JPH0763036B2 - Bending electromagnet with return yoke - Google Patents

Description

The present invention relates to a storage ring as a charged particle accelerating storage device for rotating or accelerating or storing charged particles on a closed orbit, that is, a structure of a deflection electromagnet of a SOR exposure apparatus. It is about.

[Conventional technology]

Conventional synchrotrons and storage rings are manufactured for high-energy physics experiments (mainly experiments for interaction of elementary particles and collisions of electrons and positrons, protons and antiprotons, and discovery of new particles). And was generally large (tens of meters to tens of kilometers in diameter).

As described above, the conventional storage ring is large and is composed of a large number of deflection electromagnets. Since each deflection electromagnet has a substantially linear structure, the magnetic field that is a condition necessary for the electrons to orbit for a long time is A two-dimensional magnetic field analysis was sufficient for optimizing the magnetic pole structure to ensure the uniformity.

On the other hand, recently, SOR light emitted when electrons or positrons orbit is used for surface analysis such as photoelectron spectroscopy or semiconductor L
Attention has been paid to its use as a light source for X-ray lithography when manufacturing SI. In this semiconductor industry this SO
The introduction of the R light source requires a storage ring that is smaller and designed specifically than before. For this reason, attempts are being made worldwide to reduce the size of storage rings.

One important direction for miniaturization is to make the deflection electromagnet superconducting and deflect electrons by 180 degrees with one deflection electromagnet to make the orbital radius of the electron on the order of several tens of centimeters. This is described, for example, in “Heuberga, Solid State Engineering, p. 93, 1986, February (A. Heuberger, Solid State Technology, p. 93, February.
1986) ”.

Therefore, the conventional two-dimensional analysis is insufficient, and the handling of the three-dimensional analysis is indispensable. However, the required homogeneity of the magnetic field is ensured in a wide area of a plane perpendicular to the orbital axis through which the electrons pass. Magnetic structure has not been realized yet. In addition, enormous computer power is required for three-dimensional analysis including a magnetic body, and the deflection electromagnets such as the above-mentioned Heiberger are also air core type, and iron is not used.

[Problems to be solved by the invention]

On the other hand, in an attempt to miniaturize the storage ring, there is an attempt to deflect electrons 360 degrees in a circular ring. This is described in, for example, (Takahashi, Japan Society for the Promotion of Science, Crystal Processing and Evaluation Technology, 145th Committee, Subcommittee B (using synchrotron radiation), 9th Research Material, page 17). In the case of this example, although magnetism is used, a two-dimensional analysis is sufficient because of the circular structure. However, a structure including a magnetic substance with a 180-degree deflection requires a three-dimensional analysis that requires enormous computer power as described above, and no specific structure has been proposed to date.

Moreover, the conventional superconducting bending electromagnet is manufactured for the above elementary particle experiment, and the structure is linear and has a so-called cos θ winding coil structure with no space for SOR light extraction. A uniform area of the magnetic field was secured in the axis and in the plane perpendicular to it.
It cannot be used as an electromagnet for SOR light utilization equipment.

That is, the conventional problem is that the miniaturization of the storage ring and the uniform magnetic field distribution along the electron orbit have not been realized.

The present invention has been made in view of such a point, and an object of the present invention is to downsize a SOR for the semiconductor industry.
It is to provide a deflection electromagnet for an exposure apparatus.

[Means for solving problems]

In order to achieve such an object, the present invention relates to a deflection electromagnet with a return yoke for generating a deflection magnetic field in the vacuum duct of a charged particle accelerating and accumulating apparatus having a horizontal cross section of a substantially fan shape. An exciting coil having a pair of upper and lower portions sandwiching the coil and forming a loop so that currents in the opposite directions flow inward and outward along the vacuum duct, and a magnetic body surrounding the exciting coil and the vacuum duct. Is that the vertical gap of the outer coil along the vacuum duct is larger than the vertical gap of the inner coil, and the coil at the transition between the outer coil and the inner coil jumps outward at an angle of 30 ± 15 degrees. It is arranged as follows.

[Action]

In the present invention, a small storage ring and a uniform magnetic field distribution along the electron orbit can be realized.

〔Example〕

First, the features of the present invention will be described. The most main feature of the present invention is that a single deflection electromagnet deflects electrons by 180 degrees and a uniform magnetic field is realized in a wide area in a plane perpendicular to the orbital axis of the electron and the electron.

In addition, we have clarified the three-dimensional coil structure, including the magnetic material (return yoke), which reduces the orbital radius to several tens of centimeters by making it superconducting while ensuring a region for extracting SOR light.

In addition, since the magnetic material is placed around the coil, the magnetomotive force of the coil is reduced by 30% compared to the air core, and the axial electromagnetic force applied to the coil is reduced to less than half. And

In an attempt to realize a conventional small storage ring, as described above, the 180 degree deflection has an air-core type, and the 360 degree deflection has a structure including a magnetic material. This time, we proposed a concrete structure that includes a magnetic body with 180 degree deflection.

This time, we performed a three-dimensional magnetic field analysis including a magnetic material and performed SOR
We were able to realize a coil arrangement and magnetic structure that facilitated light extraction. The coil arrangement and the structure of the magnetic body will be described below.

FIGS. 1 (a) and 1 (b) show the structure of the iron return yoke and the position of the coil according to the present invention, in which 1 is an inner coil, 2 is an outer coil, 3 is a coil of the crossover portion, 4
Is the return yoke. 2 to 5 are diagrams showing the detailed arrangement of the coils. (A) shows the outer shape of the actual coil winding, and (b) shows the center line of the coil and the outer shape of the vacuum duct 5. In the actual magnetic field calculation, it is sufficient to calculate using this line current model.

FIG. 6 to FIG. 8 are coil truncation arrangement views of the coil in the return yoke 4 when taken out from above (± z direction) and side (± x direction). Only the center line of is shown. X ≧ 0, y ≧ in FIG.
The center line of the coil in the space of 0, z ≧ 0 is z = D1, x ² +
An arc of y ² ＝ R1 ^{2 and} an arc of z ＝ D2, x ² ＋ y ² ＝ R2 ² (however, D
1>D2> 0, R1>R2> 0) and α ≦ θx ≦ 90 degrees (see FIG. 7 (a)). That is, the center line of the coil coincides with the circular arc within a predetermined range. Where α and θx are 3
It represents the angle of the dimensional cylindrical coordinates, and α is a constant value within the range of 0 ° ≦ α ≦ 90 °. In this example, α ≠ 0. 8 is a part of ^{z = D1, x 2 + y} 2 = R1 2 arcs and ^{z = D2, x 2 + y} 2 = R2 2 of arc y ≧ a. Here, a is a constant value satisfying 0 ≦ a <R2, and in this example, a ≠ 0. Figure 7,
In any of FIG. 8, the plane including the center lines of the inner coil 1 and the outer coil 2 in it is the plane of z = 0 and ± 30 degrees.
They intersect at an angle of 15 degrees, and the line of intersection is y = tan α · x or y
= Parallel to α. FIG. 6 corresponds to the case where α = 0 in FIG. 7 or a = 0 in FIG.

Hereinafter, the embodiment of FIGS. 1 to 4 will be described in detail.
By adding the return yoke 4, the uniformity is not obtained in the optimized arrangement with the air-core type coil. The coil layout newly obtained by the parameter survey is as follows.

Due to the coil arrangement structure shown in FIGS. 2 to 5, the electron orbit radius is set to several tens of cm (52.38 cm in this example, which corresponds to the orbit radius of 3.5 T, 550 MeV). In order to secure a uniform region along the orbital axis through which the electrons pass, the outer coil 2 is made higher than the inner coil 1, and the coil 3 at the connecting portion connecting the two coils is placed outside to a certain extent. It has a structure that jumps up only at an angle. The detailed coil arrangement is shown below (see Fig. 10).

Radius of outer coil center R1 = 784.9mm Height of outer coil center D1 = 161.3mm Inner coil center radius R2 = 268.4mm Inner coil center height D2 = 124.8mm Jumping angle of the coil at the transition point = 30 degrees Here, the thickness of the coil is defined by the magnetomotive force and the maximum current density that can be passed through the coil, and depends on factors such as the characteristics of the wire, the empirical magnetic field in the coil, and the excitation speed.

FIGS. 9 (a) to 9 (j) are distributions of the homogeneity of the magnetic field in the plane along the electron orbit axis and perpendicular to the axis in the above coil arrangement. This figure shows the direction from the top along the electron orbit axis in the θx direction.
The magnetic field homogeneity (Uniformity, hereinafter abbreviated as "U") is shown for each 10-degree section from 90 degrees (y-axis) to 0 degrees (x-axis). The horizontal axis in the figure indicates the radial position when a cross section perpendicular to the electron orbit axis is taken. (Units
cm). The vertical axis represents the homogeneity U, and each curve of the solid line, the chain line, the one-dot chain line, and the two-dot chain line shows the homogeneity U with respect to the position parameter of the height z = 0 cm, 1 cm, 2 cm, 3 cm in the direction perpendicular to the electron orbit axis. Indicates. Here, the homogeneity U is the value of the z component BZ of the magnetic field at the position determined by the horizontal axis and the parameter, and z =
It is a quantity defined by the following formula from the value of BZ BZ0 corresponding to the position of the electron's equilibrium orbit at 0 cm (position of 0 on the horizontal axis in the figure).

U = (BZ-BZ0) / BZ0 The uniformity U on the vertical axis in FIG. 9 is 0 in the center and ± on one scale.
It is 0.5 × 10 ^-3 . That is, this figure shows approximately ± 5 × 10 ^{− in} a wide area of 10 cm × 6 cm (z = 3 cm × 2 = 6 cm in the height direction due to the symmetry of the system) of a plane perpendicular to the electron's orbital axis. It shows that the uniformity of ⁴ is achieved. This value is almost the same as the magnetic field accuracy (uniformity) required for the bending electromagnet of the conventional electron storage ring. Thus, without adding a correction coil, a coil having a vertical symmetry with respect to the plane of x = 0 is arranged so that the vertical gap of the outer coil 2 is larger than the vertical gap of the inner coil 1. A structure that includes a magnetic substance that is arranged symmetrically with respect to the plane of z = 0 and that is also symmetrical with respect to the plane of z = 0. The magnetic field accuracy of this level is achieved in a wide radial area. These calculations are
It is a result of a three-dimensional magnetic field analysis including a magnetic substance by Savart's law and a finite element, and the above coil arrangement is also a value obtained as a result of a parameter survey by this program.

Next, the influence of the hoisting angle of the coil 3 and the placement accuracy of the inner coil 1 and the outer coil 2 in the transition portion will be described. Regarding the hoisting angle of the coil 3 at the crossover portion, the above-mentioned coil arrangement condition, that is, 30 degrees is optimal. When the hoisting angle is changed, the homogeneity of the magnetic field is disturbed near the exit of the deflection electromagnet. . However, as shown in Fig. 6 (b), 30 ±
Within the range of 15 degrees, generally good uniformity can be obtained. The iron, which is the above-mentioned magnetic material, has a role only as a shield and a return yoke, and has a small degree of saturation and is away from the electron orbit axis. That is, in this type of return yoke structure, the current supplied from the external power source is proportional to the magnitude of the magnetic field on the electron orbit axis, and the magnetic field homogeneity distribution hardly changes depending on the excitation rate (current value). It retains almost the same properties as an air core. Therefore,
The coil placement accuracy may be considered to be the same as the value for the air core. That is, the values are shown in the shaded portion of the quadrilateral in FIG.

Next, the effect of using the magnetic material will be described. By using the magnetic material, the following effects are exhibited.

The magnetomotive force of the coil can be reduced by about 30% as compared with the case of a perfect air core. Specifically, the magnetomotive force required to generate a magnetic field of 3.5 T can be reduced to 3.0 MAT. At this time, the magnetomotive force can be further reduced by moving the upper return yoke closer to the coil, but iron may start to saturate strongly and disturb the magnetic field distribution, so keep it at an appropriate value. is necessary.

When the magnetomotive force (excitation rate) is changed, there is almost no iron saturation effect, or even if iron is partially saturated, the effect is small because the iron is away from the electron orbit axis. That is, the linearity between the magnetic field and the external power source, which is the property of a coil having an almost perfect air core, is maintained. Specifically, the distribution showing the homogeneity of the magnetic field hardly changes even if the excitation rate is changed. Alternatively, the distribution of the magnetic field in the orbital axis direction at the crossover portion does not change depending on the excitation rate. Therefore, there is a feature that power supply tracking is easy.

The iron return yoke is placed away from the coil to avoid saturation. For this reason, even if a hole is formed on the side surface of the shield to pass the beam line of SOR light, there is almost no effect on the uniformity distribution.

The axial electromagnetic force is reduced to less than half, and the structure of the collar and the cryostat can be further reduced by reducing the amount of deflection.

The stray magnetic field can be significantly reduced.

The empirical magnetic field of the coil can be reduced, which facilitates the design of the superconducting magnet.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a pair of exciting coils having a loop formed so that currents in opposite directions flow inward and outward along the vacuum duct are placed above and below the vacuum duct, and the exciting coil and the vacuum duct are connected to each other. Equipped with a surrounding magnetic body,
The upper and lower gaps of the outer coil are made larger than the upper and lower gaps of the inner coil, and the coil at the crossover is arranged so as to bounce outward at an angle of 30 ± 15 degrees, which results in a large area inside the deflection electromagnet. It is possible to obtain good magnetic field homogeneity over a wide range, and it is possible to put a small storage ring into practical use.This makes it possible to form a minute pattern in the lithography process of a semiconductor LSI. There is an effect that it can be installed as an exposure device.

[Brief description of drawings]

1 (a) and 1 (b) are layout diagrams showing an embodiment of a deflection electromagnet with a return yoke according to the present invention, and FIGS.
The figure is a layout showing the detailed layout of the coil as seen from various angles, Figures 6 to 8 are layout drawings of coil truncation, Figure 9 is a graph showing the homogeneity of the magnetic field, and Figure 10 is the layout of the coil center line. It is explanatory drawing which shows the permissible range. 1 ... Inner coil, 2 ... Outer coil, 3 ... Crossover coil, 4 ... Return yoke, 5 ... Vacuum duct.

Claims (3)

[Claims] 1. A deflection electromagnet with a return yoke for generating a deflection magnetic field in the vacuum duct of a charged particle accelerating and accumulating device, wherein a horizontal cross section of the vacuum duct is substantially fan-shaped. And a magnetic body surrounding the vacuum duct, the exciting coil forming a loop so that currents in opposite directions flow inward and outward along the vacuum duct, and the exciting coil is arranged along the vacuum duct. The vertical gap of the outer coil is larger than the vertical gap of the inner coil, and the coil at the transition between the outer coil and the inner coil is arranged so as to bounce outward at an angle of 30 ± 15 degrees. A bending electromagnet with a return yoke, which is characterized in that 2. The magnetic body is formed so as to equalize the magnetic resistance of the magnetic flux path passing through the outside of the vacuum duct and the magnetic resistance of the magnetic flux path passing through the inside of the vacuum duct. Bending electromagnet with return yoke as described. 3. The deflection electromagnet with a return yoke according to claim 1, wherein the coil forming the deflection electromagnet is a superconducting coil.