High Current Metal Ion Source Research Articles

Status of vacuum arc ion sources (invited) (abstract)

Vacuum arc ion sources have been developed and used in a growing number of laboratories around the world. Beams have been produced from most of the solid metals of the periodic table as well as alloys and mixtures, with ion energy up to several hundred keV and beam current up to several A. Typically the source is repetitively pulsed with a pulse length on the order of a millisecond and duty cycle of 1%, and dc operation has been demonstrated also. The main application has evolved for ion implantation, primarily for metallurgical, ceramic, and polymer surface modification (i.e., nonsemiconductor applications), but also for semiconductor implantation in some special cases; the source is also used for heavy ion injection into particle accelerators. This kind of high-current metal ion source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Here the source fundamentals are briefly reviewed and the source performance and beam characteristics summarized. We survey some of the vacuum arc ion source development that has been accomplished over the past decade at many laboratories around the world, applications to which the source has been put, and recent progress in source innovations that has been accomplished by the community.

Deposition of droplet-free films by vacuum arc evaporation-results and applications

A pulsed high current metal ion source that produces a metallic plasma flux was designed and successfully used for film deposition. The plasma flux consists of the fully ionized plasma beam produced by a pulsed high current vacuum arc transported through a curved magnetic duct. Deposition rates of more than ten nm/s were achieved. The deposited layers are free of macroparticles, holes, and pits. Films of about 50 nm thickness have been deposited homogeneously (thickness variation below 5%) on a 4 in substrate after 300 pulses. Repetition rates are adjustable from more than 100 Hz down to a single pulse depending on the acceptable thermal input. Several applications are described in the paper: 1) deposition of hard, amorphous carbon films (diamond like carbon), 2) droplet-free TiN films for advanced applications, 3) transparent Al/sub 2/O/sub 3/ protective coatings, and 4) metallization for microelectronics.

High Current Metal-Ion Source for Activated Deposition

A metal ion source with ion currents up to above 5A has been designed and succesfuly applied for activated deposition. It is based on cathodic vacuum are discharges as it is used for deposition of thin films. Such are generate fully ionized plasma with ions, accelerated to kinetic, energies of some ten eV, the ions striking the substrate with these high energies are able in forme amorphous or nanocrystalline films as e.g. hard amorphous carbon films, hard films of metallic nitrides further, the high energies of the particles prevent island growth so that nonporous and smooth layers will be deposited. However, the main disadvantage of vacuum are vaporization - the particle emission - up to now significantly limited the area of application of this deposition technology. Using magnetic fillers - transport of vacuum are plasmas through curved magnetic field - the particles can be removed completely, but the deposition rate is lowered due to significant losses of plasma (about 75%) in the filter to achieve deposition rates of industrial relevance, a new source of pure metal ions, consisting of a high current pulsed are evaporator combined with a sectioned filter unit was developed and successfully tested. The transport efficiency of 25% is of the same order as with best dc-filters, but due to the high current deposition rate of some ten nm per second can be achieved. The deposited layers are tree from particles, holes and pits. As an example films of about 50 nm have been deposited in some seconds homogeneously (thickness variation below 5%) on a 4 inch substrate. Repetition rates can be adjusted from more than 100 Hz down to single pulses in dependence on the allowed thermal input. The following applications were already processed successfully. 1. Metal ion source for plasme immersed implantation (PIII) an effective way for 3 dimensional implantation of industrial parts 2. Hard, amorphous carbon films with a hardness up to above 70 GPa for hard disk and compact disc depositions as well as protective layer for optics and tools 3. Deposition of dropletfree TiN depositions for advanced applications 4. Transparent layers of Al 2 O 3 with medium hardness for protection of optical elements made from organic glasses 5. Metallic films, as copper for the metallization of microelectronic structures and for high reflecting surfaces.

Vacuum arc ion sources

The vacuum arc is a rich source of highly ionized metal plasma that can be used to make a high current metal ion source. Vacuum arc ion sources have been developed for a range of applications including ion implantation for materials surface modification, particle accelerator injection for fundamental nuclear physics research, and other fundamental and applied purposes. The beam parameters can be attractive, and the source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Beams have been produced from over 50 of the solid metals of the periodic table, with mean ion energy up to several hundred keV and with beam current up to several amperes. Typically the source is repetitively pulsed with pulse length of order a millisecond and duty cycle of order 1%, and operation of a dc embodiment has been demonstrated. Here the source fundamentals and operation are reviewed, the source and beam characteristics summarized, and some applications examined.

Vacuum arc ion sources: Some vacuum arc basics and recent results (invited)

Vacuum arc ion sources have been developed and used in a growing number of laboratories around the world. Primary applications of this high current metal ion source have evolved for metallurgical ion implantation and for accelerator injection. Novel source versions and features have been developed, including an electronically switchable ‘‘partitioned cathode’’ whereby the metal species generated can be switched from pulse to pulse, a combined metal/gaseous source with a long lasting trigger, a low energy (∼1 keV) miniature source version, and a broad beam (50 cm diam extractor) multicathode version. Progress has been made also in characterization and manipulation of the plasma prior to extraction, e.g., in the understanding of the ion charge states produced and the development of macroparticle-removing magnetic filters. Advances in vacuum arc ion source design and operation have been accompanied by a deeper understanding of plasma production in vacuum arc cathode spots, and several features of vacuum arc ion sources can be explained by the specifics of ion formation within the spots. Here we present a short overview of some fundamental vacuum arc processes and examine some of the recent developments in vacuum arc ion source design and application.

Vacuum arc ion sources for particle accelerators and ion implantation

The vacuum arc is a generator of highly ionized metal plasma. This method of plasma production can be used to construct a high-current metal ion source. A succession of such metal-vapor vacuum arc ion sources has been developed at Berkeley. Beams from 50 of the solid metals of the periodic table have been produced with mean ion energy up to several hundred keV, and with pulsed beam currents in the ampere range. Typically the source is repetitively pulsed with a pulse length of 250 mu s and a duty cycle of the order of 1%. A DC embodiment from which a large-area titanium beam with steady-state ion current of 600 mA was produced has been tested. A 50-cm-diameter set of beam formation grids has been used to form a beam of area 1000 cm/sup 2/ at an energy of 100 keV and a pulsed beam current of approximately 10 A. The source can also be seen as a tool for the study of vacuum arc plasmas. Vacuum arc ion charge state distributions have been studied in this way. The general features and performance characteristics of the sources and their use for accelerator injection and ion implantation applications are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Extraction characteristics of a high current metal ion source

A metal ion source has been developed for extracting high current ion beams of high melting point metals. In the discharge chamber, metal vapor was confined in high-temperature shields, and the pure metal plasma was produced by the arc discharge. In order to prevent the vapor deposits, the extraction electrodes were also required to be high temperature. Thus, multislit electrodes were improved to maintain fine beam optics even if they were heated. To investigate the metal ion extraction characteristics, Al ion beams were extracted and compared with Ar ion beams. Furthermore, high current Al, Cr, Si, and Ti ion beams were extracted, and the extracted current ≳100 mA was obtained for each metal.

Formation of iridium silicide layer by high dose iridium ion implantation into silicon

We have investigated the formation of IrSi 3 layers buried in (111) silicon. The layers are formed by iridium ion implantation at room temperature using a metal vapor vacuum arc (MEVVA) high current metal ion source with an average beam energy ≈ 130 keV. Doses of the Ir ions ranging from 2 × 10 16 to 1.5×10 17/cm 2 Were implanted into (111) Si. We have successfully formed a buried silicide layer in silicon by room temperature implantation and annealing. The formation of IrSi 3 phase is realized after annealing at temperatures as low as 500°C. A continuous IrSi 3 layer of ≈ 200 Å thick buried under ≈ 400 Å of Si was achieved with samples implanted with doses not less than 3.5 × 10 16/cm 2. Implanted doses above 8 × 10 16cm 2 resulted in the formation of an IrSi 3 layer on the surface due to excessive sputtering of Si by the Ir ions. The effects of implant dose on the phase formation mechanism, the interface morphology and the implanted atom redistribution are discussed. Radiation damage and regrowth of the Si due to the implantation process was also studied.

Milliampere metal ion beam formation using multipoint emission by an impregnated-electrode-type liquid-metal ion source

Intense metal ion beams are required in advanced materials science in which the kinetic energy and the potential energy should be controlled. In the present study, intense metal ion beams were formed using multipoint emission by a high-intensity impregnatedelectrode-type liquid-metal ion source. New ion sources with respectively five and eight emission points were developed and their characteristics were examined with germanium and gold as source materials. As a result, it was shown that an ion current proportional to the number of cusps of the emitter tip could be obtained by multipoint emission. A maximum germanium ion current of more than 4 mA was obtained with the eight-point emission source. The multipoint emission of the impregnated-electrode-type liquid-metal ion source proved to be a potential method for developing a high-current metal ion source.

Charge state distribution studies of the metal vapor vacuum arc ion source

We have studied the charge state distribution of the ion beam produced by the MEVVA (metal vapor vacuum arc) high current metal ion source. Beams produced from a wide range of cathode materials have been examined and the charge state distributions have been measured as a function of many operational parameters. In this article we review the charge state data we have accumulated, with particular emphasis on the time history of the distribution throughout the arc current pulse duration. We find that, in general, the spectra remain quite constant throughout most of the beam pulse, as long as the arc current is constant. There is an interesting early-time transient behavior when the arc is first initiated and the arc current is still rising, during which time the ion charge states produced are observed to be significantly higher than during the steady current region that follows.

Broad-beam multi-ampere metal ion source

An embodiment of the MEVVA (metal vapor vacuum arc) high current metal ion source has been developed in which the beam is formed from a 10-cm-diam set of extractor grids and which produces a peak beam current of up to several amperes. The source, MEVVA V, operates in a pulsed mode with a pulsewidth, at present, of 0.25 ms and a repetition rate of up to several tens of pulses per second (power supply limited). The multi-cathode feature that was developed for the prior source version, MEVVA IV, has been incorporated here also; one can switch among any of 18 separate cathodes and thus metallic beam species. Maximum beam extraction voltage is over 90 kV, and since the ion charge states are typically from Q=1 to 5, depending on the metal employed, the ion energy in the extracted beam can thus be up to several hundred keV. This source is a new addition to the MEVVA family of metal ion sources, and we are at present investigating the operational regimes and the limits to the source performance. In this article we describe the source, and present some preliminary results.

Multiply charged metal ion beams

The metal vapor vacuum arc is a prolific generator of highly ionized metal plasma in which the ions are in general multiply stripped. We have utilized this plasma production mechanism to make a high current metal ion source. The metal vapor vacuum arc ion source is thus a laboratory tool for providing high quality, high current beams of a wide range of metal ion species. Charge state spectra have been measured using a time-of-flight diagnostic. In this paper we review the ion source development program, describe the various embodiments of the concept that have been made, and summarize those experimental results relating to the ion charge states that can be produced.

High current metal ion beam transport in the UNILAC injector at GSI

Transport of high current beams of metal ions through the injector beam line of the heavy ion linear accelerator, UNILAC, has been demonstrated using the MEVVA high current metal ion source. Improved operation of the MEVVA source has been achieved in various ways, including shot-to-shot reproducibility of the beam pulse, beam noise, pulse shape, and absence of “missing” pulses. The source was first tested on a high current test stand beam line, and then moved over to regularly used UNILAC injector terminal. Flat and reproducible titanium ion beam pulses were efficiently transported through the system from the ion source to the Wideroe preaccelerator entrance. A beam current of 20 mA (pulse current) of titanium (all charge states, q = 1, 2, 3) was accelerated to an energy of 280 Q keV through the single-gap accelerating structure, and a current of over 5 mA of Ti 2+ was measured at the Wideroe entrance 13 m downstream.

Ion Beam Modification of the Y-Ba-Cu-O System with the Mevva High Current Metal Ion Source

AbstractWe have used high-dose metal ion implantation to ‘fine tune’ the composition of Y-Ba- Cu-O thin films. The films were prepared by either of two rf sputtering systems. One system uses three modified Varian S-guns capable of sputtering various metal powder targets; the other uses reactive rf magnetron sputtering from a single mixed-oxide stoichiometric solid target. Film thickness was typically in the range 2000–5000 A. Substrates of magnesium oxide, zirconia-buffered silicon, and strontium titanate have been used. Ion implantation was carried out using a metal vapor vacuum arc (MEVVA) high current metal ion source. Beam energy was 100–200 keV, average beam current about 1 mA, and dose up to about 1017 ions/cm2. Samples were annealed at 800 – 900°C in wet oxygen. Film composition was determined using Rutherford Backscattering Spectrometry (RBS), and the resistivity versus temperature curves were obtained using a four-point probe method. We find that the zero-resistance temperature can be greatly increased after implantation and reannealing, and that the ion beam modification technique described here provides a powerful means for optimizing the thin film superconducting properties.

Formation of Buried Iridium Silicide Layer in Silicon by High Dose Iridium Ion Implantation

AbstractWe have investigated the formation of IrSi3 layers buried in &lt;111&gt; silicon. The layers are formed by iridium ion implantation using a metal vapor vacuum arc (MEVVA) high current metal ion source at room temperature with average beam energy = 130 keV. Doses of the Ir ions ranging from 2×1016 to 1.5×1017/cm2 were implanted into &lt;111&gt; Si. The formation of IrSi3 phase is realized after annealing at temperatures as low as 500°C. A continuous IrSi3 layer of =200 Å thick buried under =400 Å Si was achieved with samples implanted with doses not less than 3.5×1016/cm2. Implantated doses above 8×1016/cm2 resulted in the formation of an IrSi3 layer on the surface due to excessive sputtering of Si by the TI ions. The effects of implant dose on phase formation, interface morphology and implanted atom redistribution are discussed. Radiation damage and regrowth of Si due to the implantation process was also studied.

Multiply stripped ion generation in the metal vapor vacuum arc

We consider the charge state distribution of ions produced in the metal vapor vacuum arc plasma discharge. A new kind of high current metal ion source in which the ion beam is extracted from a metal vapor vacuum arc plasma has been used to obtain the spectra of multiply charged ions produced within the cathode spots. The cathode materials used and the species reported on here are: C, Mg, Al, Si, Ti, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, In, Sn, Gd, Ho, Ta, W, Pt, Au, Pb, Th, and U; the arc current was 200 A for all measurements. Charge state spectra were measured using a time-of-flight method. In this paper we report on the measured charge state distributions and arc voltages and compare the distributions with the predictions of a theory in which ionization occurs in the cathode spots via stepwise ionization by electron impact.

Applications of the MEVVA high current metal ion source

A new kind of ion source has been developed in which a MEtal Vapor Vacuum Arc (MEVVA) is used to produce the plasma from which the ion beam is extracted. The novel and exciting feture of this source is the very high metal ion beam current attainable. A total ion beam current of over 1 Ae has been extracted from the embodiment of the concept that we are presently using, and this is not a limit of the method. The source was developed to upgrade the uranium ion beam intensity of the Bevatron, LBL's heavy ion synchrotron, for basic nuclear physics research. Other important applications include its use within the Heavy Ion Fusion research effort; for ion implantation; and for other basic research uses. In this paper the source is described briefly, its performance outlined, and its potential and limitations for a variety of applications is discussed.