JPH025331A - Duopigatron ion source - Google Patents

Abstract

PURPOSE:To generate a large amount of polyvalent ions with a compact device by forming an enlongated hole in an intermediate electrode, and providing a reflecting electrode in front of an anode, and causing the intermediate electrode to be in a float state after discharge is generated. CONSTITUTION:An intermediate electrode 6 is provided between a cathode 3 and an anode 4 in an ion generating room 1, and a reflecting electrode 9, for absorbing magnetic lines of force from a magnet 8, is provided on the opposite side of the intermediate electrode 6 with respect to the anode 4. A thin hole 7 with a diameter (a) and a length (l) is provided in the intermediate electrode 6 coaxially with a orifice 5 provided in the anode 4. After He gas is introduced from an introduction opening 2 and plasma is generated, the intermediate electrode 6 is caused to be in a float state. The plasma generated in the vicinity of anode 4 is blocked by the thin hole 7 so that it does not diffuse towards the cathode 3, and is drawn out by strong magnetic force as a large amount of polyvalent ions. Thus the device can be formed in a compact form.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention mainly relates to a DuoPIGatron ion source suitable for obtaining multivalent ions such as He''+.

(Prior Art) As a conventional ion source, a cathode C made of a filament is provided in a vacuum ion generation chamber equipped with an inlet a for He or other discharge gas as shown in FIG. An anode e having an orifice d facing each other is provided, and an intermediate electrode g having a pore f coaxial with the orifice d is provided between the cathode C and the anode e, and a magnetic field in the axial direction of the pore f is provided. A device is known that is provided with a forming magnet. In this case, the intermediate electrode g is set at a lower potential than the anode e, and is connected to the anode e through a soft iron magnetic path, so that a strong magnetic field in the axial direction of the orifice d is applied between the intermediate electrode g and the anode e. Make between
The plasma generated between the cathode C and the anode e is confined by the potential of the intermediate electrode g and the magnetic field, and the anode e
Ions are extracted by an extraction electrode i provided on the outside of the ion.

(Problems to be Solved by the Invention) The conventional ion source is relatively small and compact, but this makes it difficult to generate many multiply charged ions, such as 1e++, which have a high ionization potential of 54 eV. In order to obtain a large number of multivalent ions, the discharge voltage must be increased, and as a result, the size of the insulating member and the like increases, resulting in an inconvenience that the ion source becomes large.

An object of the present invention is to provide a small and compact ion source that can obtain a large amount of multivalent ions.

(Means for Solving the Problems) In the present invention, a cathode is provided in a vacuum ion generation chamber into which He or other discharge gas is introduced, and an anode having an orifice is provided opposite to the cathode. An intermediate electrode having a pore coaxial with the orifice is provided in the middle, and a magnet is further provided to form a magnetic field in the axial direction of the orifice to draw out ions generated in the ion generation chamber to the outside through the orifice. In this structure, a reflective electrode that absorbs the lines of magnetic force of the magnet is provided on the opposite side of the anode to the intermediate electrode, and the pores of the intermediate electrode are formed to be long and thin, so that the ion generation chamber can absorb the ions after plasma is generated. The above problem was solved by setting the intermediate electrode to a float potential.

(Function) For example, He gas is introduced into the vacuum ion generation chamber to generate 1O
The pressure is about -2 Torr, and a strong magnetic field, for example, about 102 to 2 x 102 Gauss, is applied by a magnet along the axis of the orifice of the anode, and the anode is applied at 70 V and 5 A with the cathode as a reference.

A voltage of 20 V and 0.025 A is applied to the intermediate electrode 1:1, and a voltage of 20 KV is applied to the extraction electrode 1 to perform discharge. In this case, the discharge voltage between the cathode and anode is somewhat higher than that of a normal duoplasmatron ion source, and although this alone does not generate a large amount of multiply charged ions, it does not make the pores of the intermediate electrode narrower. The anode is formed to be long, and a reflective electrode is provided on the opposite side of the anode to the intermediate electrode to absorb the lines of magnetic force of the magnet.Furthermore, after the discharge between the cathode and the anode is ignited, the current to the intermediate electrode is cut off and the electrode floats. A large amount of multivalent ions can be obtained by forming this state.

To explain this further, the plasma generated by the discharge between the cathode and the anode has a thin and long pore between them, so it is difficult to diffuse and move in the axial direction of the pore. When the float becomes low, its diffusion and movement is further prevented, and the lines of magnetic force generated in the axial direction by the magnet are absorbed by the reflective electrode in front of the anode, increasing the magnetic flux density near the anode, thereby increasing the magnetic flux density near the anode. As the plasma density and plasma temperature increase, the He gas is ionized by high energy and a large amount of Tle ions are generated. ■
The e++ ions are extracted in the form of a beam by the potential of the front extraction electrode, and are provided to a surface analysis device that utilizes Rutherford backscattering, for example.

(Embodiment) An embodiment of the present invention will be explained with reference to FIG.
(3) is a cathode made of a filament provided in the ion generation chamber (1), and (4) is an anode provided opposite to the cathode (3). , an orifice (5) is formed in the anode (4). (6) is the cathode (3) and anode (4).
), in which a long pore <7) with a diameter a and a length l is formed coaxially with the axis of the orifice (5). (8) is a magnet that generates a magnetic field in the axial direction of the orifice (5); (9)
is a reflective electrode provided on the opposite side of the intermediate electrode (6) of the anode (4), l''IG is an extraction electrode, and
) and an extraction electrode ('lG) are formed with an ion extraction port (11) 421 that coincides with the axis of the orifice (5), respectively.

To explain its operation when generating a beam of IIo''+ ions, the inside of the ion generation chamber (1) is evacuated, and He gas is introduced into the chamber from the introduction port (2).
After setting it to O-2 Torr, the cathode (3) is set as the base, and the anode (4) is set to 80 to 200 V, 1 to 5 A.
.

A voltage of 25 KV is applied to the reflective electrode (9) to -Ov1 to the extraction electrode 0V, and a magnetic field of 100 to 200 Gauss is applied on the axis of the orifice (5) by the magnet (8). When a discharge is ignited between the cathode (3) and the anode (4), the supply of current to the intermediate electrode (6) is stopped and the intermediate electrode (6) is placed in a floating state. The plasma generated near the anode (4) is blocked by the narrow pores (1) of the intermediate electrode (6) and does not diffuse toward the cathode (3), and the intermediate electrode (6) is in a floating state. As a result, the plasma is pushed in the direction of the anode (4), and the magnetic field lines of the magnet (8) are pushed toward the reflective electrode (9).
), a relatively strong magnetic field is generated near the anode (4). According to this, it is possible to increase the plasma density and plasma temperature near the anode (4), and because the high plasma energy can ionize the He gas, a large amount of IIe+'' ions can be generated near the anode (4). The generated Ilc″1 ions are transferred to the extraction electrode (′lv
The He+'' ion source is drawn forward by a potential of A significantly larger amount of Ilc~ ions was also obtained.

(Effects of the Invention) As described above, according to the present invention, the pores of the intermediate electrode are formed long and thin, the reflective electrode is provided in front of the anode, and the intermediate electrode is floated after discharge occurs, so that the pores near the anode are The density and temperature of the plasma increases, and sufficient plasma energy is available to ionize the gas into multiply charged ions.
It can generate a large amount of multiply charged ions, its dimensions are not much different from conventional dioplasmatron ion sources, and it has advantages such as being small and compact, making it convenient to use.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of a conventional dioplasmatron ion source, and FIG. 2 shows a cross-sectional view of an embodiment of the present invention. (1)...Ion generation chamber (3)...Cathode (
4)... Anode (5)... Orifice (
6)...Intermediate electrode (8)...Magnet book...Extractor electrode (7)...Small hole (9)...Reflecting electrode Permit Application Published by Keihon Vacuum Technology Co., Ltd.

Claims (1)

[Claims] A cathode is provided in a vacuum ion generation chamber into which a discharge gas such as He is introduced, an anode having an orifice is provided opposite to the cathode, and a pore coaxial with the orifice is provided between the anode and the cathode. An electrode is provided, and a magnet is further provided to form a magnetic field in the axial direction of the orifice, so that ions generated in the ion generation chamber are drawn out through the orifice,
A reflective electrode that absorbs the lines of magnetic force of the magnet is provided on the side opposite to the intermediate electrode of the anode, the pores of the intermediate electrode are formed long and thin, and the intermediate electrode is set at a float potential after plasma is generated in the ion generation chamber. Duopigatron ion source featuring: