JP2013089635A - Plasma light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma light source capable of generating ideal planar discharge for generating plasma that radiates extreme-ultraviolet light.SOLUTION: The plasma light source comprises: a pair of coaxial electrodes 10 disposed to face each other and generate plasma that radiates extreme-ultraviolet light and confine the plasma; and a voltage application device 30 which applies a discharge voltage having an inverted polarity to each coaxial electrode 10. Each coaxial electrode 10 has a rod-like center electrode 12 extending on a single axis Z-Z, a plurality of external electrodes 14 provided on a plane that is axisymmetric with respect to the central axis Z of the center electrode 12, and an insulator 16 which insulates between the center electrode 12 and each external electrode 14. The gap G between the center electrode 12 and each external electrode 14 increases from the side facing the other coaxial electrode 10 toward the opposite side.

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 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. The plasma in the magnetic bin is Z pinched. 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 application device (not shown) is connected to each coaxial electrode, and energy corresponding to the light emission energy of the generated plasma is supplied from this voltage application device. Therefore, it is possible to stably obtain extreme ultraviolet light emitted from plasma for a long time (on the order of μsec).

JP 2010-147231 A

  When the plasma light source is used as a light source of an exposure apparatus, the size of plasma (that is, the emission size of extreme ultraviolet light) is limited by the specifications of the optical system. Under this restriction, since the distance between the side surface of the center electrode and the inner surface of the guide electrode is about 2.5 mm, discharge is likely to occur, but there is a possibility of generating extra plasma that does not contribute to the generation of extreme ultraviolet light. There is. When excess plasma is generated, a part of the supplied discharge current flows into this plasma. Therefore, the intensity of extreme ultraviolet light generated between the two coaxial electrodes may be reduced.

  In view of such concerns, an object of the present invention is to provide a plasma light source capable of generating an ideal planar discharge for generating plasma that emits extreme ultraviolet light.

  A first 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 a polarity with respect to each of the coaxial electrodes Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, and a plane axially symmetric with respect to the center axis of the center electrode. A plurality of external electrodes provided on the center electrode and an insulator that insulates between the center electrode and each of the external electrodes, and the distance between the center electrode and each of the external electrodes faces the other coaxial electrode The gist is that it increases from the side to the opposite side.

  A second 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 has a polarity with respect to each of the coaxial electrodes Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, a cylindrical external electrode surrounding the outer periphery of the center electrode, An insulator that insulates between the center electrode and the external electrode, and the distance between the side surface of the center electrode and the inner surface of the external electrode is directed from the side facing the counterpart coaxial electrode to the opposite side. The main point is that it has increased with the increase.

  The plasma light source according to the first aspect may further include an energy storage circuit that stores a discharge voltage from the voltage application device as discharge energy for each external electrode.

 The plasma light source according to the first aspect may further include a discharge current blocking circuit that blocks a discharge current from returning to the voltage application device.

  The voltage application device includes a positive voltage source that applies a positive discharge voltage higher than that of the external electrode to one central electrode of the pair of coaxial electrodes, and the other center of the pair of coaxial electrodes. You may have a negative voltage source which applies a negative discharge voltage lower than the guide electrode to an electrode.

  The voltage application device may include a trigger switch that simultaneously applies the positive voltage source and the negative voltage source to the respective coaxial electrodes.

  The plasma light source may further include a laser device that irradiates the surface of the insulator with laser light to perform ablation of the irradiated region.

  The plasma light source may further include a laser device that irradiates the surface of the central electrode of each of the coaxial electrodes with laser light to ablate the irradiation region. Further, a metal layer serving as the plasma medium may be provided in the irradiation region on a side surface of each of the center electrodes irradiated with the laser light.

  The plasma light source may further include an ultraviolet light source that irradiates the surface of the insulator with ultraviolet light.

  ADVANTAGE OF THE INVENTION According to this invention, the plasma light source which can generate | occur | produce the ideal planar discharge for producing | generating the plasma which radiates | emits extreme ultraviolet light 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. 3A and 3B are cross-sectional views taken along the line III-III of FIG. 2, in which FIG. It is operation | movement explanatory drawing of the plasma light source which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 1st modification of the plasma light source which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 2nd modification of the plasma light source which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the 3rd modification of the plasma light source 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 this embodiment includes a pair of coaxial electrodes 10, a chamber 20, and a voltage application device 30.

  The pair of coaxial electrodes 10 are installed in the chamber 20 and are positioned 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. At this time, 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 a gas containing at least one of Li, Xe, and Sn, for example.

  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, 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. 3A, the external electrode 14 is a rod-shaped conductor that extends in parallel with the central axis Z of the central electrode 12. A plurality of external electrodes 14 are arranged for each angle θ along the circumferential direction so as to surround the outer periphery of the center electrode 12. In other words, the plurality of external electrodes 14 are provided on an axisymmetric surface with respect to the central axis Z. In the example shown in FIG. 3A, six external electrodes 14 are arranged around the center electrode 12 every 60 °.

  Each external electrode 14 is inclined so as to approach toward a tip end portion (a portion facing the symmetry plane 1) 12 b of the center electrode 12. In other words, the distance G between the center electrode 12 and each external electrode 14 increases from the side facing the counterpart coaxial electrode 10 toward the opposite side.

  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. 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.

  Further, by inclining the external electrode 14 toward the distal end portion 12b of the center electrode 12, the electric field strength between the external electrode 14 and the central electrode 12 can have a gradient that increases toward the distal end portion 12b. . As is well known, discharge is more likely to occur and sustain as the electric field strength increases. In other words, the smaller the electric field strength, the less likely the discharge will occur. In the present embodiment, the interval between the external electrode 14 and the center electrode 12 is wider on the insulator 16 side described later. Therefore, when the planar discharge 2 is generated between the external electrode 14 and the center electrode 12, it is possible to suppress the occurrence of a discharge on the insulator 16 side accompanying the discharge. That is, it becomes a main current path of discharge, and generation of unnecessary plasma that adversely affects compression and acceleration of desired plasma (discharge) can be suppressed.

  Further, the planar discharge 2 not only moves to the symmetry plane 1 under the force of the self magnetic field, but also moves due to the electric field gradient described above. That is, this electric field gradient promotes the movement of the planar discharge 2 to the symmetry plane 1. Therefore, since the planar discharge 2 can be formed thinly along the central axis Z, the energy density per unit space can be increased. As a result, the intensity (light output) of the extreme ultraviolet light finally obtained can be improved.

  Even when the size of the light for exposure is specified as in the case of the light source for the exposure apparatus, the distance between the external electrode 14 and the center electrode 12 on the insulator 16 side described later is increased regardless of the specification. Can do. Therefore, generation | occurrence | production of an unnecessary discharge can be suppressed.

  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.

  The external electrode 14 is not limited to the rod-shaped body having a circular cross section shown in FIG. 3A, 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.

  A thin film 17 such as Li or a Li compound is formed on the surface of the insulator 16 between the center electrode 12 and the external electrode 14. When the planar discharge 2 is generated between the center electrode 12 and the external electrode 14, a gas containing Li as a plasma medium is generated from the thin film 17.

  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 with the polarity reversed to the coaxial electrode 10.

  Specifically, the voltage application device 30 includes a positive voltage source (HV Charging Device) 32, a negative voltage source (HV Charging Device) 34, and a trigger switch 36.

  On the output side of the positive voltage source 32, a positive discharge voltage higher 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) via the trigger switch 36.

  On the output side of the negative voltage source 34, a negative discharge voltage lower than that of the external electrode 14 is applied to the center electrode 12 of the other coaxial electrode 10 (for example, the right side in FIG. 1) via the trigger switch 36.

  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) from the positive voltage source 32 and the negative voltage source 34. Voltage) is simultaneously applied to the respective coaxial electrodes 10.

  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. Specifically, the gap switch 38 is a short-time electrical connection between the output side of the positive voltage source 32 (or the output side of the negative voltage source 34) and the center electrode 12 of one (or the other) coaxial electrode 10. Connection.

  The high voltage pulse generator 40 applies a high voltage pulse for generating this minute discharge to the gap switch 38. Accordingly, when the high voltage pulse of the high voltage pulse generator 40 is applied to the gap switch 38 with the high voltage from the positive voltage source 32 and the negative voltage source 34 applied, the positive voltage source 32 and the negative voltage source 34 are applied. Are electrically connected to each central electrode 12.

  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 output timing of each high voltage pulse is simultaneous, the delay pulse generator 42 may be omitted.

  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 positive voltage source 32 and the negative 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 that faces the center electrode 12 as a curved surface, and fixes a portion that is preferentially discharged. 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 positive voltage source 32 and the negative 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 positive voltage source 32 or the negative 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 positive voltage source 32 and the negative 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, the plasma light source of the present invention is configured to form a tubular discharge (described later) between the pair of coaxial electrodes 10 to contain the plasma in the axial direction.

  FIG. 4 is an operation explanatory view of the plasma light source of FIG. In this figure, (A) is when a sheet discharge is generated, (B) is during the movement of the sheet discharge, (C) is during plasma formation, (D) is when the sheet discharge and the tubular circle are connected. , (E) shows the time of formation of the plasma confined magnetic field.

  The operation of the plasma light source of the present invention will be described below with reference to this figure.

  In the plasma light source of the present embodiment, the pair of coaxial electrodes 10 described above are disposed in the chamber 20 so as to face each other, and a plasma medium is supplied into the coaxial electrode 10. The chamber 20 is maintained at a temperature and pressure suitable for generating plasma. Further, a discharge voltage with the polarity reversed is applied to each coaxial electrode 10 by the voltage application device 30. The application of the discharge voltage will be described in detail. With the high voltage from the positive voltage source 32 and the negative voltage source 34 applied to the gap switch 38, the high voltage pulse of the high voltage pulse generator 40 is applied to the gap switch 38. The As a result, the gap switch 38 becomes conductive, and the discharge voltages of the positive voltage source 32 and the negative voltage source 34 are applied to the respective coaxial electrodes 10.

  As shown in FIG. 4A, by this voltage application, a planar discharge 2 is generated on the surface of the insulator 16 in each of the pair of coaxial electrodes 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, thereby obtaining a planar discharge 2 in which the discharge is distributed over the entire circumference of the center electrode 12. It is done. Further, the inclination of the external electrode 14 with respect to the center electrode 12 promotes the movement of the planar discharge 2 in the direction toward the tip 12b (direction A in the figure), and conversely the direction toward the insulator 16 (in the figure). (B direction) is suppressed. Furthermore, the occurrence of other discharges in the space closer to the insulator 16 than the position of the planar discharge 2 is also suppressed.

  Due to the planar discharge 2, the Li or Li compound thin film 17 formed on the surface of the insulator 16 in each of the coaxial electrodes 10 and 10 is evaporated to generate a gas containing Li.

  At this time, the center electrode 12 of the left coaxial electrode 10 is applied with a positive voltage (+), and the surrounding external electrode 14 is applied with a negative voltage (−). On the other hand, the central electrode 12 of the right coaxial electrode 10 is applied with a negative voltage (−), and the surrounding external electrode 14 is applied with a positive voltage (+). The external electrode 14 is always grounded, but in a short period immediately after the discharge voltage is applied, it is substantially disconnected from the ground potential by the inductance of the wiring for grounding. Accordingly, each of the pair of opposed external electrodes 14 is equivalent to a state where voltages having different polarities are applied, and a potential difference is generated between the two.

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

  As shown in FIG. 4D, 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. 4E, the planar 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.

  When this tubular discharge 4 is formed, a plasma confining magnetic field (magnetic bin) 5 is formed, and as a result, the plasma 3 can be confined 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 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 including extreme ultraviolet light can be stably generated for a long time with high energy conversion efficiency.

  According to this embodiment, in each coaxial electrode, it becomes easy to obtain discharge over the entire circumference of the center electrode. As a result, a planar discharge distributed in a substantially annular shape is obtained. That is, since the uneven distribution of the discharge around the center electrode is suppressed, a substantially equal force due to the self magnetic field is applied to the planar discharge in each coaxial electrode. Therefore, since each planar discharge collides in the middle of each coaxial electrode, plasma containing extreme ultraviolet light can be stably generated for a long time. Since the occurrence rate of unevenly distributed discharge can be suppressed, energy conversion efficiency can be improved.

  The external electrode provided around the center electrode 12 may be a cylindrical electrode 15 (hereinafter referred to as the external electrode 15) centered on the central axis Z of the center electrode 12. In this case, if the diameter formed by the inner surface 15a of the external electrode 15 is D in the cross section orthogonal to the central axis Z, the external electrode 15 is gradually reduced in diameter D toward the symmetry plane 1. It is formed. In other words, the gap G between the inner surface 15a of the external electrode 15 and the side surface 12a of the center electrode 12 increases from the side facing the counterpart coaxial electrode 10 toward the opposite side. FIG. 3B is an example of the external electrode 15 having such a structure, and is formed in a hollow conical shape.

  In addition, the inclination angle of the external electrode 14 and the external electrode 15 with respect to the center electrode 12 is about 15 ° in this embodiment, but the present invention is not limited to this value and can be changed as appropriate. Further, the inclination angle may change so as to decrease from the insulator 16 side toward the tip end portion 12b. That is, each external electrode 14 or external electrode 15 may be curved in a cross section including the central axis Z.

(Modification)
A modification of the above-described embodiment will be described. 5 to 7 are modifications of the plasma light source of the present embodiment, FIG. 5 is a schematic configuration diagram according to the first modification, FIG. 6 is a schematic configuration diagram according to the second modification, and FIG. It is a schematic block diagram concerning the modification of 3. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted. For convenience of explanation, only one of the pair of coaxial electrodes 10 is shown, and the other is not shown.

  The modification shown in each drawing differs from the plasma light source described at the beginning in the method and configuration for generating the planar discharge 2. Therefore, the configuration of the coaxial electrode 10 is the same in any modification.

  As shown in FIG. 5, in the first modification of the present embodiment, a surface using a laser beam 62 of a pulse laser device (laser device) 60 instead of inducing the planar discharge 2 using the trigger switch 36. Induces a state discharge 2. Specifically, ablation is performed by irradiating the surface of the insulator 16 (for example, the thin film 17) with the laser beam 62 in a state where the discharge voltage of the voltage applying device 30 is applied to the coaxial electrode 10, and the surface discharge 2 To trigger. In addition, the discharge voltage at this time is set to a value that does not generate discharge by itself. That is, the voltage is lower than the voltage when the trigger switch 36 is applied.

  The pulse laser device 60 is, for example, a YAG laser, and outputs a double wave of the fundamental wave as a laser beam 62 for ablation. The laser light 62 can be applied to the surface of the insulator 16 (for example, the thin film 17) from the gap between the external electrodes 14. When the external electrode 15 (see FIG. 3B) is used, the through hole 13 for introducing the laser beam 62 may be formed on the side surface.

  By this ablation, a part of the thin film 17 is released as a gas (or plasma) 18 and induces a discharge between the center electrode 12 and each external electrode 14. Further, the sheet discharge 2 shown in FIG. 4A is formed by this discharge. Thereafter, the state of FIG. 4B is reached to the state of FIG. 4E, and the plasma light 8 including extreme ultraviolet light is stably obtained.

  In this modified example, since the initial discharge is generated by ablation, the trigger switch 36 becomes unnecessary. Instead, the location where the induced discharge is generated may be limited to the vicinity of the irradiation region of the laser light 62. Therefore, it is preferable to irradiate the laser beam 62 to a plurality of locations of the insulator 16 at the same time, and the number is at least two. This is based on the experimental result that when the laser beam 62 is irradiated to one place of the insulator 16, the area of the induced discharge is 180 degrees or more in terms of the opening angle range viewed from the center electrode 12. . Considering this result, it can be said that it is desirable to irradiate the laser beam 62 at a rotationally symmetric position with respect to the center electrode 12 as the number of irradiated portions of the laser beam 62 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.

  In the above-described modification, the irradiation location of the laser beam 62 can be controlled, so that the occurrence location of creeping discharge on the insulator 16 can be controlled, and the number of occurrences can also be controlled. Therefore, it is easy to control the discharge over the entire circumference of the center electrode 12.

  Moreover, since the irradiation timing of the laser beam 62 can be adjusted, it becomes easy to generate many creeping discharges simultaneously. Furthermore, by using the induction of discharge due to ablation, it becomes possible to lower the dielectric breakdown voltage necessary for the occurrence of creeping discharge. For example, it is possible to reduce the discharge voltage of the voltage application device 30 as compared with the embodiment that does not use laser light. In this case, since excessive discharge energy is suppressed, it is possible to suppress the progress of damage to the coaxial electrode 10 due to heat, for example.

  As shown in FIG. 6, in the second modification of the present embodiment, a state in which the discharge voltage from the voltage application device 30 is applied to the coaxial electrode 10 instead of inducing the planar discharge 2 using the trigger switch 36. Then, the irradiation region is ablated by irradiating the side surface (external electrode 14) of the central electrode 12 with the laser light 62 of the pulse laser device (laser device) 60 from the gap between the adjacent external electrodes 14. A metal layer (thin film) 27 containing Li serving as a plasma medium in advance is provided on the side surface of the central electrode 12 serving as an irradiation region. By this ablation, a part of the metal layer 27 is released as a gas (or plasma) 28 and induces a discharge between the center electrode 12 and each external electrode 14. Further, the sheet discharge 2 shown in FIG. 4A is formed by this discharge. Thereafter, the state of FIG. 4B is reached to the state of FIG. 4E, and the plasma light 8 including extreme ultraviolet light can be obtained more stably.

Similarly to the first modified example described above, this modified example may limit the location where the induced discharge is generated in the vicinity of the irradiation region of the laser light 62. Therefore, it is preferable to irradiate the laser beam 62 to a plurality of locations on the metal layer 27 simultaneously, and the number thereof is at least two. The structure which irradiates the laser beam 62 to a plurality of places can be the same as that of the first modification. The second modification can achieve the same effect as the first modification described above.
As shown in FIG. 7, in the third modification of the present embodiment, in addition to the configuration of the plasma light source shown in FIG. 1, there is an ultraviolet light source 64 that irradiates the surface of the insulator 16 (for example, the thin film 17) with ultraviolet light 66. Provided. The ultraviolet ray 66 has an effect of lowering an applied voltage for generating creeping discharge on the insulator 16. In other words, the ultraviolet light source 64 assists the generation of discharge by the trigger switch 36. As a result, an initial discharge over the entire circumference of the center electrode 12 can be easily obtained, and an ideal sheet discharge 2 can be stably obtained. After that, as in the other embodiments, the state of FIG. 4B is changed to the state of FIG. 4E, and the plasma light 8 including extreme ultraviolet light can be obtained more stably.

  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, 4 ... Tubular discharge, 5 ... Magnetic bin, 6 ... Plasma medium, 8 ... Plasma light, 10 ... Coaxial electrode, 12 ... Center electrode, 14 ... (plurality) External electrode, 15 ... (cylindrical) external electrode, 16 ... insulator, 17 ... thin film, 20 ... chamber, 30 ... voltage application device, 32 ... positive voltage source, 34 ... negative voltage source, 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, 64 ... Ultraviolet light source, 66 ... UV

Claims (9)

A pair of coaxial electrodes that are arranged opposite to each other, 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. Prepared,
Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, a plurality of external electrodes provided on a plane axially symmetric with respect to the center axis of the center electrode, the center electrode, and the An insulator that insulates between the external electrodes;
The plasma light source characterized in that the distance between the center electrode and each external electrode increases from the side facing the counterpart coaxial electrode toward the opposite side. A pair of coaxial electrodes that are arranged opposite to each other, 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. Prepared,
Each of the coaxial electrodes includes a rod-shaped center electrode extending on a single axis, a cylindrical outer electrode surrounding the outer periphery of the center electrode, and an insulator that insulates between the center electrode and the outer electrode. Have
The plasma light source characterized in that the distance between the side surface of the center electrode and the inner surface of the external electrode increases from the side facing the counterpart coaxial electrode toward the opposite side.   The plasma light source according to claim 1, further comprising an energy storage circuit that stores a discharge voltage from the voltage application device as discharge energy for each external electrode.   4. The plasma light source according to claim 3, further comprising a discharge current blocking circuit for blocking discharge current from returning to the voltage application device.   The voltage application device includes a positive voltage source that applies a positive discharge voltage higher than that of the external electrode to one central electrode of the pair of coaxial electrodes, and the other center of the pair of coaxial electrodes. The plasma light source according to claim 1, further comprising a negative voltage source that applies a negative discharge voltage lower than that of the external electrode to the electrode.   6. The plasma light source according to claim 5, wherein the voltage application device includes a trigger switch for simultaneously applying the positive voltage source and the negative voltage source to respective coaxial electrodes.   The plasma light source according to claim 5, further comprising a laser device that irradiates the surface of the insulator with laser light to perform ablation of the irradiation region.   A laser device that irradiates the surface of the central electrode of each of the coaxial electrodes with laser light to perform ablation of the irradiation region is further provided. 6. The plasma light source according to claim 5, further comprising a metal layer serving as the plasma medium.   The plasma light source according to claim 6, further comprising an ultraviolet light source for irradiating the surface of the insulator with ultraviolet light.

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