JP2017195143A - Plasma light source and method for generating plasma light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a plasma medium stably between a center electrode and an external electrode.SOLUTION: A plasma light source 1 includes: a pair of coaxial electrodes 10 having a center electrode 11, an external electrode 12, and an insulator 13 and generating plasma for emitting extreme ultraviolet light and confining the plasma; a plasma medium supply unit 41 for supplying a plasma medium M; and a medium vapor forming section 30 for irradiating the plasma medium M with laser light L. The medium vapor forming unit 30 has a laser device 31 for generating the laser light L and an optical path control unit 32 for changing the irradiation position of the laser light L in the plasma medium M.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plasma light source and a method for generating plasma light.

  As a technique in this field, a plasma light source described in Patent Document 1 is known. The plasma light source generates a discharge by supplying vapor of a plasma medium between the center electrode and the external electrode in a state where a voltage is applied between the center electrode and the external electrode.

JP 2013-254663 A

  The plasma light source of Patent Literature 1 generates vapor of a plasma medium by generating ablation. Ablation occurs when a solid or liquid plasma medium is irradiated with laser light to supply energy to the plasma medium. Here, depending on the surface state of the plasma medium, there is a possibility that the supply of energy due to the irradiation of the laser beam becomes unstable. If the supply of energy to the plasma medium becomes unstable, the vapor of the plasma medium is hardly generated stably. For this reason, it becomes difficult to stably supply the vapor of the plasma medium between the center electrode and the external electrode, and as a result, the generation of plasma light may become unstable.

  Therefore, in the technical field, it is desired to stably supply a plasma medium between the center electrode and the external electrode.

  A plasma light source according to an aspect of the present invention is disposed so as to face each other on an axis, and an external electrode disposed so as to be separated from the central electrode, an insulator that insulates the central electrode from the external electrode, and A pair of coaxial electrodes for generating plasma that emits extreme ultraviolet light and confining the plasma, a plasma medium supply unit that supplies a plasma medium for generating plasma, and irradiating the plasma medium with laser light A medium vapor forming unit, and the medium vapor forming unit includes: a laser device that generates laser light; and an optical path control unit that is disposed on the optical path of the laser light and changes an irradiation position of the laser light in the plasma medium. Have.

  In this plasma light source, the optical path control unit changes the irradiation position of the laser beam in the plasma medium exposed to the opening. Thereby, the temperature rise at the irradiation position of the laser beam is suppressed, and the state in which the laser beam is irradiated onto the mirrored plasma medium is avoided. Accordingly, since the ratio of the reflected laser light is reduced as compared with the case where the laser light is continuously applied to one point of the plasma medium, the reduction of the energy of the laser light absorbed by the plasma medium is suppressed. Thereby, the supply of energy for generating ablation to the plasma medium is stabilized, so that the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  In some embodiments, the plasma medium supply unit includes an opening, and includes a plasma medium holding unit that holds the plasma medium so that the plasma medium is exposed from the opening, and the optical path control unit is exposed from the opening. The optical path may be controlled so that the laser beam scans on the surface of the plasma medium. According to such a configuration, it is possible to suitably suppress an increase in the light reflectance of the plasma medium. Accordingly, since the supply of energy for generating ablation to the plasma medium is stabilized, the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  In some embodiments, the optical path control unit is disposed on the optical path and reflects the laser beam, and the light reflection unit changes the attitude of the light reflection unit with respect to the laser beam incident on the light reflection unit. And an attitude control unit that changes the direction of the optical path of the laser beam reflected by. According to such a configuration, the irradiation position of the laser beam on the surface of the plasma medium can be easily controlled.

  In some embodiments, the plasma medium supply unit may be provided in the center electrode, and the opening of the plasma medium supply unit may be provided in the outer peripheral surface of the center electrode. According to such a configuration, the vapor of the plasma medium can be suitably supplied between the center electrode and the external electrode.

  In some embodiments, the medium vapor forming unit may include an energy control unit that reduces energy supplied to the plasma medium by irradiating the plasma medium with laser light. When the laser medium is continuously irradiated with the laser beam, the temperature of the surface of the plasma medium at the irradiation position rises and the mirror surface progresses. Therefore, the medium vapor forming unit reduces the energy supplied to the plasma medium by laser light irradiation. This decrease in energy suppresses a temperature rise on the surface of the plasma medium. Therefore, since the mirror surface of the plasma medium is prevented from being mirrored, a decrease in the energy of the laser light absorbed by the plasma medium is suppressed. Accordingly, since the supply of energy for generating ablation to the plasma medium is stabilized, the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  In some embodiments, the plasma medium supply unit includes an opening, holds the plasma medium so that the plasma medium is exposed from the opening, stores the plasma medium, and stores the plasma medium in the plasma medium holding unit. A plasma medium storage unit that provides the plasma medium; and a temperature control unit that controls the temperature of the plasma medium. The temperature control unit has a surface temperature of the plasma medium exposed from the opening that is equal to or lower than a melting point of the plasma medium. Thus, the temperature of the plasma medium may be controlled. In this plasma light source, the temperature of the plasma medium is controlled so that the surface temperature of the plasma medium exposed from the opening is below the melting point of the plasma medium. According to this control, the solid plasma medium and the liquid plasma medium can coexist in the opening. For example, a solid plasma medium has a thin film shape and is in a floating state on a liquid plasma medium. On the surface of such a plasma medium, the light reflectance is lower than that of a surface in which the plasma medium is entirely liquid. Therefore, since the reflection of the laser beam irradiated to the plasma medium is suppressed, a decrease in the energy of the laser beam absorbed by the plasma medium is suppressed. Thereby, the supply of energy for generating ablation to the plasma medium is stabilized, so that the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  A method for generating plasma light according to another aspect of the present invention includes an external electrode and a center electrode that are disposed so as to face each other on an axis, and are disposed so as to be separated from the center electrode. In a pair of coaxial electrodes that generate plasma that radiates ultraviolet light and confine the plasma, a step of applying a voltage between the center electrode and the external electrode, and a vapor of a plasma medium for generating plasma as the center electrode Supplying between the external electrode and supplying the vapor of the plasma medium between the central electrode and the external electrode includes irradiating the plasma medium with laser light, and irradiating the laser light In this step, the laser beam is irradiated to the plasma medium while changing the irradiation position of the laser beam in the plasma medium.

  In this plasma light generation method, the irradiation position of the laser light in the plasma medium exposed to the opening is changed. Thereby, the temperature rise at the irradiation position of the laser beam is suppressed, and the state in which the laser beam is irradiated onto the mirrored plasma medium is avoided. Accordingly, since the ratio of the reflected laser light is reduced as compared with the case where the laser light is continuously applied to one point of the plasma medium, the reduction of the energy of the laser light absorbed by the plasma medium is suppressed. Thereby, the supply of energy for generating ablation to the plasma medium is stabilized, so that the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  The step of supplying the vapor of the plasma medium between the central electrode and the external electrode includes the step of controlling the temperature of the plasma medium, and the plasma medium holding unit holding the plasma medium so that the plasma medium is exposed from the opening. A step of supplying a medium; and a step of irradiating the plasma medium exposed from the opening with a laser beam, and in the step of controlling the temperature, the surface temperature of the plasma medium exposed from the opening is below the melting point of the plasma medium. As such, the temperature of the plasma medium may be controlled. In this plasma light generation method, the temperature of the plasma medium is controlled so that the surface temperature of the plasma medium exposed from the opening is equal to or lower than the melting point of the plasma medium. According to this control, the solid plasma medium and the liquid plasma medium can coexist in the opening. For example, a solid plasma medium has a thin film shape and is in a floating state on a liquid plasma medium. On the surface of such a plasma medium, the light reflectance is lower than that of a surface in which the plasma medium is entirely liquid. Therefore, since the reflection of the laser beam irradiated to the plasma medium is suppressed, a decrease in the energy of the laser beam absorbed by the plasma medium is suppressed. Thereby, the supply of energy for generating ablation to the plasma medium is stabilized, so that the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  In the step of irradiating the laser beam, the laser beam may be irradiated to the plasma medium while reducing the energy supplied to the plasma medium by irradiating the plasma medium with the laser beam. This method of generating plasma light reduces the energy supplied to the plasma medium by laser light irradiation. This decrease in energy suppresses a temperature rise on the surface of the plasma medium. Therefore, since the mirror surface of the plasma medium is prevented from being mirrored, a decrease in the energy of the laser light absorbed by the plasma medium is suppressed. Accordingly, since the supply of energy for generating ablation to the plasma medium is stabilized, the vapor of the plasma medium is stably generated. For this reason, the vapor | steam of a plasma medium can be stably supplied between a center electrode and an external electrode.

  According to the present invention, the plasma medium can be stably supplied between the center electrode and the external electrode.

FIG. 1 is a diagram illustrating a configuration of a plasma light source according to the first embodiment. FIG. 2 is a diagram illustrating a configuration of the coaxial electrode and the optical path control unit illustrated in FIG. 1. FIG. 3 is a diagram showing the irradiation position of the laser beam. FIG. 4 is a diagram illustrating a configuration of the plasma medium supply unit. FIG. 5 is a flowchart showing steps of generating plasma light according to the first embodiment. FIG. 6 is a diagram illustrating scanning of laser light on the plasma medium. FIG. 7 is a diagram for explaining the operation of the plasma light source. FIG. 8 is a graph showing the supply amount of the plasma medium. FIG. 9 is a diagram illustrating a configuration of a plasma light source according to the second embodiment. FIG. 10 is a diagram illustrating a configuration of a plasma medium supply unit according to the second embodiment. FIG. 11 is a flowchart showing steps of generating plasma light according to the second embodiment. FIG. 12 is a photograph showing the appearance of the surface of the plasma medium. FIG. 13 is a diagram illustrating a configuration of a plasma light source according to the first modification. FIG. 14 is a diagram illustrating a configuration of the coaxial electrode and the optical path control unit illustrated in FIG. 13. FIG. 15 is a flowchart showing steps of generating plasma light according to the first modification. FIG. 16 is a diagram illustrating the operation of the focus control unit. FIG. 17 is a diagram illustrating a position where the plasma medium supply unit is arranged in the plasma light source according to the second modification. FIG. 18 is a diagram illustrating a current path formed when the plasma light source according to the second modification is operated. FIG. 19 is a diagram illustrating a position where the plasma medium supply unit is arranged in the plasma light source according to the third modification.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

<First Embodiment>
The plasma light source 1 shown in FIG. 1 employs a so-called opposed plasma focus method. The plasma focus method is devised in the field of nuclear fusion, and includes a coaxial electrode 10 having a center electrode 11 and a plurality of external electrodes 12 surrounding the center electrode 11. When the opposed plasma focus type plasma light source 1 operates, first, a high voltage is applied between the center electrode 11 and the external electrode 12. A ring-shaped initial plasma is generated between the center electrode 11 and the external electrode 12 by inputting some trigger. The initial plasma moves toward the tip of the center electrode 11 by electromagnetic force. The initial plasma converges at the tip of the center electrode 11 and reaches a high temperature and high density state.

  In a plasma light source 1 that employs a counter-type plasma focus system, coaxial electrodes 10 as plasma sources are disposed so as to face each other. Then, plasmas reaching the tip of each center electrode 11 collide with each other, whereby high-temperature and high-density plasma is formed. Extreme ultraviolet light is generated from this high temperature and high density plasma.

  One method for generating initial plasma is a method in which a plasma medium is evaporated (ablated) with laser light. By irradiating a solid or liquid plasma medium with laser light, the plasma medium is evaporated to generate medium vapor. A discharge is generated between the center electrode 11 and the external electrode 12 through the medium vapor. The plasma medium may be solid, liquid, or gas, and is selected according to the wavelength of light to be generated. In the opposed plasma focus method, liquid or solid lithium may be used as a plasma medium.

  Hereinafter, the plasma light source 1 according to the embodiment will be described with reference to FIG. The plasma light source 1 is applied to, for example, an exposure apparatus for manufacturing a semiconductor element. The plasma light source 1 is configured to generate extreme ultraviolet light (EUV light) having a wavelength of 13.5 nm, for example. The plasma light source 1 enables photolithography to form a fine pattern by generating EUV light.

  The plasma light source 1 includes a pair of coaxial electrodes 10 that generate plasma, a voltage application device 20 (voltage application unit) that generates a potential difference in the coaxial electrode 10, a medium vapor formation unit 30 that forms medium vapor, and plasma A plasma medium supply unit 41 for supplying a medium.

  The pair of coaxial electrodes 10 are accommodated in the chamber 2 and are disposed on the axis A so as to face each other. The pair of coaxial electrodes 10 are arranged symmetrically with respect to the virtual central plane P. A constant space (space) is provided between the pair of coaxial electrodes 10. One or a plurality of exhaust pipes 3 are provided in the chamber 2, and a vacuum pump (not shown) is connected to the exhaust pipe 3. The inside of the chamber 2 is maintained at a predetermined degree of vacuum. The chamber 2 is grounded. The coaxial electrode 10 includes one central electrode 11, a plurality of external electrodes 12, and one insulator 13.

  The center electrode 11 is a rod-shaped conductor extending along the axis A. In other words, the center electrode 11 of the left coaxial electrode 10 in FIG. 1 extends toward the right coaxial electrode 10. The center electrode 11 is made of a metal that is not easily damaged by high-temperature plasma. The center electrode 11 is made of a refractory metal such as tungsten (W) or molybdenum (Mo). The axis A of the center electrode 11 is orthogonal to the above-described center plane P. The end surface of the center electrode 11 facing the center surface P has, for example, a hemispherical shape. The side surface of the center electrode 11 has a conical shape, for example.

  In FIG. 1, the external electrode 12 of the left coaxial electrode 10 is a rod-shaped conductor extending toward the right coaxial electrode 10. The external electrode 12 may extend in a direction inclined with respect to the axis A. For example, the external electrode 12 may extend in a direction parallel to the side surface of the center electrode 11 so that the distance from the side surface of the conical center electrode 11 to the external electrode 12 is always constant. The external electrode 12 is made of a metal that is not easily damaged by high-temperature plasma. The external electrode 12 is made of a refractory metal such as tungsten (W) or molybdenum (Mo). The end surface of the external electrode 12 facing the central surface P may be a curved surface or a flat surface.

  As shown in FIG. 2, the external electrode 12 is disposed around the center electrode 11. The external electrode 12 has a predetermined interval with respect to the center electrode 11. The plurality of external electrodes 12 are arranged at equal intervals (that is, rotationally symmetric) in the circumferential direction of the axis A. The coaxial electrode 10 has six external electrodes 12. The six external electrodes 12 are arranged every 60 ° with respect to the axis A. Note that the number of external electrodes 12 is not limited to six, and can be appropriately set according to the size and shape of the center electrode 11 and the external electrode 12, the distance between them, and the like. By disposing a plurality of external electrodes 12 around the center electrode 11, initial discharge (for example, creeping discharge) is generated between the center electrode 11 and the external electrode 12. This initial discharge reaches the sheet discharge 6 (see FIG. 7).

  As shown in FIG. 1 again, the insulator 13 is, for example, a ceramic plate having a disk shape. The insulator 13 supports the base portions of the center electrode 11 and the external electrode 12 and defines the distance therebetween. The insulator 13 electrically insulates the center electrode 11 and the external electrode 12 from each other.

  The voltage application device 20 generates a potential difference by applying a discharge voltage of the same polarity or reverse polarity to the coaxial electrode 10. The voltage application device 20 includes two high-voltage power supplies (HV Charging Devices) 21 and 22. The output side of the first high-voltage power supply 21 is connected to the center electrode 11 of one coaxial electrode 10 (for example, on the left side in the drawing). The first high-voltage power source 21 applies a positive discharge voltage higher than that of the external electrode 12 corresponding to the center electrode 11. The first high voltage power supply 21 may apply a negative discharge voltage lower than that of the external electrode 12 corresponding to the center electrode 11. The output side of the second high-voltage power source 22 is connected to the center electrode 11 of the other coaxial electrode 10 (for example, on the right side in the drawing). The second high-voltage power supply 22 applies a positive discharge voltage higher than that of the external electrode 12 corresponding to the center electrode 11. The second high voltage power supply 22 may apply a negative discharge voltage lower than that of the external electrode 12 corresponding to the center electrode 11. Any external electrode 12 may be grounded. In the following description, the first high-voltage power supply 21 is simply referred to as the power supply 21. Similarly, the second high-voltage power supply 22 is simply referred to as the power supply 22.

  In addition, the common side (return side) of the power supplies 21 and 22 may be provided with a line inductively coupled using a Rogowski coil or the like. With these lines, the current passing through the center electrode 11 (that is, all discharge currents) can be observed with an oscilloscope (Oscilloscope).

  The plasma light source 1 further includes an energy storage circuit 26 that stores the discharge voltage from the voltage application device 20 as discharge energy for each external electrode 12. The energy storage circuit 26 includes a plurality of capacitors 26 a that individually connect the center electrode 11 and the external electrode 12. The capacitor 26 a is connected to the output side and the common side of the power supplies 21 and 22. By providing the capacitor 26 a for storing discharge energy for each external electrode 12, discharge can occur in all the external electrodes 12. That is, even when a slight shift occurs in the discharge generation timing, a large amount of discharge energy is prevented from being consumed by the first discharge generated. By providing the energy storage circuit 26, the ideal planar discharge 6 generated over the entire circumference of the center electrode 11 can be obtained in the coaxial electrode 10.

  The plasma light source 1 further includes a discharge current blocking circuit 28 that blocks the discharge current from returning to the voltage application device 20. The discharge current blocking circuit 28 includes an inductor 28a that connects between the external electrode 12 and the voltage application device 20 (specifically, the common side of the power supplies 21 and 22). Since the inductor 28a has a sufficiently high impedance with respect to the discharge current, the discharge current that has passed through the center electrode 11 and the external electrode 12 can be returned to the energy storage circuit 26 that is the generation source thereof. Thereby, it is possible to prevent the discharge energy accumulated in the capacitor 26a from being supplied to the external electrodes 12 other than the external electrode 12 directly connected to the capacitor 26a. As a result, it is possible to prevent the generation distribution of discharge in the circumferential direction of the center electrode 11 from being biased.

  The operation of the voltage application device 20 described above will be described. First, charges are stored (charged) in the capacitor 26a by the power sources 21 and 22 in advance. Then, when the vapor of the plasma medium M is supplied between the center electrode 11 and the external electrode 12, a current flows from the positive electrode side to the negative electrode side of the capacitor 26a. As this current, a current corresponding to the amount of charge accumulated in the capacitor 26a flows in a pulsed manner according to the time constant of the electric circuit. That is, the charge flows in the order of the center electrode 11, the sheet discharge 6, and the external electrode 12, and finally returns to the negative electrode side of the capacitor 26a. While this current flows, the planar discharge 6 emits light by moving to the tip of the center electrode 11 and converging as a single plasma at the tip.

  The medium vapor forming unit 30 includes a laser device 31 that emits a laser beam L, and provides the laser beam L to the plasma medium supply unit 41. For example, the beam diameter of the laser beam L is 30 mm. On the surface Ma of the plasma medium M (see FIG. 4) irradiated with the laser light L, a part of the plasma medium M is emitted as vapor (medium vapor) of the plasma medium M by ablation. The medium vapor includes neutral gas or ions. Further, the laser device 31 generates an initial discharge of plasma (that is, a planar discharge 6: see the part (b) of FIG. 7). The laser device 31 is, for example, a YAG laser, and outputs a fundamental wave or a double wave of the fundamental wave as a short-pulse laser beam L for ablation.

  The medium vapor forming unit 30 further includes an optical path control unit 32. As shown in FIG. 2, the optical path control unit 32 provides the laser light L to the plasma medium supply unit 41 by dividing the laser light L and changing the direction of the optical path of the laser light L. The optical path control unit 32 includes a beam splitter 34 and a mirror 35 (light reflection unit). The beam splitter 34 is disposed on the optical path of the laser light L emitted from the laser device 31. The beam splitter 34 transmits a part of the incident laser light L and reflects the rest in a direction corresponding to the incident direction. That is, the beam splitter 34 has an optical path parallel to the optical path direction of the incident laser light L and an optical path in a direction corresponding to the incident angle of the laser light L with respect to the optical path direction of the incident laser light L. Form. The mirror 35 reflects all of the incident laser light L in a direction corresponding to the incident direction. That is, the mirror 35 forms an optical path inclined by 90 ° with respect to the optical path direction of the incident laser light L.

  The arrangement of the beam splitter 34 and the mirror 35 shown in FIG. 2 is an example, and a necessary number of beam splitters 34 and mirrors 35 are used according to the positional relationship between the laser device 31 and the plasma medium supply unit 41. The optical path may be arranged so that a desired optical path is formed.

  In addition to the beam splitter 34 and the mirror 35, the optical path control unit 32 further includes an attitude control unit 36 that controls the attitude of the mirror 35. Specifically, the attitude control unit 36 is a device that rotates the mirror 35 around a predetermined axis A1 and controls the angle of the mirror 35 with respect to the laser light L incident on the mirror 35. As shown in FIG. 3, when the incident direction of the laser beam L is constant, if the mirror 35 is rotated clockwise by a minute angle, the incident angle of the laser beam L to the mirror 35 changes. The direction of the laser light L reflected by the mirror 35 changes corresponding to the incident angle of the laser light L. In this case, the irradiation position of the laser beam L changes. As described above, the reflection direction of the laser light L is changed by changing the angle of the mirror 35. When the reflection direction of the laser beam L changes, the irradiation position of the laser beam L to the plasma medium supply unit 41 changes.

  At the time of irradiation with the laser beam L, the discharge voltage by the voltage application device 20 has already been applied to the center electrode 11 and the external electrode 12 of the coaxial electrode 10. Therefore, when the ablation described above occurs, a discharge is induced between the center electrode 11 and the external electrode 12. Further, a planar discharge 6 is formed by this discharge.

  There is a possibility that the location where discharge occurs is limited to the irradiation region of the laser light L and the vicinity thereof. Therefore, it is preferable to irradiate a plurality of laser beams L at intervals along the circumferential direction of the axis A, and the number is at least two. This is based on an experimental result in which the region of the induced discharge has an opening angle of 180 degrees or more with the axis of the center electrode 11 as a base point. Considering this result, it is desirable to irradiate the laser beam L at a rotationally symmetric position with respect to the center electrode 11 as the number of irradiated portions is smaller. Note that simultaneous irradiation of a plurality of laser beams L can be easily achieved by forming a plurality of optical paths having optical path lengths using optical elements such as a beam splitter and a mirror.

  As shown in FIG. 4, the plasma medium supply unit 41 supplies a plasma medium M used for generating plasma light. The plasma medium M can be selected according to the required wavelength of ultraviolet rays. For example, when 13.5 nm ultraviolet light is required, the plasma medium M is lithium (Li), xenon (Xe), tin (Sn), or the like. When ultraviolet light with a wavelength of 6.7 nm is required, at least one of gadolinium (Gd), terbium (Tb), or the like is used as the plasma medium M.

  The plasma medium supply unit 41 includes a plasma medium holding unit 42, a plasma medium storage unit 43, a pressure supply unit 44, and a heat medium supply unit 45.

  The plasma medium holding part 42 is a groove having a concave cross section provided on the outer peripheral surface of the center electrode 11 and includes an opening 42a. The groove of the plasma medium holding part 42 is filled with a liquid plasma medium M. The liquid plasma medium M is supplied from the plasma medium storage unit 43 to the plasma medium holding unit 42 through a channel hole provided in the bottom surface of the plasma medium holding unit 42.

  The plasma medium storage unit 43 is provided in the center electrode 11 and stores a solid or liquid plasma medium M. The plasma medium storage unit 43 is a space provided inside the center electrode 11, and the space is filled with the plasma medium M. The plasma medium storage unit 43 is connected to the plasma medium holding unit 42 through a flow path hole. Further, the plasma medium storage unit 43 is connected to the pressure supply unit 44 through a pressure hole different from the flow path hole. The pressure supply unit 44 moves the plasma medium M stored in the plasma medium storage unit 43 to the plasma medium holding unit 42. Specifically, the pressure supply unit 44 supplies a gas having a predetermined pressure (for example, argon gas of 2.5 Torr) to the plasma medium storage unit 43 through the pressure hole. The plasma medium M is pushed out to the plasma medium holding part 42 by this pressure.

  The heat medium supply unit 45 supplies heat for melting the plasma medium M stored in the plasma medium storage unit 43 to the plasma medium storage unit 43 from the outside. The heat medium supply unit 45 includes an external tank 45a and a heat exchange unit 45b. The external tank 45a keeps the temperature of the heat medium at a predetermined temperature and supplies the heat medium to the heat exchange unit 45b. The heat exchanging unit 45 b is provided in the vicinity of the plasma medium storage unit 43 and supplies the heat of the heat medium to the plasma medium M. The heat medium also has a function of cooling the temperature of the center electrode 11 heated by the plasma. The heat medium receives the heat of the center electrode 11 while flowing in the center electrode 11 and discharges it to the outside.

  Subsequently, the operation of the plasma light source 1 will be described with reference to FIGS. 5, 6 and 7. 7A is a state when the laser beam L is irradiated, FIG. 7B is a state when the sheet discharge 6 is generated, and FIG. 7C is a state where the sheet discharge 6 is moving. FIG. 7D shows the state where the planar discharge 6 has reached the vicinity of the tip of the electrode, FIG. 7E shows the state during the initial confinement of the plasma 7, and FIG. Indicates the state of the high-temperature and high-density plasma 7.

  First, the inside of the chamber 2 is maintained at a temperature and pressure suitable for generating the plasma 7. A discharge voltage is applied to the coaxial electrode 10 before discharge by the voltage application device 20 (step S1: see FIG. 5). Next, medium vapor is supplied between the center electrode 11 and the external electrode 12 (step S2: see FIG. 5). This step S2 will be described in more detail. First, the pressure supply unit 44 supplies a gas having a predetermined pressure to the plasma medium storage unit 43. By supplying the gas having the predetermined pressure, the plasma medium M is supplied to the plasma medium holding unit 42 (step S4: see FIG. 5). Part of the plasma medium M supplied to the plasma medium holding unit 42 is exposed from the opening 42a. And the laser apparatus 31 irradiates the laser beam L with respect to the plasma medium M exposed from the opening part 42a (refer step S5: FIG. 5). In step S <b> 5, the irradiation position of the laser light L is changed on the surface Ma of the plasma medium M by the attitude control unit 36 controlling the angle of the mirror 35. For example, when the attitude control unit 36 changes the angle of the mirror 35, the irradiation position of the laser light L is scanned two-dimensionally along a preset trajectory R (step S5a). For example, as shown in FIG. 6, the posture control unit 36 is preset by changing the angle of the mirror 35 so that the irradiation position of the laser light L is not fixed at a predetermined position on the surface Ma of the plasma medium M. The irradiation position of the laser beam L is scanned two-dimensionally along the locus R.

  Further, as shown in FIG. 7A, when the plasma medium M of the plasma medium supply unit 41 is irradiated with the laser light L in a state where a discharge voltage is applied, immediately after that, the center electrode 11 and Discharge occurs between the external electrodes 12. A discharge occurs between each of the plurality of external electrodes 12 and the center electrode 11. As shown in part (b) of FIG. 7, the planar discharge 6 distributed over the entire circumference of the center electrode 11 is obtained.

  As shown in part (c) of FIG. 7, the planar discharge 6 moves in a direction (direction toward the central plane P) discharged from the electrode by the self magnetic field. The shape of the planar discharge 6 at this time is substantially annular when viewed from the axis A.

  Here, since the plasma light source 1 includes the energy storage circuit 26, the probability of occurrence of the planar discharge 6 is increased by the cooperation of the energy storage circuit 26 and the plurality of external electrodes 12. The plurality of external electrodes 12 arranged discontinuously at intervals makes it easier to form the planar discharge 6 than when a continuous tubular (tubular) external electrode is employed. Is advantageous.

  Thereafter, the planar discharge 6 reaches the tip of the coaxial electrode 10 as shown in FIG. When the sheet discharge 6 reaches the tip of the center electrode 11, the starting point of the discharge current is shifted from the side surface 11b of the center electrode 11 to the end surface 11a. Due to this current transition, the plasma containing lithium (Li) that has moved along with the pair of planar discharges 6 converges to become high density and high temperature.

  Since this phenomenon proceeds at the coaxial electrode 10 with the center plane P interposed therebetween, the initial plasma is pushed out from one coaxial electrode 10 toward the other coaxial electrode 10. As a result, the initial plasma receives pressure from both directions along the axis A and moves to an intermediate position where the coaxial electrode 10 faces (that is, the position of the central plane P), and a single plasma having the plasma medium M as a component. 7 is formed.

  As shown in part (e) of FIG. 7, even after the plasma 7 is formed, the current continues to flow through the planar discharge 6 so as to surround the plasma 7 as a whole, and the plasma 7 is near the middle of the center electrode 11. Hold on.

  While the planar discharge 6 is occurring, the density and temperature of the plasma 7 are increased, and ionization of ions including lithium (Li) proceeds. As a result, as shown in part (f) of FIG. 7, plasma light 9 including extreme ultraviolet light is emitted from the plasma 7. In this state, the plasma light 9 can be generated over a long period of time as the current continues to flow through the planar discharge 6.

  Here, ablation of the plasma medium M by irradiation with the laser beam L will be described. As already described, the plasma medium M is filled in the groove-shaped plasma medium holding part 42 of the plasma medium supply part 41 in a liquid state. The plasma medium M is exposed from the opening 42 a of the plasma medium holding unit 42. The laser beam L is applied to the surface of the plasma medium M exposed from the opening 42a. When the plasma medium M is in a liquid state, its surface has a high light reflectance. Therefore, when the laser beam L is irradiated onto the surface Ma of the plasma medium M, a part of the laser beam L is reflected, and the amount of energy supplied for causing ablation to the plasma medium M is reduced. This makes it difficult for the vapor of the plasma medium M to be stably generated. For this reason, it becomes difficult to stably supply the vapor of the plasma medium M between the center electrode 11 and the external electrode 12. In other words, the supply of the plasma medium M between the center electrode 11 and the external electrode 12 becomes unstable.

  FIG. 8 is a graph conceptually showing a time history of spectral intensity in the plasma medium M generated by ablation. The unstable supply of the plasma medium M here means a state in which the amount of the plasma medium M that is actually supplied gradually deviates from the supply target value G1 of the plasma medium M (FIG. 8). (See graph G3). That is, it does not indicate the fluctuation (the graph G2 in FIG. 8) of the amount actually supplied with respect to the supply target value G1 of the plasma medium M.

  When the laser beam L is irradiated to the plasma medium M, energy is provided to the plasma medium M. Accordingly, the temperature of the plasma medium M is higher at the irradiation position of the laser beam L than at the position where the laser beam L is not irradiated. When the temperature of the plasma medium M rises, the plasma medium M is melted and liquefied, and the surface thereof can be in a mirror state with high light reflectance.

  In the plasma light source 1 and the plasma light generation method of the present embodiment, the optical path control unit 32 changes the irradiation position of the laser light L in the plasma medium M exposed to the opening 42a. Thereby, the temperature rise in the irradiation position of the laser beam L is suppressed, and the state in which the laser beam L is irradiated onto the mirror-finished plasma medium M is avoided. Accordingly, since the ratio of the reflected laser light L is reduced as compared with the case where the laser light L is continuously applied to one point of the plasma medium M, the reduction in the energy of the laser light L absorbed by the plasma medium M is suppressed. Is done. As a result, the supply of energy for generating ablation to the plasma medium M is stabilized, so that the vapor of the plasma medium M is stably generated. For this reason, the vapor of the plasma medium M can be stably supplied between the center electrode 11 and the external electrode 12.

Second Embodiment
Next, a plasma light source according to the second embodiment will be described. As shown in FIG. 9, the plasma light source 1A according to the second embodiment is different from the plasma light source 1 in that it includes a plasma medium supply unit 41A. Since the other configuration of the plasma light source 1A is the same as that of the plasma light source 1, duplicate description is omitted. Hereinafter, the plasma medium supply unit 41A will be described in detail.

  As shown in FIG. 10, the plasma medium supply unit 41A includes a temperature control unit 46 in addition to the plasma medium holding unit 42, the plasma medium storage unit 43, the pressure supply unit 44, and the heat medium supply unit 45. Have

  The temperature controller 46 controls the temperature of the plasma medium M so that the solid plasma medium M and the liquid plasma medium M coexist in the opening 42a. If the surface temperature of the plasma medium M exposed from the opening 42a greatly exceeds the melting point of the plasma medium M, the solid plasma medium M cannot exist. Therefore, the surface temperature of the plasma medium M is controlled so as not to exceed the melting point of the plasma medium M, that is, not more than the melting point of the plasma medium M.

  Specifically, the temperature control unit 46 indirectly controls the temperature of the plasma medium M in the opening 42a. As described above, the external tank 45a of the heat medium supply unit 45 maintains the temperature of the heat medium at a predetermined temperature. The temperature control unit 46 sets the temperature of the heat medium in the external tank 45a. When the temperature of the heat medium is set to a predetermined temperature, the temperature of the plasma medium M in the plasma medium storage unit 43 converges to a temperature corresponding to the temperature of the heat medium. This convergence temperature is a temperature within a range 2 ° C. higher than the melting point of the plasma medium M and 1 ° C. lower than the melting point. For example, the convergence temperature range is 179 ° C. to 182 ° C. Then, the plasma medium M in the plasma medium storage unit 43 is moved from the plasma medium storage unit 43 to the plasma medium holding unit 42 and is affected by heat transfer until reaching the surface Ma irradiated with the laser light L. As a result, the plasma medium M on the surface Ma converges to a temperature slightly below the melting point of the plasma medium M.

  In short, the temperature control unit 46 controls the temperature of the heat medium so that the surface temperature of the plasma medium M does not exceed the melting point of the plasma medium M.

  In order to obtain the temperature of the plasma medium M, for example, the temperature acquisition unit 47 may be attached to the plasma medium storage unit 43. The temperature acquisition unit 47 may be provided in another place according to the convenience of temperature control of the plasma medium M. For example, the temperature acquisition unit 47 may be attached to the plasma medium holding unit 42 in order to obtain the temperature of the plasma medium M held by the plasma medium holding unit 42. The temperature acquisition unit 47 may be attached to a pipe connecting the external tank 45a and the heat exchange unit 45b in order to obtain the temperature of the heat medium supplied to the heat exchange unit 45b.

  The plasma light source 1A having the temperature control unit 46 operates according to the flow shown in FIG. In FIG. 11, steps S1, S4, and S5a are the same as in the first embodiment. Step S2 further includes a step S3 for controlling the temperature of the plasma medium M. In step S3, the temperature control unit 46 indirectly controls the surface temperature of the plasma medium M. Specifically, the temperature of the heat medium is set so that the plasma medium M in the plasma medium reservoir 43 is in a temperature range that is 2 ° C. higher than the melting point of the plasma medium M and 1 ° C. lower than the melting point.

  The plasma light source 1A includes first and second means for suppressing mirroring on the surface Ma of the plasma medium M. As a first means, the plasma light source 1 </ b> A has an optical path control unit 32. According to the attitude control unit 36 of the optical path control unit 32, the irradiation position of the laser light L on the surface Ma of the plasma medium M can be controlled. As a second means, the plasma light source 1 </ b> A has a temperature control unit 46. According to the temperature controller 46, the temperature of the plasma medium M is controlled so that the surface Ma of the plasma medium M exposed from the opening 42a includes the solid plasma medium M and the liquid plasma medium M. it can.

  The second means will be specifically described. In the plasma light source 1A and the plasma light generation method of the present embodiment, the surface temperature of the plasma medium M exposed from the opening 42a is equal to or lower than the melting point of the plasma medium M. The temperature of the plasma medium M is controlled. According to this control, the solid plasma medium M and the liquid plasma medium M can coexist in the opening 42a. For example, the solid plasma medium M is in the form of a thin film and floats on the liquid plasma medium M. On the surface of such a plasma medium M, the light reflectance is reduced as compared with a surface in which the plasma medium M is entirely liquid. Therefore, since the reflection of the laser beam L irradiated to the plasma medium M is suppressed, the energy reduction of the laser beam L absorbed by the plasma medium M is suppressed. As a result, the supply of energy for generating ablation to the plasma medium M is stabilized, so that the vapor of the plasma medium M is stably generated. For this reason, the vapor of the plasma medium M can be stably supplied between the center electrode 11 and the external electrode 12.

  In the plasma light source 1 </ b> A having the first means and the second means described above, since the mirror surface on the surface Ma of the plasma medium M is suitably suppressed, the plasma medium M between the center electrode 11 and the external electrode 12 is suppressed. Steam can be supplied more stably.

<Example>
The relationship between the temperature of the constant temperature oil which is a heat medium and the state of the surface Ma of the plasma medium M was confirmed. In this embodiment, the plasma medium M is lithium (melting point: 180.54 ° C.). The (a) part of FIG. 12 is a photograph of the surface Ma of the plasma medium M when the temperature of the constant temperature oil is set to 185 ° C. (B) part of FIG. 12 is the photograph which image | photographed the surface Ma of the plasma medium M when the temperature of constant temperature oil is set to 180 degreeC. As shown in part (a) of FIG. 12, it was found that when a constant temperature oil set to 185 ° C. was provided, a strong light reflection region E1 was present on the surface Ma of the plasma medium M. . Therefore, it has been found that when the constant temperature oil set at 185 ° C. is provided, the mirror surface on the surface Ma of the plasma medium M cannot be suppressed. On the other hand, as shown in part (b) of FIG. 12, when the constant temperature oil set to 180 ° C. is provided, there is almost no strong light reflection region on the surface Ma of the plasma medium M, and the reflectance It has been found that there is a region E2 having a low. Thereby, when providing the thermostat set to 180 degreeC, it turned out that mirror surface formation in the surface Ma of the plasma medium M can be suppressed.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

<Modification 1>
For example, as illustrated in FIG. 13, the medium vapor forming unit 30 </ b> A may include a laser device 31, an optical path control unit 32 </ b> A, and an energy control unit 33.

  The energy control unit 33 reduces the energy supplied to the plasma medium M by irradiating the plasma medium M with the laser light L. As shown in FIG. 14, the energy control unit 33 includes a focus control unit 37. The focus control unit 37 is disposed between the optical path control unit 32A and the plasma medium supply unit 41A, and adjusts the condensing position of the laser light L with respect to the plasma medium M. The focus control unit 37 includes a lens 37a and a lens driving unit 37b. The lens 37a is disposed between the mirror 35 of the optical path control unit 32A and the plasma medium supply unit 41A on the optical path, and converges the laser light L to the focal position FP. For example, the focal length of the lens 37a is 300 mm. The lens driving unit 37b reciprocates the lens 37a along the direction of the optical axis A2 of the lens 37a. As shown in FIGS. 16A, 16B, and 16C, when the lens 37a is moved, the focal position FP of the laser light L is also along the optical axis A2 corresponding to the movement of the lens 37a. Move. For example, the lens driving unit 37b sets the focal position FP of the laser light L to the surface Ma of the plasma medium M (see the part (a) in FIG. 16). In addition, the lens driving unit 37b sets the focal position FP of the laser light L to a position away from the surface Ma of the plasma medium M (see the parts (b) and (c) in FIG. 16).

  In addition, the energy control part 33 may have the light intensity control part 39 (refer FIG. 13) connected to the laser apparatus 31 as needed. The light intensity control unit 39 controls the light intensity of the laser light L emitted from the laser device 31.

  The plasma light source 1B having the energy control unit 33 operates according to the flow shown in FIG. In FIG. 15, steps S1, S4, and S5a are the same as in the first embodiment. Step S3 is the same as in the second embodiment. Step S5 further includes step S5b in addition to step S5a. Step S5b controls the focal position FP. When it is determined that the surface Ma of the plasma medium M is being mirror-finished, the lens driving unit 37b is driven, and the focal position FP of the laser light L is separated from the surface Ma of the plasma medium M (for example, FIG. 16 (see part (b)). That is, step S5b is executed when necessary according to the state of the surface Ma of the plasma medium M. Execution of step S5b may be determined based on, for example, an image of the surface Ma of the plasma medium M, or may be determined based on the spectrum of the plasma medium M in the chamber 2.

  The plasma light source 1B includes first means, second means, and third means for suppressing mirroring on the surface Ma of the plasma medium M. As a first means, the plasma light source 1B has an optical path control unit 32A. According to the attitude control unit 36 of the optical path control unit 32A, the irradiation position of the laser light L on the surface Ma of the plasma medium M can be controlled. As a second means, the plasma light source 1 </ b> B has a temperature control unit 46. According to the temperature controller 46, the temperature of the plasma medium M is controlled so that the surface Ma of the plasma medium M exposed from the opening 42a includes the solid plasma medium M and the liquid plasma medium M. it can. As a third means, the plasma light source 1 </ b> B has an energy control unit 33. The focus control unit 37 of the energy control unit 33 can control the focus position FP of the laser light L.

  The third means will be specifically described. In the plasma light source 1B and the plasma light generation method of the present embodiment, the focus control unit 37 constituting the energy control unit 33 determines the focus position FP of the laser light L, that is, the condensing position. Control. The focus control unit 37 adjusts the focus position FP of the laser light L to the surface Ma of the plasma medium M (see the part (a) in FIG. 16). When the irradiation of the laser beam L is continued in a state where the focal position FP of the laser beam L is adjusted to the surface Ma of the plasma medium M, the temperature of the surface Ma of the plasma medium M at the irradiation position increases, and the mirror surface progresses. In this case, the focus control unit 37 adjusts the focus position FP of the laser light L to a position separated from the surface Ma of the plasma medium M (see the parts (b) and (c) in FIG. 16). Then, since the laser beam L is not focused on the surface Ma of the plasma medium M, the energy density of the laser beam L at the irradiation position decreases. Accordingly, since the supply of energy to the plasma medium M is suppressed, the temperature rise on the surface Ma of the plasma medium M is suppressed. Therefore, since the mirror surface of the surface Ma of the plasma medium M is suppressed, the reflection of the laser light L is suppressed. For this reason, the fall of the energy of the laser beam L absorbed by the plasma medium M is suppressed. Accordingly, since the supply of energy for generating ablation with respect to the plasma medium M is stabilized, the vapor of the plasma medium M is stably generated. For this reason, the vapor of the plasma medium M can be stably supplied between the center electrode 11 and the external electrode 12.

  In the plasma light source 1B having the first means, the second means, and the third means, the mirror surface on the surface Ma of the plasma medium M is preferably suppressed, so that the center electrode 11 and the external electrode 12 In the meantime, the vapor of the plasma medium M can be supplied more stably.

<Modification 2>
In the plasma light source 1, the plasma medium supply unit 41 is provided in the center electrode 11. The plasma medium supply unit 41 may not be provided on the center electrode 11.

  As shown in FIG. 17, the plasma light source 1C according to the modified example has two plasma medium supply parts 41B for one coaxial electrode 10A. The number of plasma medium supply parts 41B is not limited to two, and can be set as appropriate according to the size and shape of the coaxial electrode 10A. The pair of plasma medium supply parts 41B is disposed around the coaxial electrode 10A. Specifically, the pair of plasma medium supply units 41B are arranged around the axis A with an interval of 180 degrees. In other words, the pair of plasma medium supply parts 41 </ b> B are arranged point-symmetrically with respect to the axis A. Further, the pair of plasma medium supply parts 41B are arranged at positions where the distances from the axis A are equal to each other. Further, the pair of plasma medium supply parts 41 </ b> B are arranged at equal intervals on a virtual circumferential line centering on the axis A. In addition, the plasma medium supply unit 41B is disposed between the tip of the center electrode 11A and the insulator 13 in the direction of the axis A.

  The position where the plasma medium supply unit 41B is disposed will be described in detail. The plasma medium supply unit 41B is not in physical contact with the center electrode 11A and the external electrode 12. First, a virtual plane orthogonal to the axis A is defined. FIG. 17 shows the end face of the coaxial electrode 10A in this virtual plane. Each of the six external electrodes 12 has an axis B. Then, an imaginary line B2 passing through the axis B of the adjacent external electrodes 12 is defined. Then, in the coaxial electrode 10A, six virtual lines B2 are defined, and a hexagonal region BS surrounded by these six virtual lines B2 is defined. The center electrode 11A is disposed at the center of this region BS. On the other hand, the plasma medium supply unit 41B is disposed outside the region BS. In short, the plasma medium supply unit 41B is disposed outside the closed region BS including all the external electrodes 12 and surrounding the center electrode 11A. It can be said that the plasma medium supply unit 41B and the center electrode 11A are arranged with the virtual line B2 interposed therebetween.

  Here, the electrical state in the plasma light source 1C in operation will be described. FIG. 18 shows a current path K formed by the coaxial electrode 10A and the voltage application device 20 when the polarity of the center electrode 11A is positive. As shown in FIG. 18, the current path K reaches the center electrode 11A from the positive electrode side of the capacitor 26a through the electric circuit. Here, although the center electrode 11A and the external electrode 12 are physically separated from each other, during operation, the medium vapor V exists between the center electrode 11A and the external electrode 12, so that the sheet discharge 6 is generated. Occur. Therefore, the current reaches the external electrode 12 from the central electrode 11A via the medium vapor V. Then, the external electrode 12 reaches the negative electrode side of the capacitor 26a through an electric circuit.

  The plasma medium supply unit 41B is not incorporated in the current path K formed by the voltage application device 20 and the coaxial electrode 10A. Further, the current flowing through the coaxial electrode 10A when plasma light is generated does not flow into the plasma medium supply unit 41B. That is, the plasma medium supply unit 41B is electrically insulated from the current path K.

  The plasma medium supply unit 41B only needs to be electrically disconnected from the current path K. The plasma medium supply unit 41B that is electrically disconnected from the current path K may be electrically grounded. According to this electrical configuration, charging of the plasma medium M is prevented. Further, according to this electrical configuration, the potential of the plasma medium M can be made constant without being affected by the high voltages of the center electrode 11A and the external electrode 12.

  Further, the plasma medium supply unit 41B electrically disconnected from the current path K may be connected to a predetermined potential. Specifically, the plasma medium holding unit 42B that holds the plasma medium M is formed of a conductive material such as metal, and a potential is applied to the plasma medium holding unit 42B. For example, according to the configuration connected to a relatively low potential, the potential of the plasma medium M can be positively stabilized. In addition, ionization of the plasma medium M is promoted. This ionized plasma medium M is more likely to trigger a discharge than a neutral gas. As an example, when the plasma medium M is lithium and a positive potential is applied to the plasma medium M, a part of lithium floats as lithium ions (positive ions) by laser ablation. The positive ions that have reached the discharge space are more likely to be a discharge trigger than the neutral gas.

  In addition, as long as the plasma medium supply unit 41B is electrically disconnected from the current path K, the plasma medium supply unit 41B may be in an electrically floating state.

  In the plasma light source 1C, medium vapor V is supplied between the center electrode 11A and the external electrode 12 during operation. This medium vapor V induces a discharge between the center electrode 11A and the external electrode 12. When the planar discharge 6 is generated between the center electrode 11A and the external electrode 12, a current path K is formed through the center electrode 11A, the medium vapor V, and the external electrode 12. Here, since the plasma medium supply unit 41B is electrically insulated from the current path K, the current flowing through the current path K does not pass through the plasma medium supply unit 41B. When current flows through the conductor, Joule heat is generated, but since no current flows through the plasma medium supply unit 41B, Joule heat is not generated. Accordingly, since the temperature rise of the plasma medium M is suppressed and the state of the plasma medium M is stabilized, it is possible to stably cause the ablation of the plasma medium M. As a result, the vapor of the plasma medium M can be stably supplied between the center electrode 11A and the external electrode 12.

  Since the plasma medium supply unit 41B is not disposed on the center electrode 11A and the external electrode 12, it can be separated from charge / discharge for generating plasma. Therefore, the plasma medium M can be continuously and stably supplied between the center electrode 11A and the external electrode 12 to which a high voltage and a high current are applied.

  The temperature of the center electrode 11A and the external electrode 12 may increase due to heat input from the plasma. However, in the plasma light source 1C of the present embodiment, since the plasma medium supply unit 41B is not disposed on the center electrode 11A and the external electrode 12, the influence of the temperature of the center electrode 11A and the external electrode 12 is suppressed, and the plasma medium M Can be easily maintained in a certain state. For this reason, it is possible to prevent the plasma medium M from being excessively heated and causing unintended evaporation. Basically, EUV light must be handled in a vacuum. According to the plasma light source 1 </ b> C, unintended evaporation is suppressed, so that the inside of the chamber 2 can be easily maintained at a predetermined pressure, so that the pressure environment of the discharge space can be maintained.

  In short, in the plasma light source 1C, since the plasma medium M is electrically disconnected from the current path K, it is released from a high voltage / high current environment. Accordingly, a situation where the plasma medium M flows or scatters due to discharge or the like is avoided. The plasma light source 1C facilitates continuous and more stable supply. In the plasma light source 1C, the plasma medium M is also physically separated from the central electrode 11A and the external electrode 12 where the temperature is high. Accordingly, since the temperature rise of the plasma medium M is also suppressed, the temperature of the plasma medium M can be controlled separately from the center electrode 11A and the external electrode 12. For this reason, it becomes easy to keep the vapor pressure of the plasma medium M constant.

  As described above, in the plasma light source 1C, the plasma medium M is released from the electrical influence, the supply method and temperature control of the plasma medium M are facilitated, and the medium supply to the discharge space is easily controlled. M can be stabilized electrically, and ionization of the plasma medium M can be promoted. As a result, it is possible to improve the output stability and emission intensity of the plasma light source 1C. Further, the specifications of the cooling function of the center electrode 11A and the external electrode 12 can be relaxed without being restricted by the temperature restriction of the plasma medium M.

  In the plasma light source 1C, the position where the vapor of the plasma medium M is generated is different from the position where the plasma 7 is generated. According to this configuration, EUV light generated from the plasma 7 is not hindered by the vapor of the plasma medium M. Therefore, EUV light can be emitted efficiently.

<Modification 3>
As illustrated in FIG. 19, the plasma light source 1 </ b> D may further include a limiter 50 (supply control unit). The limiter 50 controls the direction in which the medium vapor V diffuses and the supply amount of the medium vapor V. The limiter 50 is disposed between the plasma medium supply unit 41B and the coaxial electrode 10A. The limiter 50 includes a plate-shaped main body 51 (shielding portion), a light transmission portion 52 provided in the main body 51, and a through hole 53. The light transmission part 52 may be a through hole or a transparent member with respect to laser light such as glass. The laser beam L is applied to the plasma medium M through the light transmission part 52. The plasma medium M irradiated with the laser light L is ablated and a medium vapor V is generated. The medium vapor V diffuses radially around the plasma medium M. A part of the medium vapor V is blocked by the main body 51 of the limiter 50 and does not reach the coaxial electrode 10A. Another medium vapor V passes through the through-hole 53 and reaches the coaxial electrode 10A. That is, since it becomes possible to give directionality to the diffusion of the medium vapor V, the medium vapor V can be supplied to a desired position in the discharge space. Therefore, plasma diffusion in the direction of the axis A can be suppressed, and the discharge start position can be limited to a desired range. When the discharge positions in the direction of the axis A of the external electrode 12 are aligned, plasma convergence is improved and high-temperature and high-density plasma can be formed.

1, 1A, 1B, 1C, 1D Plasma light source 2 Chamber 3 Exhaust pipe 6 Surface discharge 7 Plasma 9 Plasma light 10, 10A Coaxial electrode 11, 11A Center electrode 11a End surface 11b Side surface 12 External electrode 13 Insulator 20 Voltage application device 21 First High Voltage Power Supply 22 Second High Voltage Power Supply 26 Energy Storage Circuit 26a Capacitor 28 Discharge Current Blocking Circuit 28a Inductor 30, 30A Medium Vapor Forming Unit 31 Laser Device 32, 32A Optical Path Control Unit 33 Energy Control Unit 34 Beam Splitter 37 Focus Control Unit 37a Lens 37b Lens drive unit 39 Light intensity control unit 35 Mirror 36 Attitude control unit 41, 41A, 41B Plasma medium supply unit 42, 42B Plasma medium holding unit 42a Opening 43 Plasma medium storage unit 44 Pressure supply unit 45 Heat medium supply unit 45a External tank 45b Heat exchange part 4 Temperature control unit 47 the temperature acquiring unit 50 the limiter 51 body 52 the light transmitting portion 53 through hole A axis B axis B2 imaginary line BS region L laser beam P center plane K current path R locus V medium vapor

Claims (9)

An axial electrode is disposed so as to face each other, and has a central electrode and an external electrode disposed so as to be separated from the central electrode, and an insulator that insulates the central electrode from the external electrode, and emits extreme ultraviolet light. A pair of coaxial electrodes for generating radiating plasma and confining said plasma;
A plasma medium supply unit for supplying a plasma medium for generating the plasma;
A medium vapor forming unit that irradiates the plasma medium with laser light, and
The medium vapor forming part is
A laser device for generating the laser beam;
An optical path control unit disposed on the optical path of the laser light and changing an irradiation position of the laser light in the plasma medium. The plasma medium supply unit includes an opening, and includes a plasma medium holding unit that holds the plasma medium so that the plasma medium is exposed from the opening.
The plasma light source according to claim 1, wherein the optical path control unit controls the optical path so that the laser beam scans the surface of the plasma medium exposed from the opening. The optical path control unit is
A light reflecting portion arranged on the optical path and reflecting the laser beam;
An attitude control unit that changes the orientation of the optical path of the laser beam reflected by the light reflecting unit by changing the attitude of the light reflecting unit with respect to the laser light incident on the light reflecting unit;
The plasma light source according to claim 1, comprising: The plasma medium supply unit is provided on the center electrode,
The plasma light source according to any one of claims 1 to 3, wherein the opening of the plasma medium supply unit is provided on an outer peripheral surface of the center electrode.   The plasma light source according to any one of claims 1 to 4, wherein the medium vapor forming unit includes an energy control unit that reduces energy supplied to the plasma medium by irradiating the plasma medium with the laser beam. . The plasma medium supply unit includes:
A plasma medium holding unit that includes an opening, and holds the plasma medium such that the plasma medium is exposed from the opening;
A plasma medium storage unit that stores the plasma medium and provides the plasma medium to the plasma medium holding unit;
A temperature control unit for controlling the temperature of the plasma medium,
6. The temperature control unit according to claim 1, wherein the temperature control unit controls the temperature of the plasma medium so that a surface temperature of the plasma medium exposed from the opening is equal to or lower than a melting point of the plasma medium. The plasma light source described. An axial electrode is disposed so as to face each other, and has a central electrode, an external electrode disposed so as to be separated from the central electrode, and the central electrode, and generates plasma that emits extreme ultraviolet light and emits the plasma. Applying a voltage between the central electrode and the external electrode in a pair of coaxial electrodes to be confined;
Supplying a vapor of a plasma medium for generating the plasma between the central electrode and the external electrode,
Supplying the vapor of the plasma medium between the central electrode and the external electrode,
Irradiating the plasma medium with laser light,
In the step of irradiating the laser beam, the plasma medium is irradiated with the laser beam while changing the irradiation position of the laser beam in the plasma medium. Supplying the vapor of the plasma medium between the central electrode and the external electrode,
Controlling the temperature of the plasma medium;
Supplying the plasma medium to a plasma medium holding unit that holds the plasma medium so that the plasma medium is exposed from the opening;
Irradiating the plasma medium exposed from the opening with a laser beam, and
8. The generation of plasma light according to claim 7, wherein in the step of controlling the temperature, the temperature of the plasma medium is controlled so that the surface temperature of the plasma medium exposed from the opening is equal to or lower than the melting point of the plasma medium. Method.   The step of irradiating the laser beam includes irradiating the plasma medium with laser light while reducing energy supplied to the plasma medium by irradiating the plasma medium with the laser light. Of plasma light generation.