Electron Cyclotron Resonance Plasma Research Articles

A novel state-resolved actinometry method to determine the nitrogen atom number density in the ground state and intra-shell excited states in low-pressure electron cyclotron resonance plasmas

The active-particle number density is a key parameter for plasma material processing, space propulsion, and plasma-assisted combustion. The traditional actinometry method focuses on measuring the density of the atoms in the ground state, but there is a lack of an effective optical emission spectroscopy method to measure intra-shell excited-state densities. The latter atoms have chemical selectivity and higher energy, and they can easily change the material morphology as well as the ionization and combustion paths. In this work, we present a novel state-resolved actinometry (SRA) method, supported by a krypton line-ratio method for the electron temperature and density, to measure the number densities of nitrogen atoms in the ground and intra-shell excited states. The SRA method is based on a collisional-radiative model, considering the kinetics of atomic nitrogen and krypton including their excited states. The densities measured by our method are compared with those obtained from a dissociative model in a miniature electron cyclotron resonance (ECR) plasma source. Furthermore, the saturation effect, in which the electron density remains constant due to the microwave propagation in an ECR plasma once the power reaches a certain value, is used to verify the electron density measured by the line-ratio method. An ionization balance model is also presented to examine the measured electron temperature. All the values obtained with the different methods are in good agreement with each other, and hence a set of verified rate coefficient data used in our method can be provided. A novel concept, the ‘excited-state system’, is presented to quickly build an optical diagnostic method based on the analysis of quantum number propensity and selection rules.

Low temperature (210 °C) fabrication of Ge MOS capacitor and controllability of its flatband voltage

Germanium (Ge) and germanium tin (GeSn) are strong candidate materials for novel electronic device such as spin MOS field-effect transistor (FET) or flexible devices. A high-quality insulating layer on Ge(Sn) should be formed at low temperatures to realize these applications. In this study, we fabricated a Ge MOS capacitor (CAP) and n-MOSFET with a SiO2/GeO2 gate dielectric using an electron cyclotron resonance plasma process and subsequent post-deposition annealing at a low temperature of 210 °C. The MOSCAPs show the typical electrical characteristics without significant degradation compared with the samples fabricated at a higher temperature of 450 °C. The n-MOSFET shows distinct output characteristics with clear saturation behavior and high current drivability. From the flatband voltage comparison among different annealing temperatures, high-temperature annealing induces the interface dipole formation in the gate insulator, significantly shifting flatband voltage to a negative direction. X-ray photoelectron spectroscopy analysis suggests that the origin of the interface dipole is oxygen atom movement at a SiO2/GeO2 interface. This information will be an important guideline for fabricating a high-quality insulator on Ge(Sn) at low temperatures.

Metal evaporation dynamics in electron cyclotron resonance ion sources: plasma role in the atom diffusion, ionisation, and transport

We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The 134Cs, 176Lu, and 48Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the γ activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall γ-detection system’s efficiency using GEANT4, including the poisoning γ-signal from the walls of the trap, relevant for the γ-tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.

Metallic Neutral Vapours Diffusion in Electron Cyclotron Resonance Ion Sources: Fluid Dynamics and Particle Tracing Simulations

Resistive oven technique is used to inject vapours of metallic species in electron cyclotron resonance (ECR) plasma traps, where plasma provides step-wise ionization of neutral metals, producing charged ion beams for accelerators. We present a numerical survey of metallic species suitable for oven injection in ECR ion sources, studying neutrals diffusion and deposition under molecular flow regime. These aspects depend on geometry of the evaporation inlet, thermodynamics, and plasma parameters, which strongly impact on ionization and charge-exchange rate, thus on the fraction of reacting neutrals. We considered diffusion of metals with and without plasma. The plasma and its parameters have been modelled considering an established self-consistent particle-in-cell model. Numerical predictions might be relevant to reduce the metal consumption, to increase the overall efficiency, and to improve the plasma ion source performances. As test case, we studied the 134Cs isotope, as one of the alkali metals of interest for the modern nuclear physics.

Optical and Mechanical Properties of Si-Based Thin Films for Photonic Applications

In this talk, we will review recent advances in the fabrication and characterization of silicon-based thin film structures for photonic applications, including rare earth doped silicon oxynitrides and luminescent silicon carbonitrides.For Si-based materials to be used in solid-state lighting (SSL) and silicon photonics schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished using rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. After a brief review of the latest developments in the field, this talk will focus on Eu-doped films, which are attractive for silicon photonic applications due to their intense emission in the visible spectral region [1]. The films are fabricated by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) and doping is accomplished using a novel hybrid radio frequency (RF) magnetron sputtering source in the ECR-PECVD reactor chamber [2]. This approach contrasts with traditional doping methods which use metal-organic precursors to introduce rare-earth dopant species into the host matrix. We will discuss the relationship between the photoluminescence, elasticity, and hardness of Eu doped silicon oxynitride (SiON) thin films.As the efficiency of photonic devices can be influenced by the mechanical properties of the deposited films, a good understanding of their mechanical properties is required for the integration of these films in photonic devices. SiNx thin films, for example, play an important role in strain engineering of active photonic devices, such as diode lasers fabricated on GaAs or InP substrates. We will discuss results of a collaboration between McMaster and the Université de Rennes in France, aimed at quantifying the effects of structured dielectric thin films on the generation of a mechanical strain field in the semiconductor through tuning the amount of mechanical stress present in the dielectric thin film, as a function of the details of the deposition process [3].[1] Fahmida Azmi et al., “Tunable Emission from Eu:SiOxNy Thin Films Prepared by Integrated Magnetron Sputtering and Plasma Enhanced Chemical Vapor Deposition”, J. Vac. Sci. Technol. A 40, 043402 (2022); https://doi.org/10.1116/6.0001761[2] J.W. Miller et al., “Integrated ECR-PECVD and Magnetron Sputtering System for Rare-Earth-Doped Si-Based Materials”, Surface and Coatings Technology 336, 99 (2018); doi: 10.1016/j.surfcoat.2017.08.051[3] Brahim Ahammou et al., “Strain engineering in III-V photonic components through structuration of SiNx films”, J. Vac. Sci. Technol. B 40, 012202 (2022); doi: 10.1116/6.0001352

Enhancing tribological performance of graphene sheet-embedded carbon films on steel substrates via texture engineering and chromium doping

Amorphous carbon (a-C) film is a promising solid lubricant coating due to its unique structure and excellent properties. However, its poor adhesion and long running-in period hinder the application in metal components. Graphene sheet-embedded carbon (GSEC) film has a significantly shorter running-in period but suffers from inferior tribological properties due to its rough surface and weak mechanical characteristics. In this study, we utilized an electron cyclotron resonance (ECR) plasma nano-surface manufacturing device to deposit GSEC films onto steel substrate surfaces. By manipulating the surface/interface texture and incorporating chromium (Cr) doping, the tribological properties of the GSEC films were improved both chemically and physically. The results demonstrated that the textured carbon film exhibited superior adhesion to the steel substrate and a wear life that was three orders of magnitude longer than the untextured GSEC film, under low normal load conditions while sliding against the GCr15-bearing steel ball. After doping the Cr into textured carbon films, there was a significant reduction in the friction coefficients, and the wear type of carbon film transformed from adhesive wear to abrasive wear. Moreover, the doped carbon films demonstrated prolonged wear lives under high normal loads. This improvement can be attributed to the formation of hard CrC nanocrystalline, which effectively reduced surface roughness and enhanced the mechanical properties of the carbon films. Notably, even under a contact pressure of 0.83 GPa, the doped carbon film maintained favorable tribological performances. These findings have extended the potential applications of carbon films on metal substrates.

Ion concentration ratio measurements of ion beams generated by a commercial microwave electron cyclotron resonance plasma source.

A commercially available electron cyclotron resonance (ECR) plasma source (GenII Plasma Source, tectra GmbH) is widely used for surface processing. This plasma source is compatible with ultrahigh vacuum systems, and its working pressure is relatively low, around 10-6-10-4 Torr even without differential pumping. Here, we report ion flux concentration ratios for each ion species in an ion beam from this source, as measured by a mass/energy analyzer that is a combination of a quadrupole mass spectrometer, an electrostatic energy analyzer, and focusing ion optics. The examined beams were those arising from plasmas produced from feed gases of H2, D2, N2, O2, Ar, and dry air over a range of input power and working pressures. H2(D2) plasmas are widely used for nuclear fusion applications and, hence, the ion concentration ratios of H+, H2+, and H3+ reported here will be useful information for research that applies this plasma source to well-controlled plasma-material interaction studies. Ion energy distributions, stability of operation, and impurity concentrations were also assessed for each of the plasma species investigated.

Dual low pressure plasma process for SiCN:H thin films deposition: A comparative study

SiCN:H thin films have large possibilities of applications due to their versatile chemical and physical properties. Plasma Assisted Chemical Vapor Deposition (PACVD) process is widely used for SiCN:H deposition. Here we discuss on the potentialities of dual Electron Cyclotron Resonance (ECR) and Radio Frequency Magnetron Sputtering (rf MS) plasmas coupling for SiCN:H deposition in Ar/N2/Si(CH3)4 gas mixture. The study is carried out by varying the autopolarisation voltage Vbias of the silicon target. ECR plasma gives low deposition growth rate about 50 nm/h. The films are transparent. SiCN nanopillars with high aspect ratio are obtained. Rf MS plasma gives high deposition growth rate up to 2200 nm/h. The films are opaque in the near UV and transparent in the visible depending on their thickness. The optical index at 630 nm is 1.95, the Tauc's band gap is 3.0 eV and do not change with Vbias. Dual ECR/rf MS plasma gives high deposition growth rate up to 2300 nm/h. The films are transparent. The optical index varies between 1.7 and 2.05 at 630 nm and the Tauc's band gap decreases linearly between 4.75 and 3.4 eV with Vbias. Dual ECR/rf MS plasma coupling is a very promising PACVD process for thin films deposition.

Laser Thomson scattering system for anisotropic electron temperature measurement in NUMBER

A laser Thomson scattering system is developed to obtain anisotropic electron temperature in a pulse operated electron cyclotron resonance plasma device. Injecting a laser with an oblique angle to the external magnetic field and detecting scattering photon from a line of sight along another oblique angle enable us to obtain parallel and perpendicular components of electron temperature. Backward (165°) scattering spectrum corresponds to quasi perpendicular velocity distribution, while that for forward (15°) scattering; quasi parallel. Collecting lenses are set in vacuum to maximize solid angle in a limited space of port, where the laser path and collecting optics share an ICF152 flange. Rayleigh scattering intensity is measured as a function of argon gas pressure. An initial result on residual stray light intensity is equivalent to the argon Rayleigh scattering intensity under ≤ 1 kPa of filled pressure. In order to obtain Thomson scattering spectra, a notch filter type stray light rejection optics, which utilize a reflective type volume holographic grating, is evaluated. Notch width (0.2 nm) and flat transmittance (≥ 90%) outside the notch measured for a prototype show that it is an effective optics.

Optical and Structural Properties of Europium-Doped Silicon Oxide Fabricated Using Integrated Sputtering and Chemical Vapour Deposition

Europium (Eu) doped silicon oxide (SiOx) thin films containing Eu concentrations of 0.2 to 6.4 at% were fabricated using a hybrid deposition system combining a magnetron sputtering gun serving as the doping source with electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). The influence of annealing conditions on the structural and luminescence properties was thoroughly studied. The optical properties of the films were investigated by performing variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) measurements. The Eu-related emission was found to be highly dependent on the deposition parameters and annealing conditions. Eu2+ and Eu3+ emissions, which are attributed to blue and red light emissions, respectively, were observed. The structural properties were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, and the formation of nanoclusters was confirmed. At annealing temperatures of 900 °C and beyond, EuxSiyOz crystals were formed, and Eu ions were optically activated. As the light emissions of these thin films are in the blue and red wavelength range, they are promising candidates to be used as greenhouse covers and transparent solar cells.

Structural and tribological behaviours of silicon doped amorphous carbon films

We report on the structural evolution and low-friction behaviour of silicon (Si) doped amorphous carbon (a-C) films. Si-doped a-C films were fabricated by controlling the magnetron Si target currents under an electron cyclotron resonance (ECR) plasma system. Structural analysis indicated that Si atoms doped into the a-C lattice preferentially replaced certain sp3 C atoms, and subsequently formed bonds with other sp3 C atoms. Nanoindentation and nanoscratch tests showed that the Si-doped a-C films had hard surfaces with a hardness of approximately 24 GPa and a scratch depth of 40–60 nm. Ball-on-disk tribological evaluations further showed that these films exhibited low-friction behaviour, with a minimal friction coefficient of 0.02. Detailed transfer film characterisation revealed the formation of rich oxide and graphene structures within the stable contact-sliding interface of the Si-doped a-C film. The low friction mechanism was summarized as H–H interactions from the surface terminal passivation of Si dangling bond with hydroxide (-OH) or hydrogen (-H) groups and π*-π* interactions occurring between the graphene layers co-reducing the friction force. These findings shed light on the significance of doped Si atoms in the structural design and low-friction applications of carbon films.

A sheath correction method for electron density measurements with the microwave resonant curling probe

A correction method accounting for plasma sheath effects that appear when performing an electron density measurement with a microwave resonant probe immersed in plasma is described. The diagnostic is the novel curling probe (CP) that has already shown promising capabilities in various plasma sources. The correction method is based on the evaluation of two effects relative to the resonant probe operation and its interface with the plasma. First, the characteristic decay length of the electromagnetic field emitted by the CP, which defines the probed volume, has been characterized for the different harmonic resonance modes. Second, a semi-analytical model has been adapted to describe the plasma structure forming near the probe, which quantitatively describes the electron density profiles across the sheath structure. The correction method is then developed uniquely from numerical simulations and is independent of other diagnostics. Experimental results inside two plasma sources, an inductively coupled plasma and an electron cyclotron resonance plasma thruster, are presented and discussed. The validity of the method is assessed (i) by comparing CP corrected densities with Langmuir probe results, (ii) by varying the probe orientation to the expanding plasma flow, and (iii) by using two harmonics of the probe. The method is shown to significantly improve the accuracy of electron density measurements. Possible improvements to the method are also discussed.

Silver ion beam formation and implantation on nano-pyramidal template for isolated nano-dot formation

We report the development of silver (Ag) ion-beam by Electron Cyclotron Resonance (ECR) plasma sputtering and synthesis of Ag nano-dot arrays by implantation of the Ag+ ions on a pre-fabricated silicon nano-template. Ag atoms are mixed with the argon plasma by sputtering a biased silver plate placed inside the ECR chamber. The extracted and mass-separated Ag+ ions are transported to a UHV target chamber for implantation. The variation of the flux of Ag+ ion beam is studied by changing the various parameters, such as applied bias voltage of Ag plate, microwave power, argon gas pressure and specifically, the position of silver plate from the ECR plasma center. It is observed that the sputtering rate of Ag and thereby the final Ag beam current strongly depends on the applied bias and position of the plate. The dependence of microwave power and gas pressure on beam intensity is also investigated and explained in terms of ionization and mean free path of the ionized atoms. Finally, 6 keV Ag+ ions are implanted on pre-patterned nano-pyramidal templates to form an array of Ag nano dots on a large area, by exploiting the geometrical shape of the templates and the directionality of the ion beam.

51‐3: Copper Thin Film Dry Etching Equipment via ECR Plasma Source

This paper presents Gen. 2 (370 mm * 470 mm) size thin copper film dry etching performance that is etched by high electron temperature plasma source with low temperature substrate. Dry etching is performed using HCl gas in a reactive ion etching mode. In addition, scanning low temperature susceptor and the electron cyclotron resonance (ECR) plasma produced by rectangular‐type microwave slot antenna (ReSLAN) are used.

Nucleation of cubic boron nitride on boron-doped diamond via plasma enhanced chemical vapor deposition

Cubic boron nitride (c-BN), with a small 1.4% lattice mismatch with diamond, presents a heterostructure with multiple opportunities for electronic device applications. However, the formation of c-BN/diamond heterostructures has been limited by the tendency to form hexagonal BN at the interface. In this study, c-BN has been deposited on free standing polycrystalline and single crystal boron-doped diamond substrates via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD), employing fluorine chemistry. In situ x-ray photoelectron spectroscopy (XPS) is used to characterize the nucleation and growth of boron nitride (BN) films as a function of hydrogen gas flow rates during deposition. The PECVD growth rate of BN was found to increase with increased hydrogen gas flow. In the absence of hydrogen gas flow, the BN layer was reduced in thickness or etched. The XPS results show that an excess of hydrogen gas significantly increases the percent of sp2 bonding, characteristic of hexagonal BN (h-BN), particularly during initial layer growth. Reducing the hydrogen flow, such that hydrogen gas is the limiting reactant, minimizes the sp2 bonding during the nucleation of BN. TEM results indicate the partial coverage of the diamond with thin epitaxial islands of c-BN. The limited hydrogen reaction is found to be a favorable growth environment for c-BN on boron-doped diamond.

A comparison between ion irradiation assisted- and electron irradiation assisted-oxygen plasma treatment on modification of nanostructured carbon films

Oxygen plasma treatment has been used for surface modification of carbon materials. However, the working mechanism is not well clarified. Here, the ion irradiation assisted- and electron irradiation assisted-oxygen plasma etching were proposed and realized in an electron cyclotron resonance plasma processing system. The effects of the ion assisted- and electron assisted-argon plasma and oxygen plasma etching on the surface morphology and nanostructure of graphene nanocrystallites embedded carbon film were compared. In the ion assisted plasma etching, compared with argon plasma, the oxygen introduction made the sp2/sp3 and ID/IG of the film upper layer further decrease. While in the electron assisted plasma etching, after O2 introduction, the sp2/sp3 and ID/IG in the film upper layer increased. Then the oxygen plasma treatment mechanism was proposed. In the ion assisted oxygen plasma treatment, the attracted oxygen positive ions took major effect, which would reduce the threshold energy for atom displacement and then implant more carbon or oxygen atoms into the film subsurface to make the film denser. In the electron assisted oxygen plasma treatment, the neutral oxygen took major effect, which would preferentially react with the more unstable amorphous carbon and then make the film equipped with more sp2 bonds.

Hydrogen Plasma under Conditions of Electron-Cyclotron Resonance in Microelectronics Technology

This paper presents the results of hydrogen electron-cyclotron resonance (ECR) plasma in micro-electronics technology. Its effect on the radiation resistance of the IC and on the quality of the ohmic contact during the formation of UBM metallization is demonstrated. The devices obtained with the use of plasma ECR and without it are analyzed.

Tailoring the tribological properties of nanostructured carbon films under water lubrication

Carbon films have been considered suitable to be applied in water lubrication since they exhibit excellent friction-reducing and wear resistance, chemical inertness, etc. However, the basic understanding of tribological behaviors of carbon-based films under water lubrication still needs to be explored. In the present work, carbon films with different nanostructures were prepared by the electron cyclotron resonance (ECR) plasma nano-surface manufacturing system, and micro-textures with different sizes were prepared on the surface of carbon films by plasma etching. The influence of nanostructure and surface texture on the tribological properties of carbon films was investigated. The results show that different nanostructured carbon films can obtain lower friction coefficients and longer wear life under water lubrication than under dry condition. Due to low surface roughness, high hardness, and compact structure, the tribological properties of amorphous carbon (a-C) films under water lubrication are much better than those of graphene sheet-embedded carbon (GSEC) films. The prepared surface texture has a negative effect on the hard a-C film, but it can make the soft GSEC film generate soft wear debris at the initial stage. With the action of water, the soft wear debris is bonded on the surface of the contacting ball to form a silt-like transfer film, which increases the wear life by nearly three orders of magnitude. These results extend the basic understanding of the tribological behavior of carbon film under water lubrication, which is crucial in both fundamental and applied science.

Plume characterization of a waveguide ECR thruster

A circular waveguide electron cyclotron resonance plasma thruster prototype driven by microwaves at 5.8 GHz (80–300 W) is characterized. The magnetic field is generated by a combination of Sm-CoYXG32 magnets and an electromagnet, which enables the tuning of the resonance position and magnetic nozzle shape. The main plasma plume properties are analyzed by using electrostatic probes when the mass flow rate (Xenon), microwave power, electromagnet current, and propellant injector design are varied. An estimation of the propulsive performance of the device is also presented. Results show that a single radial injector hole is not sufficient for a symmetric ion current profile and that magnetic nozzle shape and strength tuning can significantly affect the divergence angle and thruster floating potential. A utilization efficiency of up to 70% and electron temperatures of up to 16 eV have been measured.

Electron Cyclotron stray radiation detector studies for JT-60SA

Most of the present and future magnetic fusion devices rely on high power mm-waves injection for a variety of applications like plasma breakdown, heating and control. Since under specific operating conditions the mm-waves might not be fully absorbed, potentially damaging in-vessel components, the detection of the non-absorbed radiation is recommended. Among the options for stray radiation detection, we consider here the possibility to exploit the solid body bolometer and its use for JT-60SA. Analysis of the residual power fraction expected for low absorption plasma conditions is presented, considering the dependence on the Electron Cyclotron Resonance Heating (ECRH) system and plasma parameters of JT-60SA. The residual power hitting the wall is evaluated looking at direct illumination and cross-polarization effects. The possibility to integrate a sensor for EC stray radiation, adapting the solution of the detector developed for ITER, is the main outcome of this study. In the ITER bolometer the differential thermocouple principle is considered to single out the nuclear heating and the microwave loads. A key component of the detector is the metal body with a ceramic coating layer, optimized for 170 GHz and 60 GHz. Mm-waves characterization of different coating samples has been performed to identify the optimal solution for JT-60SA considering its multi-frequency ECRH system (138 GHz, 110 GHz, 82 GHz), and will be here presented. The experience from JT-60SA equipped with these sensors will be also useful for their future use in ITER.