JP3430557B2 - Accelerator tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerating tube for accelerating an ion beam, which is capable of suppressing the divergence of the beam and controlling the beam profile to have an appropriate shape. There are many devices using an ion beam, such as an ion implantation device, an ion etching device, an ion beam irradiation device, and an ion beam measuring device. This includes an ion source, a beam transport system, a holding and transporting device for the object to be treated and the like. An acceleration tube, a deceleration tube, etc. for accelerating or decelerating are provided in the beam transportation system. In the case of positive ions, the accelerating tube includes an electrode to which a positive voltage is applied and an electrode having a lower potential. There may be intermediate potential electrodes.

On the contrary, the speed reducer has electrodes arranged so that the voltage rises. The acceleration voltage is the energy of the ions
To decide. When the ions are accelerated and driven into the sample, the ions enter the sample with the acceleration energy. The effect on the sample is different due to the difference in energy. The depth of driving also differs. The acceleration voltage can be adjusted by changing the power supply voltage.

[0003]

2. Description of the Related Art Ion beams have a wide range of uses such as modification of substances, creation of new substances, and analysis of physical properties. A thin ion beam with a small current can be easily made, and the transport system is also simple. However, in order to improve the processing capacity, a beam with a large diameter and a large current is required. If the ion beam has a large current, the ion density inside is high, so
The action of the Coulomb repulsive force due to the space charge becomes stronger, and the ion beam diverges. The ion beam may be accelerated after leaving the ion source and may be directly injected into the sample. Alternatively, it may be further decelerated by the deceleration tube and incident on the sample. Secondary electrons are emitted by implanting ions into the sample.

When the secondary electrons travel backward along the beam line in the direction opposite to the positive ion beam, an extra current flows through the ion source, increasing the load on the power source. Further, the backflowing secondary electrons are accelerated and enter the ion source chamber, which may cause thermal damage to the chamber. Further, when electrons collide with a wall surface in the chamber, X-rays are generated. High risk. Therefore, in order to prevent the backward migration of secondary electrons, a secondary electron suppressing electrode is often provided between the acceleration tube and the sample. This is often a cylindrical electrode. A negative voltage is applied to this electrode. Since a negative voltage is applied, secondary electrons cannot trace back here and are driven back to the sample side.

FIG. 1 is a schematic sectional view of a conventional ion beam irradiation system. The ion beam 1 generated by the ion source (not shown) passes through the acceleration electrode 2 and is accelerated between the ion beam 1 and the ground electrode 3. The acceleration electrode 2 is positively biased by the power supply 4. The ion source is, of course, biased to the same or higher potential. A protruding equipotential line 5 is formed between the acceleration electrode 2 and the ground electrode 3. For this reason, the beam is subjected to a converging action. The ion beam further flies, passes through the secondary electron suppressing electrode 6, and reaches the sample 8. Secondary electrons are generated because high-energy ions hit the sample. The secondary electron suppression electrode 6 repels this. Secondary electrons never enter the ion source.

[0006]

In the conventional ion beam irradiation system, since the current is small, the diffusion of the beam is not a serious problem. However, as the ionic current increases, beam spread due to space charge becomes a problem. Further, as the sample becomes larger, it is desirable that the beam diameter be larger. That is, there is a strong demand for an ion beam with a large diameter and a large current. When the accelerating voltage is high, the beam transportation system is often long, but in this case, the traveling time is long and the spread of the beam cannot be ignored.

There is a higher demand. Depending on the shape of the sample and the state of the sample, there is a demand for the beam to have a cross-sectional shape that is not a simple circle but a modified shape such as a square shape or an elliptical shape. In this case, conventional acceleration tubes and deceleration tubes cannot be used.

Although the current is large, the acceleration voltage may be low. In this case, the traveling time becomes long and the action of the Coulomb repulsive force between the space charges becomes more remarkable. As described above, when the beam enters the accelerating tube, the beam has a converging action due to the inclination of the equipotential surface, but the ground electrode 3 has a diverging action on the contrary. In addition, there is a repulsive force due to its own space charge, and the beam advances while diverging in the transport system. The longer the beam line, the greater the divergence. When the divergence is large, some ions collide with the wall surface of the transport system on the way and are lost. In addition, there may be wasted ions that do not hit the sample. Higher divergence also increases beam loss during transit.

[0009]

In the accelerating tube of the present invention, magnets are arranged so that they have a radial magnetization direction and alternate magnetization directions along the peripheral surface of a secondary electron suppression electrode for repelling secondary electrons. The magnet rows are arranged in one step or in a plurality of steps in the longitudinal direction so that the magnetization directions are alternated.

[0010]

Since a plurality of magnets are arranged radially on the circumference, arc-shaped magnetic force lines are formed so as to connect the end faces of adjacent magnets. The magnetic field does not reach the center of the hole of the secondary electron suppression electrode. There are two or three such magnetic field lines. When an ion beam tries to cross an arc-shaped magnetic force line, a Lorentz force acts in a direction orthogonal to both the flight direction of the beam and the direction of the magnetic force line. In a certain angle range with respect to the central axis, this is the force toward the center, and in the other range, the force is toward the outside. In the former case, the beam is bent in the direction of convergence. In the latter case, the beam is bent in the diverging direction. Since there are a plurality of stages and the magnetization directions are opposite to each other, the beam diverged in the first stage receives a force that converges in the next stage. The beam that converges first receives a force that diverges next.

Thus, the beam in any area receives the force of convergence. The fact that the magnetization directions of the magnets arranged in a circle are reversed between adjacent magnets is necessary for forming a strong magnetic field between the magnets in the circumferential direction. In addition, it is indispensable to arrange the magnets in multiple stages and to alternately apply the diverging action and the converging action in order to substantially converge the beam.

However, for the purpose of shaping the beam cross-sectional shape, it is not necessary to arrange the magnets in multiple stages. For example, it is possible to provide six magnets in only one stage. This allows the beam to have a triangular cross-sectional shape. If it is desired to have an elliptical shape, four magnets are arranged in one or two stages. The length of the magnet is also one of the parameters. By arranging magnets having the same length and the same strength in two stages, the beam can be isotropically converged. However, if the lengths are different, the beam becomes elliptical.

[0013]

2 to 5 show an accelerating tube according to an embodiment of the present invention. First there is the accelerating electrode 2, which is given a positive voltage. Next is the ground electrode 3. Then, there is the secondary electron suppressing electrode 6, and the ion beam passes through the hole in the center of the electrode. A negative voltage is applied to the secondary electron suppression electrode 6. The secondary electron suppression electrode 6 is a nonmagnetic material. Four magnets 11, 12, 13, 14 are arranged on the outer circumference of this electrode so that the magnetization direction is the radiation direction and the magnetization direction is reversed between the adjacent magnets. These magnets may be permanent magnets or electromagnets. If a permanent magnet is used, no electric power is required and the cost can be reduced. Although the use of an electromagnet requires an operating cost, the beam cross-sectional shape can be arbitrarily changed.

In this example, there are four magnets, which are arranged in two stages. Since the magnetization directions of the adjacent magnets are different from each other, the magnetic force lines emitted from the end surface of a certain magnet enter the end surface of the adjacent magnet. That is, a cusp magnetic field with the end face of the magnet as a cusp is generated. Since the magnetic fields of adjacent magnets cancel each other at a long distance, a short-distance magnetic field is formed. The direction of the magnetic field is substantially along the circumferential surface. The end surface of the magnet may be flat, but it is better to make it round like this. It is best to make the magnet cross section a right-angled hyperbola. Alternatively, it is preferable that the magnet has a width of 2a and has a circular surface with a radius of R = 1.125a to 1.25a.

As shown in FIG. 4, the positive ion beam is a low beam.
A force is applied in the direction of the arrow by the Lenz force. In this example, the beam deflected vertically receives an inward force. Turn inward for. The beam that is deflected to the left and right receives an outward force. This gives a beam with an elliptical cross section.

Such a magnet array is provided in two stages along the longitudinal direction of the secondary electron suppressing electrode 6. As shown in FIG.
The beam receiving the inward force at the beginning is the second row of magnets 2
An outward force is applied by 1, 22, 23, and 24. On the contrary, the beam that first receives the outward force receives the inward force by the magnet array in the second stage. Thus, the beam can be transformed into a beam having a circular cross section or a rectangular cross section.

The point of the present invention is to suppress the beam spread by the magnet array provided on the secondary electron suppressing electrode 6. The number of magnets that make up the magnet array is 6 in addition to 4, 8
It may be an even number such as 10 or 10. Further, the number of magnet rows provided in the longitudinal direction of the secondary electron suppressing electrode 6 may be one row other than two rows, and may be three rows, four rows, or more.

In FIGS. 6 and 7, the number of magnets is 6, and this is 2
An example of tiering is shown. The magnet row of the first stage is composed of magnets 15 and 1
It consists of 6, 17, 18, 19, and 20. The second row of magnet rows is composed of magnets 25, 26, 27, 28, 29, 30. The magnetization direction of the magnets is reversed between the adjacent magnets. 1st stage 2
The magnetization directions of the magnets in the stages are determined complementarily. According to this, the beam can be transformed into a hexagonal beam. By adjusting the strength and length of the magnet, a beam having a converging property can be obtained. The number of magnets in one stage may be six, and may be three or four.

8 and 9 show an example in which the number of magnets is eight. The first stage is shown in FIG. 8 and the second stage is shown in FIG. The first row of magnets includes magnets 31, 32, 33, 34, 35, 36, 3
It consists of 7, 38. The second row of magnets consists of magnets 41, 42,
It consists of 43, 44, 45, 46, 47 and 48.

FIG. 10 shows a case where the magnet array has four stages.
As the number of stages in the magnet array increases, the shape of the beam can be controlled more delicately. In the case of a quadrupole, two magnet rows are required. 6
Even in the case of a heavy pole, it is better to have two stages. 1 if it is an octopole
Can be tiered. In FIG. 11, a flange 60 is formed on the end surface of the secondary electron suppression electrode 6. As a result, the lines of electric force on the inlet side of the secondary electron suppressing electrode 6 can be deformed to correct the shape of the beam cross section.

[0021]

According to the present invention, a plurality of magnets are provided along the circumference and a plurality of steps are provided along the longitudinal direction on the secondary electron suppressing electrode of the accelerating tube of the ion beam of large diameter and large current. ,
This suppresses the spread of the beam. In particular, when the current is large but the acceleration voltage is low, the divergence should be remarkable, but the magnet of the present invention can effectively prevent the divergence. The beam spread can be adapted to the sample size. Since the divergence is reduced, the beam transportation efficiency is improved.

Further, the final beam cross-sectional shape can be controlled to a desired shape by appropriately arranging the magnet arrangement and strength. It is possible to generate an ion beam having an elliptical cross section, a rectangular cross section, or a star cross section, instead of a simple circular cross section beam. If the cross-sectional shape of the beam needs to be controlled depending on the application, the magnet should be an electromagnet.

However, when the electromagnet is used, the size of the device becomes large and the cost becomes high. If cheaper and smaller size is required, it is better to use a permanent magnet.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a conventional ion beam transport system.

FIG. 2 is a longitudinal Y-sectional view of a beam transport system showing the configuration of the present invention.

FIG. 3 is an X sectional view in the longitudinal direction of the beam transport system showing the configuration of the present invention.

FIG. 4 is an XY cross-sectional view of the ion beam transport system of FIGS. 2 and 3 in which the secondary electron suppression electrode is cut by the first row of magnets.

5 is an XY cross-sectional view of the secondary electron suppressing electrode cut by the second row of magnets in the ion beam transport system of FIGS. 2 and 3. FIG.

FIG. 6 is an XY cross-sectional view of the secondary electron suppressing electrode cut by a first-stage magnet array of another embodiment in which six magnets are arranged on the outer peripheral surface of the secondary electron suppressing electrode.

FIG. 7 is an XY cross-sectional view in which the secondary electron suppressing electrodes are cut by a second-stage magnet array of another embodiment in which six magnets are arranged on the outer peripheral surface of the secondary electron suppressing electrodes.

FIG. 8 is an XY cross-sectional view in which the secondary electron suppressing electrode is cut by the first-stage magnet array of the third embodiment in which eight magnets are arranged on the outer peripheral surface of the secondary electron suppressing electrode.

FIG. 9 is an XY cross-sectional view in which the secondary electron suppressing electrodes are cut by the second-stage magnet array of the third embodiment in which eight magnets are arranged on the outer peripheral surface of the secondary electron suppressing electrodes.

FIG. 10 is a longitudinal sectional view of a fourth embodiment in which four stages of magnet rows are arranged on the outer peripheral surface of the secondary electron suppressing electrode.

FIG. 11 is a longitudinal sectional view showing another embodiment in which the shape of the secondary electron suppressing electrode is modified.

[Explanation of symbols]

1 ion beam 2 Accelerating electrode 3 ground electrode 4 power supply 6 Secondary electron suppression electrode 7 power supply 8 samples 11-20 magnets 21-30 magnets

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 37/04 G21K 5/04 H01J 37/30

Claims (2)

(57) [Claims] 1. An accelerating tube biased to a positive voltage for accelerating an ion beam generated by an ion source, and a negative electrode for returning secondary electrons generated by irradiating the sample with the ion beam to the sample side. It includes a biased secondary electron suppression electrode and a single-stage or multiple-stage magnets arranged along the peripheral surface of the secondary electron suppression electrode so that the magnetization directions alternate, and passes through the secondary electron suppression electrode. An accelerating tube characterized in that an ion beam is converged or shaped into a desired cross-sectional shape. 2. An accelerating tube biased to a positive voltage for accelerating an ion beam generated by an ion source, and a negative electrode for returning secondary electrons generated by irradiating the sample with the ion beam to the sample side. It includes a biased secondary electron suppressing electrode and one or more stages of magnets arranged so that the magnetization directions alternate along the peripheral surface of the secondary electron suppressing electrode, and the end face of the magnet is a right-angled hyperbola or magnet. Is a circular end face having a width of 2a and a radius of 1.125a to 1.25a, and the ion beam passing through the secondary electron suppressing electrode is converged or shaped into a desired cross-sectional shape. Accelerating tube.