JPH01209645A - Ion source and electron gun - Google Patents

Abstract

PURPOSE:To prevent the flowing-in of positive ions or electrons to an accelerator by providing permanent magnets to an electrode at the lowermost downstream, and making the potential of the electrode at the immediately upper side of the lowermost electrode higher than that of the lowermost electrode. CONSTITUTION:Of plural acceleration electrodes 3-5, to the electrode 5 at the lowermost downstream along the advancing direction of the negative ions or electrons, permanent magnets 7 and 8 are arranged, while the potential of the electrode 4 (deceleration electrode) immediately upper side from the lowermost electrode 5 is made higher than that of the lowermost electrode 5. As a result, the reverse flow of the positive ions can be prevented by the electrostatic barrier, and the electrons generated at a drift 6 can be prevented from flowing in the deceleration electrode 4 by a magnetic field produced by the permanent magnets 7 and 8. The flowing-in of the positive ions or the electrons to the accelerator can be prevented consequently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an ion source and an electron gun-ζ that electrostatically accelerate ions and electrons and utilize them as a high-energy beam.

(Conventional technology) The ion source consists of an ion generation section and an acceleration section.

A conventional example will be explained using FIG. 6, taking as an example an ion source that accelerates positive ions.

Reference numeral 1 denotes an ion generation section which generates ions through gas discharge or the like. 2 and 5 are electrodes for acceleration, and a voltage necessary for acceleration is applied between 2 and 5. Reference numeral 3.4 is an electrode for applying voltage in divided parts, and the number of electrodes increases or decreases depending on the method of use.

Of these, 4 has a role other than dividing the voltage, as will be described later, and is placed at a lower potential than 5.

The potential distribution along the central axis of each electrode is shown in FIG. In the figure, 5 is set to the ground potential. After being accelerated, the ions extracted from 1 pass through the drift section 6 where there is no electric field. In this region, ions and electrons are created by collisions between the background gas and the ion beam. Among these, negatively charged particles such as electrons are accelerated in the opposite direction to positive ions and enter the particle with large energy. In order to prevent this backflow of electrons, etc., the positive ion source uses 4
is placed at a potential lower than 5 to prevent the inflow of electrons.

In order to place 4 at a low potential -ζ, positive ions and the like flow in from 6ζ and 6, but this usually does not pose a serious problem fζ. In a negative ion source, the configuration shown in FIG. 6 is reversed.

As shown in FIG. 7, 1 is the lowest potential. At this time, positive ions flow from #6, are accelerated, and flow from #1. In order to prevent the influx of positive ions, it seems possible to put 4 at a higher potential f than 5, as in Figure 6, and create an electrostatic barrier against positive ions, but this time, the electrons from 6 are transferred to 4. flows towards. In the case of FIG. 2, it was stated that the influx of positive ions from 6 to 4 is not much of a problem, but in FIG. 7, the influx of electrons to 4 increases significantly compared to the case of ions. Since the ratio is proportional to the square root of the mass ratio of ions and electrons, the electron current flowing into 4 is several tens to hundreds of times as large as the ion current flowing into 41 in the case of Fig. 6. The heat load becomes too large. Therefore, in the case of a negative ion source, except for electrode 4, an electrode configuration is often adopted in which the backflow of positive ions is prepared. In this case, as mentioned above, it is difficult to reduce the pressure in the range of 6 and suppress the generation of positive ions, but with the conventional apparatus, it is difficult to prevent unnecessary electron ions from flowing into the extreme part of the acceleration.

An object of the present invention is to provide a means for forming a barrier against backflow positive ions I while preventing the inflow of electrons in a negative ion source.

(Means for Solving the Problems) In the negative ion source according to the present invention, the most downstream! A permanent magnet is disposed at the pole, and the electrode in front of the permanent magnet (hereinafter referred to as a deceleration electrode) has a higher potential than the most downstream electrode.

(Function) According to the present invention, backflow of positive ions is prevented by an electrostatic barrier. In addition, the electrons generated in the drift part are transferred to the most downstream electrode C.
The magnetic field created by the permanent magnet installed in ζ can prevent the flow into the deceleration electrode.

(Example) FIG. 1 shows an embodiment of the ion source according to the present invention.

6 to l has the same function as in FIG. However, to 3-3-
3 is still an electrode for applying voltage in divided parts,
Normally, when negative ions are extracted from the ion generating section, electrons are also extracted, so it is necessary to separate them. 3～3
-3 is a t-pole configuration for separating electrons and negative ions, but since it is not directly related to the present invention, its explanation will be omitted.

In the drift part 6, ions and electrons are generated by the collision between the ion beam and the gas. As before, an electrostatic barrier is used to prevent the backflow of positive ions. For this purpose, the deceleration electrode 4 is placed at a higher potential than the deceleration electrode 5. If this continues, electrons will flow from 6 to 4, but the action of the 51 permanent magnets suppresses the electron flow.

When a magnetic field is generated to cross the beam path as shown in the figure, if the strength of the magnetic field is above an appropriate value, electrons cannot move across the lines of magnetic force, preventing electrons from flowing into 4. Can be done. By the way, this magnetic field is strong enough to suppress the movement of electrons, so it is not affected by high-speed ions.

FIG. 2 shows a modification of the invention. Although FIG. 1 illustrates the case where there is one ion extraction hole, in the ion source, a porous electrode in which a plurality of electrodes are provided on one sheet is often used as shown in FIG. 2. Even in the case of a porous electrode, the same effect can be obtained by arranging a permanent magnet for each extraction hole as in Figure @1. There is also a method of treating several extraction holes at once as shown in FIG.

By the way, although the present invention has been described with reference to a negative ion source, similar effects can be obtained with an electron gun.

FIG. 3 shows a typical electrode arrangement for an electron gun.

9 is a cathode for electron emission, and 10.11 is an electrode for acceleration. FIG. 3 has the same configuration as FIG. 8, except that 1 is replaced by 91. At this time, a backflow of positive ions also occurs, and the impact of the ions on the cathode is known to be one of the causes of shortening the life of the cathode. Even in the case of an electron gun, the same effect as in the case of a negative ion source can be obtained by adopting the configuration shown in FIG.

In the above example, the permanent magnets are arranged parallel to the beam, but the orientation is not limited to this.

The point is that the magnet line only needs to cross the beam, and the arrangement shown in FIG. 5 may be used.

Although the above explanation did not mention the shape of the beam, it goes without saying that it does not depend on the shape.

(Effects of the Invention) As described above, according to the present invention, by using the deceleration electrode and the permanent magnet in combination, it is possible to prevent positive ions from flowing into the child acceleration section.

[Brief explanation of the drawing]

FIG. 1 is an electrode configuration diagram of a negative ion source according to the present invention, and FIG.
The figure shows a configuration diagram of an example in which the present invention is applied to a porous type electrode, Figure 3 is a configuration diagram of the electrode arrangement of an electron gun, Figure 4 is a configuration diagram of an example in which the invention is applied to an electron gun, and Figure 5 shows a configuration diagram of an example in which the present invention is applied to an electron gun. 6 is a block diagram showing another example of magnet arrangement, FIG. 6 is a block diagram showing a conventional example of a positive ion source, and FIG. 7 is a block diagram showing another embodiment of the magnet arrangement. FIG. 8 is a configuration diagram showing a conventional example of a negative ion source. 1... Ion generation section, 2, 3, 4, 5, 10.11.
・Acceleration 'lt pole, 6... Drift part, 7, 8...
- Permanent magnet, 9... Cathode for electron emission.

Claims (2)

[Claims] (1) In a negative ion source that generates negative ions in the ion generation section and extracts and accelerates them using an electric field, a permanent magnet is attached to the most downstream electrode along the direction of ion movement among the multiple acceleration electrodes. An ion source characterized in that the electrode potential immediately upstream of the most downstream electrode is higher than that of the most downstream electrode. (2) In an electron gun that is equipped with an electron-emitting cathode section and accelerates electrons using an electric field, a permanent magnet is disposed in the most downstream electrode along the electron traveling direction among multiple accelerating electrodes, and the most downstream electrode is provided with a permanent magnet. An electron gun characterized in that the electrode potential immediately upstream of the downstream electrode is higher than that of the most downstream electrode.