JP2000003689A - Electron gun and exposure device using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-precision electron gun and an exposure device applying electron beams such as a micro-pattern exposure device (EB exposure device) for semiconductor and electron beam drawing device, etc., capable of high-precision processing by using the electron gun. SOLUTION: In this magnetic field immersion electron gun 1 on the system that a magnetic field is superimposed on a bipolar area including an emitter (an electron emission source) 3 to focus beams, and in the exposure device loaded with the electron gun 1, an electron lens electrode 6 of the electron gun 1 is integrally formed with a magnetic pole unit 12. The magnetic pole unit 12 preferably generates a magnetic field by a permanent magnet which is also preferably applied with surface treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun for emitting thermoelectrons and electric field electrons from a cathode, and an electron beam using the electron gun for a fine pattern exposure apparatus (EB exposure apparatus) for semiconductors and an electron beam drawing apparatus. The present invention relates to an applied exposure apparatus.

[0002]

2. Description of the Related Art In a fine pattern exposure apparatus used for manufacturing semiconductors, high brightness is required to obtain a fine pattern.

For this purpose, it is necessary to irradiate the wafer with a high current density, but it is desirable that the irradiation angle be small due to aberration of the electron lens electrode.

[0004] The brightness is the electron current density (current angular density) per unit area. However, since the value of this brightness cannot be increased by the lens of the electron optical system after the electron gun,
It is important that the electron gun has high brightness. A major factor that lowers the brightness of the electron gun is the aberration of the electron lens electrode in the electron gun.

The aberration of the electron lens electrode can be roughly classified into
(A) geometric aberration (spherical aberration, axial asymmetric aberration), (b) diffraction aberration, and (c) chromatic aberration. Of these aberrations, reduction of chromatic aberration (chromatic aberration is proportional to the energy width) is particularly important as fine processing is performed.

Chromatic aberration occurs when a change occurs in the acceleration voltage of the anode of the electron gun and the lens current of the electron lens electrode. As a result, the magnification and the rotation angle are changed in proportion to the distance from the beam axis, and the image is blurred. Would. Therefore, in order to reduce chromatic aberration, both the acceleration voltage power supply and the electron lens electrode excitation current power supply need to have high stability.

In terms of performance, electron guns used in EB exposure apparatuses and the like are characterized in that FEG (field emission type electron gun) / TFEG (thermal field emission type electron gun) uses conventional LaB ₆ (lanthanum hexaboride). Energy width is 1 compared to electron emission gun
/ 5, which is a preferable performance.

However, the tip of the emitter (cathode) of the field emission type electron gun and the thermal field emission type electron gun is formed in a very small needle shape (radius of 1 μm or less), and the electrons radiate from the cathode and diverge. I do. For this reason, in order to obtain a large current, it is necessary to collect electron beams having a large aperture angle, and the electron beam diameter increases due to the spherical aberration of the electron lens electrode system of the electron gun, and the brightness decreases.

As a countermeasure, a magnetic field immersion electron gun is sometimes used. The magnetic field immersion electron gun is a system in which a magnetic field is superimposed on a bipolar region including an emitter (electron emission source) to converge a beam and reduce aberration of an electron lens electrode.

FIG. 9 is a block diagram showing the configuration of a field emission type electron gun disclosed in Japanese Patent Application Laid-Open No. 9-7538. The electron gun 31 moves the emitter 3 along the beam axis 32.
3. A suppressor electrode 34, an extractor electrode 35, an electron lens electrode 36, and an anode electrode 37 are arranged, and the magnetic field generated by the coil 44 is guided by the magnetic pole. Further, a strong magnetic field is applied to the tip of the emitter 33 by incorporating the extractor electrode 35 at the tip of the magnetic pole.

Further, the electron gun comprises an emitter, an extractor electrode (first anode electrode), and second and third anode electrodes, and a magnetic field generated by the coil is transmitted from the extractor electrode (first anode electrode) to Technology applied to the third anode electrode part (Improvement
of Beam Characteristicsb
y Superimpossing a Magneti
c Fieldon a Field Emissio
n Gun "Electron Microsc." V
ol. 38, no. 2, 83-94, 1989).

However, in this technique, the coil and the magnetic pole have a different structure from the preceding electrode, and no integration is performed. Therefore, the position of the magnetic pole is away from the electron beam axis by several mm to several tens mm, and the magnetic field that can be applied is several tens m
It is about T (millitesla).

In the technique disclosed in Japanese Patent Application Laid-Open No. Hei 6-139076, an emitter, a suppressor electrode, an extractor electrode, and an anode electrode are used, and the effect of the lens is achieved by a condenser lens using a coil. In this case, a part of the barrel of the electron gun is integrated with the magnetic pole. This is an attempt to make the magnetic pole as close to the beam axis as possible.

According to the technique disclosed in Japanese Patent Application Laid-Open No. 6-162979, the electron gun is composed of an emitter, a suppressor electrode, an extractor electrode, an electron lens electrode, and an anode electrode.
It is applied to the extractor electrode, electron lens electrode, and anode electrode. At this time, since the coil and the magnetic pole have a different configuration from the previous electrode and are located outside the lens barrel, the magnetic pole position is several mm from the electron beam axis as in the case described above.
The magnetic field that can be applied is about several tens mT (millitesla). In this case, the magnetic pole and the electrode are not integrated.

[0015]

However, in the electron gun of the technology disclosed above, the magnetic field is often generated by a coil. In addition, at this time, the field electron emission phenomenon of the emitter portion in the vacuum chamber is 10 ⁻⁹ Torr.
It must be in a high vacuum state on the order of r.

However, since the lead wire constituting the coil has to use a wire material such as copper which is coated with a polymer insulating material such as polyimide, if these materials are used in a high vacuum, the gas is not used. It is common to place the coil outside of the vacuum chamber for release.

Incidentally, in Japanese Patent Application Laid-Open No. 9-7538, a drawing in which the coil is sealed by a gasket member is illustrated, though the description in the detailed description of the invention is omitted. Also, in the other disclosed examples, the coils are all placed in the atmosphere outside the vacuum chamber.

That is, as a result, the emitter portion is placed under a high vacuum in the vacuum chamber, and the coil is placed in the atmosphere or the low vacuum region outside the vacuum chamber. Of course,
It is necessary to devise such a method as to be installed away from the emitter or to integrate a part of the beam barrel with the magnetic pole. Although some effect can be expected by this, electrodes and magnetic poles such as emitter, suppressor electrode, extractor electrode, of course,
You have to keep a certain distance. Therefore, there is a problem that it is extremely difficult to apply a strong magnetic field.

To explain the second problem, there is a technique in which a magnetic field is applied by a permanent magnet depending on the type of the electron gun. However, these techniques integrate an extractor electrode and a magnetic pole and connect the tip of the magnetic pole to the electron beam axis. , A strong magnetic field of several hundred mT is applied to the tip of the emitter.

As described above, the method of applying a magnetic field to the extractor electrode has the effect of weakening the divergence effect near the emitter and the extractor electrode where electrons are strongly diverged and improving the convergence of the beam. Can reduce the spherical aberration coefficient defined by the image plane (image plane). However, in this case, the region of the applied magnetic field is narrow (the length on the axis is narrow).

Therefore, there is a problem that sufficient convergence cannot be obtained, and the position where the beam is converted from divergence to convergence near the extractor electrode on the beam axis cannot be changed.

[0022]

According to the first aspect of the present invention, a vacuum vessel, a cathode disposed in the vacuum vessel for generating an electron beam, and a magnetic field applied to the electron beam generated by the cathode are provided. A magnetic pole unit, an anode for accelerating an electron beam generated at the cathode in a beam axis direction to form an electron beam path, and an electron beam disposed between the anode and the cathode and accelerated by the anode. An electron gun having an electron lens electrode for generating an electric field that causes the electric field to converge on the beam axis, wherein the electron lens electrode and the magnetic pole unit have an integral structure.

According to the second aspect of the present invention, in the electron gun according to the first aspect, the magnetic pole unit generates a magnetic field by a permanent magnet.

According to a third aspect of the present invention, there is provided the electron gun according to the first aspect, wherein the permanent magnet of the magnetic pole unit is subjected to a surface treatment.

According to a fourth aspect of the present invention, there is provided the electron gun according to the first aspect, wherein the magnetic pole unit generates a magnetic field by a surface-treated electromagnetic coil.

According to a fifth aspect of the present invention, there is provided an exposure apparatus including the electron gun according to any one of the first to fourth aspects.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the electron gun of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 are cross-sectional views of the main parts of an electron gun according to the present invention. That is, as shown in FIG. 1, the electron gun 1 is moved along a beam axis 2 by, for example, zirconium oxide /
An emitter 3 made of tungsten (ZrO / W) is arranged, and a suppressor electrode 4, an extractor electrode 5, an electron lens electrode 6, and an anode electrode 7 are sequentially arranged in front of the emitter 3. A permanent magnet 8, an outer magnetic pole 9, and an inner The tip of the magnetic pole of the magnetic pole unit 12 composed of the magnetic pole 10 is connected to the extractor electrode 5 and the electron lens electrode 6 via the insulator 13.
It is connected to the. However, in FIG.
And the extractor electrode 5 are not connected and are separated.

Although not shown, these electrodes and the magnetic pole unit 12 are arranged inside the electron gun chamber and are placed in a high vacuum environment. Further, the emitter 3, the suppressor electrode 4, the extractor electrode 5, the electron lens electrode 6, the anode electrode 7
Is applied with a high voltage through a lead wire (not shown).

The high voltage is, for example, -500 V with respect to the emitter for the suppressor electrode 4, 1 to 5 KV for the extractor electrode 5, and 1 to 30 KV for the anode electrode 7.
V and a voltage such as 1 to 30 KV for the electron lens electrode 6. The voltage of the electron lens electrode 6 is adjusted such that a crossover (focal point) is formed on an aperture surface formed of a metal plate having a small hole provided in front of an anode electrode 7 (not shown). . These electrodes and the permanent magnet 8 are set to a high vacuum by a vacuum pump such as an ion pump (not shown).

The outer magnetic pole 9 and the inner magnetic pole 10 are made of a material having a high magnetic permeability such as pure iron or soft magnetic iron, and a permanent magnet 8 made of samarium cobalt or the like is disposed inside the magnetic pole. It is installed so as to sandwich it. Further, the space portion forms a structure filled with a non-magnetic material such as copper.

As a method for applying a magnetic field, a method using a permanent magnet 8 of samarium cobalt plated with copper or nickel is used.

That is, usually, since the permanent magnet 8 such as samarium cobalt is a sintered metal, it holds a gas inside. Therefore, when used in a vacuum, the internal gas is released and a high vacuum cannot be obtained. Therefore, in this case, a member in which the surface of the permanent magnet 8 is plated with copper, nickel, or the like is used to prevent the release of the internal gas.

The permanent magnet 8 is a samarium-cobalt magnet. However, the magnet is not limited to the samarium-cobalt magnet, but may be a cerium-cobalt-based magnet, a neodymium-iron-boron-based magnet, a ferrite-alnico-based magnet, a plastic magnet-based magnet, or an iron-chromium-cobalt magnet. It can be used regardless of the type, such as system.

The permanent magnet 8 is plated with a metal such as copper nickel. However, the present invention is not limited to this. A treatment using a general metal or an alloy thereof, and a treatment using a multilayer film of a general metal or an alloy thereof. Gas, such as various coating treatments, not only plating treatments, or coating treatments with non-metals such as glass, and other sealing treatments with containers made of thin plates using stainless steel or other metals or non-metals If it is a treatment for not releasing, it can be used as appropriate.

Further, in the above-described case, the example in which the permanent magnet 8 is used to form the magnetic field has been described, but the magnetic field may be formed by the coil 14. In this case, the coil 14 is sealed with an appropriate insulating member, or subjected to a process of solidifying the wire bundle of the wire rod, and the structure of the magnetic pole excludes integration with only the extractor electrode 5 electrode. And

FIG. 3 is a cross-sectional view of a main part of the electron gun 1 of the present invention using the coil 14, and FIG. 4 is a modified example thereof. That is, in FIG. 3, the coil 14 is sealed with an insulating member (not shown), and the extractor electrode 5 and the electron lens electrode 6 are integrated via the insulator 13. Also, in FIG. 4, similarly, it is integrated with the electron lens electrode 6, but the extractor electrode 5 is not connected and is separated.

As a means for applying a strong magnetic field to an electron beam, the prior art discloses a technique in which an extractor electrode 5 and a magnetic pole are integrated to apply a strong magnetic field. In such a configuration, the magnetic field application region is limited to a narrow region. This is because the magnetic pole is integrated with the extractor electrode 5 only.

In the present invention, the shape of the tip of the magnetic pole is made slower than that of the prior art so that a magnetic field can be applied to a wide range, and the magnetic pole is not the extractor electrode 5 but the electron lens electrode 6 or the extractor. The electrode 5 is integrated with the electron lens electrode 6 or in a form including other electrodes. Thus, a magnetic pole is arranged near the beam so that a strong magnetic field can be applied to the beam.

The structure is as shown in FIGS. Although not shown in the drawing, it is also possible to integrate any other electrode and the combination of the electrode and the magnetic pole.

In the above-described example of the potential in the case of integration (FIGS. 1 to 4), the electrodes and the magnetic poles are integrated via an insulator. It is also possible to eliminate the insulator between one of the electrodes and apply a potential to the magnetic pole itself.

FIGS. 5A and 5B are block diagrams showing a case where a plurality of electrodes are integrated. FIG.
In (a), the magnetic pole can be set to an arbitrary potential because the magnetic pole and the integrated electrode are all through an insulator. FIG. 5 (b)
Since the magnetic pole is integrated with one electrode without an insulator, the magnetic pole itself has the same potential as the electrode.

6 (a), 6 (b), 6 (c) and 6 (d) are views showing the configuration of the main part of an electron gun showing an integrated application example. FIG.
(A) is an example in which the magnetic pole is mechanically integrated with the electrode and not integrated with the extractor electrode 5. The magnetic pole is connected to the lens barrel (a) of the electron gun 1 by an insulating connecting part (b).
The electron lens electrode 6 is coupled with an insulating coupling component (c), and the extractor electrode 5 is coupled with the lens barrel (a) via the insulating coupling component (d). Therefore, the extractor electrode 5 is not integrated with the magnetic pole.

FIG. 6B shows an example in which the magnetic pole is integrated with the electron lens electrode 6 and also with the extractor electrode 5. In this example, it is clear from the fact that the magnetic poles are joined at (c) at the tip.

FIG. 6C also shows an example in which the magnetic pole is integrated with the electron lens electrode 6 and the extractor electrode 5. In this example, the electron lens electrode 6 is coupled at the tip of the magnetic pole with an insulating coupling component (c), and the extractor electrode 5 is coupled with another portion of the magnetic pole at an insulating coupling component (e),
It is not directly connected to the lens barrel (a). Therefore, this structure (c) is also an example of integration.

FIG. 6D also shows an example in which the magnetic pole is integrated with the electron lens electrode 6. In this example, the extractor electrode 5 is made integral by using the insulative coupling part (d ') or (e') when (e ') is used,
When (d ') is used, it is separated.

7A to 7C show an electron gun according to the present invention, and FIGS. 7A to 7C show conventional electron guns. This is an electron gun 1 described in Japanese Patent Application Laid-Open No. 9-7538, which is disclosed in the section of the technique described above. (A) and (a ') show the structure of the main part of the electron gun, and (b) and (b') show the magnetic field on the beam axis 2 generated by the permanent magnet 8 and the coil magnet (lateral). The axis is the position of the z-axis, and the vertical axis is the intensity of the magnetic field, which is an arbitrary unit.) Further, (c) and (c ′) show the trajectories of the electron beam in the radial direction about the axis. (The horizontal axis indicates the position of the Z axis, and the vertical axis indicates the distance from the beam axis in arbitrary units).

In FIG. 7B, a negative magnetic field (a point where a reversal magnetic field exists) exists because of the permanent magnet 8, whereas in FIG. 7B ', the magnetic field is The feature is that all are positive (one direction).

That is, FIG. 7B shows a configuration in which the magnetic field generated by the permanent magnet 8 has a peak near the extractor electrode 5 and its skirt extends beyond the center of the electron lens electrode 6. I have. In this way, the trajectory of the beam in the electron gun 1 configured so that the influence of the magnetic field has a certain magnitude even at the position of the electron lens electrode 6 is as shown in FIG. Here, the graph N of (c) is a locus in the case where there is no magnet, and is the same as N 'in the diagram of (c') of FIG. Further, the graph M is a locus when the permanent magnet 8 is arranged.

A feature of the beam trajectory is that the beam goes from divergence to convergence at a position Zm before the position Zc where the beam is farthest from the axis. by this,
The trajectory M converges on an aperture (position Zap) at a convergence angle β (<α) smaller than the trajectory N. Therefore, the effect of the magnetic field of the magnet appears as a change in the current angular density J = 1 / (πβ ² ) in addition to the change in the spherical aberration coefficient. In particular, since the current angular density J has a relation of one-square to the convergence angle, the reduction of the Yeast angle can be obtained as a favorable effect that the current angular density changes at a rate of square to the current angular density. Become.

On the other hand, FIG. 7 (b ′) shows a configuration in which the magnetic field generated by the coil-type magnet has a peak near the extractor electrode 5, and its base is located at the electrode center of the electron lens electrode 6. I have. FIG. 7 (c ′) shows the trajectory of the beam in the electron gun 1 configured so that the effect of the magnetic field is hardly exerted on the electrode of the electron lens electrode 6.

Here, the graph N 'of (c') is a locus when the current of the coil 14 is 0 A or the magnetic field of the coil 14 is zero, and the graph M 'is a case where the current of the coil 14 flows. It is a locus of. The feature of the beam trajectory is that at a position Zc far from the axis of the beam, the distance from the axis of the beam is reduced by △. Also,
In this case, the convergence angle α at the aperture (position Zap) not shown in the figure is N and M, and changes slightly.
Therefore, the effect of the magnetic field of the coil 14 is observed as a change in the spherical aberration coefficient, and the angular current density J = 1 / (πβ
² ) The change is small.

The above-described exposure technique using the electron beam emitted from the electron gun 1 can be used for direct drawing, reduced projection, step-and-repeat, and one-time batch projection. An example used in an electron beam writing apparatus will be described below.

FIG. 8 is a configuration diagram showing the structure of an electron optical system on which the electron gun 1 is mounted. Inside the housing, from above, the electron gun 1, the first shaping aperture 21, the shaping deflector 22, the second shaping aperture 23, the swing-back deflector 24, the blanking electrode 25, the magnification correcting lens 26, the deflector, A focusing lens 27 and a processing chamber 2B are provided in this order.

A sample moving stage (not shown) is provided inside the processing chamber 28. This stage has a laser interferometer (not shown) that accurately measures XY coordinates. The positioning is performed with an accuracy of several nm from. The positioning is performed by detecting a mark provided on the moving table or the sample.

[0056] Here, in order to take a long time to stabilize the current in the electron gun 1, it is necessary to reduce the influence of the gas generated from the wafer as a sample, the differential pumping, the electron gun chamber 5 × 10 ^- It is configured to maintain a high vacuum of ⁹ Torr or more.

The control system transfers data from a computer (not shown) to the drawing control system via an interface. The drawing control system selects an aperture figure corresponding to the pattern to be drawn on the wafer from the second forming aperture 23 described above,
The required voltage from which this can be selected is input to the shaping deflector 22, and the beam is returned on-axis by the swing-back deflector 24. The selected drawing pattern is imaged on the sample (wafer) surface using the magnification correction lens 26 and the focusing lens 27. At this time, an image is formed after the focus of the focusing lens is accurately adjusted based on an accurate distance measured in advance from the focusing lens 27 to the sample. In addition, the deflector formed in the focusing lens also forms an image of the drawing pattern on a portion other than the axis. The minimum dimension of a pattern that can be drawn is limited by aberrations and blurring of the electron optical system, and a dimension of about 0.1 μm or less is possible.

At this time, a single drawing pattern on the sample is exposed, for example, at L μm × L μm (3 μm × 3 μm).
The light is deflected by NN ′ solids (for example, 10 × 12) by the above-described deflector in the focusing lens, and exposure is performed. As a result, N
The exposure of the area of L μm × N ′ · L μm (30 μm × 36 μm) is completed. Next, the sample is moved on the moving stage, and on-axis exposure and deflection exposure are repeated to operate to complete exposure of the entire sample (for example, the entire surface of a 12-inch wafer).

As described above, a magnetic field immersion electron gun of a type in which a magnetic field is superimposed on a bipolar region including an emitter (electron emission source) to converge a beam and the electron gun are mounted on the electron gun. Since the electron lens electrode and the magnetic pole unit are integrally formed, the electrons that can converge only at an emission angle of about several mrads are usually reduced from tens to hundreds of mrads.
Can be converged, and the number of electrons that can be used after passing through the aperture can be increased from the usual order of several nA to several hundred nA or several μA.

Further, the current angular density at which the beam that can pass through the aperture in the absence of a magnetic field is several mA / str to several tens mA / str is increased from tens mA / str to several tens mA / s
tr can be improved.

Further, a complicated structure of the electron gun chamber using the insulating sealing material is not required, and the cost can be reduced by reducing the number of parts. Further, by using a permanent magnet for forming a magnetic field, the configuration is smaller than that of an electromagnetic magnet, and the magnetic field portion can be accommodated on the order of several tens mm to 100 mm in diameter.

Further, by increasing the accuracy of the shape and dimensions of the permanent magnet, the accuracy of assembling the electron gun is improved, and the alignment or adjustment mechanism of the electrodes can be simplified.

Further, in order to prevent a problem due to the existence of the reversing magnetic field (minus magnetic field), the location of the reversing magnetic field is set to a position behind the emitter, so that the influence of the reversing magnetic field can be reduced. It became so.

[0064]

According to an exposure apparatus such as an electron beam lithography apparatus equipped with the electron gun of the present invention, a fine pattern can be processed with extremely high precision.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of an electron gun using a permanent magnet of the present invention.

FIG. 2 is a cross-sectional view of a main part of another electron gun using the permanent magnet of the present invention.

FIG. 3 is a cross-sectional view of a main part of an electron gun using the coil of the present invention.

FIG. 4 is a cross-sectional view of a main part of another electron gun using the permanent magnet of the present invention.

5A is a block diagram of a case where a plurality of electrodes are integrated, and FIG. 5B is a block diagram of another case where a plurality of electrodes are integrated.

FIGS. 6A, 6B, 6C, and 6D are configuration diagrams of main parts of an electron gun showing respective application examples in which electrodes are integrated.

FIGS. 7A to 7C are graphs showing the configuration and characteristics of the electron gun of the present invention. (A ')-(c') The graph which shows the structure and characteristic of the conventional electron gun.

FIG. 8 is a configuration diagram showing a structure of an electron optical system of an electron beam writing apparatus equipped with the electron gun of the present invention.

FIG. 9 is a configuration diagram showing the configuration of a conventional field emission electron gun.

[Explanation of symbols]

1, 31: electron gun, 2, 32: beam axis, 3, 33: emitter, 4, 34: suppressor electrode, 5, 35: extractor electrode, 6, 36: electron lens electrode, 7, 37 ...
Anode electrode, 8 permanent magnet, 9 outer magnetic pole, 10 inner magnetic pole, 12 magnetic pole unit, 13 insulator, 14, 4
4 coil, 21 first molding aperture, 22 molding deflector, 23 second molding aperture, 24 swing-down deflector, 25 blanking electrode, 26 magnification correction lens,
27: deflector and condenser lens, 28: processing chamber

Continuation of the front page (72) Inventor Atsushi Ando 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 2H097 BA02 CA16 LA10 5C030 BB01 BB06 CC01 CC03 CC10 5F056 CB01 CB31 EA02

Claims (5)

[Claims] 1. A vacuum vessel, a cathode disposed in the vacuum vessel for generating an electron beam, a magnetic pole unit for applying a magnetic field to the electron beam generated by the cathode, and a beam axis for generating an electron beam by the cathode. An anode that accelerates in the direction to form an electron beam path, and an electron lens that is disposed between the anode and the cathode and generates an electric field that causes the electron beam accelerated by the anode to converge on the beam axis. The electron gun according to claim 1, wherein the electron lens and the magnetic pole unit have an integral structure. 2. The electron gun according to claim 1, wherein the magnetic pole unit generates a magnetic field by a permanent magnet. 3. The electron gun according to claim 1, wherein the permanent magnet of the magnetic pole unit has been subjected to a surface treatment. 4. The electron gun according to claim 1, wherein the magnetic pole unit generates a magnetic field by a surface-treated electromagnetic coil. 5. An exposure apparatus comprising the electron gun according to claim 1.