JP5849746B2 - Plasma light source - Google Patents

Description

  The present invention relates to a plasma light source that generates extreme ultraviolet light.

  Photolithography, which is one factor that determines a process rule, is an extremely important technique for further miniaturization of semiconductor circuits. Currently, a process rule of about 45 nm is obtained by combining an ArF excimer laser (wavelength 193 nm) with a liquid immersion technique, but light with a shorter wavelength is required to cope with further miniaturization. Under such circumstances, an extreme ultraviolet (EUV) light source (also referred to as a soft X-ray source) is most promising as a next-generation photolithography light source that generates light shorter than the laser light.

  As a method for generating extreme ultraviolet light, there is a method using high energy density plasma. In this method, high-temperature plasma is generated in a plasma light source, and extreme ultraviolet light emitted as radiation is used for exposure. The high-temperature plasma is mainly generated by a laser generated plasma (LPP) method using pulsed laser irradiation or a discharge plasma (DPP) method using pulse discharge. In any of the above methods, the generated light is pulsed light.

  Patent Document 1 discloses a plasma light source and a plasma light generation method created by the inventors of the present application. The plasma light source of the same document includes a pair of coaxial electrodes disposed to face a symmetry plane. Each coaxial electrode is composed of a central electrode, a guide electrode, and an insulating member, and the central axes of the coaxial electrodes are located on the same line. The guide electrode is a cylindrical electrode surrounding the center electrode, and a coaxial structure is formed by the guide electrode and the center electrode. The insulating member is located between the center electrode and the guide electrode and at a position away from the symmetry plane, defines the positions of the center electrode and the guide electrode, and supports both. On the surface of the insulating member, a metal such as Li that becomes a plasma medium described later is deposited.

  High voltage pulses having opposite polarities are applied to the pair of coaxial electrodes. By applying the high voltage pulse, a planar discharge current (planar discharge) is generated between the center electrode and the guide electrode of each coaxial electrode. The planar discharge receives a force by the self magnetic field and moves toward the plane of symmetry. Furthermore, when each planar discharge reaches the tip of each coaxial electrode, the plasma medium sandwiched between the two planar discharges becomes high density and high temperature, and a single plasma is generated between the two central electrodes. To do.

  On the other hand, the polarities of the voltages applied to each of the pair of opposed center electrodes are opposite to each other. Similarly, the polarities of the voltages applied to the pair of opposing guide electrodes are also opposite to each other. Therefore, the planar discharge between the center electrode and the guide electrode in each coaxial electrode is replaced with the discharge between the pair of center electrodes and the discharge between the pair of guide electrodes. The discharge after the replacement is changed into a hollow and tubular discharge (tubular discharge) along the central axis of each coaxial electrode.

  When the tubular discharge is generated, a magnetic field (magnetic bin) that confines the plasma generated between the center electrodes is formed. Furthermore, the plasma in the magnetic bin is Z-pinch. That is, the plasma in the magnetic bin is compressed toward the central axis common to the coaxial electrodes by the self magnetic field.

  On the other hand, a voltage applying device is connected to each coaxial electrode, and energy corresponding to the light emission energy of the generated plasma is supplied from the voltage applying device.

JP 2010-147231 A

  In photolithography, control of the exposure time is extremely important. Therefore, it is necessary not only to ensure sufficient intensity of light, but also to obtain the intensity stably. In other words, in the plasma light source as described above, it is important to surely discharge each time and continuously generate pulsed plasma.

  In view of the above circumstances, an object of the present invention is to provide a plasma light source capable of stably generating a discharge for generating plasma that emits extreme ultraviolet light.

  One aspect of the present invention is a plasma light source, which is opposed to each other, generates a plasma that emits extreme ultraviolet light, and confines the plasma, and the polarity is reversed with respect to each of the coaxial electrodes Each of the coaxial electrodes is provided so as to surround a rod-shaped center electrode extending on a single axis and an outer periphery of the center electrode. An external electrode and an insulator that insulates between the central electrode and the external electrode, and the laser device includes a central electrode having a relatively negative potential among the central electrodes of the pair of coaxial electrodes. The tip is irradiated with a preheating laser beam that promotes the emission of electrons, and a laser beam for plasma generation is applied to the central electrode of each of the coaxial electrodes or the plasma medium region formed on the insulator. It shines and is summarized in that the ablating of the irradiated region.

  The laser device may further irradiate the tip of the center electrode, which has a relatively positive potential at each center electrode of the pair of coaxial electrodes, with a preheating laser beam.

  The preheating laser beam is within a period from when the plasma generating laser beam is irradiated until the plasma sheet between the center electrode and the external electrode generated by the ablation reaches the tip of the center electrode. May be irradiated.

The external electrode may be composed of a plurality of rod-shaped electrodes.

  ADVANTAGE OF THE INVENTION According to this invention, the plasma light source which can generate | occur | produce the discharge for producing | generating the plasma which radiates | emits extreme ultraviolet light stably can be provided.

It is a schematic block diagram of the plasma light source which concerns on one Embodiment of this invention. It is a figure which shows the principal part of the coaxial electrode shown in FIG. It is a figure which shows the III-III cross section of FIG. It is operation | movement explanatory drawing of the plasma light source which concerns on one Embodiment of this invention. It is operation | movement explanatory drawing of the plasma light source which concerns on one Embodiment of this invention. It is a figure which shows the modification of the coaxial electrode which concerns on one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

  First, the coaxial electrode in the plasma light source of this embodiment will be described. FIG. 1 is a schematic configuration diagram showing a plasma light source of the present embodiment. As shown in this figure, the plasma light source of the present embodiment includes a pair of coaxial electrodes 10, a pulse laser device (hereinafter referred to as a laser device) 20, and a voltage application device 30. The pair of coaxial electrodes 10 are installed in a chamber (not shown), and the surroundings are kept in a vacuum. The chamber is grounded.

  The pair of coaxial electrodes 10 are located symmetrically with respect to the symmetry plane 1. In other words, the coaxial electrodes 10 are arranged so as to face each other with a certain distance around the symmetry plane 1. Each coaxial electrode 10 includes a center electrode 12, a plurality of external electrodes 14, and an insulator 16. A plasma medium that emits extreme ultraviolet light is introduced between the center electrode 12 and the external electrode 14. The plasma medium is a gas containing at least one of Li, Xe, and Sn, for example. As will be described later, this gas is obtained by ablation of a metal layer (thin film) 27 as a plasma medium region provided on the side surface of the center electrode 12.

  As shown in FIG. 1 to FIG. 3, the center electrode 12 has a single axis ZZ common to the coaxial electrodes 10 as a central axis (hereinafter, this axis is referred to as the central axis Z). It is a rod-shaped conductor extending on Z. The center electrode 12 is formed using a metal that can withstand damage due to high-temperature plasma. Examples of such metals include refractory metals such as tungsten and molybdenum.

  In the present embodiment, the end surface of the center electrode 12 facing the symmetry plane 1 is a hemispherical curved surface. However, the end surface is not limited to a hemispherical curved surface, and may be a simple flat surface, for example. Further, the portion where the end face is formed may be formed in a substantially conical shape whose apex faces the symmetry plane 1.

  On the side surface of the center electrode 12, a metal layer (thin film) 27 containing Li is formed as a plasma medium region. The metal layer 27 is irradiated with laser light 24a (24b) from the laser device 20. The metal layer 27 may be formed as a whole over the circumferential direction of the central axis Z, or may be formed only at a location where the laser beam 24a (24b) is irradiated as shown in FIG. In the example shown in FIG. 1, metal layers 27 are formed at two locations across the central axis Z.

  The external electrode 14 is a rod-shaped conductor extending in parallel with the central axis Z of the center electrode 12, and has an angle along the circumferential direction of the center electrode 12 while being spaced apart from the center electrode 12 by a certain distance G (see FIG. 2). A plurality are arranged for each θ (see FIG. 3). In other words, each external electrode 14 is arranged in parallel with the center electrode 12 and is provided so as to surround the center electrode 12. In the example shown in FIG. 3, six external electrodes 14 are arranged around the center electrode 12 every 60 °.

  Compared with the guide electrode shown in Patent Document 1, the external electrode 14 of the present embodiment divides the guide electrode of Patent Document 1 into a plurality of electrodes along the circumferential direction, and further divides the center electrode 12 of each of the divided electrodes. It can also be understood that the surface on the opposite side is a curved surface that protrudes (convex) toward the center electrode 12.

  As described above, by arranging the plurality of external electrodes 14 around the center electrode 12, the initial discharge (for example, creeping discharge) reaching the sheet discharge 2 shown in FIG. Can be generated between. That is, since the initial discharge is generated over the entire circumference of the center electrode 12, the formation of the annular planar discharge 2 is facilitated. The planar discharge is a planar discharge current that spreads two-dimensionally and is also called a current sheet or a plasma sheet.

  The external electrode 14 is formed using a refractory metal such as tungsten or molybdenum that can withstand damage caused by high-temperature plasma, like the center electrode 12. Further, the end face of the external electrode 14 facing the symmetry plane 1 may be either a curved surface or a flat surface. Furthermore, the cylinder may be the same as the guide electrode of Patent Document 1.

  The external electrode 14 is not limited to the rod-like body having a circular cross section shown in FIG. 3, and it is sufficient that at least the side facing the center electrode 12 has a curved surface protruding (convex) toward the center electrode 12. For example, the external electrode 14 may have a semicircular cross section, and the arc may be disposed toward the center electrode 12.

  The external electrodes 14 are preferably arranged at equal intervals along the circumferential direction of the center electrode 12. For example, from the viewpoint of processing and assembly, each external electrode 14 is preferably installed at a rotationally symmetric position with respect to the center electrode 12. However, according to the present invention, such an arrangement is not exact. Further, the number of external electrodes 14 is not limited to six, and is appropriately set according to the size and shape of the center electrode 12 and the external electrode 14, the distance G between the two.

  The insulator 16 is formed using, for example, ceramic, supports the base portions of the center electrode 12 and the external electrode 14, defines a gap G, and electrically insulates between them. The insulator 16 is formed in a disk shape, for example.

  Next, an electrical system in the plasma light source of this embodiment will be described. As shown in FIG. 4, the plasma light source includes a voltage application device 30 connected to each coaxial electrode 10. The voltage application device 30 applies a discharge voltage with the polarity reversed to each coaxial electrode 10.

  Specifically, the voltage application device 30 includes a negative voltage source (HV Charging Device) 32 and a positive voltage source (HV Charging Device) 34.

  On the output side of the negative voltage source 32, a negative discharge voltage lower than that of the external electrode 14 is applied to the center electrode 12 of one of the coaxial electrodes 10 (for example, the left side in FIG. 1). For example, when the external electrode 14 is grounded, the potential of the corresponding center electrode 12 is negative.

  The output side of the positive voltage source 34 applies a positive discharge voltage higher than that of the external electrode 14 to the center electrode 12 of the other coaxial electrode 10 (for example, the right side in FIG. 1). For example, when the external electrode 14 is grounded, the potential of the corresponding center electrode 12 is positive.

  In addition, in order to observe the electric current which passed through each center electrode 12 with an oscilloscope (Oscilloscope), each common side (return side) of the negative voltage source 32 and the positive voltage source 34 is inductively coupled using a Rogowski coil or the like. There may be provided a track.

  As described above, a plurality of external electrodes 14 are provided around each center electrode 12. In order to obtain an ideal sheet discharge 2, it is necessary to generate a discharge between each external electrode 14 and the center electrode 12. For this reason, each external electrode 14 of the present embodiment has a surface facing the center electrode 12 as a curved surface, and fixes a location where discharge is preferentially performed. On the other hand, it is difficult to generate discharge between each external electrode 14 and the center electrode 12 strictly at the same time. That is, there is a slight deviation in the timing of occurrence of each discharge. Therefore, there is a possibility that the discharge energy supplied from the negative voltage source 32 and the positive voltage source 34 is preferentially spent for the first generated discharge. In this case, it becomes difficult to generate a plurality of discharges substantially simultaneously.

  Therefore, the plasma light source of this embodiment includes an energy storage circuit 50 that stores the discharge voltage from the voltage application device 30 as discharge energy for each external electrode 14. For example, as shown in FIG. 1, the energy storage circuit 50 includes a plurality of capacitors C that individually connect the center electrode 12 and each external electrode 14. Each capacitor C is connected to the output side and the common side of the negative voltage source 32 or the positive voltage source 34.

  Thus, by providing the capacitor C for storing discharge energy for each external electrode 14, it is possible to generate discharge in all the external electrodes 14. That is, it is possible to prevent a large amount of discharge energy from being consumed by the first generated discharge, and to obtain an ideal planar discharge 2 generated over the entire circumference of the center electrode 12.

  Furthermore, the plasma light source of the present embodiment may include a discharge current blocking circuit 52 that blocks the discharge current from returning to the voltage application device 30. For example, as shown in FIG. 1, the discharge current blocking circuit 52 is an inductor L that connects between each external electrode 14 and the voltage applying device 30 (specifically, the common side of the negative voltage source 32 and the positive voltage source 34). Composed. The inductor L has a sufficiently high impedance with respect to the discharge current. Therefore, the discharge current that has passed through the center electrode 12 and the external electrode 14 can be returned to the energy storage circuit 50 that is the generation source. That is, since the discharge energy accumulated in each capacitor C can be prevented from being supplied to the external electrodes 14 other than the external electrode 14 directly connected to the capacitor C, the discharge distribution in the circumferential direction of the center electrode 12 is biased. Can be prevented.

  With the above configuration, a tubular discharge (described later) is formed between the pair of coaxial electrodes 10, and plasma is confined in the axial direction.

  As described above, the plasma light source of the present embodiment includes the laser device 20. The laser device 20 is a YAG laser, for example, and outputs a double wave of the fundamental wave as a short-pulse laser beam 24 for ablation.

  The laser beam 24 is branched into at least two laser beams 24a and 24b as plasma generation laser beams by an optical element such as a beam splitter (half mirror) 26a or a mirror 26b, and a metal layer (plasma medium) of each center electrode 12 is split. (Region) 27 is irradiated. Ablation occurs on the surface of the metal layer 27 irradiated with these laser beams 24a and 24b.

  On the other hand, when the laser beams 24 a and 24 b are irradiated, a discharge voltage from the voltage application device 30 is applied to the center electrode 12 and the external electrode 14 of each coaxial electrode 10. Therefore, when a part of the metal layer 27 is released as a gas (or plasma) by ablation, a discharge between the center electrode 12 and each external electrode 14 is induced. Furthermore, the sheet discharge 2 shown in FIG. 4B is formed by this discharge.

  In addition, the generation | occurrence | production location of the said discharge may be restrict | limited to the irradiation area | region of the laser beam 24a (24b), and its vicinity. Therefore, it is preferable to irradiate a plurality of laser beams 24a (24b) at a distance along the circumferential direction of the central axis Z at the same time, and the number thereof is at least two (see FIG. 1).

  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 12 as a base point. Considering this result, it is desirable to irradiate the laser beams 24a and 24b to the rotationally symmetric positions with respect to the center electrode 12 as the number of irradiated portions is smaller. Note that simultaneous irradiation with a plurality of laser beams 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.

  Further, the laser device 20 applies a laser beam 24c as a preheating laser beam to the distal end portion 12a of the center electrode 12 having a relatively negative potential among the center electrodes 12 and 12 of the pair of coaxial electrodes 10 and 10. Irradiate. That is, in the embodiment shown in FIG. 1, the laser beam 24 c is irradiated to the tip portion 12 a of the left central electrode 12.

  The laser beam 24c is obtained, for example, by arranging a beam splitter 26c in the optical path of the laser beam 24. Alternatively, as indicated by a dotted line in FIG. 1, a pulse laser device (laser device) 22 synchronized with the pulse laser device may be provided separately. In any case, the laser beam 24c needs to be heated to such an extent that ablation occurs in the irradiated region. Electron emission at the tip 12a can be promoted by irradiation with the laser beam 24c.

When the electron emission at the distal end portion 12a is promoted, the probability of generation of the plasma 3 between the center electrodes 12 and 12 is improved. The reason is as follows. When the center electrode 12 is at a positive potential, the external electrode 14 located around it serves as the electron emission source when the discharge occurs. FIG. 5A shows the electron current F when the planar discharge 2 reaches the vicinity of the tip 12a of the central electrode 12 having a positive potential. As shown in this figure, electrons contributing to the planar discharge 2 flow from the front end portion 14 a of the external electrode 14 toward the front end portion 12 a of the center electrode 12.

On the other hand, when the center electrode 12 has a negative potential, the center electrode 12 serves as an electron emission source when a discharge occurs. FIG. 5B shows the electron current F when the planar discharge 2 reaches the vicinity of the tip 12a of the central electrode 12 having a negative potential. As shown in this figure, electrons flow from the tip 12 a of the center electrode 12 contributing to the planar discharge 2 toward the tip 14 a of the external electrode 14.

  The area of electron emission that contributes to the planar discharge 2 at both tip portions 12a and 14a is referred to as an effective electron emission area S. Due to the structure of the coaxial electrode 10, the negative potential external electrode 14 has a larger effective electron emission area S than the negative potential center electrode 12. That is, when the external electrode 14 is set to a negative potential with respect to the center electrode 12 (potential arrangement in FIG. 5A), the center electrode 12 is set to a negative potential with respect to the external electrode 14. Thus, it is easier to obtain sustained electron emission over a wider area than in the case of the potential arrangement (the potential arrangement in FIG. 5B). Accordingly, the planar discharge 2 in the potential arrangement of FIG. 5A is more likely to reach the tip 12a than the planar discharge 2 in the potential arrangement of FIG.

  In other words, the sheet discharge 2 in the potential arrangement of FIG. 5B is likely to be attenuated due to insufficient supply of electrons as it proceeds to the tip 12a. As a result, there is a possibility that the generation probability of the plasma 3 at both the center electrodes 12 and 12 is reduced. In this embodiment, the laser beam 24c is irradiated to the front-end | tip part 12a of the center electrode 12 set to the negative potential, and electron emission around an irradiation area | region is accelerated | stimulated. Thereby, the shortage of supply of electrons to the planar discharge 2 is resolved, and the planar discharge 2 can smoothly reach the tip end portion 12a even in the potential arrangement of FIG. As a result, the generation probability of the plasma 3 (see FIG. 4D) between the center electrodes 12 and 12 can be improved.

  Regarding the irradiation timing of the laser beam 24c, from the viewpoint of promoting the arrival of the planar discharge 2 to the tip 12a, the central electrode 12 generated by this irradiation from the irradiation of the laser beams 24a and 24b for ablating the metal layer 27 is used. And the planar discharge 2 between the external electrodes 14 is set within a period until it reaches the tip 12a of the center electrode 12. This period is appropriately set according to the length from the irradiation point of the laser beams 24a and 24b to the tip portion 12a of the center electrode 12, the amount of current of the planar discharge 2, and the like.

  As shown by the dotted line in FIG. 1, the above-mentioned preheating laser beam is applied to the tip 12a of the center electrode 12 having a relatively positive potential among the center electrodes 12, 12 of the pair of coaxial electrodes 10, 10. The laser beam 24d may be irradiated. In other words, in the embodiment shown in FIG. 1, the laser beam 24d is irradiated to the tip portion 12a of the right center electrode 12 together with the irradiation of the laser beam 24c to the tip portion 12a of the left center electrode 12. In this case, since the supply of electrons is abundant at the tip of any coaxial electrode 10, the probability of generation of the plasma 3 (see FIG. 4D) between the center electrodes 12 and 12 can be further improved. .

  The laser beam 24d may be obtained by disposing the beam splitter 26d in the optical path of the laser beam 24 emitted from the laser device 20 as in the case of the laser beam 24c, or from the pulse laser device (laser device) 22. May be obtained.

  FIG. 4 is an operation explanatory diagram of the plasma light source shown in FIG. In this figure, (A) is when the laser beams 24a and 24b are irradiated, (B) is when the planar discharge 2 is generated, (C) is during the movement of the planar discharge 2, and (D) is when the plasma 3 is formed. (E) shows the respective states when the planar discharge 2 and the tubular discharge are switched, and (F) shows each state when the plasma confined magnetic field is formed.

Hereinafter, the operation of the plasma light source of the present embodiment will be described with reference to FIG.
As described above, in the plasma light source of the present embodiment, the pair of coaxial electrodes 10 are disposed to face each other in a chamber (not shown). The inside of the chamber is maintained at a temperature and pressure suitable for plasma generation. A discharge voltage whose polarity is reversed by the voltage application device 30 is applied to each coaxial electrode 10. In FIG. 4, the relative polarities of the electrodes are indicated by (+) and (-) in each figure.

  As shown in FIG. 4A, the metal layer 27 of each center electrode 12 is simultaneously irradiated with the laser beam 24a or the laser beam 24b in a state where a discharge voltage is applied. Immediately thereafter, as shown in FIG. 4B, a discharge is generated between the center electrode 12 and the external electrode 14 of each coaxial electrode 10. As described above, a plurality of external electrodes 14 are provided, and a discharge is generated between each of the external electrodes 14 and the center electrode 12, so that a planar discharge 2 in which the discharge is distributed over the entire circumference of the center electrode 12 is obtained. Formation of the planar discharge 2 causes Li to evaporate from the metal layer 27 in each coaxial electrode 10 to generate a gas containing Li.

  The laser beam 24c is applied to the tip 12a of the center electrode 12 on the left side in the drawing simultaneously with the laser beams 24a and 24b. Alternatively, the tip end portion 12a is irradiated within the period until the planar discharge 2 reaches the tip end portion 12a. Irradiation with the laser beam 24c preliminarily heats the irradiation region and its surroundings, and electrons are emitted. In addition, when also irradiating the laser beam 24d (indicated by a dotted line), the laser beam 24c is irradiated at the same time.

  As shown in FIG. 4C, the planar discharge 2 moves in the direction of being discharged from the electrode by the self magnetic field (the direction toward the symmetry plane 1 in FIG. 4).

  As shown in FIG. 4D, when the planar discharge 2 reaches the tips of the pair of coaxial electrodes 10, the plasma medium 6 sandwiched between the pair of planar discharges 2 (see FIG. 4C). ) Has a high density and a high temperature, and a single plasma 3 is formed at the opposite intermediate position of each coaxial electrode 10 (that is, the symmetry plane 1 of the center electrode 12).

  As shown in FIG. 4E, when the respective planar discharges 2 further move and come into contact with each other, a single plasma 3 is surrounded and held in the axial direction by each planar discharge 2.

  The pair of opposed center electrodes 12 are respectively applied to a positive voltage (+) and a negative voltage (−), and the surrounding external electrodes 14 are applied to a voltage having a polarity opposite to that of the corresponding center electrode 12. ing. Therefore, as shown in FIG. 4F, the sheet discharge 2 is switched between the pair of opposed center electrodes 12 and the tubular discharge 4 discharged between the opposed external electrodes 14. Here, the tubular discharge 4 means a hollow cylindrical discharge current surrounding the axis ZZ (center axis Z).

  When this tubular discharge 4 is formed, a plasma confined magnetic field (magnetic bottle) 5 is formed, and as a result, the plasma 3 is sealed in the radial direction and the axial direction. That is, the central portion of the magnetic bin 5 is large due to the pressure of the plasma 3 and both sides thereof are small, and a magnetic pressure gradient in the axial direction toward the plasma 3 is formed. The plasma 3 is constrained to an intermediate position by this magnetic pressure gradient. Furthermore, the plasma 3 is compressed (Z pinch) in the center direction by the self-magnetic field of the plasma current, and the restraint by the self-magnetic field also acts in the radial direction.

  In this state, if energy corresponding to the light emission energy of the plasma 3 is continuously supplied from the voltage application device 30, the plasma light 8 including extreme ultraviolet light can be generated over a long period of time with high energy conversion efficiency.

  According to the present embodiment, the emission of electrons from the center electrode 12 is promoted by the irradiation of the laser beam 24 c on the distal end portion 12 a of the center electrode 12. Therefore, the pair of planar discharges 2 and 2 traveling toward each other collide in the middle of each center electrode 12 (that is, the symmetry plane 1) without disappearing. That is, since the discharge for generating the plasma 3 is generated stably, the probability of generating the plasma 3 can be improved, and as a result, extreme ultraviolet light can be obtained stably for a long time.

  As shown in FIG. 6, a metal layer (thin film) 27 that emits Li as a plasma medium region may be formed on the surface of the insulator 16 between the center electrode 12 and the external electrode 14. Alternatively, this surface may be formed of a material containing Li. In any case, the irradiation position of the laser beam 24a (24b) is on this surface. The irradiation positions are preferably at least two positions that are rotationally symmetric with respect to the center electrode 12. In this case, creeping discharge is generated on the surface of the insulator 16 by the irradiation of the laser beam 24a (24b), and thereafter the same planar discharge 2 as described above is obtained.

  The present invention is not limited to the above-described embodiment, but is shown by the description of the scope of claims, and further includes all modifications within the meaning and scope equivalent to the description of the scope of claims.

DESCRIPTION OF SYMBOLS 1 ... Symmetrical plane, 2 ... Planar discharge, 3 ... Plasma, 4 ... Tubular discharge, 5 ... Magnetic bin, 6 ... Plasma medium, 8 ... Plasma light, 10 ... Coaxial electrode, 12 ... Center electrode, 12a ... Center electrode 14 ... external electrode, 14a ... external electrode tip, 16 ... insulator, 20 ... laser device, 22 ... laser device, 24 ... laser light, 27 ... metal layer (plasma medium region), 30 ... voltage Application device 32 ... Negative voltage source 34 ... Positive voltage source 50 ... Energy storage circuit 52 ... Discharge current blocking circuit

Claims (4)

A pair of coaxial electrodes that are arranged opposite to each other to generate plasma that emits extreme ultraviolet light and confine the plasma; and a voltage application device that applies a discharge voltage with the polarity reversed to each of the coaxial electrodes; With a laser device,
Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, an external electrode provided so as to surround an outer periphery of the center electrode, and an insulator that insulates between the center electrode and the external electrode And
The laser device irradiates the tip of the center electrode having a relatively negative potential among the center electrodes of the pair of coaxial electrodes with a preheating laser beam that promotes electron emission, and each of the coaxial electrodes A plasma light source characterized in that a plasma generation laser beam is irradiated to a plasma medium region formed on the central electrode or the insulator of an electrode to ablate the irradiation region.   2. The laser device according to claim 1, wherein the laser device further irradiates a tip of the center electrode having a relatively positive potential at each center electrode of the pair of coaxial electrodes with a preheating laser beam. Plasma light source.   The preheating laser beam is within a period from when the plasma generating laser beam is irradiated until the plasma sheet between the center electrode and the external electrode generated by the ablation reaches the tip of the center electrode. The plasma light source according to claim 1, wherein the plasma light source is irradiated on the plasma light source.   4. The plasma light source according to claim 1, wherein the external electrode is composed of a plurality of rod-shaped electrodes.

Images