Vacuum Arc Ion Source Research Articles

Temporal development of ion beam mean charge state in pulsed vacuum arc ion sources

Vacuum arc ion sources, commonly also known as "Mevva" ion sources, are used to generate intense pulsed metal ion beams. It is known that the mean charge state of the ion beam lies between 1 and 4, depending on cathode material, arc current, arc pulse duration, presence or absence of magnetic field at the cathode, as well as background gas pressure. A characteristic of the vacuum arc ion beam is a significant decrease in ion charge state throughout the pulse. This decrease can be observed up to a few milliseconds, until a "noisy" steady-state value is established. Since the extraction voltage is constant, a decrease in the ion charge state has a proportional impact on the average ion beam energy. This paper presents results of detailed investigations of the influence of arc parameters on the temporal development of the ion beam mean charge state for a wide range of cathode materials. It is shown that for fixed pulse duration, the charge state decrease can be reduced by lower arc current, higher pulse repetition rate, and reduction of the distance between cathode and extraction region. The latter effect may be associated with charge exchange processes in the discharge plasma.

Boron cathodic arc as an ion source for shallow junction ion implantation of boron

For the last ten years, one of the most important topics in the literature for ion implantation of semiconductors has concerned delivery of boron ions at low energies for the 65, 45, and 32nm technologies and beyond. The vacuum arc ion source produces a very strong (2A), fully space-charge compensated plasma of 100% ionized boron single atoms with no gas atoms and few foreign atoms in the plasma. These qualities potentially make delivery of boron for ion implantation rather simple in comparison with competing techniques. Key issues pertaining to possible use of the source in a simple delivery scheme are dealt with experimentally. These issues are macroparticle filtering, impurity content, doubly charged ion content, and implantation results at low energy. Quantitative results for the first two are presented. These results include design strategies and performance of a novel macroparticle filter. Satisfactory performance, as far as multiple charging is concerned, is inferred from the implantation results. That conclusion follows from the fact that secondary-ion-mass spectroscopy profiles in silicon reflect range containment of the B that is as good, or better, than for other techniques. It is further concluded that there are no fundamental obstacles to further advancement of the technology in the doping application. A simple compact prototype front end concept is proposed.

Origin of Ferromagnetism in Co-Ion-Implanted Anatase TiO2 Thin Films

Ferromagnetic Co-doped anatase TiO2 films were prepared by implantation of Co ions into TiO2 thin films using a metal vapor vacuum arc ion source at various beam currents. The saturation magnetization (Ms) of these films increased with annealing temperature. The maximum Ms observed was about 2.3 µB/Co. High-resolution transmission electron microscopy and X-ray photoelectron spectrometry were performed to study the possible origin of the ferromagnetism. It is believed that the high magnetic moment values observed are associated with Co atoms doped to the Ti2+ sites and the intermediate spin state.

COMPARISON OF WEAR RESISTANCE MECHANISMS OF DIE STEEL IMPLANTED WITHCANDMoIONS

Mo and C ions extracted from a metal vapor vacuum arc ion source were implanted into the surface of die steel (H13) to compare the wear resistance mechanisms of the implanted samples, respectively. The concentration depth profiles of implanted ions were measured using Rutherford backscattering spectroscopy and calculated by a code called TRIDYN. The structures of the implanted steel were observed by X-ray photoelectron spectroscopy and grazing-angle X-ray diffraction, respectively. It was found that the conventional heat-treated H13 steel could not be further hardened by the subsequent implanted C ions, and the thickness of the implanted layer was not an important factor for the Mo and C ion implantation to improve the wear resistance of the H13 steel. Mo ion implantation could obviously improve the wear resistance of the steel at an extraction voltage of 48 kV and a dose of 5 × 1017cm-2due to formation of a modification layer of little oxidation with Mo2C in the implanted surface.

Cathodic Vacuum Arc Plasma of Thallium

Thallium arc plasma was investigated in a vacuum arc ion source. As expected from previous considerations of cathode materials in the Periodic Table of Elements, thallium plasma shows leadlike behavior. Its mean ion charge state exceeds 2.0 immediately after arc triggering and diminishes to the predicted 1.60 and 1.45 after about 100 and 150 mus, respectively. The most likely ion velocity is initially 8000 m/s and decays to 6500 and 6200 m/s after 100 and 150 mus, respectively. Both ion charge states and ion velocities decay further toward steady-state values, which are not reached within the 300-mus pulses used here. It is argued that the exceptionally high vapor pressure and charge exchange reactions are associated with the establishment of steady-state ion values

Field emission from gadolinium silicide prepared by ion implantation with electron beam annealing

A silicon-based field emission cathode, the rare earth silicide GdSi2 was prepared by implanting Gd ions into silicon using a metal vapor vacuum arc ion source and subsequently annealed by electron beam. For as-implanted samples, turn-on field was about 21V∕μm at a current density of 1μA∕cm2 and a field emission current density of 1mA∕cm2 was reached at an applied field of 34V∕μm. After annealing, the turn-on field could be as low as 9V∕μm and the current density of 1mA∕cm2 can be reached at an applied field of 14V∕μm. X-ray diffraction with x-ray photoelectron spectroscopy analyses and atomic force microscopy were used to characterize microstructure changes of the samples. The results showed that these excellent field emission characteristics were attributed to the GdSi2 compounds formed in the samples. The field emission mechanism was discussed in terms of Fowler-Nordheim (FN) theory. It was found that FN plots could be divided into two segments obviously, and this was perhaps because of the thermal effect in the process of field emission.

Control of ion charge states in vacuum arc ion source by imposition of a non-uniform magnetic field

The influence of the magnetic field geometry configuration on electron temperature and ion charge state in the vacuum arc ion source has been studied theoretically. It is found that a high value of electron temperature and ionization rate is retained at the exit from the annular anode (where cathodic plasma jet becomes current-free) if a strong magnetic field in the order of 1 T is imposed on this part of jet. It is shown that the maximum value of the mean ion charge can be obtained by imposing on the inter-electrode gap an external magnetic field with the slightly divergent field lines. The divergence angle of the field lines yielding a maximum of ion charge depends on the vacuum arc parameters and usually is in the order of 2–5°.

Surface resistivity tailoring of ceramic insulators for an ion microprobe application

An important technique used for the grading of voltage drop along high voltage ceramic insulators is to provide some surface conduction to bleed off accumulated surface charge. We have used metal ion implantation to modify the surface of high voltage ceramic vacuum insulators to provide a uniform surface resistivity of order 10 10 Ω/square. A vacuum arc ion source based implanter was used to implant Pt at an energy of about 125 keV to a dose of order 10 16 ions/cm 2 into the surface of ceramic rods used to support the ion focusing system of the Columbia University high voltage ion microprobe. Here we describe the experimental set-up used to do the ion implantation and summarize the results of our exploratory work on implantation into test coupons and into the ceramic rods.

Post-annealing effect on the microstructure and photoluminescence properties of the ion beam synthesized FeSi2 precipitates in Si

FeSi2 precipitates with various structural properties embedded within silicon matrix were formed by iron ion implantation using a metal vapor vacuum arc ion source followed by thermal annealing at various conditions. The microstructure and phase properties of the implanted samples were studied by transmission electron microscopy. The orientation relationships and thus the interfacial coherence between the FeSi2 precipitates and the Si matrix were observed to change with the annealing conditions. A good correlation is identified in-between the structural properties and the photoluminescence properties of these samples.

Crystal orientation dependence of ferromagnetism in Fe-implanted MgO single crystals

Single crystals of MgO with (100), (110) and (111) orientations were implanted with 64 keV Fe ions at a dose of 1.9×10 17 ions/cm 2 by using metal-vapor vacuum arc ion source (MEVVA). The magnetic properties were investigated by a superconducting quantum interference device magnetometer and Rutherford backscattering spectrometry (RBS) was used to analyze the Fe concentration and distribution. The presence of Fe nanoparticles in MgO matrix was verified by magnetization measurements. Results show that all the samples behave with ferromagnetism at 5 K and 300 K, and the coercive field, H C , follow well the relation: H C ( 110 ) < H C ( 100 ) < H C ( 111 ) at measured temperatures. The orientation dependence of the coercive field may result from the different distribution of Fe nanoparticle size.

Structures and light emission properties of nanocrystalline FeSi 2/Si formed by ion beam synthesis with a metal vapor vacuum arc ion source

Thin layers of nanocrystalline FeSi 2 embedded in Si structures have been formed by Fe implantation using a metal vapor vacuum arc (MEVVA) ion source under various implantation and thermal annealing conditions. The microstructures were studied in details and correlated with the photoluminescence (PL) properties. It is found that higher lattice coherence between the FeSi 2 nanocrystals and the Si matrix is associated with better light emission efficiency. Multiple-cycle implantation schemes were introduced and it is shown that with appropriate process design the dose quenching effect can be suppressed to achieve light emission enhancement in higher dose samples. De-convolution of the PL spectra into two or three peaks was performed and their temperature and excitation power dependence were analyzed. The analysis results indicate that the 1.55-μm emission really originated from FeSi 2 and that the emission peaks are likely donor- or accepted-level-related. MOS structures with the incorporation of implanted nanocrystalline FeSi 2 were fabricated. Electroluminescence (EL) spectra from these devices showed two peak features of which one peak corresponds to FeSi 2 emission and the other corresponds to enhanced Si band-edge emission. Clear room-temperature EL signals from these device structures were observed. A model is proposed to qualitatively understand the temperature dependence of the EL spectra.

Effects of Annealing on Structural and Magnetic Properties of Cobalt Implanted TiO2 Thin Films

AbstractSince the observation of room-temperature ferromagnetism (RTFM) in Co-doped anatase TiO2 [1], there have been many reports on the study of the magnetic properties of Co-doped TiO2 prepared by various methods with diversified results. The origin of the RTFM in these systems is still a topic of controversy today. In this work, TiO2 thin films were prepared by RF sputtering onto thermally grown oxide layers on Si substrates. Cobalt implantation was performed using a metal vapor vacuum arc (MEVVA) ion source to various doses ranging from 3×1015 cm-2 to 4×1016 cm-2. Post-implantation annealing was performed in a vacuum chamber at various temperatures ranging from 400°C to 700°C for 2 hours and 4 hours. Characterization of these films as-implanted and after thermal annealing under various conditions was performed using Rutherford backscattering spectrometry, energy filtered and high-resolution transmission electron microscopy, x-ray diffractometry, x-ray photoelectron spectroscopy, and vibrating sample magnetometry. The dependence of the magnetic properties on the implantation and annealing conditions were studied in detail. Clear RTFM properties were observed. The saturation magnetic moment per implanted Co atom (MS) seems to increase with increasing dose within the implantation dose range in this study. At a fixed dose, the MS value also shows a generally increasing trend with increasing annealing temperature and annealing time. Quite a number of samples showed MS values exceeding the bulk Co value of 1.69 ìB/Co significantly and the maximum MS value observed is about 3.16 µB/Co. Such high MS values indicate that the RTFM must not come from Co clusters alone. Possible origins of the RTFM properties will be discussed in conjunction with the structural properties.

The composition, phase structure and tribological properties of H13 steel implanted with Mo

Mo ions extracted from a metal vapor vacuum arc ion source were implanted into H13 steel with a high implantation dose of 5 × 1017 cm−2 and a pulsed ion beam flux of about 300 μA cm−2. An optical interference microscopy and pin on disc apparatus investigated the wear and friction characteristics of the steel. The Mo concentration depth profile was measured by using Rutherford backscattering spectroscopy. It was observed by X-ray photoelectron spectroscopy and grazing angle X-ray diffraction that carbide of Mo appeared in the doped region. The concentration depth profile and microstructure analysis could serve to illuminate the wear resistance improvement mechanisms of the Mo implanted steel.

Surface properties and microstructure of implanted TiN films using MEVVA ion source

The PVD–TiN film was implanted with titanium and nitrogen ions and the improvement in surface wear resistance was investigated. Ti ion implantation was done using a metal vapor vacuum arc (MEVVA) ion source with an implantation dose of 2 × 10 16 ions/cm 2 and at an extraction voltage of 48 kV. The wear characteristics of the implanted samples were measured and compared with the performance of the unimplanted one by a pin-on-disc apparatus and an optical interference microscope. The structures of the samples were observed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A dynamic TRIM called as TRIDYN was used to calculate the concentration depth profiles of implanted ions in TiN to investigate wear resistance mechanisms. The results showed that the improved wear resistance of the TiN film was mainly due to forming of nano-order TiN crystal grains in a thick amorphous layer and the decreased local state number of Ti after Ti ion implantation.

CHARACTERIZATION OF SURFACE PROPERTIES AND MICROSTRUCTURE OF PVD-TiN FILMS USING MEVVA ION IMPLANTATION

The PVD- TiN film was implanted with titanium ions and the improvement in surface wear resistance was investigated. Ti ion implantation was done using a metal vapor vacuum arc (MEVVA) ion source with an implantation dose of 2 × 1016 ions/cm2 and at an extraction voltage of 48 kV. The wear characteristics of the implanted zone was measured and compared to the performance of the unimplanted zone by a pin-on-disc apparatus and an optical interference microscope. The structure of the implanted zone and unimplanted one was observed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A dynamic TRIM called TRIDYN was used to calculate the concentration depth profile of implanted Ti in TiN to investigate the profile of multi-charge state ions. The results showed that the improved wear resistance of the TiN film was mainly due to the presence of nano-order TiN crystal grains after Ti ion implantation.

High-current vacuum-arc ion and plasma source “Raduga-5” application to intermetallic phase formation

Phase composition, structural state, and mechanical properties of the ion-doped surface layers of Ni, Ti, and Fe targets with Al and Ti ions implanted into using the metal ion beam and plasma source Raduga 5 have been investigated. The high-intensity mode of implantation allowed us to obtain the ion-doped layers with the thickness exceeding the ion projected range by several orders of magnitude. By the transmission electron microscopy, it has been found that the fine-dispersed equilibrium intermetallic phases (Me3Al, MeAl) and the solid solution of aluminum were formed in the doped Ni, Ti, and Fe surface layers at the depth of up to 2600nm. The maximum dopant concentration reached 75%. It has been shown that the average size of the formed phases was of 70nm. The microhardness of the different target surface layers increased by 1.5–3 times. The wear resistance of the samples did not change within the temperature range of 300–700K.

Modified miniature metal vapor vacuum arc source for the Shanghai electron beam ion trap

A modified miniature metal vapor vacuum arc ion source has been developed for the Shanghai electron beam ion trap. Several kinds of elements have been tested to extract lowly charged ions, such as Fe, Au, Ge, Mo, Ti, Al, and Cu. Besides high enough ion beam current and a short pulse width, we focus on the operation reliability, long term operation, and convenience of use.

ITEP Bernas ion source with additional electron beam

A joint research and development program is underway to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. For the MeV range the investigations were focused on charge-state enhancement for ions generated by the modified Bernas ion sources. Based on the previously successful ITEP experience with the e-metal vapor vacuum arc ion source [e.g., Batalin et al., Rev. Sci. Instrum. 75, 1900 (2004)], the injection of a high-energy electron beam into the Bernas ion source discharge region is expected to enhance the production of high charge states. Presented here are construction details and studies of electron-beam influence on the enhancement of ion-beam charge states generated by the modified Bernas ion source.

High current vacuum-arc ion source for ion implantation and coating deposition technologies

This work is devoted to the development and investigation of a high current ion source based on dc vacuum-arc plasma generation. Extraction and acceleration of ion beams are realized in a repetitively pulsed mode with the pulse repetition rate up to 200 pps, the pulse duration up to 400μs, the accelerating voltage up to 40 kV, and the pulsed ion-beam current up to 2 A. To remove microparticles from the vacuum-arc plasma a straight-line plasma filter is used. Examples of the source use for realization of high-intensity and high-concentration ion implantation regimes including those with formation of doped layers at depths that exceed ion projective range for more than an order of magnitude are presented. At the expense of change in order and intensity of ion and plasma material treatment, the advantage of application of one source for execution of material surface pretreatment and activation regimes, formation of wide transition layers between the substrate and coating, coating deposition, and high-intensity ion mixing using ions of the same type was shown.

Vacuum arc ion sources: recent developments and applications

The vacuum arc ion source has evolved over the past 20 years into a standard laboratory tool for the production of high current beams of metal ions, and is now used in a number of different embodiments at many laboratories around the world. The primary application of this kind of source has evolved to be ion implantation for material surface modification. Another important use is for injection of high current beams of heavy metal ions into the front ends of particle accelerators, and much excellent work has been carried out in recent years in optimizing the source for reliable accelerator application. The source also provides a valuable tool for the investigation of the fundamental plasma physics of vacuum arc plasma discharges. As the use of the source has grown and diversified, at the same time, the ion source performance and operational characteristics have been improved in a variety of different ways also. Here we review the growth and status of vacuum arc ion sources around the world and summarize some of the applications for which the sources have been used.