JPH04351840A - E-b separator - Google Patents

Abstract

PURPOSE:To maintain constant level of intensity of a magnetic field in a wide range, and to carry out mass separation for a charged particle beam of large width by providing auxiliary magnets with the same polarities opposed to one another, outside of a parallel flat plate electrode, and in parallel thereto. CONSTITUTION:A parallel flat plate electrodes 1 are opposed to one another, and a beam is guided so that it is in parallel to the electrode. Main magnets 2 are provided on both sides of the electrode 1 so that different polarities are opposed to one another. Auxiliary magnets 3, 4... that are in parallel to the electrode 1 are provided on the outside of the electrode 1, and the auxiliary magnets are formed in pair with the same poles opposed to one another, and the same magnetic poles as the opposed magnetic pole of the nearer one of the main magnets 2 are opposed to one another. In a coordinate in which the center of a region for passing beam will be origin, in a region of x>0, the same poles are directed inward, while in a region of x<0, the same poles of different polarities are directed inward.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved Wien filter type mass separator that selects ions of a specific mass from an ion beam by the action of orthogonal electric and magnetic fields.

0002

2. Description of the Related Art The most commonly used mass separator is one that utilizes a sector-shaped electromagnet. This creates a magnetic field of constant strength between opposing fan-shaped electromagnets, making the flight trajectory of charged particles flying with constant energy into a circular arc trajectory. The greater the mass, the smaller the curvature of the arc, and the smaller the mass, the greater the curvature of the arc, so the trajectories of particles with different masses can be separated. By providing a suitable slit behind the magnet, only particles of a desired mass can be taken out. This type of mass separator has a drawback in that the magnet is large and occupies a large amount of space because it draws an arcuate trajectory. Another disadvantage is that it is difficult to adjust the beam line before and after the mass separator because the beam line is not straight.

[0003] There is a Wien filter that can perform mass separation while maintaining a straight line. In this method, an electric field and a magnetic field are formed so as to be orthogonal to each other, and charged particles are passed through at right angles to these fields. The effects of the electric field and magnetic field acting on charged particles are contradictory, but the effect of the magnetic field differs depending on the velocity v. If energy is constant (acceleration voltage is constant), a difference in mass will appear as a difference in velocity v. E=v
Only charged particles with a mass that satisfies B can travel straight through the Wien filter. In order for the Wien filter to have such a mass separation effect, both the electric and magnetic fields must be constant in the region through which the beam passes. If the electrodes and magnets have infinite sizes, they can form a constant electric and magnetic field. However, in reality, the electrode plate only has a finite extent, and the magnet is not that large. Due to their finite dimensions, the electric and magnetic fields are not uniform in the area surrounded by these. Electric field only in a very narrow area in the center,
The magnetic field becomes uniform. If this is the case, it is only necessary to pass the charged particle beam through a narrow central region of the Wien filter. However, depending on the purpose, it may be necessary to mass-separate charged particles with a wide cross-sectional area. It may also be desirable to mass-separate charged particles having a band-shaped cross section.

0004

FIG. 4 shows a cross section of a Wien filter type mass separator in such a case. An electrostatic field E is generated between the parallel plate electrodes 11, 11 facing each other. The magnets 10, 10 provided in a direction perpendicular to these are set so that different poles thereof face each other. During this time, an electric field and a magnetic field are formed so as to be perpendicular to each other. A charged particle beam 14 having a wide band-like cross section passes through the space surrounded by these. If the distance between the electrodes 11 and 11 increases, the disturbance of the electric lines of force at both ends will increase, so the distance between the electrodes is narrowed. However, since the beam 14 is wide, the distance between the magnets 10 and 10 increases. .

An explanation will be given with the direction of the magnetic field lines of the magnet as the x-axis, the direction of the electric field as the y-axis, and the direction of flight of the beam as the z-axis. The beam passes near y=0. The magnetic field lines are x
However, when y=0, the lines of magnetic force do not necessarily point in the x direction, but have a y-direction component, and are distorted into a convex lens shape. The magnitude and direction of the magnetic field deviate from the desired values. Although the charged particle beam 14 is wide,
Regarding the y direction, it is possible to narrow down to the vicinity of y=0. Then, the influence of disturbance of the magnetic field in the y direction should be reduced. However, even so, the beam may not be able to be narrowed down completely in the y direction, and as long as there is a finite width, precise mass separation cannot be achieved due to the influence of the magnetic field disturbed in the shape of a convex lens. In other words, if y=0, the magnetic flux density will be lower than the value of y=0, so even if a charged particle has the desired mass, the deflection force due to the magnetic field will become weaker, and it will be bent in the direction of the electric field.
This means that it cannot pass through the slit at the back. Conversely, even if a charged particle has a small mass (v is large), y
If it passes through an area that deviates from =0, it will pass through the slit at the rear. If you want to avoid this and perform more precise mass separation, it is necessary to correct the disturbance in the magnetic field, even if it is slight.

[0006]

[Means for Solving the Problems] The mass separator of the present invention has opposing parallel plate electrodes to which an electrostatic voltage is applied, and parallel plate electrodes that are parallel to each other so as to generate magnetic flux in a direction perpendicular to the normal line of the parallel plate electrodes. It includes magnets installed on the sides of the parallel plate electrodes so as to face each other, and charged particles are passed between the electrodes and between the magnets in a direction perpendicular to both the electric field generated by the parallel plate electrodes and the magnetic field generated by the magnets to travel straight. In a mass separator that performs mass separation by allowing only charged particles to pass through, the main pair of magnets is provided outside the parallel plate electrode and has the same polarity as the magnetic pole on the opposing surface of the nearer magnet. It is characterized by having a plurality of auxiliary magnets with magnetic poles facing each other.

[0007]

[Operation] The auxiliary magnet has the effect of effectively suppressing the lines of magnetic force created by the main magnet inward. For this reason, even in areas where y=0 is not present (a region quite far from the center), the direction of the magnetic field is in the x direction, and the magnitude is the same as the value at y=0. Therefore, in the region where the charged particle beam exists, both the electric field and the magnetic field can be maintained at a constant magnitude and direction. Mass separation can be performed as theoretically calculated.

[0008]

Embodiment FIG. 1 shows a schematic perspective view of an ExB mass separator according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the same, showing the distribution of magnetic field lines. Parallel plate electrodes 1, 1 are arranged to face each other. The beam is assumed to be introduced parallel to this. Main magnets 2, 2 are installed on both sides of the parallel plate electrodes 1, 1 so that their different poles face each other. This may be a permanent magnet or an electromagnet. In addition to these basic formats, the present invention provides auxiliary magnets 3, 4, . . . parallel to the parallel plate electrodes on the outside thereof. The auxiliary magnets are provided in pairs so that the same poles face each other, and the same magnetic poles as the opposite magnetic pole of the closer magnet among the main magnets face each other.

In FIG. 1, the auxiliary magnets are 3, 3 and 4, 4.
There are two pairs. Of course, it may be more than this. In this example, the auxiliary magnet on the right side is installed so that its north poles face each other. This is because the opposing magnetic pole of the right main magnet 2 is the north pole. The auxiliary magnet on the left is installed so that its S poles are facing each other. This is because the opposing magnetic pole of the left main magnet 2 is the S pole. Expressed in a coordinate system with the origin at the center of the area through which the beam passes, in the area where x>0, the same poles point inward, and in the area where x<0, the same poles with different polarities point inward. It turns out to be facing the same direction. Do not place it at the point where x=0, that is, in the middle. As long as this point is avoided, any number of pairs of auxiliary magnets may be provided.

As shown in FIG. 2, the auxiliary magnets 3 and 4 have the effect of suppressing the lines of magnetic force, which have spread into a convex lens shape as shown in FIG. 4, toward the center. Therefore, in a fairly wide range on both sides of y=0, the magnetic field is oriented in the x direction and has a constant strength. Of course, the strength of the auxiliary magnet,
The dimensions are not arbitrary; they must be calculated so as to produce parallel magnetic fields.

The main magnets 2, 2 may be electromagnets or permanent magnets, but in the case of permanent magnets, rare earth (Sm-Co)
) or a Ne-Fe magnet. Since a strong saturation magnetic flux can be obtained, the device can be made smaller. The auxiliary magnets 3, 4, . . . may also be electromagnets or permanent magnets. However, if the main magnet 2 is an electromagnet and the generated magnetic field changes, the magnetic field that the auxiliary magnets 3 and 4 should generate will also change, so it is better to use electromagnets. However, there are cases where the correction magnetic field to be generated by the auxiliary magnet does not need to change much, so in this case, a combination in which the main magnet is an electromagnet and the auxiliary magnet is a permanent magnet is possible. Changing the mass of the particles to be selected is done by changing the electric field.

What is shown in FIGS. 1 and 2 is the basic form of the mass separator of the present invention. This shape also works well. However, if this continues, a strong DC magnetic field will be formed in the vicinity. This may affect the health of various equipment and workers. Furthermore, if this state continues, the magnetic resistance of the magnetic circuit will be high, making it difficult to obtain a strong magnetic flux density. Therefore, as shown in FIG. 3, a magnetic shield 6 can be provided to surround the main magnet and the auxiliary magnet. The magnetic shield 6 may be made of iron, ferrite, or other ferromagnetic material. Almost all of the magnetic lines of force coming out from the magnet pass through the magnetic shield 6. Magnetism does not leak outside the magnetic shield, so there is no effect on peripheral equipment or workers. Furthermore, since the magnetic resistance can be lowered, the magnetic flux density obtained can be increased even if the same magnet is used.

[0013]

[Effect of the invention] In a Wien filter type mass separator that separates charged particles by the action of an electric field and a magnetic field, the strength of the magnetic field can be kept constant over a wide range even if the distance between opposing magnets is wide. Can be done. Therefore, a wide charged particle beam can be precisely mass separated. It is suitable as a mass separator for high-power ion beam irradiation equipment and high-power ion implantation equipment.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the basic configuration of an E×B separator of the present invention.

FIG. 2 is a diagram showing the distribution of magnetic lines of force in a cross-sectional view of the same object.

FIG. 3 is a perspective view of the E×B separator of the present invention with an added magnetic shield.

FIG. 4 is a sectional view of a conventional ExB separator.

[Explanation of symbols]

1 Parallel plate electrode 2 Main magnet 3 Auxiliary magnet 4 Auxiliary magnet 6 Magnetic shield

Claims (2)

[Claims] 1. Opposing parallel plate electrodes to which an electrostatic voltage is applied, and opposing sides of the parallel plate electrodes so as to generate magnetic flux in a direction perpendicular to the normal line of the parallel plate electrodes. Mass separation is achieved by passing charged particles between the electrodes and between the magnets from a direction perpendicular to both the electric field generated by the parallel plate electrodes and the magnetic field generated by the magnet, allowing only the charged particles traveling in a straight line to pass through. In a mass separator that performs An ExB separator characterized by having an auxiliary magnet. 2. Opposing parallel plate electrodes to which an electrostatic voltage is applied, and opposing sides of the parallel plate electrodes so as to generate magnetic flux in a direction perpendicular to the normal line of the parallel plate electrodes. Mass separation is achieved by passing charged particles between the electrodes and between the magnets from a direction perpendicular to both the electric field generated by the parallel plate electrodes and the magnetic field generated by the magnet, allowing only the charged particles traveling in a straight line to pass through. In a mass separator that performs An ExB separator characterized in that an auxiliary magnet is provided and a magnetic shield made of a cylindrical magnetic material surrounds the main magnet and the auxiliary magnet.