JPH065239A - Ion acceleration device - Google Patents

Abstract

PURPOSE:To lower energy of X-rays generated from a vacuum exhaust tube for being easily shielded and to reduce a dose of X-rays leaking to the outside. CONSTITUTION:A plurality of electrodes 22 bonded and attached to an insulating material 21 while having a hole in the central part are mounted on the inside of a vacuum exhaust tube 12, one side (left side) is connected to a pump connection tube 15 through a ground side mounting flange 23 and the other side (right side) is connected to the exhaust tube 13 through a high voltage side mounting flange 24. Permanent magnets 31 are mounted on the respective electrodes 22 of the vacuum exhaust tube 12 respectively to form magnetic fields in the regions of the holes of the electrode central parts in the same in-plane directions as the electrodes 22. The magnetic fields deflect the tracks of the electrons to be accelerated between the respective electrodes by the magnetic fields so as to reduce X-rays generated at the time of colliding with high energy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion accelerator used for an ion beam analyzer, an ion implanter and the like.

[0002]

2. Description of the Related Art FIG. 3 is a plan view showing the whole of a conventional ion implanter. The ion accelerator, which constitutes a stage preceding the scanning unit 18, is mounted on an insulating column mounted on the floor of the shield box 1. A high voltage terminal 2 is attached, and an acceleration tube 3 is attached between the side wall of the shield box 1 and the side wall of the high voltage terminal 2. An ion source 4, a mass separation magnet 5, a gas box 6, and an ion source generating power source 7 are installed in the high-voltage terminal 2, and a power supply device 8 mounted outside is connected via a bushing 9. It is also connected to the high voltage generator 10 via a bushing 11. Further, a vacuum exhaust pipe 12 is attached between the side wall of the shield box 1 and the side wall of the high-voltage terminal 2, and one side (right side in the figure)
Is connected to the ion source 4 via the exhaust pipe 13 and the ion source exhaust chamber 14, and the other side (left side in the figure) is connected to the vacuum pump 16 for exhausting the ion source 4 via the pump connecting pipe 15. It is connected.

On the other hand, the acceleration tube 3 is connected to a scanning unit 18 equipped with a vacuum pump 17 for evacuating the vicinity of the acceleration tube 3 outside the shield box 1.
The scanning unit 18 is connected to a target chamber 20 in which a target (sample holder) 19 is housed.

FIG. 4 is a sectional view of a conventional vacuum exhaust pipe 12 mounted between the side wall of the shield box 1 and the side wall of the high voltage terminal 2. In the drawing, the inside of the vacuum exhaust pipe 12 is attached to an insulating material 21 and a plurality of (steps) disk-shaped metal electrodes 22 having an opening in the center are attached to hold a vacuum. One side (left side in the figure) of the exhaust pipe 13 is connected to the pump connecting pipe 15 via the gland side mounting flange 23, and the other side (right side in the figure) of the exhaust pipe 13 via the high voltage side mounting flange 24. Flange 13
a, and both of these mounting flanges 23, 24
And the insulating material 21 are bonded. In the figure, 25
Is a resistor mounted between the electrodes 22 of each stage between the high voltage terminal 2 and the shield box 1, and 2
6 is an O-ring.

Next, the operation will be described. Ion source 4
Inside the vacuum pump 1 through the ion source exhaust chamber 14, the exhaust pipe 13, the vacuum exhaust pipe 12 and the pump connection pipe 15.
Exhausted by 6. A material gas is introduced into the ion source 4 from a gas cylinder housed in a gas box 6 and, at the same time, power is supplied from the plasma generating power source 7 into the ion source 4, whereby the ion source 4 is supplied.
Plasma is generated inside. When ions are extracted from the generated plasma at several tens of kV and enter the mass separation magnet 5, the ions are bent by the magnetic field, so only the desired ions are selected and the ions enter the accelerating tube 3.

On the other hand, the electric power consumed in the high voltage terminal 2 is supplied to the high voltage terminal 2 by the power supply device 8 through the bushing 9. Also, the acceleration tube 3
In order to accelerate the ions entering the
The high voltage generator 10 allows the high voltage terminal 2 to have a number 1
A voltage of 0 kV to over 400 kV is applied. The ions that have entered the accelerating tube 3 are accelerated to the ground potential with the energy of the product of the voltage applied to the high voltage terminal 2 and the valence of the ions.

Further, when a voltage is applied to the high voltage terminal 2, discharge is likely to occur inside the acceleration tube 2 if the pressure inside the acceleration tube 3 is high, so the vacuum pump 17 exhausts the voltage. The ion beam accelerated by the accelerating tube 3 operates the scanning unit 18 to scan the ions reaching the target (sample holder) 19 installed in the target chamber 20 in the vertical and horizontal directions, Irradiate the surface of the sample with ions.

FIGS. 5 (a) to 5 (d) are operation explanatory views showing the generation process of X-rays leaking from the surface of the shield box 1 to which the vacuum exhaust pipe 12 is attached during ion acceleration. The ○ marks indicate neutral particles (molecular and atomic states) of the material gas, ● marks indicate ions, and ・ marks indicate electrons.

As shown in FIG. 5A, the gas box 6
Material gas is introduced into the ion source 4 from the gas cylinder of
Plasma is generated and ions are extracted from the ion source 4 into the ion source exhaust chamber 14. Immediately after the extraction, the ions collide with the neutral particles and the neutral particles have velocity components in irregular directions. Or are converted into ions and the ions are generated, and the neutral particles and ions enter the vacuum exhaust pipe 12 through the exhaust pipe 13. At this time, a voltage of several hundred kV is applied to the high-voltage terminal 2 by the high-voltage power supply 10, and therefore the vacuum exhaust pipe 12 is connected to the electrode 22.
And a resistor 25 attached to each step between the electrode and its
An accelerating electric field is formed in the central portion of the vacuum evacuation pipe 12, so that the accelerating pipe 3 operates in the same manner.

FIG. 5 (b) is an operation explanatory view showing the behavior of the ions incident on the vacuum exhaust pipe 12, and the ions incident on the vacuum exhaust pipe 12 from the potential of the high voltage terminal 2 to the ground of the shield box 1. It is accelerated toward the electric potential. Further, the neutral particles of the material gas, which are not extracted as ions from the ion source 4 and have not been ionized as plasma, flow into the vacuum exhaust pipe 12 through the exhaust pipe 13. The neutral particles flowing into the vacuum exhaust pipe 12 collide with the ions accelerated in the vacuum exhaust pipe 12 to generate ions having an irregular velocity component and neutral particles, and the generated ions And the neutral particles further collide with the neutral particles, the number of ions increases in an avalanche phenomenon, and the ions are accelerated toward the ground potential.

FIG. 5 (c) is an operation explanatory view showing a state of being accelerated in the vacuum exhaust pipe 12, and the ions accelerated in the vacuum exhaust pipe 12 and having high energy are the electrodes 2 made of metal.
When it collides with 2, secondary electrons are emitted from the metal surface of the electrode 22. Ions collide with each of these electrodes 22, and the secondary electrons emitted from the electrodes at each stage have an electric polarity opposite to that of the ions. Therefore, the secondary electrons are directed toward the high-voltage terminal 2 in the vacuum exhaust pipe 12. Be accelerated.

FIG. 5 (d) is an operation explanatory view showing the state of secondary electrons accelerated in the direction of the high voltage terminal 2.
Electrons emitted from the electrodes 22 pass through holes (openings) in the central portions of the electrodes 22 mounted inside the vacuum exhaust pipe 12, so that the electrons collide with electrodes on the higher voltage side than the electrodes from which the electrons are emitted. Without acceleration, the energy is accelerated to a high energy, and a part of the residual gas in the exhaust pipe 13 is ionized to generate ions, which contributes to the avalanche phenomenon. Then, some of the accelerated electrons collide with the metal tube wall of the ion source exhaust chamber 14 in the high voltage terminal 2. When a high-speed electron collides with the metal tube wall, X-rays (continuous and characteristic X-rays) are emitted, and a part of the X-ray is absorbed by the wall of the shield box 1, while the other part is a side wall of the shield box 1. Through the gap between the vacuum exhaust pipe 12 and the vacuum exhaust pipe 12, or through the vacuum exhaust pipe 12 and the pipe wall of the pump connecting pipe 15 to leak outside.

[0013]

As described above, in the conventional device, secondary electrons are generated by collision of the ions with the electrode 22 in the vacuum exhaust pipe 12, and the secondary electrons are generated in the vacuum exhaust pipe 12. Since there is no barrier in the ion beam, the electrons are accelerated to high energy, and the electrons collide with the tube wall of the ion source exhaust chamber 14 to generate X-rays having high energy, which leaks to the outside of the shield box 1. There was a point.

The present invention solves the above-mentioned problems of the prior art, and lowers the energy of X-rays generated from the vacuum exhaust pipe, easily shields it, and reduces the X-ray dose leaking to the outside. It is an object of the present invention to provide an ion accelerator equipped with a possible vacuum exhaust pipe.

[0015]

In order to achieve the above object, the present invention attaches a magnet to an electrode for evenly dividing a voltage in a vacuum exhaust pipe constituting an ion accelerator, and attaches a magnet to a central portion of the electrode. It is characterized by forming a magnetic field in the region of the hole.

[0016]

Since the present invention is configured as described above, a pair of permanent magnets facing the N pole and the S pole attached to the electrodes of each stage in the vacuum exhaust pipe are used to form a central portion of the electrodes. A magnetic field is formed in the area of the hole in the same in-plane direction as the electrode. on the other hand,
The electrons generated between each electrode in the vacuum exhaust pipe are accelerated by the potential difference between the electrodes, but the orbit of the electrons is deflected by the magnetic field of the permanent magnet, and the electrons pass through the hole in the center of the electrode to be accelerated to high energy. Electrons are reduced. As a result, the electrons collide with the vacuum exhaust pipe and the electrodes before being accelerated to high energy, so that the X-rays generated by the collision are reduced.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. 1A is a vertical cross-sectional view of a vacuum exhaust pipe showing an embodiment of the present invention, FIG. 1B is a cross-sectional view taken along the line AA of FIG. 1A, and FIG. (A) is a cross-sectional view taken along the line BB, and (d) is an enlarged cross-sectional view of a C portion in (a).
The same reference numerals as those shown in FIG. 4 indicate the same or similar parts.

In FIG. 1A, a plurality of disc-shaped metal electrodes 22 attached to an insulating material 21 and having a hole in the center thereof are attached inside the vacuum exhaust pipe 12 to apply a vacuum. It is held, and one side (the left side in the figure) is connected to the pump connecting pipe 15 via the gland side mounting flange 23,
The other side (right side in the drawing) is connected to the flange of the exhaust pipe 13 via the high-voltage side mounting flange 24, which is no different from the conventional example (FIG. 4), but in the present invention (embodiment), The difference is that a permanent magnet 31 is attached to each of the electrodes 22.

The permanent magnet 31 has screw holes 31a corresponding to the pitches of two taps (screw holes) formed in the electrode 22, as shown in the enlarged sectional view of FIG. As the permanent magnet 31 is sandwiched by the screw 32, the electrode 22
Are attached so that the two polarities N and S face each other.

The polarities of the permanent magnets 31 attached to the electrodes 22 of the respective stages are different from the polarities of the permanent magnets 31 attached to the adjacent electrodes, as shown in FIGS. It is arranged so that it always has the same polarity. For example, the N-pole is attached to the upper part of the AA cross section (Fig. (B)) so that the N pole faces toward the center of the electrode, and B-
In the B section ((c) figure), it is attached to the upper part of the electrode so that the N pole faces the center of the electrode.

However, the facing surfaces of the magnets facing each electrode need to have different poles in order to create a magnetic field in the area of the hole of each electrode, but the polarities of the magnets of all electrodes should be aligned. , Direction of magnetic field lines formed on each electrode (magnetic)
It is not always necessary in the present invention to arrange the above.

Next, the operation will be described. Up to the process in which ions are incident on the vacuum exhaust pipe 12 of the present embodiment and collide with the internal electrode 22 to generate secondary electrons, a conventional example (FIG. 4). Since it is the same as that of the vacuum exhaust pipe 12), the description after the generation of the secondary electrons will be described with reference to FIG.

FIG. 2 (a) is a cross-sectional view of the vacuum exhaust pipe 12 similar to FIG. 1 (b), and FIG. 2 (b) is II of FIG. 2 (a).
It is a principal part sectional view by the II line. In FIG. 2B, a secondary electron e1 is generated by the ion (black circle) i1 that collides downward with the electrode 22a in the figure, and is accelerated to the high voltage side (upward in the figure). A magnetic field formed by a pair of permanent magnets 31 attached to the electrode 22a in the direction of the true angle on the paper (the circled X in the figure indicates that the magnetic field lines are working downward). While passing, a Lorentz force causes a circular motion with a certain radius to collide with the electrode 22 and the tube wall (insulating material 21) of the vacuum exhaust tube 12 and disappear. Even if the energy of the ions collides with the electrode 22 with the energy of 400 to 500 keV, the energy of the secondary electrons emitted from the electrode is considered to be several hundred eV or less because the mass ratio is several thousand times larger for the ions. To be
Therefore, the magnetic field generated by the permanent magnet 31 is several tens of degrees on the surface of the magnet.
Even with a permanent magnet having a magnetic flux density of 0 Gauss, the radius of electrons due to the Lorentz force is about several mm, and the electrons are emitted from the electrode 22 and immediately collide with the electrode or the tube wall.

Next, considering the behavior of the electron (electron e2 in FIG. 2B) generated between the electrodes, this electron is subjected to the acceleration of the potential difference per electrode between the electrodes 22.
If the voltage of the high voltage terminal 2 is 400 kV and the number of electrode stages is 20, the potential difference per stage is 20.
Since it becomes kV, the electron has an energy of about 20 keV. When this electron e2 is bent by the magnetic field of the permanent magnet 31 attached to the electrode 22b, the radius becomes several cm, and even in this case, the electron collides with the tube wall.

From the above, in the vacuum exhaust pipe 12 of the present invention (embodiment), the orbits of the electrons are deflected by the magnetic field of the permanent magnet 31 attached to each electrode 22, and pass through the hole in the center of the electrode. The number of electrons accelerated to high energy decreases. Therefore, the number of electrons that collide with the ion source exhaust chamber 14 with high energy is reduced. Further, the trajectory of the ions entering the vacuum exhaust pipe 12 is also bent by the magnetic field in the same direction, collides with the wall surface of the vacuum exhaust pipe 12, loses energy, and the generation of secondary electrons is suppressed.

[0026]

As described above, according to the present invention,
In an ion accelerator having a vacuum exhaust pipe for exhausting the interior of the ion source between a high-voltage terminal having an ion source inside and a shield box surrounding it surrounding with a ground potential, in the electrode of the vacuum exhaust pipe. By attaching a magnet and forming a magnetic field in the hole area at the center of the electrode, the orbit of electrons generated in the vacuum exhaust tube is deflected by the magnetic field of the magnet, so that the center of the electrode 22 of the conventional vacuum exhaust tube 12 is deflected. The probability of passing through the holes in the section to be accelerated to the potential of the high voltage terminal 2 and reaching the ion source exhaust chamber 14 with high energy is reduced. In other words, the electrons collide with the walls and electrodes inside the vacuum exhaust pipe before being accelerated to high energy. As a result, since the X-ray generated by collision has a low energy of electron collision, the maximum energy (shortest wavelength becomes longer) of continuous X-ray generated by collision decreases, and the intensity of the energy spectrum of X-ray is reduced. The energy that gives the peak is also low. Further, the area of the energy spectrum, that is, the total intensity of continuous X-rays also decreases. As a result, it is possible to reduce the X-ray dose that leaks from the side wall of the shield box.

[Brief description of drawings]

1 shows an embodiment of the present invention, (a) is a vertical sectional view of a vacuum exhaust pipe, (b) is a sectional view taken along line AA of (a), (c).
6A is a cross-sectional view taken along the line BB of FIG. 7A, and FIG. 8D is an enlarged cross-sectional view of a C portion of FIG.

FIG. 2 is a schematic view of the operation of the vacuum exhaust pipe of the present invention, (a)
Is a cross-sectional view and (b) is a main-portion cross-sectional view taken along line II-II of (a).

FIG. 3 is a plan view showing an ion implanter including a conventional ion accelerator.

FIG. 4 is a cross-sectional view of a conventional vacuum exhaust pipe.

5 (a) to (d) are schematic views of a conventional X-ray generation mechanism in a vacuum exhaust pipe.

[Explanation of symbols]

 1 Shield Box 2 High Voltage Terminal 12 Vacuum Exhaust Pipe 13 Exhaust Pipe 15 Pump Connection Pipe 16 Vacuum Pump 21 Insulating Material 22, 22a, 22b Electrode 23, 24 Mounting Flange 25 Resistance 31 Permanent Magnet 32 Flat Head Screw

Claims (1)

[Claims] 1. An ion accelerating device having a vacuum exhaust pipe for exhausting the interior of an ion source between a high voltage terminal having an ion source inside and a shield box surrounding the high voltage terminal surrounding the ion source. An ion accelerating device characterized in that a magnet is attached to an electrode of an exhaust pipe, and a magnetic field is formed in the same in-plane direction as that of the electrode in a region of a hole in a central portion of the electrode.