JPH07182998A - Accelerator tube - Google Patents

Abstract

PURPOSE:To obtain an electrode structure which prevents beam dispersion by controlling the profile of ion beams passing an accelerator tube in a wide energy range and a wide current range. CONSTITUTION:A decelerator electrode 6 having higher electric potential than that of a high potential electrode is provided between a high potential electrode 1, and a suppression electrode 2, similarly between the electrode 1 and a grounding electrode 3, thereby, ion beams are temporarily decelerated, and the beams are accelerated by means of a higher voltage. Since the acceleration voltage can be increased freely, the convergence effect of beams can be obtained. Even the energy or current of the ion beams changes, the convergence effect can be ensured by changing the voltage of the decelerator electrode 6.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an accelerating tube for accelerating a beam of charged particles. In particular, the present invention relates to an accelerating tube capable of controlling the beam profile for a wide range of beam current and beam energy and suppressing the spread of the beam. The accelerating tube accelerates a charged particle beam traveling in a vacuum by the action of an electric field. A ring-shaped electrode and a ring-shaped insulator are alternately arranged, and an appropriate voltage is applied to the electrode. The insulator seals the path to maintain the vacuum in the path. Beams must be transported when the ion generation region and the ion irradiation region are different, such as in an ion implanter. When the beam transport system is long, the spread of the beam becomes a problem. Particularly when the current density of the beam is high, the Coulomb repulsion acts on the ions due to the effect of space charge. Especially at low speeds, the divergence effect due to the Coulomb repulsive force is remarkable. If the transport system is long, the beam diverges due to divergence, and a sufficient beam density cannot be obtained when irradiating an object.

[0002]

2. Description of the Related Art An accelerator tube, like a plasma extraction electrode of a plasma generator, is composed of three electrodes: a high potential electrode that applies a high voltage, a suppress electrode that applies a negative voltage, and a ground electrode that is a ground potential. Become. FIG. 1 is a schematic sectional view of an acceleration tube according to this conventional example. This includes three electrodes placed along the beam path. The high potential electrode 1, the suppress electrode 2 and the ground electrode 3. The acceleration power supply 4 applies a positive high voltage to the high potential electrode 1. The suppress power supply 5 applies a negative voltage to the suppress electrode 2.

The beam is accelerated by the voltage of the acceleration power source 4. The high potential electrode 1 is also called an accelerating electrode or a positive electrode. Secondary electrons are generated when the beam collides with an object or the like. The suppress electrode 2 prevents secondary electrons from flowing back to the upstream side of the beam. Therefore, it is called a suppress electrode. This is also called a deceleration electrode, a negative electrode, and a suppression electrode. Different people have different names for electrodes. Here, the high potential electrode 1,
The names of suppress electrode 2 and ground electrode 3 are adopted.

The electrode is a circular plate with an opening in the center. The beam passes through this opening. Insulators (not shown) are present between the electrode plates, and the beam path is a closed space. A vacuum pump (not shown) is connected to hold the vacuum in the path. A vacuum pump and an insulator are not shown for simplicity.

[0005]

In the accelerating tube, a positive ion beam or a negative ion beam flies at high speed. Since there are almost no electrons, the neutralization probability is small. It runs as a set of positive or negative ions. Since they are charged particles of the same kind, the Coulomb repulsive force acts on each other. This has the effect of spreading the beam outward. The existence of particles with the same type of charge in space is called space charge. The spread of the beam due to the repulsive force due to the space charge is called the space charge effect. It is not a problem when the charge density is low or when the speed is high. However, if the charge density is high or the speed is slow,
Space charge divergence becomes a serious problem.

In the conventional accelerating tube, the structure of the electrode is designed so as to suppress the divergence due to space charge and converge the beam. However, it has a convergence effect only for a beam with certain limited conditions. If the conditions are different, there is no longer any effect of preventing divergence.

In the electrode structure consisting of the high-potential electrode 1, the suppress electrode 2 and the ground electrode 3 of FIG. 1, the spacing between electrodes, the diameter, and the voltage are appropriately determined, and a convergence effect is obtained for a beam under the following conditions. Suppose there is. For example, 40keV, 50m
The incident beam of A is accelerated by 60 keV, 100 keV, 5
It is assumed that the output beam is designed to have a small divergence of 0 mA.

When an incident beam of 40 keV and 50 mA is accelerated by 20 keV to a beam of 60 keV and 50 mA with this accelerating tube, there is almost no convergence effect. This is because the acceleration voltage is small. Therefore, the spread of the beam cannot be suppressed.
The beam diverges. If the acceleration conditions are different, the divergence prevention effect is no longer effective.

In this case, the incident beam is 20 keV, 50
It is also possible to obtain an ion beam of 60 keV by accelerating at 40 keV with mA. Since the acceleration voltage is large, a convergence effect can be expected. However, it is not always the case that the acceleration voltage here can be close to 60 keV. A mass spectrometer may be placed in front of the accelerating tube to remove impurities. High energy is required for mass spectrometry. In that case, it cannot be transported to the acceleration tube with low energy.

A mechanism for converging the beam regardless of the incident energy of the ion beam, the current density and the acceleration energy is desired. It is an object of the present invention to provide an accelerating tube capable of converging an ion beam regardless of the current density and the energy of the beam.

[0011]

The accelerating tube of the present invention comprises a high potential electrode 1 to which a high voltage is applied, and a high potential electrode 1 provided after this.
It is composed of a deceleration electrode 6 to which a higher voltage is applied, a suppress electrode 2 after which a negative voltage is applied, and a ground electrode 3 having a ground potential. Each electrode is a circular or polygonal conductive plate, but has a hole in the center for the ion beam to pass through. The present invention is novel in that a deceleration electrode 6 is added. The deceleration electrode 6 is located between the high potential electrode 1 and the suppress electrode 2. The deceleration electrode has the highest potential and the suppress electrode has the lowest potential. The largest electric field is between the deceleration electrode and the suppress electrode, where local acceleration occurs.

[0012]

In the ion beam transport system, the beam tends to converge by acceleration. The divergence is due to the force acting in the direction orthogonal to the beam. Acceleration is a force in the beam direction. This alone cannot suppress the spread of the beam. However, the lines of electric force formed between the electrodes having holes and the equipotential surface are not perpendicular or parallel to the electrodes. The equipotential surface between the high potential electrode with holes and the low potential electrode is distorted like a lens. The lines of electric force are spindle-shaped. Therefore, the beam passing between the high potential electrode and the low potential electrode converges. However, if the accelerating voltage is not high enough, the effect is weak.

The accelerating tube of the present invention comprises a high potential electrode 1 and
The deceleration electrode 6 having a higher voltage is installed. Instead of accelerating immediately after passing through the high-potential electrode, it decelerates once. The beam spreads a little due to this deceleration. However, the high voltage generated between the deceleration electrode 6 and the suppress electrode 2 causes the ion beam to have a focusing effect. Therefore, there are two actions of the deceleration electrode 6 that can travel without the beam diverging.

One is the acceleration energy corresponding to the deceleration voltage.
Is to increase. The voltage difference between the high-potential electrode (deceleration electrode) and the low-potential electrode (suppress electrode) is increased to increase the distortion of the equipotential surface and the lines of electric force to increase the convex lens effect. The other is to reduce the kinetic energy of the ions by decelerating to facilitate movement in the direction perpendicular to the beam direction and to enhance the lens effect.

The deceleration electrode 6 spreads the beam between the high-potential electrode and the deceleration electrode, but this is not a problem because the incident energy of the beam to this region is high.

[0016]

EXAMPLE An electrode structure of an acceleration tube according to the present invention will be described with reference to FIG. A high-potential electrode 1, a deceleration electrode 6, a suppress electrode 2, and a ground electrode 3 are provided in this order from the direction of the ion beam. In each case, there is an opening for passing an ion beam in the center. A high voltage is applied to the high potential electrode 1 by the acceleration power supply 4. A negative voltage is applied to the suppress electrode 2 by the suppress power supply 5. When the ion beam hits the object, secondary electrons are emitted. The suppressed electrode has a function of preventing secondary electrons from returning to the ion source. A higher voltage is applied to the deceleration electrode 6 by the deceleration power supply 7 connected to the positive electrode of the acceleration power supply 4. The deceleration power supply 7 is a variable power supply, and the magnitude of deceleration energy can be arbitrarily adjusted.

FIG. 3 shows a streamline of a beam when the accelerator tube having the electrode structure of the present invention is not decelerated. The incident beam is an Ar ion beam of 40 keV and 50 mA. The voltage of the high potential electrode 1 is 20 kV and the voltage of the deceleration electrode 6 is 20 kV.
The voltage of the kV and the suppress electrode is -5 kV. No deceleration voltage is applied to the deceleration electrode. In this case, this is the same as the conventional example, and the ion beam spreads.

FIG. 4 shows the case where a deceleration voltage of 20 kV is applied to the deceleration electrode 6 in the electrode structure of the present invention. The high potential electrode 1 is 20 kV, the deceleration electrode 6 is 40 kV, and the suppress electrode 2 is -5 kV. In this case, there is a convergence effect.
It becomes a thin beam and passes through the acceleration tube. It can be seen that a converging effect can be obtained by applying a deceleration voltage to the deceleration electrode, reducing the speed of the beam, and then greatly accelerating again.

[0019]

According to the present invention, since the deceleration electrode 6 is provided between the high potential electrode 1 and the suppress electrode 2, the acceleration voltage between the deceleration electrode and the suppress electrode can be made large, and the acceleration voltage can be increased. The convergence effect is increased by increasing. Since the speed of the beam is once reduced by the deceleration electrode, the convergence of the beam is further increased. Since the voltage parameter is increased by one, controllability is enhanced. The voltage applied to the high-potential electrode is determined in advance because it is determined by the final acceleration voltage. It cannot be changed. However, the voltage applied to the deceleration electrode 6 is a parameter that can be arbitrarily changed. Changing this does not affect the final energy of the beam.

Even if the energy of the beam or the beam current changes, the beam can be converged by adjusting the deceleration voltage. This is because there is one more parameter. In a wide range of current and energy, divergence of the beam can be suppressed. Optimal for accelerating tubes such as long beam transport systems.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an acceleration tube according to a conventional example.

FIG. 2 is a schematic cross-sectional view of an acceleration tube of the present invention.

FIG. 3 is a cross-sectional view showing a streamline of an ion beam when the deceleration voltage is 0 V in the acceleration tube having the electrode structure of the present invention.

FIG. 4 is a cross-sectional view showing a streamline of an ion beam when the deceleration voltage is 20 kV in the acceleration tube having the electrode structure of the present invention.

[Explanation of symbols]

 1 High-potential electrode 2 Suppress electrode 3 Ground electrode 4 Acceleration power supply 5 Suppress power supply 6 Deceleration electrode 7 Deceleration power supply

Claims (1)

[Claims] 1. A beam provided in a transportation system of an ion beam.
A high-potential electrode having an opening to which a high voltage is applied, and an accelerating tube for accelerating the beam, and a high-voltage electrode which is provided subsequent to the high-potential electrode and which has an opening and to which a higher voltage is applied. The deceleration electrode, a suppressed electrode that is provided following the deceleration electrode and to which a negative voltage is applied, and a ground electrode that is provided next to the suppressed electrode and has an opening and that has a ground potential.The ion beam is a high potential electrode. An accelerating tube characterized by being decelerated between deceleration electrodes and being more strongly accelerated between a deceleration electrode and a suppress electrode.