RU2002333C1 - Ion source - Google Patents

Abstract

Usage: for a complex surface of vacuum-plasma processing of tools, machine parts and other products. SUMMARY OF THE INVENTION; a two-stage vacuum-arc discharge with an integrally-cold cathode is excited in the discharge cavity of the vacuum chamber of the ion source. For this, a partition is established between the anode and cathode, dividing the discharge cavity into cathode and anode parts. In addition, the anode part of the discharge cavity is connected through the emission grid to the working cavity of the vacuum chamber, and a current turnip is installed in the circuit of the two-stage discharge power source, the actuator of which is located in the circuit of the grid power source and the accelerating voltage source. 2 cpfs, 2 ill.

Description

IS

FIELD OF THE INVENTION This invention relates to techniques for producing high-current large-cross section ion beams.

Widespread ion sources Kaufman. In them, the electrons are emitted by a heated cathode located on the axis of a cylindrical discharge chamber placed in a weak longitudinal magnetic field. The anode is part of the cylinder. Electrons move in crossed magnetic and electric fields along spiral paths around the axis, as a result of which their mean free path and the likelihood of ionization of the working gas increase. Ions are pulled, accelerated and focused by a two- or three-electrode ion-optical system. A disadvantage of Kaufman sources is the relatively short service life of the heated cathodes (several tens of hours).

A source of large-section charged particle beams based on a glow discharge with a cold hollow cathode is known. The source contains a chamber in which U-shaped hollow cathodes form a discharge cavity. An anode passes through an opening in the hollow cathode into the discharge cavity. All cathodes are isolated from each other and connected to an adjustable source of discharge voltage through separate resistors, which prevents the discharge from moving into an arc. The emission grid with high transparency (70-90%) is isolated from the discharge cavity and the working cavity of the vacuum chamber. The ion source has a pelvic discharge power source from which its ions are extracted, a voltage source connected to the grid by a negative pole and cut off the electron current from the synthesized plasma through the grid to the cavity of the discharge chamber, and an accelerating voltage source.

In a source with an emission grid area of 1000 cm, the ion current is 1 A. Thus, the ion current density is 1 mA / cm. An increase in the ion current density can be achieved by branching the cage surface, which complicates the design.

Abstracts, become A.S. Metel. Sources of charged large particle beams based on a glow discharge with a cold hollow cathode, Ulan-Ude Publishing House, Burt Institute of Natural Sciences, Siberian Branch of the Academy of Sciences of the USSR, June 1991. p. 77-81, Fig. 2. In: Plasma emission electronics.

The purpose of the invention is to increase the ion current density.

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This goal is achieved by the fact that in the proposed ion source containing a vacuum chamber with a working and discharge cavities communicating with each other through an emission grid and electrically isolated from it, a gas discharge cathode and anode are installed in the latter, as well as a gas power source a discharge connected to the electrodes, an accelerating voltage source, the negative pole of which is connected to the wall of the working cavity, and a voltage source, the negative pole of which is connected to the emission grid, the cathode is made in the form of an integrated cold cathode of a vacuum arc discharge, a partition is installed between the cathode and anode, not permeable to metal ions generated from the cathode surface, but permeable to electrons, separating the discharge cavity into the cathode and anode parts, the anode part of the discharge cavity is communicated with the working cavity of the vacuum chamber through the emission grid, and a current relay is installed in the power circuit of the vacuum-arc discharge, the actuator of which is included in the accelerating voltage circuit and and into the grid power circuit. The ion source may be provided with an additional electrode insulated from the chamber, connected to the negative pole of the additional current source and located in the anode part of the discharge cavity against the grid. The additional electrode is preferably made of a material other than the cathode material.

The achievement of this goal is achieved by using a more powerful vacuum-arc discharge, which determines the degree of plasma ionization, and, therefore, the ion current extracted from it does not depend on the geometric dimensions of the cathode, to create a plasma from which ions are generated. It has thermophysical properties. It is not difficult to obtain discharge currents of tens of mA / cm2.

1 shows an ion source; Fig. 2 is a variant of a source with an additional sprayed electrode.

The ion source (Fig. 1) contains a vacuum chamber 1, in the discharge cavity 2 of which an integral-cold cathode 3 of a vacuum-arc discharge and anode 4 are placed opposite each other. Near the cathode 3, it is impermeable to metal ions generated from the surface of the cathode,

but the electron-permeable partition 5, which divides the discharge cavity 2 into the cathode and anode parts 6 and 7. The discharge cavity is electrically insulated from the working cavity 8 of the vacuum chamber 1 by insulators 9. Between the anode part 7 of the discharge cavity 2 and the working cavity 8 of the vacuum chamber 1, a grid 10 is installed on the insulators 11.

The ion source is powered by a vacuum arc discharge power source 12, an accelerating voltage source 13 (camera power supply), and a voltage source 14 (power grid 10). A current relay 15 is installed in the vacuum arc arc power supply circuit, the actuator 16 of which (normally open contacts) is included in the power supply circuit of the Yui emission grid in the accelerating voltage circuit.

In the anode part 6 of the discharge cavity 2, an additional spray electrode 18 (Fig. 2), electrically insulated from the chamber by means of an insulator 17, connected to the negative pole of the power supply 19 can be installed. The ion source operates as follows. The vacuum chamber 1 is evacuated by a pumping system to a pressure of 10 Pa and then working gas (e.g. argon) is injected into it to a pressure of 10 Pa. By using the ignition system between the cathode 3 and the anode 4, a two-stage vacuum arc discharge (DDR) is excited in the discharge cavity 2. The discharge is formed by a septum 5, which is impermeable to metal ions generated from the surface of the cathode. The cathode portion 6 of the discharge cavity 2 is filled with a metal-gas plasma. Metal ions are generated in the cathode spot of the arc and propagate from the surface of the cathode 3 along straight paths. Since the partition 5 is impermeable to metal ions, metal ions are trapped therein and do not enter the anode part 7 of the discharge cavity 2.

The anode part 7 of the discharge cavity 2 is filled with a positive column of purely gas plasma formed by electrodes passing through the baffle 5 under the influence of the electric field of the anode 4. When a discharge current occurs in the circuit of the cathode 3 and anode 4, the current relay 15, which is activated by its executive body 16 (normally open contacts) includes an accelerating voltage source 13 and a voltage source 14. This sequence of inclusion of sources

voltage (first turns on the source 12, and only after the excitation of the discharge - sources 13 and 14) due to the need to excite the discharge. Voltage

on the grid, it is selected from the condition of the necessary ion energy and creating a boundary of the gas plasma, from the surface of which the acceleration of ions occurs, which does not go beyond the grid. The first condition is specified

technological requirements, the second is determined from the condition

d 2 °

1 (2e) 1/4 U2 / 4 (9 p1M / T7

where d is the width of the layer of ionic bulk charge separating the ion collector (network) from the plasma boundary;

h is the characteristic size of the grid (the distance between adjacent grid elements),

M is the mass of the ion:

Uo is the voltage between the plasma and the grid;

j is the current density of positive ions on the grid.

Under the action of a negative potential relative to the positive column of the gas discharge plasma, positive plasma ions are accelerated in the bulk charge layer. Part of the ion flux is deposited on the grid 10, and part (approximately proportional

the transparency coefficient of the grid) flies through the grid 10 and processes the products placed in the working cavity 8 of the vacuum chamber 1. Neutralization of the bulk charge of ions is carried out by secondary electrons formed during the bombardment of products and the walls of the chamber 1 by accelerated ions. The voltage source 14 creates a double layer in the working cavity 8 of the vacuum chamber between the grid and

secondary plasma in the volume of cavity 8, which prevents the escape of electrons from the volume of the sheet 8 into the anode part 7 of the discharge cavity 2. It was experimentally shown that the magnitude of the ion current extracted from

positive column of gas plasma of the DDR for the entire area of the ion collector SK (the area of the ion collector is the entire area of the anode part 7 of the discharge cavity 2. including the area of the anode 4, grid 10 (Sc) and septum 5) taking into account the transparency coefficient of grid 10

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(Since the discharge current in a TDDR is determined only by the thermophysical properties of the cooled cathode, the ion current in the device is limited mainly by the thermal capabilities of grid 10.

The operability of the ion source was determined using the apparatus shown in Fig. 1. In the vacuum chamber of the installation, it was mounted on the upper flange, on which an aluminum cathode is located, a partition 4 in the form of a chevron. The evaporator (cathode 3) was mounted on a rubber pad, which served as a sealant and sealant at the same time. A water-cooled copper anode with a diameter of 90 mm was placed on the lower flange of the chamber. Through the entire chamber from the upper to the lower flanges, a grid of four sections isolated from each other with a diameter of 100 mm and a total length of 320 mm was installed (transparency coefficient of the grid 0.5). The discharge was supplied from a power supply 11. Voltage at bit 42V at current

about

discharge 40 A. The voltage of the source 13 of the accelerating voltage was 500V.

about

The total current strength in the grid sections is 3.1 A. The strength of the ion current measured in the USCO circuit

the shear voltage was 5.9 A. With a grid area of 1000 cm2, the ion current density is 2.9 mA / cm2, which is 2.9 times higher than in the device, taken as a prototype. An obstacle to further

An increase in the ion current extracted from the source is the limited power of the accelerating voltage source 13 used for this purpose. The experiment showed that increasing current

discharge leads to a proportional increase in the ion current.

Claims (3)

1. ION SOURCE, containing a vacuum chamber with a working and discharge cavities communicating with each other through an emission grid and electrically isolated from it, the cathode and anode of a gas discharge, a gas discharge power supply connected to the electrodes, a source an accelerating voltage, the negative pole of which is connected to the wall of the working cavity, and a voltage source, the negative pole of which is connected to the emission grid, characterized in that the cathode is made in the form of a tegral -holodnogokatoda vacuum-arc discharge, a partition is installed between the cathode and anode, not permeable to metal ions generated from the surface of the cathode, but permeable to electrons, separating a discharge cavity to the cathode and anode parts, while through the emission grid with the working cavity of the vacuum chamber, the anode part of the discharge cavity is communicated; moreover, a current relay is installed in the vacuum arc discharge power supply circuit, the actuator of which is included in the power supply circuit of the emission grid and accelerating voltage circuit. 2. The source according to claim 1, characterized in that it is provided with an additional atomized electrode, electrically insulated from the camera and connected to the negative pole of the additional current source, wherein the atomized electrode is located in the anode part of the discharge cavity opposite the emission grid. 3. A source according to claim 2, characterized in that the additional sprayed electrode is made of a material different from the cathode material. I AM