JPH0744020B2 - X-ray extractor for plasma X-ray source - Google Patents

Description

TECHNICAL FIELD The present invention relates to an X-ray source used in, for example, X-ray lithography, and more particularly to an X-ray extraction device thereof.

[Prior Art] One of the most effective submicron transfer techniques is an X-ray exposure method using soft X-rays having a wavelength of 5 to 15Å. Conventionally, in such an X-ray source for X-ray exposure, a metal such as Al, Si, Mo is irradiated with an electron beam to generate an X-ray, but the X-ray generation efficiency is as low as 10 ⁻⁴ or less. However, it has a drawback that high-power X-rays cannot be obtained. Therefore, recently, a plasma X-ray source that generates X-rays from high-temperature, high-density plasma has been attracting attention as an X-ray source for X-ray exposure because its generation efficiency is as high as several percent. In this plasma X-ray source, as a method of forming high-temperature and high-density plasma that generates X-rays, there is a laser plasma method of irradiating a metal surface with laser light at a power density of 10 ^-13 W / cm ² or more. The discharge plasma method in which a large current is passed through the plasma to compress and heat the plasma by electromagnetic action is mainly used.

On the other hand, in order to efficiently take out the generated X-rays having a wavelength of 5 to 15Å, for example, to the outside of the container, a metal foil such as beryllium having a thickness of several microns or a polymer film such as polypropylene is used as the X-ray extraction film. There is.

[Problems to be solved by the invention]

However, in any of the plasma formation methods described above, the generation time of X-rays is 1 to 100 ns at a time, which is pulse-like, and after the X-rays are generated from the plasma, the plasma rapidly collapses,
High-speed particles such as electrons, ions, and high-temperature gas that compose plasma are scattered in all directions from the plasma. When high-speed particles accompanying such plasma collapse collide with the thin and shock-resistant X-ray extraction film as described above, the film is damaged, and as a result, only X-rays generated from plasma cannot be stably extracted. Will end up. For this reason,
Conventionally, it has been considered practically impossible, though desired, to use a plasma X-ray source as an X-ray source for X-ray exposure.

[Means for solving problems]

The X-ray extraction device of the plasma X-ray source of the present invention has an X-ray extraction for extracting the X-rays 2 generated from the plasma of the plasma forming unit 1 to the outside of the container 3, as shown in the basic configuration of FIG. A valve 6 for injecting a gas to form a gas mass 5 and a control device 7 for controlling opening / closing of the valve 6 are provided between the window 4 and the plasma forming unit 1.

[Action]

At the time of X-ray generation, the control device 7 opens the valve 6 in synchronization with the plasma formation timing in the plasma forming unit 1 and injects a gas having a small X-ray absorption such as hydrogen, helium, oxygen or nitrogen to form a gas mass 5. To do. The high-speed particles from the plasma collide with the gas mass 5 and lose their energy, and do not reach the X-ray extraction window 4.

〔Example〕

FIG. 2 is a block diagram showing an embodiment in which the present invention is applied to an X-ray exposure apparatus. In the figure, 11 is a plasma forming unit that generates X-rays, 111 is a power supply for plasma formation that is electrically connected to the plasma forming unit 11, 12 is X-rays that are generated from the plasma forming unit 11, and 13 is plasma formation. A container for keeping the portion 11 at a predetermined low pressure, and 14 are X-ray extraction windows for taking out the X-rays 12 generated from the plasma forming portion 11 to the outside of the container 13. The X-ray extraction window 14 is made of a material such as beryllium foil or a polyethylene film that easily transmits X-rays, and is a thin film having a thickness of several microns. 15 is hydrogen,
A gas mass made of an element having small X-ray absorption such as helium, oxygen, and nitrogen, 16 is a valve capable of opening and closing at high speed for forming the gas mass 15, and 17 is a control device of the valve 16.

In the valve 16, 161 is a piston, which is made of metal such as Al and Ti, and 162 is a valve driving power source. Reference numeral 163 denotes a coil. When a current flows through the coil 163 by the valve drive power source 162, the piston 162 is driven by an electromagnetic action that acts between the coil 162 and the current induced in the metal piston 161, and the gas injection hole 164
It is supposed to open. Reference numeral 165 is a spring for pushing back the piston 161, 166 is a gas reservoir for gas constituting the gas mass 15, and 167 is a gas introduction pipe for introducing gas into the gas reservoir 166.

Reference numeral 18 is a diffusion prevention tube for slowing the diffusion speed of the gas mass 15, and the X-ray 12 from the plasma forming unit 11 is X-rayed.
It has X-ray passage holes 181, 182 for passing through the wire extraction window 14. Further, 19 is an exhaust device connected to the container 13, 20
Is an X-ray mask for transferring a pattern using the X-rays taken out from the X-ray taking-out window 14, and 21 is a wafer to which the pattern is transferred. The control device 17 directly drives and controls the valve drive power supply 162 in accordance with the drive of the plasma forming power supply 111.

In order to operate this, first the exhaust device 19 exhausts the inside of the container 13 to a predetermined pressure, and then the valve 16 is operated by a signal from the control device 17. That is, the piston 161 is moved by the electromagnetic force of the coil 163 to inject a gas from the gas ejection hole 164, and a gas mass such as hydrogen or helium is injected into the diffusion prevention pipe 18.
Forming fifteen. Immediately after that, the controller 17 operates the plasma forming power source 111 to form plasma and generate X-rays. The X-rays 12 generated from the plasma are taken out of the container 13 through the gas lump 15 and the X-ray taking-out window 14, and the pattern of the X-ray mask 20 is transferred onto the wafer 21. For diffusion prevention
The gas mass 15 formed in 18 diffuses through the X-ray passage holes 181 and 182, and is exhausted by the exhaust device 19.

Here, if the moving speed (diffusion speed) of the gas is 1000 m / s, it takes 5 × 10 ⁻⁵ seconds to move 5 cm, but this 5 × 10 ⁻⁵ second time is, for example, laser plasma. This is sufficiently longer than the time required for X-ray generation, such as 10 ^-9 seconds with an X-ray source and 10 ^-6 seconds with a discharge plasma X-ray source. Therefore, by adjusting the timing of the plasma formation and the formation time of the gas lump 15 by the control device 17, the gas lump 15 does not diffuse into the plasma forming unit 11 to affect the plasma formation, and the plasma formation is stable. It is possible to generate X-rays.

When there is a gas mass 15 between the plasma forming unit 11 and the X-ray extraction window 14 as described above, high-speed electrons, ions, high-temperature gas particles, etc. that form plasma at the same time as the X-rays 12 from the plasma forming unit 11 are formed. Particles fly out and collide with this gas mass 15. At this time, if the density of the gas mass 15 is sufficiently high, the high-speed particles from the plasma collide with atoms and molecules such as hydrogen and helium forming the gas mass 15 many times, and the direction of the high-speed particles is changed. I will lose that energy, X
It will not reach the wire extraction window 14. On the other hand, since X-ray absorption of hydrogen, helium, etc. is small, the X-ray 12 reaches the X-ray extraction window 14 without being attenuated.

Here, when He gas is used as the gas mass 15 and Ne gas is used for plasma generation, the process in which high-energy Ne ions emitted from plasma collide with He gas atoms and lose their energy will be roughly estimated. He and Ne atomic diameters are
Since they are 2.18Å and 2.59Å respectively, considering the hard sphere collision model, the collision cross section σ between He and Ne is approximately When the pressure of He gas mass is 10 Torr, the mean free path λ of Ne atom is Assuming that the He gas mass is 1 cm thick, it has jumped into the He gas mass. Ne atoms are thought to cause at least 1 / λ collisions. That is, the number of collisions n is Therefore, about 600 collisions between Ne and He atoms occur.

Next, we estimate the energy lost by fast atoms due to interatomic collisions. The energy lost when an atom of mass me collides with a stationary atom of mass mm at a velocity ve is given by the following equation (Yoshinori Hatta, “Gas Discharge”, Modern Science Company, Showa
46 years).

Considering collisions at all angles below the central collision, the average ratio δ of energy lost in one collision is approximately given by the following equation.

Where E₀Is the initial energy of fast colliding atoms
It Hard sphere model ignoring the above thermal motion of atoms
Using the result calculated in_eHigh-speed Ne jumping into a gas block
Think about the atom. The mass ratio between He and Ne atoms is
Since it is approximately 1: 5, if this relationship is substituted into the above equation, δ
It becomes 0.28. That is, when He atoms collide,
You will lose 30% of that energy. For example, Ne atom
Energy when colliding with He gas mass is 50 keV (plasm
(Corresponding to the discharge voltage at the time of formation),
Relaxed to a thermal kinetic energy of 0.025 eV by collision.
The number of collisions required to generate the collision is given by the following equation.

5 x 10^Four× 0.28_n= 0.025 from now on After about 12 collisions, most of the fast Ne atoms are
You will lose minutes of energy.

As described above, since several hundreds of Ne-He collisions occur in the He gas mass, the above results show that the fast Ne atoms almost lose their energy in the He gas mass.

Here, the gas species of the gas mass used for blocking the fast quons or atoms will be examined. To use for this mass of gas,
It is desirable that the X-ray transmittance is high, the collision cross-section with ions or fast atoms is large, and the mass is large so that energy can be easily absorbed. The table below shows the X-ray transmittances of general gases such as He, N ₂ and Ar when the gas pressure of the gas mass is 10 Torr and the thickness in the X-ray extraction direction is 2 cm.

From the above table, for X-ray sources that generate X-rays with a relatively short X-ray wavelength of 5 Å, even Ar gas with a large atomic weight can be used because of its low X-ray absorption, but X-ray wavelengths of 12 Å It can be seen that He gas is desirable for the radiation source. In this way, the gas species of the gas lump may be changed according to the X-ray wavelength generated by the X-ray source.

Further, for example, when carbon is used for the electrode of the plasma forming unit 11 and therefore a carbon film is attached to the X-ray extraction window 14, oxygen is used as the gas species of the gas mass 15 or a gas mixed with oxygen. Is used, the oxygen in the gas mass 15 is activated by the extreme ultraviolet light generated at the same time as the X-rays 12 in the plasma forming part 11, and reacts with the carbon on the X-ray extraction window 14.
Exhausted as CO ₂ or CO gas, it has the effect of removing the carbon film adhering to the window. Since the dirt on the X-ray extraction window 14 is removed, the X-rays can be stably extracted.

By forming the gas lumps 15 in this way, the X-ray extraction window 14 is less damaged by the high-speed particles from the plasma, its life is extended, and X-rays can be stably extracted.

The same technique can be used not only for protecting the X-ray extraction window 14, but also for protecting various detectors and the like in the plasma forming container which are easily damaged by high-speed particles.

FIG. 3 shows the configuration of an apparatus for measuring the effect of removing and deflecting fast ions in a gas mass when the gas injection discharge method is used as the plasma formation method. here,
112 is a high voltage electrode to which a high voltage is applied, 113 is a gas injection ring for injecting a plasma forming gas between the electrodes, and 114 is a counter electrode. Further, 22 is a ring-shaped gas mass, and the gas injection ring 11
3 is formed by the gas injected. A pinch plasma 23 is a pinch plasma to apply a high voltage between the electrodes to discharge it, and the annular gas mass 22 is turned into a plasma, and a current of about several hundred kA is caused to flow. It is formed on the central axis of the electrode. 115 is a pinch plasma 23
Is a magnet for deflecting electrons generated simultaneously with X-rays. Further, 24 is a Faraday cup, which is provided on the central axis of the pinch plasma 23. It is generally known that a large number of high-speed particles are scattered in the direction of the plasma axis in a cylindrical pinch plasma such as the pinch plasma 23.
The ion flow is captured by Faraday Cup 24. 25 is a charge measuring resistor of the Faraday cup 24, one end of which is grounded. The voltage change across the resistor 25 is measured with an oscilloscope.

FIG. 4 and FIG. 5 show an example of the measurement result. Here, neon gas is used for the annular gas mass 22 for plasma formation, and helium gas is used for the gas mass 15 for blocking high-speed particles.

FIG. 4 shows an example of measurement when the valve 16 is not operated and there is no gas mass 15, and a large amount of ion flow is detected.

Here, the current applied to the pinch plasma 23 is 30 at the peak.
0kA, distance between Faraday cup 24 and plasma 23 is 15cm
Is. Also, at the position of the Faraday cup 24,
When the Al foil was placed, it was severely damaged and was damaged by one discharge.

FIG. 5 shows an example of measurement under the same plasma formation conditions as in FIG. 4 by driving the valve 16 and passing the helium gas mass 15. The amount of detected ions is extremely small. In fact, placing a 5 μm thick Al foil on the Faraday cup 24 did not cause any damage. From the above results, it was clarified that the effect due to the presence of the gas mass 15 was remarkable.

As is clear from the experiment, the fast ions generated from the plasma disappear by colliding with the gas mass 15. Similarly, most of the constituent atoms of the plasma and the fast neutral particles of the electrode material are also removed. Further, the extreme ultraviolet light generated simultaneously with the X-rays from the plasma is also absorbed by the gas mass, so that the X-ray extraction window 14 is less likely to be heated by the extreme ultraviolet light having high energy.

FIG. 6 is a configuration diagram showing a second experimental example of the present invention.
The feature is that a charged particle remover for changing the flow of plasma is used together with a gas mass for removing high-speed particles.

In FIG. 6, reference numeral 31 is a charged particle remover arranged immediately below the plasma forming unit 11. 311 is a magnet, 312 is a magnetic circuit forming yoke, and these magnet 311 and yoke 312 form a magnetic field of about 3 kG which is not parallel to the X-ray traveling direction. A plasma reflector 313 has an X-ray passage hole 314. X of diffusion prevention tube 18 in which particle blocking gas mass is formed
A foil 32 of beryllium or the like is stretched over the X-ray passage hole 182 on the side of the line extraction window. Reference numeral 33 is a magnet that applies a magnetic field to the inside of the diffusion prevention tube 18 and that generates a magnetic field of about 3 kG, and 34 is a magnetic circuit forming yoke. Although not shown in the figure, the X-ray extraction window 14 and the control device 17
Is provided in the same manner as in the embodiment shown in FIG.

In the above structure, the electrons emitted from the plasma forming unit 11 have a Larmer radius of about 1 cm even if they are high-energy electrons of about 100 keV.
Plasma is also deflected by the plasma reflector 31
The direction of the flow can be changed by 3. Furthermore, the number that could not be removed by this charged particle remover 31 + ke
Some of the ions of V or higher and some of the high-speed particles collide with the gas mass in the diffusion prevention tube 18, lose their energy and are changed in direction, and do not reach the X-ray extraction window. In this embodiment, since one X-ray passage hole 182 of the diffusion prevention tube 18 is closed with the foil 32, the diffusion speed of the gas mass is further reduced as compared with the case where it is opened. Prevention tube
The gas molecule density in 18 becomes higher. As a result, the probability that the high-speed particles collide with the gas molecules increases, and the effect of blocking the high-speed particles increases. Also, even if this gas mass itself is ionized by extreme ultraviolet light from plasma, etc.
The magnetic field created by 33 blocks the foil 32 from reaching the foil,
32 damage is small. This foil 32 can also be used as an X-ray extraction window.

The X-ray extraction device of the plasma X-ray source according to the present invention can be similarly used for an X-ray source for X-ray lithography, an X-ray source for medical X-ray analysis, and the like.

〔The invention's effect〕

As described above, according to the present invention, the gas injection valve and its control circuit are provided so that the gas mass is formed between the plasma forming portion and the X-ray extraction window. High-speed particles such as electrons, ions, and neutral particles that are emitted at the same time as the generation of the rays collide with the gas mass and disappear or lose their energy, so that only X-rays reach the X-ray extraction window, The damage of the X-ray extraction window by the fast particles is extremely small. Further, since the extreme ultraviolet light generated from the plasma is also mostly absorbed by the gas mass, the X-ray extraction window is not heated by that much. Further, the electrode constituent substance melts and evaporates at the time of discharge, but the vapor also collides with the gas mass and changes its direction, so that the X-ray extraction window is less contaminated.

In this way, the X-ray extraction window is less damaged, so X
The X-ray extraction window can be extracted efficiently because the X-ray extraction window can be made thin. Furthermore, the distance between the plasma forming part and the X-ray extraction window can be shortened, and high-power X-rays can be obtained. In addition, the life of the X-ray extraction window is extended, and X-rays can be extracted stably.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a configuration diagram showing an embodiment in which the present invention is applied to an X-ray exposure apparatus, and FIG. 3 is a diagram showing that plasma is formed by a gas injection discharge method. FIG. 4 and FIG. 5 are diagrams showing an example of the experimental results of the experimental apparatus that clarified the effects of the invention, and FIG. 4 is a diagram showing an ion flow detected when a gas mass is not formed. FIG. 5 is a diagram showing an ion flow detected when a gas mass is formed, and FIG. 6 is a configuration diagram showing a second embodiment of the present invention in combination with a charged particle remover. 1,11 …… Plasma formation part, 2,12 …… X-rays generated, 3,13
…… Container, 4,14 …… X-ray extraction window, 5,15 …… Gas block,
6,16 …… Gas injection valve, 7,17 …… Control device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Yoshihara, 3-1, Morinosato Wakamiya, Atsugi City, Kanagawa Prefecture, Atsugi Telecommunications Research Laboratories, Nippon Telegraph and Telephone Corporation (56) Reference JP-A-58-113898 (JP, A) Kai 59-128747 (JP, A)

Claims (1)

[Claims] 1. A plasma X-ray source for generating X-rays using high-temperature and high-density plasma, and an X-ray extraction window for extracting X-rays generated from plasma to the outside, and this X-ray extraction window.
A valve for ejecting glass to form a gas mass between the wire extraction window and the plasma forming part, and a control device for controlling the opening / closing of the valve in accordance with the plasma forming timing. X-ray extraction device for plasma X-ray source.