JPH0373101B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an X-ray generator that forms plasma in a vacuum and extracts soft X-rays generated from the plasma into a desired atmosphere.

[Prior Art] With the increase in the density of integrated circuits, fine and highly accurate transfer technology is required, and X-ray exposure is one such method. Conventionally, as an X-ray source for an X-ray exposure device,
An electron beam excitation method was used in which metals such as aluminum, silicon, and palladium were irradiated with electron beams to generate X-rays, but the X-ray generation efficiency was low at 10 ^-4 , making it difficult to produce high-power X-rays. The problem was that productivity was low. As an X-ray source that solves this problem, there is a plasma X-ray generator that has a higher X-ray generation efficiency than an electron beam excitation method and is expected to generate high-output X-rays. Plasma X-ray generators include polyethylene capillary discharge, plasma focus, and gas injection discharge, but in polyethylene capillary discharge, polyethylene evaporates to form high-density plasma and only long-wavelength X-rays are generated. ,
Not suitable for X-ray exposure. Furthermore, since plasma focus uses creeping discharge, there is a problem that the creeping surface is contaminated and the X-ray output stability is poor. Compared to these plasma X-ray sources, the gas injection discharge method provides a wavelength suitable for X-ray exposure and has good X-ray output stability.

FIG. 13 shows an example of an X-ray exposure apparatus using a conventional gas injection type plasma X-ray generator. In the figure, 1 is a vacuum container, 2 is a vacuum chamber, 3 is a vacuum pump, and 4 is an upper electrode with an electrode part 4A and an electrode support part 4B.
It is made up of. There is a gas passage 4C in the electrode part 4A.
is provided. Further, the electrode support portion 4B is provided with a high-speed opening/closing gas valve 5 having a gas reservoir 5A and a piston 5B. The gas reservoir 5A and the gas passage 4C in the electrode section 4A are connected by a gas passage 5C. A driving device for the piston 5B is not shown. 6 is the lower electrode, and the electrode part 4A of the upper electrode
It consists of an electrode part 6A and an electrode support part 6B, which face each other. The electrode portion 6A has a mesh or a hole. The support portion 6B is made of a conductive material and has a hole 6C for exhaust. 7 is a gas mass ejected from the gas passage 4C, 8 is a pinched plasma,
9 is the generated X-ray, 10 is a particle group, 11 is an X-ray extraction window, 12 is a mask, 13 is a wafer, 14 is 2
A charged particle remover 15 consisting of permanent magnets is an insulator that insulates the upper electrode 4, the lower electrode 6, and the vacuum vessel 1. 16 is a capacitor, and the lower electrode 6 is connected to the capacitor 16 via a lead wire 18. 17 is a discharge switch, one end of which is connected to the capacitor 16, and the other end connected to the upper electrode 4.

To generate gas injection discharge, the vacuum chamber 2 is evacuated to about 10 ^-5 to ^{10 -6} Torr using the vacuum pump 3.
A discharge gas such as neon or krypton is introduced from the gas cylinder 19 to the high-speed opening/closing gas valve 5. Next, after the capacitor 16 is charged by the charging power source 20, the power source 22 of the high-speed opening/closing gas valve 5 is operated according to the signal from the signal generator 21, driving the high-speed opening/closing gas valve 5, and the upper electrode 4 to which a high voltage is applied. A gas mass 7 is formed between the electrode section 4A of the lower electrode 6 and the opposing electrode section 6A of the lower electrode 6. At the same time, the signal from the signal generator 21 passes through the delay pulser 23, which is set so that the time when the discharge gas is injected between the upper electrode part 4A and the lower electrode part 6A coincides with the time when the discharge starts. The high voltage pulse is input to the high voltage pulse generator 24 and operates the discharge switch 17, and the upper electrode 4 which is insulated with the insulator 15
A high voltage is applied between the lower electrode 6 and the gas mass 7 to ionize the gas mass 7 and generate a cylindrical plasma. moreover,
The interaction between the magnetic field created by the current flowing along the central axis of the columnar plasma (hereinafter referred to as the plasma axis direction) and the ions and electrons in the plasma converges the plasma, compresses the plasma, and creates a high-temperature, high-density plasma 8. generate. This high temperature high density plasma 8
X-rays 9 are generated by interaction between ions and electrons inside. In addition to X-rays, the high-temperature, high-density plasma 8 emits particle groups 10 consisting of electromagnetic waves such as light, charged particles such as ions and electrons, and high-temperature gas. Group 1
A large amount of 0 is emitted.

In plasma axial exposure where the diameter of the X-ray source is small and is suitable for fine pattern transfer, the X-ray extraction window 11 is seriously damaged by particles, light, etc. with high energy flying in the plasma axis direction. In order to avoid damage caused by charged particles during plasma axial exposure, conventionally a charged particle remover 14 is inserted between the pinched plasma 8 and the X-ray extraction window 11 to remove the charged particles, as shown in FIG. A method was used to remove charged particles using a magnetic field. However, most of the charged particles reflected by the upper electrode with the gas injection path are emitted toward the X-ray extraction window, so the number of charged particles in the direction of the X-ray extraction window increases dramatically, and charged particle removers alone cannot Particles cannot be completely removed. Therefore, by using an X-ray extraction window made of thick beryllium, etc., the X-ray extraction window 1
1 damage was prevented. Therefore, there was a problem that the X-ray extraction efficiency was poor, the time required for X-ray exposure was increased, and the throughput was reduced.

To avoid uneven exposure, usually 10 to 20 shots are repeatedly discharged during one exposure. Repeated discharge involves repeating exhaust, gas injection, and discharge. However, in conventional devices, when the discharge repetition rate is increased, gas removal near the discharge electrode parts 4A and 6A is insufficient, and parts other than the electrode parts 4A and 6A are In order to obtain stable X-ray output, it is necessary to reduce the
It had to be used at a certain repetition rate, and no improvement in throughput could be expected.

In addition, when the plasma pinches and collapses, the gas that collides with the upper electrode and is reflected is radiated toward the X-ray extraction window, so during high-repetition discharges, the gas is insufficiently exhausted toward the X-ray extraction window. These gases attenuate the X-rays in the direction of the X-ray extraction window. For example, as shown in Figure 14, the wavelength is 12 Å.
For X-rays, if a neon gas of 70 Torr with a thickness of about 1 to 2 cm exists near the center of the lower electrode, the X-ray output decreases to about 1/2.

Furthermore, since high-temperature, high-density plasma is emitted in the plasma axis direction, the central part of the upper electrode suffers from severe wear and other problems.

In addition, in other exposure devices, in order to avoid the influence of particle groups such as loaded particles and high-temperature gas,
The plasma radiation in the radial direction is 1/100 to 1/1 of that in the axial direction.
000, the X-ray extraction window 11, mask 12, wafer 13, etc. are installed in the radial direction of the pinched plasma 8 as shown in FIG. 15, and the X-rays are extracted from the X-ray extraction window 11. There is an exposure device. Note that in FIG. 15, the gas supply system for discharge and the electrical system for discharge are omitted from illustration. FIG. 16 shows the shape of the X-ray source as an X-ray pinhole photograph taken from the radial direction of the X-ray source where the X-ray mask is installed. In such radial exposure, when proximity exposure is performed with a mask-wafer interval of 10 to 20 μm, the pinched plasma, that is, the length d of the X-ray source and the X-ray source distance, are D, penumbra blur δ determined by wafer-mask spacing s
=ds/D became large, making it impossible to transfer fine patterns.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of an X-ray generator that takes out the plasma in the axial direction with little penumbra blur, namely,
Damage to the X-ray extraction window and upper electrode, instability of X-ray output during high-speed repetitive discharge, and attenuation of X-ray output due to gas have been improved, and the X-ray extraction window has been made thinner.
It is an object of the present invention to provide an X-ray generator capable of high-speed X-ray exposure and high-speed repetitive exposure.

[Means for solving the problem] In order to achieve such an object,
In the line generator, a gas passage for injecting discharge gas is provided on one side of a pair of opposing electrodes for plasma formation, and each of the pair of electrodes has one end facing opposite to each electrode. At least one through hole is provided, the other end of which is open in the surface, open in a surface other than the opposing surface of each electrode, and connected to the vacuum.

[Operation] Plasma can be generated by providing a set of discharge electrodes for forming plasma with a through hole that opens at one end on the opposing surface of both electrodes, and the other end opens on a surface other than the opposing surface and connects to a vacuum. Damage to the X-ray extraction window due to ions, electrons, high-temperature gas, etc. generated from the plasma can be reduced, and a thin-film X-ray extraction window can be used, while the distance to the X-ray source can be shortened, making it possible to efficiently capture X-rays generated from the plasma. Available at Furthermore, high-speed repetitive exposure becomes possible.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

Embodiment 1 FIG. 1 shows an example of an X-ray exposure apparatus using an embodiment of the X-ray generating apparatus of the present invention. In the figure, the 12th
Portions that are the same as or similar to those of the conventional example shown in the figures are given the same numbers and their explanations will be omitted. The biggest difference between this embodiment and the conventional example is that the upper electrode 4 has one end opened on the surface of the lower electrode 6 of the electrode section 4A facing the electrode section 6A, and the other end opened on the side surface of the electrode support section 4B. The point is that a through hole 31 is provided. Through hole 31
The upper electrode 4 is deeply inserted into the vacuum chamber 2 so that all ends thereof open into the vacuum chamber, and the shape of the lower electrode support portion 6B is also matched to the upper electrode 4. The space between the upper electrode 4 and the lower electrode 6 is evacuated by the vacuum pump 3 through the hole 6C. FIG. 2 is a diagram showing a cross section of the upper electrode support portion 4B of FIG. 1 taken along the line X--X. In this figure, an example is shown in which the through hole 31 extends upward from the center of the electrode section 4A, branches in three directions within the support section 4B, and opens at three locations on the side surface of the support section 4B. is not limited to three directions, and may not have branches. 5C is a gas passage connecting the gas reservoir 5A and the gas passage 4C in the electrode section 4A. In Figure 2, gas passages 5C, 4
Although we have shown an example in which C is formed by a large number of circular tubular passages,
The gas passages 5C and 4C may be formed of a plurality of passages each having an arcuate cross section, or may have an annular cross section if the through hole 31 does not have a branch.

The embodiment shown in FIG. 1 is operated in the same manner as the prior art example described above.
That is, the inside of the vacuum chamber 2 is evacuated to about 10 ^-5 to 10 ^-6 Torr, gas is injected between the electrode parts 4A and 6A to form a gas mass 7, and a high voltage is applied between both electrodes to cause discharge. is caused to occur, plasma 8 is formed, and X-rays 9 are generated. For example, copper, copper-
Use tungsten alloy, etc. The generation time of X-rays in one discharge is 1 μsec or less. Exposure work is performed by repeating the cycle of exhaust, gas injection, discharge, and X-ray generation.

In addition to X-rays 9, a group of particles 10 such as ions, electrons, and high-temperature gas generated during the collapse process of the high-density plasma are emitted from the plasma 8 pinched between the electrodes. While X-rays are emitted almost isotropically from each point of the plasma to the surroundings, ions, electrons, high temperature gas, etc. are emitted mainly in the plasma axis direction. In the present invention, since the upper electrode 4 on the gas injection side in the plasma axis direction also has the through hole 31, the pinched plasma 8
The particles generated from the X-ray extraction window 11 are absorbed not only toward the X-ray extraction window 11 but also toward the upper electrode 4. 3A and 3B show the results of measuring the electromotive force caused by ions emitted toward the X-ray extraction window with a Faraday cup placed at the position of the mask 12. 3A shows the result when a conventional electrode is used, and FIG. 3B shows the result when the upper electrode 4 of the present invention having the through hole 31 shown in the embodiment of FIG. 1 is used. It is clearly seen that the electrode having the through holes 31 has fewer ions that are part of the particle group. In the present invention, as shown in FIG. 3, the number of particles moving toward the X-ray extraction window is reduced, and damage to the X-ray extraction window 11 is also reduced. Therefore, it is possible to make the X-ray extraction window 11 thinner, and the X-ray extraction efficiency is improved, which helps improve throughput.

As mentioned above, during repeated discharge for X-ray exposure, it is necessary to rapidly exhaust the gas injected between the electrodes. If the exhaust is insufficient, abnormal discharge tends to occur and the output of X-rays decreases. FIG. 4 shows the results of investigating the relationship between the speed of repeated discharge and the X-ray output. Curve a is the case when a conventional electrode is used, and curve b is the case where the upper electrode with the through hole 31 is used. This is the case with an X-ray generator. With conventional X-ray generators, when repeated discharge is performed at 3Hz, the X-ray output is 1
It drops to about 80% of that of Hz. In contrast, in the device of this embodiment, the upper electrode 4 is provided with the through hole 31 having an opening on the surface facing the lower electrode of the electrode section 4A, so that the pinched plasma collides with the upper electrode and is reflected. Since the gas near the electrodes is exhausted without causing any abnormal discharge, the gas near the electrodes is exhausted quickly, and X-ray output similar to that at 1 Hz can be stably obtained without abnormal discharge even during high-speed operation of about 3 Hz.

Furthermore, in the X-ray generator of the present invention, the upper electrode is less likely to be damaged. FIGS. 5A and 5B are cross-sectional views of the copper upper electrode after 1000 shot discharges, where A is a conventional device and B is an embodiment of the present invention. In the conventional device, the center of the electrode portion 4A melts and is consumed as shown by 4D. In the embodiment of the present invention shown in FIG. 5B, since the center of the electrode is open, high-temperature, high-density plasma does not hit the electrode intensively, and electrode wear is only slightly reduced on the electrode surface. be.

FIG. 6 shows another form of the through hole 31. In this example, one end of the through hole 31 is connected to the electrode portion 6A of the electrode portion 4A.
The other end is opened at the side surface of the electrode section 4A. As shown in the figure, connect the electrode part 4A to the outer cylinder 4.
It is easy to create by combining E and the inner cylinder 4F.

Embodiment 2 FIG. 7 is a diagram showing another embodiment of the present invention.
In the figure, illustration of a discharge gas supply system and an electrical system for discharge is omitted. In this embodiment, the through hole 31 of the upper electrode 4 is connected to another exhaust device. Here, 32 is a vacuum pump such as a turbo molecular pump, and 33 is a piping system connecting the pump and the through hole 31 of the upper electrode. Particle groups 10 generated in the plasma axis direction when the plasma is pinched pass through the through hole 31 of the upper electrode 4 and the piping system, and are exhausted by the vacuum pump 32. Therefore, X-ray extraction window 1
The number of particle groups 10 in one direction is reduced, the X-ray extraction window can be made thinner, and the X-ray extraction efficiency is improved.

FIG. 8 is a sectional view showing another form of the electrode portion 4A of the upper electrode 4. By curving the tip of the outer tube 4E of the electrode section 4A inward, the injected gas can be concentrated at the center of the electrode, and the gas can be exhausted through the through hole 31 more efficiently.

Embodiment 3 FIG. 9 shows another embodiment of the present invention. In this example, gas is injected from the lower electrode 6 side. In FIG. 9, the gas injection system and electrical system outside the vacuum chamber are not shown. Although the discharge gas is injected from the lower electrode side through the gas passage 6E, plasma formation and X-ray generation by discharge can be performed in exactly the same manner as in the embodiments shown in FIGS. 1 and 7. The electrode portion 4A of the upper electrode 4 in this embodiment has a cylindrical shape, and a through hole 31 is formed in the center thereof. Since the particle group 10 is exhausted to the upper part of the vacuum container through the through hole 31, the X-ray extraction window 1
Radiation in one direction is reduced. A heat-resistant block 3 is placed directly above the through hole 31 of the vacuum container 1.
4 to reflect the particle group 10 laterally, damage can be reduced even if the height of the vacuum container is lowered, and it is also convenient for exhausting the particle group.

Embodiment 4 FIG. 10 is a diagram showing another embodiment of the present invention. In this embodiment, the X-ray extraction window 11 is
First film 11A, second film 11B, third film 11
It starts with C. The rest of the structure is the same as the embodiment shown in FIG.

Most of the particle group 10 is exhausted through the through hole 31, but some part is emitted toward the X-ray extraction window. The charged particles therein are removed by the charged particle remover 14, but the high temperature gas and some of the charged particles that cannot be removed reach the X-ray extraction window 11. The first film 11A is for removing the remaining particle group and has relatively high heat resistance.
Metal thin films such as beryllium, aluminum, and titanium that have good X-ray transmission, carbon, Si-N, SiN ₄ ,
Inorganic films such as SiC and BN, organic films such as polyimide,
Alternatively, a composite membrane of these is desirable. The second film 11B is a film for maintaining a vacuum, and includes a thin metal film such as beryllium, aluminum, and titanium, an inorganic film such as carbon, Si-N, _SiN4 , SiC, and BN.
It is preferable to use an organic film such as polypropylene, Mylar, or polyimide, or a composite film of these films, and these films may be reinforced with metal mesh, carbon mesh, silicon mesh, or the like. The third film 11C is a film that separates the X-ray extraction chamber 35 from the atmosphere. A gas with high X-ray transmittance, such as helium, is introduced into the X-ray extraction chamber 35 from the gas inlet 35A, and is discharged from the gas outlet 35B. A mask, wafer, etc. is placed in close proximity to the third membrane. The distance between the first film and the second film is short, and the distance between the second film and the third film is short.
Since the spaces between the membranes are filled with helium, the attenuation of X-rays is small even with the triple membrane structure. The third film only needs to have high X-ray transmittance, and may be a metal thin film such as beryllium, aluminum, titanium, carbon, Si-N, SiN ₄ ,
An inorganic film such as SiC or BN, an organic film such as polypropylene, Mylar, or polyimide, or a composite film thereof can be used, and a thin film of 1 μm or less can be used.

The X-ray extraction window 11 with such a triple membrane structure is
Since each film can be made thinner, the overall X-ray transmittance can be increased. Furthermore, the first
As shown in Figure 0, the upper electrode with the through hole 31 reduces the emission of particle groups toward the X-ray extraction window, allowing the first film to be made thinner and reducing the intensity of the X-rays extracted. can be made higher.

Embodiment 5 FIG. 11 shows still another embodiment of the present invention.
In the figure, only the discharge electrode section and the X-ray extraction window section are shown. The feature of this embodiment is that the upper electrode 4 is provided with a through hole 31, the normal direction of the X-ray extraction window 11 and the central axis of a set of electrodes for plasma generation are tilted, and the X-ray extraction window 11 The central position of the plasma 8 is offset from the axial extension line of the generated plasma 8. The effect of the through hole 31 is as explained in the previous embodiments. While the X-rays 9 generated from the pinched plasma 8 are emitted almost isotropically from each point of the plasma to the surroundings, groups of particles such as ions, electrons, and high-temperature gas are emitted centered in the plasma axis direction. Ru. In the X-ray generator with the configuration shown in Fig. 11,
Although the X-rays 9 irradiate the X-ray extraction window 11, they are not exhausted from the through hole 31, and the particle group 10 emitted toward the lower electrode 6 hardly collides with the X-ray extraction window 11. If the angle between the normal line of the X-ray extraction window and the central axes of the upper and lower electrodes exceeds 45°, the above-mentioned drawback of radial exposure, that is, penumbra blur will increase, which is not preferable. Although the lower limit of the effective tilt angle differs depending on the configuration of the exposure apparatus, 2° to 3° is sufficient for normal apparatus configurations. In combination with the effect of the through hole 31, damage to the X-ray extraction window can be further reduced. As a result, a thin film X-ray extraction window can be used and at the same time the distance between the X-ray sources can be shortened, so that X-rays generated from plasma can be used with high efficiency.

As shown in FIG. 12, the upper electrode 4 has a through hole 3.
1, and the central axes of the electrodes are set at 11A, 11B, 11
It is also possible to tilt with respect to the normal direction of the X-ray extraction window 11 having the triple membrane structure of C. According to the configuration of the embodiment shown in FIG. 12, the effect of the through hole 31, the effect of the X-ray extraction window of the triple membrane structure, the
Since the effects of the inclination of the radiation extraction window are multiplied, the X-rays generated from the plasma can be used with high efficiency, and the throughput of X-ray exposure can be improved.

In addition, when a discharge electrode equipped with a through hole is combined with an X-ray extraction window having a triple membrane structure, and when the central axis of the discharge electrode equipped with a through hole is inclined with respect to the normal direction of the X-ray extraction window, The form of the through hole when
It goes without saying that the present invention is not limited to the embodiments shown in FIGS. 10, 11, and 12. Furthermore, it is preferable to provide the gas reservoir 5A and piston 5B inside the discharge electrode for rapid gas injection, but it is preferable to provide them outside the discharge electrode and only the gas passage inside the discharge electrode. It is also possible to provide

Although the explanation has been given using an X-ray exposure device as an example, the X-ray generator according to the present invention having an electrode provided with a through hole communicating with a vacuum can be used as an X-ray analyzer, an X-ray microscope, or a chemical reaction device using X-ray excitation. , miniaturization of these devices by applying them to film forming devices that utilize X-ray excitation and etching devices that utilize X-ray excitation;
It can be used to promote reactions, etc.

[Effects of the Invention] As explained above, in a set of discharge electrodes for forming plasma, one end is opened to the opposing surfaces of both electrodes, and the other end is opened to a surface other than the opposing surface and connected to a vacuum. By providing a through hole, damage to the X-ray extraction window due to ions, electrons, high-temperature gas, etc. generated from the plasma can be reduced, and a thin-film X-ray extraction window can be used, while at the same time the distance between the X-ray source and the X-ray source can be shortened. It has the advantage of being able to use the X-rays generated from the X-rays with high efficiency, and X-rays can be generated at a high repetition rate. Highly efficient X-ray extraction improves throughput, and at the same time, since the diameter of the X-ray source is smaller than in radial extraction, submicron transfer is possible with proximity exposure. Furthermore, since there is no metal part in the plasma axis direction where high-density plasma is concentrated in the electrode with a gas venting structure, there is an advantage that the electrode wears out very little.

[Brief explanation of drawings]

FIG. 1 is a structural diagram showing an X-ray exposure apparatus to which an embodiment of the X-ray generator according to the present invention is applied, and FIG. 2 is a cross-sectional view of the upper electrode 4 in FIG. Figures 3A and B are characteristic diagrams showing the electromotive force caused by ions to explain the effect of through holes, and Figure 4 is
Diagram showing the relationship between linear output ratio and discharge repetition rate, 5th
Figures A and B are cross-sectional views showing the state of the electrode after 1000 shot discharges, Figure 6 is a cross-sectional view showing another form of through hole provided in the discharge electrode, and Figure 7 is an X-ray generator according to the present invention. FIG. 8 is a cross-sectional view showing an example of the structure of an electrode part, and FIGS. 9 to 12 are respectively a structural diagram showing an X-ray exposure apparatus to which another embodiment of the present invention is applied. Fig. 9 is a structural diagram showing an X-ray exposure apparatus to which still another embodiment is applied. Fig. 9 shows an embodiment in which gas is injected from the lower electrode side, and Fig. 10 shows a discharge electrode with a through hole and a triple window structure. FIG. 11 and FIG. 12 are examples in which the central axis of the discharge electrode is inclined with respect to the normal direction of the X-ray extraction window. Figure 13 shows the conventional
Structure diagram of an X-ray exposure device using a ray generator, Part 1
Figure 4 shows the relationship between the length of X-ray transmission through neon gas and the X-ray transmittance at a wavelength of 12A using neon gas pressure as a parameter. A structural diagram of the exposure device, FIG. 16 is a diagram showing the shape of the plasma seen from the X-ray extraction direction of the conventional device shown in FIG. 15, and FIG. 17 is a diagram showing the penumbra blur in the conventional device shown in FIG. 15. FIG. 1... Vacuum container, 2... Vacuum chamber, 4... Upper electrode, 4A... Electrode part, 4B... Electrode support part, 4C
...Gas passage, 5...High speed opening/closing gas valve, 5A
... Gas reservoir, 5B ... Piston, 6 ... Lower electrode, 6A ... Electrode part, 6B ... Electrode support part, 6C
...hole, 6E...gas passage, 7...gas mass, 8...
...Plasma, 9...X-ray, 10...Particle group, 11
...X-ray extraction window, 11A...First membrane, 11B
...Second film, 11C...Third film, 31...Through hole, 32...Exhaust device.

Claims (1)

[Claims] 1. In an X-ray generation device that forms plasma in a vacuum, generates X-rays from this plasma, and extracts them from an X-ray extraction window, one of a pair of opposing electrodes for plasma formation is A gas passage for injecting discharge gas is provided, and each of the pair of electrodes has one end open to the opposing surface of each electrode and the other end opened to a surface other than the opposing surface of each electrode. An X-ray generator characterized in that at least one through hole is provided which is connected to a vacuum. 2. The X-ray generator according to claim 1, wherein the other end of the through hole opens at a plurality of locations on a surface other than the opposing surface. 3. The X-ray generator according to claim 1, wherein the other end of the through hole is connected to an exhaust device. 4. The normal direction of the X-ray extraction window and the center axis of the set of electrodes are inclined, and the center position of the X-ray extraction window is shifted from the axial extension line of the plasma to be formed. An X-ray generator according to any one of claims 1 to 3. 5. The X-ray extraction window is used with a first membrane provided in the vacuum chamber, a second membrane provided to separate the vacuum chamber and the X-ray extraction chamber, and the X-ray extraction chamber. The X-ray generator according to any one of claims 1 to 4, further comprising a third film provided to separate the X-ray generator from the atmosphere.