Electron Cyclotron Resonance Plasma Source 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.

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.

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.

Iodine electron cyclotron resonance plasma source for electric propulsion

With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.

Comments on mechanisms for self-E → H and inverse H → E mode transitions in radio frequency inductively coupled plasmas

The previously observed self-E → H and inverse H→E mode transitions were explained by unrelated mechanisms. The argument in this Brief Communication finds that both mode transitions can be interpreted via wall-heating that affects electron density by changing neutral density. In the self-E → H mode transition, the shift of the preset E-mode discharge to the E → H mode-transition point is caused by the increasing neutral density in the cooling down process of the chamber wall overheated in the preceding high-power H-mode discharge. The requirement for the inverse H →E mode transitions is a small-sized cylindrical radio frequency (RF) inductively coupled plasma source powered by multi-turn coil under which the strong wall-heating in the ramping-up phase of RF power or RF coil current leads to a reduction of neutral density in the subsequent ramping-down phase. The wall-heating can affect all processes in gas discharges but is most remarkable near a mode transition. The wall-heating effect on discharge mode transition has not been intensively investigated but was only suggested to explain the unknown mode transition in an electron cyclotron resonance plasma source [Jarnyk et al., Appl. Phys. Lett. 62, 2039 (1993)].

55‐3: Development of Low‐Temperature Metal Dry‐Etching Equipment via ECR Plasma Source

This paper presents the dry etching performance and expectation of highly conductive thin metal films that are hardly etched at low temperature with conventional plasma dry etching equipment. Dry etching is performed using a combination of H2 and HCl gases in a reactive ion etching system with low temperature susceptor and electron cyclotron resonance (ECR) plasma source. We could achieve high electron temperature enough to dissociate and ionize H and Cl radicals from H2 and HCl molecules.

Investigation of plasma mode transition and hysteresis in electron cyclotron resonance ion thrusters

Plasma mode-transition and hysteresis have been reported in several electron cyclotron resonance (ECR) plasma sources and have also been observed in ECR ion thrusters. From observation outside the thruster, the optical emission is significantly changed after plasma mode-transition, which indicates the electron heating, excitation and ionization processes are also changed. Therefore, to investigate these processes quantitatively, the ground-state neutral density and spontaneous emission by electron impact excitation are directly measured using two-photon absorption laser-induced fluorescence spectroscopy. This measurement system is applied to two types of thrusters. In one thruster, both mode-transition and hysteresis were observed, while in another, no hysteresis was observed due to the partial prevention of ECR heating. The experimental results indicate that the spontaneous emission sharply increases by the mode-transition and hysteresis. The tendency for this increase was relatively small with the partial prevention of ECR heating; however, the mode-transition was not deleted. Analysis of the excitation and ionization process revealed that the increase of indirect (stepwise) excitation and ionization from metastable particles can contributes to the sharp increase of the spontaneous emission. In addition, quantitative estimation of the collisional and ECR heating indicated that collisional heating cannot be neglected after the mode-transition, which indicates that collisional heating can contribute to the sharp increase due to the increase of electron temperature. The indirect ionization and collisional heating could thus be the main cause of the mode-transition and hysteresis.

One-Step Etching Characteristics of ITO/Ag/ITO Multilayered Electrode in High-Density and High-Electron-Temperature Plasma.

This paper presents the dry etching characteristics of indium tin oxide (ITO)/Ag/ITO multilayered thin film, used as a pixel electrode in a high-resolution active-matrix organic light-emitting diode (AMOLED) device. Dry etching was performed using a combination of H2 and HCl gases in a reactive ion etching system with a remote electron cyclotron resonance (ECR) plasma source, in order to achieve high electron temperature. The effect of the gas ratio (H2/HCl) was closely observed, in order to achieve an optimal etch profile and an effective etch process, while other parameters—such as the radio frequency (RF) power, ECR power, chamber pressure, and temperature—were fixed. The optimized process, with an appropriate gas ratio, constitutes a one-step serial dry etch solution for ITO and Ag multilayered thin films.

Detailed Density and Ion Energy Profiles Downstream of a Small ECR Plasma Source

The exhaust ion stream from an electron cyclotron resonance (ECR) plasma source is investigated in detail. Two sets of coils allow for different shapes of the external field under which the plasma is created. Parameters in the form of electron density $n_{e}$ , electron temperature $T_{e}$ , and ion energy distribution function (IEDF) are evaluated using Langmuir probes and retarding field energy analyzers (RFEAs). Parameters are evaluated under 10 and 20 W of microwave energy at pressures in argon between $1\times 10^{-3}$ and $2\times 10^{-3}$ mbar. In the middle of the plasma, we see electron temperatures in the range of 4–5 eV for most measurements and electron densities of up to $5\times 10^{16}/\text{m}^{3}$ in agreement with particle and power balance models. For a purely expanding magnetic field, the detailed IEDFs indicate a directed ion speed within the plasma column of up to $3.1\times 10^{3}$ m/s with respect to the low-energy background. With increasing downstream magnetic field, the low-energy part of the IEDFs vanishes downstream of the magnetic mirror. Structures with energies increasing in the radial direction appear as radial confinement improves.

Numerical modeling of the effect of mirror magnetic field strength on electron distributions in electron cyclotron resonance plasma sources

Abstracts In the process of surface treatment by electron cyclotron resonance (ECR) plasma source, the magnetic field plays an important role in introducing the confinement of electrons. To investigate the influence of the magnetic field configuration on electron distribution conditions, this study presents a two-dimensional model of the ECR plasma source. According to the resulting distributions of the electron density and temperature, it is found that the plasma density in the mirror magnetic field is higher than that in the divergent magnetic field. At the same time, the application of the mirror magnetic field is valid for decreasing the electron temperature due to both effects of plasma confinement and particle collisions. Furthermore, the decrease of the minimum strength of the mirror magnetic field and the increase of the strength at the injection side contribute to higher electron density and lower electron temperature owing to the gradient of magnetic field.

Study on Uniform Plasma Generation Mechanism of Electron Cyclotron Resonance Etching Reactor

Electron cyclotron resonance (ECR) plasma sources have been used widely in ultra large-scale integration (ULSI) manufacturing processes for many years. ECR plasma sources can generate plasma stably, even at very low pressures below 0.1 Pa, and the plasma’s spatial distribution can be controlled easily using the static magnetic field distribution. Furthermore, the plasma generation region can be located away from the chamber walls, which leads to reduced plasma contamination from the walls. In addition, uniform plasmas can be generated using these sources to achieve uniform plasma processing, which is crucial for large-diameter wafers such as 300 or 450 mm wafers. However, the mechanism for generation of uniform plasma using an ECR plasma source for semiconductor manufacturing is not well understood because of the complexity of the microwave propagation in the plasma. We use a plasma simulation technique to understand the uniform plasma generation mechanism in this work. We have conducted an integrated ECR plasma simulation of an etcher used for semiconductor manufacturing that combines 1) a microwave analysis in magnetized plasma, 2) a plasma generation analysis, and 3) a plasma diffusion analysis. We obtained consistent solutions for each analysis in practical calculation times of a few minutes. Additionally, we verified the simulation results by comparison with experimental plasma density measurements. We then discussed the uniform plasma generation mechanism in the ECR plasma source using simulated results for the microwave distribution in the etching reactor.

On the heating mechanism of electron cyclotron resonance thruster immerged in a non-uniform magnetic field

To study the heating mechanism of electron cyclotron resonance thruster (ECRT) immersed in a non-uniform magnetic field, experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP. It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field (0.0875 T), while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field (till 0.0170 T). Evidence of radial hollow density profile indicates that upper hybrid resonance, which has strong edge heating effect, is the heating mechanism of low-field ECRT. The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed. Interestingly, the evolutions of electron temperature and electron density with input power experience a ‘delayed’ jump, which may be correlated with the different power levels required for cyclotron and ionization. Moreover, when the field strength decreased, the variation of electron density behaves in an opposite trend with that of electron temperature, implying a possible competition of power deposition between them. The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field, and designing efficient ECRT using low magnetic field for economic space applications.

Modeling of plasma density, argon ion energy and ion velocity functions in a dipolar electron cyclotron resonance plasma source

Improving the surface feature precision of semiconductor devices largely depends on the ion distribution functions, which are non-Maxwellian and varying in processing plasmas spatially. In this work, a hybrid plasma model (HPM) is developed for an Ar discharge of dipolar electron cyclotron resonance (ECR) to explore the characteristics of ion energy distributions (IEDs), ion angular distributions (IADs) and ion velocity distributions (IVDs). The hybrid model contains a fluid model that determines the electric space characteristics of plasmas, as well as a Particle in Cell/Monte Carlo (PIC/MC) model that simulates ion distributions in consideration of the collisions between ions and neutrals. The influences of the pressure, magnet current, and position on the ion distributions are also discussed. The simulation results reveal the features of IEDs which transforms from a single energy peak into a bimodal distribution with the increasing pressure. IADs have a significant peak at a small angle, and most ions strike to the substrate surface with an angle less than 10°. Increasing the magnet current contributes to broader IEDs yet does not significantly alter neither IADs nor IVDs. The sensitive position dependence of ion distributions reveals considerable anisotropy of ions on the ECR surface.

Study on charge neutralization effect by electron cyclotron resonance plasma source in high vacuum

Electric charge deposition is cause of failures in a variety of in-vacuum manufacturing processes. Therefore, high efficient charge neutralization method is required. The goal of our study is to improve the charge neutralization speed in vacuum. Our research aims to the application of an electron cyclotron resonance(ECR) plasma source as neutralizer in vacuum. ECR neutralizer has been developed to neutralize ions emitted by ion thrusters, preventing the spacecraft from charging. We improved the neutralization current and investigated the charge neutralization of insulating film as an application for roll-to-roll system. Conveying films at high speed in vacuum, the films are entangled with each other because of friction charging. By placing the ECR neutralizer at 1.5m from a roll-to-roll system, we can convey the film roll at 1000m/min, the highest speed currently used in the industry. Our neutralization system runs at a gas flow rate of just 0.05mg/s of xenon. The 10W class ECR neutralizer is hence proved to be an effective charge neutralization method also for non-propulsion applications in high vacuum.

Evaluation of Silicon Nitride Film Formed Using Magnetic-Mirror Confined Plasma Source

Silicon nitride (SiN) films were deposited by a newly-proposed mirror-plasma enhanced chemical vapor deposition (MPECVD) method using SiH4 and N2 based plasmas. MPECVD method utilizes the magnetic-mirror confined electron cyclotron resonance plasma source to realize low ion-bombardment damage plasma processings. The deposition temperature ranged from room temperature to 400°C in the experiment. The SiN films having excellent wet etching resistance against HF solution could be obtained. In addition, the conformal SiN-film deposition on the Si trench pattern was confirmed with mostly keeping the wet etching resistance against HF solution for all the regions of the top, the sidewall and the bottom surface. Both the conformality and the wet etching resistance against HF solution of the SiN film on the trench pattern were better than the case of the conventional PECVD.

Numerical Identification of Trivelpiece–Gould Waves in an Electron Cyclotron Resonance Etching Reactor

Electron cyclotron resonance (ECR) plasma sources have been widely used for ultra-large-scale integration manufacturing processes because of their wide operating range and excellent uniformity over 300- or 450-mm diameter wafer. However, microwave electromagnetic fields in magnetized plasma-filled reactors are not well understood because of the complexity of electromagnetic wave field analysis. We conducted microwave electromagnetic field analysis of an ECR plasma etcher by the finite-element method using a simulation platform. Complicated electric field patterns were clearly observed under some conditions. We investigated the patterns in detail to determine whether they were spurious or not. The patterns proved to be Trivelpiece–Gould waves according to their characteristics imposed by the dispersion relation of waves. This analysis approach is a powerful method because very fine-wave structures can be identified.

Diagnostics of microwave assisted electron cyclotron resonance plasma source for surface modification of nylon 6

Looking at the increasing scope of plasma processing of materials surface, here we present the development and diagnostics of a microwave assisted Electron Cyclotron Resonance (ECR) plasma system suitable for surface modification of polymers. Prior to the surface-treatment, a detailed diagnostic mapping of the plasma parameters throughout the reactor chamber was carried out by using single and double Langmuir probe measurements in Ar plasma. Conventional analysis of I-V curves as well as the elucidation form of the Electron Energy Distribution Function (EEDF) has become the source of calibration of plasma parameters in the reaction chamber. The high energy tail in the EEDF of electron temperature is seen to extend beyond 60 eV, at much larger distances from the ECR zone. This proves the suitability of the rector for plasma processing, since the electron energy is much beyond the threshold energy of bond breaking in most of the polymers. Nylon 6 is used as a representative candidate for surface processing in the presence of Ar, H2 + N2, and O2 plasma, treated at different locations inside the plasma chamber. In a typical case, the work of adhesion is seen to almost get doubled when treated with oxygen plasma. Morphology of the plasma treated surface and its hydrophilicity are discussed in view of the variation in electron density and electron temperature at these locations. Nano-protrusions arising from plasma treatment are set to be responsible for the hydrophobicity. Chemical sputtering and physical sputtering are seen to influence the surface morphology on account of sufficient electron energies and increased plasma potential.

New Compact Electron Cyclotron Resonance Plasma Source for Silicon Nitride Film Formation in Minimal Fab System

A compact magnetic-mirror confined electron cyclotron resonance plasma source for low-damage plasma processings was developed, especially aiming for the realization of high-quality silicon nitride film formation for the sub-micron complementary metal-oxide semiconductor device processes in the minimal fab system. The developed plasma source was installed in the minimal tool, and deposition of silicon nitride film was performed. The magnetic mirror confinement method worked well to excite the high-density plasma with low plasma excitation power of 10 W or less. By adopting the substrate position slightly apart from the core plasma region with the pressure range of 25 Pa, the silicon nitride film having the similar N/Si ratio to the ideal value of Si3N4 could be obtained in the room-temperature deposition. Under this condition, impurity concentration of oxygen in the film could be suppressed less than 1%, which was even smaller than that in the controlled low-pressure chemical-vapor deposited film at 750 °C.

Characterization of He-Induced Bubble Formation in Tungsten due to Exposure from an Electron Cyclotron Resonance Plasma Source

A compact electron cyclotron resonance plasma source has been utilized at Sandia National Laboratory to expose heated W samples (1270 K) to 50–75 eV He ions at fluxes on the order of 1019 m−2 s−1 and fluences on the order of 1024 m−2. Scanning electron microscopy (SEM) analysis of the surface has indicated bubbles up to 150 nm in diameter that exhibit signs of bursting near the surface. Comparisons have been made between W samples prepared from warm-rolled W sheet stock and ITER-Grade W rod stock. Focused ion beam (FIB) cross sectioning has been used with SEM and transmission electron microscopy (TEM) to identify large sub surface bubbles (100 nm diameter) at depths up to one micron as well as a dense layer of smaller bubbles (<10 nm diameter) within the first 100 nm of the surface, similar to bubble layers observed on higher flux experiments. SEM-Electron Backscatter Diffraction (EBSD) analysis has identified a unique surface morphology feature associated with the exposed ITER-Grade W as well as features similar to previous EBSD studies of rolled W stock. Thermal desorption spectroscopy (TDS) analysis has identified that pre-existing He bubbles found in the Sandia He-ion exposed samples do alter the D trapping and desorbing behavior in W. The findings from these preliminary characterization studies are presented and discussed in context with results from similar plasma exposure stages at other facilities around the world.

Low-temperature deposition of SiNx, SiOxNy, and SiOx films from plasma discharge of SiH4 for polycarbonate glazing applications

To improve the abrasion resistance of polycarbonate, which can be used as a replacement for glass, SiNx, SiOxNy, and SiOx thin films were deposited at low temperatures using a slot antenna electron cyclotron resonance (SLAN ECR) plasma source. The SLAN ECR plasma source has a high ionization rate even at low pressure and can thus rapidly deposit films with good mechanical properties at low temperatures. When SiH4 gas is used as the Si precursor, the deposition rates of thin films can exceed 100nm/min at 6.65Pa. As the N2 or O2 flow decreases, the deposition rate is decreased, but the hardness H and elastic modulus E of the films gradually increases. The maximum hardness values of the prepared SiNx, SiOxNy, and SiOx films are 16.8, 14.9, and 11.4GPa, respectively. The H/E and H3/E2 values of such films are associated with abrasion resistance. However, the correlation between the H/E and H3/E2 values and the abrasion resistances of our films is not strong. It is shown by annealing and abrasion experiments that the porosities of these films are more closely related than the H/E and H3/E2 values to their abrasion resistances. When a hyper-thermal neutral beam (HNB) is used at low pressures, denser films are deposited. The hardness values of these films are also significantly higher.