JP2614457B2 - Laser plasma X-ray generator and X-ray exit opening / closing mechanism - Google Patents

Description

The present invention relates to an improvement in a laser plasma X-ray generator, and is mainly used as a light source for X-ray lithography and X-ray microscopes.

(Prior art) A laser plasma X-ray generator generates high-temperature, high-density plasma by converging and irradiating a high-power, pulsed laser beam having a predetermined repetition frequency onto a fixed target material, and radiating the plasma. X-rays are used as light sources for X-ray lithography and X-ray microscopes.

In a conventional X-ray generator, a metal target rotating body 2 is usually disposed in a vacuum chamber 1 as shown in FIG.
The X-ray 5 is emitted to the outside of the X-ray exit port 6 while irradiating the light onto the light-converging point of the X-ray.

As the target material, generated X-rays (0.1 to 3
Metal solid materials such as copper and aluminum are considered to be optimal in terms of energy (keV). By shaping a metal plate into a cylinder or a rotationally symmetric body and rotating it, a new smooth solid surface is always obtained. It is configured to come to the focal point of the laser light. In order for the new solid surface to come to the focal point of the laser, the target material evaporates around the focal point due to the irradiation of the laser beam, and a crater-like trace is generated. Is unstable.

The X-ray emission port 6 of the vacuum chamber 1 is usually sealed with a thin film having a high X-ray transmittance such as beryllium so as to maintain the degree of vacuum in the chamber 1 and to move the X-ray from the low-pressure chamber 1 to the high-pressure outside. It is configured so that a line can be efficiently derived.

The conventional laser plasma X-ray generator shown in FIG. 6 is excellent in that the stability of focusing laser light on the surface of the target material is high and that the degree of vacuum in the chamber 1 can be maintained extremely easily. It has practical utility.

However, the X-ray generator still has many problems to be solved.

The first problem is a problem of X-ray attenuation due to a thin film of beryllium or the like provided at the X-ray exit 6. Although the X-ray transmittance is high, attenuation of X-rays due to the thin film is unavoidable. In particular, when the pressure difference between the inside and outside of the chamber 1 is large and the area of the X-ray exit 6 is large, the film thickness is small. Must be made thicker inevitably, and there is a problem that attenuation of X-rays increases.

Further, when the injection port 6 is opened to avoid attenuation of X-rays, it becomes difficult to maintain the degree of vacuum in the chamber 1 and various inconveniences occur due to leakage of metal vapor as described later.

The second problem is a problem of vapor deposition of metal vapor generated by heating. Since a metal target is used, a metal vapor is generated by laser heating, and the metal vapor is deposited on the inner wall surface of the chamber 1 and the thin film of the X-ray emission port 6. As a result, there is a problem that the X-ray transmittance of the thin film is reduced, the X-rays are attenuated, and X-rays with stable intensity cannot be obtained.

In a place where the X-ray emission port 6 is opened, metal vapor flows out through the opening. As a result, it accumulates on an X-ray irradiation target such as an X-ray mask, causing destruction of the irradiation target and deterioration of performance.

The third problem is that of replacing the metal target rotating body 2. As described above, the target surface on which the crater-like trace has been generated by the irradiation of the laser beam cannot be reused because the stability of the light concentration deteriorates. Therefore, even if the target is formed in a rotationally symmetrical body, it must be replaced after each use for about one hour, which makes the operation complicated and requires large-scale equipment for automatic replacement. There is a problem that the cost rises sharply.

On the other hand, various ideas have been disclosed so far in order to solve the above-mentioned problems.

For example, as a device for solving the problem of X-ray attenuation due to the thin film provided at the X-ray exit 6, an apparatus in which a mask or a substrate with a resist is directly disposed in a vacuum chamber (Japanese Patent Application Laid-Open No. Sho 60/1985).
No.-7130) and the first sealed chamber with high vacuum generating X-rays and X
A second sealed chamber filled with helium gas or the like having a small linear attenuation rate is connected via an intermediate chamber, and the pressure difference between the second sealed chamber and the outside is reduced to substantially zero, so that the second sealed chamber is closed. An X-ray generator (Japanese Patent Laid-Open Publication No.
No. 58-225636).

However, in the former device of JP-A-60-7130, X
Even if the attenuation of the line can be prevented, problems such as damage to the mask due to vapor deposition of metal vapor are unavoidable, and practical application is extremely difficult.

Further, even in the latter device disclosed in JP-A-58-225636,
Since the first closed chamber having a high vacuum degree and the second closed chamber near the atmospheric pressure are communicated via the intermediate chamber, it is not only extremely difficult to maintain the degree of vacuum in the first closed chamber, but also the second closed chamber. There is a disadvantage that the effect of thinning the thin film is offset by the attenuation of the X-rays by the helium gas in the closed chamber.

In order to solve the problem of metal vapor deposition, an RF oscillation coil is disposed outside the chamber wall, and when metal vapor deposition occurs, a gas (for example,
Cl ₂ ) is introduced, and this gas is turned into a plasma by the energy of the RF oscillation coil to thereby deposit particles (for example, Al).
Particle) into a gas (for example, Al ₂ Cl ₃ ) and discharging it to the outside (JP-A-58-40757), or as a target material, the product after plasma conversion is combined with the atmosphere or the material itself A device that prevents deposition on the inner wall of the chamber by using a substance that is gasified by decomposition of
No. 8842) is disclosed.

However, in the former Japanese Patent Application Laid-Open No. 58-40757, it is necessary to introduce a gas and perform a plasma conversion operation every time vapor deposition occurs, which complicates the operation and makes continuous operation of the X-ray generator impossible. There is a drawback that you can not. Further, when the oscillation coil is driven, if the mask, the resist and the like are placed in the chamber, there is a disadvantage that the mask and the like are damaged by the plasma.

Also, in the latter Japanese Patent Application Laid-Open No. 58-158842, although the use of a substance in which the target substance and the product after plasma conversion become a gas has been started, the method of supplying the target substance and the X-ray radiation No specific means are disclosed for preventing X-ray attenuation in the mouth, and practical application is extremely difficult.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problem in the conventional laser plasma X-ray generator, that is, the X-ray emission film due to the thin film.
Attenuation of radiation (when the X-ray exit is open,
It is difficult to maintain the degree of vacuum in the chamber), and the evaporated target material adheres to the inner wall surface of the chamber and fluctuates in X-ray transmittance. Leakage to the outside and damage to the mask, etc.)
An object of the present invention is to solve the problem that the line generator cannot be used continuously for a long time.

(Means for Solving the Problems) According to the present invention, an irradiation surface of a new target material can be easily and continuously supplied to a focal point of a laser beam, and an X-ray exit can be synchronized with irradiation of a pulse laser. By opening the aperture at least, a laser plasma X-ray generator capable of preventing attenuation of X-rays, preventing leakage of vapor of a target material, facilitating maintenance of the degree of vacuum in the chamber, and the like can be obtained.

More specifically, according to the present invention, a chamber having an entrance for pulsed laser light and an X-ray exit and having a depressurized inside is provided with a chemical vaporizer which vaporizes by laser heating to a focal point of the pulsed laser light. A target material supply / transfer device for continuously supplying / transferring a stable liquid or fixed target material, and a device provided opposite to the X-ray emission port,
An X-ray emission port opening / closing mechanism that opens the X-ray emission port in synchronization with the laser pulse.

Further, according to the present invention, as the above-mentioned X-ray emission opening / closing mechanism, two rotating disks each having a small hole are arranged side by side so that a part of the two disks can be overlapped and both small holes can be matched. The rotating disk is supported at a position facing the X-ray emission port, and the difference between the rotation frequencies of the two rotating disks is made equal to the repetition frequency of the laser pulse light. A configuration for synchronizing the generation of X-rays by plasma is used.

According to one embodiment of the present invention, a laser plasma X-ray generator using a liquid or a solid that is a rare gas or an inert gas at room temperature as the above-described target material is obtained.

According to another aspect of the present invention, the target material supply / transfer device includes a laser plasma X having an endless belt.
A line generator is obtained.

According to still another aspect of the present invention, there is provided a laser plasma X-ray generator in which the target material supply / transfer device is constituted by a pipe having an open end.

According to another aspect of the present invention, there is provided a laser plasma X-ray generator in which the target material supply / transfer device includes a device for cooling and recovering the target material contained in the exhaust gas from the chamber.

According to still another aspect of the present invention, there is provided a laser plasma X-ray generator in which the opening time of the X-ray emission port due to the coincidence of the two small holes is substantially equal to the time width of the pulsed laser beam.

According to another aspect of the present invention, there is provided a laser plasma X-ray generator in which both rotating disks are disposed outside and forward of the X-ray exit.

(Function) A target material comprising a liquid or solid inert element is supplied to a target material transfer device in a chamber by a target material supply device, and the target material is continuously transferred to a focal point of the pulsed laser beam by the transfer device. Supplied to

On the other hand, a pulse laser beam emitted from a laser light source is incident on the focusing point through a focusing mechanism.
The target material heated by the pulsed laser beam is turned into plasma, and X-rays are emitted from the target material turned into plasma.

The target material that is turned into plasma and gaseous is
The gas is discharged to the outside of the chamber by the exhaust device, and is sent to a cooling / recovering device provided in the target material supply device. Here, the target material re-liquefied or re-solidified by cooling is continuously supplied to the target material transfer device in the chamber.

On the other hand, the X-rays emitted from the plasma-converted target material are emitted to the outside of the chamber through the opening of the X-ray emission opening / closing mechanism disposed opposite to the X-ray emission opening.

The X-ray emission opening / closing mechanism is opened when two small holes respectively formed on both rotating disks exactly coincide with each other, and the opening / closing mechanism is opened in synchronization with the pulse laser beam, and the opening / closing time of the opening / closing mechanism is opened. Is set to substantially coincide with the pulse width time of the light of the pulse laser.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic cross-sectional view of a laser plasma X-ray generator according to the present invention, and FIG. 2 is a schematic explanatory view of an X-ray emission opening / closing mechanism.

In FIG. 1, reference numeral 10 denotes a metal chamber whose internal pressure is reduced, 14 denotes a target material transfer device for continuously supplying a target material to a focal point of a pulse laser beam, and 20 denotes a target material transfer device.
Is a target material supply device for supplying the target material from the outside of the chamber to the target material transfer device, 2
Reference numeral 1 denotes an X-ray emission opening / closing mechanism that regulates opening / closing of the X-ray emission opening.

The chamber 10 is formed airtight from stainless steel or the like, and the inside thereof is maintained at a low vacuum of about 10 torr or less by an exhaust device 11. An entrance 12 for pulsed laser light is formed in the side wall of the chamber 10, and a pulsed laser light 13a from a laser light source 13 is incident on a target material 15 on a target material transfer device 14 through a laser focusing mechanism 12a. Is done.

An X-ray emission port 16 is formed in the front wall of the chamber 10, and X-rays 17 radiated from the target material 15, which has been turned into plasma by pulsed laser light, enter the emission port 16.

Inside the chamber 10, a target material transfer material 14 for transferring the target material 15 to the focal point 18 of the pulse laser beam 13a is provided. In the present embodiment, an endless belt is used as the target material transfer device 14, and this is rotated at a constant speed in the direction of the arrow by a driving device (not shown), so that a liquid or solid target material 15 is formed. Can be continuously supplied to the laser focal point 18.

A target material 15 described later is supplied to the target transfer device 14 from a target material supply device 20 through a target material supply path 19.

The target material supply device 20 includes a target material 15
The storage and pressurization device 20b, the cooling and recovery device 20a, etc.
The target material 15 vaporized by the condensing irradiation of a is introduced into the cooling / recovery device 20a via the exhaust device 11, and is re-liquefied or re-solidified by cooling, and then supplied to the target material transfer device 14 through the supply path 19. Go being.

In the above embodiment, the target supply path 19
Although a pipe is used as the material, any structure other than a pipe may be used as long as the liquid or solid target material 15 can be effectively supplied to the target material transfer device 14.

As the target substance 15, a rare gas such as krypton, xenon, or argon or a substance that is chemically inert, easily vaporizes at a temperature of −50 ° C. or more, and has a liquefaction point or a solidification point at a temperature lower than that, Used in a liquefied or solidified state (hereinafter referred to as a cryotarget).

The adoption of the cryo-target as the target material 15 of the plasma laser X-ray generator is based on an experiment on the atomic number dependence of the X-ray generation efficiency found by the present inventors as shown in FIGS. 4 and 5. It was obtained based on the results.

Fig. 4 shows the X-ray radiation energy intensity (J / Sr keV E
_L ) (where J is joule, Sr is steradian (solid angle), keV is kilo-electon volt, and E _L is laser energy (J).) The horizontal axis is photon energy of X-ray (keV), That is, it is expressed as an X-ray spectrum, which is expressed for target materials having different atomic numbers. In FIG. 4, for example, atomic number 6 (carbon C)
Shows a peak value of X-ray radiation energy when the photon energy is between 0.3 and 0.6 keV, and atomic number 64 (gadolinium Gd) shows that the photon energy is between 0.1 and 0.5 keV and between 1.3 and 2.0 kV.
The peak value of the X-ray radiant energy is seen between eV.

In FIG. 5, the vertical axis indicates the square of the atomic number, and the horizontal axis indicates the photon energy. The peak value of the X-ray radiant energy shown in FIG. 4 is indicated by a bold line. The electron orbital K shell, L
It can be seen that the husk, M husk and N husk are classified into each group. Such a classification should be called the pseudo-Moselet's law. From FIG. 5, it is possible to determine a target material that radiates X-rays of a required wavelength most efficiently. That is, by referring to FIG. 5, the high X-ray radiant energy regions of argon (atomic number 18), krypton (atomic number 36) and xenon (atomic number 54) can be known.

Thus, for practical use of X-ray lithography, X-rays having a photon energy of 1.0 to 3.0 keV are optimal.
FIGS. 4 and 5 show that the target material which efficiently emits a line is krypton, xenon or argon. Inert gases such as krypton, xenon and argon are gases at room temperature and are chemically stable. Therefore, it does not deposit on the surface of another material at room temperature as described above.

On the other hand, a laser plasma target needs to have a solid or a density close to that of a solid. Therefore, it is desirable to cool and liquefy or solidify such an inert gas as a laser target (cryotarget). Xenon has a liquefaction point of -107.1 ° C and a solidification point of -111.9 ° C, and krypton has a temperature of -152.9 ° C and -156.6 ° C, respectively. It can be liquefied or solidified, and there is no practical problem.

The light source 13 of the pulsed laser light 13a incident on the cryogenic target is a high-output, high-repetition-type pulsed laser light source.
The above-mentioned cryogenic target is used, the laser beam intensity after focusing is 10 ¹³ w / cm ² or more, and the focusing diameter is 100 to 500μ.
m, in order to emit X-rays with the optimal photon energy (1.0 to 3.0 keV) as a light source for a lithography apparatus, a laser wavelength of 0.53 μm, an output of about 50 W, and a pulse width of 0.1 nse
c, A pulse laser light source with a repetition frequency of 100 Hz.

The laser light source has an output of 10W or more and a pulse width of 1
A light source having a repetition frequency of 0 to 0.1 nsec and a repetition frequency of 10 to 1000 Hz is practically desirable.

FIG. 3 shows the target material transfer device 14 shown in FIG.
Of the second embodiment is shown. In this example, a tip 140 of a target material supply path (transfer pipe) 190 is narrowed down, and a pipe body 140 whose tip is expanded in a flared shape is used as a target material transfer device. In this embodiment, an appropriate amount of the target material 15 is extruded from the tip of the pipe body 140, and a pulsed laser beam is applied to the outer surface of the tip of the extruded target material.
This pipe body 140 may be combined with the endless belt shown in FIG.

For example, the liquid target material 1
When 5 is sequentially fed out as droplets of an appropriate size, since the subsequent liquid target material 15 and the droplet to be irradiated are almost thermally disconnected from each other, the liquid target material 15 is given by the laser beam. Heat is not easily transferred into the liquid target material 15, which not only reduces heat loss, but also prevents the liquid target to be subjected to the next laser irradiation from being heated and vaporized before being irradiated with the laser light. I can do it.

Further, when the ejection of the droplet and the irradiation of the pulse laser are synchronized, the decrease in the heat loss becomes even more remarkable.

Returning to FIG. 1, the X-ray emission opening and closing mechanism 21 according to the present invention
Is disposed outside the X-ray emission port 16 formed in the front wall of the chamber 10 so as to face the X-ray emission port 16 and has one small hole 22 or one small hole.
It is composed of two rotating disks 24 and 25 provided with a hole 23 and rotation driving motors 26 and 27.

As shown in FIG. 2, the rotating disks 24 and 25 are juxtaposed with their peripheral portions superimposed on each other and with a very small gap in the front-rear direction. Supported. That is, both disks 24, 25 are
2 and 23 are arranged side by side so that they can coincide exactly in the front-rear direction at the overlapping portion of both disks, and when both small holes 22 and 23 are simultaneously located at the center of the straight line connecting both support shafts 24a and 25a Then, the X-rays 17 incident on the X-ray exit 16 pass through the opening formed by the small holes 22 and 23 and are radiated to the outside.

The two disks 24 and 25 are rotated by motors 26 and 27 at constant rotation frequencies ₁ and ₂ (in this example, ₁ = 500 Hz and ₂ = 600 Hz) in the directions of the arrows, respectively. the difference V = the rotational frequency | ₁ - ₂ | is just repetition frequency V ₀ (the example of the pulse laser beam 13a mentioned above: V ₀ = 100H
The rotation speed detection devices 28 and 29 and the control device 30 are automatically controlled so as to be equal to z).

That is, by making the difference V between the rotation frequencies of the two disks 24 and 25 coincide with the repetition frequency V ₀ of the pulse laser light source 13a, the X-rays generated by the laser plasma enter the X-ray exit 16 and The opening and closing of the openings 22 and 23 are synchronized with each other, and the opening and closing mechanism 21 opens the X-ray exit in synchronization with the incidence of the X-rays 17. Will be closed.

Also, the opening time of the X-ray emission opening mechanism 21 (in this example: 64)
μs) are the rotational frequencies ₁ and ₂ of the two rotating disks 24 and 25, the dimensions of the small holes 22 and 23 (in this example: 1 cm ^□ ), and the distances between the small holes 22 and 23 and the rotating shafts 24a and 25b. The opening time is determined by appropriately selecting (example: 5 to 10 cm) (this example: 64 μs),
The aperture time is sufficiently shorter than the laser repetition period (this example: 10 ms). The opening time is sufficiently longer than the pulse width of the pulse laser beam, that is, the X-ray pulse width (about 17 ns in this example).

Further, the two disks 24, 25 are arranged with a small gap in the front-rear direction (this example: 1 to 2 mm), and the gap between the rear disk 25 and the chamber front wall is also a small gap (this example: 1 ~
2 mm), the amount of outside air leaking into the vacuum chamber 10 through the X-ray emission port 16 is extremely small, and the exhaust device 11 is overloaded, or the exhaust gas in the recovery cooling device 20 Cooling of target material from inside
There is no hindrance to recovery.

Further, in this embodiment, the X-ray emission opening / closing mechanism 21 is provided outside the chamber 10, but the rotating disks 24, 25 and the like can be provided in the chamber. In addition, small hole 2
The shapes of 2, 23 can be arbitrarily selected, and the number of small holes need not be limited to one for each disk.

(Effect of the Invention) In the present invention, a target material transfer device is provided in the chamber, and the target material is supplied to the transfer device from outside the chamber, and a new target material is continuously supplied to the laser focus point. Configuration.
It is not necessary to replace the target rotating body with high frequency as in the past, so that the operability is remarkably improved and stable continuous X-ray irradiation becomes possible.

In addition, since a chemically stable liquid or solid material that is gasified by laser heating is used as the target material, there is no problem of vapor deposition on the inner wall of the chamber, etc. By cooling and collecting the target material, the target material can be efficiently recycled.

In addition, the X-ray emission opening / closing mechanism opens the X-ray emission in synchronization with the generation of X-rays and for a time longer than the pulse width of the pulse laser. X-rays having a stable intensity can be obtained, and the degree of vacuum in the chamber can be easily maintained.

As described above, the present invention solves the problems of target material deposition and supply of target material, which have been pending for many years,
In addition, the problem of differential pressure exhaust is solved at once.
The present invention has excellent practical utility that enables provision of a low-cost and practical laser plasma X-ray generator.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a laser plasma X-ray generator according to one embodiment of the present invention. FIG. 2 is a structural explanatory view of the X-ray emission opening / closing mechanism. FIG. 3 is an explanatory view showing another embodiment of the target substance transfer device. 4 and 5 are examples of experimental results showing the dependence of X-ray generation efficiency by a laser on the target atomic number.
FIG. 4 shows a spectrum intensity, and FIG. 5 shows a locus at a position where the spectrum intensity is large. FIG. 6 is a schematic view of a conventional laser plasma X-ray generator. 10 ... chamber, 11 ... exhaust device, 12 ... laser light entrance, 13 ... laser light source, 14, 140 ... target material transfer device, 15 ... target material, 16 ... X-ray emission port, 17
... X-ray, 18 ... Laser focus point, 19,190 ... Target material supply path, 20 ... Target material supply device, 21 ... X-ray emission opening and closing mechanism, 22,23 ... Small holes, 24,25 …… Rotating disk, 26,
27 ... motor, 28,29 ... rotation speed detector, 30 ... control device.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-133644 (JP, A) JP-A-61-153935 (JP, A) Fully open Showa 55-173900 (JP, U) Really open Showa 62- 177033 (JP, U)

Claims (2)

(57) [Claims] 1. A chamber having an entrance for pulsed laser light, an X-ray exit, and capable of reducing the pressure inside the chamber, and the pulsed laser light is transmitted so that a focal point is located in the chamber. Means for guiding through the entrance, continuous supply and transfer means for continuously supplying and transferring a chemically stable liquid or solid target material vaporized by heating of the pulsed laser beam to the focal point; An X-ray emission port mechanism that is provided to face the X-ray emission port and opens the X-ray emission port in synchronization with the pulsed laser beam, wherein the continuous supply and transfer means passes through the focal point. An endless belt provided, and means for guiding the target material to a predetermined point on the endless belt, and rotating the endless belt to move the target material from a predetermined point on the endless belt to the light-converging point. Laser plasma X-ray generator, characterized in that the transport. 2. A structure in which a pulsed laser beam is applied to a target material provided in a decompression chamber, and X-rays emitted from the plasma-converted target material are taken out through an X-ray emission port provided in the chamber. In the X-ray emission opening and closing mechanism used for the laser plasma X-ray generator, two disks each having a small hole,
The means for pivotally supporting the two disks and the disks are rotated at a position adjacent to the X-ray emission port so that a part of both disks overlap with each other, so that the small holes of both disks can coincide with each other. Means for making the difference between the rotation frequencies of both disks substantially equal to the repetition frequency of the pulsed laser light, the opening of the X-ray emission port due to the coincidence of the two small holes, and the X-ray generation by the laser plasma. An X-ray emission opening / closing mechanism, which synchronizes with the generation.