JP5515040B2 - Plasma light source and plasma light generation method - Google Patents

Description

  The present invention relates to a plasma light source and a plasma light generation method, and more particularly to a plasma light source using a magnetized coaxial gun and a plasma light generation method using the same.

  Conventionally, a plasma light source is used as a light source for a reduction exposure apparatus or the like used for manufacturing a semiconductor integrated circuit. A plasma light source can generate ultraviolet light by generating high-temperature and high-density plasma. However, because of the high temperature, debris (harmful dust) generated by evaporation of parts in the device is emitted from the emitted light. There are problems such as hindering transmission. Therefore, for example, Patent Document 1 proposes a plasma light source provided with a debris prevention means.

  FIG. 1 is a diagram showing a configuration of a plasma light source disclosed in Patent Document 1, FIG. 1 (a) is a sectional view in the axial direction of the plasma light source, and FIG. 1 (b) is b in FIG. 1 (a). It is -b sectional drawing (the surrounding cylinder 54 is abbreviate | omitted). As shown in the figure, the plasma light source disclosed in Patent Document 1 is mainly composed of a capillary structure 52, a partition cylinder 53, an outer cylinder 54, and a power supply 55. The capillary structure 52 is a cylindrical structure and is disposed in the partition cylinder 53. A large number of capillaries (through holes having a diameter of about 3 mm) 521 are formed on concentric circles of the capillary structure 52. The shaft of the capillary structure 52 is attached to a rotating shaft 522 driven by a motor (not shown). As illustrated, the partition cylinder 53 is arranged so as to partition the inside of the outer cylinder 54. The partition cylinder 53 is provided with one through hole. In addition, an electrode 511 and an electrode 512 are provided inside and outside the partition cylinder 53 so as to sandwich the capillary structure 52 therebetween. The electrode 511 and the electrode 512 are also provided with through holes. The centers of the through holes of the partition cylinder 53, the electrode 511, and the electrode 512 are provided so as to substantially coincide with the axis of an arbitrary capillary 521. The outer cylinder 54 is provided with a gas introduction port 541 and an exhaust port 542. Plasma generating gas is introduced into the partition cylinder 53 from the gas inlet 541 and exhausted from the exhaust port 542. The power supply 55 applies a discharge voltage to the electrodes 511 and 512. The gas introduced into the partition cylinder 53 generates plasma and generates ultraviolet light due to discharge in the capillary 521 between the electrodes 511 and 512. At that time, the capillary structure 52 rotates, for example, for each discharge, and is driven so that the next capillary 521 is opposed to the electrodes 511 and 512. Since the capillary structure 52 is configured to rotate for each discharge and change the capillary 521 related to the discharge, the heat load can be dispersed and debris can be prevented from being generated from the capillary 521.

  The plasma light source described in Patent Document 1 configured as described above uses a capillary structure for generating plasma, and the capillary structure must be rotated to prevent debris. Therefore, a drive device for the capillary structure and its control device are required, and the structure becomes complicated.

  A magnetized coaxial gun described in Patent Document 2 by the same applicant as the present application is one that does not require such a complicated structure.

  FIG. 2 is a diagram for explaining the magnetization coaxial gun of Patent Document 2, FIG. 2 (a) is a sectional view of the magnetization coaxial gun in the central axis direction, and FIG. 2 (b) is FIG. 2 (a). FIG. 2C is a schematic perspective view of the spheromak. As illustrated, the magnetization coaxial gun MG includes an inner conductor 61, a cylindrical outer conductor 62, and a bias coil BM. Further, the inner conductor 61 and the outer conductor 62 are arranged coaxially. A hollow portion 611 is formed in the inner conductor 61, and a plasma generating gas (for example, helium gas, argon gas, etc.) is introduced from the hollow portion 611 into the outer conductor 62. A ring-shaped convex portion 621 is formed on the inner surface of the outer conductor 62. The bias coil BM is a solenoid coil that generates a DC bias magnetic field and is wound around the outer conductor 62. One end of the outer conductor 62 is partitioned by an insulating member 63 and the other end is opened. A power source (discharge power source) 64 composed of, for example, a crowbar circuit is connected to the inner conductor 61 and the outer conductor 62. The DC bias coil BM is excited so that a magnetic field B is generated by a DC power supply (not shown). When a discharge signal is applied from the crowbar circuit to the inner conductor 61 and the outer conductor 62, a discharge current flows between the convex portions 621 of the inner conductor 61 and the outer conductor 62, and plasma P is generated. The plasma P is accelerated to the open end side by its own discharge current and the Lorentz force generated by the magnetic field generated by the current. At that time, the plasma P is confined in the magnetic field in the toroidal direction and the magnetic field in the poloidal direction by the magnetic field generated by its own discharge current and the magnetic field B generated by the bias coil BM. When the plasma P in this state advances to the open end, it becomes a donut-shaped spheromak SM and is emitted from the open end at a high speed. Although the plasma P is generated even when the convex portion 621 of the external conductor 62 is not provided, the discharge is concentrated on the convex portion 621 by providing the convex portion 621, so that the plasma P is stabilized. Can be generated automatically and sent to the open end side.

  As shown in FIG. 2C, the spheromak SM is a plasma mass in a state where the plasma P is confined in the toroidal magnetic field Bt and the poloidal magnetic field Bp. The directions of the magnetic field Bt in the toroidal direction and the magnetic field Bp in the poloidal direction are determined by the polarity of the power source applied to the inner conductor 61 and the outer inner conductor 62 and the polarity of the magnetic field generated by the bias coil BM.

JP 2003-288998 A JP 2006-310101 A

  However, the magnetized coaxial gun disclosed in Patent Document 2 does not sufficiently emit light in the ultraviolet region. Therefore, it has been difficult to use a magnetized coaxial gun as an EUV (extreme ultraviolet) light source that can be used in the semiconductor manufacturing process. Therefore, it has been desired to develop a plasma light source that emits light with high luminance even in the ultraviolet region.

  In view of such a situation, an object of the present invention is to provide a plasma light source and a plasma light generation method capable of generating high-luminance light even in the ultraviolet light region.

  In order to achieve the above-described object of the present invention, a plasma light source of the present invention is wound around an inner conductor, a cylindrical outer conductor that is coaxially disposed on the inner conductor and that is open at one end, and the outer conductor. A pair of magnetized coaxial guns that generate a spheromak each having a bias coil and a power supply circuit that supplies power between an inner conductor and an outer conductor, the central axes of the pair of magnetized coaxial guns coincide with each other and the outer conductor A pair of magnetized coaxial guns, a pair of opposed gun coupling openings to which the open ends of the outer conductors of the pair of magnetized coaxial guns are respectively coupled, and a window portion for extracting light And a magnetic flux holding container.

  Here, the pair of magnetized coaxial guns are controlled by the bias coil and the power supply circuit so that the direction of the magnetic field in the toroidal direction of each spheromak is reversed and the direction of the magnetic field in the poloidal direction is the same or reversed. Just do it.

  Further, the power supply circuit of the pair of magnetized coaxial guns may apply a continuous pulse signal between the inner conductor and the outer conductor.

  Further, the plasma light generation method of the present invention is configured so that the open ends of the pair of magnetized coaxial guns whose open ends of the outer conductors are opposed to each other so that the central axes coincide with each other are respectively connected to the pair of gun coupling openings of the magnetic flux holding container. Spheromaks generated by a pair of magnetized coaxial guns are connected to each other to emit light into the magnetic flux holding container to generate light.

  Here, the generated light may be ultraviolet light.

  The plasma light source and the plasma light generation method of the present invention have an advantage that high-luminance light can be generated particularly in the ultraviolet light region. There is also an advantage that debris can be reduced.

FIG. 1 is a diagram for explaining the configuration of a conventional plasma light source. FIG. 2 is a diagram for explaining the configuration of a conventional magnetized coaxial gun. FIG. 3 is a diagram for explaining the configuration of the plasma light source of the present invention. FIG. 4 is a graph showing emission wavelength distribution characteristics comparing the plasma light source of the present invention with a plasma light source using a single magnetized coaxial gun. FIG. 5 is a graph showing the change over time of the discharge current output of the power supply circuit when the duty ratio of the continuous pulse signal of the power supply circuit of the plasma light source of the present invention is changed. FIG. 6 is a graph showing the temporal change characteristic of the emission intensity when the duty ratio of the output of the power supply circuit is changed in the plasma light source of the present invention. FIG. 7 is a graph for explaining the light emission characteristics due to the difference in the magnetic field direction in the poloidal direction of the pair of coaxial magnetization guns of the plasma light source of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. 3 is a diagram for explaining the configuration of the plasma light source of the present invention, FIG. 3 (a) is a cross-sectional view of the plasma light source in the central axis direction, and FIG. 3 (b) is a diagram of FIG. 3 (a). It is bb sectional drawing, FIG.3 (c) is a schematic perspective view of a spheromak. As shown in the figure, the plasma light source of the present invention is mainly composed of a pair of magnetization coaxial guns MG 1 and MG 2 and a magnetic flux holding container 3.

  Hereinafter, since the basic configuration is common in the description of the pair of magnetization coaxial guns MG1 and MG2, the reference numerals will be described using the magnetization coaxial gun MG1, and the magnetization coaxial gun MG2 is written in parentheses. It shows with. The magnetization coaxial gun MG1 (MG2) that generates the spheromak is mainly composed of an inner conductor 11 (21), an outer conductor 12 (22), a bias coil BM1 (BM2), and a power supply circuit 14 (24). Yes. The outer conductor 12 (22) is disposed coaxially with the inner conductor 11 (21), and has a cylindrical shape with one end opened. The other end of the open end is partitioned by an insulating member 13 (23). The bias coil BM1 (BM2) is wound around the outer conductor 12 (22). The bias coil BM1 (BM2) provides a DC bias magnetic field inside the outer conductor 12 (22). The power supply circuit 14 (24) supplies power between the inner conductor 11 (21) and the outer conductor 12 (22). Here, the power supply circuit 14 (24) is configured using, for example, a capacitor, and the output of the power supply circuit 14 (24) is, for example, a DC discharge voltage of the capacitor or a discharge flowing between conductors at that time. Current.

  Further, the pair of magnetized coaxial guns MG1 and MG2 configured as described above are arranged so that the central axes of the pair of magnetized coaxial guns MG1 and MG2 coincide and the open ends of the outer conductors 12 and 22 face each other. Yes.

  The magnetic flux holding container 3 has a pair of gun coupling openings 31 and 32 and a window 33 that face each other. More specifically, the magnetic flux holding container 3 in the illustrated example is a cylindrical metal container, for example, and a pair of gun coupling openings 31 and 32 are provided on the side surface of the cylinder, and the window 33 is formed on the top of the cylinder. Is provided. Moreover, it is preferable that the central axes of the pair of opposing gun coupling openings 31 and 32 coincide with the central axis of the magnetic flux holding container 3. The open ends of the outer conductors 12 and 22 of the pair of magnetization coaxial guns MG1 and MG2 are coupled to the pair of gun coupling openings 31 and 32, respectively. The window 33 is a part for extracting generated light. In the illustrated example, one window portion 33 is shown, but the present invention is not limited to this, and a plurality of window portions may be provided. Further, the magnetic flux holding container 3 is not limited to a cylindrical shape, and may be a cylindrical body such as a quadrangular shape or a hexagonal shape, or may be a spherical shape such as a spherical shape or an elliptical shape. There may be. Also, the gun coupling openings 31 and 32 are not limited to sleeve-like ones as shown in the drawings, and may be simply opened in the side surface of the magnetic flux holding container.

  The open ends of the outer conductors 12 and 22 of the pair of magnetization coaxial guns MG1 and MG2 are coupled to the gun coupling openings 31 and 32, respectively. That is, the pair of magnetization coaxial guns MG1 and MG2 are in a positional relationship facing each other with the magnetic flux holding container 3 interposed therebetween.

  A process of generating plasma light using the plasma light source of the present invention configured as described above will be described. First, plasma generation gas (for example, helium gas, argon gas, etc.) is introduced into the outer conductor 12 (22) from, for example, the hollow portion 111 (211) of the inner conductor 11 (21). The power supply circuit 14 (24) supplies power between the inner conductor 11 (21) and the outer conductor 12 (22). The bias coils BM1 and BM2 are excited by a DC power source (not shown) so as to generate magnetic fields B1 and B2 in the same direction as shown, for example.

  When the discharge voltage of the capacitor of the power supply circuit 14 (24) is applied to the inner conductor 11 (21) and the outer conductor 12 (22) of the magnetization coaxial gun MG1 (MG2), the inner conductor 11 (21) and the outer conductor 12 (22). ) During which the discharge current flows and plasma P1 (P2) is generated. The plasma P1 (P2) is accelerated by the Lorentz force toward the open end of the outer conductor 12 (22) by its own current and a magnetic field generated by the current. At that time, the plasma P1 (P2) is confined in the toroidal magnetic field and the poloidal magnetic field by the magnetic field due to the discharge current of the plasma P1 (P2) and the magnetic field B1 (B2) by the bias coil BM1 (BM2). It becomes a state. Therefore, when the plasma P1 (P2) proceeds to the open end, it becomes a donut-shaped spheromak SM1 (SM2) and is released into the magnetic flux holding container 3 at a high speed. As shown in FIG. 3 (c), the spheromak SM1 (SM2) emitted is in a state where the plasma P1 (P2) is confined to the magnetic field Bt1 (Bt2) in the toroidal direction and the magnetic field Bp1 (Bp2) in the poloidal direction. It is a plasma lump.

  Here, as shown in FIG. 3C, when the spheromak SM1 and the spheromak SM2 are viewed, the toroidal magnetic fields Bt1 and Bt2 are reversed in direction, but the poloidal magnetic fields Bp1 and Bp2 are bias coils BM1. , BM2 gives the same direction when the magnetic fields B1 and B2 are applied in the same direction. That is, in the plasma light source of the present invention, when the magnetization coaxial guns MG1 and MG2 are configured to generate a spheromak in which the magnetic field in the toroidal direction is opposite in direction and the magnetic field in the poloidal direction is in the same direction, Control may be performed so that power in the opposite direction is supplied between the inner conductors 11 and 21 and the outer conductors 12 and 22 and power in the same direction is supplied to the bias coils BM1 and BM2. When the magnetized coaxial guns MG1 and MG2 are configured to generate a spheromak in which the magnetic field in the toroidal direction is reversed and the magnetic field in the poloidal direction is also reversed, the inner conductors 11 and 21 and the outer conductor are formed. Control may be performed so that power in the reverse direction is supplied between 12 and 22 and power in the reverse direction is also supplied to the bias coils BM1 and BM2. These may be variously selected according to the interaction with the wall surface of the magnetic flux holding container 3, the wavelength range to be used, the application, and the like.

  The spheromak SM1 and the spheromak SM2 released into the magnetic flux holding container 3 collide with each other at a high speed in the magnetic flux holding container 3. Spheromac SM1 and SM2 as shown in FIG. 3 (c) cancel each other because the magnetic fields Bt1 and Bt2 in the toroidal direction of the spheromaks SM1 and SM2 are opposite in direction at the time of the collision. Since Bp1 and Bp2 have the same direction, they do not cancel each other. When the poloidal magnetic fields Bp1 and Bp2 are controlled so that their directions are reversed, the poloidal magnetic fields Bp1 and Bp2 also cancel each other. The spheromaks SM1 and SM2 generate a high-luminance light by changing a part of the magnetic energy into thermal energy due to the collision and becoming high temperature. The spheromak SM1 and the spheromac SM2 in the magnetic flux holding container 3 are considered to be magnetically re-coupled by collision.

  In this way, the open ends of the pair of magnetized coaxial guns whose open ends of the outer conductors are opposed to each other so that the central axes coincide are connected to the pair of gun coupling openings of the magnetic flux holding container, respectively, and a pair of magnetized coaxial guns are connected. By emitting the spheromak generated by the gun into the magnetic flux holding container and causing them to collide, light can be generated with high brightness.

  The plasma light source of the present invention does not extract the light generated at the time of plasma generation as in the conventional plasma light source, but extracts and uses the light generated when the plasma (spheromak) collides. Compared with the case where light is directly extracted, it is possible to extract light with high luminance, that is, high emission intensity.

  In addition, since the plasma light source of the present invention generates plasma in the magnetization coaxial gun and generates light in the magnetic flux holding container, the plasma generation location and the light generation location are separated. Therefore, even if debris occurs in the magnetized coaxial gun, most of the debris is not ionized, so it is difficult to carry it into the magnetic flux holding container like plasma, and the influence of debris is reduced. Also, the debris scattering direction in the magnetized coaxial gun, that is, the axial direction of the magnetized coaxial gun, and the extraction direction of the emitted light, that is, the axial direction of the window portion of the magnetic flux holding container are orthogonal to each other. The effect of debris is reduced.

  In addition, since the plasma light source of the present invention is mainly composed of a magnetized coaxial gun and a magnetic flux holding container, the structure used is a capillary structure as in Patent Document 1 cited in the prior art. It is simple compared to things.

  Here, the emission wavelength distribution characteristics of the single magnetized coaxial gun and the one in which the magnetized coaxial guns are opposed to each other like the plasma light source of the present invention are compared. FIG. 4 is a graph showing emission wavelength distribution characteristics comparing the plasma light source of the present invention and a plasma light source using a single magnetized coaxial gun, and FIG. 4A is a plasma using a single magnetized coaxial gun. FIG. 4B is a graph of a plasma light source of the present invention using a magnetized coaxial gun arranged to face each other.

  Comparing FIG. 4 (a) and FIG. 4 (b), it can be seen that the plasma light source of the present invention in which the magnetized coaxial guns are opposed to each other has a higher emission intensity as a whole. If there is only a difference using one magnetized coaxial gun and two magnetized coaxial guns, the difference in emission intensity should be about twice, but as shown in the figure, the wavelength at which more than twice the emission intensity is obtained. There are many. In particular, in the ultraviolet region, there is a wavelength at which the emission intensity of the plasma light source of the present invention is 6 times or more. Therefore, it can be seen that the plasma light source of the present invention can emit high-luminance light, and this tendency is more remarkable in the ultraviolet region.

  Further, the same applicant as the present application disclosed that in Japanese Patent Application Nos. 2008-189468 and 2009-171864, the output of the power supply circuit is not a direct current discharge current but a continuous pulsed discharge current, thereby increasing the emission intensity. Has invented a magnetized coaxial gun that is high and capable of controlling debris. The present invention is also applicable to the magnetization coaxial gun of the plasma light source of the present invention. That is, by configuring the power supply circuit to apply a continuous pulse signal between the inner conductor and the outer conductor, it is possible to increase the light emission intensity of the magnetization coaxial gun itself. Therefore, if a pair of magnetized coaxial guns with increased emission intensity are used, it is possible to generate light with higher brightness.

  Here, the fact that the debris can be controlled by changing the duty ratio of the continuous pulse signal output from the power supply circuit is explained using the time-varying characteristics of the emission intensity at the wavelength of the spectral line of the electrode material depending on the duty ratio. To do. The continuous pulse signal output from the power supply circuit means a continuous pulse voltage applied between the outer conductor and the inner conductor or a continuous pulse current flowing at that time. FIG. 5 shows the change over time of the discharge current of the power supply circuit when the duty ratio of the continuous pulse signal of the power supply circuit of the plasma light source of the present invention is changed. In the figure, the thick solid line is a direct current discharge current characteristic without changing the duty ratio, the thin solid line is a continuous pulsed discharge current characteristic with a duty ratio of 1; 1, and the broken line is a duty ratio of 1: 4. It is a discharge current characteristic of a continuous pulse. In this specification, the duty ratio of 1: 1 means that the ratio of output Hi to Low is 1: 1, and the duty ratio of 1: 4 means that the ratio of output Hi to Low is It means 1: 4.

  Plasma light is emitted using such a power supply circuit. FIG. 6 is a graph showing the temporal change characteristic of the light emission intensity when the duty ratio of the output of the power supply circuit is changed in the plasma light source of the present invention, and FIG. In the case of the discharge current, FIG. 6B shows a case of a continuous pulsed discharge current with a duty ratio of 1: 1, and FIG. 6C shows a case of a continuous pulsed discharge current of a duty ratio of 1: 4. It is a graph. Here, the emission intensity characteristic of FIG. 6 is a characteristic in the vacuum ultraviolet region of 158.1 nm, which is a spectral line of iron derived from the electrode material.

  Referring to FIG. 6 (a), since there is light of iron spectral lines derived from the electrode material, the electrode material is scraped by a thermal load, and debris derived from the electrode material is generated. I understand. 6A and 6B, the characteristic of the duty ratio of 1: 1 is slightly higher with respect to the peak value of the emission intensity. Note that the light emission time is slightly higher in the example of FIG. 6B when viewed at the same elapsed time. Referring to FIG. 6C, it can be seen that the emission intensity is reduced by about half when the duty ratio is 1: 4. In other words, it can be seen that by mixing the duty ratio, the mixing of impurities due to the thermal load of the electrode can be controlled.

  Next, in the plasma light source of the present invention, a description will be given of the difference in light emission characteristics between the case where the poloidal magnetic field directions of the pair of coaxial magnetization guns are reversed. FIG. 7 is a graph for explaining the light emission characteristics due to the difference in the direction of the magnetic field in the poloidal direction of the pair of coaxial magnetization guns of the plasma light source of the present invention, and FIG. FIG. 7B shows the change over time in the emission intensity of monovalent helium ions. In the figure, Case 1 is a characteristic when the direction of the magnetic field in the poloidal direction is the same, and Case 2 is a characteristic when the direction of the magnetic field in the poloidal direction is opposite. In all cases, the magnetic field in the toroidal direction is in the reverse direction, and the input power used for the discharge is the same. From FIG. 7, it can be seen that the total light emission amount is higher in Case 1. Moreover, in Case 2, since about 50% of strong light emission is observed in the ion spectrum immediately after the collision, a high heating effect due to the collision is estimated, but since there is no confinement coordination, the temperature decreases quickly, and finally the high temperature It seems that the light emission level is similar in the region. Therefore, when only high-energy plasma at the beginning of discharge at the time of collision is used, the direction of the magnetic field in the poloidal direction may be reversed, for example, Case2. At this time, if discharge is performed by the continuous pulse signal as described above, high-energy plasma can be used efficiently.

  As described above, according to the present invention, it is possible to generate light with high luminance, particularly in the ultraviolet region.

  Note that the plasma light source and the plasma light generation method of the present invention are not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

11, 21 Inner conductor 12, 22 Outer conductor 13 Insulating member 14, 24 Power supply circuit 3 Magnetic flux holding container 31, 32 Gun coupling opening 33 Window BM1, BM2 Bias coil MG1, MG2 Magnetized coaxial gun SM1, SM2 Spheromak

Claims (7)

A plasma light source that emits light, the plasma light source comprising:
A power supply circuit that supplies power between the internal conductor, the cylindrical external conductor that is coaxially disposed on the internal conductor and that is open at one end, a bias coil that is wound around the external conductor, and the internal conductor and the external conductor A pair of magnetized coaxial guns for generating spheromaks, each of which is arranged such that the central axes of the pair of magnetized coaxial guns coincide with each other and the open ends of the outer conductors face each other,
A magnetic flux holding container having a pair of opposing gun coupling openings to which the open ends of the outer conductors of the pair of magnetized coaxial guns are respectively coupled, and a window for extracting light;
A plasma light source comprising:   The plasma light source according to claim 1, wherein the pair of magnetized coaxial guns are configured such that the direction of the magnetic field in the toroidal direction of each spheromak is reversed and the direction of the magnetic field in the poloidal direction is the same or reversed. A plasma light source controlled by a bias coil and a power supply circuit.   3. The plasma light source according to claim 1, wherein the pair of magnetized coaxial gun power supply circuits apply a continuous pulse signal between the inner conductor and the outer conductor. The open ends of a pair of magnetized coaxial guns whose open ends of the outer conductors are opposed to each other so that the central axes coincide with each other are connected to the pair of gun coupling openings of the magnetic flux holding container,
Spheromaks generated by a pair of magnetized coaxial guns are each emitted into a magnetic flux holding container and collide to generate light.
Method for generating plasma light   5. The plasma light generating method according to claim 4, wherein the generated light is ultraviolet light.   6. The method of generating plasma light according to claim 4, wherein the spheromaks generated by the pair of magnetized coaxial guns each have a toroidal magnetic field in the opposite direction and a poloidal magnetic field in the same or opposite direction. A method for generating plasma light.   7. The plasma light generating method according to claim 4, wherein a continuous pulse signal is applied to the pair of magnetized coaxial guns.

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