JP5953735B2 - Plasma light source - Google Patents

Description

  The present invention relates to a plasma light source for EUV radiation.

  Lithography using an extreme ultraviolet light source is expected for fine processing of next-generation semiconductors. Lithography is a technique for forming an electronic circuit by exposing a resist material to light and a beam by reducing and projecting them onto a silicon substrate through a mask on which a circuit pattern is drawn. The minimum processing dimension of a circuit formed by photolithography basically depends on the wavelength of the light source. Therefore, it is essential to shorten the wavelength of the light source for next-generation semiconductor development, and research for this light source development is underway.

  The most promising next generation lithography light source is an extreme ultraviolet light source (EUV: Extreme Ultra Violet), which means light in the wavelength region of approximately 1 to 100 nm. The light in this region has a high absorptance with respect to all substances, and a transmissive optical system such as a lens cannot be used. Therefore, a reflective optical system is used. In addition, the optical system in the extreme ultraviolet region is very difficult to develop, and exhibits a reflection characteristic only at a limited wavelength.

  Currently, a Mo / Si multilayer reflector having a sensitivity of 13.5 nm has been developed, and if a lithography technique combining light of this wavelength and the reflector is developed, it is expected that a processing dimension of 30 nm or less can be realized. ing. Development of a lithography light source with a wavelength of 13.5 nm is urgently required to realize further microfabrication technology, and radiation from a high energy density plasma has attracted attention. The plasma light source is described in Patent Document 1.

  Light source plasma generation can be broadly classified into laser irradiation (LPP: Laser Produced Plasma) and gas discharge (DPP: Discharge Produced Plasma) driven by pulse power technology. An LPP type EUV light source is described in Patent Document 2.

  An EUV lithography light source is required to have a high average output, a small light source size, a small amount of scattered particles (debris), and the like. At present, the EUV emission amount is extremely low with respect to the required output, and increasing the output is one of the major issues. On the other hand, if the input energy is increased for increasing the output, the damage caused by the thermal load will be caused by the plasma generator and The lifetime of the optical system is reduced. Therefore, high energy conversion efficiency is indispensable to satisfy both high EUV output and low heat load.

  In the initial stage of plasma formation, in addition to consuming a lot of energy for heating and ionization, high-temperature and high-density plasma that emits EUV generally expands rapidly, so the radiation duration τ is extremely short. . Therefore, in order to improve the conversion efficiency, it is important to maintain the plasma in a high temperature and high density state suitable for EUV radiation for a long time (on the order of μsec).

  Room-temperature solid media such as Sn and Li have high spectral conversion efficiency, but the plasma generation is accompanied by phase changes such as melting and evaporation, so the effect of contamination inside the device due to debris (derived from discharge) such as neutral particles Becomes larger. Therefore, the target supply and recovery system must be strengthened as well.

  The radiation time of the current general EUV plasma light source is about 100 nsec, and the output is extremely insufficient. In order to achieve both high conversion efficiency and high average output for industrial applications, it is necessary to achieve an EUV radiation time of several μsec per shot. In other words, in order to develop a plasma light source having high conversion efficiency, it is necessary to achieve stable EUV radiation by constraining plasma in a temperature density state suitable for each target for several μsec (at least 1 μsec or more).

  Furthermore, the conventional capillary discharge has a drawback that the effective radiation solid angle is small because the plasma is confined in the capillary.

  Therefore, the inventors of the present application can stably generate plasma light for EUV radiation for a long time (on the order of μsec), and the damage caused by the thermal load of the component equipment is small, and the generated plasma light is effective. The “plasma light source and plasma light generation method” (Patent Document 3) was invented for the purpose of increasing the solid solid angle and supplying the plasma medium continuously.

  FIG. 1 is a diagram showing an embodiment of the plasma light source, which includes a pair of coaxial electrodes 50 arranged to face a symmetry plane 51, and a pair of coaxial electrodes 50 each having a planar discharge current (surface). And a single plasma is formed at the opposite intermediate position of each coaxial electrode 50, and then the planar discharge is switched to a tubular discharge between a pair of coaxial electrodes. By forming a magnetic field (magnetic bin) that contains the plasma, plasma light for EUV radiation is stably generated for a long time (on the order of μsec).

Japanese Patent Application Laid-Open No. 2004-226244, “Extreme Ultraviolet Light Source and Semiconductor Exposure Apparatus” Japanese Patent Application Laid-Open No. 2011-54376, “LPP EUV light source and generation method thereof” JP 2010-147231 A, “Plasma light source and plasma light generation method”

  By the way, in the plasma light source, it is difficult to control the potential at the coaxial electrode, and therefore, it is also difficult to control switching of the planar discharge between the coaxial electrodes 50 to the tubular discharge.

  The present invention has been developed to solve the above-described problems. That is, an object of the present invention is to generate a sheet discharge at a pair of coaxial electrodes, form a single plasma at the opposite intermediate position of each coaxial electrode, and then generate a sheet discharge. Provided is a plasma light source that forms a magnetic field (magnetic bin) for confining plasma by switching to a tubular discharge between a pair of coaxial electrodes, and provides a plasma light source that facilitates switching from a planar discharge to a tubular discharge. For the purpose.

According to the present invention, the first and second coaxial electrodes arranged opposite to each other, and the discharge environment holding for holding the plasma medium in the first and second coaxial electrodes at a temperature and pressure suitable for plasma generation. And a voltage applying device for applying a discharge voltage having a reversed polarity to the first and second coaxial electrodes, and forming a tubular discharge between the first and second coaxial electrodes. A plasma light source that contains plasma in the axial direction,
The plasma light source is provided, wherein the second coaxial electrode is in an electrically floating state with respect to the first coaxial electrode.

  It is preferable that the second coaxial electrode is electrically insulated from the first coaxial electrode.

  The discharge environment holding device preferably includes a chamber that holds the first and second coaxial electrodes, and an insulating member is provided between the second coaxial electrode and the chamber.

The first and second coaxial electrodes include a rod-shaped center electrode extending on a single axis, a tubular guide electrode surrounding the center electrode at a predetermined interval, and a gap between the center electrode and the guide electrode. It consists of a ring-shaped insulator that is located and insulates between them,
It is preferable that the center electrodes of the first and second coaxial electrodes are located on the same axis and are symmetrically spaced apart from each other.

  The voltage application device includes: a positive voltage source that applies a positive discharge voltage higher than the guide electrode to one central electrode of the first and second coaxial electrodes; and the first and second coaxial electrodes It is preferable to have a negative voltage source that applies a negative discharge voltage lower than that of the guide electrode to the other center electrode, and a trigger switch that simultaneously applies the positive voltage source and the negative voltage source to the respective coaxial electrodes.

  It is preferable that the discharge environment holding device includes a gas supply means for supplying a discharge generation assist gas that promotes the generation of discharge.

  According to the apparatus of the present invention, a pair of coaxial electrodes arranged opposite to each other are provided, and a planar discharge current (planar discharge) is generated in each of the pair of coaxial electrodes. A single plasma is formed at the opposite intermediate position of the coaxial electrode, and then the planar discharge is switched to a tubular discharge between a pair of coaxial electrodes to form a magnetic field (magnetic bin) that contains the plasma. , Plasma light for EUV radiation can be stably generated for a long time (on the order of μsec).

  In addition, compared with conventional capillary discharge or vacuum discharge metal plasma, a single plasma is formed at the opposite intermediate position of a pair of coaxial electrodes, and the energy conversion efficiency can be greatly improved. The thermal load on each electrode is reduced, and the damage caused by the thermal load on the component equipment can be greatly reduced.

  Further, since plasma that is a light emission source of plasma light is formed at an intermediate position between the pair of coaxial electrodes, an effective solid angle of radiation of the generated plasma light can be increased.

  Furthermore, the tubular discharge can be reliably formed by facilitating the switching of the current path from the planar discharge to the tubular discharge.

  Furthermore, by supplying the discharge assist gas by the gas supply unit, the current path from the planar discharge to the tubular discharge can be reliably switched.

It is an embodiment figure of the conventional plasma light source. 1 is an embodiment diagram of a plasma light source according to the present invention. FIG. It is operation | movement explanatory drawing of the plasma light source by this invention. It is a figure which shows a modification. It is a figure which shows a 1st comparative example. It is a figure which shows the electric potential distribution in a 1st comparative example. It is a figure which shows the 2nd comparative example. It is a figure which shows the electric potential distribution in a 2nd comparative example. It is a figure which shows a 3rd comparative example.

  Hereinafter, preferred embodiments 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.

  FIG. 2 is a diagram showing an embodiment of a plasma light source according to the present invention.

  In this figure, the plasma light source of the present invention includes first and second coaxial electrodes 10, 10 ′, a chamber 20, and a voltage application device 30.

  The first and second coaxial electrodes 10, 10 ′ are arranged in the chamber 20 so as to face each other about the symmetry plane 1.

  In this example, the first coaxial electrode 10 is directly attached to the chamber 20 and is electrically connected to the chamber 20. On the other hand, the second coaxial electrode 10 ′ is attached to the chamber 20 via the ring-shaped insulator 18 and is electrically insulated from the chamber 20.

  The first coaxial electrode 10 includes a rod-shaped center electrode 12, a tubular guide electrode 14, and a ring-shaped insulator 16. Similarly, the second coaxial electrode 10 ′ includes a rod-shaped center electrode 12 ′, a tubular guide electrode 14 ′, and a ring-shaped insulator 16 ′.

  The rod-shaped center electrodes 12 and 12 'are conductive electrodes extending on a single axis ZZ.

  In this example, the end faces of the center electrodes 12, 12 'facing the symmetry plane 1 are arcuate. This configuration is not essential, and a concave hole may be provided on the end surface to stabilize the planar discharge 2 and the tubular discharge 4 described later, or a flat surface.

  Tubular guide electrodes 14 and 14 'surround the center electrodes 12 and 12' at a predetermined interval and hold a plasma medium therebetween. The plasma medium is preferably a Li gas, but may be a Xe or Sn gas. Further, the end surfaces of the guide electrodes 14, 14 'facing the symmetry plane 1 may be arcuate or flat.

  The ring-shaped insulators 16 and 16 ′ are hollow cylindrical electrical insulators positioned between the center electrodes 12 and 12 ′ and the guide electrodes 14 and 14 ′, and the center electrodes 12 and 12 ′ and the guide electrode 14. , 14 'are electrically insulated.

  In the insulators 16 and 16 ′, the surface between the center electrodes 12 and 12 ′ and the guide electrodes 14 and 14 ′ is caused by the surface discharge 2 between the center electrodes 12 and 12 ′ and the guide electrodes 14 and 14 ′. A thin film 17 of Li or Li compound is formed so that Li generates gas.

  The shape of the insulators 16 and 16 'is not limited to this example, and may be other shapes as long as the center electrode 12 and the guide electrode 14 are electrically insulated.

  The ring-shaped insulator 18 is a hollow cylindrical electrical insulator positioned between the guide electrode 14 ′ of the second coaxial electrode 10 ′ and the chamber 20. Insulate.

  The shape of the insulator 18 is not limited to this example, and may be other shapes as long as the guide electrode 14 ′ of the second coaxial electrode 10 ′ and the chamber 20 are electrically insulated. .

  In the first and second coaxial electrodes 10 and 10 'described above, the center electrodes 12 and 12' are positioned on the same axis ZZ and are symmetrically spaced from each other at a constant interval.

  The chamber 20 constitutes a discharge environment holding device, supplies a plasma medium into the first and second coaxial electrodes 10, 10 ', and the first and second coaxials at a temperature and pressure suitable for plasma generation. The shaped electrodes 10 and 10 'are held. The chamber 20 is connected to a vacuum pump by an exhaust pipe 22 and is maintained at a predetermined pressure.

  The chamber 20 is preferably made of metal and is preferably grounded. The chamber 20 is preferably provided with a predetermined opening window for extracting plasma light 8 (EUV).

  In contrast to the chamber 20 and the first coaxial electrode 10, the second coaxial electrode 10 ′ is separated by an insulator 18 and is not electrically connected in a state where no discharge is formed. In a floating state. As will be described later, when the discharge is formed, the potential of the second coaxial electrode 10 ′ becomes constant with respect to the first coaxial electrode 10 and the chamber 20.

  The voltage application device 30 applies a discharge voltage with the polarity reversed to the first and second coaxial electrodes 10, 10 ′.

  The voltage application device 30 includes a positive voltage source 32, a negative voltage source 34, and a trigger switch 36.

  In this example, the positive voltage source 32 and the negative voltage source 34 are each composed of a high voltage charger (HV Charging Device) and a capacitor. The trigger switch 36 includes a delay pulse generator (Delay Pulse Generator), a high voltage pulse generator (HV Pulser), and a gap switch. In this example, the delay pulse generator generates a trigger pulse without delay.

  The positive voltage source 32 applies a positive discharge voltage higher than that of the guide electrode 14 to the center electrode 12 of the first coaxial electrode 10.

  The negative voltage source 34 applies a negative discharge voltage lower than that of the guide electrode 14 ′ to the center electrode 12 ′ of the second coaxial electrode 10 ′.

  In the present embodiment, for convenience, the positive voltage source 32 applies a voltage to the first coaxial electrode 10 and the negative voltage source 34 applies a voltage to the second coaxial electrode 10 ′. The present invention is not limited to this. The positive voltage source 32 may apply a voltage to the second coaxial electrode 10 ′, and the negative voltage source 34 may apply a voltage to the first coaxial electrode 10.

  The positive voltage source 32 and the negative voltage source 34 are provided with inductively coupled lines in order to observe the current supplied to the center electrodes 12 and 12 ′ with an oscilloscope.

  The trigger switch 36 operates the positive voltage source 32 and the negative voltage source 34 at the same time, and simultaneously applies positive and negative discharge voltages to the respective coaxial electrodes 12 and 12 ′.

  With this configuration, the plasma light source of the present invention is configured to form a tubular discharge (described later) between the first and second coaxial electrodes 10 and 10 'to contain the plasma in the axial direction.

  FIG. 3 is an operation explanatory diagram 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 during charge transfer, and (E) is plasma confinement. It shows the time of magnetic field formation.

  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 invention, the first and second coaxial electrodes 10, 10 ′ are arranged to face each other, the plasma medium is supplied into the first and second coaxial electrodes 10, 10 ′ by the discharge chamber 20, and A temperature and pressure suitable for plasma generation are maintained, and a voltage application device 30 applies a discharge voltage whose polarity is reversed to the first and second coaxial electrodes 10, 10 ′.

  As shown in FIG. 3 (A), by applying this voltage, the first and second coaxial electrodes 10, 10 ′ have a planar discharge current (hereinafter referred to as planar discharge) on the surfaces of the insulators 16, 16 ′. 2) occurs. The planar discharge 2 is a planar discharge current that spreads two-dimensionally, and is also referred to as a “current sheet” in the examples described later.

  By such a planar discharge 2, the surface of the Li or Li compound thin film 17 formed on the surface of the insulator 16 in the first and second coaxial electrodes 10, 10 ′ evaporates to generate Li gas.

  At this time, the center electrode 12 of the first coaxial electrode 10 is applied with a positive voltage (+), the guide electrode 14 is applied with a negative voltage (−), and the center electrode 12 of the second coaxial electrode 10 ′ is applied with a negative voltage. (−), The guide electrode 14 ′ is applied to a positive voltage (+).

  As shown in FIG. 3B, the planar discharge 2 moves in a direction (direction toward the center in the figure) discharged from the electrode by the self magnetic field.

  As shown in FIG. 3C, when the planar discharge 2 reaches the tips of the first and second coaxial electrodes 10, 10 ′, the plasma medium 6 sandwiched between the pair of planar discharges 2 Becomes a high density and a high temperature, and a single plasma 3 is formed at an intermediate position (symmetric plane 1 of the center electrodes 12 and 12 ') of the first and second coaxial electrodes 10 and 10'.

  As shown in FIG. 3D, when the planar discharge 2 extending from the tips of the first and second coaxial electrodes 10 and 10 'comes into contact, the first and second coaxial electrodes 10 and 10' It becomes a conductive state.

  As a result, electric charges are transferred from the first coaxial electrode 10 ′ to the second coaxial electrode 10 ′ that has been in an electrically floating state, and the potential of the second coaxial electrode 10 ′ is changed between the first and second coaxial electrodes 10 ′. The two coaxial electrodes 10 and 10 'are naturally determined so that current flows through the center electrodes 12 and 12' and the guide electrodes 14 and 14 'in the forward direction.

  The charge transfer is naturally adjusted to be matched in a configuration including the first and second coaxial electrodes 10, 10 '. Here, since the potential of the second coaxial electrode 10 ′ is in a state in which a current flows in a forward direction in which the entire system including the first and second coaxial electrodes 10 and 10 ′ is most stable, There is no need to control.

  By such charge movement, the pair of opposed center electrodes 12 and 12 ′ become a positive voltage (+) and a negative voltage (−), and similarly, the pair of opposed guide electrodes 14 and 14 ′ are also positive. Since the voltage (+) and the negative voltage (−) are obtained, as shown in FIG. 3 (E), the sheet discharge 2 is caused by a pair of opposed center electrodes 12 and a pair of opposed guide electrodes 14, 14. It is switched to the tubular discharge 4 that discharges between the ′. Here, the tubular discharge 4 means a hollow cylindrical discharge current surrounding the axis ZZ.

  When this tubular discharge 4 is formed, a plasma confinement magnetic field (magnetic bin) indicated by reference numeral 5 in the figure is formed, and 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. 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 emission energy of the plasma 3 is continuously supplied from the voltage application device 30, the plasma light 8 (EUV) can be stably generated for a long time with high energy conversion efficiency.

  According to the plasma light source of the present invention described above, the first and second coaxial electrodes 10 and 10 ′ arranged to face each other are provided, and planar discharges are respectively applied to the first and second coaxial electrodes 10 and 10 ′. A current (planar discharge 2) is generated, and a single plasma 3 is formed by the planar discharge 2 at an intermediate position where the first and second coaxial electrodes 10 and 10 'face each other. Since the plasma discharge magnetic field 5 (magnetic bin 5) for confining the plasma 3 is formed by switching to the tubular discharge 4 between the first and second coaxial electrodes 10, 10 ', the plasma light for EUV radiation is long. It can be generated stably (in the order of μsec).

  In addition, compared with the conventional capillary discharge or vacuum photoelectric metal plasma, a single plasma 3 is formed at the intermediate position where the first and second coaxial electrodes 10, 10 'are opposed to each other, and the energy conversion efficiency is greatly improved ( 10 times or more), the thermal load of each electrode during plasma formation is reduced, and the damage due to the thermal load of the component equipment can be greatly reduced.

  In addition, since the plasma 3 which is the light source of the plasma light is formed at the intermediate position where the first and second coaxial electrodes 10 and 10 ′ are opposed to each other, the effective radiation solid angle of the generated plasma light can be increased.

  Further, in the present invention, the second coaxial electrode 10 ′ is attached to the chamber 20 via the insulator 18 and is in an electrically floating state with respect to the first coaxial shape 10 and the chamber 20. However, the electric charge moved from the first coaxial electrode 10 to the second coaxial electrode 10 ′ by the discharge between the first and second coaxial electrodes 10, 10 ′, and was electrically floating. The charge is transferred from the first coaxial electrode 10 to the second coaxial electrode 10 ′, and the potential of the second coaxial electrode 10 ′ is the center electrode of the first and second coaxial electrodes 10, 10 ′. 12 and 12 'and the guide electrodes 14 and 14' are naturally determined at potentials that allow current to flow in the forward direction.

  Thus, according to the present invention, the potentials of the center electrodes 12, 12 'and the guide electrodes 14, 14' of the first and second coaxial electrodes 10, 10 'are naturally increased so that a current flows in the forward direction. Adjusted. Therefore, it becomes easy to switch the planar discharge 2 between the first and second coaxial electrodes 10, 10 'to the tubular discharge 4, and the tubular discharge 4 can be provided reliably.

[Modification]
FIG. 4 is a diagram illustrating a modification of the present embodiment. In this modification, a gas supply unit 40 for supplying a discharge assist gas is further provided in the embodiment shown in FIG.

  In this modification, the gas supply unit 40 supplies hydrogen as a discharge assist gas to the chamber 20 so that the chamber 20 is filled with hydrogen from several mTorr to several Torr. The hydrogen supplied to the chamber 20 acts as an electron source without emitting or absorbing EUV.

  In this modification, as shown in FIG. 3A, a voltage is applied to the first and second coaxial electrodes 10, 10 ′, and creeping discharge is generated on the surfaces of the insulators 16, 16 ′. At this time, hydrogen supplied from the gas supply unit 40 in addition to Li evaporated from the surfaces of the insulators 16 and 16 'is ionized into plasma, so that the plasma density is increased due to the contribution of hydrogen compared to the embodiment shown in FIG. To increase.

  Further, as shown in FIG. 3B, when the planar discharge 2 moves in the direction of being discharged from the first and second coaxial electrodes 10, 10 ′, hydrogen in the traveling path is gradually accumulated and the surface discharge is performed. A so-called snow-scraping effect occurs in which the density of the plasma sheet of the discharge 2 increases.

  At this time, due to the presence of hydrogen, the plasma sheet tip of the planar discharge 2 is braked, the plasma sheet is compressed in the thickness direction, and the density of the plasma sheet increases. Further, due to the increase in the density of the plasma sheet of the planar discharge 2, the impedance of the plasma sheet is lowered, and the leakage current flowing through the part other than the plasma sheet is relatively reduced.

  As shown in FIG. 3C, when the planar discharge 2 reaches the tips of the first and second coaxial electrodes 10, 10 ′, the density of the plasma discharge of the planar discharge 2 is ensured. As the discharge current passing through the plasma sheet of the planar discharge 2 increases, the potential of the second coaxial electrode 10 ′ is adjusted by the charge transfer caused by the plasma as shown in FIG. Here, the introduction of hydrogen improves the in-plane uniformity of the plasma sheet of the planar discharge 2 and improves the current switching efficiency.

  In this modification, hydrogen is exemplified as the discharge assist gas, but the discharge assist gas is not limited to hydrogen. For example, helium can be used instead of hydrogen.

[Comparative Example 1]
FIG. 5 shows a first comparative example. The first comparative example is the embodiment shown in FIG. 2 except that the insulator 18 is removed and the second coaxial electrode 10 ′ is directly attached to the chamber 20 and the flange portion of the chamber 20 is grounded. .

  Since the other configuration is the same as that of the embodiment shown in FIG. 2, the same reference numerals are given and the description thereof is omitted.

  The planar discharge 2 in the figure schematically shows the direction in which current flows from the center electrodes 12, 12 'to the guide electrodes 14, 14' by arrows.

  FIG. 6 shows a potential distribution in a state in which the planar discharge 2 is formed on the first and second coaxial electrodes 10 and 10 ′ in the first comparative example (corresponding to FIG. 3B). FIG.

From the potential V _{1 at} the positive potential point P ₁ of the positive voltage source 32 to the potential V _{2 at} the discharge generation position P ₂ of the center electrode 12 and the potential V ₃ at the discharge generation position P ₃ of the guide electrode 14, the chamber 20. The potentials V ₁ , V ₂ , V ₃ , and V ₄ gradually decrease until reaching the potential V ₄ at the ground point P ₄ .

Similarly, from the potential V ₁ ′ at the negative potential point P ₁ ′ of the negative voltage source 33 to the potential V ₂ ′ at the discharge generation position P ₂ ′ of the center electrode 12 ′, the discharge generation position P ₃ ′ of the guide electrode 14 ′. The potentials V ₁ ′, V ₂ ′, V ₃ ′, and V ₄ ′ gradually rise to the potential V ₄ ′ at the ground point P ₄ ′ of the chamber 20 through the potential V ₃ ′ at.

The potentials V ₄ and V ₄ ′ at the ground points P ₄ and P ₄ ′ of the chamber 20 are ground potentials.

Here, the potentials at the tips of the guide electrodes 14, 14 ′ of the first and second coaxial electrodes 10, 10 ′ (at the discharge generation positions P ₃ , P ₃ ′ of the first and second guide electrodes 14, 14 ′). For the voltages V ₃ and V ₃ ′), the potential V ₃ at the tip of the guide electrode 14 of the first coaxial electrode 10 is equal to the potential V ₃ ′ at the tip of the guide electrode 14 ′ of the second coaxial electrode 10 ′. Higher.

  The potential arrangement at the tips of the guide electrodes 14 and 14 'of the first and second coaxial electrodes 10 and 10' is such that the guide electrode of the second coaxial electrode 10 'in a state where the tubular discharge 4 is formed. The direction is opposite to that in the flow of current from 14 ′ to the guide electrode 14 of the first coaxial electrode 10.

  That is, in the state where the tubular discharge 4 is formed, the potential at the tip of the guide electrode 14 of the first coaxial electrode 10 is lower than the potential at the tip of the guide electrode 14 ′ of the second coaxial electrode 10 ′. There is a need.

  Therefore, in the first comparative example, the switching from the planar discharge 2 (corresponding to FIG. 3C) to the tubular discharge 4 (corresponding to FIG. 3E) is the reverse of this. Difficult due to potential arrangement in the direction.

[Comparative Example 2]
FIG. 7 shows a second comparative example. In the second comparative example, in the embodiment shown in FIG. 2, the insulator 18 is excluded, the second coaxial electrode 10 ′ is directly attached to the chamber 20, the flange portion of the chamber 20 is grounded, The tip ends of the guide electrodes 14 and 14 ′ of the first and second coaxial electrodes 10 and 10 ′ are connected (connected) by a metal member 19.

  The metal member 19 can be attached in three directions, four directions or the like so as to be rotationally symmetric with respect to the axis ZZ.

  Since the other configuration is the same as that of the embodiment shown in FIG. 2, the same reference numerals are given and the description thereof is omitted.

  The planar discharge 2 in the figure schematically shows the direction in which current flows from the center electrodes 12, 12 'to the guide electrodes 14, 14' by arrows.

  FIG. 8 shows a potential distribution in a state in which the planar discharge 2 is formed on the first and second coaxial electrodes 10 and 10 ′ in the first comparative example (corresponding to FIG. 3B). FIG.

From the potential V _{1 at} the positive potential point P ₁ of the positive voltage source 32 to the potential V _{2 at} the discharge generation position P ₂ of the center electrode 12 and the potential V ₃ at the discharge generation position P ₃ of the guide electrode 14, the chamber 20. The potentials V ₁ , V ₂ , V ₃ , and V ₄ gradually decrease until reaching the potential V ₄ at the ground point P ₄ .

Similarly, from the potential V ₁ ′ at the negative potential point P ₁ ′ of the negative voltage source 33 to the potential V ₂ ′ at the discharge generation position P ₂ ′ of the center electrode 12 ′, the discharge generation position P ₃ ′ of the guide electrode 14 ′. The potentials V ₁ ′, V ₂ ′, V ₃ ′, and V ₄ ′ gradually rise to the potential V ₄ ′ at the ground point P ₄ of the chamber 20 via the potential V ₃ ′ at.

In the second comparative example, not only the chamber 20 is grounded at the ground points P ₄ and P ₄ ′ but also the tips of the guide electrodes 14 and 14 ′ of the first and second coaxial electrodes 10 and 10 ′ are connected members. Since the connection is made at 19, the potential arrangement is more complicated than in the first comparative example.

That is, the potential difference between the discharge generation points P ₃ and P ₃ ′ in the guide electrodes 14 and 14 ′ of the first and second coaxial electrodes 10 and 10 ′ is smaller than that in the first comparative example. the potential V ₄ in the ground point P ₄ of the chamber 20 in the path through the coaxial electrodes 10, lower than the _'potential V ₄ in _the' second ground point P ₄ of the chamber 20 in the path through the coaxial electrodes 10 ' doing.

Also in the second comparative example, the potentials at the tips of the guide electrodes 14 and 14 'of the first and second coaxial electrodes 10, 10' (the discharge generation position P _{3 of} the first and second guide electrodes 14 and 14 '). , P ₃ ′ corresponds to voltages V ₃ and V ₃ ′), although the potential difference is smaller than that in the first comparative example, the potential V ₃ at the tip of the guide electrode 14 of the first coaxial electrode 10 is smaller. Is higher than the potential V ₃ ′ at the tip of the guide electrode 14 of the second coaxial electrode 10 ′.

  The potential arrangement at the tips of the guide electrodes 14 and 14 'of the first and second coaxial electrodes 10 and 10' is such that the guide electrode of the second coaxial electrode 10 'in a state where the tubular discharge 4 is formed. The direction is opposite to that in the flow of current from 14 ′ to the guide electrode 14 of the first coaxial electrode 10.

  That is, in the state where the tubular discharge 4 is formed, the potential at the tip of the guide electrode 14 of the first coaxial electrode 10 is lower than the potential at the tip of the guide electrode 14 ′ of the second coaxial electrode 10 ′. There is a need.

  Accordingly, in the second comparative example, as in the first comparative example, the planar discharge 2 (corresponding to FIG. 3C) is changed to the tubular discharge 4 (corresponding to FIG. 3E). Is difficult because of the potential arrangement in the reverse direction.

[Comparative Example 3]
FIG. 9 shows a third comparative example. The third comparative example shows a state where a leak current is generated in the embodiment shown in FIG.

  In the embodiment shown in FIG. 2, a voltage is applied to the first and second coaxial electrodes 10 and 10 ′ as shown in FIG. 3A to be generated on the surfaces of the insulators 16 and 16 ′. The creeping discharge is caused by Li gas evaporated from the surface of the insulator 16.

  As shown in FIG. 3B, when the planar discharge 2 moves in the direction of being discharged from the first and second coaxial electrodes 10, 10 ', the total plasma amount of the planar discharge 2 is generated by the creeping discharge. Limited to plasma. The movement of the planar discharge 2 is electromagnetic acceleration in a high vacuum, and the plasma sheet thickness of the planar discharge 2 increases due to plasma diffusion, and the plasma density of the planar discharge 2 decreases.

  In the first and second coaxial electrodes 10 and 10 ′, the impedance of the sheet discharge 2 is decreased due to the decrease in plasma density, and the portion other than the sheet discharge 2 is caused by plasma diffused from the plasma sheet of the sheet discharge 2. In some cases, a leakage current is generated by the discharge 52 flowing, and the current flowing through the planar discharge 2 is reduced.

  In FIG. 9, the plasma 53 diffused in the first and second coaxial electrodes 10 and 10 ′, the discharge 52 due to the leakage current, and the planar discharge 2 that has advanced from the first and second coaxial electrodes 10 and 10 ′. A single plasma 51 is shown that has collided in the plane of symmetry 1.

  Such a leak current can be prevented by supplying the discharge assist gas into the chamber 20 by the gas supply unit 40 as shown in the above-described modification.

  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.

1 symmetry plane, 2 planar discharge, 3 plasma,
4 tubular discharge, 5 plasma confinement magnetic field, 6 plasma medium,
7 Laser light, 8 Plasma light (EUV),
10 first coaxial electrode, 10 ′ second coaxial electrode 12, 12 ′ center electrode,
14, 14 'guide electrode 16 insulator,
20 chambers,
30 voltage application device, 32 positive voltage source,
34 Negative voltage source, 36 Trigger switch,
40 Gas supply section

Claims (5)

First and second coaxial electrodes arranged opposite to each other, a discharge environment holding device for holding the plasma medium in the first and second coaxial electrodes at a temperature and pressure suitable for plasma generation, and the first And a voltage applying device for applying a discharge voltage having a polarity reversed to the second coaxial electrode, and forming a tubular discharge between the first and second coaxial electrodes to confine plasma in the axial direction. A plasma light source,
The first and second coaxial electrodes are positioned between a center electrode and a bar-shaped center electrode extending on a single axis, a guide electrode surrounding the center electrode with a certain distance therebetween, and the center electrode. It consists of a ring-shaped insulator that insulates between them,
The center electrodes of the first and second coaxial electrodes are located on the same axis and are symmetrically spaced apart from each other,
The second coaxial electrode is in an electrically floating state with respect to the first coaxial electrode, but when a single plasma is formed between the first and second coaxial electrodes, Charges from the first coaxial electrode to the second coaxial electrode so that the first and second coaxial electrodes are in a conductive state and are matched in a configuration including the first and second coaxial electrodes. And the potential of the second coaxial electrode is naturally determined so that a current flows in the forward direction through the center electrode and the guide electrode of the first and second coaxial electrodes. .   The plasma light source according to claim 1, wherein the second coaxial electrode is electrically insulated from the first coaxial electrode.   The discharge environment holding device includes a chamber for holding first and second coaxial electrodes, and an insulating member is provided between the second coaxial electrode and the chamber. Item 2. The plasma light source according to Item 1.   The voltage application device includes: a positive voltage source that applies a positive discharge voltage higher than the guide electrode to one central electrode of the first and second coaxial electrodes; and the first and second coaxial electrodes A negative voltage source that applies a negative discharge voltage lower than that of the guide electrode to the other center electrode, and a trigger switch that simultaneously applies the positive voltage source and the negative voltage source to the respective coaxial electrodes, The plasma light source according to claim 1.   2. The plasma light source according to claim 1, wherein the discharge environment holding device includes gas supply means for supplying a discharge generation assist gas that promotes the generation of discharge.

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