JP2000098100A - Soft X-ray parallel beam forming device - Google Patents

Abstract

(57) [Summary] [Problem] A generated soft X-ray has an axially symmetric intensity distribution,
Also, a soft X-ray parallel light beam forming apparatus which generates a large amount of light is provided. SOLUTION: A water drop 2 as a target substance is ejected from a nozzle 1 provided in a vacuum vessel. The pulsed laser beam 3 is condensed and irradiated on the ejected water droplet 2, whereby a plasma 5 is formed. The soft X-rays generated from the plasma 5 are reflected by a multilayer rotating parabolic mirror 6 whose focal point is the position where the plasma 5 is generated, and converted into a parallel light flux 7. A hole is formed in the center of the multilayer rotating paraboloid mirror 6, and the irradiation of the pulse laser beam 3 is performed through this hole. The intensity distribution of the soft X-rays emitted from the plasma 5 is almost symmetric with respect to the optical axis of the irradiated pulsed laser beam 3,
Since this optical axis coincides with the axis of symmetry of the multilayer rotating parabolic mirror 6, the parallel light flux 7 formed after being reflected by the multilayer rotating parabolic mirror 6 also has a substantially axially symmetric intensity distribution. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft X-ray parallel luminous flux generator used for a soft X-ray projection exposure apparatus or the like, and more particularly to an axially symmetric (symmetric with respect to an optical axis) and large light quantity. The present invention relates to a soft X-ray parallel light beam generator capable of generating a soft X-ray parallel light beam.

[0002]

2. Description of the Related Art At present, in the manufacture of semiconductor integrated circuits, a method of transferring a very fine pattern formed on a mask by reducing and projecting it on a resist-coated silicon wafer by visible light or ultraviolet light. Is widely practiced. However, with the miniaturization of the pattern size, even the ultraviolet light is approaching the diffraction limit, and reduction projection exposure using soft X-rays having a shorter wavelength than the ultraviolet light and a wavelength of 13 nm or 11 nm has been proposed.

When a soft X-ray having a wavelength of 13 nm or 11 nm is used, a laser plasma X-ray source (hereinafter referred to as LPX) is considered as one candidate of the light source (soft X-ray source). When pulsed light emitted from a laser device is focused and irradiated on a substance, if the irradiation intensity exceeds 10 ¹⁰ W / cm ² , atoms of the substance are stripped of electrons by the strong electric field and turned into plasma, Soft X-rays are radiated from the plasma. The brightness of soft X-rays radiated from the plasma is very high, and LPX is very compact as an apparatus as compared with a synchrotron radiation generating facility. Therefore, LPX is very promising not only for soft X-ray reduction projection exposure but also as a radiation source for X-ray microscopes and analyzers.

When using LPX for soft X-ray reduction projection exposure, a major problem is the generation of scattered particles. When a solid material such as a metal is irradiated with an excitation laser beam as a target material, the ions forming the plasma or the plasma are blown off by rapid expansion, and the target material near the plasma scatters around. In order to use the generated soft X-rays, soft X-ray optical elements such as multilayer mirrors and thin-film filters are arranged around the plasma, but scattered particles accumulate on this surface,
It reduces its optical performance (reflectance, transmittance, etc.).
In soft X-ray reduction projection exposure, plasma is continuously generated at a high repetition frequency (for example, 1 KHz or more) for a long period (several months), so that the amount of scattered particles is enormous. Therefore, how to suppress the generation of the flying particles has been a major issue.

[0005] Richardson et al. Proposed LPX targeting fine water droplets (US Pat. No. 5,577,091). They introduce small water droplets into a vacuum vessel and irradiate them with laser light to generate plasma. Water, which is the target material, evaporates at the time of plasma formation, and even if it adheres to somewhere, it is easy to remove, so that the problem of flying particles can be avoided.

In soft X-ray reduction projection exposure, various requirements are also placed on an illumination optical system for illuminating a mask in order to form a very fine pattern near the diffraction limit. To satisfy such demands, Japanese Patent Application No. 10-0474
FIG. 3 shows an example of an X-ray illumination optical system proposed in Japanese Patent Publication No.
Shown in

A soft X-ray parallel light beam 21 from a soft X-ray generator (not shown) is reflected by multiple light source forming optical elements 22 and 23 and irradiates the surface of a mask 26 via a condensing mirror 24 and a plane mirror 25. I do. The soft X-rays reflected by the mask 26 are reduced-transferred onto a silicon wafer 28 by a reduction projection optical system 27 onto an image of a pattern formed on the surface of the mask 26.

In soft X-ray reduction projection using this illumination optical system, the area to be projected has an annular arc shape.
Therefore, the area on the mask 26 to be illuminated is also in the shape of a circular arc, and in order to illuminate the area, a fly-eye mirror 27 as shown in FIG. I have. The fly-eye mirror 29 is formed by arranging a large number of unit reflectors 29a each having a shape of a part of a ring (a part of an arc of a ring) and having no gap in the vertical direction with the center axis thereof aligned. It is arranged in a large number without any gap in the lateral direction, and has a shape as shown in FIG.

When the axisymmetric parallel light beam enters the fly-eye mirror, the illumination area can be uniformly illuminated without waste, and illumination with the same resolution can be obtained for a pattern having any direction on the mask.

As a soft X-ray source for generating soft X-rays having substantially parallel light beams, a soft X-ray source as shown in FIG. 5 may be used. In FIG. 5, a droplet-shaped or solid particle-shaped target material 32 ejected from a nozzle 31 is irradiated with pulsed laser light 33 which is excitation energy light, and thereby a plasma 34 is generated. The timing of the ejection of the target material from the nozzle 31 and the timing of the irradiation of the pulse laser light 33 are controlled by a control device (not shown) so that the plasma 34 is generated at a fixed position. The position where the plasma 34 is generated coincides with the focal position of the rotating parabolic mirror 35. The surface of the rotating parabolic mirror 35 has a soft X
A multilayer film having high reflectivity for the line is coated. Therefore, of the soft X-rays generated from the plasma 34, those incident on the rotating parabolic mirror 35 are reflected on the surface thereof, become a parallel light flux 36, and are emitted to the outside.

[0011]

When a plasma is generated using fine droplets or fine solid particles as a target material,
Since the angular distribution of the soft X-ray intensity radiated from the plasma is generally not uniform, for example, a soft X-ray parallel beam that is axially symmetric cannot be obtained with a soft X-ray source having an arrangement as shown in FIG.
Further, in a soft X-ray source having an arrangement as shown in FIG.
Since the nozzle 31 blocks the parallel light beam 36, this also breaks the axial symmetry of the soft X-ray source. Further, as a light source of the soft X-ray reduction projection exposure apparatus, it is desirable to supply as much light as possible in order to improve the processing speed. Therefore, it has been desired to form an axially symmetric soft X-ray parallel light beam having a small amount of soft X-ray light.

The present invention has been made in view of such circumstances, and is an apparatus for generating a soft X-ray parallel light beam, wherein the generated soft X-ray has an axially symmetric intensity distribution and the generated light amount It is an object of the present invention to provide a soft X-ray parallel light beam forming apparatus having a large value.

[0013]

The object of the present invention is to provide a target material supply means for supplying a target material in the form of droplets or fine particles in a container which can be decompressed by an exhaust device, and to supply an excitation energy beam to the target material. A soft X-ray parallel light beam forming apparatus having an excitation energy irradiation means for condensing and irradiating to generate a plasma, and a soft X-ray optical element for extracting soft X-rays generated from the plasma as substantially parallel light beams. The reflection surface of the optical element (first optical element) on which the emitted soft X-ray is incident first has a substantially axially symmetric shape, and the excitation energy beam is irradiated with the symmetry axis of the first optical element as the optical axis. Performed from the first optical element side, the target material supply means,
The problem is solved by a soft X-ray parallel light beam forming device, which is arranged at a position that does not block the optical path of the soft X-ray to be used.

In this means, the irradiation of the excitation energy beam is performed from the first optical element side with the symmetry axis of the first optical element as an optical axis, so that the distribution of the amount of soft X-rays generated from the plasma is It becomes symmetric with respect to the axis of symmetry. The soft X-rays are reflected on the surface of the first optical element and finally emitted to the outside as soft X-rays of substantially parallel light flux. Since the axis of symmetry is the same as the axis of symmetry of the distribution of the amount of X-rays, the distribution of the reflected soft X-ray also has a distribution symmetric with respect to this axis of symmetry. Therefore, an axisymmetric soft X-ray can be obtained.

The amount of soft X-rays generated from the plasma has a distribution such that the amount of light on the irradiation direction side of the excitation energy beam increases. Therefore, by irradiating the excitation energy beam from the first optical element side, the amount of soft X-rays that are reflected by the first optical element and become parallel light beams can be increased. Furthermore, since the target material supply means is arranged at a position not to block the optical path of the soft X-ray to be used, it does not block a part of the soft X-ray and degrade the axial symmetry of the parallel light flux.

In this means, it is needless to say that the terms “substantially parallel” and “substantially axial symmetry” include perfect parallel and complete axial symmetry.
Are all such concepts.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a main part of a soft X-ray parallel beam forming apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a nozzle, 2 is a water droplet, 3 is a pulse laser beam, 4 is a lens, 5 is plasma, 6 is a multilayer rotating parabolic mirror, and 7 is a parallel beam of soft X-rays.

In FIG. 1, water is supplied to a nozzle 1 provided in a vacuum vessel from a water droplet supply device (not shown), and a water droplet 2 as a target substance is ejected from the nozzle 1. The pulsed laser beam 3 is condensed and radiated onto the ejected water droplet 2 via the lens 4, thereby forming a plasma 5. The soft X-rays generated from the plasma 5 are reflected by a multilayer paraboloid of revolution 6 having a paraboloid of revolution whose focal point is the position where the plasma 5 is generated, and are converted into a parallel light flux 7. A hole is formed in the center of the multilayer rotating parabolic mirror 6, and irradiation of the pulsed laser beam 3 is performed through the hole along the symmetry axis of the multilayer rotating parabolic mirror 6. In addition,
The emission of the water droplet 2 and the irradiation of the pulse laser beam 3 are controlled by a control device (not shown) so as to be synchronized. When the water droplet comes to the focal position of the multilayer rotating parabolic mirror 6, the pulse laser beam 3 is emitted. Irradiation is performed.

In this arrangement, the intensity distribution of the soft X-ray emitted from the plasma 5 is substantially symmetric with respect to the optical axis of the irradiated pulsed laser beam 3, and this optical axis is the axis of symmetry of the multilayer rotating parabolic mirror 6. Therefore, the parallel light flux 7 formed after being reflected by the multilayer rotating parabolic mirror 6 also has a substantially axially symmetric intensity distribution. Further, since the radiation intensity of the soft X-ray has a distribution having a peak in the direction of the irradiated pulse laser beam 3, more soft X-rays are incident on the multilayer rotating parabolic mirror 6 and the formed parallel X-ray is formed. The light amount of the light beam also increases. Also,
Since the nozzle 1 is arranged outside the optical path of the soft X-ray,
It does not affect the shape or intensity distribution of the parallel light flux 7 of the line.

FIG. 2 shows a configuration diagram of an example of a soft X-ray parallel beam forming apparatus according to an embodiment of the present invention. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 2, reference numeral 8 denotes a vacuum vessel, 9 denotes a water droplet supply device, 10 denotes a laser beam introduction window, 11 denotes an X-ray shielding plate, 12 denotes a water droplet recovery device, and 13 denotes a protection plate.

A water drop supply device 9 is disposed inside the vacuum vessel 8, and a water drop 2 as a target material is ejected from the tip of the nozzle 1. A multilayer rotating paraboloid mirror 6 having a multilayer film having a high reflectivity to soft X-rays formed on the surface thereof is provided in a vacuum vessel 8.
Is arranged. The direction of the nozzle 1 is adjusted so that the ejected water droplet 2 passes through the focal point of the multilayer rotating paraboloid mirror 6. The water droplet 2 is irradiated with pulse laser light 3 from an Nd: YAG laser, and is irradiated and focused on the water droplet 2 through a laser introduction window 10 by a lens 4. Thereby, the plasma 5 is generated. Injection of water droplet 2 and pulsed laser beam 4 from Nd: YAG laser
The irradiation time is controlled by a control device (not shown). When the water droplet 2 reaches the focal point of the multilayer rotating parabolic mirror 6, the pulse laser beam 3 is irradiated.

The soft X-rays emitted from the plasma 5 are converted into a parallel light flux 7 by the multilayer rotating parabolic mirror 6 because the plasma 5 is at the focal point of the multilayer rotating parabolic mirror 6.
A circular shielding plate 11 that blocks unnecessary soft X-rays and light of other wavelengths is arranged on the soft X-ray optical system on which the parallel light flux 7 is incident so that the light is not incident. In order to collect the supplied water droplets 2 when laser light irradiation is not performed, a water droplet collecting device 12 is arranged in the vacuum vessel.

Immediately after the supply of the water droplet 2 is started, the trajectory of the ejected water droplet 2 is not stable, and is not suitable for generating the plasma 5. Therefore, until the trajectory of the water droplet 2 is stabilized, the protection plate 13 is moved in the direction of the arrow to protect the surface of the multilayer rotating parabolic mirror 6, and the water droplet 2 is collected by the water droplet collection device 12. After the trajectory of the water droplet 2 is stabilized, the protection plate 13 is moved out of the optical path of the soft X-ray, and irradiation of the pulse laser beam 2 is started.

The angular distribution of the intensity of the soft X-ray emitted from the plasma also depends on the diameter of the droplet and the focused spot, but generally has a distribution that is axially symmetric with respect to the optical axis of the laser beam. In the present embodiment, the optical axis of the pulsed laser beam 3 and the central axis of the multilayer rotating parabolic mirror 6 are the same, and there is nothing other than the circular shielding plate 11 that blocks parallel light beams. The intensity distribution in a parallel light beam formed by reflection by the film rotation parabolic mirror 6 is axially symmetric. Since the support of the shielding plate 11 is made of a very thin wire (not shown), there is no problem.

In this embodiment, water droplets are used as the target material to form plasma, but the material of the target material is not limited to this. In addition, the liquid is not limited to liquid, and fine solid particles may be used. Further, a gas or liquid material may be cooled at room temperature to be liquefied or solidified.
Further, a solid material may be heated at normal temperature to be a liquid.
Further, in the present embodiment, a multilayer rotating paraboloid mirror is used to form a parallel light beam, but the optical system that forms the parallel light beam is not limited to this.

[0026]

As described above, according to the apparatus for forming a soft X-ray parallel light beam of the present invention, it is possible to form a soft X-ray parallel light beam having a large amount of light with an axial symmetry. Therefore, uniform illumination can be performed by using the soft X-ray parallel beam forming apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a main part of a soft X-ray parallel light beam forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an example of a soft X-ray parallel light beam forming apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an outline of an example of a conventional soft X-ray reduction projection exposure apparatus.

FIG. 4 is a diagram illustrating a configuration of a fly-eye mirror that is a multiple light source forming optical element.

FIG. 5 is a diagram illustrating an example of a soft X-ray source that generates soft X-rays having substantially parallel light beams.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Nozzle 2 ... Water droplet 3 ... Pulse laser beam 4 ... Lens 5 ... Plasma 6 ... Multilayer rotating parabolic mirror 7 ... Parallel light flux of soft X-ray 8 ... Vacuum container 9 ... Water droplet supply device 10 ... Laser light introduction window 11 ... X-ray shielding plate 12 ... water droplet recovery device 13 ... protection plate

Claims (1)

[Claims] 1. A target material supply means for supplying a droplet or fine particle target material in a container which can be decompressed by an exhaust device, and an excitation energy beam is focused and irradiated on the target material to form a plasma. A soft X-ray parallel light beam forming apparatus having a soft X-ray optical element for extracting soft X-rays generated from plasma as substantially parallel light beams, wherein soft X-rays radiated from plasma are first emitted. The reflection surface of the optical element (first optical element) incident on the surface has a substantially axially symmetrical shape, and the irradiation of the excitation energy beam
The process is performed from the first optical element side with the symmetry axis of the optical element as the optical axis, and the target material supply means is arranged at a position not to block the optical path of the soft X-ray to be used. Light beam forming device.