RF Ion Source Research Articles

Optical and Structural Properties of Tantalum Pentoxide Thin Films by Ion Assisted Deposition Method with Radio Frrequency Ion Source.

Ion assisted deposition has been applied widely in present optical industry, to obtain more dense films, but it is often required to attain longer filament lifetime of the ion source particularly in the case of successively reactive oxidation processes under an additional oxygen gas inlet such as in oxide films for laser mirror application. It is the reason why radio frequency ion source is keenly interested at the present moment. Therefore we have investigated the optical and structural properties of Ta2O5 films as the functions of ion energy (300-750eV), substrate temperature (ambient or 300°C ), arrival ratio (0.2-0.8 atoms/ion), and providing the oxygen ions by RF ion source to bombardment. Typically, Ta2O5 thin films with refractive index larger than 2.25 and extinction coefficient less than 6×10-4 in visible region have been obtained under the conditions of oxygen ion energy of 500 eV, at the substrate temperature of 300°Cand with the arrival ratio of 0.4 atoms/ion. Their cross sections of the films are shown the amorphous-like, amorphous columnar, and polycrystalline columnar structures by SEM and XRD. Several results of surface roughness of these films by AFM and OP, and the packing densities of these films by spectrometer (OPM-V1) are also presented.

Industrial application of ion assisted surface modification

Ion technologies for the improvement of surface properties of material are under change due to economic requirements. The beam implanter technology developed for processing of flat semiconductor wafers is too expensive for high dose surface modification of three-dimensional steel components. We present results obtained with a bandshaped RF ion source operated together with large area magnetron sputter sources. Low dose Ar + ion beam mixing is performed to promote the adhesion of hard TiN protective coatings deposited at a temperature of 200°C onto ball bearing steel. By using a rotating substrate holder film deposition and ion implantation are alternated and the surfaces of many parts can be modified within the same charge in a cost effective way. Alternative approaches are also discussed.

A new apparatus for photon- and ion-beam-assisted deposition

Over the last decade ion-beam-assisted deposition (IBAD) has become a well-known technique for deposition of thin films because of its ability to control properties of coatings. A new IBAD system is introduced which includes a facility to illuminate samples by UV light during the deposition process in order to enhance motion of deposited atoms and interfacial reactions between substrate and coating. The IBAD system consists of two vacuum chambers, the preparation chamber and the analysis chamber, which are connected by a straight tube for sample transfer. Samples may be moved through the tube between the two chambers by a linear feedthrough. The preparation chamber includes a filamentless rf ion source, an electron-beam evaporator, and a tube with a nozzle delivering reactive gases near the sample during deposition. In addition to the ion-assisted deposition process, a technique based on photon irradiation has been employed to obtain significant improvements of structure and properties of deposited metal layers. As these films reflect a large fraction of light in the visible range, we use UV-light illumination. The samples are irradiated by UV light with a mercury arc lamp during deposition. To achieve the high degree of process automation most process parameters are controlled with a computer system. The analysis chamber includes a reverse view LEED/AES system, which is used to analyze composition and surface structure of thin the films.

A heavy ion implanting facility at the Chiang Mai University

Nitrogen ion implantation is widely used to improve the wear and corrosion resistance of metals and alloys. Different kinds of ions, including metal and heavier ions can be used for this purpose. The proposed ion implanter as a 0°- and a 45°-beam line. The 0°-beam line has been installed and tested by using an RF source with an ion energy of about 140 keV. The nitrogen beam current is about 200 μA at the target position. The beam can be magnetically swept to cover a 10 cm × 10 cm target area. Preliminary tests with an ion dose of about 10 17 ions/cm 2 improved the hardness of stainless steel and aluminium samples. The 45°-beam line and the analyzing magnet are under construction. When this will be completed, the present RF ion source will be replaced by a Danfysik 910 ion source which can be used for producing metal and heavier ions.

State of the art of radio-frequency ion sources for space propulsiona)

After 30 years of research, development, and qualification work of radio-frequency ion thrusters (RIT), the RIT 10 engine has now been tested successfully in space onboard the European Retrievable Carrier (EURECA). RIT 10 produces a thrust of 10 mN and is designed for north–south stationkeeping of geosynchronous satellites. Besides, the European Space Agency (ESA/ESTEC) plans to implement ion propulsion in their technological satellite ARTEMIS, where ion thrusters shall be used operationally for north–south stationkeeping. In parallel, development and tests of a scaled-up 50 mN engine RIT 15 have been continued successfully with xenon and krypton as propellants. A large ion engine with a 35 cm ionizer diameter, the RIT 35, has been developed for primary propulsion of interplanetary probes aiming at a thrust level in the 250 mN range. A laboratory prototype has been subjected to extensive testing and performance mapping. Recently, this work has been continued in European cooperation due to a redirection of contracts. The ion source diameter has been reduced to 26 cm but the performance should be kept using a British high perveance grid at the German rf-ion source.

Use of electron gun to regulate the radio-frequency plasma performance and beam optics

The addition of electrons in both rf plasma and ion beam extracted from a rf ion source enhanced the source’s performance and beam optics. The increase of plasma intensity increases the charge state of the extracted ions. The mixing of electrons with the ions within the ion beam decreases the space charge effect on beam expansion.

State of the art of radio-frequency ion sources for space propulsion (abstract)a)

After 30 years of research, development, and qualification work of radio-frequency ion thrusters (RIT), the RIT 10 engine has now been tested successfully in space onboard the European Retrievable Carrier (EURECA). RIT 10 produces a thrust of 10 mN and is designed for north–south stationkeeping of geosynchronous satellites. Besides, the European Space Agency (ESA/ESTEC) plans to implement ion propulsion in their technological satellite ARTEMIS, where ion thrusters shall be used operationally for north–south stationkeeping. In parallel, development and tests of a scaled-up 50 mN engine RIT 15 have been continued successfully with xenon and krypton as propellants. A large ion engine with a 35 cm ionizer diameter, the RIT 35, has been developed for primary propulsion of interplanetary probes aiming at a thrust level in the 250 mN range. A laboratory prototype has been subjected to extensive testing and performance mapping. Recently, this work has been continued in European cooperation due to a redirection of contracts. The ion source diameter has been reduced to 26 cm but the performance should be kept using a British high perveance grid at the German rf-ion source.

Formation of n+ a-Si:H Thin Layer by Ion-Doping Technique

Profiles and quantities of impurities implanted by an ion-doping technique have been investigated by secondary ion mass spectrometry (SIMS) measurements and MonteCarlo simulations. The ion-doping technique in this paper is one of large-area ion implantation without mass separation using an rf ion source. In the ion-doping experiments, the ion source gas used was 5% phosphine in hydrogen, and the ion acceleration voltage was in the range of 6 kV-30 kV. The hydrogen ions were estimated to be mainly H2+ and H3+, and some ions were PHx+. The fraction of ions containing phosphorus was about 50% of the total ion dose. Formation of an n+ a-Si:H thin layer by the ion-doping technique at room temperature was also confirmed from electrical measurements of doped a-Si:H films. The values of conductivities obtained were 10-4∼10-3 S/cm. The n+ a-Si:H layers formed by the ion-doping technique are applicable to the fabrication of a-Si:H thin-film transistors (TFTs).

The study of a fundamental law in extracting metal ions from a rf ion source by applying a plasma chemical reaction

Experimental metal ions are extracted from a rf ion source by applying a plasma chemical reaction. The process has been generalized into a law; it is used in practicing and many metal ions are extracted, such as: Re+, W+, Mo+, Ta+, Pt+, Pd+, Au+, Ag+, Nb+, Ti+, V+, Cr+, Ni+, Fe+, Cu+, Zn+, Ga+, Ge+, Se+, Si+, Al+, Mg+, Be+, Li+, Bi+, In+, Sn+, Pb+, Cd+, etc., and rare-earth ions Y+, Nd+, Ce+, Sm+, Tm+, Dy+, Gd+, Er+, and so on.

Development of large area rf ion sources for fusion applications

A rf ion source with a large extraction area suitable for fusion applications is considered. The source is a metallic magnetic multipole bucket with an internal antenna to couple the rf (at a frequency of 2 MHz) to the plasma. The source is diagnosed by an array of Langmuir probes to measure uniformity, density, and temperature and a small probe accelerator to extract a negative ion beam. A two-turn antenna is found to couple more power into the plasma than a half-turn antenna. When operated as a negative ion source at low powers, the source efficiency is found to be high and not to have a strong dependence on gas pressure. An extracted negative ion current density of about 4 mA/cm2 at 7 mTorr was obtained when 3 kW of power was coupled into the plasma.

Production of mixed metal–gas and pure metal ion beams with an electrodeless rf ion source in the low keV regime

Mixed metal–gas or even pure metal ion beams with current densities in the order of 1 mA cm−2 can be generated by electron beam evaporation of metals into the plasma chamber of an rf ion source operated in electron-cyclotron wave resonance. The operation principle of this novel ion beam source is described, and examples for the production of Ag+ and Cu+ beams with varying fractions of Ar+ ions are presented.

Performance of the rf-ion sources RIM for reactive and nonreactive gases

A family of rf-ion sources for material processing RIM with ionizer diameters between 4 and 15 cm have been developed. Contrary to dc-ion sources, no filaments are needed in rf-discharges. By that, rf-ion sources are excellently suited to operate with reactive (and nonreactive) gases. The performance data of RIM sources for Ar, O2, and N2 are presented. The ion energies can be varied between 25 eV and 2.5 keV. The loss powers (by dissociation, eddy currents, radiation, etc.) have been determined. Probe measurements in the ion beam show the dependency of the beam divergence on the ion energy. Furthermore, ion beam effects (like charge exchange, beam neutralization by admission of electrons at ion energies <500 eV, etc.) were investigated.

The rf-ion source ‘‘PRIS’’ with a metal ionizer chamber and a plasma embedded rf-coupling coil

The family of 10 cm diam ion sources PRIS is built for ion beam processing. It comprises two groups: The high energy version PRIS 10 HE and the low energy version PRIS 10 LE. The conventional rf-ion sources RIM 10 consist mainly of a quartz discharge chamber surrounded from an outside by a rf-induction coupling coil. In some cases, quartz cannot be used for manufacturing the discharge chamber (e.g., fragility of quartz, operating with condensible metal vapor). Therefore, in the PRIS sources, we replaced the quartz ionizer vessel by a metallic discharge chamber and put the rf antenna inside the discharge plasma. The performance data and the ion beam characteristics of PRIS are presented for argon and oxygen.

Study of beam brightness in a radial extraction rf ion source with injected electrons

The use of electron injection into rf plasma of the radial extraction rf ion source improves the beam brightness due to the decrease of electron temperature of the plasma. Also, an emphasis was given to other factors that affect beam brightness such as aberration in the extraction cathode lens and effect of perveance.

Self-aligned broad-beam ion optics

A new type of broad-beam ion optics has been developed. It avoids misalignment of the electrode grids and can be installed without any adjustment procedure. The compact ion optics is a two-electrode system that is aligned by the fabrication process. A ceramic carrier is used as a base plate. The electrodes are deposited as films on both sides of the carrier. This fabrication process ensures that the position of the grids is fixed to each other for the entire life of the ion optics. By this procedure the geometrical factors influencing the beam properties remain constant. The extraction optics were tested in a broad-beam RF-ion source designed for reactive gas operation. The values for the ion currents obtained are comparable to values from conventional multi-aperture ion optics. Ion current densities in the range of 1 mA/cm/sup 2/ could be measured. Beam divergence has been measured and values are similar to those from conventional ion optics. >

A new 3 MeV microprobe system with a liquid-metal ion source

A new 3 MeV microprobe system has been constructed at the Ion Engineering Center Corporation, Osaka, in summer 1990. This system has a gas ion source (rf ion source) and an impregnated-electrode-type liquid-metal ion source, which was developed in Kyoto University, Japan. High-vapor-pressure metals (max. 0.1 Torr at melting point, e.g. Ag, Y, Cu, Au) can be used in this ion source, so various ion species (from H to Au) will be available in this system. The results of calculation of ion beam trajectories show that less then 19 μm beam spot size and 100 pA/smm 2 beam intensity can be obtained for gold ions.

Integrated silicon grid ion extraction system for O2 processes

A novel multibeamlet very low energy ion extraction optic technology avoiding cumbersome grid readjustment and thermal degradation of beam properties during a reactive process has been developed. In this approach anisotropically etched silicon grids ([100]-oriented Si wafers) are permanently integrated into a holder made of layered ceramics or micromachined AlN. The performance of such extraction systems having 300, 600, and 900 μm grid separation was tested in a 3 cm capacitively coupled rf-ion source. Stable system operation with use of oxygen has been achieved for an extended period of time (>100 h) for a total extraction voltage of 140 V which represents the maximum voltage to be applied for a grid separation of 0.3 mm. Additionally detailed Faraday-cup measurements of the extracted ion beam have been carried out for a total voltage range of 0–600 V, a vacuum chamber pressure of 1×10−4–1×10−3 mbar, rf-power levels of 10–170 W, a net-to-total voltage ratio of 0.5–1.0 and an axial magnetic field of up to 22 mT. For O2 an ion current density of 1.3 mA/cm2 could be extracted with ions having a mean energy of 60 eV. Even for energies as low as 50-eV current densities of 0.8 mA/cm2 could be achieved. In combination with the filamentless capacitively coupled rf source used, this approach has promise in various fields of materials research and processing such as ion beam assisted deposition of high-Tc YBaCuO layers and etching/modification of diamondlike, diamond and polymer thin films.

The determination of the geometric parameters of the extraction system in an rf ion source

This paper gives a theoretical calculation, from basic formulae, of the geometric parameters for the extraction system of an rf ion source. Some numerical results from these formulae compared favourably with experimental data, indicating that the theoretical method can be used as a good guide for designing such an extraction system.

A new 3.5 MV single stage accelerator for a nuclear microprobe

Vivirad is now constructing a 3.5 MV single stage machine of a new design based on some of the Vivitron techniques and including some new features. Several porticos of discrete electrodes are part of the main structure assembled as for a tandem. It is driven by a belt which is strongly decoupled from the accelerator part. It is planned to use either a rf ion source or a Penning ion source depending on the ions to be accelerated.

The plasma-chemical reactions of several materials in a rf ion source

The plasma-chemical reactions of several materials are described in this paper. Materials such as quartz and platinum are used for containers of chemical reactions in various fields. Because of their stability chemical reactions do not occur easily, but such reactions can occur within the plasma of a rf ion source, and ion beams of such materials have been extracted from the ion source. This is because of the energetic plasma constituents and the bombardment of material surfaces by these high-energy particles. Various high-temperature chemical reactions can take place in the low-temperature (cool) plasma environment.