Metal Vapor Vacuum Arc Ion Source Research Articles

Ion angular distribution in plasma of vacuum arc ion source with composite cathode and elevated gas pressure

The Metal Vapor Vacuum Arc (MEVVA) ion sources are capable of generating ion beams of almost all metals of the periodic table. For this kind of ion source, a combination of gas feeding with magnetic field allows the simultaneous generation of both metal and gaseous ions. That makes the MEVVA ion source an excellent instrument for science and application. This work presents results of investigation for ion angular distributions in vacuum arc plasma of Mevva-V.Ru ion source for composite cathodes and for elevated gas pressure. It was shown that for all the cathode materials, singly charged ions have wider angular distribution than multiply charged ions. Increasing the working gas pressure leads to a significant change in the angular distribution of gaseous ions, while with the distribution of metal ions gas remains practically unchanged. The reasons for such different influences are discussed.

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.

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.

Modification of surface mechanical properties of aluminum by high current Mo ion implantation using a MEVVA ion source

The surface modification of Al by high current Mo ion implantation using a metal vapor vacuum arc (MEVVA) ion source has been studied. A high aluminum content intermetallic compound Al 12 Mo was formed using Mo ion implantation into Al with a current density of 64 μA/cm 2 (the temperature of the sample rises to ∼410 °C ) to a dose of 3×10 17 ions/cm 2 The hardening aluminide layer with a thickness of about 1600 nm was obtained and the hardness of the Al surface increased with increasing the Mo ion dose up to six times larger than that of the unimplanted one. Also, the elastic modulus of the Al surface was increased by the aluminides.

Enhancement of ion beam charge states by adding a second anode to the metal-vapor vacuum-arc ion source

We report detailed investigations of ion charge state enhancement in an alternative metal-vapor-vacuum arc ion source configuration, consisting of two anodes with staggered (but partially overlapping) high current discharges in axial high magnetic field gradients. The experiments demonstrated that driving an additional current in a vacuum arc in a magnetic mirror configuration resulted in substantial ion charge state enhancement. Maximum ion charge states of Pb 6+ and U 8+ were extracted. Results are presented for high charge state uranium beam generation and acceleration in the 27 MHz heavy-ion RFQ LINAC TIPr-1.

Electrical transport properties of NiSi2 layers synthesized by metal vapor vacuum-arc ion implantation: Temperature dependence and two-band model

Nickel disilicide (NiSi2) layers were synthesized by nickel ion implantation into silicon substrates using a metal vapor vacuum-arc ion source. The electrical transport properties were studied before and after annealing using sheet resistivity and Hall effect measurements from 30 to 400 K, and the results showed surprising features very different from those generally reported NiSi2 layers. The temperature dependence of sheet resistivity Rs(T) and Hall mobility μH(T) in the as-implanted samples showed peculiar peak and valley features varying from sample to sample, depending on the preparation conditions. However, after annealing, the differences between samples seemed to have diminished in that they all showed similar shapes in both the Rs(T) and the μH(T) curves. A two-band model was proposed to explain the observed electrical transport properties.

Increase in the Charge State of the Uranium Ion Beam Generated by the MEVVA Ion Source

The Metal Vapor Vacuum Arc (MEVVA) ion source and its modifications are investigated at the Institute of Theoretical and Experimental Physics (ITEP). In a series of the experiments, the possibility of increasing the charge state of the generated uranium ion beam was revealed. The charge state increases as a result of developing a high-current vapor vacuum arc discharge from the source cathode to an auxiliary anode located in an increasing axial magnetic field. The uranium ion beam with a total current of 150 mA was obtained, U7+ uranium ions being 10% of the current.

Magnetic properties of nanoclusters formed by implantation of Fe into Ge using a metal-vapor vacuum arc ion source

The magnetic properties of Fe ions implanted into a germanium crystal by metal-vapor vacuum arc ion source were investigated using a Quantum Design SQUID magnetometer. The presence of Fe nanoclusters in Ge was verified by magnetization measurements. A Langevin fit was used to obtain the size distribution of the clusters. The results demonstrated that the clusters are magnetic. The magnetic behavior of the clusters was characterized by zero-field-cooled and field-cooled measurements for temperatures 4.2 to 300 K. The implanted layer with magnetic clusters shows negative magnetoresistance with a positive magnetoresistance background due to the Ge substrate for parallel magnetic-field geometry at temperatures 180 to 300 K. The negative magnetoresistance is found to become dominant with decrease of temperature. The negative magnetoresistance is attributed to the existence of magnetic clusters in the implanted layer.

PREPARATION AND INFRARED ABSORPTION PROPERTIES OF BURIED SiC LAYERS

Buried SiC layers were formed by using a metal vapor vacuum arc (MEVVA) ion source,with C＋ ions implanted into Si substrates under different doses.In the present study, the extracted voltage was 50kV and the ion dose was varied from 3.0×1017—1.6×1018cｍ-2.According to infrared absorption measurements,it was found that the structure of the buried SiC layers depended on the ion dose.Moreover,the results also demonstrated that the buried SiC layers including cubic crystalline SiC could be synthesized at an averaged substrate temperature of lower than 400℃ with the MEVVA ion source.

Formation of Ti silicides by metal-vapor vacuum arc ion source implantation

Metal-vapor vacuum arc ion source was employed to synthesize Ti silicides by Ti implantation directly into Si or through a deposited titanium film on Si wafers. The implantation was conducted at room temperature at an extracted voltage of 40 kV. In the directly implanted Si wafers, the transition of Ti disilicides from a metastable C49-TiSi2 to an equilibrium phase C54-TiSi2 was observed when the current density was of 125 μA/cm2 at a nominal dose range of 3–5×1017/cm2, while in the Si wafers with a deposited Ti film, C54-TiSi2 was formed when the current density was of 125 μA/cm2 at a fixed nominal dose of 5×1017/cm2. The temperature rise caused by ion implantation was calculated by solving a differential thermal conduction equation and the results were employed to discuss the formation mechanism of Ti silicides.

MEVVA ion source for the ITEP synchrotron

A MEVVA (metal vapor vacuum arc) ion source has been made and tested at the Institute of Theoretical and Experimental Physics (ITEP), Moscow. The ions are created in the plasma formed from the cathode metal vapor of a vacuum arc discharge. An ion beam current of about 200–400 mA in repetitively triggered pulses of width 0.1 ms has been obtained. The ion charge state distributions have been measured for seven elements (Be,C,Al,Fe,Cu,Zr,W) and they are in reasonable agreement with results of other workers. The MEVVA ion source is simple to operate and has a reliability acceptable for use as an ion source for ITEP synchrotron injection.

The Beijing metal vapor vacuum arc ion source program

Work on metal vapor vacuum arc (MEVVA) ion source development was initiated at the Institute of Low Energy Nuclear Physics, Beijing Normal University, in 1988. MEVVA ion sources I, II, IIA, and III have been designed, fabricated, and tested, and an ion implantation facility with three MEVVA ion sources has been developed and is now undergoing testing. Here the status of the MEVVA ion source research and development program is described.

Development of MEVVA ion source

Research results of the metal vapor vacuum arc (MEVVA) ion source are reported in this paper. As cathode materials, for example, Al, Ti, Fe, and Cu are used, respectively. A triggering pulse with a pulse height of 12 kV, pulse length of 90 μs, and repetition rate of 1–5 pulses/s is applied between the trigger electrode and the cathode. The pulse duration of the extracted ion beam is 800 μs. When the extraction voltage is 28 kV, the extracted beam current intensity for Al, Ti, Fe, and Cu is 255, 290, 240, and 300 mA, respectively.

Compaction, distribution, and chemical bonding of tungsten-implanted glassy carbon

The composition, distribution, and chemical bonding of tungsten-implanted glassy carbon have been studied for ion doses between 3.5×1014 and 1.5×1017 ions/cm2. The implantations were performed using a metal-vapor vacuum arc ion source which for an extraction potential of 20 kV yields a mean implant energy of 60 keV. The implanted layer was examined by Rutherford backscattering spectrometry and Auger profiling spectroscopy. In addition, volume effects were assessed by measuring the step height between implanted and unimplanted regions. It has been established that the implanted tungsten is bonded in a carbidic configuration. This is in agreement with thermodynamic data which favors carbide formation rather than separate phases of metallic tungsten and graphitic carbon. For the highest dose studied, 1.5×1017 ions/cm2, the tungsten distribution was found to be nearly constant near the surface followed by a decrease at larger depths. For ion doses up to 3.6×1016 ions/cm2, the maximum tungsten distribution was found to occur at a depth 300±100 Å and the implanted and retained doses were found to be equal. For tungsten ion doses between 7.35×1014 and 1×1016 ions/cm2, the implanted region was found to be compacted by 300±100 Å. The latter is attributed to an irradiation-induced densification of glassy carbon from 1.5 to 2.1 g/cm3. This compaction effect is also found to occur upon C+ (30 keV) implantation for ion doses between 3×1016 and 1.3×1017 ions/cm2. In this case the implanted layer was compacted by 400±100 Å. For higher tungsten doses, a steep increase in compaction of the tungsten implanted layer was observed. This is attributed to chemical and sputtering effects.

Metal vapor vacuum arc ion implantation for seeding of electroless Cu plating

A metal vapor vacuum arc (MEVVA) ion source has been used to implant Pd into SiO 2 substrates. The ion implanted area formed a seeding layer on which a Cu film was successfully plated through an electroless plating process. It was found that the required Pd dose for Cu plating to occur is on the order of 3×10 15 cm −2 when the implantation was performed with a 20 kV extraction voltage. Taking advantage of the large pulsed ion current capability (up to 1 A) of the MEVVA ion source, the needed Pd dose for seeding was achieved in minutes. With direct Pd implantation, an intermediate activation step using PdCl 2 solution can be eliminated. The Cu plating rate was not a sensitive function of temperature and no incubation period was found in our experiments.

A broad-beam, high-current metal-ion implantation facility

We have developed a high-current metal-ion implantation facility with which high-current beams of virtually all the solid metals of the periodic table can be produced. The facility makes use of a metal-vapor vacuum-arc ion source which is operated in a pulsed mode, with 0.25 ms pulse width and a repetition rate up to 100 pps. Beam extraction voltage is up to 100 kV, corresponding to an ion energy of up to several hundred keV because of the ion charge-state multiplicity; beam current is up to several amperes peak and around 10 mA time-averaged delivered onto target. Implantation is done in a broad-beam mode, with a direct line-of-sight from ion source to target. Here we describe the facility and some of the implants that have been carried out using it, including the “seeding” of silicon wafers prior to CVD with titanium, palladium or tungsten, the formation of buried iridium silicide layers, and actinide (uranium and thorium) doping of III–V compounds.

Ion spectra of the metal vapor vacuum arc ion source with compound and alloy cathodes

In metal vapor vacuum arc (MEVVA) ion sources, vacuum arc plasma with cathodes of single, pure elements has been utilized for the production of metal ions. In this study, we have investigated the charge state distributions of ions produced in vacuum arc plasmas in a MEVVA ion source for the case when the cathode is an alloy or a compound material. The ion charge state spectra were analyzed by means of a time-of-flight apparatus. We have compared the ion spectra for a cathode of an alloy or a compound material with its constituent elements: TiC/TiN/TiO2/Ti/C, SiC/Si/C, WC/W/C U/UN/(UN-ZrC)/Zr/C, and brass/Zn/Cu. We find that the MEVVA produces ions of all constituent elements in the compound and the alloy cathodes. The charge state distribution of each element differs, however, from the charge state distribution obtained in the vacuum arc with a cathode made of the pure, single constituent element. Fractional values of the total ion numbers of each constituent element in the extracted beam depart from the stoichiometry of the elements in the cathode material. In an operation with a TiC cathode, we irradiated a 304 stainless-steel plate with the extracted beam. Results from glow-discharge spectroscopy (GDS) of the surface show that both titanium and carbon are implanted in the substrate after the irradiation.

Advances in metal ion sources

Beams of metallic ion species can be produced by the ECR (electron cyclotron resonance) ion source and by the MEVVA (metal vapor vacuum arc) ion source. Although the ECR source is fundamentally a gaseous ion source, metal ion beams can be produced by introducing metallic feed material into the plasma discharge using a number of techniques. The ion charge states can be very high, which is a significant advantage to most applications. The MEVVA ion source, on the other hand, is specifically a metal ion source. It has produced metallic ion beams from virtually all the solid metallic elements at a current of typically hundreds of milliamperes; the ions produced are in general multiply ionized, but not as highly stripped as those generated in the ECR source. Although the MEVVA source at present operates in a pulsed mode with a low duty cycle ( ≤ 1%), work is in progress to increase the duty cycle significantly. In this paper the operation and performance of the LBL ECR and MEVVA ion sources, with respect to metal ion generation, are described.

On the Current Intensity Limit of a Vacuum-Arc Ion Source

The maximum ion current that can be extracted as a high-energy beam from a metal-vapor vacuum-arc ion source is considered. Results are presented of measurements of the plasma ion current in the metal-vapor vacuum-arc II (MEVVA II) ion source. It is shown that this source is an efficient generator of metal ions, an intense flux of which is efficiently transported to the beam extractor. The maximum metal-ion current that is available for extraction at the extractor location is 5 percent of the arc current. The limitation to the intensity of the metal-ion beam that can be produced by this kind of ion source is found to be in the extractor design.

The MEVVA ion source for high current metal ion implantation

The MEVVA (Metal Vapor Vacuum Arc) ion source is a new kind of source which can produce high current beams of metal ions. Beams of a wide range of elements have been produced, spanning the periodic table from lithium up to and including uranium. The source extraction voltage is up to 60 kV, and we are increasing this up to 120 kV. A total ion beam current of over 1 A has been extracted from the present embodiment of the concept, and this is not an inherent limit. The ion charge state distribution varies with cathode material and are current, and beams like Li +, Co +.2+.3+ and U 3+.4+.5+.6+ for example, are typical; thus the implantation energy can be up to several hundred kV without additional acceleration. The ion source has potential applications for ion implantation and ion beam mixing for achievement of improved corrosion resistance or wear resistance in metals or surface modification of ceramic materials and semiconductors. Here we outline the source and its performance, and describe some very preliminary implantation work using this source.