High intensity proton source based on a hollow-cathode reflex discharge.

We describe here the electrode system, design, and parameters of an ion source based on a Penning-type hollow-cathode reflex discharge developed for generation of proton beams. Especially for proton beam generation, a modified geometry of both hollow and reflex cathodes was fabricated. The working gas is molecular hydrogen. Ion extraction and beam formation are performed using a three-electrode single-aperture optical system with a 3-mm diameter emission aperture. At an accelerating voltage of 33-35 kV and a discharge current of 0.55 A in continuous mode, the ion beam current was 15-17 mA, and in pulsed mode, at a discharge current of about 2 A, the beam current was 55 mA. The beam consists mainly of H+, H2+, and H3+ ions, with the proton (H+) fraction up to 27% in continuous mode and 40% in pulsed mode.

Forevacuum plasma-cathode electron source for generation of a ribbon beam over a wide pressure range.

We describe the results of our investigations of the generation of a ribbon electron beam (10 × 220 mm2) by a two-stage discharge system based on a hollow-cathode glow discharge plasma. The source design enables operation in the pressure range 2 × 10-2 to 10 Pa. At a beam accelerating voltage of 8 kV, the beam current is 450 mA at a pressure of 2 × 10-2 Pa and 150 mA at a pressure of 10 Pa. To achieve a uniform current density distribution of the beam over its cross-sectional area, a special design of emission electrode was employed. This enabled us to reduce non-uniformities of the beam current density distribution to a level of 10%.

Ion beam composition in ion source based on magnetron sputtering discharge at extremely low working pressure.

In an ion source based on a pulsed planar magnetron sputtering discharge with gas (argon) feed, the fraction of metal ions in the ion beam decreases with decreasing gas pressure, down to the minimum possible working pressure of the magnetron sputtering discharge. The use of a supplementary vacuum arc plasma injector provides stable operation of the pulsed magnetron sputtering discharge at extremely low pressure and without gas feed. Under these conditions, the pressure dependence of the gaseous ion fraction displays a maximum (is nonmonotonic).

Broad-beam plasma-cathode electron beam source based on a cathodic arc for beam generation over a wide pulse-width range.

We describe the design, parameters, and characteristics of a modified wide-aperture, plasma-cathode electron beam source operating in the pressure range of 3 Pa-30 Pa and generating large-radius, low-energy (up to 10 keV) electron beams with a pulse width varying from 0.05 ms to 20 ms and a beam current up to several tens of amperes. A pulsed cathodic arc is used to generate the emission plasma, and a DC accelerating voltage is used to form the electron beam. Modernization of the design and optimization of the operating conditions of the electron source have provided a multiple increase in the pulse duration of the electron beam current and the corresponding increase in the beam energy per pulse, as compared to previously developed pulsed forevacuum electron sources.

Plasma electron source for generating a ribbon beam in the forevacuum pressure range.

We describe a plasma-cathode electron beam source based on a hollow cathode glow discharge and operating in the forevacuum pressure range that produces a steady-state ribbon beam. The electron beam is generated in the pressure range of 10-30 Pa. A multi-aperture electron extraction and beam formation system is used to provide beam stability and enhanced uniformity of beam current density, allowing the use of this kind of device for beam-plasma surface modification over relatively large areas.

Pulsed vacuum arc plasma source of supersonic metal ion flow.

Supersonic plasma flows with densities of 1013-1016 cm-3 find application in various fields of physics and technology such as surface modification, simulation of plasma impact in fusion facilities, and laboratory studies of space phenomena. The work outlined here describes a pulsed vacuum arc source of supersonic dense metal plasma flow. The design, working principle, features of the power supply circuit, and main parameters of the plasma source in relation to the parameter of the vacuum arc pulse are discussed. Flows of ionized aluminum, copper, tantalum, and molybdenum were investigated. At a vacuum arc current amplitude of 25 kA, the source generated a plasma with a density of 3 × 1015 cm-3. The ion velocity in the plasma flow and the ion charge state composition were measured. For an aluminum cathode, we have carried out measurements of the macroparticle fraction and the erosion rate. This supersonic metal ion plasma flow source is primarily designed for studying the flow interaction with an inhomogeneous magnetic field, with simultaneous application of electron cyclotron resonance irradiation from high-power pulsed gyrotrons, but may also find other applications.

Forevacuum-pressure plasma-cathode high-power continuous electron beam source.

We describe a plasma-cathode electron beam source based on a hollow-cathode discharge that is capable of generating a 9 kW dc electron beam at an accelerating voltage of 20 kV, with helium as a working gas at a pressure of 30 Pa. A test run of ∼50 operational hours did not indicate any significant degradation of the electron source extraction system or other structural components, and we estimate the operational lifetime of the source at about 100-120 h.

Double-coil magnetic focusing of the electron beam generated by a plasma-cathode electron source.

We present the results of our investigations of magnetic focusing of the electron beam generated by a plasma-cathode electron source in the forevacuum pressure range (10-30 Pa). We show that a magnetic double-focusing system employing two separate field coils with the main magnetic coil located close to the beam collector at the focal plane provides effective and efficient focusing of the electron beam. With our e-beam source, this focusing system produces a power density of more than 1 MW/cm2 at the electron beam focus with an accelerating voltage of 30 kV and a beam current up to 60 mA. For comparison, the maximum beam power density provided by plasma-cathode electron sources at pressures of less than 0.1 Pa is at the level of 10 MW/cm2.

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.

Generation of space charge compensated low energy ion flux.

The results of an experimental study of low-energy (<200 eV) ion flux generation with space charge neutralization are presented. Argon was used as a working gas. The working gas pressure in the vacuum chamber was 2-4 x 10(-2) Pa. Ion beam was extracted from the hollow cathode of main discharge plasma by a single mesh extractor with subsequent deceleration of ions to a required energy in a layer between the mesh and the beam plasma. The ion beam current was measured on the collector located on the distance of 30-60 cm from the discharge system. The penetration of electron component from the main discharge plasma through the mesh into the region of the ion beam drift space was realized by potential barrier reduction, in conditions of the optimal extractor potential with respect to the hollow cathode. The space charge neutralization of low-energy ion beam resulted in drift space plasma potential reduction and ion beam current growth. At the main discharge current of 1 A and main discharge voltage of 300 V, the ion beam current of up to 100 mA with the ion energy of 50-150 eV was obtained.

Side extraction duoPIGatron-type ion source.

We have designed and constructed a compact duoPIGatron-type ion source, for possible use in ion implanters, in which ions are extracted from a side aperture in contrast to conventional duoPIGatron sources with axial ion extraction. The size of the side extraction aperture is 1 x 40 mm(2). The ion source was developed to study physical and technological aspects relevant to an industrial ion source. The side extraction duoPIGatron has a stable arc, uniformly bright illumination, and dense plasma. The present work describes some operating parameters of the ion source using argon and BF(3). Total unanalyzed beam currents were 40 mA with Ar at an arc current of 7 A and 13 mA with BF(3) gas at an arc current of 9 A.

Experimental comparison of time-of-flight mass analysis with magnetic mass analysis.

A series of experiments was carried out in which both a magnetic analyzer (mass separator) and a time-of-flight (TOF) spectrometer were used for ion charge/mass spectral analysis of the ion beam formed by a dc Bernas ion source made for semiconductor implantation. The TOF analyzer was a detachable device that provides rapid analysis of charge-to-mass composition of moderate energy ion beams. The magnetic analyzer was a massive device using a 90 degrees -sector bending magnet with radius of the central orbit of 35 cm. Comparison of these two methods for measuring ion beam composition shows good agreement.

Inverted end-Hall-type low-energy high-current gaseous ion source.

A novel approach to low-energy, high-current, gaseous ion beam generation was explored and an ion source based on this technique has been developed. The source utilizes a dc high-current (up to 20 A) gaseous discharge with electron injection into the region of ion generation. Compared to the conventional end-Hall ion source, the locations of the discharge anode and cathode are inverted: the cathode is placed inside the source and the anode outside, and correspondingly, the discharge current is in the opposite direction. The discharge operates in a diverging axial magnetic field, similar to the end-Hall source. Electron generation and injection is accomplished by using an additional arc discharge with a "cold" (filamentless) hollow cathode. Low plasma contamination is achieved by using a low discharge voltage (avoidance of sputtering), as well as by a special geometric configuration of the emitter discharge electrodes, thereby filtering (removing) the erosion products stemming from the emitter cathode. The device produces a dc ion flow with energy below 20 eV and current up to 2.5 A onto a collector of 500 cm(2) at 25 cm from the source edge, at a pressure > or =0.02 Pa and gas flow rate > or =14 SCCM. The ion energy spread is 2 to 3 eV (rms). The source is characterized by high reliability, low maintenance, and long lifetime. The beam contains less than 0.1% of metallic ions. The specific electric energy consumption is 400 eV per ion registered at the collector. The source operates with noble gases, nitrogen, oxygen, and hydrocarbons. Utilizing biasing, it can be used for plasma sputtering, etching, and other ion technologies.

High current multicharged metal ion source using high power gyrotron heating of vacuum arc plasma.

A high current, multi charged, metal ion source using electron heating of vacuum arc plasma by high power gyrotron radiation has been developed. The plasma is confined in a simple mirror trap with peak magnetic field in the plug up to 2.5 T, mirror ratio of 3-5, and length variable from 15 to 20 cm. Plasma formed by a cathodic vacuum arc is injected into the trap either (i) axially using a compact vacuum arc plasma gun located on axis outside the mirror trap region or (ii) radially using four plasma guns surrounding the trap at midplane. Microwave heating of the mirror-confined, vacuum arc plasma is accomplished by gyrotron microwave radiation of frequency 75 GHz, power up to 200 kW, and pulse duration up to 150 micros, leading to additional stripping of metal ions by electron impact. Pulsed beams of platinum ions with charge state up to 10+, a mean charge state over 6+, and total (all charge states) beam current of a few hundred milliamperes have been formed.

Bernas ion source discharge simulation.

As the technology and applications continue to grow up, the development of plasma and ion sources with clearly specified characteristic is required. Therefore comprehensive numerical studies at the project stage are the key point for ion implantation source manufacturing (especially for low energy implantation). Recently the most commonly encountered numerical approach is the Monte Carlo particle-in-cell (MCPIC) method also known as particle-in-cell method with Monte Carlo collisions. In ITEP the 2D3V numerical code PICSIS-2D realizing MCPIC method was developed in the framework of the joint research program. We present first results of the simulation for several materials interested in semiconductors. These results are compared with experimental data obtained at the ITEP ion source test bench.

Status of ITEP decaborane ion source program.

The joint research and development program is continued to develop steady-state ion source of decaborane beam for ion implantation industry. Both Freeman and Bernas ion sources for decaborane ion beam generation were investigated. Decaborane negative ion beam as well as positive ion beam were generated and delivered to the output of mass separator. Experimental results obtained in ITEP are presented.

Ion sources for energy extremes of ion implantation.

For the past four years a joint research and development effort designed to develop steady state, intense ion sources has been in progress with the ultimate goal to develop ion sources and techniques that meet the two energy extreme range needs of meV and hundreads of eV ion implanters. This endeavor has already resulted in record steady state output currents of high charge state of antimony and phosphorus ions: P(2+) [8.6 pmA (particle milliampere)], P(3+) (1.9 pmA), and P(4+) (0.12 pmA) and 16.2, 7.6, 3.3, and 2.2 pmA of Sb(3+)Sb(4+), Sb(5+), and Sb(6+) respectively. For low energy ion implantation, our efforts involve molecular ions and a novel plasmaless/gasless deceleration method. To date, 1 emA (electrical milliampere) of positive decaborane ions was extracted at 10 keV and smaller currents of negative decaborane ions were also extracted. Additionally, boron current fraction of over 70% was extracted from a Bernas-Calutron ion source, which represents a factor of 3.5 improvement over currently employed ion sources.

Small plasma source for materials application.

We describe a small hollow-cathode plasma source suitable for small-scale materials synthesis and modification application. The supporting electrical system is minimal. The gaseous plasma source delivers a plasma ion current of up to about 1 mA. Here we outline the source construction and operation, and present some of its basic performance characteristics.

Operating modes of a hydrogen ion source based on a hollow-cathode pulsed Penning discharge.

An ion source based on a hollow-cathode Penning discharge was switched to a high-current pulsed mode (tens of amperes and tens of microseconds) to produce an intense hydrogen ion beam. With molecular hydrogen (H2), the ion beam contained three species: H(+), H2(+), and H3(+). For all experimental conditions, the fraction of H2 (+) ions in the beam was about 10 ÷ 15% of the total ion beam current and varied little with ion source parameters. At the same time, the ratio of H(+) and H3(+) depended strongly on the discharge current, particularly on its distribution in the gap between the hollow and planar cathodes. Increasing the discharge current increased the H(+) fraction in ion beam. The maximum fraction of H(+) reached 80% of the total ion beam current. Forced redistribution of the discharge current in the cathode gap for increasing the hollow cathode current could greatly increase the H3(+) fraction in the beam. At optimum parameters, the fraction of H3(+) ions reached 60% of the total ion beam current.

A vacuum spark ion source: High charge state metal ion beams.

High ion charge state is often important in ion beam physics, among other reasons for the very practical purpose that it leads to proportionately higher ion beam energy for fixed accelerating voltage. The ion charge state of metal ion beams can be increased by replacing a vacuum arc ion source by a vacuum spark ion source. Since the voltage between anode and cathode remains high in a spark discharge compared to the vacuum arc, higher metal ion charge states are generated which can then be extracted as an ion beam. The use of a spark of pulse duration less than 10 µs and with current up to 10 kA allows the production of ion beams with current of several amperes at a pulse repetition rate of up to 5 pps. We have demonstrated the formation of high charge state heavy ions (bismuth) of up to 15 + and a mean ion charge state of more than 10 +. The physics and techniques of our vacuum spark ion source are described.