic vat polymerization for CubeSat and laboratory plasma diagnostics

We report the design, fabrication, and characterization of novel, digitally manufactured, compact retarding potential analyzers (RPAs), i.e., multi-electrode instruments that can be used as in-orbit mass spectrometers and as on-ground/in-orbit ion energy analyzers. Unlike most RPAs reported in the literature, our devices enforce active aperture alignment across the grid stack, maximizing ion transmission. The RPA electrode housing (the most critical component of the RPA, as it precisely positions the electrodes to maximize grid stack transmission while avoiding space charge effects and providing electrical insulation) is additively manufactured in Vitrolite® (a printable glass-ceramic) via vat polymerization, resulting in non-porous, high-temperature compatible, and high-vacuum compatible hardware. Metrology of as-printed (green) Vitrolite Ⓡ parts shows an in-plane, per axis manufacturing accuracy of 60 µm (i.e., the in-plane length of the voxels) and an out-of-plane manufacturing accuracy of 100 µm (i.e., the height of the slices). Vitrolite Ⓡ 3D-printed objects annealed at 900 °C show a ~5 % shrinkage, a slightly larger maximum tensile stress, a similar Young’s modulus, and a larger compression yield stress compared to green samples. Also, the assembly misalignment between the grids and a 3D-printed housing annealed at 900 °C is a twofold larger compared to using a green housing. Annealing 3D-printed Vitrolite Ⓡ at temperatures above 900 °C causes significant distortion of the printed part due to material reflow, which is incompatible with a precision engineering application. Four different RPA designs were synthesized to probe the ionosphere (design with floating grid alignment at the aperture level) and laboratory plasmas (designs with floating grid aperture alignment at the cluster level). Simulations conducted in this study show that the RPA design that enforces floating grid aperture alignment at the aperture level attains the best performance, although RPA designs that implement floating grid aperture alignment at the cluster level are more resilient to grid misalignment. Experimental characterization of the RPAs using an ion source and a helicon plasma source is consistent with expected performance and the literature. Plasmas with a Debye length as small as 50 µm were successfully characterized using the reported sensors, matching the performance of state-of-the-art RPAs manufactured via semiconductor microfabrication. • Study reports the first plasma sensors enabled by glass-ceramic 3D printing. • Four sensor designs for probing ionospheric and laboratory plasmas were developed. • Sensors successfully characterized plasmas with a Debye length as small as 50 µm. • Device performance on par with that of state-of-the-art, Si microfabricated sensors.

Damage-free hydrogenation of graphene via ion energy control in plasma

We proposed appropriate plasma conditions for hydrogenation of graphene without structural defect formation using ion energy analysis. Graphene sheets were exposed to plasma having H3 + ions with energies of 3.45, 5.35, and 7.45 eV. Only the specimen treated by the plasma with the lowest energy was converted back to graphene by thermal annealing, and the others showed irreversible characteristics because of the vacancy defects generated by high-energy ions. Finally, we demonstrated the reversible characteristic in graphene field-effect transistor using the plasma with appropriate ion energy and Joule heating, indicating that damage induced by plasma was negligible.

Measurement of Ion Energy Distribution and Deposition of Ti Thin Films Using ABPPS Technology on Glass Substrate

Ion energy distributions (IEDs) play an important role in material processes and thin film deposition. We developed a newly designed multistep pulsed power supply (modulator) for the asymmetric bipolar pulsed power sputtering (ABPPS) technology and studied the effect of reverse bias voltage in improving the properties of thin films through Ti deposition. Using an ion energy analyzer, we confirmed IEDs and relative ion intensity under a reverse bias voltage of the modulator at the substrate position. A dense plasma was generated near the sputter target at reverse bias voltages above 300 V. Experiments were conducted by varying the bias voltage applied to the sputter target and the duty cycle of the modulator. Our results demonstrate that the in-house-built ABPPS system can be used to clean the sample surfaces without requiring additional energy sources or substrate bias and that thin films prepared using this system have a smoother surface than those prepared by conventional sputtering.

Aluminum ion plasma monitored by SiC detectors from low to high laser intensity and from ns up to fs pulse duration

Thick and thin films of Al targets were irradiated in vacuum with different IR lasers at intensities between 1010 W/cm 2 and 1019 W/cm2, with pulse duration ranging between 3 ns and 45 fs. The laser-generated plasma was monitored in forward and backward directions, from thin and thick targets, by using SiC detectors, ion collectors, ion energy analyzer, optical spectrometer, Thomson parabola spectrometer and X-ray streak camera. Ion emission shows a maximum ion acceleration proportional to the laser intensity, which reaches about 1 MeV per charge state at 1016 W/cm2. Using fs laser, Al ion acceleration occurs at energies up to about 26 MeV and protons are accelerated at energies up to about 2.0 MeV.In the used experimental conditions, the maximum ion acceleration can be controlled by the laser parameters, irradiation conditions, and target geometry, such as the pulse energy, the focal position and the target thickness. Although different lasers and irradiation conditions were employed, the produced ion charges per solid angle of detection remain comparable, as it will be discussed.

From Energetics to Intracluster Chemistry: Valence Photoionization of Trifluoromethylsulfur Pentafluoride (CF3SF5) by Double Velocity Map Imaging.

Trifluoromethylsulfur pentafluoride (CF3SF5) was valence threshold photoionized in a double imaging photoelectron photoion coincidence spectrometer using vacuum ultraviolet synchrotron radiation. In the 12.5-16.4 eV photon energy range, CF3+, SF5+, and SF3+ cations were observed in both room temperature (RT) and molecular beam (MB) experiments. Their fractional abundances exhibited differences beyond the sample temperature. Kinetic energy analysis of the fragment ions confirmed the difference in the dissociative photoionization mechanism. In the RT experiment, the CF3+ kinetic energies were extrapolated to a 11.84 ± 0.15 eV threshold, which was used in an ion cycle to determine the enthalpy of formation of CF3SF5 as ΔfH°298K(CF3SF5) = -1593 ± 16 kJ mol-1. We also updated the enthalpy of formation of the sulfur pentafluoride radical as ΔfH°298K(SF5) = -854 ± 7 kJ mol-1 and discuss the discrepancy between the CF3 ionization energy based on the Active Thermochemical Tables and the value anchored to the CF ionization energy. A computed reaction enthalpy network optimization resulted in ΔfH°298K(CF3SF5) = -1608 ± 20 kJ mol-1. Both values for ΔfH°298K(CF3SF5) agree with previous ab initio ones in contrast to the original, experimental determination. SF3+ is formed by F-transfer processes both in the RT and MB experiments. Although the same peaks were observed in both experiments, the lower SF3+ onset energy and the more slowly rising CF3+ kinetic energy release in the MB experiment revealed clustering and intracluster F-transfer reactions upon ionization. The monomer and dimer cation potential energy surfaces were explored to rationalize the observations. In the dimer cation, the observer CF3SF5 catalyzes fluorine transfer and promotes CF4 formation, which ultimately leads to the SF3+ fragment ion.

A Study on the Improvement of Etch Uniformity in an Ion Beam Etcher with a Magnetized Inductively Coupled Plasma Source

A magnetized inductively coupled plasma ion beam etcher (MICP-IBE) was designed by employing electromagnets around the etcher (IBE). A magnetic field can be set up such that the magnitude of the magnetic flux density on the screen grid increases or decreases with the radial distance from the screen grid center. Four different types of magnetic field conditions were considered. The plasma densities and electron temperatures were measured as functions of radial distance from the screen grid center under each condition. In addition, ion flux was measured with respect to radial distance from the substrate center using ion energy analyzer (IEA), after which the uniformity characteristics of the ion flux in the substrate were investigated. The dry etching characteristics of CoFeB, a typical alloy being used in the magnetic memory device, were investigated. The uniformity characteristics of the ion flux and the etch rate can be improved with the proper design of magnetic field conditions; however, the improvement was confirmed to be limited. In this respect, a new screen and acceleration grid were designed that have different grid hole densities with radial distance from the grid center (hereafter referred to as the proposed grid). Using the proposed grid, the ion flux and etch rate of CoFeB were measured with respect to radial distance from the substrate center, to see if the radial etch rate uniformity can be improved further. The CoFeB etch rate non-uniformity in the proposed grid (11.65%) was lower than that for the conventional grid (17.5%).

Simulation study on measurement characteristics of ion energy analyzer

The ion energy analyzer (IEA), also known as the retarding potential analyzer (RPA), is widely used as an important tool for measuring plasma energy in situ and is widely used in ionospheric detection satellites. The ion energy of the ionosphere is too low to be stabilized, thus the measurement characteristics of the IEA can’t be effectively studied through experiments. As there is no such problem in simulation, simulation has become a powerful tool for studying IEA. This paper analyzes the low-energy ion measurement characteristics of the IEA through the simulation software COMSOL, introduces the working principle of the IEA, and gives a comprehensive formula derivation for the ion measurement process. Based on simulation and analysis of three candidate design schemes, one of the schemes whose transmission curve is closest to the ideal step function is chosen. In theory, the measurement results of this scheme have the least error. The comprehensive error analysis results at various ion temperatures also show that the gap between the measurement results and the theoretical value of the scheme is narrow. The ion energy distribution can be measured more accurately. Finally, the effects of electric field distortion, plasma sheath, grid alignment and ion temperature are studied. According to these simulations, some experimental phenomena can be reasonably explained.

Thrust evaluation of compact ECR plasma source using 2-zone global model and plasma measurements

Plasma thrusters are required for deep space applications for reducing the fuel payload. This paper evaluates the capability of a compact ECR plasma source (CEPS) as a standalone plasma thruster in space. The unique magnetic field profile of CEPS’ ring magnets enables very efficient plasma production and electron heating within the CEPS plasma source section (ID ≈ 8.5 cm, length ≈ 11.6 cm) resulting in high plasma potentials. Experiments were undertaken with the CEPS attached coaxially to a larger expansion chamber (ID ≈ 48.2 cm, length ≈ 75 cm). Diagnostics included specially designed Langmuir probes (LP) and ion energy analyzers (IEA) that are capable of withstanding the harsh plasma conditions in front of and within the CEPS. LP measurements reveal high-density argon plasma (≈1012 cm−3), with high bulk electron temperatures (≈20 eV) and plasma potentials (≈100 V) at very modest microwave power (≈600 W) over a wide range of pressures (0.3–1 mTorr). An important observation is the fall of almost the full plasma potential inside the CEPS within a short distance close to its exit, giving rise to strong ambipolar electric fields suitable for accelerating ions. IEA measurements confirmed the presence of streaming ions with energies ≈87 eV at ≈2 cm in front of the CEPS. Estimates based on the IEA results yield thrust values ≈50 mN at ≈0.5 mTorr. A 2-zone, global model was developed to determine the steady state plasma parameters (including plasma flow velocity) in the geometry of the experimental system (without magnetic field). The model reproduced the key experimental plasma parameters and was extended to compute plasma thrust under actual space-like conditions. The computed thrust values for xenon are higher (≈80 mN) than that for argon (≈40–45 mN) at ≈600 W of microwave power.

Development and Evaluation of Ion Energy Analyzer for Energetic Ion Measurement in a Linear Plasma Device NUMBER

Development and Evaluation of Ion Energy Analyzer for Energetic Ion Measurement in a Linear Plasma Device NUMBER

Dry Etching Characteristics of 16-nm Amorphous Carbon Layer in a Dual-Frequency Plasma Etcher

The etching characteristics of a patterned amorphous carbon layer (ACL) in a magnetized inductively coupled plasma (MICP) etcher were investigated. The etch rate and etched profile dependences on the source power, the neutral gas pressure and the dual bias power ratio were investigated. We measured the ion energy distribution (IED), the ion flux, plasma density and electron temperature using an ion energy analyzer (IEA) and a dual Langmuir probe (DLP). The etching rate and the anisotropy of ACL relative to change in the dual bias power ratio of two bias power generators operating at frequencies of 2 and 13.56 MHz were observed. The bowed profile could be improved by appropriate adjustment of the dual bias power ratio.

TiO2 powder modified by plasma afterglow: A correlation between active species, microstructure, and optical properties

TiO2 powder was modified by the afterglow of plasma of pure N2 or H2, and mixed N2 + H2 gas. The ion species in plasma afterglow were measured by an ion-energy analyzer. It is found that the main ion is N2+ in N2 afterglow and the yield is changed to NH4+ with a six times higher concentration, when 10% H2 was input. The modified TiO2 shows significant differences of microstructure and optical properties depending on the plasma gas used. This work enables one to find a correlation between active species in the plasma afterglow and TiO2 microstructure/optical properties.

Characterization of low-pressure high-current cascaded arc plasma in large volumes

A comprehensive study of behavior and parameters of the low-pressure (1–20 mTorr) large-area plane–symmetric direct current arc discharge plasma in pure Ar and Ar-N2 mixtures was carried out. A low-pressure arc discharge was ignited in a large chamber between a planar vacuum arc cathode with magnetic steering of arc spots and a surrounding grounded primary anode while a long-length remote arc discharge was extended toward a remote linear anode parallel to the cathode plate. The arc column moved up and down along the cylindrical cathode target positioned perpendicular to the cathode-to-remote anode direction, following the motion of the cathodic arc spots. Current-voltage characteristics of the low-pressure direct current arc discharge, electron density, electron temperature, electron energy distribution function (EEDF), ion energy distribution function (IEDF) and dissociation of nitrogen molecules in the discharge were studied using electro-technical methods, electrostatic probes, a microwave resonant probe, an ion energy analyzer and optical emission spectroscopy (OES) methods. A number of OES methods were used to determine temperature and density of electrons in the discharge: the Te was measured using 1) the IArI,415/IArI,306 intensity ratio, 2) an intensity ratio of the (0–0) vibrational bands of 1st negative and 2nd positive systems of N2; the ne was obtained by 1) the IArII,487/IArI,451 intensity ratio and 2) ratio of N2(C3Πu,v = 1) and N2(C3Πu,v = 0) populations. In addition, the nitrogen dissociation degree was monitored using INI,868.03/IArI,852.14 and INI,862.92/IArI,852.14 intensity ratios. Spectral and probe measurements of Te and ne in the large-area arc discharge show reasonable agreement. The electron population analysis based on the second derivative of the Langmuir probe current-voltage characteristics allowed accurate measurements of electron population parameters in the discharge including EEDF, electron drift velocity along with plasma potential, electron density and energy. Modeling of the low-pressure large-volume arc discharge using the axially symmetric drift-diffusion approximation exhibited good qualitative and acceptable quantitative agreement between calculated plasma parameters and experimental data.