JPH03208250A - Analysis electromagnet - Google Patents

Abstract

PURPOSE:To improve the evenness, the transport efficiency, and the like of the charged particle beams by forming the cross section forms at the opposite sides of negative poles of an iron core to make the gap between both members, the widest at the center, and narrower gradually to the both sides. CONSTITUTION:On the roots of magnetic poles 21 and 22 of an iron core 2, coils 3 and 4 are wound. And at a gap between the magnetic poles 21 and 22, an analysis tube 5 to make the passage of charged particle beams 6 such as ion beams into a vacuum ambiance, made out of non-magnetic material bent along the magnetic poles 21 and 22 is provided. The cross section forms of the opposite surfaces 21a and 22a sides of the negative poles 21 and 22 are formed making the gap between the members the largest at the center and narrower gradually to the both sides. In such a way, a generation of aberration of charged particle beams to be analyzed is reduced, and the evenness, the transport efficiency, and the like of the beams can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is used for example in ion implantation devices, accelerators, etc., and is used for mass analysis, energy analysis, etc. of charged particle beams such as ion beams. Concerning an analytical electromagnet that performs analysis.

[Conventional technology]

A conventional example of this type of analytical electromagnet is shown in FIG.

This analytical electromagnet is a so-called C-type analytical electromagnet, and has two magnetic poles 21 facing each other with a gap.
and 22, and includes an iron core 2 having a C-shaped overall cross-sectional shape and a fan-shaped planar shape.

This iron core 2 (more specifically, each magnetic pole 21, 22
Coils 3 and 4 are wound around the base of the tube. The gear/knob portion between the magnetic poles 21 and 22 is made of a non-magnetic material bent along the magnetic poles 21 and 22, which creates a vacuum atmosphere in the passage of the charged particle beam 6 such as an ion beam. An analysis tube 5 is provided.

In such an analysis electromagnet, by passing the accelerated charged particle beam 6 through the analysis tube 5, only the charged particle beam 6 having a desired mass or energy can be selectively derived.

[Problem to be solved by the invention]

Each magnetic pole 21, 2 in the conventional analytical electromagnet as described above
The shapes of the two opposing surfaces 21a and 22a are basically planar shapes parallel to each other as shown in the illustrated example.

However, this type of analytical electromagnet cannot be made very large due to cost constraints, and therefore the width of the magnetic poles 21 and 22 cannot be made sufficiently large. The magnetic flux density on the surface A becomes weaker as it goes from the center to the edge, and has a parabolic distribution, as shown by the solid line in FIG. 6, for example.

When the magnetic flux density becomes such, the charged particle beam 6 is influenced by it (the influence becomes larger as the size of the charged particle beam 6 becomes larger), and aberrations such as deformation and deviation of the focusing position occur. As a result, the uniformity of the charged particle beam 6 is adversely affected, and the transport efficiency of the charged particle beam 6 is also adversely affected as the charged particle beam 6 hits a structure.

On the other hand, the opposing surfaces 21a, 2 of each magnetic pole 21, 22
In some cases, protruding shims 23 as shown by the two-dot chain lines in FIG. inside 2
As shown by the dotted chain line, the magnetic flux density is increased only in the vicinity of the shim 23, so the magnetic flux density distribution is sagging in the middle, which is not very good.

Therefore, the main object of the present invention is to provide an analytical electromagnet that can make the magnetic flux density distribution on the central plane between the magnetic poles uniform over a wide area as described above.

[Means to solve the problem]

In order to achieve the above object, the analytical electromagnet of the present invention has a cross-sectional shape on the opposing surface side of each M1 pole of the iron core as described above.
The gap between them is widest at the center and gradually narrows on both sides.

[Effect]

When the opposing surfaces of both magnetic poles have a planar shape, the magnetic flux density distribution on the central plane between the magnetic poles becomes parabolic as described above.

On the other hand, if the cross-sectional shape of the opposing surfaces of each magnetic pole is made as in the present invention, the magnetic flux density on the center plane between the magnetic poles will decrease relatively at the center and relatively increase at the ends. The magnetic flux density distribution, which tends to become parabolic, is corrected, and its uniformity is improved over a wide area.

〔Example〕

FIG. 1 is a schematic vertical sectional view showing an analysis electromagnet according to an embodiment of the present invention. The same reference numerals are given to the same or corresponding parts as in the conventional example shown in FIG. 5, and the differences from the conventional example will be mainly explained below.

In this embodiment, each magnetic pole 21, 2 as described above is used.
2, the cross-sectional shape of the opposing surfaces 21a and 22a of each magnetic pole 21
, 22 is shaped like a parabola that is symmetrical about the center.

As mentioned above, when the opposing surfaces of the magnetic poles 21 and 22 are planar, the magnetic flux density distribution therebetween becomes a parabola. Therefore, from the viewpoint of characteristics, the cross-sectional shape of the opposing surfaces of each magnetic pole 21 and 22 should be shaped like this. It is preferable to make it a parabola as in the example, and in that case, the parabola will be corrected to the opposite parabola, so the magnetic flux density distribution on the central plane A can be spread over a wide area. It is possible to approximate a straight line and make it very uniform over the entire area (for example, over almost the entire area from one end side to the other end side of the magnetic poles 21 and 22).

However, from the viewpoint of ease of processing, the above-mentioned parabola should be straightened, and each magnetic pole 21, 2
The cross-sectional shape of the opposing surfaces 21a and 22a of 2 is one pole 21 each.
, 22, it is preferable to form it into a symmetrical shape (triangular or mountain-shaped) with respect to the center. Even in this case, the magnetic flux density distribution on the central plane A is made uniform over a fairly wide area. be able to.

FIG. 3 shows an example of the calculation results of the magnetic flux density distribution on the central plane A when the gradients of the opposing surfaces 21a, 22a of the respective magnetic poles 21, 22 in the analytical electromagnet shown in FIG. 2 are changed.
FIG. 4 shows the scale on the magnetic flux density side expressed as an error with respect to the magnetic flux density at the center.

In both figures, the gap length G at the end between the magnetic poles 21 and 22 is kept at 60 mm, and the gamb length G0 at the center is kept at 60 m.
m (this corresponds to the conventional example), 61 mm, 62 mm,
By changing the diameter to 64 mm, the slope of the opposing surfaces of the magnetic poles 2l and 22 is changed.

As can be seen from both figures, the opposing surfaces 21 of each magnetic pole 21, 22
If the gradients of a and 22a are selected appropriately (for example, if the gap length G0 at the center is set to 61 mm or slightly smaller), the magnetic flux density distribution can be made uniform over a fairly wide area (for example, ±0.1%). (within or close to the error).

It goes without saying that the above structure can also be applied to so-called H-type analytical electromagnets in which the inner shape of the iron core is H-shaped.

〔Effect of the invention〕

As described above, according to the present invention, the cross-sectional shape of the opposing surfaces of each magnetic pole of the iron core is made such that the gap between them is widest at the center and gradually narrows on both sides. The magnetic flux density distribution on the central plane can be made uniform over a wide area.

As a result, it is possible to reduce the occurrence of aberrations in the charged particle beam to be analyzed, and improve beam uniformity, transport efficiency, etc.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical sectional view showing an analysis electromagnet according to an embodiment of the present invention. FIG. 2 is an analysis of another embodiment of this invention! FIG. 3 is a schematic vertical cross-sectional view showing a magnet. FIG. 3 is a diagram showing an example of the calculation result of the magnetic flux density distribution on the center plane between the magnetic poles when the slope of the opposing surface of each magnetic pole in the analytical IIT magnet shown in FIG. 2 is changed. FIG. 4 is a diagram showing the scale on the magnetic flux density side of FIG. 3 as an error with respect to the magnetic flux density at the center. FIG. 5 is a schematic longitudinal sectional view showing an example of a conventional analysis if magnet. FIG. 6 is a diagram showing a schematic example of magnetic flux density distribution on the center plane between magnetic poles in a conventional analysis electromagnet. 2... Iron core, 21.22... Magnetic pole, 21a, 22a
... Opposing surface, 3.4... Coil, 5... Analysis tube,
6...Charged particle beam.

Claims (1)

[Claims] (1) In an analytical electromagnet comprising an iron core having two magnetic poles facing each other with a gap, a coil wound around this iron core, and an analysis tube installed in the gap of the iron core, each magnetic pole of the iron core is An analytical electromagnet characterized in that the cross-sectional shape of opposing surfaces of the magnet is such that the gap between them is widest at the center and gradually narrows on both sides.