JP2006156359A - Plasma generation apparatus and spectrum control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma generation apparatus in which synchrotron radiation based on plasma generation is extracted efficiently. <P>SOLUTION: A magnetic field Bz is applied along the direction of a Z-axis by coils 6A and 6B before initial plasma P1 is generated. The strength of the applied magnetic field Bz is adjusted by a magnetic field adjusting portion 7. The contraction speed of plasma is moderated and the degree of moderation can be adjusted. Therefore, the degree that the maximum contraction duration of plasma is prolonged is arbitrarily adjustable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma generator using a pinch discharge method and a spectrum control method.

  In recent years, plasma using a pinch discharge method such as a Z pinch discharge method as a light source for lithography for nano-scale microfabrication and a light source for a soft X-ray microscope capable of observing living organisms with high resolution. Development of light sources is underway. This Z-pinch is a phenomenon in which the plasma column itself is caused by the azimuthal self-magnetic field created by this current when a large current flows in the axial direction (Z direction) of the discharge tube in which the target gas (low pressure gas) is sealed. It is a phenomenon of compression (compressed plasma is generated).

  7A to 7C show a generation process of contracted plasma by a conventional Z pinch discharge method (see, for example, Non-Patent Document 1). In this generation process, first, when a large current Iz is passed in the Z-axis direction in the generated annular initial plasma P101, an electromagnetic force Fr is generated toward the center of the initial plasma P101 (FIG. 7A). ). Therefore, the initial plasma P101 is gradually contracted on the Z-axis (plasma P102 in FIG. 7B) and finally contracted to a size of 200 to 300 μm, and reaches a maximum contraction state at a high temperature and a high energy density ( FIG. 7 (C)). In this way, a small and high energy density contracted plasma P103 is generated, and light of an extremely short wavelength (mainly a wavelength region from vacuum ultraviolet rays to X-rays) is emitted based on the generation of the contracted plasma P103. It is like that.

Waisman, Eduardo and three others “Fast Bz stabilization for uniform fill z-pinch; theoretical study”, [online], The NASA Astrophysics Data System, November 1998, [searched April 20, 2004], Internet <URL : http://adsabs.harvard.edu/cgi-bin/nph-bib#query?bibcode=1998APS..DPP.B1F10W&amp;db#key=PHY&amp;data#type=HTML&amp;format=>

  By the way, the light emission by the pinch discharge method such as the Z pinch discharge method has a problem that the spectral characteristic of the emitted light based on the plasma generation cannot be controlled. Therefore, for example, even when it is desired to selectively improve only the intensity of a specific wavelength region, it is necessary to improve the intensity of the entire spectrum, and the energy input to the apparatus is unnecessarily increased. .

  Thus, it has been difficult to efficiently extract the radiated light based on the generation of plasma by the conventional technique in which the spectral characteristic of the radiated light cannot be controlled.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a plasma generation apparatus and a spectrum control method capable of more efficiently extracting radiation light based on plasma generation.

  The first plasma generator of the present invention generates an initial plasma and contracts the initial plasma on a predetermined axis, thereby generating a contracted plasma, and before the initial plasma is generated. A magnetic field application unit that applies a magnetic field along the axis and a magnetic field strength adjusting unit that adjusts the strength of the magnetic field applied by the magnetic field application unit are provided.

  Here, the “initial plasma” is an annular plasma generated by the dielectric breakdown of the target gas, and means a plasma state before becoming a contracted plasma.

  The spectral control method of the present invention generates an initial plasma and contracts the initial plasma on a predetermined axis to generate a contracted plasma, and applies a magnetic field along the axis before the initial plasma is generated. In addition, by adjusting the intensity of the applied magnetic field, the spectral characteristics of the emitted light based on the contracted plasma are controlled.

  In the first plasma generation apparatus and spectrum control method of the present invention, since the magnetic field is applied along the predetermined axis before the initial plasma is generated, the magnetic flux generated by the magnetic field is generated when the initial plasma is contracted. It is bundled in the center direction of the contracted plasma, and as it contracts, the magnetic flux density in the center portion increases rapidly. Here, since the electromagnetic force is proportional to the square of the magnetic flux density, the electromagnetic force in the direction opposite to the contraction direction (outward) increases as the plasma contracts, and as a result, the degree of contraction of the plasma (contraction) (Velocity) is relaxed, and the duration of the maximum contraction state (maximum contraction duration) in the contraction plasma is increased. Further, since the degree of relaxation of the contraction speed can be adjusted by the strength of the magnetic field to be applied, the degree of the maximum contraction duration can be arbitrarily adjusted.

  The second plasma generator of the present invention generates an initial plasma and contracts the initial plasma on a predetermined axis, thereby generating a contracted plasma, and the initial plasma in the contraction process of the initial plasma. A magnetic field applying unit that applies a magnetic field and a magnetic field intensity adjusting unit that adjusts the strength of the magnetic field applied by the magnetic field applying unit so that an electromagnetic force is generated in a direction opposite to the contraction direction of the magnetic field.

  In the second plasma generating apparatus of the present invention, the electromagnetic force is generated in a direction opposite to the contracting direction of the initial plasma in the contracting process of the initial plasma, and the magnetic force is applied. As a result, the contraction rate of the plasma is relaxed, and the maximum contraction duration in the contraction plasma is increased. Further, since the degree of relaxation of the contraction speed can be adjusted by the strength of the magnetic field to be applied, the degree of the maximum contraction duration can be arbitrarily adjusted.

  In the first plasma generator of the present invention, the magnetic field application unit includes a coil, and the magnetic field strength adjusting means adjusts the magnitude of the current flowing through the coil, thereby adjusting the strength of the magnetic field. Also good. When configured in this manner, the degree of relaxation in the contraction speed of the plasma is adjusted by adjusting the current passed through the coil.

  In the first plasma generator of the present invention, the magnetic field intensity adjusting means adjusts the intensity of the magnetic field so that the intensity of a specific wavelength component is selectively increased in the radiation light based on the contracted plasma. Is preferred.

  In the first plasma generating apparatus of the present invention, the magnetic field applied by the magnetic field applying unit may be a direct-current magnetic field having a predetermined strength or a pulsed magnetic field.

  According to the first plasma generating apparatus or spectrum control method of the present invention, since the magnetic field is applied along the predetermined axis before the initial plasma is generated and the strength of the applied magnetic field is adjusted, Since the contraction speed of the plasma can be relaxed and the degree of the relaxation can be adjusted, and the maximum contraction duration of the contracted plasma can be adjusted accordingly, the emitted light based on the plasma generation can be extracted more efficiently.

  According to the second plasma generator of the present invention, the magnetic field is applied so that the electromagnetic force is generated in the direction opposite to the contraction direction of the initial plasma during the contraction process of the initial plasma. Since the electromagnetic contraction can reduce the rate of plasma contraction and adjust the degree of relaxation, which can also adjust the degree to which the maximum plasma contraction duration is increased, more efficient radiation light based on plasma generation Can be taken out.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional perspective view showing the structure of a plasma generator according to an embodiment of the present invention. The plasma generator 1 is a plasma light source that generates contracted plasma P using a Z-pinch discharge method and emits light (radiated light L) based on the contracted plasma. The plasma generator 1 is connected to the capacitor 2 and the capacitor 2. And a pair of annular electrodes (cathode 31 and anode 32) facing each other, an electrode support 4 disposed between the cathode 31 and anode 32, and the capacitor 2 and the cathode 31 and anode 32 are connected. Alternatively, a switch SW to be disconnected, a pair of annular coils (coils 6A and 6B) disposed so as to sandwich the cathode 31 and the anode 32, a driving power source 5 for driving the coils 6A and 6B, respectively, and a connection to the driving power source 5 The magnetic field adjusting unit 7 is configured. The spectrum control method according to one embodiment of the present invention is embodied by the plasma generator according to the present embodiment, and will be described below.

  The capacitor 2 is a part that charges a high-voltage charge (input energy E0 described later) based on a high-voltage power source (not shown). Each of the cathode 31 and the anode 32 functions as an electrode, and is made of, for example, xenon (Xe) or the like by applying a voltage based on the input energy E0 between these electrodes from the capacitor 2 via the switch SW. The target gas G is discharged, and an annular plasma P (initial plasma P1 described later) corresponding to the shape of these annular electrodes is generated. The cathode 31 and the anode 32 will be described in detail later, but a large current of 10 to 50 kA is applied to the generated plasma P in the direction between the electrodes (Z-axis direction described later) (Z-pinch discharge). System) and contracted plasma (contracted plasmas P2 and P3 described later) are generated. Here, “pinch” means that when a large current flows along a predetermined axis in a discharge tube filled with a target gas, the initial plasma itself is compressed by the azimuthal self-magnetic field created by this current. (Compressed plasma is generated). The cathode 31 and the anode 32 are electrically isolated from each other and supported by the insulating electrode support 4. Further, the cathode 31, the anode 32, and the electrode support 4 are each arranged in a vacuum vessel in which a target gas G is enclosed.

  The coils 6A and 6B apply magnetic fields B1 and B2 between the cathode 31 and the anode 32 (in the Z-axis direction to be described later) based on the current supplied from the drive power supply 5, respectively. Although details will be described later, these magnetic fields B1 and B2 are applied before the plasma P is generated, and the degree of contraction of the plasma P (a contraction speed described later) is thereby reduced. It is like that. These magnetic fields B1 and B2 may be a direct-current magnetic field having a predetermined strength or a pulsed magnetic field.

  The magnetic field adjustment unit 7 adjusts the currents flowing through the coils 6A and 6B via the drive power supply 5, thereby adjusting the strengths of the magnetic fields B1 and B2 applied from the coils 6A and 6B, respectively. By adjusting the strength of the magnetic fields B1 and B2 in this way, the degree of relaxation in the contraction speed of the plasma P described above can be controlled as will be described in detail later.

  Here, the capacitor 2, the switch SW, the cathode 31, the anode 32, and the electrode support 4 correspond to a specific example of “plasma generator” in the present invention. The drive power supply 5 and the coils 6A and 6B correspond to a specific example of “magnetic field application unit” in the present invention, and the magnetic field adjustment unit 7 corresponds to a specific example of “magnetic field adjustment unit” in the present invention.

  Next, the operation of the plasma generator 1 having such a configuration will be described in detail with reference to FIGS. Here, FIG. 2 schematically shows the contraction process of plasma P (generation process of contraction plasma), and FIG. 3 shows the relationship between the plasma radius and time.

  First, in this plasma generator 1, magnetic fields B1 and B2 are applied between the cathode 31 and the anode 32 before the plasma P is generated. Specifically, based on control by the magnetic field adjustment unit 6, current is supplied from the drive power supply 5 to the coils 6 </ b> A and 6 </ b> B, whereby magnetic fields B <b> 1 and B <b> 2 are applied between the cathode 31 and the anode 32.

  Next, when the switch SW is turned on with the magnetic fields B1 and B2 applied, a high voltage based on the input energy E0 is applied between the cathode 31 and the anode 32 by the capacitor 2 charged with a high voltage charge. Is applied. When the target gas G is discharged based on this voltage, an annular initial plasma P 1 as shown in FIG. 2A is generated near the surface of the electrode support 4.

  Next, as shown in FIG. 2A, while applying a magnetic field Bz in the Z-axis direction (the above-described magnetic fields B1 and B2) to the initial plasma P1, it is between the cathode 31 and the anode 32, that is, similarly to the Z-axis. When a large current of about 10 to 50 kA flows in the direction, an electromagnetic force Fr is generated in the central direction of the initial plasma P1, and as shown in FIG. 2B, the initial plasma P is gradually contracted on the Z axis. (Shrinking plasma P2).

  Here, in the plasma generation apparatus 1 of the present embodiment, since the magnetic field Bz is applied along the contraction axis direction (Z-axis direction) of the contraction plasma P2, as shown in FIG. The magnetic flux by the magnetic field Bz is bundled in the center direction of the contracted plasma P2. Therefore, as the plasma is contracted, the magnetic flux density in the central portion increases rapidly.

  Here, since the electromagnetic force is proportional to the square of the magnetic flux density, as the plasma contracts, an electromagnetic force in the opposite direction (outward) to this contracting direction is generated and its magnitude rapidly increases. As a result, the plasma shrinkage rate is relaxed. Therefore, for example, as shown in FIG. 3, the magnetic field Bz is applied as compared with the duration T0 (maximum contraction duration) of the maximum plasma contraction state in the conventional case where the magnetic field Bz is not applied (graph G0 in the figure). In this embodiment (graph G1 in the figure), the maximum contraction duration T1 of plasma is longer, in other words, the plasma is more stabilized in the maximum contraction state. Similarly, as shown in FIG. 3, the plasma radius at the maximum contraction in the present embodiment (graph G1) is larger than the plasma radius at the maximum contraction in the conventional case (graph G0). . That is, in the present embodiment, the plasma contraction rate is reduced as compared with the conventional case, and thereby the maximum contraction duration is longer.

  Further, since the strength of the magnetic field Bz, that is, the magnitude of the current flowing through the coils 6A and 6B can be adjusted by the magnetic field adjustment unit 7, the degree of relaxation of the contraction speed can be arbitrarily adjusted by the strength of the applied magnetic field Bz. As a result, the degree of the maximum contraction duration can be arbitrarily adjusted.

  In this way, as shown in FIG. 2C, the plasma is finally contracted in a maximum contracted state (contracted plasma P3) in which the degree of contraction is relaxed and the degree of relaxation is adjusted as compared with the conventional case. Thus, a contracted plasma P3 having a minute and high energy density is generated. Based on the generation of the contracted plasma P3, light (radiated light L) having an extremely short wavelength (a wavelength region mainly ranging from vacuum ultraviolet rays to X-rays) is emitted.

  Next, specific examples of the plasma generator according to the present embodiment will be described with reference to FIGS. Here, FIG. 4 shows an example of the relationship between the intensity of the magnetic field Bz and the emission intensity of the radiated light L (in the case of radiated light in the extreme ultraviolet region) with spectral characteristics, and FIG. FIG. 6 shows an example of the relationship between the intensity and the light output at a wavelength of 13.5 nm (when the input energy stored in the capacitor 2 is E0 = 15 J). FIG. FIGS. 6A and 6B are photographs of the central part of the plasma for explaining an example of the change. FIG. 6A shows a case where a magnetic field Bz of about 300 (Gauss) is applied, and FIG. 6B shows a conventional case where no magnetic field Bz is applied. Respectively. In this embodiment, xenon (Xe) is used as the target gas G.

  First, as shown in FIG. 4, it can be seen that the emission intensity of the emitted light L is higher in the present embodiment in which the magnetic field Bz is applied than in the conventional case in which the magnetic field Bz is not applied. This is because, as described above, in the present embodiment, the maximum plasma contraction duration is longer than in the conventional case, and the plasma is further stabilized in the maximum contraction state. Therefore, it can be seen that by applying the magnetic field Bz in the plasma contraction process, the emission intensity of the emitted light L is increased, and light can be emitted more efficiently.

  Further, since the emission intensity of the radiated light L also changes in accordance with the intensity of the magnetic field Bz to be applied, the radiated light is adjusted by adjusting the intensity of the magnetic field Bz, that is, the magnitude of the current flowing through the coils 6A and 6B. It can be seen that the spectral characteristics of L, specifically, the emission intensity can be controlled. More specifically, for example, as shown in FIG. 5, when there is an optimum value of the light output (the emission intensity of the radiated light L) according to the intensity of the magnetic field Bz to be applied, this optimum value is obtained. In addition, the intensity of the magnetic field Bz can be adjusted. In the example of FIG. 5, it can be seen that the light output at the wavelength of 13.5 nm can be maximized by setting the intensity of the magnetic field Bz to about 300 (Gauss).

  Furthermore, the ratio of the emission intensity that increases according to the intensity of the applied magnetic field Bz is slightly different depending on the wavelength of the radiated light L (for example, in the case of FIG. 4, in the wavelength region of about 11 nm or about 13 In the wavelength region of about 5 nm, the rate of increase is large), and the magnetic field Bz is set so that the emission intensity of the radiated light in a specific wavelength region increases more than the emission intensity of the radiated light in other wavelength regions. It can be seen that it is possible to selectively increase the emission intensity of the emitted light of the target wavelength by adjusting.

  6A and 6B, in the conventional case where the magnetic field Bz is not applied (FIG. 6B), the shape of the contracted plasma is elliptical, while the magnetic field Bz is applied. In the case of this example (FIG. 6A), the shape of the contracted plasma is circular, and it can be seen that the plasma is more uniformly contracted and stabilized in this example. Further, compared with the conventional case, the contracted plasma is slightly larger in the case of the present embodiment (diameter 350 μm with respect to the diameter 270 μm), and it can be seen that the degree of maximum contraction is actually relaxed.

  As described above, in the present embodiment, the magnetic field Bz is applied along the Z-axis direction by the coils 6A and 6B before the initial plasma P1 is generated, and the strength of the applied magnetic field Bz is adjusted by the magnetic field adjustment unit 7. Since the plasma shrinkage rate can be relaxed and the degree of relaxation can be adjusted, and the degree of increase in the maximum plasma contraction duration can be adjusted accordingly, light using the pinch discharge method In radiation, radiation light L based on plasma generation can be extracted more efficiently.

  Moreover, since the intensity of the magnetic field Bz to be applied is adjusted by the magnetic field intensity adjusting unit 7, the spectral characteristics of the emitted light L can be controlled. Specifically, by adjusting the degree of contraction (contraction rate) of the plasma, it is possible to increase the intensity of the radiated light L as a whole, or to selectively increase the intensity of light of the target wavelength. Become.

  In addition, since the magnetic field Bz is applied by the drive power supply 5 and the coils 6A and 6B, the magnetic field adjustment unit 7 adjusts the current flowing through the coils 6A and 6B via the drive power supply 5 to thereby actually increase the magnetic field Bz. It becomes possible to adjust the intensity of the.

  Further, the energy state (density / temperature) when the plasma contracts can be controlled by adjusting the strength of the magnetic field Bz to be applied. For example, without increasing the input energy by increasing the number of luminescent particles. , The intensity of light of the target wavelength can be selectively increased. Therefore, it is possible to efficiently increase the intensity of light having the target wavelength.

  In addition, since the plasma stability can be improved, it is possible to reduce the generation of extra high-speed ions due to the fluid instability of the plasma.

  Further, by applying the magnetic field Bz, the charged particles in the plasma undergo a spiral motion, so that the plasma resistance increases and the plasma can be heated more efficiently.

  Furthermore, since the intensity | strength of the emitted light L can be raised, the emitted light of a very short wavelength can be generated with high efficiency. Therefore, for example, when this radiated light L is used for microfabrication of a nanoscale semiconductor or the like, the manufacturing cost of such a semiconductor or the like can be reduced. In addition, for example, when this synchrotron radiation L is applied to a soft X-ray microscope, research using a biological microscope, which has been mainly performed using a synchrotron (SOR), is performed using a small soft X-ray microscope. It becomes possible to conduct such research even in a small laboratory.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to this embodiment, and various modifications can be made.

  For example, in the above-described embodiment, the case where the current flowing through the coils 6A and 6B is adjusted to adjust the strength of the magnetic field Bz has been described. However, the method of adjusting the strength of the magnetic field Bz is not limited to this method. Specifically, for example, there is a method of adjusting the strength by optimizing the magnetic field Bz using a permanent magnet.

  In the above embodiment, the case where the magnetic field Bz is applied from before the initial plasma P1 is generated until the maximum contraction of the contraction plasma is described. However, the application of the magnetic field Bz is stopped before the maximum contraction. It may be. Even when the application of the magnetic field Bz is stopped halfway in this way, the magnetic field Bz is continuously bundled in the plasma if it is applied when the initial plasma P1 is generated. The same effects as in the embodiment can be obtained.

  Furthermore, in the above embodiment, the case of plasma generation by the Z pinch discharge method has been described as an example of the pinch discharge method. However, the present invention is not limited to other pinch discharge methods such as a plasma focus discharge method or a θ pinch discharge method. The present invention can also be applied to the case of plasma generation by the above, and the same effect as in the above embodiment can be obtained.

  The plasma generator and the spectrum control method according to the present invention include, for example, a lithography light source for nanoscale microfabrication and a light source for a soft X-ray microscope capable of observing living organisms with high resolution. The present invention can be used in all industrial fields that use synchrotron radiation having a short wavelength (mainly a wavelength region from vacuum ultraviolet rays to X-rays).

It is a section perspective view showing composition of a plasma generator concerning one embodiment of the present invention. It is a schematic diagram for demonstrating the generation | occurrence | production process of the contraction plasma which concerns on this Embodiment. It is a characteristic view for demonstrating an example of the maximum contraction duration in contraction plasma. It is a characteristic view for demonstrating an example of the relationship between the intensity | strength of an applied magnetic field, and the emitted light intensity of emitted light. It is a characteristic view for demonstrating an example of the relationship between the intensity | strength of an applied magnetic field, and the optical output of a specific wavelength. It is a characteristic photograph for demonstrating an example of the change of contraction plasma by the presence or absence of an applied magnetic field. It is a schematic diagram for demonstrating the generation | occurrence | production process of the contraction plasma by the conventional plasma generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plasma generator, 2 ... Capacitor, 31 ... Cathode, 32 ... Anode, 4 ... Electrode support body, 5 ... Drive power supply, 6A, 6B ... Coil, 7 ... Magnetic field adjustment part, SW ... Switch, G ... Target gas, P: Plasma, P1: Initial plasma, P2, P3: Contracted plasma, B1, B2, Bz: Applied magnetic field, Iz: Current, Fr: Electromagnetic force, L: Synchrotron radiation.

Claims (7)

A plasma generating section for generating a contracted plasma by generating an initial plasma and contracting the initial plasma on a predetermined axis;
A magnetic field applying unit that applies a magnetic field along the axis before the initial plasma is generated;
And a magnetic field intensity adjusting means for adjusting the intensity of the magnetic field applied by the magnetic field applying unit. The magnetic field application unit includes a coil,
The plasma generating apparatus according to claim 1, wherein the magnetic field intensity adjusting unit adjusts the intensity of the magnetic field by adjusting a magnitude of a current flowing through the coil. 3. The magnetic field intensity adjusting unit adjusts the intensity of the magnetic field so that the intensity of a specific wavelength component is selectively increased in the radiation light based on the contracted plasma. The plasma generator described. The plasma generating apparatus according to any one of claims 1 to 3, wherein the magnetic field applied by the magnetic field applying unit is a direct-current magnetic field having a predetermined intensity. The plasma generator according to any one of claims 1 to 3, wherein the magnetic field applied by the magnetic field generator is a pulsed magnetic field. A plasma generating section for generating a contracted plasma by generating an initial plasma and contracting the initial plasma on a predetermined axis;
A magnetic field application unit that applies a magnetic field so that an electromagnetic force is generated in a direction opposite to the contraction direction of the initial plasma in the contraction process of the initial plasma;
And a magnetic field intensity adjusting means for adjusting the intensity of the magnetic field applied by the magnetic field applying unit. By generating an initial plasma and contracting the initial plasma on a predetermined axis, a contracted plasma is generated,
Spectral control characterized by controlling the spectral characteristics of the radiation light based on the contracted plasma by applying a magnetic field along the axis and adjusting the strength of the applied magnetic field before the initial plasma is generated. Method.

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