JPH07335160A - Mass separating electrode - Google Patents

Abstract

PURPOSE:To prevent dielectric breakage of an insulative board even when unnecessary ion beam runs against an ion suppressing electrode to cause sputter of an electrode material by pinching the insulative board which is short in the vertical direction by a positive and a negative electrode, and providing a void below. CONSTITUTION:A mass separating device to extract an ion beam having a large area from an ion source and subject it to a mass separation process using the action of an electric field and magnetic field intersecting perpendicularly is equipped with a mass separating electrode 5. The electrode 5 is configured so that an insulative board 22 is pinched by apositive electrode 20 and a negative electrode 21 to form an electrode couple and that a void 28 is provided between the electrode plates 20, 21 in a position downstream about the beam advancing direction so that the insulative board 22 is shorter than the electrode plates 20, 21. Even though unneccesary ion beam 25 runs against an ion suppressing electrode 6 to cause sputtering of the metal of electrode 6, the position lies under the shadow of the electrode plates 20, 21, and a major portion of the undersurface of the insulative board 22 is free from metall attachment. Therefore, the positive electrode 20 and negative electrode 21 will not be shortcircuited, and the ion source can be operated for a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of an E.times.B mass separation device for separating ions having a desired mass from other ions by applying an electric field and a magnetic field at the same time. The ion source is a device for introducing a source gas, converting it into plasma, and converting this into an ion beam. The ion beam extracted from the ion source is
It can be used for various purposes such as irradiating an object and implanting ions and improving physical properties. In the ion source, various impurity ions may be generated in addition to the desired ions. When a thin ion beam is used, a mass separation device using a fan-shaped electromagnet can be used. Since a strong electromagnet is used, mass resolution can be increased.
However, in the case of an ion beam having a large diameter, the conventional fan magnet mass separation device cannot be used. This is because the magnet is large and bulky.

Large-area ion beams have come to be used in order to shorten the ion beam irradiation treatment time. It is called a surface ion beam. In order to generate this, a large number of ion through holes are drilled vertically and horizontally in the electrode provided at the outlet of the ion source. Since the beam is extracted through a large number of ion through holes, it is possible to effectively extract an ion beam having a large area. Thus, the ion beam passing through a large number of ion passage holes cannot be mass-separated by the fan-shaped magnet. Therefore, the surface ion beam is usually not mass separated. The object to be processed is directly irradiated with the ion beam generated by the ion source without mass separation.

[0003]

However, there are some applications in which the incorporation of impurity ions into the ion beam is particularly disliked. In such a case, it is desirable to provide a small-sized mass separation device for each small ion passage hole. Therefore, we use a Wien filter that separates the mass by the action of the electric field and the magnetic field. This is also called a Wien filter, but it is also called an E × B type mass separator because it performs mass separation by the action of an electric field (E) and a magnetic field (B). Wean filters are installed in each of the vertical and horizontal ion through holes. In this case, the magnetic field and the electric field are asymmetric. It is desirable that all of them be adjustable, but an electromagnet makes them bulky. Therefore, a permanent magnet is used to generate the magnetic field. The permanent magnet has a small volume and does not require an electric wire. Since it is a permanent magnet, the magnetic flux density is fixed. Those that give an electric field are formed by opposing parallel plates as electrodes and applying a voltage between them. An arbitrary electric field can be generated by changing the voltage.

It is assumed that there are MK ion through holes arranged in M rows × K columns. Electric fields and magnetic fields shall be generated in the same direction in all ion passage holes. In order to generate a magnetic field, two permanent magnets must be arranged so that the opposite poles face each other. Also, one permanent magnet can be used in common with the holes in the adjacent rows. After all, for MK ion through holes, M
K permanent magnets are required. Since the permanent magnets are isolated, they can be freely distributed. Electrodes that give an electric field have a wiring problem. Therefore, the positive and negative electrodes are opposed to each other through the ion passage hole. Since one pair of counter electrodes is required for one row, it is necessary to provide 2M electrodes in the end.

FIG. 1 is a vertical sectional view of an electrode portion of a device for generating a surface ion beam. FIG. 3 is a plan view of the separation electrode in which the permanent magnet and the electrode are arranged side by side. This shows a 3 × 4 ion through hole, but there are actually more through holes. This is the separation electrode proposed in Japanese Patent Application No. 5-154511 of the present applicant. A plurality of electrodes are provided at the outlet of the ion source 1. Source gas inlet 2 for ion source 1
Then, the source gas is introduced into the ion source 1. The raw material gas is excited by direct current discharge, microwave discharge, high frequency discharge, etc. to generate plasma, which is extracted as an ion beam by the action of the voltage applied to the electrodes. The problem here is related to the structure of the electrodes.

In this example, six electrode plates are installed at the exit opening of the ion source. From the side closer to the chamber, the plasma electrode 3, the extraction electrode 4, the mass separation electrode 5, the ion suppression electrode 6, the electron suppression electrode (deceleration electrode) 7, and the ground electrode 8 are provided. These electrode plates 3 to 8 are parallel plates. Ion through holes are formed at the same position in the plane direction. Since the holes are lined up in the axial direction, the plasma generated in the chamber goes straight out to the outside. These electrode plates are metal plates in which a large number of through holes are formed. In order to extract the ion beam from the ion source 1, an appropriate voltage is applied to the electrodes. An acceleration voltage V _acc is applied to the plasma electrode 3 by the acceleration power supply 9. This is for accelerating the ion beam to an appropriate speed and hitting the object.

A deceleration power supply 10 applies to the electron suppression electrode 7
A negative voltage of V _sp is applied. This repels secondary electrons generated by the ion beam. Power supply 11
(V _ex ), V is more than voltage V _{acc of} plasma electrode 3
_A voltage (V _acc -V _ex ) lower by _ex is applied to the extraction electrode 4. The voltage difference V _ex between the plasma electrode 3 and the extraction electrode 4
Causes ions to be extracted from the ion source chamber. The mass separation electrode 5 includes two types of electrode plates. Positive and negative voltages are applied to these electrodes with reference to the extraction electrode. To this end, separate power supplies 13, 14 are provided. The mass separation electrode 5 is an electrode that mass-separates ions by the action of an electric field and a magnetic field. The permanent magnets are attached to all the through holes so as to face each other, and the electrode plates are provided in a direction orthogonal to the permanent magnets. This is for mass-separating a plane ion beam having a large cross-sectional area. The structure of the mass separation electrode will be described with reference to FIG. 3, which is a cross-sectional plan view.

A large number of permanent magnets 41 are arranged in the row direction (X direction).
Are supported by a holding plate 40 of a suitable non-magnetic insulator. The polarities of these permanent magnets are in the same direction. In this figure, the magnetic force lines are generated in the upward direction (Y direction) in all the ion passage holes 15. A large number of electrode pairs 19 are provided so as to be orthogonal to the permanent magnet group. That is, the electrode pairs 19 extend in the column direction. A large number of electrode pairs 19 are installed in parallel in the row direction. If there are M rows and K columns of ion passing holes, (M + 1) K permanent magnets are required. The number of electrode pairs is the same in the column direction, and thus is smaller. The number of electrode pairs is K + 1.

This arrangement is simpler because the direction of the electrode pair and the direction of the permanent magnet can be made the same. The electrode pair is composed of metal electrodes 20, 21 and an insulating plate 22 made of ceramic or the like between them. The electrode plates are divided into two groups, those for applying a positive voltage and those for applying a negative voltage. These are referred to as the positive electrode 20 and the negative electrode 21. This is because the power supplies 14 and 13 apply positive and negative voltages to the extraction electrode 4 and the ion suppression electrode 6, respectively. One electrode pair 19 is a positive electrode 20, an insulating plate 2
2 and the negative electrode 21 are combined. These are integrally formed in advance.

The positive electrodes 20 are collectively screwed rods 3
It is connected by 0 and the nut 31. It is connected to the power supply 14 as previously described. The negative electrodes 21 are also connected together by another screw rod 30 and a nut 31. It is connected to the power supply 13. Nonmagnetic insulator holding plate 40
Is a plate extending in the row direction, and there is a hole through which the electrode pair 19 passes, through which all electrode pairs 19 pass. A grid is formed by the electrode pair 19 and the holding plate 40, and the grid holes serve as the ion beam through holes 15.

[0011]

FIG. 2 shows a mass separation electrode 5
It is a partially expanded sectional view of FIG. Unwanted charged particles 25 are contained in the ion beam coming from the ion source. This should be eliminated by the mass separation electrode. The unnecessary beam 25 is bent by the action of the electric and magnetic field and collides with the ion suppressing electrode 6. Then, the ion suppression electrode 6 is sputtered. The copper particles 26 are knocked out from the ion suppression electrode 6. The copper particles 26 are repelled and scattered in all directions. A considerable amount of copper particles adhere to the lower surface of the electrode pair. A part is attached to the lower surface of the insulating plate 22. The deposit 27 on the lower surface of the insulating plate 22 gradually increases. When the deposit 27 spreads, a part of the lower surface of the insulating plate 22 becomes conductive and the positive electrode 20 and the negative electrode 21 are electrically connected. In this case, the electrodes are short-circuited, and the operation of the ion source must be stopped.

An example used for ion doping will be described. Amorphous Si is irradiated with B ₂ H ₆ as an ion beam in order to introduce a p-type dopant. Alternatively, in order to introduce an n-type dopant, PH ₃ is used as an ion beam for irradiation. In any case, a large amount of hydrogen ions (protons) are generated in the ion source. This passes through the plasma electrode 3, is mass-separated by the mass separation electrode 5, and collides strongly with the ion suppression electrode 6 therebelow. This sputters copper. The insulating plate 22 has a thickness of 1 mm, for example.
It is thin. The inter-electrode voltage of the mass separation electrode 5 is about 100V. Sputtered particles may adhere to the lower surface of the insulating plate and break the insulation. An object of the present invention is to provide a mass separation electrode 5 in which the insulation of the insulating plate is not broken even when the unwanted ion beam collides with the ion suppression electrode 6 and the electrode material is sputtered. That is, it is an object of the present invention to solve the dielectric breakdown due to sputtered particles.

[0013]

A mass separation electrode of an ion source according to the present invention is a pair of electrodes in which an insulating plate is sandwiched between a positive electrode and a negative electrode, and the insulating plate is made smaller than the electrode plate in the vertical direction to provide insulation. A void is formed in the lower part of the plate so that the lower surface of the insulating plate becomes a blind spot from the sputtered particles.

[0014]

In the mass separation electrode of the ion source of the present invention, a short insulating plate is vertically sandwiched between the positive electrode and the negative electrode, and a void is formed below. For this reason, even if unnecessary ion beams hit the ion suppression electrode and sputter the metal of the electrode, the metal shadows the electrode plate and the metal does not adhere to most of the lower surface of the insulating plate. Therefore, the insulation of most of the insulating plates can be ensured. The positive and negative electrodes do not short circuit. The operation of the ion source can be continued for a long time.

FIG. 7 briefly illustrates the principle of the present invention. Of the three members of the electrode pair, the insulating plate 2 is more preferable than the electrode plates 20 and 21.
The lower surface 29 of 2 is raised. A void 28 is formed between the lower halves sandwiched between the electrode plates 20 and 21. Most of the lower surface 29 of the insulating plate 22 is in the shadow of the front electrode 21. Even if the unnecessary ion beam 25 collides with the ion suppression electrode immediately below the mass separation electrode and the electrode material 26 (for example, copper) is hammered out, it becomes a shadow of the electrode 21 in front, so that the material 26 is an insulating plate. Almost not attached to the lower surface 29 of 22. Even if the deposit 27 is partially formed, the entire lower surface 29 is not covered with the deposit 27. Therefore, the electrodes 20, 2 on both sides
1 is not short circuited by metal deposits.

[0016]

EXAMPLE FIG. 4 is a schematic perspective view of an electrode pair according to an example of the present invention. The positive electrode 20 is a rectangular metal plate, and the negative electrode 21.
Is a metal plate of the same size. There is an insulating plate 22 in the middle. Let K be the height of the electrode plate and H be the height of the insulating plate. These three members have the same length L in the longitudinal direction. The side closer to the extraction electrode 4 is flush. However, the insulating plate 22 has a recessed shape near the ion suppression electrode. A gap 28 is formed between the electrode plates. The lower surface 29 of the insulating plate 22 is at a position retracted from the lower surface of the electrode plate. The height S of the void is S = K-H.

FIG. 5 shows the shape of the electrode plate. (1) is a front view, (2) is a plan view, and (3) is a bottom view. (4) is a 4-4 sectional view of (1), and (5) is a 5-5 sectional view of (1). (6) is a 6-6 sectional view of (1). Although the electrode plates have the same shape, there is a notch 32 in a part of the upper side. In this portion, screw holes 33 are drilled in the other electrode plates and the insulating plate. As shown in (4) to (6), the lower surface of the insulating plate is higher than the electrodes on both sides.
When you look up at the lower surface of the insulating plate from diagonally below, most of it will be in the shadow of the electrode.

FIG. 6 is a schematic vertical sectional view of the entire ion source having the electrode structure of the present invention. The ion source 1 introduces a raw material gas and turns it into plasma. 6 in the opening of the ion source 1
A sheet of electrodes is provided. Plasma electrode 3, extraction electrode 4,
A mass separation electrode 5, an ion suppression electrode 6, an electron suppression electrode (deceleration electrode) 7, and a ground electrode 8. Ion beam through holes are formed at the same positions in these electrode plates. The plasma electrode 3 has a through hole 23, the extraction electrode 4 has a through hole 24, and the mass separation electrode 5 has a through hole 15. Further, the ion suppressing electrode 6 has a through hole 16, the electron suppressing electrode 7 (deceleration electrode) has a through hole 17, and the ground electrode 8 also has a through hole 18. These through holes are adapted to match the beam traveling direction.

An acceleration voltage V _acc is applied to the plasma electrode 3 and the ion source chamber by an acceleration power supply 9. The extraction power source 11 applies a voltage V _ex lower than the acceleration voltage to the extraction electrode 4 and the ion suppression electrode 6. As a result, plasma is extracted as an ion beam. Since the mass separation electrode 5 is sandwiched by the electrodes 4 and 6 having the same potential, the voltages applied to the electrode plates 20 and 21 of the mass separation electrode 5 are symmetrical with respect to the upper and lower electrode potentials. A positive voltage is applied to the electrode 20 and a negative voltage is applied to the electrode 21. This is 100V-200
It is the degree of V.

As shown in FIG. 3, the electrode pairs 19 are arranged in the column direction, and the permanent magnets 41 are arranged in the row direction. The magnetic field is in the column direction (Y
Direction). The Lorentz force of the magnetic field on the positive ions acts in the X direction. The electric field can be in the row direction (-X direction). The through hole 15 extends in the Z direction. The electric field (-X) and the action of the magnetic field (X) are opposite to each other. The ion beam is mass-separated by the action of E × B. Only an ion beam having a desired energy and mass can go straight through the through hole 15. Only those with a velocity w in the Z direction of w = E / B can pass through here. If the mass is larger than this, the velocity w is smaller than this, so the electric field is superior and the direction of the electric field (-X)
Turn to. In the case of a small mass, since w is larger than this, the magnetic field prevails and bends in the direction (X) opposite to the electric field.

The mass separation electrode 5 bends a beam of ions other than a desired ion beam and applies it to the ion suppressing electrode 6 to remove them. Ion beams 25 (for example, hydrogen ions) other than the desired ions are bent by the mass separation electrode 5 and collide with the ion suppression electrode 6, as shown in FIG. Due to the high energy, a part of the material of the electrode 6 is sputtered by the collision. Material atoms 26 (eg, copper) are knocked out. Conductive material 2 on all sides
I get 6. Although this goes straight, it is shielded by the lower surfaces of the electrode plates 20 and 21, and hardly adheres to the lower surface 22 of the insulating plate. Although the deposit 27 is slightly attached, the deposit 27 is not continuously attached to the entire surface, so that the insulating property can be maintained. Actually, there are through holes on both sides of one electrode pair as shown in FIG. 6, and the ion beam passes through the left and right through holes. Sputtered particles from the electrode 6 fly to the electrode pair from the left and right. However, since the insulating plate is covered on both sides by the electrode plates, sputtered particles from both sides can be prevented.

[0022]

Since the lower ends of the intermediate insulating plates are made higher than the lower ends of the metal electrode plates 20 and 21 on both sides of the electrode pair of the mass separation electrode 5, ion beams other than the desired ions are directly below. Even when the electrode is sputtered by colliding with the ion suppression electrode 6 of No. 1, sputtered particles do not adhere to the entire lower surface of the insulating plate. Therefore, the electrodes on both sides are not short-circuited. All electrode plates are common and biased by power supplies 13 and 14. If there is a short circuit at even one point, mass separation will no longer be possible. In the present invention, it is possible to prevent a short circuit between the electrodes at all points of the electrode pair. This is a useful invention because a short circuit accident can be prevented by a simple device.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an electrode of an ion source according to a conventional example having a mass separation electrode.

FIG. 2 is a cross-sectional view of the lower part of the mass separation electrode in the ion source electrode of FIG.

FIG. 3 is a cross-sectional plan view of a mass separation electrode provided with a wean filter in each ion beam through hole.

FIG. 4 is a perspective view of an electrode pair of the mass separation electrode of the present invention.

FIG. 5 is a diagram of an electrode pair of the mass separation electrode of the present invention. (1) is a front view, (2) is a plan view, (3) is a bottom view, (4) is a 4-4 sectional view of (1), (5) is a 5-5 sectional view, (6)
6-6 is a sectional view.

FIG. 6 is a longitudinal sectional view of an electrode of the ion source of the present invention having a mass separation electrode.

FIG. 7 is a cross-sectional view for explaining that sputtered particles do not adhere to the entire lower surface of the insulating plate in the present invention.

[Explanation of symbols]

1 ion source 2 raw material gas inlet 3 plasma electrode 4 extraction electrode 5 mass separation electrode 6 ion suppression electrode 7 electron suppression electrode (deceleration electrode) 8 ground electrode 9 acceleration power supply 10 deceleration power supply 11 extraction power supply 12 ion beam 13 for mass separation electrode Negative power source 14 Positive power source for mass separation electrode 15 Ion beam through hole 20 Positive electrode of electrode pair of mass separation electrode 21 Negative electrode of electrode pair of mass separation electrode 22 Insulation plate of electrode pair of mass separation electrode 25 By mass separation electrode Ion beam to be removed 26 Particles (for example, copper particles) sputtered from the ion suppression electrode 27 Deposit 28 Void of electrode pair 29 Lower surface of insulating plate 30 Screw rod 31 Nut

Claims (1)

[Claims] 1. An apparatus for extracting an ion beam having a large area from an ion source and mass-separating the ion beam by the action of an electric field and a magnetic field which are orthogonal to each other, and comprising a plurality of insulating plates sandwiched between two electrode plates. A pair of electrodes arranged in parallel, a holding plate made of a non-magnetic material arranged in parallel at right angles to the electrode pair, and a permanent magnet attached to the holding plate so that different poles face each other. A positive voltage is applied to the corresponding positive electrode of
A negative voltage is applied to the other corresponding negative electrode of the electrode pair to form an electric field between the counter electrodes in the ion beam through hole formed between the electrode pair and the holding plate, and the electric field is generated by the permanent magnet in the same through hole. Only the ion beams having the desired mass and energy are orthogonal to the magnetic field.
The insulating plate of the electrode pair is lower in height than the electrode plates on both sides, and a gap is formed between the electrode plates on the downstream side in the beam traveling direction. A mass separation electrode characterized by the above.