JP2013254693A - Plasma light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma light source that stably produces extreme ultraviolet light for a long period of time.SOLUTION: A plasma light source includes: a pair of coaxial electrodes 10 and 10 that are arranged so as to face each other and that generate and confine therebetween plasma that radiates extreme ultraviolet light; and a voltage applying device 30 that applies a discharge voltage of the same polarity to each coaxial electrode 10. Each coaxial electrode 10 has: a bar-like center electrode 12 that extends on a single axis Z-Z; external electrodes 14 that are provided so to surround the outer boundary of the center electrode 12; and an insulator 16 that insulates the center electrode 12 and the external electrodes 14 from each other.

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 light generation method using an extreme ultraviolet light source, 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 based on the DPP method as the extreme ultraviolet light source described above. The plasma light source of the same document includes a pair of coaxial electrodes disposed opposite to a symmetry plane, and high voltages whose polarities are reversed are applied to the center electrodes of the coaxial electrodes. When an annular sheet discharge is generated in each coaxial electrode in this state, each sheet discharge proceeds toward the tip of the coaxial electrode by a self-magnetic field. As a result, the planar discharge reaches between a pair of coaxial electrodes, and high-temperature and high-density plasma that emits extreme ultraviolet light is generated.

JP 2010-147231 A

  In photolithography, control of the exposure time is extremely important. Therefore, it is necessary not only to secure sufficient intensity and luminance, but also to obtain these stably. In other words, in the above-described plasma light source, it is important to surely discharge each time and continuously generate pulsed plasma. Further, in order to obtain extreme ultraviolet light, it is indispensable to increase the temperature of plasma. However, in a plasma light source based on the DPP method, deterioration and damage of electrodes due to an increase in plasma temperature and generation of unnecessary materials are unavoidable. Therefore, it is necessary to suppress the energy spent for generating unnecessary light in the supplied energy and efficiently generate extreme ultraviolet light having a desired wavelength.

  In view of the above circumstances, an object of the present invention is to provide a plasma light source capable of stably obtaining extreme ultraviolet light for a long time.

  One embodiment of the present invention is a plasma light source, which is opposed to each other and generates a pair of coaxial electrodes that emit extreme ultraviolet light therebetween and confine the plasma, and is identical to each of the coaxial electrodes. Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, an external electrode provided so as to surround the outer periphery of the center electrode, The gist is to have an insulator that insulates the center electrode from the external electrode.

  The outer electrode of each of the coaxial electrodes may be composed of a plurality of rod-shaped electrodes arranged in the circumferential direction of the center electrode.

  The outer electrode of each coaxial electrode may comprise a single cylindrical electrode.

  The plasma light source may further include a laser device that emits the plasma medium and generates an initial discharge of the plasma by irradiating the surface of the central electrode of each coaxial electrode with laser light.

  The plasma light source may further include a laser device that irradiates the surface of the insulator of each of the coaxial electrodes with laser light to emit the plasma medium and generate an initial discharge of the plasma.

  The voltage application device may include a trigger switch that simultaneously applies the discharge voltage between the center electrode and the external electrode of each of the coaxial electrodes.

  ADVANTAGE OF THE INVENTION According to this invention, the plasma light source which can obtain extreme ultraviolet light stably for a long time can be provided.

It is a schematic block diagram of the plasma light source which concerns on 1st 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. (A) thru | or (F) is the figure which showed the action | operation of the plasma light source which concerns on 1st Embodiment of this invention in time series. It is a figure which shows the confinement state of the plasma in the plasma light source which concerns on one Embodiment of this invention. It is a schematic block diagram of the plasma light source of the plasma light source which concerns on 2nd Embodiment of this invention. It is a figure which shows the initial state of the planar discharge in the plasma light source which concerns on 2nd Embodiment of this invention. It is a schematic block diagram which shows the 1st modification of the coaxial electrode which concerns on each embodiment of this invention. It is a schematic block diagram which shows the 2nd modification of the coaxial electrode which concerns on each embodiment of this invention, (A) is sectional drawing containing the axis line ZZ of a center electrode, (B) is B in (A). It is -B sectional drawing.

  Hereinafter, a plasma light source according to an embodiment of the present invention will be described 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 embodiment)
First, the coaxial electrode in the plasma light source according to the first embodiment of the present invention 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 this embodiment includes a pair of coaxial electrodes 10, 10, a chamber 20, and a voltage application device 30.

  The pair of coaxial electrodes 10 are installed in the chamber 20 with a symmetrical positional relationship 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 from the symmetry plane 1. The chamber 20 is connected to a vacuum pump (not shown) via the exhaust pipe 22 and is maintained at a predetermined degree of vacuum. The chamber 20 is grounded.

  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 selected according to the required ultraviolet wavelength. For example, when 13.5 nm ultraviolet light is required, the gas contains at least one of Li, Xe, Sn, and the like. When 6.7 nm ultraviolet light is required, Gd, Tb, Bi, etc. emit the ultraviolet light. A gas containing at least one of the following.

  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 is not easily damaged by 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, this shape is not essential, and a concave portion as shown in FIG. 1 may be provided on the end face, or a simple flat surface.

  As shown in FIG. 2, a metal layer (thin film) 27 as a plasma medium region is formed on the side surface of the center electrode 12. The metal layer 27 is irradiated with a laser beam 64a (64b) branched from a laser beam 64 of a laser device 60 described later (see FIG. 1). The metal layer 27 includes a metal that emits extreme ultraviolet light, such as Li or Gd, and is formed only at a location irradiated with the laser light 64a (64b) as shown in FIG. Alternatively, it may be formed entirely along the circumferential direction of the central axis Z. In the example shown in FIG. 2, the metal layer 27 is formed at two locations across the central axis Z.

  As shown in FIG. 3, the external electrode 14 is a rod-shaped conductor that extends parallel to the central axis Z of the center electrode 12, and is spaced along the circumferential direction of the center electrode 12 with a certain distance from the center electrode 12. A plurality are arranged for each angle θ. In other words, each external electrode 14 is disposed in parallel with the center electrode 12 and surrounds the periphery of the center electrode 12. In the example shown in FIG. 3, six external electrodes 14 are arranged around the center electrode 12 every 60 °.

  Each external electrode 14 has a cross section including only one point G at which the distance from the center electrode 12 is shortest in a plane perpendicular to the axial direction. The cross section having such a shape is, for example, a circle shown in FIG. The cross section is not limited to this circular shape, and it is sufficient that at least the surface facing the center electrode 12 has a curved surface protruding toward the center electrode 12. In any case, the point G is arranged around the center electrode 12 at every angle θ.

  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 between them, and the like.

  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.

  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 planar discharge 2 shown in FIG. 12 can be generated. That is, by preferentially generating the initial discharge including each point G in the discharge path, it is possible to generate the initial discharge over the entire circumference of the center electrode 12, thereby forming the annular planar discharge 2. Becomes easier. The planar discharge is a planar discharge current that spreads two-dimensionally and is also called a current sheet or a plasma sheet.

  The insulator 16 is formed using, for example, ceramic, supports the base portions of the center electrode 12 and the external electrode 14, defines the distance between them, and electrically insulates between them. The insulator 16 is formed in a disk shape, for example, and has a through hole through which the center electrode 12 and the external electrode 14 pass.

  Next, an electrical system in the plasma light source of this embodiment will be described. As shown in FIG. 1, the plasma light source includes a voltage applying device 30 connected to each coaxial electrode 10. The voltage application device 30 applies a discharge voltage having the same polarity to each coaxial electrode 10.

  Specifically, the voltage application device 30 according to the first embodiment includes two high-voltage power supplies (HV Charging Devices) 32 and 34. The output side of the high-voltage power source (hereinafter simply referred to as power source) 32 is connected to the center electrode 12 of one of the coaxial electrodes 10 (for example, the left side in FIG. 1) and is higher than the external electrode 14 corresponding to the center electrode 12. Apply a positive discharge voltage. The output side of a high-voltage power source (hereinafter simply referred to as a power source) 34 is connected to the center electrode 12 of the other coaxial electrode 10 (for example, the right side in FIG. 1) and is higher than the external electrode 14 corresponding to the center electrode 12. Apply a positive discharge voltage. Therefore, for example, when any of the external electrodes 14 is grounded, the potential of the corresponding center electrode 12 becomes positive.

  It should be noted that a Rogowski coil or the like is used for each common side (return side) of the high-voltage power supplies 32 and 34 in order to observe the current (that is, all discharge currents) passing through each center electrode 12 with an oscilloscope. An inductively coupled line may be provided.

  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 all the external electrodes 14 and the center electrode 12. In addition, it is desirable that these discharges are distributed around the center electrode 12 at equal intervals. For this reason, each external electrode 14 of the present embodiment has a surface facing the center electrode 12 as a curved surface to define a place where discharge is preferentially performed. However, even if the discharge location is fixed and a laser beam 64 described later is irradiated onto the metal layer 27 of each central electrode 12 at the same time, the discharge between each external electrode 14 and the central electrode 12 can be generated strictly at the same time. In reality, there is a slight deviation in the timing of occurrence of each discharge. Discharge energy supplied from each of the high-voltage power sources 32 and 34 tends to be preferentially consumed with respect to the first generated discharge. In this case, it is 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 each output side and each common side of the high-voltage power supplies 32 and 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 includes an inductor L that connects between each external electrode 14 and the voltage application device 30 (specifically, each common side of the high-voltage power supplies 32 and 34). . Since the inductor L has a sufficiently high impedance with respect to the discharge current, 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 thereof. 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.

  As described above, the plasma light source of the present embodiment irradiates the surface of the central electrode 12 of each coaxial electrode 10 with laser light, thereby releasing the medium of the plasma 3 and the initial discharge of the plasma 3 (ie, the surface). A laser device 60 for generating a discharge 2). The laser device 60 is, for example, a YAG laser, and outputs a double wave of the fundamental wave as a short pulse laser beam 64 in order to perform ablation.

  The laser beam 64 is branched into at least two laser beams 64a and 64b by an optical element such as a beam splitter (half mirror) 66a and a mirror 66b, and irradiated to the metal layer (plasma medium region) 27 of each center electrode 12. The On the surface of the metal layer 27 irradiated with the laser beams 64a and 64b, a part of the metal layer 27 is emitted as neutral gas or ions as a plasma medium by ablation.

  On the other hand, when the laser beams 64 a and 64 b are irradiated, the discharge voltage from the voltage application device 30 has already been applied to the center electrode 12 and the external electrode 14 of each coaxial electrode 10. Therefore, when the ablation described above occurs, a discharge between the center electrode 12 and each external electrode 14 is induced. Further, a planar discharge 2 (see 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 64a (64b) and its vicinity. Therefore, it is preferable to irradiate a plurality of laser beams 64a (64b) at the same time at intervals along the circumferential direction of the central axis Z, and the number 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 64a and 64b to a rotationally symmetric position 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.

  FIG. 4 is an operation explanatory diagram of the plasma light source shown in FIG. In this figure, (A) is when the laser beams 64a and 64b 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 generated. , (E) shows the respective states of the plasma 3 at the initial confinement, and (F) shows the state of the high-temperature and high-density plasma 3.

Hereinafter, the operation of the plasma light source of the present embodiment will be described with reference to these drawings.
As described above, in the plasma light source of the present embodiment, a pair of coaxial electrodes 10 are disposed opposite to each other around the symmetry plane 1 in a chamber (not shown). The inside of the chamber is maintained at a temperature and pressure suitable for plasma generation. In addition, a discharge voltage having the same polarity is applied to each coaxial electrode 10 before discharge by the voltage application device 30. In FIG. 4, the relative polarities of the electrodes are indicated by (+) and (−).

  As shown in FIG. 4A, the metal layer 27 of each center electrode 12 is simultaneously irradiated with the laser beam 64a or the laser beam 64b in a state where a discharge voltage is applied. Immediately thereafter, 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 discharge occurs between the center electrode 12 and each of the external electrodes 14. Therefore, as shown in FIG. 4B, 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 releases Li-containing gas or ions from the metal layer 27 in each coaxial electrode 10.

  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). The shape of the planar discharge 2 at this time is substantially annular when viewed from the axis ZZ.

  Thereafter, as shown in FIG. 4D, the planar discharge 2 reaches the tip of the coaxial electrode 10. Even after reaching the tip of the coaxial electrode 10, the force in the direction toward the symmetry plane 1 by the self-magnetic field is maintained. Further, when the planar discharge 2 reaches the center electrode 12, the circumferential side surface 12b of the center electrode 12 which is the starting point of the discharge current is interrupted, and the starting point of the discharge current is forcibly shifted to the tip 12a. To do. In other words, the discharge current flows intensively from the tip 12a. The current density around the tip 12a rapidly increases due to the pinch effect due to the current concentration, and the plasma medium 6 containing Li around the tip 12a sandwiched between the pair of planar discharges 2 (FIG. 4C). Reference) becomes high density and high temperature.

  Further, since this phenomenon proceeds at each coaxial electrode 10 across the symmetry plane 1, the plasma medium 6 is pushed out from one coaxial electrode 10 toward the other coaxial electrode 10. As a result, the plasma medium 6 receives pressure from both directions along the axis ZZ (center axis Z) and moves to an intermediate position where the coaxial electrodes 10 face each other (that is, the symmetry plane 1 of the center electrode 12). A single plasma 3 having the plasma medium 6 as a component is formed.

  As shown in FIG. 4 (E), even after the plasma 3 is formed, the respective planar discharges 2 move until they contact or intersect each other, so as to surround the plasma 3 as a whole and It is held near the middle of the electrode 12.

  As described above, while the sheet discharge 2 is generated, the current of each sheet discharge 2 is concentrated on the front end portion 12a of each center electrode 12. Accordingly, a pinch effect toward the axis ZZ acts on the plasma 3 around the tip portion 12a, the plasma 3 is increased in density and temperature, and ionization of ions including Li proceeds. Therefore, as shown in FIG. 4F, plasma light 8 including extreme ultraviolet light is radiated from the plasma 3. In this state, if the energy corresponding to the light emission energy of the plasma 3 is continuously supplied from the voltage application device 30, the plasma light 8 can be generated for a long time with high energy conversion efficiency.

  As shown in FIG. 5, in the plasma light source of this embodiment, the electric field and magnetic field around each coaxial electrode 10 when the plasma 3 is generated are distributed symmetrically with respect to the symmetry plane 1. Therefore, the plasma 3 is also distributed symmetrically with respect to the symmetry plane 1, and the bias of each coaxial electrode 10 to one side is suppressed. Further, the center electrode 12 of each coaxial electrode 10 is always set to a higher potential than the corresponding external electrode 14. That is, the plurality of external electrodes 14 around the center electrode 12 are always responsible for the electron supply source. Therefore, during the generation of the planar discharge 2 and the plasma 3, it is possible to secure a sufficient and steady emission area of electrons flowing through them, so that the planar discharge 2 can be stably maintained, and the tip 12 a can be smoothly smoothed. Transition and sufficient convergence at the tip 12a. Further, the plasma 3 can be easily converged between the tip portions 12a and 12a. That is, since the conversion efficiency of the input energy into the extreme ultraviolet light is increased, the plasma 3 can be efficiently increased in temperature and density, and the extreme ultraviolet light can be stably obtained for a long time (for example, on the order of μsec).

(Second Embodiment)
Next, the plasma light source which concerns on 2nd Embodiment of this invention is demonstrated based on an accompanying drawing. In the plasma light source of the first embodiment, the laser device 60 is used to generate the planar discharge 2, but in the plasma light source of the second embodiment, creeping discharge by a high voltage pulse is used to generate the planar discharge 2. In addition, about the member same as 1st Embodiment in a figure, the same code | symbol is attached | subjected and said description is used, and description here is abbreviate | omitted.

  The configuration of the plasma light source of the second embodiment is the same as that of the plasma light source of the first embodiment. That is, the plasma light source of the second embodiment also includes a pair of coaxial electrodes 10, 10, a chamber 20, and a voltage application device 30 as shown in FIG. However, the coaxial electrode 10 and the voltage applying device 30 are slightly changed because the creeping discharge is adopted.

In the coaxial electrodes 10 and 10 of the second embodiment, the metal layer (thin film) 27 as the plasma medium region is
Of the surface of the insulator 16, it is formed in a portion between the center electrode 12 and the external electrode 14. When the planar discharge 2 along the insulator 16 is generated between the center electrode 12 and the external electrode 14, a part of the metal layer 27 is discharged as neutral gas or ions as a plasma medium from the surface. Is done.

  The voltage application device 30 according to the second embodiment includes a trigger switch 36 in addition to two high voltage power supplies (HV Charging Devices) 32 and 34.

  The trigger switch 36 includes a gap switch 38, a high voltage pulse generator (HV Pulser) 40, and a delay pulse generator (Delay Pulse Generator) 42, and a high voltage (discharge voltage) from the high voltage power sources 32 and 34, It applies to each coaxial electrode 10 simultaneously.

  The gap switch 38 generates a small discharge between two terminals having a large potential difference, thereby inducing a discharge between the terminals and obtaining a short-term electrical connection. That is, the gap switch 38 achieves a short-time electrical connection between the output side of the high-voltage power supply 32 (or the output side of the high-voltage power supply 34) and the center electrode 12 of one (or the other) coaxial electrode 10.

  The high voltage pulse generator 40 applies a high voltage pulse for generating this minute discharge to the gap switch 38. Therefore, when the high voltage pulse from the high voltage pulse generator 40 is applied to the gap switch 38 with the high voltage from the high voltage power sources 32 and 34 applied to each coaxial electrode 10, the high voltage power source 32 and one of the centers are arranged. The electrodes 12 and the high-voltage power supply 34 and the other center electrode 12 are electrically connected.

  The delay pulse generator 42 appropriately adjusts the timing at which the high voltage pulse is output from each high voltage pulse generator 40. When the simultaneous output timing can be obtained from each high voltage pulse, the delay pulse generator 42 may be omitted.

  The operation of the plasma light source according to the second embodiment is the same as the operation of the plasma light source according to the first embodiment except that the method of generating (igniting) the planar discharge 2 is different. That is, the gap switch 38 is maintained in a state in which the inside of the chamber 20 is maintained at a temperature and pressure suitable for plasma generation, and a high voltage from the high-voltage power supplies 32 and 34 is applied to the corresponding gap switch 38. The high voltage pulse of the high voltage pulse generator 40 is applied to As a result, the gap switch 38 becomes conductive, and the discharge voltages of the high-voltage power sources 32 and 34 are applied to the respective coaxial electrodes 10. As shown in FIG. 7, by this voltage application, a planar discharge 2 is generated between each of the plurality of external electrodes 14 and the center electrode 12, and a discharge is generated between each external electrode 14 and the center electrode 12. As a result, the planar discharge 2 in which the discharge is distributed over the entire circumference of the center electrode 12 is obtained.

  By such a planar discharge 2, a part of the metal layer 27 formed on the surface of the insulator 16 in each coaxial electrode 10, 10 is evaporated, and ions and gases containing Li are released. Thereafter, as in the first embodiment, the state of FIG. 4B is reached and the state of FIG. 4F is reached, and the plasma light 8 including extreme ultraviolet light is obtained from the high-temperature and high-density plasma 3. That is, the same effect as that of the plasma light source of the first embodiment can be obtained with the plasma light source of the second embodiment.

(Modification)
A modification of each of the above embodiments will be described.
As shown in FIG. 2, a metal layer 27 a made of the same material as the metal layer (thin film) 27 may be provided at the tip 12 a of each center electrode 12. The tip portion 12a is a place where the current of the planar discharge 2 is concentrated, and becomes extremely high during the generation of the planar discharge 2 and the plasma 3. Therefore, by providing the metal layer 27a as the plasma medium region at the tip 12a, the supply amount of the plasma medium to the plasma 3 can be increased, and the intensity of the desired extreme ultraviolet light can be increased. .

  In the first embodiment, as shown in FIG. 8, a metal layer (thin film) 27 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. Good. Or you may form this surface with the material containing the substance used as plasma media, such as Li. The structure of the coaxial electrode is the same as that of the second embodiment. In any case, the irradiation position of the laser beam 64a (64b) 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 64a (64b), and thereafter the sheet discharge 2 similar to the above is obtained.

  Further, as shown in FIGS. 9A and 9B, each coaxial electrode 10 includes a cylindrical electrode 15 centered on the central axis Z of the center electrode 12 instead of the plurality of external electrodes 14. Also good. A through hole (not shown) for passing the laser beam 64a (64b) is appropriately formed in the side surface 15a of the cylindrical electrode 15. In this case, it is difficult to control the location of the initial discharge as compared with the configuration in which a plurality of external electrodes 14 are provided, but only one energy storage circuit 50 and discharge current blocking circuit 52 is required for each coaxial electrode 10. The configuration of the voltage application device 30 is simplified.

  In addition, this invention is not limited to embodiment mentioned above, is shown by description of a claim, and also includes all the changes within the meaning and range equivalent to description of a claim.

DESCRIPTION OF SYMBOLS 1 ... Symmetrical plane, 2 ... Planar discharge, 3 ... Plasma, 6 ... Plasma medium, 8 ... Plasma light, 10 ... Coaxial electrode, 12 ... Center electrode, 14 ... External electrode, 16 ... Insulator, 17 ... Metal layer (Thin film), 20 ... chamber, 30 ... voltage application device, 32, 34 ... high voltage power supply, 36 ... trigger switch, 38 ... gap switch, 40 ... high voltage pulse generator, 42 ... delay pulse generator, 50 ... energy storage circuit 52 ... Discharge current blocking circuit, 60 ... Laser device, 62 ... Laser light

Claims (6)

A pair of coaxial electrodes that are arranged opposite to each other and generate plasma that emits extreme ultraviolet light therebetween and confine the plasma, and a voltage application device that applies a discharge voltage of the same polarity to each of the coaxial electrodes Prepared,
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 the center electrode from the external electrode. A plasma light source characterized by comprising: 2. The plasma light source according to claim 1, wherein the external electrode of each of the coaxial electrodes includes a plurality of rod-shaped electrodes arranged in a circumferential direction of the center electrode. The plasma light source according to claim 1, wherein the external electrode of each of the coaxial electrodes comprises a single cylindrical electrode.   2. The apparatus according to claim 1, further comprising a laser device that emits the plasma medium and generates an initial discharge of the plasma by irradiating the surface of the central electrode of each of the coaxial electrodes with laser light. 4. The plasma light source according to any one of 3 above.   4. The laser device according to claim 1, further comprising a laser device that irradiates a surface of the insulator of each of the coaxial electrodes with a laser beam to emit the plasma medium and generate an initial discharge of the plasma. The plasma light source according to any one of the above.   The said voltage application apparatus has a trigger switch which applies the said discharge voltage simultaneously between the said center electrode and the said external electrode of each said coaxial electrode, The Claim 1 thru | or 3 characterized by the above-mentioned. Plasma light source.

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