Permanent Magnet Electron Cyclotron Resonance Research Articles

Design of a compact, permanent magnet electron cyclotron resonance ion source for proton and H2+ beam production

A 2.45 GHz microwave ion source was developed at China Institute of Atomic Energy (CIAE) for proton beam production of over 60 mA [B.-Q. Cui, Y.-W. Bao, L.-Q. Li, W.-S. Jiang, and R.-W. Wang, Proceedings of the High Current Electron Cyclotron Resonance (ECR) Ion Source for Proton Accelerator, APAC-2001, 2001 (unpublished)]. For various proton beam applications, another 2.45 GHz microwave ion source with a compact structure is designed and will be built at CIAE as well for high current proton beam production. It is also considered to be used for the test of H(2)(+) beam, which could be injected into the central region model cyclotron at CIAE, and accelerated to 5 MeV before extraction by stripping. The required ECR magnetic field is supplied by all the permanent magnets rather than electrical solenoids and six poles. The magnetic field distribution provided by this permanent magnets configuration is a large and uniformly volume of ECR zone, with central magnetic field of a magnitude of approximately 875 Gs [T. Taylor and J. S. C. Wills, Nucl. Instrum. Methods Phys. Res. A 309, 37 (1991)]. The field adjustment at the extraction end can be implemented by moving the position of the magnet blocks. The results of plasma, coupling with 2.45 GHz microwave in the ECR zone inside the ion source are simulated by particle-in-cell code to optimize the density by adjusting the magnetic field distribution. The design configuration of the ion source will be summarized in the paper.

Magnetic Field Design for a 2.45-GHz ECR Ion Source withPermanent Magnets

We optimize the magnetic field configuration for a 2.45 GHz electron cyclotron resonance (ECR) ion source with permanent magnets, which is designed to construct a compact heavy-ion accelerator for intensive studies on nucleosynthesis. The magnetic system consists of two radially magnetized solenoids, a hexapole magnet, and a central ring magnet. We report magnetic field measurements of the permanent-magnet ECR ion source and compare with the results with those obtained using an Opera3D calculation.

Experiments With Fundamental Aspects Performed in a Small ECR Ion Source for a New Carbon Therapy Facility

A small permanent magnet electron cyclotron resonance ion source (ECRIS) has been developed for the production of C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> ions for the third carbon-therapy facility in Japan. The emphasis of the design is on stability, easy operation and prevention of maintenance, where high charge state production is not a requirement. Tests with different feed-gases have shown that carbon-hydrogen compounds are favorable, in particular with carbon to hydrogen ratio of 1:1. A parallel study of (highly charged) C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5+</sup> production revealed that the various compounds of feed-gas are behaving as if feeding the two components separately. This includes the behavior of replacing hydrogen by deuterium. From these a plausible reason was found for the observed failure of hydrogen as a mixing gas. Other experiments with the small source were performed to study the effect of inserting an aluminum (-oxide) cylinder inside the electron cyclotron resonance plasma-chamber. Earlier research found an increase in production of high charge states, but a good explanation was still missing. By adapting an insulated cylinder that can be biased positively, it was shown that ion diffusion to the side walls can be reduced, in particular when the cylinder is made of strips covering the pole pieces of the hexapole magnet. The new tool can be used to study the mechanism in more detail and also has possibilities of further improving a source for higher charge state production.

Identification of the ECR zone in the SWISSCASE ECR ion source

The magnetic field of the permanent magnet electron cyclotron resonance (ECR) ion source SWISSCASE located at the University of Bern has been numerically simulated and experimentally investigated. For the first time the magnetized volume qualified for electron cyclotron resonance at 10.88 GHz and 388.6 mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. The observed pattern of carbon coatings on the source correlates strongly with the electron and ion distribution in the ECR plasma of SWISSCASE. Under certain plasma conditions the ion distribution is tightly bound to the electron distribution and can considerably simplify the numerical calculations in ECR related applications such as ECR ion engines and ECR ion implanters.

Field structure and electron life times in the MEFISTO electron cyclotron resonance ion source

The complex magnetic field of the permanent magnet electron cyclotron resonance (ECR) ion source MEFISTO located at the University of Berne has been numerically simulated. For the first time the magnetized volume qualified for electron cyclotron resonance at 2.45GHz and 87.5mT has been analyzed in highly detailed 3D simulations with unprecedented resolution. New results were obtained from the numerical simulation of 25,211 electron trajectories. The evident characteristic ion sputtering trident of hexapole confined ECR ion sources has been identified with the field and electron trajectory distribution. Furthermore, unexpected long electron trajectory lifetimes were found.

Study on proton fraction of beams extracted from electron cyclotron resonance ion source

A permanent magnet electron cyclotron resonance ion source PMECR II is used to generate proton ions for radio frequency quadrupole (RFQ) injection at Peking University (PKU). The proton fractions of the extracted beam were measured at the positions both after extraction system of ion source and the end of low energy beam transport line (LEBT). Experiments show that the proton fraction has a rise time within a beam pulse, and its value varies with pulse width and microwave power. The proton fractions measured at different positions are comparable.

Electron cyclotron resonance ion sources in use for heavy ion cancer therapy

The use of electron cyclotron resonance (ECR) ion sources for producing ion beams for heavy ion cancer therapy has been established for more than ten years. After the Heavy Ion Medical Accelerator (HIMAC) at Chiba, Japan started therapy of patients with carbon ions in 1994 the first carbon ion beam for patient treatment at the accelerator facility of GSI was delivered in 1997. ECR ion sources are the perfect tool for providing the required ion beams with good stability, high reliability, and easy maintenance after long operating periods. Various investigations were performed at GSI with different combinations of working gas and auxiliary gas to define the optimal beam conditions for an extended use of further ion species for the dedicated Heidelberg Ion Beam Therapy (HIT) facility installed at the Radiological University Hospital Heidelberg, Germany. Commercially available compact all permanent magnet ECR ion sources operated at 14.5 GHz were chosen for this facility. Besides for (12)C(4+) these ion sources are used to provide beams of (1)H(3)(1+), (3)He(1+), and (16)O(6+). The final commissioning at the HIT facility could be finished at the end of 2006.

A latest developed all permanent magnet ECRIS for atomic physics research at IMP

Electron cyclotron resonance (ECR) ion sources have been used for atomic physics research for a long time. With the development of atomic physics research in the Institute of Modern Physics (IMP), additional high performance experimental facilities are required. A 300kV high voltage (HV) platform has been under construction since 2003, and an all permanent magnet ECR ion source is supposed to be put on the platform. Lanzhou all permanent magnet ECR ion source No. 2 (LAPECR2) is a latest developed all permanent magnet ECRIS. It is a 900kg weight and ∅650mm×562mm outer dimension (magnetic body) ion source. The injection magnetic field of the source is 1.28T and the extraction magnetic field is 1.07T. This source is designed to be running at 14.5GHz. The high magnetic field inside the plasma chamber enables the source to give good performances at 14.5GHz. LAPECR2 source is now under commissioning in IMP. In this article, the typical parameters of the source LAPECR2 are listed, and the typical results of the preliminary commissioning are presented.

Rf modes and plasma formation of electron cyclotron resonance ion source

The plasma chamber of electron cyclotron resonance (ECR) ion sources may be considered as a cavity resonator in radio-frequency (rf) technology. The microwave frequency then has to be tuned to the resonant frequency of a preferable mode. In order to produce ions with higher charge state, the rf characteristics of the plasma chamber should be investigated. As the first study, the rf simulation and the experimental measurement were carried out for a permanent magnet ECR ion source, which was developed at Tokyo Institute of Technology (TokyoTech). The frequency spectrum of microwave power transmission was measured to check the resonance points of the plasma chamber. The mode analysis was performed by a theoretical calculation and with a three-dimensional simulation code. These results and the effect of the electric-field distribution on ECR plasma will be presented.

Silicon nitride films deposited at substrate temperatures &amp;lt;100 °C in a permanent magnet electron cyclotron resonance plasma

Deposition of silicon nitride at low temperatures by plasma-enhanced chemical vapor deposition requires an efficient source of activated precursors and high-current, low-energy ion assist. We report the deposition of silicon nitride at substrate temperatures &amp;lt;100 °C using a permanent magnet electron cyclotron resonance plasma reactor capable of generating uniform plasmas over 300 mm diameters. The effects of gas mixture, silane flow, pressure, and microwave power on the film deposition rate, composition and bonding, index of refraction, stress, and etch rate in buffered oxide etch solution are reported. The N2/SiH4 flow ratio and microwave power both influence the film index and hydrogen content and bonding. For a SiH4 flow of 30 sccm and N2/SiH4 ∼0.75, hydrogen is equally distributed between Si–H and N–H sites and total hydrogen content is minimized. At a deposition rate of 500–600 Å/min, a threshold in microwave power of ∼1100 W exists, above which films with buffered oxide etch rates &amp;lt;150 Å/min result. Near the threshold microwave power compressive stress &amp;lt;400 MPa is observed, with increasing stress at higher microwave powers.

Microstructure and dielectric properties of silicon nitride films deposited by electron cyclotron resonance plasma chemical vapor deposition

The microstructures and dielectric properties of silicon nitride (SiNx) films have been investigated. These films were prepared by permanent magnet electron cyclotron resonance plasma chemical vapor deposition by varying the substrate temperature between 56 and 400 °C and microwave power between 65 and 520 W. It exhibits a fractal structure with fractal dimension Df=1.45 or fractal-like structures for the films deposited without additional heating. When the substrate temperature is raised above 200 °C, the uniform dense structure can be obtained. The frequency dependence of the dielectric constant (ε′) in the frequency range 5–106 Hz for the films deposited below 100 °C follows a three fractional power law of (ε′−ε∞′)∝ωni−l (i=1, 2, and 3). The exponents ni are n1=0.73–0.93, n2=0.95–0.98, and n3=0.87–0.99 in the frequency range of 5–102 Hz, 102–104 Hz, and 104–106 Hz, respectively. The frequency dependence of ε′ also follows a single power law of (ε′−ε∞′)∝ωn−1 with n=0.95–0.82 for the films deposited in the substrate temperature range of 200–400 °C. The dielectric property of the single power law is in agreement with the intrinsic dielectric property of Si3N4 films, which is related to electron hopping conduction. The dielectric property of the fractional power law is considered to relate to the fractal structure of SiNx films. These are partially in agreement with that of the many-cluster anomalous conduction theory of fractal structure.

Constraints due to the production of radioactive ion beams in the SPIRAL project

The radioactive ion beams that will be delivered by the SPIRAL facility will be produced by the interaction of a stable high energy (95 MeV/A) and high intensity (2×1013 particle/s) primary ion beam delivered by the GANIL cyclotrons with a carbon target heated to 2000 °C. During this interaction, some radioactive atoms will be created and will diffuse out of the target before entering into an electron cyclotron resonance (ECR) ion source where they will be ionized and extracted. The production of radioactive ion beams with this method implies high radiation fields that activate and can damage materials located in the neighborhood of the target. Therefore, the production system which is composed of the permanent magnet ECR ion source coupled to a graphite target will be changed after two weeks of irradiation. As this ensemble will be very radioactive, this operation has to be supervised by remote control. The radiation levels around the target–ion source system and a detailed description of the different precautions that have been taken for safety and for prevention of contamination and irradiation are presented.

Influence on selective SiO2/Si etching of carbon atoms produced by CH4 addition to a C4F8 permanent magnet electron cyclotron resonance etching plasma

Changes in the densities of fluorocarbon radicals and fluorine atoms in a size-scalable large-area compact permanent magnet electron cyclotron resonance etching plasma source employing C4F8 gas with CH4 addition have been investigated. Measurements using infrared laser absorption spectroscopy and actinometric optical emission spectroscopy show that, for a pure C4F8 plasma, the dominant species is CF2 radicals with a density of the order of 1013 cm−3, followed by fluorine atoms, CF3 and CF2 radicals which have a density an order of magnitude lower at 1012 cm−3. The densities of the different fluorocarbon radical species were found to display different dependencies on increasing CH4 gas addition. Hollow cathode absorption spectroscopy was used to estimate the carbon atom density for the first time, to the best of our knowledge, in an etching plasma. The carbon atom density in the plasma increases linearly with CH4 gas addition between 20 and 80%. Analysis of actual SiO2/Si etching revealed that the etch selectivity and carbon atom to fluorine atom ratio follows a similar trend indicating a direct correlation between the carbon atom density in the plasma and the etch selectivity.

Diagnostics of Fluorocarbon Radicals in a Large-area Permanent Magnet Electron Cyclotron Resonance Etching Plasma

Diagnostics of fluorocarbon radicals and fluorine (F) atom species in a size-scaleable large-area permanent magnet electron cyclotron resonance (ECR) etching plasma employing CF4 and C4F8 gases are carried out. Non-intrusive infrared laser diode absorption spectroscopy and actinometric measurement techniques are used in evaluating the performance of the permanent magnet ECR plasma source and in studying the kinetic processes associated with etching plasma chemistry. Successful measurements of the absolute CF and CF2 radical and F atom densities have been achieved. In particular for C4F8 plasma, enhanced CF and CF2 radical densities which afford higher selectivity in the etching of SiO2 on Si are discussed. At a pressure of 0.4 Pa and an input microwave power of 900 W the CF and CF2 radical and F atom densities in C4F8 plasma were 1.7×1013 cm-3, 6.0×1013 cm-3 and 1.5×1013 cm-3, respectively. These results are also discussed in comparison with results for a conventional electromagnet ECR plasma source.

Characterization of Ar/Cu electron-cyclotron-resonance plasmas using optical emission spectroscopy

Optical emission spectroscopy is used to investigate trends with changes in processing parameters for Ar/Cu plasmas in an electron-cyclotron-resonance (ECR) plasma deposition system. The primary motivation for this work is to monitor trends in ionization fractions for copper deposition plasmas using a noninterfering diagnostic tool. The system, which consists of a solid copper sputter target coupled to a permanent magnet ECR microwave plasma system, is operated in the range of 1–6 mTorr argon with net microwave input power of 500–1500 W. Emission from the following excited states is monitored: Ar neutrals (696.5 nm); Ar ions (488 nm); Cu neutrals (521.8 and 216.5 nm); and Cu ions (213.6 nm). Cu ion emission and Cu neutral emission monotonically increase with net microwave input power but at slightly different rates for different pressures, while argon-ion emission as a function of pressure shows a broad peak around 4 mTorr. The ratio of Cu ion emission to Cu neutral emission is used as an indicator of the relative ionization efficiency for Cu and peaks near 5 mTorr. Spectroscopic estimates of electron temperature differences between pure Ar and Ar/Cu plasmas are also presented.

Cu metallization using a permanent magnet electron cyclotron resonance microwave plasma/sputtering hybrid system

A permanent magnet electron cyclotron resonance microwave plasma source has been coupled to a copper sputter target to produce ionized copper fluxes for submicron integrated circuit metallization. A custom launcher assembly allows the use of microwave powers up to 5 kW in a metal deposition environment to produce plasma densities ≳1012 cm−3, well above the cutoff density at 2.45 GHz of ∼1×1011 cm−3. Six hundred nm, 1.1:1 aspect ratio features have been filled with copper, and 250 nm, 6:1 aspect ratio features have been successfully lined. Copper ionization fractions for the conditions used for lining and filling, determined by a combination of Langmuir probe measurements and optical emission spectroscopy, are between 10% and 35%.

Performance and modeling of a permanent magnet electron cyclotron resonance plasma source

A plasma etch reactor with a permanent magnet electron cyclotron resonance (ECR) source and multipolar process chamber has been characterized with plasma parameter and etch measurements. The ECR source uses a compact permanent magnet structure, rather than current‐driven electromagnet coils, to establish the axial magnetic field required for ECR operation. The source is compact and requires no input electrical or cooling power. Plasma densities greater than 1011 cm−3 and ion current densities above 10 mA cm−2 are obtained; the plasma parameter uniformity is 1.2% (1σ) over 20 cm. The etch rate in undoped polysilicon is 3450 A/min without applied bias, and the etch rate uniformity is 1.8% (1σ) over a 14 cm wafer diameter. The radial and axial plasma parameter profiles agree with the predictions of an ambipolar diffusion model.

Permanent magnet electron cyclotron resonance plasma source with remote window

An electron cyclotron resonance (ECR) plasma has been used in conjunction with a solid metal sputter target for Cu deposition over 200 mm diameters. The goal is to develop a deposition system and process suitable for filling submicron, high-aspect ratio ULSI features. The system uses a permanent magnet for creation of the magnetic field necessary for ECR, and is significantly more compact than systems equipped with electromagnets. A custom launcher design allows remote microwave injection with the microwave entrance window shielded from the copper flux. When microwaves are introduced at an angle with respect to the plasma, high electron densities can be produced with a plasma frequency significantly greater than the electron cyclotron frequency. Copper deposition rates of 1000 Å/min have been achieved.

Large-diameter plasma profile monitoring system using Faraday cup and Langmuir probe arrays

Details of a personal computer-based data acquisition system, which allows monitoring of large-diameter plasma source ion current profiles and Langmuir probe data, using an interchangeable rotatable, Faraday cup array and Langmuir probe array respectively are described. The arrays span the plasma diameter and can be rotated under computer control. Software-selectable monitor modes allow investigation of the angular and temporal dependence of ion current profiles, basic plasma parameters and their associated non-uniformities. Isolated aluminium plates can be fixed to the respective arrays to investigate the intrusive influence of a substrate holder and substrate bias on plasma parameters. Angular dependences is of ion current non-uniformity values of a large-diameter permanent magnet electron cyclotron resonance source are reported to demonstrate the benefits of the system over a single-probe/cup system.

The relative effect on the oxygen concentration in YBa2Cu3O7−δ of atomic and ionic oxygen fluxes, produced by a small compact electron cyclotron resonance source

The relative effect of atomic and ionic oxygen for the oxidation of YBa2Cu3O7−δ thin films is investigated. To this goal, the characteristics of an oxygen plasma produced by a small, compact, permanent magnet electron cyclotron resonance plasma source were investigated as a function of a bias applied to the plasma. With no bias, a plasma potential of 23 eV was measured by an energy analysis of the ions. With increasing positive plasma bias voltage, the ion current decreases and its energy increases above the 23 eV by the amount of applied bias voltage. When a negative voltage is applied to the plasma, both electron and ion current drastically decrease, while the atomic flux remains high. The atomic oxygen flux was measured by the oxidation rate of Ag and the etching rate of a standard photoresist as a function of distance from the source and the bias voltage. We find that the resistivity of a YBa2Cu3O7−δ film in the plasma is well characterized by the flux of atomic oxygen and that there is no significant effect of oxygen ions.