Extreme ultraviolet light source device and method for producing extreme ultraviolet light

An EUV (Extreme Ultra Violet) light source device ionizes a target material in an ionizer, and supplies the ionized target material to a point of generating a plasma. This reduces the generation of debris. The ionizer simultaneously irradiates laser beams of plural wavelengths corresponding to the excited level of tin on a target material to ionize the target material. The ionized target material is extracted from the ionizer with a high voltage applied from an ion beam extractor, and accelerated and supplied to a plasma generation chamber. When driver laser beam is irradiated on the ionized target material, a plasma is generated, thereby emitting EUV radiation.

BACKGROUND OF THE INVENTION

The present invention relates to an extreme ultraviolet light source device and a method for generating extreme ultra violet.

For example, a semiconductor chip may be created by reduction projection of a mask on which a circuit pattern is drawn onto a wafer having a resist applied thereon, and by repeatedly performing processing, such as etching and of thin film formation. The progressive reduction of the scale of semiconductor processing demands the use of radiation of further short wavelength.

Thus, research is being made on a semiconductor exposure technique which uses radiation of extremely short wavelength of 13.5 nm or so and a reduction optics system. This type of technique is termed EUVL (Extreme Ultra Violet Lithography: exposure using extreme ultra violet light). Hereinafter, extreme ultraviolet light will be abbreviated as “EUV light”.

Three types of EUV light sources are known: an LPP (Laser Produced Plasma: plasma produced by a laser) type light source, a DPP (Discharge Produced Plasma) type light source, and an SR (Synchrotron Radiation) type light source. The LPP type light source is a light source which generates a plasma by irradiating laser beam on a target material, and employs EUV radiation emitted from this plasma. The DPP type light source is a light source which employs a plasma generated by an electrical discharge. The SR (synchrotron radiation) is a light source which uses orbital radiation. Of those three types of light sources, the LPP type light source is more likely to obtain high-output EUV radiation as compared to the other two types because the LPP type light source can provide an increased plasma density, and can ensure a larger solid angle over which the radiation is collected.

Since EUV radiation has a very short wavelength and can easily be absorbed by a matter, the EUVL uses a reflection type optical system. Such a reflection type optical system is built by employing a multilayer film in which, for example, molybdenum (Mo) and silicon (Si) are used. Since an Mo/Si multilayer film has a high reflectivity of near 13.5 nm, EUV radiation of a wavelength of 13.5 nm is used in the EUVL.

Since the reflectivity of the multilayer film is around 70%, however, the output gradually decreases as the reflection is repeated. Since the EUV radiation is reflected more than ten times within the exposure device, it is necessary for the EUV light source device to supply high-output EUV radiation to the exposure device. It is therefore expected that the use of an LPP type light source as an EUV light source device will become more popular (see JP-A-2006-80255).

LPP type EUV light source devices use tin (Sn), xenon (Xe), lithium (Li) or the like as a target material, and irradiate laser beam thereon. Particularly, an LPP type light source that uses a combination of tin droplets, which is a liquid metal, and a carbon dioxide (CO2) pulsed laser is promising for this light source because it can reduce the masses of the targets and have a relatively high emission efficiency of EUV radiation as compared with the other LPP type light sources.

To obtain a high EUV radiation emission efficiency, the density of a target needs to be set to about 1017/cm3to 1018/cm3. The density of solid or liquid tin is however 4×1022or so which is higher than the optimal density. It is not therefore possible to efficiently obtain EUV radiation through a single irradiation of laser beam. In this respect, there has been proposed a technique of adjusting the density of a tin target by irradiating laser beam on the tin target two times (see the specification of USP-A-2006/0255298 and the pamphlet of WO2003/096764). In this technique, a heating pulsed laser beam is irradiated on a tin target to diffuse the tin target and reduce the density thereof. Then, a main pulsed laser beam is irradiated on the tin target to turn into plasma the target, thereby efficiently generating EUV radiation.

See “Principles of Charged Particle Acceleration written by Stanley Humphries, Jr. (published by John Wiley & Sons, Inc.) too.

According to the related art, a target material is supplied in the form of droplets with a diameter of, for example, several tens of μm. However, only 1/10 of the total mass of the droplets or less actually becomes a plasma which contributes to generation of EUV radiation, while the remainder mass becomes minute particles called debris. It is a problem of the related art that the debris damages an EUV collector mirror, thereby reducing the EUV radiation output.

An EUV collector mirror, which collects EUV radiation radiated from a plasma and supplies the laser beam to the exposure device, is provided in the vicinity of the point of generating the plasma. As the debris which is electrically neutral is diffused to the EUV collector mirror, the life and reflectivity of the EUV collector mirror are reduced. For example, fast debris collides against the top surface of the EUV collector mirror, damaging the EUV collector mirror. Middle speed debris is deposited on the top surface of the EUV collector mirror, lowering the reflectivity of the EUV collector mirror.

When a metal material like tin is used as a target material, therefore, a large quantity of electrically neutral debris is produced, which significantly shortens the lifetime of the EUV collector mirror or the like. Because most of debris is electrically neutral, it is difficult to control the behavior of the debris with electromagnetic force. Accordingly, the related art does not efficiently restrain the diffusion of debris to the EUV collector mirror. When the EUV light source device is operated, therefore, the debris damages the EUV collector mirror, thus making it necessary to frequently perform a work of replacing the EUV collector mirror or the like. As a result, the operation rate of the EUV light source device drops.

Meanwhile, the related art that irradiates laser beam twice can obtain EUV light with a little higher conversion efficiency. This related art is not much different in that a wasteful material which does not contribute to a plasma is supplied into the plasma generation chamber, thereby generating electrically neutral debris.

SUMMARY OF THE INVENTION

Accordingly, the present invention addresses the above-identified problems associated with the related arts, and it is an object of the invention to provide an extreme ultraviolet light source device and a method for generating extreme ultra violet light, which can restrain uncontrollable debris from being generated in a plasma generation chamber for generating a plasma by ionizing a target material and supplying the ionized target material to an area where the plasma is to be generated. It is another object of the invention to provide an extreme ultraviolet light source device and a method for generating extreme ultra violet light, which can restrain electrically neutral debris from being generated in a plasma generation chamber by generating an ionized target material at a place apart from the plasma generation chamber and supplying the ionized target material to the plasma generation chamber at a high speed while suppressing spreading of the ionized target material. Further objects of the invention may be readily apparent from the following description of the presently preferred embodiments.

To achieve the objects, according to one aspect of the invention, there is provided an extreme ultraviolet light source device that generates extreme ultra violet light by irradiating laser beam on a target material for turning into a plasma thereof, comprising a target material supply section that supplies the target material, an ionization section that ionizes the target material supplied from the target material supply section, a plasma generation chamber that is supplied with the ionized target material and generates a plasma, and a plasma generation laser light source that irradiates laser beam on the target material supplied to a predetermined area in the plasma generation chamber to turn into plasma the target material, thereby emitting extreme ultra violet light.

The ionization section can ionize the target material by irradiating laser beam thereon.

The ionization section can include a vaporization laser light source that vaporizes the target material supplied from the target material supply section by irradiating vaporization laser beam on the target material, and an ionization laser light source that ionizes the target material vaporized by the vaporization laser beam by irradiating ionization laser beam on the target material.

The ionization section can include a vaporization electron beam device that vaporizes the target material supplied from the target material supply section by irradiating a vaporization electron beam on the target material, and an ionization laser light source that ionizes the target material vaporized by the electron beam device by irradiating ionization laser beam on the target material.

The ionization laser light source can be configured as a pulsed laser light source.

The ionization laser light source can simultaneously output laser beams of plural kinds of wavelengths prepared beforehand in association with an excited level of the target material.

The target material can be a tin or a tin compound including stannane (SnH4), and the ionization laser light source can output laser beams of three to five wavelengths in total including at least one of three wavelengths of near 286.4 nm, near 300.9 nm, and near 317.5 nm, and two wavelengths of near 811.6 nm and near 823.7 nm.

The ionization laser light source may be configured to include a base wave generator having a titanium sapphire laser, and a higher harmonics generator as a pulsed laser light source.

The ionization section may be provided with a first collection section for collecting the target material.

The target material may be a tin or a tin compound including stannane (SnH4), and the ionization section may be provided with a heater section that melts the target material deposited inside the ionization section to be collected by the first collection section.

The ionization section may be provided with a first magnetic field generating section that generates a magnetic field in such a way as to enclose the target material supplied from the target material supply section.

The extreme ultraviolet light source device can further comprise an extraction section that extracts the target material ionized by the ionization section out thereof and supplies the ionized target material to the plasma generation chamber, and a convergence section provided between the plasma generation chamber and the extraction section to converge the ionized target material traveling toward the plasma generation chamber in a direction substantially perpendicular to the traveling direction of the ionized target material.

A second magnetic field generating section that generates a magnetic field may be provided in such a way as to enclose a transit area between the extraction section and the convergence section.

An acceleration section for accelerating the ionized target material may be provided in a transit area between the extraction section and the convergence section.

A third magnetic field generating section that generates a magnetic field in the predetermined area may be provided in the plasma generation chamber.

A second collection section for collecting the target material after generation of the plasma may be provided in the plasma generation chamber.

A fourth magnetic field generating section that generates a magnetic field may be provided in such a way as to enclose a connecting section which connects the plasma generation chamber to the second collection section.

A compression section for compressing the ionized target material can be provided between the ionization section and the plasma generation chamber.

A neutralization section for electrically neutralizing the ionized target material can be provided in a transit area between the convergence section and the plasma generation chamber.

The plasma generation laser light source can be configured as a laser light source that outputs carbon dioxide gas laser light.

According to another second aspect of the invention, there is provided an extreme ultra violet light generation method of executing an ionization step of ionizing a target material supplied from a target material supply device for supplying the target material, a supply step of supplying the ionized target material to a predetermined area in a plasma generation chamber while inhibiting expansion of the ionized target material, and a step of irradiating laser beam for plasma generation on the ionized target material supplied to the predetermined area in the plasma generation chamber to turn into plasma the ionized target material, thereby emitting extreme ultra violet light.

In the ionization step, a first sub step of vaporizing the target material, and a second sub step of irradiating ionization laser beam on the vaporized target material for ionization thereof can be executed.

The ionization laser beam may include laser beams of plural kinds of wavelengths prepared beforehand in association with an excited level of the target material.

According to a further aspect of the invention, there is provided an extreme ultraviolet light source device that generates extreme ultra violet light by irradiating laser beam on a target material for turning into a plasma thereof, comprising a target material supply section that supplies the target material, an ionization section provided near and downstream of the target material supply section to irradiate predetermined laser beam on a predetermined amount of the target material supplied from the target material supply section to generate an ionized target material of a predetermined size and predetermined density, a plasma generation chamber provided apart from and downstream of the ionization section to generate a plasma, a supply section that supplies the ionized target material to the plasma generation chamber by performing convergence and transportation of the ionized target material using at least one of electric power and magnetic force, and a plasma generation laser light source that irradiates plasma generation laser beam on the ionized target material supplied to the plasma generation chamber to turn into plasma the ionized target material, thereby emitting extreme ultra violet light.

The extreme ultraviolet light source device may further comprise a fifth magnetic field generating section that is disposed in such a way as to enclose a transit area between the extraction section and the plasma generation chamber, and generates a magnetic field in the traveling direction of the ionized target material, and an electron beam output section that irradiates an electron beam toward the magnetic field generated by the fifth magnetic field generating section.

The extreme ultraviolet light source device may be configured in such a way that an irradiation timing for the ionization laser beam is set with an irradiation timing for the vaporization laser beam as a reference, and an irradiation timing for the laser beam for turning the target material into a plasma in the plasma generation chamber is set with the irradiation timing for the ionization laser beam as a reference.

The extreme ultraviolet light source device may be configured in such a way that an irradiation timing for the vaporization laser beam is set with a timing at which the target material supply section supplies the target material as a reference, an irradiation timing for the ionization laser beam is set with the irradiation timing for the vaporization laser beam as a reference, and an irradiation timing for the laser beam for turning the target material into a plasma in the plasma generation chamber is set with the irradiation timing for the ionization laser beam being a reference.

The extreme ultraviolet light source device may be configured in such a way that an irradiation timing for the vaporization laser beam, an irradiation timing for the ionization laser beam, and an irradiation timing for the laser beam for turning the target material into a plasma in the plasma generation chamber are set with a timing at which the target material supply section supplies the target material being a reference.

The target material supply section can be configured to include a target material supply body for supplying the target material and is provided with a groove portion where laser beam is irradiated, a rotary section that rotates the target material supply body, and a replenishment section that replenishes the target material into the groove portion according to rotation of the target material supply body.

The target material supply body is formed into a disk shape from the target material or a material different therefrom, and has one surface rotatably supported by the rotary section.

The target material supply body is formed, into a cylindrical shape, of the target material or a material different therefrom, and has the groove portion provided at a peripheral surface thereof, and has a rotary shaft having both ends rotatably supported.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. According to the embodiments, an ionizer20provided at a location different from the location of a plasma generation chamber60generates an ionized target material91, and supplies the ionized target material91to the plasma generation chamber60. Because the ionized target material is generated in the ionizer20, it is possible to prevent an excessive target material unnecessary for generation of a plasma from being supplied to the plasma generation chamber60. Further, because the ionized target material can be controlled by electric force or magnetic force, the ionized target material can be supplied to the plasma generation chamber60while suppressing diffusion of the ionized target material.

First Embodiment

A first embodiment of the invention will be described referring toFIGS. 1 to 5.FIG. 1is an explanatory diagram showing the general configuration of an EUV light source device1,FIG. 2is an explanatory diagram showing the ionizer20, etc. in enlargement,FIG. 3is an explanatory diagram for collecting a target material,FIG. 4is an explanatory diagram of a laser light source210to be used in the ionizer20, andFIG. 5is an energy level diagram showing laser beams of a plurality of wavelengths which are simultaneously irradiated from the laser light source210.

An EUV light source device1shown inFIG. 1can be configured to include, for example, a target supply device10, the ionizer20, an ion beam extractor30, a drift tube40, a convergence device50, the plasma generation chamber60, a driver laser light source70, and a target collecting device80. However, the illustrated configuration merely exemplifies the embodiment of the invention, and is not limited to the illustrated configuration. It should be apparent to those skilled in the art that the additional structures, modifications and the like can be implemented without departing from the spirit or scope of the invention.

The target supply device10is equivalent to the “target material supply section”, and supplies targets such as tin in the form of solid or liquid. Tin may be supplied as a tin compound such as stannane (SnH4). Note that when tin is supplied in the form of liquid, pure tin can be heated to the melting point to be liquefied, or can be supplied in the form of a solid or liquid or in the form of a solution containing tin or a colloidal solution containing tin or a tin compound. Although tin will be explained as a target material by way of example according to the embodiment, which is not limited to, other materials, such as lithium (Li), may be used. In addition, various methods to be described in the following descriptions of embodiments can be adopted as a method of supplying a target material.

The ionizer20as the “ionization section” is the device that ionizes a target material supplied from the target supply device10. The target supply device10is provided adjacent to, and downstream of, the target supply device10. The “downstream” herein indicates the moving direction of a target material, and the rightward direction inFIG. 1is downstream while the leftward direction inFIG. 1is upstream.

The ion beam extractor30as the “extraction section” is the device that extracts the ionized target material91generated by the ionizer20therefrom, and feeds out the ionized target material toward the plasma generation chamber60. The ion beam extractor30is provided adjacent to, and downstream of, the ionizer20. The ion beam extractor30has, for example, a ring-like electrode31and a power source32which applies a predetermined high voltage (negative voltage) to the electrode31. A high voltage applied to the electrode31causes the ionized target material91, generated in the ionizer20, to be extracted therefrom and fed out toward the plasma generation chamber60. For the sake of descriptive convenience, a target material and an ionized target material will be occasionally called “target” and “ion beam” herein, respectively.

The drift tube40is the device that transports the ion beam (ionized target material)91toward the plasma generation chamber60. The drift tube40is provided adjacent to, and downstream of, the ion beam extractor30. The drift tube40is provided in such a way as to connect the ion beam extractor30to the convergence device50. The drift tube40is configured to have a magnetic field generator, such as a electromagnet, which generates a magnetic field to prevent the ion beam from spreading in the radial direction. The drift tube40corresponds to the “second magnetic field generating section”. In the following description, the magnetic field generator that constitute the “first, second, third or fourth magnetic field generating sections” is a cylindrical electromagnet or the like, and the ion beam passes through the circular center opening thereof. The center axis of the magnetic flux produced by the magnetic field generator is arranged to be substantially coincide with the axis along which the ion beam passes.

The convergence device50as the “convergence section” is configured as an electrostatic lens such as a quadrupole lens or einzel lens, or a magnetic lens or the like, and is the device which prevents the ion beam from spreading in a direction (up and down direction inFIG. 1) orthogonal to the traveling direction of the ion beam (right and left direction inFIG. 1). The convergence device50is provided adjacent to, and downstream of, the drift tube40. The convergence device50can be provided between the ion beam extractor30and the plasma generation chamber60.

The plasma generation chamber60is provided adjacent to, and downstream of, the convergence device50, and the interior of the plasma generation chamber60is kept in a vacuum state. The plasma generation chamber60is provided with, for example, an EUV collector mirror61, an incident window62, electromagnets63and64, a connecting section60A, and a collection passage60B. The connecting section60A connects the plasma generation chamber60to an exposure device2. The collection passage60B connects the plasma generation chamber60to a target collecting device80.

The EUV collector mirror61reflects and focuses EUV radiation. The top surface of the EUV collector mirror61is formed as, for example, a concave surface of a rotary ellipsoid or the like, a paraboloid, a spherical surface, or a concave surface having a plurality of curvatures. A multilayer film having a molybdenum film and a silicon film, for example, is provided on the top surface of the EUV collector mirror61to reflect EUV radiation of a wavelength of 13 nm or so.

The incident window62is a window portion through which driver laser beam passes. The driver laser beam is irradiated on the ionized target material that has reached to a predetermined position in the plasma generation chamber60. This generates a plasma92, thus emitting EUV radiation. The EUV radiation is focused into an intermediate focus (IF) by the EUV collector mirror61, and is connected to the exposure device2via the connecting section60A.

The pair of magnetic field generators63,64are provided in such a way as to sandwich the optical path of EUV radiation LB2traveling toward the intermediate focus IF from the right and left directions inFIG. 1. The individual magnetic field generators63,64correspond to the “third magnetic field generating section”. Each magnetic field generator63,64is configured as an electromagnet, for example.

When currents in the same direction are let to flow in the magnetic field generators63,64, a magnetic field is generated in the plasma generation chamber60. This magnetic field has a high flux density in the vicinity of each magnetic field generator63,64, and a low flux density at a middle point between the magnetic field generators63,64. A target material93after emission of EUV radiation is caught by the magnetic fields generated by the magnetic field generators63,64, and moves rightward (downstream side) inFIG. 1while making a spiral motion due to the Lorentz force. Then, the target material93flows into the target collecting device80as the “second collection section” to be collected therein. A magnetic field generator81as the “fourth magnetic field generating section” is provided outside the collection passage60B. The line of magnetic force generated from the magnetic field generator81restrains expansion of the target material93. As described later, the target collecting device80is provided with a heater82(seeFIG. 3).

The driver laser light source70outputs laser beam LB1for exciting the ionized target material91to generate the plasma92. The driver laser light source70is configured as, for example, a carbon dioxide pulsed laser light source, and outputs a pulse of driver laser beam LB1of a wavelength of about 10.6 μm. The laser beam LB1is input into the plasma generation chamber60through a focusing lens71and the incident window62to be irradiated on the ionized target material. Although a carbon dioxide pulsed laser light source is used as an example of the driver laser light source according to the embodiment, the invention is not limited thereto.

FIG. 2is an explanatory diagram showing the target supply device10, the ionizer20, etc. in enlargement. The target supply device10supplies a predetermined amount of a liquid target material (tin in the embodiment) to the ionizer20at a time.

The target supply device10is configured to have, for example, a tank11, a supply tube12connecting the bottom of the tank11and the ionizer20, and a heater13provided around the tank11and the supply tube12.

The target supply device10is held at a temperature equal to or higher than the melting point of the target material by the heater13. The heater13is configured as an electric heater which converts electric energy to heat energy. The tank11retains a liquid target material90. The supply tube12has one end connected to the tank11, and the other end connected to an inlet portion26provided inside the ionizer20.

The ionizer20has, for example, an ion beam generation chamber21, magnetic field generators25,27, the inlet portion26and a heater28. A target collecting device22as the “first collection section” is connected to the bottom of the chamber21via a collection passage22A.

The chamber21is the space for ionizing the target material. The inlet portion26for letting the target material from the target supply device10to enter the chamber21is provided at one wall of the chamber21. An aperture21EX for connection to the ion beam extractor30is provided at the other side wall of the chamber21.

A thin-pipe or porous inlet port26A is provided at the center portion of the inlet portion26. The liquid target material90supplied from the target supply device10is supplied into the chamber21by a small amount at a time in such a way as to be percolated through the inlet port26A.

A plurality of incident windows202are provided at the other side wall of the chamber21around the aperture21EX. The lower incident window202inFIG. 2allows vaporization laser beam LB3to enter the chamber21. The upper incident window202inFIG. 2allows ionization laser beam LB4to enter the chamber21.

A plurality of laser light sources200and210are provided outside the chamber21. One laser light source200is a vaporization laser light source for vaporizing the target material. The vaporization laser light source200irradiates the vaporization laser beam LB3on the target material90to vaporize the target material90. The vaporization laser beam LB3enters the chamber21via a focusing lens201and the incident window202to be irradiated on the target material supplied into chamber21through the inlet port26A.

The other one laser light source210is an ionization laser light source. The ionization laser light source210irradiates the ionization laser beam LB4on the vaporized target material for ionization thereof, thus generating the ionized target material91(ion beam91). The ionization laser beam LB4enters the chamber21via the focusing lens201and the incident window202to be irradiated on the vaporized target material near the inlet port26A for ionization thereof. The details of the ionization laser light source210will be given later referring toFIGS. 4 and 5.

The magnetic field generator25is provided outside the chamber21in such a way as to cover the chamber21. The magnetic field generator25will be occasionally called as “external magnetic field generator25” hereinafter. The magnetic field generator27is provided inside the chamber21in such a way as to enclose the inlet portion26. The magnetic field generator27will be occasionally called as “internal magnetic field generator27” hereinafter. Those magnetic field generators25,27provided at the chamber21correspond to the “first magnetic field generating section”; or, the external magnetic field generator25corresponds to the “first magnetic field generating section”.

The external magnetic field generator25prevents the ion beam91from spreading in the radial direction (planar direction perpendicular to the traveling direction of the ion beam91) with the help of the line of magnetic force along the traveling direction of the ion beam91. The internal magnetic field generator27generates a line of magnetic force in the vicinity of the inlet port26A to prevent the vaporized and ionized target material91from spreading in the radial direction.

As mentioned above, the target collecting device22is provided at the bottom of the chamber21via the collection passage22A. The target collecting device22is provided with the heater28. The target material90deposited inside the chamber21flows out into the target collecting device22via the collection passage22A to be collected therein.

Of the entire target material90supplied into the chamber21from the target supply device10, the target material which has not be extracted as the ion beam91by the ion beam extractor30is stored in the target collecting device22. That is, a minim amount of ionized target material91needed for plasma generation is generated in the ionizer20, and an unnecessary target material90which does not contribute to generation of the plasma92is collected in the target collecting device22so that the unnecessary target material90does not flow into the plasma generation chamber60.

FIG. 3is an explanatory diagram exemplarily showing a temperature control structure for the heaters provided at the target supply device10, the ionizer20, etc. As mentioned above, the heaters are respectively provided at the target supply device10, the ionizer20and each target collecting device22,80to heat the components or keep the temperatures thereof according to the embodiment.

As shown inFIG. 3, for example, a first control section100controls the temperature of the heater13provided at the target supply device10(hereinafter “first set temperature TS1”) to a value higher than the melting point of the target material90and less than the boiling point of the target material90(melting point of the target material<TS1<boiling point of the target material).

A second control section101controls the temperature of the heater28provided at the ionizer20and the target collecting device22and the heater82provided at the target collecting device80(hereinafter “second set temperature TS2”) to, for example, the melting point of the target material (TS2≧melting point of the target material).

The first set temperature TS1is greater than the second set temperature TS2(TS1>TS2). Accordingly, the target supply device10is held at a relatively high temperature, so that the target material supplied into chamber21from the target supply device10is easily vaporized by the vaporization laser beam LB3.

Because the chamber21or the like is set to the melting point of the target material90, it is possible to prevent the target material deposited on the inner wall or the like of the chamber21from being solidified and collect the target material90in a liquid state in the target collecting device22. Likewise, the target collecting device80can collect the target material in a liquid state. The temperature control structure shown inFIG. 3is merely one example, and is not restrictive in the invention. For example, the temperature control structure may be made to set the first set temperature TS1of the heater13to the melting point of the target material90(TS1≧melting point of the target material).

FIG. 4is an explanatory diagram showing an example of the configuration of the ionization laser light source210. The ionization laser light source210includes, for example, one YAG (Yttrium Aluminum Garnet) laser211, three titanium sapphire lasers214(1) to214(3), second harmonic generators (SHG: Second Harmonic Generation)212,215, a third harmonic generator (THG: Third Harmonic Generation)216, and half mirrors213.

The YAG laser211irradiates, for example, a pulse of laser beam of a wavelength of 1 μm every 10 μsec. The wavelength of the laser beam output from the YAG laser211is adjusted by the second harmonic generator212. The YAG laser211and the second harmonic generator212constitute an excitation source. Note that another type of laser may be used instead of the YAG laser.

The laser beam from the excitation source is input to the three titanium sapphire lasers214(1) to214(3) via the respective half mirrors213. Each of the titanium sapphire lasers214(1) to214(3) includes a prism2141and a Q switch2142in addition to a mirror, a laser medium and or the like. The prism2141serves to select a wavelength of the laser beam output from each of the titanium sapphire lasers214(1) to214(3) and narrower the band thereof. The Q switch2142serves to synchronize the output timing for laser beam output from each of the titanium sapphire lasers214(1) to214(3).

The laser beam output from the first titanium sapphire laser214(1) is converted to laser beam LB4aof a wavelength of 286.42 nm via the second harmonic generator215, the third harmonic generator216and a reflection optical system217.

Laser beam LB4boutput from the second titanium sapphire laser214(2) has a wavelength of 811.62 nm. Laser beam LB4coutput from the third titanium sapphire laser214(3) has a wavelength of 823.67 nm. The wavelengths of the input laser beams can be set to 811.62 nm and 823.67 nm respectively by the prisms2141in the titanium sapphire lasers214(2),214(3).

FIG. 5is an energy level diagram of tin which is the target material90. As radiation of a first wavelength (λ1=286.42 nm) is applied to tin with a base level 5p23P0, a first excited level is acquired. As radiation of a second wavelength (λ2=811.62 nm) is applied to tin with the first base level, a second excited level is acquired. As radiation of a third wavelength (λ2=823.67 nm) is applied to tin with the second base level, a third excited level is acquired. Because the third excited level exceeds a threshold value for ionization, tin is ionized.

The description of the embodiment will be given of the case of tin with the base level 5p23P0. λ1=300.92 nm is used as the wavelength of laser beam for tin with the base level 5p23P1. λ1=317.51 nm is used as the wavelength of laser beam for tin with the base level 5p23P2. The ratio of the three base levels 5p23P0, 5p23P1and 5p23P2depends on the temperature of vaporized tin. The temperature of vaporization tin depends on the intensity of vaporization laser beam. Therefore, the distribute of a desirable one of the three base levels, e.g., 5p23P0, can be maximized by optimizing the intensity of the vaporization laser beam. It is possible to take a structure of simultaneously irradiating laser beams of three wavelengths of λ1=286.42 nm, λ1=300.92 nm and λ1=317.51 nm in order to excite all of the three base levels 5p23P0, 5p23P1and 5p23P2though complex the structure of the ionization laser beam device becomes. In this case, there are five wavelengths of laser beams in total.

According to the embodiment, laser beams of three wavelengths are simultaneously output to ionize tin, which is not limited to. It is possible to take, for example, a multiphoton ionizing structure to be discussed below though the efficiency of ionization becomes lower. Laser beam (=λ4=456.5 nm) is used as the structure of three-photon ionization based on laser beam of a single wavelength. Laser beam (=λ5=270-318 nm) is used as the structure of two-photon ionization based on laser beam of a single wavelength. Laser beam of the first wavelength (=λ1=286.42 nm) and laser beam of the second wavelength (=λ6=614-618 nm) are used as the structure of three-photon ionization based on two-wavelength laser beam.

According to the embodiment, the ionization laser light source210simultaneously outputs and irradiates three-wavelength laser beams LB4a(=λ1), LB4b(=λ2) and LB4c(=λ3) on tin or the target material90to increase the excited level of tin to spontaneously ionize the target material90. This method can ionize about 10% of tin supplied as the target material90. The ionized tin is extracted by the ion beam extractor30and supplied to the plasma generation chamber60. Tin which has not been ionized is collected in the target collecting device22, and is not supplied to the plasma generation chamber60.

As the laser beams LB4a, LB4b, LB4ccorresponding to the respective excited levels of tin are simultaneously irradiated on tin according to the embodiment, the ionized target material91with a relatively low temperature can be obtained. Accordingly, the ionized target material91suitable for generation of EUV radiation can be supplied to the plasma generation chamber60.

On the other hand, if the target material90is ionized by using a microwave or arc discharge, the ionized target material91becomes very hot. Before the ionized target material91reaches the point of plasma generation in the plasma generation chamber60, therefore, the density of the ionized target material91falls down to or below the density that is appropriate for generation of EUV radiation. In the embodiment, the ionized target material91with a relatively low temperature and high density can be obtained by simultaneously applying the multi-wavelength laser beams LB4a, LB4b, LB4ccorresponding to the excited levels of tin.

The operation of the EUV light source device1will be described referring toFIGS. 1 and 2. The ionizer20first irradiates the vaporization laser beam LB3on the target material90supplied from the target supply device10to vaporize the target material90, and then simultaneously irradiates the three types of laser beams LB4a, LB4b, LB4con the vaporized target material to generate an ionized target material91(ion beam).

The ionized target material91is pulled toward a high voltage produced by the ion beam extractor30, accelerated and supplied to the plasma generation chamber60. The drift tube40and the convergence device50are disposed in the supply passage from the ion beam extractor30to the plasma generation chamber60. The drift tube40and convergence device50suppress the ionized target material91from spreading in the radial direction during traveling, thus preventing the density of the ionized target material from becoming lower than the density appropriate for generation of EUV radiation. InFIG. 1, the outside diameter of the supply passage of the ionized target material91till the point of plasma generation in the plasma generation chamber60is indicated by an envelope.

Because the target material91is ionized, it tends to spread due to the repulsive force acting among cations. As the target material91spreads, the density becomes lower, thus reducing the efficiency of generating EUV radiation. When the target material91spreads larger than the beam size of the driver laser beam LB1, the irradiation efficiency in the case of irradiating the driver laser beam LB1on the ionized target material becomes lower, thus reducing the generation efficiency of EUV radiation. To cope with this matter, the drift tube40as a magnetic field generator and the convergence device50including an electrostatic lens or the like are used to prevent the ionized target material91from spreading before reaching the point of plasma generation.

When the ionized target material91reaches the point of plasma generation in the plasma generation chamber60, the driver laser beam LB1is irradiated on the ionized target material91, producing the plasma92. The EUV radiation emitted from the plasma92is supplied to the exposure device2via the EUV collector mirror61, etc.

The target material93after emission of the EUV radiation is retained in the target collecting device80via the collection passage60B while keeping the high speed. The magnetic field generator81prevents the target material93from being deposited in the collection passage60B. InFIG. 1, the maximum outside diameter of the target material93in the passage from the point of plasma generation in the plasma generation chamber60to the target collecting device80is indicated by an envelope.

According to the embodiment with the foregoing configuration, the target material90is supplied to the plasma generation chamber60after being ionized, the necessary amount of the target material91with a density appropriate for generation of EUV radiation can be supplied to the point of plasma generation.

According to the embodiment, the ion beam extractor30pulls only the ionized target material91, and accelerates and supplies the ionized target material91toward the plasma generation chamber60. The electrically neutral target material90which has not been ionized is collected in the target collecting device22, and is not supplied to the plasma generation chamber60. That is, according to the embodiment, the target material90which may become uncontrollable debris can be prevented from being supplied to the plasma generation chamber60. This suppresses generation of debris, thus making it possible to prevent damaging or degradation of the EUV collector mirror61and improve the reliability, the lifetime and the operation time of the EUV light source device1.

According to the embodiment, the target material91appropriate for generation of EUV radiation is generated in the ionizer20and is supplied to the plasma generation chamber60. That is, the target material91appropriate for generation of EUV radiation can be adjusted beforehand using the ionizer20separated from the plasma generation chamber60. For example, the necessary amount of the target material for generation of EUV radiation can be obtained by adjusting the diametric size of the inlet port26A, the pressure in the tank11, etc. Then, the drift tube40and the convergence device50can allow the target material91ionized by the ionization laser light source210to be transported to the point of plasma generation in such a way as not to diffuse the target material91, thus making it possible to increase the generation efficiency of EUV radiation.

According to the embodiment, the target material90is ionized at once by simultaneously irradiating the multi-wavelength laser beams LB4a, LB4b, LB4ccorresponding to the excited levels of the target material90on the target material. It is therefore possible to obtain the ionized target material91with a lower temperature than that obtained in the case of using arc discharge or the like, thus making it possible to suppress the density and shape of the ionized target material91from being changed. This can improve the generation efficiency of EUV radiation.

Second Embodiment

A second embodiment will be described referring toFIG. 6. The individual embodiments to be described hereinafter are modifications of the first embodiment. Therefore, the following description is mainly about differences from the first embodiment.FIG. 6is an explanatory diagram showing the general configuration of an EUV light source device1A according to the second embodiment.

The EUV light source device1A, like the EUV light source device1shown inFIG. 1, includes a target supply device10, an ionizer20, an ion beam extractor30, a plasma generation chamber60, a driver laser light source70, a target collecting device80, and so forth. The EUV light source device1A differs from the EUV light source device1inFIG. 1in that an accelerating tube110, a compressor (buncher)120and a neutralizer130are additionally provided between the ion beam extractor30and the plasma generation chamber60, and the drift tube40is eliminated.

The accelerating tube110as the “acceleration section” is provided in place of the drift tube40. The accelerating tube110has a plurality of ring-like electrodes111among which predetermined voltages are applied. That is, a voltage is applied to each electrode111in such a way that the voltage between the adjoining electrodes gradually rises. This causes the ionized target material91which has entered the accelerating tube110to move toward the plasma generation chamber60while being accelerated.

The compressor120as the “compression section” is provided adjacent to, and downstream of, the accelerating tube110. The compressor120compresses the ionized target material91in the moving direction thereof. That is, the compressor120compresses the ionized target material91, which moves rightward from the left inFIG. 6, in the right and left direction. The compressor120has, for example, a pair of electrodes having apertures through which the ionized target material91passes. A pulse high voltage whose polarity changes is applied to the pair of electrodes in synchronism with the passing of the ionized target material91through the pair of electrodes, thus ensuring pulse compression in the traveling direction of the ionized target material91. As mentioned in the foregoing description of the first embodiment, the convergence device50is provided adjacent to, and downstream of, the compressor120converges the ionized target material91in the planar direction orthogonal to the moving direction thereof.

The neutralizer130as the “neutralization section” is provided adjacent to, and downstream of, the convergence device50. The neutralizer130irradiates an electron beam on the positively ionized target material91to electrically neutralize the target material91. Alternatively, the neutralizer130may be configured as a plasma generator to generate a plasma through which the ionized target material91is let to pass to be electrically neutralized.

Even when the target material91becomes electrically neutral, the moving speed hardly changes, so that the electrically neutral target material91moves toward the point of plasma generation at a high speed. A target material93after generation of EUV radiation moves fast toward the target collecting device80to be collected therein.

The embodiment with this configuration also has advantages similar to those of the first embodiment. Further, the use of the accelerating tube110in place of the drift tube40in the embodiment can allow the ionized target material91to be transported at a higher speed. It is therefore possible to suppress diffusion of the ionized target material91.

According to the embodiment, because the compressor120is provided downstream of the accelerating tube110, the target material91which stretches in the moving direction by passing through the accelerating tube110can be converged in the moving direction. That is, provided that the right and left direction inFIG. 6is called the longitudinal direction, the target material stretched in the longitudinal direction can be compressed. This can allow the target material91with the shape adjusted to be supplied to the point of plasma generation plasma, making it possible to increase the generation efficiency of EUV radiation.

According to the embodiment, the neutralizer130is provided before the plasma generation chamber60to electrically neutralize the target material before being supplied to the plasma generation chamber60. Accordingly, the target material91can be prevented from spreading in the chamber60by the repulsive force acting among ions, making it possible to supply the target material91with the appropriate density and shape maintained to the point of plasma generation, thus increasing the generation efficiency of EUV radiation.

Third Embodiment

A third embodiment will be described referring toFIG. 7. According to the embodiment, the vaporization laser light source200is eliminated, and an ionization laser light source220alone carries out both of the vaporization and ionization of a target material90.FIG. 7is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement.

For example, as the temperature of the heater13which heats the target supply device10or keeps the temperature thereof is set higher than the melting point of the target material90, both the vaporization and ionization of the target material90can be carried out merely by irradiating laser beam LB5on the target material90supplied through the inlet port26A. The laser light source220which is used for both of vaporization and ionization can simultaneously output laser beams of three types of wavelengths as described in the foregoing description of the first embodiment.

The embodiment with this configuration also has advantages similar to those of the first embodiment. Further, because the single laser light source220serves as an ionization laser light source and a vaporization laser light source, it is possible to reduce the number of laser light sources, thus lowering the manufacture cost and maintenance cost.

Fourth Embodiment

A fourth embodiment will be described referring toFIG. 8. According to the embodiment, an electron beam device230is used in place of the vaporization laser light source200.FIG. 8is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement.

According to the embodiment, an electron beam eB1is irradiated on a target material90to vaporize the target material90. Therefore, the focusing lens201and the incident window202are unnecessary. The embodiment with this configuration also has advantages similar to those of the first embodiment.

Fifth Embodiment

A fifth embodiment will be described referring toFIG. 9. According to the embodiment, a target material of tin, stannane or the like is supplied as droplets into the ionizer20.FIG. 9is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement.

A target supply device10A retains a liquid target material90A in a tank11A. The target supply device10A supplies a droplet target material into the ionizer20through a nozzle12A by means of a piezoelectric element or the like. The vaporization and ionization of the droplet target material are almost simultaneously executed at a predetermined point91A, and the resultant target material is extracted by the ion beam extractor30. A magnetic field generator27A suppresses the ionized target material91from spreading.

The embodiment with this configuration also has advantages similar to those of the first embodiment. Further, as the droplet target material is supplied into the ionizer20, it is possible to supply the target material with a desired shape and in a desired mass according to the embodiment. Therefore, the ionized target material91appropriate for generation of EUV radiation can be generated in the ionizer20relatively easily.

Sixth Embodiment

A sixth embodiment will be described referring toFIG. 10.FIG. 10is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement. According to the embodiment, a target material90B such as tin or stannane is supplied into the ionizer20in the form of a liquid jet.

A target supply device10B retains the target material90B in a tank11B, and ejects the target material90B as a fast gas stream through a nozzle12B. Vaporization laser beam LB3and ionization laser beam LB4are irradiated on the liquid target material90B at a predetermined point91B. The embodiment with this configuration also has advantages similar to those of the first embodiment.

Seventh Embodiment

A seventh embodiment will be described referring toFIG. 11.FIG. 11is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement. According to the embodiment, a disk-shaped material90C is supplied to the ionizer20.

A target supply device10C rotates the disk-shaped material90C by means of a rotary motor14. According to the embodiment, vaporization laser beam LB3and ionization laser beam LB4are irradiated on the rotating disk-shaped material90C, thus generating an ionized target material91. The embodiment with this configuration also has advantages similar to those of the first embodiment. Note that the target material to be supplied can be formed on the top surface of a disk-shaped material.

Eighth Embodiment

An eighth embodiment will be described referring toFIG. 12.FIG. 12is an explanatory diagram showing the essential portions of an EUV light source device according to the embodiment in enlargement. According to the embodiment, a target material is formed in a tape-like form or wire-like form, and then supplied to the ionizer20. Note that the target material to be supplied can be formed on the top surface of a tape-like or wire-like material.

A target supply device10D moves a target material90D formed in a tape-like form or wire-like form by means of a feeding device15. Vaporization laser beam LB3and ionization laser beam LB4are irradiated on the tape-like or wire-like target material90D, thus generating an ionized target material91. The embodiment with this configuration also has advantages similar to those of the first embodiment.

Ninth Embodiment

A ninth embodiment will be described referring to FIGS.13to15. According to the embodiment, an electron beam301is used in place of the neutralizer130(seeFIG. 6). The electron beam301serves to guide an ionized target material91to a predetermined position in the plasma generation chamber60.

FIG. 13shows the general configuration of an EUV light source device1B according to the embodiment. The EUV light source device1B includes an electron gun300which outputs an electron beam in the traveling direction of an ionized target material91(ion beam), and an electromagnet320provided downstream of the convergence device50to generate a magnetic field.

An electron source which emits thermal electrons from a filament or the like, for example, can be used for electron gun300as the “electron beam output section”. According to the embodiment, the ion current density (ion density) is set to be large. Accordingly, it is desirable to use the electron gun300where a large current can flow.

The electron gun300has a mechanism310which accelerates the electron beam output and converges the diameter of the electron beam. The electron-beam accelerating and converging mechanism310is configured as, for example, an electrostatic lens or the like.

The electromagnet320as the “fifth magnetic field generating section” generates a magnetic field for merging the ion beam91and the electron beam301. The size of the electromagnet320, if configured as a superconductive magnet, can be made smaller.

FIG. 14is a general diagram showing the relation between the magnetic field generated by the electromagnet320and the ion beam91. The electron beam301output from the electron gun300is accelerated and converged by the mechanism310to be output toward the ion beam91. At this time, the locus of the electron beam301is bent in a direction parallel to the ion beam91by the magnetic field generated by the electromagnet320, and travels toward the interior of the plasma generation chamber60.

The electron beam301is set in such a way as to have an electron energy of, for example, several tens of electron volts (eV) or higher, and an electron density of several tens of amperes (A)/cm2for the following reasons.

First, the electron energy needs to be several tens of eV so as not to electrically neutralize the ion beam91. Because the ion beam91has positive charges, the ion beam91tends to catch electrons in the electron beam301to be electrically neutralized. The strength of the action of the ion beam91to return to the electrically neutral state is expressed by the value of a recombination cross section.

The recombination cross section is a function of the speed of electrons (i.e., energy), and becomes maximum when the electron energy is several eV. That is, slow electrons travel indicates that the electrons are likely to be attracted by the positive charges and easily recombined.

According to the embodiment, the ion beam91is shaped using the property of the ions. Therefore, the electron beam301is used in the region where the electron energy becomes equal to or greater than several tens of eV so that ions and electrons are not recombined.

Next, the conditions for the current density will be described. According to the embodiment, as described above, the ion beam91is attracted by the spatial charges of the electrons, thereby converging the diameter of the ion beam91. This requires that the current density of the electron beam301should be greater than the current density of the ion beam91. Because the current density of the ion beam91is several amperes/cmm2, the current density of the electron beam301should be set to several tens of amperes/cmm2.

The electron beam301can be generated continuously or intermittently. In case of continuously generating the electron beam301, the electron beam301need not be synchronized with the ion beam91, thus ensuring a simpler control structure. However, the power consumption increases. In case of intermittently generating the electron beam301, the power consumption can be reduced. However, it is necessary to synchronize the timing of generating the electron beam301with the timing of generating the ion beam91, thus complicating the control structure.

According to the embodiment with the foregoing configuration, as the electron beam301is irradiated in parallel to the ion beam91, the ion beam91can be supplied into the plasma generation chamber60while being converged.

Tenth Embodiment

A tenth embodiment will be described referring toFIGS. 15 and 16. A method of synchronizing the timing for generating an ionized target material91with the timing for generating will be described in the description of the embodiment.

In the embodiments shown inFIGS. 2,10,11and12after a target material90is vaporized by vaporization laser beam, ionization laser beam is irradiated thereon to generate an ionized target material91. The generated ionized target material91is accelerated by the accelerating tube110. The conditions (voltage, current, time modulation, etc.) for the operations vary according to the conditions of generating a target material. Accordingly, the EUV generation time changes according to the target generation time.

The target material generating conditions include the type, temperature and state (solid or liquid) of the target material, and the energy, output, pulse width and wavelength of laser beam. Basically, if synchronization is taken based on the irradiation timing for vaporization laser beam, laser beam from the driver laser light source can be irradiated on the target material.

FIG. 15shows one example of setting the irradiation timing for the driver laser beam with an irradiation timing Tg for vaporization laser beam being a reference. Let t1be a delay time between the irradiation timing Tg for vaporization laser beam and irradiation timing Ti for ionization laser beam, and t2be a delay time between the irradiation timing Ti for ionization laser beam and irradiation timing Tld for driver laser beam. The times t1and t2are controlled by a synchronization controller C1. t1and t2are set to optimal values for efficiently generating EUV radiation.

Because a vaporization laser light source is not used in the embodiment shown inFIG. 7, only t2should be controlled. In the embodiment shown inFIG. 8, t1and t2are optimized with vaporization laser beam being replaced with an electron beam.

Because a target material is intermittently supplied as droplets in the embodiment shown inFIG. 9, the number of variables for synchronization is increased. Accordingly, let t0be a delay time from generation of droplets to the operation of the vaporization laser light source. A synchronization controller C2controls t0, t1, and t2.

According to the embodiment with this configuration, the delay times t1and t2(or t0, t1and t2) can be controlled individually. For example, a process of dropping droplets, a process of vaporizing droplets, and a process of ionizing droplets can be controlled with different accuracies, respectively.

Eleventh Embodiment

An eleventh embodiment will be described referring toFIG. 17. According to the embodiment, the reference time for synchronization is matched with the process that is executed at the earliest timing. A synchronization controller C3according to the embodiment sets the timing of generating droplets as the reference timing for synchronization. This configuration can ensure synchronization with a simpler structure.

Twelfth Embodiment

A twelfth embodiment will be described referring toFIG. 18. According to the embodiment, an EUV radiation detecting sensor65detects the output of EUV radiation, and feeds back the detection signal to a synchronization controller C4to adjust t1and t2to optimal values. The embodiment may be combined with the embodiment shown inFIG. 17.

For example, before operation of the exposure device, EUV radiation is repeatedly generated with times t1and t2being changed gradually, and the output of the EUV radiation is detected by the sensor65. This makes it possible to acquire t1and t2that provide the optimal EUV radiation. t1and t2are set to, for example, times that can provide the maximum EUV radiation. Alternatively, t1and t2can also be set in such a way as to provide a demanded EUV radiation output from the exposure device2. That is, t1and t2may be set to values that reduce the generation efficiency of EUV radiation.

Thirteenth Embodiment

A thirteenth embodiment will be described referring toFIGS. 19 to 21. According to the embodiment, a groove portion910is formed in a disk-shaped target material90E, and a replenishment section920is provided to restore the top surface of the disk-shaped target material90E.

FIG. 19is an explanatory diagram showing the disk-shaped target material90E embodiment generation of a target material supply section10E. According to the embodiment, the disk-shaped target material90E is used. As shown inFIG. 20, the groove portion910is formed in a ring shape in one side of the disk-shaped target material90E (side where laser beam is irradiated).

The other side of the disk-shaped target material90E is rotatably supported by a rotary shaft14A of a rotary section14. The replenishment section920is provided in such a way as to retain the lower side of the disk-shaped target material90E. More specifically, the replenishment section920is arranged so that the lower portion of the groove portion910is soaked with the liquid target material.

When the disk-shaped target material90E rotates, the liquid target material is deposited in and around the groove portion910, thereby restoring the radiation surface of the disk-shaped target material90E. Even if the disk-shaped target material90E is damaged by irradiation of the laser beam, therefore, the liquid target material can be immediately applied thereto to restore the disk-shaped target material90E.

For example, the liquid target material can be obtained by dissolving the target material into a solvent. In case where the target material is a metal, the liquid target material can be obtained by setting the temperature of the replenishment section920equal to or higher than the melting point.

FIG. 21shows the cross-sectional shapes of the groove portions910. As shown in FIG.21(1), the cross section of the groove portion910can be formed into an inverted triangular shape. As shown in FIG.21(2), the cross section of the groove portion910can be formed into a semicircular shape. As shown in FIG.21(3), the cross section of the groove portion910can also be formed into a semielliptic shape.

The width w1, w2, w3of the groove portion910can be set to a desired value according to the irradiation area or the like of laser beam. The depth d1, d2, d3of the groove portion910can likewise be set to a desired value. As one example, w1, w2, w3and d1, d2, d3can be set to about 0.5 mm. Note that the groove portion910may have a cross-sectional shape other than the one shown inFIG. 21.

The target material can be efficiently turned into plasma by irradiating laser beam toward the groove portion910. This is because the groove portion910increases the irradiation area of laser beam, makes it difficult for the generated plasma to be diffused from the groove portion910.

Because the liquid target material in the replenishment section920is applied to the laser beam irradiating surface of the disk-shaped target material90E, the disk-shaped target material90E need not be formed by the target material. In consideration of heat capacity, thermal conductivity, rigidity, and the like, for example, a rotary body having groove portion910may be formed of another material like diamond. The rotary body corresponds to the target material supply body.

The embodiment with the above configuration can stabilize the state of the surface where laser beam is irradiated, thus suppressing a variation in the intensity of EUV radiation. Further, vaporization and ionization of the target material can be carried out efficiently by the groove portion910.

Fourteenth Embodiment

A fourteenth embodiment will be described referring toFIGS. 22 and 23. A target material supply section1OF according to the embodiment uses a cylindrical target material90F. As shown in a perspective view ofFIG. 23, the cylindrical target material90F has a groove portion910A formed in such a way as to go around the center portion of the peripheral surface.

Both axial end portions of the cylindrical target material90F are rotatably supported by a rotary shaft14B of the rotary section14. Further, a repairing section920A is provided in such a way that at least a part of the lower portion of the cylindrical target material90F is soaked with the liquid target material.

Note that the cylindrical target material90F can be formed of a material different from the target material as per the thirteenth embodiment. The groove portion910A can be formed into various shapes as shown inFIG. 21.

The embodiment with this configuration also has advantages similar to those of the thirteenth embodiment. Further, according to the embodiment, the use of the cylindrical target material90F can make the volume larger to increase the heat capacity. When laser beam is irradiated on the groove portion910A, therefore, the influence of the irradiation of the laser beam on a thermal change can be made smaller. It is therefore possible to stabilize the density or the like of ions generated by laser beam, so that the ionized target material91can be generated stably.

In addition, both rotary-axial ends of the cylindrical target material90F are supported according to the embodiment, the rotation can be made more stable as compared with the case where only one end is supported. Therefore, the combination of the action to stabilize the rotation and prevention of a thermal change originated from the aforementioned increase in heat capacity can case the ionized target material91to be generated more stably.

Fifteenth Embodiment

A fifteenth embodiment will be described referring toFIG. 24. According to the embodiment, a taper911tilting downward toward the axial center portion is provided on the peripheral surface of a cylindrical target material90G. That is, the cylindrical target material90G is constricted in the center portion of the cylinder, and has a groove portion910B provided in such a way as to go around the center portion.

Note that the cylindrical target material90G can be formed of a material different from the target material as per the fourteenth embodiment. Further, the groove portion910B can be formed into various shapes as shown inFIG. 21.

Sixteenth Embodiment

A sixteenth embodiment will be described referring toFIGS. 25 to 27. A specific example of the accelerating tube110(seeFIG. 6) will be described in the descriptions of this embodiment and several embodiments to be discussed below. According to the embodiment, a radio-frequency quadrupole linear accelerator (RFQ: Radio-Frequency Quadrupole Linac)150is used as a specific example of the accelerating tube110. Hereinafter, this accelerator150will be called RFQ150.

FIG. 26is a perspective view showing electrodes151of the RFQ150. Four electrodes151(1) to151(4) in total are each formed as a rod-like electrode which has an approximately wedge-like cross section. The opposing two electrodes make a set, and the angle defined by the two set of electrodes is set to 90 degrees. A high-frequency voltage is applied to each of the electrodes151(1) to151(4) from a high-frequency voltage source152. Each of those electrodes will be called “electrode151” unless they should be distinguished.

A cavity154is formed at the center portion the individual electrodes face. As indicated by a two-dot chain line arrow inFIG. 26, an ionized target material91enters the cavity154from one side of the lengthwise direction of the electrodes151, passes through the cavity154, and goes out from the other side of the lengthwise direction of the electrodes151.

FIG. 27is a cross-sectional view of a pair of electrodes151. A surface153of the electrode151which faces the other electrode151is formed into an approximately sinusoidal shape. The wavelength of the sinusoidal surface153is so set as to gradually become longer in the traveling direction of the ionized target material91.

In the example inFIG. 27, the inlet-side sinusoidal surface where the ionized target material91enters has a wavelength WL1. The wavelength of the middle portion continual to the inlet-side sinusoidal surface is WL2longer than WL1(WL2>WL1). The wavelength of the outlet-side sinusoidal surface continual to the middle portion is WL3longer than WL2(WL3>WL2).

The convergence, compression and acceleration of the ionized target material91can be carried out simultaneously by applying a high-frequency voltage to the individual electrodes151configured in the above manner. See p 492-493 in “Principles of Charged Particle Acceleration written by Stanley Humphries, Jr. (published by John Wiley & Sons, Inc.) for the detailed operational principle of the RFQ150.

According to the embodiment, the use of the RFQ150as an accelerating tube can allow the convergence, compression and acceleration of the ionized target material91to be carried out simultaneously. Therefore, the RFQ150can serve as the convergence device50or the compressor120.

Seventeenth Embodiment

A seventeenth embodiment will be described referring toFIGS. 28 and 29. According to the embodiment, an electrostatic accelerating tube160is used as another specific example of the accelerating tube110.FIG. 28is a diagram showing the schematic configuration of the electrostatic accelerating tube160, andFIG. 29is a cross-sectional view of the electrostatic accelerating tube160.

The electrostatic accelerating tube160is configured by arranging a plurality of disk-shaped electrodes161at equal intervals in the coaxial direction. A hole163through which an ionized target material91passes is formed in the center of each disk-shaped electrode161.

The disk-shaped electrodes161are connected to a high voltage source162. An equal voltage is applied between the electrodes.

The individual disk-shaped electrodes161are attached to a cylindrical support165. The cylindrical support165is formed of a material having an electrical insulating property. A passage164including the individual holes163is formed in the cylindrical support165. The interior of the passage164is held in a vacuum state.

As indicated by a one-dot chain line arrow in the diagrams, the ionized target material91passes through the passage164rightward from the left side in the diagrams. Every time the ionized target material91passes through the hole163of each disk-shaped electrode161, the ionized target material91is accelerated.

Eighteenth Embodiment

An eighteenth embodiment will be described referring toFIGS. 30 and 31. According to the embodiment, a liner accelerating tube170is used as a mimic example of the accelerating tube110.FIG. 30is a diagram showing the schematic configuration of the liner accelerating tube170, andFIG. 31is a cross-sectional view of the liner accelerating tube170.

The liner accelerating tube170is configured by arranging a plurality of cylindrical electrodes171(1) to171(5) coaxially at equal intervals. A thin annular electrode171(0) is provided on the inlet side (left side inFIG. 30) where an ionized target material91enters, and another thin annular electrode171(6) is provided on the outlet side (right side inFIG. 30) from which the ionized target material91leaves.

A hole173through which the ionized target material91passes is formed in the center of each of the cylindrical electrodes171(1) to171(5). The axial lengths of the cylindrical electrodes171(1) to171(5) are so set as to become longer in order in the traveling direction of the ionized target material91.

As shown inFIG. 31, the length, L10, of the first cylindrical electrode171(1) disposed on the inlet side is set shortest. The length, L11, of the second cylindrical electrode171(2) disposed adjacent to, and downstream of, the first cylindrical electrode171(1) is set longer than L10(L11>110). The length, L12, of the third cylindrical electrode171(3) disposed adjacent to, and downstream of, the second cylindrical electrode171(2) is set longer than L11(L12>111).

Likewise, each of the length, L13, of the fourth cylindrical electrode171(4) and the length, L14, of the fifth cylindrical electrode171(5) is set longer than the length of another cylindrical electrode disposed adjacent thereto and upstream thereof.

The individual cylindrical electrodes171(1) to171(5) and the individual annular electrodes171(0) and171(6) are supported by a cylindrical support175having an electrical insulating property. A passage174including the individual holes173is formed in the support175.

Every other electrodes of the electrodes171(1) to171(5),171(0) and171(6) are electrically connected together. The ionized target material91passing through the passage174can be accelerated by applying a high-frequency voltage to the electrodes171(1) to171(5),171(0) and171(6) from a high voltage source172. See p 452-459 in the aforementioned publication for the detailed operational principle of the linear accelerating tube.

Nineteenth Embodiment

A nineteenth embodiment will be described referring toFIG. 32. According to the embodiment, an induction accelerating tube180is used as another specific example of the accelerating tube110.FIG. 32is a cross-sectional view of the induction accelerating tube180.

The induction accelerating tube180includes a ferromagnetic core181, a coil182wound around the core181, a cylindrical support185, a projection186projecting from the inner surface of the support185, an end portion183of the coil182, a passage184through which an ionized target material91passes, a gap187and a pulse power supply188.

As a pulse current from the pulse power supply188is let to flow through the ferromagnetic core181, a magnetic field is generated. A time-dependent change in the magnetic field induces an induction electric field in the gap187between the coil end portion183and the projection186. When the ionized target material91passes through the induction electric field generated in the gap187, the ionized target material91is accelerated. See p 283-313 in the aforementioned publication for the detailed operational principle of the induction accelerating tube180.

Twentieth Embodiment

A twentieth embodiment will be described referring toFIG. 33. An induction accelerating tube180A according to the embodiment has a plurality of acceleration gaps187disposed coaxially. According to the embodiment, a plurality of units each including the ferromagnetic core181, the coil182and the gap187are disposed in a direction in which an ionized target material91passes. This can allow the ionized target material91to be accelerated by each gap187, so that a faster ionized target material91can be obtained.

A twenty-first embodiment will be described referring toFIGS. 34 to 36. A specific example of the compressor120(seeFIG. 6) will be described in the descriptions of this embodiment and several embodiments to be discussed below. The compressor120according to the embodiment has two disk-shaped electrodes121(1),121(2), a high voltage control circuit123, and a cylindrical support125. The two disk-shaped electrodes121(1),121(2) form an electrode pair121P.

A hole122through which an ionized target material91passes is formed in the center of each electrode121(1),121(2). A passage124including the individual holes122is formed in the support125.

The high voltage control circuit123applies a pulsed voltage to the electrode pair121P in synchronism with the passing of the ionized target material91through the electrode pair121P. That is, the high voltage control circuit123applies the pulsed voltage, which changes in such a way that the potential of the electrode pair121P is modulated to a desired value, to the electrode pair121P at a predetermined timing. The timing of applying the pulsed voltage is determined by a timing signal.

A pulsed high voltage circuit having a fast switch can be used as the high voltage control circuit123. Alternatively, the circuit which has the ferromagnetic core181and pulse power supply188as shown inFIG. 32can be used as the high voltage control circuit123. As a pulse current is let to flow through the ferromagnetic core181, a magnetic field is generated, and a desired induction electric field induced by a time-dependent change in the magnetic field is generated at the electrode pair121P.

In the following description, let Lt be the length of an uncompressed ionized target material91which enters the compressor120, and the ionized target material91is assumed to be charged positively.

FIG. 35shows an example of a pulsed voltage to be applied to the electrode pair121P. Here, let t10be a time at which an uncompressed ionized target material91(0) has reached the inlet side of the electrode pair121P (inlet-side electrode121(1)), and let t11be a time at which the center portion of the ionized target material91will reach the inlet-side electrode121(1). Reference numeral “91(1)” is given to a compressed ionized target material whose center portion has reached the inlet-side electrode121(1).

The high voltage control circuit123operates in such a way that a rectangular wave as shown inFIG. 35. That is, the high voltage control circuit123applies the rectangular wave which rises at time t10and falls at time t11to the electrode pair121P. This can allow the forward side of the ionized target material91in the traveling direction thereof to be compressed. Therefore, the length Lt in the traveling direction of the ionized target material91becomes a shorter Lt1 (Lt1<Lt).

Although one electrode pair121P is illustrated in the embodiment, which is not restrictive, a plurality of electrode pairs121P may be disposed linearly in the traveling direction of the ionized target material91. In the case of the configuration, the high voltage control circuit123applies a predetermined high voltage pulse to each electrode pair121P at the timing at which the ionized target material91reaches each electrode pair121P.

FIG. 36shows other examples of the high voltage pulse. A sinusoidal high voltage pulse may be used as shown in FIG.36(1), or a triangular high voltage pulse may be used as shown in FIG.36(2).

A twenty-second embodiment will be described referring toFIGS. 37 and 38. According to the embodiment, the backward side of an ionized target material91in the traveling direction thereof is compressed on the outlet side of the electrode pair121P.FIG. 37shows the general outline of a compression section according to the embodiment.

Let t12be a time at which an uncompressed ionized target material91(2) has reached the outlet side of the electrode pair121P (outlet-side electrode121(2)), and let t13be a time at which the center portion of the ionized target material91will reach the outlet-side electrode121(2). Reference numeral “91(3)” is given to a compressed ionized target material whose center portion has reached the outlet-side electrode121(2).

A high voltage control circuit123A applies a negative rectangular high voltage pulse to the electrode pair121P according to the movement of the ionized target material91. The rectangular wave rises at time t12and falls at time t13. Accordingly, the backward side of the ionized target material91in the traveling direction thereof is compressed, thus shortening the length of the ionized target material91.

FIG. 38shows other examples of the high voltage pulse to be applied to the electrode pair121P. A sinusoidal high voltage pulse may be used as shown in FIG.38(1), or a triangular high voltage pulse may be used as shown in FIG.38(2).

A plurality of electrode pairs121P may be disposed in the traveling direction of the ionized target material91to compress the ionized target material91multiple times as per the twenty-first embodiment.

A twenty-third embodiment will be described referring toFIGS. 39 and 40.FIG. 39shows the general outline of a compression section according to the embodiment. According to the embodiment, an ionized target material91is compressed on both the inlet side and the outlet side of the electrode pair121P.

According to the embodiment, the distance between the inlet-side electrode121(1) and the outlet-side electrode121(2) is set to, for example, a half of a length Lt in the traveling direction of the uncompressed ionized target material91(distance between electrodes=Lt/2).

A high voltage control circuit123B consecutively applies a positive rectangular high voltage pulse and a negative rectangular high voltage pulse to the electrode pair121P according to the movement of the ionized target material91. The high voltage control circuit123B consecutively generates a first high voltage pulse of a positive potential and a second rectangular of a negative potential.

The first high voltage pulse rises at time t10at which an ionized target material91(0) reaches the inlet-side electrode121(1), and falls at time t11at which the center portion of an ionized target material91(1) reaches the inlet-side electrode121(1), as mentioned in the foregoing description of the twenty-first embodiment.

The second high voltage pulse rises at time t12at which an ionized target material91(2) reaches the outlet-side electrode121(2), and falls at time t13at which the center portion of an ionized target material91(3) reaches the outlet-side electrode121(2), as mentioned in the foregoing description of the twenty-second embodiment.

Because the distance between the electrodes is set to a half of the length Lt of the ionized target material91, the time t11at which the center portion of the ionized target material91reaches the inlet-side electrode121(1) is substantially equal to the time t12at which the leading portion of the ionized target material91reaches the outlet-side electrode121(2).

The length of the uncompressed ionized target material91(0) in the traveling direction is Lt first. When a half of the ionized target material91(1) passes the inlet-side electrode121(1), the ionized target material91(1) is compressed, so that the length becomes Lt1 (Lt1<Lt).

At this time, the leading portion of the ionized target material91(2) (which is also the ionized target material91(1)) has reached the outlet-side electrode121(2). When an ionized target material91(3) passes the outlet-side electrode121(2), its length is shorted to Lt2 from Lt1 (Lt2<Lt1).

FIG. 40shows other examples of the high voltage pulse. Two sinusoidal high voltage pulses of different polarities may be consecutively applied to the electrode pair121P as shown in FIG.40(1). Two triangular high voltage pulses of different polarities may be consecutively applied to the electrode pair121P as shown in FIG.40(2).

According to the embodiment with this configuration, the forward side and backward side of the ionized target material91can be consecutively compressed by a single electrode pair. Further, because the distance between the electrodes is set short, the compression section can be made compact.

A twenty-fourth embodiment will be described referring toFIG. 41. According to the embodiment, a plurality of electrode pairs121P each discussed in the foregoing description of the twenty-third embodiment are disposed in the traveling direction of an ionized target material91. According to the embodiment, a first electrode pair121P(1) and a second electrode pair121P(2) are used.

The first electrode pair121P(1) has an inlet-side electrode121(1) and an outlet-side electrode121(2). The distance between the electrode121(1) and the electrode121(2) is set to Lt/2.

A first high voltage control circuit123B applies a plurality of consecutive high voltage pulses of different polarities as shown inFIG. 39orFIG. 40to the first electrode pair121P(1). As mentioned above, the length of the ionized target material91in the traveling direction is compressed to Lt1 from Lt by the inlet-side electrode121(1), and the length of the ionized target material91is further compressed to Lt2 from Lt1 by the outlet-side electrode121(2).

The second electrode pair121P(1), which is provided downstream of the first electrode pair121P(1), has an inlet-side electrode121(21) and an outlet-side electrode121(22). The distance between the electrode121(21) and the electrode121(22) is set to a half (=Lt2/2) of the length of the ionized target material91after passing the first electrode pair121P(1).

A second high voltage control circuit123C likewise applies a plurality of consecutive high voltage pulses of different polarities as shown inFIG. 39orFIG. 40to the second electrode pair121P(2). The length of the ionized target material91in the traveling direction is compressed to Lt3 (not shown) from Lt2 by the inlet-side electrode121(21). Following the compression, the length of the ionized target material91is compressed to Lt4 from Lt3 by the outlet-side electrode121(22).

According to the embodiment, as apparent from the above, a plurality of electrode pairs121P(1) and121P(2) to which high voltage pulses of different polarities are to be applied are disposed along the traveling direction of the ionized target material91, and further the distance between the electrodes of each electrode pair121P(1),121P(2) is set to the half (or equal to or less than the half) of the length of the ionized target material91to be input to each electrode pair121P(1),121P(2). Therefore, the ionized target material91can be compressed further.

A twenty-fifth embodiment will be described referring toFIGS. 42 to 44. In the description of the embodiment, a specific example of the neutralizer130will be described.FIG. 42is a general configurational diagram showing how an electron beam132is irradiated on an ionized target material91by the neutralizer130.FIG. 43is an exemplary diagram of an electron gun131, andFIG. 44is a circuit diagram of a thermal emission electron gun.

As shown inFIG. 43, the neutralizer130has the electron gun131which emits the electron beam132. As shown inFIG. 44, the neutralizer130can be configured as a thermal emission electron gun.

The thermal emission electron gun130has a cathode1301configured as a tungsten filament or the like, an anode1302, a Wehnelt electrode1303, a filament circuit1304, and a bias circuit1305.

A predetermined negative voltage (filament voltage) is applied to the cathode1301by the filament circuit1304. A negative voltage (bias voltage) lower than the filament voltage is applied to the Wehnelt electrode1303by the bias circuit1305.

As the cathode1301is heated, electrons are emitted. The emitted electrons are converged to a predetermined point by an electric field generated by the Wehnelt electrode1303, and are accelerated toward the anode1302. As a result, the electron beam132is generated.

A twenty-sixth embodiment will be described referring toFIG. 45. According to the embodiment, a field emission electron gun130B is used as the neutralizer130. The field emission electron gun130A includes, for example, a first anode1310, a second anode1311, and an emitter1312.

An extracting voltage is applied between the first anode1310and the emitter1312. The extracting voltage is the voltage to extract electrons from the emitter1312. This extracting voltage forms a strong electric field at the distal end of the emitter1312, so that electrons are emitted from the emitter1312.

An accelerating voltage is applied between the second anode1311and the emitter1312. The accelerating voltage is the voltage to accelerate the electrons emitted from the emitter1312. As the electrons are accelerated, they become the electron beam132.

The invention is not limited to the foregoing embodiments. It should be apparent to those skilled in the art that various additions, modifications and the like can be implemented within the spirit or scope of the invention. In addition, configurations which are realized by combining the foregoing embodiments as needed are also encompassed within the scope of the invention.