JP5567640B2 - Extreme ultraviolet light source device - Google Patents

Description

  The present invention relates to an extreme ultra violet (EUV) light source device used as a light source of an exposure apparatus.

  In recent years, along with the miniaturization of semiconductor processes, the miniaturization of optical lithography is rapidly progressing, and in the next generation, fine processing of 100 to 70 nm and further fine processing of 50 nm or less are required. Therefore, for example, in order to meet the demand for fine processing of 50 nm or less, it is expected to develop an exposure apparatus that combines an EUV light source having a wavelength of about 13 nm and a reduced projection reflective optics.

  As an EUV light source, an LPP (laser produced plasma) light source (hereinafter also referred to as “LPP type EUV light source device”) using plasma generated by irradiating a target with a laser beam, and by discharge There are three types: a DPP (discharge produced plasma) light source using generated plasma and an SR (synchrotron radiation) light source using orbital radiation. Among these, since the LPP light source can considerably increase the plasma density, extremely high luminance close to that of black body radiation can be obtained, and light emission only in a necessary wavelength band is possible by selecting a target material. Because it is a point light source with a typical angular distribution, there is no structure such as electrodes around the light source, and it is possible to secure a very large collection solid angle of 2πsteradian. It is considered to be a powerful light source for required EUV lithography.

  Here, a principle of generating EUV light in the LPP type EUV light source apparatus will be briefly described. The target material is ejected from the nozzle, and the target material is irradiated with a laser beam to excite the target material and turn it into plasma. This plasma emits various wavelength components including extreme ultraviolet (EUV) light. Therefore, a desired wavelength component is selectively reflected and collected using a condenser mirror (EUV condenser mirror), and output to an apparatus (for example, an exposure apparatus) that uses EUV light. For example, in order to condense EUV light having a wavelength of around 13.5 nm, a condensing mirror in which a film (Mo / Si multilayer film) in which molybdenum and silicon are alternately laminated is formed on a reflecting surface is used. FIG. 6 of Patent Document 1 shows a conceptual diagram of an LPP light source.

  In such an LPP type EUV light source device, the influence of fast ions and fast neutral particles emitted from plasma is a problem. This is because the EUV collector mirror is installed in the vicinity of the plasma, and the reflective surface of the mirror is sputtered and damaged by these particles. However, the EUV collector mirror is very expensive because it requires a high surface flatness of about 0.2 nm (rms), for example, in order to maintain a high reflectance. Therefore, it is desired to extend the life of the EUV collector mirror from the viewpoints of reducing the operating cost of the EUV exposure system (exposure system that uses EUV light as a light source) and the maintenance time. Note that the scattered matter from the plasma containing fast ions and neutral particles and the debris of the target material are called debris.

  Patent Document 1 discloses an EUV light source apparatus that supplies a target at a high repetition rate at a high speed in order to reduce the influence of such debris and to improve the output of EUV light. This EUV light source device includes a target supply device having charge applying means for applying a charge to the target and acceleration means for accelerating the charged target using an electromagnetic field (second page, FIG. 1). . As disclosed in Patent Document 1, it is possible to increase the output of EUV light while increasing the working distance by accelerating the droplet target and quickly reaching the plasma emission point.

  Patent Document 2 discloses a target supply unit that supplies a target material, a laser unit that generates plasma by irradiating the target with a laser beam, and extreme ultraviolet light emitted from the plasma. An EUV light source device is disclosed that includes a condensing optical system and a magnetic field generator that generates a magnetic field in the condensing optical system when a current is supplied to trap charged particles emitted from plasma. . That is, in Patent Document 2, collision with the EUV collector mirror is prevented by trapping fast ions emitted from plasma by the action of a magnetic field. Patent Document 2 also discloses that neutral particles that do not have electric charges are similarly ionized by irradiating the neutral particles with ultraviolet rays.

Japanese Patent Laying-Open No. 2003-297737 (pages 2, 5 and 1, 6) US Patent US 6,987,279 B2 (first page)

However, if both the technology for charging and accelerating the droplet target (Patent Literature 1) and the technology for trapping ions by the action of a magnetic field (Patent Literature 2) are applied to the EUV light source device as follows: Problems occur.
That is, in general, moving charged particles receive a Lorentz force in a direction orthogonal to the moving direction due to the action of a magnetic field. Here, when the charge of the charged particle is q, the velocity is v (vector), and the magnetic flux density is B (vector), the Lorentz force F (vector) acting on the charged particle moving in the magnetic field is expressed by the following equation (1). expressed.
F = q (v × B) (1)
Therefore, when the angle between the speed v and the magnetic flux density B is θ, the Lorentz force magnitude | F | is expressed by the following equation (2).
| F | = | q | · | v | · | B | · sinθ (2)
The direction of the Lorentz force F coincides with the direction of the vector product v × B when the charge q is a positive charge. Therefore, among the ions (charged debris) generated from the plasma, those having velocity components not parallel to the magnetic flux density B (that is, charged particles crossing the magnetic flux lines) are trapped near the plasma generation point by the action of the magnetic field. Is done.

  However, in Patent Document 1, since the droplet target is charged to accelerate, if the charged target crosses the magnetic flux line while reaching the laser irradiation position, its trajectory changes due to the Lorentz force F. End up. Here, as apparent from the equations (1) and (2), the magnitude of the Lorentz force | F | depends on the charge q, the velocity v, and the magnitude of the magnetic flux density B. The trajectory also changes according to their size and cannot be predicted.

  As described above, in the LPP EUV light source device, plasma is generated by irradiating a droplet target with laser light. Therefore, it is desirable that the trajectory of the droplet target is always stable. If the trajectory of the droplet target changes, the alignment of the laser beam applied to the droplet target will be incomplete, so the excitation intensity, shape, number of times the plasma is generated, etc. will change. Because. As a result, the stability of the EUV light is lowered, and the usable EUV light is reduced. Then, the operation cost and the maintenance cost of the EUV light source apparatus increase due to the decrease in the utilization efficiency of the EUV light, and the performance of the EUV exposure apparatus decreases due to the unstable illuminance of the EUV light. The quality of the semiconductor device produced by the apparatus will be unstable.

  Therefore, the present invention provides a mechanism for supplying a droplet target to a laser irradiation position at high speed without disturbing the target trajectory in an EUV light source device, and ions (charged debris) generated from plasma by the action of a magnetic field. The purpose is to balance the trapping mechanism.

In order to solve the above-described problem, an extreme ultraviolet light source device according to one aspect of the present invention generates extreme ultraviolet light by converting a target material into plasma by irradiating the target material with laser light output from a laser light source. An extreme ultraviolet light source device comprising: (i) a chamber in which extreme ultraviolet light is generated; (ii) a target nozzle that injects a target material into the chamber; and (iii) a target material that is injected from the target nozzle. A charge supply device for charging; (iv) a pair of magnets including any one of an electromagnet, a superconducting magnet, and a permanent magnet that forms a mirror magnetic field in the chamber; and the mirror magnetic field in the trajectory of the target material substantially as a parallel, at least one auxiliary forming the auxiliary magnetic field flux lines with respect to the entering direction of the substantially straight and target material Comprising a magnetic field generating apparatus including the field-shaping device.

According to one aspect of the present invention, substantially a magnetic field is formed to trap the ions emitted from the flop plasma, in the trajectory of the target material, the magnetic flux lines with respect to the entering direction of the substantially straight and target material Since they are formed so as to be parallel to each other, even when a charged target material is introduced into such a region, it is possible to suppress fluctuation of the trajectory due to the action of a magnetic field. Therefore, the target material is stably supplied to the plasma emission point, and it is possible to achieve both high-speed supply of the target material and a technique for trapping ions.

It is a figure which shows the structure of the extreme ultraviolet light source device which concerns on the 1st Embodiment of this invention. It is a figure which shows the cross section in II-II of FIG. It is a figure for demonstrating the electron generation principle of a thermoelectron emission type electron gun. It is a figure for demonstrating the electron generation principle of a field emission type electron gun. It is a schematic diagram which shows the 1st structural example of an ECR (electron cyclotron resonance) plasma generator. It is a schematic diagram which shows the 2nd structural example of an ECR (electron cyclotron resonance) plasma generator. It is a schematic diagram which shows the structural example of a microwave plasma generator. It is a schematic diagram which shows the structural example of a dielectric charging apparatus. It is a figure for demonstrating the principle of an induction accelerator. It is a figure for demonstrating the principle of RF (high frequency) accelerator. It is a figure for demonstrating the principle of a van de graph type electrostatic accelerator. It is a figure which shows the structure of the extreme ultraviolet light source device which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the extreme ultraviolet light source device which concerns on the 3rd Embodiment of this invention. It is a figure which shows the structure of the extreme ultraviolet light source device which concerns on the 4th Embodiment of this invention. It is a figure which shows the cross section in XV-XV shown in FIG. It is a figure which shows the structure of an extreme ultraviolet light source device provided with the target position adjustment apparatus using the effect | action of an electric field. It is a figure which shows the structure of an extreme ultraviolet light source apparatus provided with the target position adjustment apparatus using the effect | action of a magnetic field. It is a top view which shows the electromagnet part shown in FIG. It is a figure which shows the example which utilizes the target position adjustment apparatus shown in FIG. 14 as an apparatus which thins out a target material.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a diagram showing a configuration of an extreme ultraviolet (EUV) light source apparatus according to the first embodiment of the present invention. 2 is a cross-sectional view taken along the line II-II shown in FIG. The extreme ultraviolet light source apparatus according to the present embodiment employs a laser generated plasma (LPP) system that generates EUV light by irradiating a target material with a laser beam and exciting it. As shown in FIG. 1, the EUV light source device includes a chamber 10 in which EUV light is generated, a target supply device 11, a target nozzle 12, a laser device 13, a condenser lens 14, and an EUV collector mirror. 15, a target recovery cylinder 16, a charge supply device 17, an acceleration device 18, electromagnets 19 a and 19 b and a yoke 19 c, a synchronous controller 20, and a target monitor 21 (FIG. 2). The EUV light source apparatus according to this embodiment may further include a target recovery pipe 22, an ion discharge pipe 23, a target discharge pipe 24, a target circulation apparatus 25, and a target supply pipe 26.

The target supply device 11 supplies a target material that is excited and turned into plasma by being irradiated with a laser beam to the target nozzle 12. Examples of the target substance include xenon (Xe), a mixture containing xenon as a main component, argon (Ar), krypton (Kr), water (H ₂ O) or alcohol that becomes a gas in a low pressure state, tin, Molten metal such as (Sn) or lithium (Li), fine metal particles such as tin, tin oxide or copper dispersed in water or alcohol, lithium fluoride (LiF) or lithium chloride (LiCl) in water An ion solution or the like in which) is dissolved is used.

  The state of the target material introduced into the target supply device 11 may be any of gas, liquid, and solid. For example, when a target material that is gaseous at normal temperature is used as a liquid target, such as xenon, liquefied xenon is supplied to the target nozzle 12 by pressurizing and cooling the xenon gas in the target supply device 11. On the other hand, when a solid substance such as tin is used as a liquid target, for example, tin is heated in the target supply device 11 so that liquefied tin is supplied to the target nozzle 12.

  The target nozzle 12 supplies the droplet-like target material 1 to a predetermined position (plasma emission point) in the vacuum chamber 10 by ejecting the target material supplied from the target supply device 11. The target nozzle 12 includes a vibration mechanism such as a piezo element, and generates droplets from the target material according to the following principle. That is, according to the Rayleigh micro-turbulence stability theory, when a target jet having a diameter d flowing at a speed v is disturbed by vibrating at a frequency f, the wavelength λ (λ = v of the target jet) is generated. When / f) satisfies a predetermined condition (for example, λ / d = 4.51), uniform-sized droplets are repeatedly formed at the frequency f. The frequency f at that time is called the Rayleigh frequency.

  The laser device 13 is a laser light source capable of pulse oscillation at a high repetition frequency (for example, a pulse width of about several nanoseconds to several tens of nanoseconds and a frequency of about 1 kHz to 10 kHz). A laser beam 2 for emitting the light is emitted. The condensing lens 14 condenses the laser beam 2 emitted from the laser device 13 and irradiates a plasma emission point (hereinafter also referred to as a laser irradiation position). Instead of the condensing lens 14, other condensing optical components or a condensing optical system in which a plurality of optical components are combined may be used.

By irradiating the target material 1 with such a laser beam 2, a plasma 3 is generated, and various wavelength components are emitted therefrom.
The EUV collector mirror 15 is a condensing optical system that collects a predetermined wavelength component (for example, EUV light in the vicinity of 13.5 nm) out of various wavelength components emitted from the plasma 3. The EUV collector mirror 15 has, for example, a concave reflecting surface on which a molybdenum (Mo) / silicon (Si) multilayer film that selectively reflects EUV light having a wavelength of around 13.5 nm is formed. By the EUV collector mirror 15, the EUV light 4 is reflected and collected in a predetermined direction (minus Y direction in FIG. 1), and is output to, for example, an exposure apparatus. Note that the EUV light condensing optical system is not limited to the condensing mirror as shown in FIG. 1, and may be configured using a plurality of optical components. It is necessary to be a system.

  The target collection cylinder 16 is disposed at a position facing the target nozzle 12 with the plasma emission point interposed therebetween. The target recovery cylinder 16 recovers the target material that has not been turned into plasma without being irradiated with the laser beam despite being ejected from the target nozzle 12. This prevents unnecessary target material from scattering and contaminating the EUV collector mirror 15 and the like, and prevents the degree of vacuum in the chamber from decreasing.

The charge supply device 17 is, for example, an electron gun, an ECR (electron cyclotron) plasma generation device, a microwave plasma generation device, or a dielectric charging device, and is charged by supplying a charge to the target material 1.
The acceleration device 18 is, for example, an electrostatic acceleration device, an induction acceleration device, or an RF (high frequency) acceleration device, and accelerates the charged target material 1 by the action of an electric field and / or a magnetic field. Thereby, the working distance can be increased without reducing the output of EUV light.
The specific configurations of the charge supply device 17 and the acceleration device 18 will be described later.

  Each of the electromagnets 19a and 19b includes a coil winding, a coil winding cooling mechanism, and the like. Desirably, a yoke (a member used to induce magnetic flux, such as electromagnetic soft iron) 19c is disposed in the electromagnets 19a and 19b. A power supply device and a controller (not shown) are connected to these electromagnets 19a and 19b, and a desired magnetic field is formed in the vacuum chamber 10 by adjusting the current supplied to each electromagnet 19a and 19b.

  The coils of the electromagnets 19a and 19b are arranged so as to be parallel or substantially parallel to each other and facing each other so that the centers of the openings coincide with each other, thereby forming a set of mirror coils. The mirror coil is supplied with current flowing in the same direction, thereby forming a mirror magnetic field in a region including the plasma generation point.

Here, the mirror magnetic field is a magnetic field having a high magnetic flux density in the vicinity of the coils of the electromagnets 19a and 19b and a low magnetic flux density in the middle of those coils. Usually, in a mirror magnetic field used in magnetic confinement fusion or the like, a magnetic field design for increasing the mirror ratio is performed in order to enhance the confinement effect of ions and plasma. However, in this embodiment, for the purpose of efficiently discharging ions in the magnetic flux line direction (Z-axis direction), the electromagnet coils of the electromagnets 19a and 19b or the yoke 19c are designed so as to reduce the mirror ratio. ing. The mirror ratio is the maximum magnetic flux density B _{1 in} the vicinity of the coil with respect to the minimum magnetic flux density B ₀ in the middle part of the two coils (that is, B ₁ / B ₀ ).

  In such a mirror magnetic field, charged particles (such as fast ions emitted from the plasma 3) move by drawing a trajectory that rotates in a plane perpendicular to the magnetic flux lines by receiving the Lorentz force. Trapped nearby. Further, when such charged particles have a velocity component in the Z direction, they move while drawing a spiral trajectory along the Z axis, and are discharged to the outside of the electromagnets 19a and 19b. This prevents charged particles from flying near the EUV collector mirror 15 and contaminating or damaging the mirror.

  Further, in the present embodiment, by generating magnetic fields having different strengths in the electromagnets 19a and 19b, respectively, as shown by the magnetic flux lines 6 in FIG. An asymmetric magnetic field is formed on the upper and lower surfaces. FIG. 1 shows magnetic flux lines 6 when the magnetic field on the electromagnet 19a side is stronger than the magnetic field on the electromagnet 19b side. Therefore, ions trapped by the action of the magnetic field are more likely to be guided to the lower magnetic flux density (downward in FIG. 1). As a result, ions can be actively guided in the direction of the target recovery cylinder 16 and the ion discharge pipe 23 without being retained near the plasma emission point.

  Furthermore, in the present embodiment, the shape of the magnetic field is controlled so that the magnetic flux lines 6 are substantially straight lines and substantially parallel to the entry direction of the target material 1 in the vicinity of the trajectory of the target material 1. Yes. In other words, a region in which the magnetic flux lines 6 are substantially straight is formed, and the target material 1 is ejected from the target nozzle 12 toward the plasma emission point along the straight region. As a result, the velocity vector and the magnetic flux density vector of the charged target material 1 become parallel, and the target material 1 does not cross the magnetic flux line 6. As a result, since the Lorentz force received by the charged target material 1 can be reduced, fluctuations in the trajectory of the target material 1 are suppressed.

  Since the electromagnets 19a and 19b and the yoke 19c are used in the vacuum chamber 10, a nonmagnetic metal such as stainless steel or aluminum or ceramics is used for maintaining the degree of vacuum in the chamber and preventing the release of contaminants. It is sealed by the formed storage container. Thereby, the coil winding or the like is separated from the vacuum space in the chamber.

In order to change the strength of the magnetic field generated by each of the electromagnets 19a and 19b, the strength of the current supplied to the electromagnets 19a and 19b is changed, or the number of turns and the diameter of the coils of the electromagnets 19a and 19b are changed. You can just let them. The details of the mirror magnetic field and the charged particle ejection by the magnetic field are described in Patent Document 2 and “Introduction to Plasma Theory” by Dwight R. Nicholson (John Wiley See Chapter 2, Section 6 of Johan Wiley & Sons, Inc.
In this embodiment, an electromagnet coil is used to form a mirror magnetic field, but a superconducting magnet or a permanent magnet may be used instead.

  The synchronous controller 20 controls the operation of the charge supply device 17 and the acceleration device 18 so that the target material 1 reaches the plasma emission point at a predetermined timing based on the output signal of the target monitor 21 described later, and also the laser. The operation timing with the apparatus 13 is synchronously controlled. This is because the EUV light source device performs laser (laser beam 2) irradiation with a pulse width of about several nanoseconds to several tens of nanoseconds from the viewpoint of improving EUV conversion efficiency.

  Referring to FIG. 2, the target monitor 21 includes a CCD camera or a linearly arranged photosensor array, and outputs a signal representing the time when the target material 1 passes a predetermined position. The position monitored by the target monitor 21 may be a laser irradiation position, or any other position as long as there is a correlation with the time at which the target material 1 reaches the laser irradiation position. For example, if the target material 1 is on the orbit, the time at which the target material 1 passes the laser irradiation position can be calculated based on the distance between the monitor position and the laser irradiation position and the speed of the target material 1.

Referring again to FIG. 1, the target recovery pipe 22 transports the target material recovered by the target recovery cylinder 16 to the target circulation device 25.
The ion discharge pipe 23 is installed so as to be connected to the opening of the electromagnet 19b (or the yoke 19c), collects ions trapped in the magnetic field and led out of the electromagnet 19b, and is used as a target circulation device. To 25.

The target discharge pipe 24 is a passage for discharging the target material remaining in the chamber 10 to the outside of the chamber 10.
The target circulation device 25 is a device for reusing the remaining target material and ions recovered through the target recovery pipe 22, the ion discharge pipe 23, and the target discharge pipe 24, and is a suction power source (suction pump). And a purification mechanism for the target material, and a pumping power source (pumping pump). The target circulation device 25 purifies the target material and the like collected from the chamber 10 in a purification mechanism, and pumps it to the target supply device 11 through the target supply pipe 26.
In order to assist the pumping action by the target circulation device 25, an exhaust pump may be separately provided in the target recovery pipe 22, the ion discharge pipe 23, and the target discharge pipe 24.

  As described above, according to the present embodiment, the magnetic field for trapping ions emitted from the plasma is formed so that the magnetic flux lines are substantially linear in the trajectory of the target material, and the charged target material is Since it introduce | transduces along the linear part, it can suppress that the track | orbit of a target material is fluctuate | varied by the effect | action of a magnetic field. Thereby, the target material can be supplied to a certain position (laser irradiation position) at a predetermined timing. Therefore, it becomes possible to reliably irradiate the target material with a laser beam, so that EUV light can be stably emitted. As a result, in the extreme ultraviolet light source device, it is possible to prevent the use efficiency of EUV light from being reduced and obtain stable illuminance. As a result, it is possible to reduce the operating cost of the EUV light source device and improve the operating rate. Further, since the exposure performance is stabilized in the exposure system using such an EUV light source device, the operating rate and the exposure processing are improved. It is possible to improve the capability and stabilize the quality of the semiconductor device.

Next, a device used as the charge supply device 17 shown in FIG. 1 will be described in detail.
FIG. 3 is a diagram for explaining the principle of electron generation of the thermionic emission electron gun. As shown in FIG. 3, by heating the filament 102 with the heating power source 101, thermoelectrons are generated from the tip of the filament 102. The thermoelectrons are accelerated by the acceleration electrode (anode) 103 and emitted toward the target material 1 (FIG. 1). At this time, when the electron acceleration energy is relatively low (for example, 100 eV or less) and the target material 1 is irradiated with electrons, the electrons adhere to the target material 1. Thereby, the target material 1 is negatively charged. On the other hand, when the electron acceleration energy is relatively high (for example, greater than 100 eV) and the target material 1 is irradiated with electrons, secondary electrons are emitted from atoms on the surface of the target material due to the collision energy of the electrons. Thereby, the target material 1 is positively charged.

  FIG. 4 is a diagram for explaining the principle of electron generation of the field emission electron gun. As shown in FIG. 4, when a strong electric field is formed by the extraction electrode (anode) 112, electrons are generated from the tip of the emitter (cathode) 111. The electrons are accelerated by the acceleration electrode (anode) 113 and emitted toward the target material 1 (FIG. 1). Also in this case, by irradiating the target material 1 with electrons having relatively low acceleration energy (for example, 100 eV or less), the electrons adhere to the target material 1 and the target material 1 is negatively charged. On the other hand, by irradiating the target material 1 with electrons having relatively high acceleration energy (for example, greater than 100 eV), secondary electrons are emitted from the target material, and the target material 1 is positively charged.

  FIG. 5 is a schematic diagram showing a first configuration example of the ECR plasma generator. The discharge chamber 121 shown in FIG. 5 is formed of, for example, a quartz tube, and a neutral particle gas (plasma gas) with an appropriate pressure is supplied to the inside thereof. As the neutral particle gas, xenon (Xe), argon (Ar), helium (He), or the like is used. In addition, a high magnetic field (for example, 875 gauss) is formed in the discharge chamber 121 by the electromagnet 122 disposed around the discharge chamber 121. Therefore, the electrons existing in the discharge chamber 121 perform a swiveling motion (cyclotron motion) that wraps around the magnetic field lines. A microwave (electric field) is introduced into the discharge chamber 121 from the microwave generator 123 through the microwave waveguide 124. At this time, when the electric field formed in the discharge chamber 121 changes at the same frequency as the cyclotron motion of the electrons, the electrons obtain energy from the electric field and enter a so-called cyclotron resonance state. For example, when a 2.45 GHz microwave is introduced to an 875 gauss magnetic field, a cyclotron resonance state is caused.

  Here, from the viewpoint of effective use of microwave energy, it is more advantageous to use a right-rotating circularly polarized microwave. The reason is as follows. That is, as shown in FIG. 5, a case is considered in which a microwave is introduced from a direction (arrow direction) coinciding with a magnetic flux into a discharge chamber 121 in which a magnetic field having a downward magnetic flux (magnetic flux density B) is formed. At this time, when horizontally polarized microwaves are applied to the electrons in the discharge chamber 121, the electrons are accelerated by the microwaves only twice per period of the electron cyclotron motion. In contrast, when electrons are irradiated with a right-rotating circularly polarized microwave, the direction of polarization of the microwave and the direction of rotation of the electron's cyclotron motion always coincide, so the electrons continue to be accelerated by the microwave. Because it becomes possible. At that time, it is possible to generate a plasma having a density higher than the electron critical density by irradiating the microwave from the higher magnetic flux density to the lower magnetic flux density. For details on the principle of generation of microwave plasma, the IEEJ / Microwave Plasma Research Special Committee, “Microwave Plasma Technology”, 1st Edition, Ohm Co., Ltd., September 25, 2003, p. See 18-21.

  The electrons thus accelerated in the cyclotron resonance state collide with surrounding neutral particles and are ionized. Then, ionization due to collision of electrons and supply of energy from the electric field to the electrons occur in a chain to generate plasma. This plasma is emitted from the discharge chamber 121 through the orifice 125 toward the space in the vacuum chamber 10 (FIG. 1) (that is, the trajectory of the target material 1).

  As shown in FIG. 5, an extraction electrode 126 having a mesh-like opening is disposed outside the orifice 125. Further, a high voltage power supply device 127 is connected to the extraction electrode 126. In such a state that a negative high voltage is applied to the extraction electrode 126, the plasma emitted from the orifice 125 is passed through the opening of the extraction electrode 126. Thereby, only positively charged plasma can be selectively extracted. By irradiating the target material 1 with such plasma, the target material 1 can be positively charged.

FIG. 6 is a schematic diagram showing a second configuration example of the ECR plasma generator.
In FIG. 6, the microwave waveguide 135 is bent into an L shape, and a portion partitioned by a window 136 is a discharge chamber 131. Accordingly, the discharge chamber 131 is formed of a conductive nonmagnetic metal material such as copper or aluminum so that the discharge chamber 131 can also serve as a waveguide and a magnetic field can be formed therein, as will be described later. Has been. Two orifices 132 for allowing the target material 1 injected from the target nozzle 12 (FIG. 1) to pass therethrough are formed at two locations (upper and lower in FIG. 6) of the discharge chamber 131 facing each other. Further, the discharge chamber 131 is filled with a neutral particle gas such as xenon (Xe), argon (Ar), or helium (He) as a plasma gas. Alternatively, when xenon is used as the target material 1, the xenon gas remaining in the vacuum chamber 10 (FIG. 1) may be used as the plasma gas.

  A high magnetic field is formed inside the discharge chamber 131 by the electromagnet 133 disposed around the discharge chamber 131, and a microwave (electric field) is transmitted from the microwave generator 134 through the waveguide 135 and the window 136. When plasma is introduced, plasma is generated in the discharge chamber 131. The principle of plasma generation is the same as that described in the first configuration example. By passing the target material 1 through such a plasma region, the target material 1 is charged. Here, normally, in the plasma, electrons move at a higher speed than ions, so that the probability that the electrons collide with the target material 1 increases. Therefore, in the present configuration example, the target material 1 is negatively charged.

FIG. 7 is a schematic diagram illustrating a configuration example of a microwave plasma generator.
In FIG. 7, a discharge chamber 141 is formed by partitioning a part of the microwave waveguide 144 with a window 145. The discharge chamber 141 is made of a metal material and closed at the end in order to confine and vibrate the microwave. Further, orifices 142 for allowing the target material 1 ejected from the target nozzle 12 (FIG. 1) to pass through are formed at two locations (upper and lower in FIG. 7) facing the discharge chamber 141. These orifices 142 are arranged so that the target material 1 passes through a region where the electric field strength of the standing wave generated in the discharge chamber 141 is the strongest.

  When a microwave is introduced into the discharge chamber 141 from the microwave generator 143 through the waveguide 144 and the window 145, the microwave is reflected at the end of the discharge chamber 141, and a standing wave is generated in the discharge chamber 141. Generated. Thereby, microwave plasma is generated in the discharge chamber 141. Then, the target material 1 is jetted from the target nozzle 12 and passes through the microwave plasma formed in the region having the strongest electric field strength among the standing waves. Thereby, the target material 1 is negatively charged. The reason for negative charging is the same as described in the second configuration example.

  FIG. 8 is a schematic diagram illustrating a configuration example of the dielectric charging device. On the downstream side of the target nozzle 12 for injecting the target material 1, an electrode 151 having an opening for allowing the target material 1 to pass therethrough is disposed. For example, a high voltage of about 1 kV is applied between the target nozzle 12 and the electrode 151 by the high voltage power supply device 152. Accordingly, when the continuous flow of the target material passing through the target nozzle 12 is split into droplets, the external material is dielectrically polarized, and as a result, the target material 1 is charged.

Next, a device used as the acceleration device 18 shown in FIG. 1 will be described in detail.
FIG. 9 is a diagram for explaining the principle of the induction accelerating device. As shown in FIG. 9A, the induction accelerating device includes a conductor 201 that forms an acceleration cavity (a passage through which accelerated particles 200 pass), a magnetic body 202 disposed in the conductor 201, And a wiring 203 formed so as to surround the magnetic body 202. The magnetic body 202 is disposed so as to surround the passage of the particle 200. As shown in FIG. 9B, the magnetic body 202 corresponds to a magnetic core of a transformer for generating a stepped induction electric field in the acceleration cavity. Further, the wiring 203 corresponds to the primary wiring of the transformer, and the conductor 201 corresponds to the secondary wiring of the transformer. When a magnetic field (magnetic flux density B _θ ) is generated in the magnetic body 202 by supplying a voltage to the wiring 203 (primary side wiring), induction occurs in the conductor (secondary side wiring) 201 surrounding the same magnetic body 202. Electric power is generated, and an induction electric field _EZ is generated in the gap 204 between the conductor 201 and the wiring 203. Charged particles 200, when passing through the gap 204 is accelerated by the electric field _{E Z.}

  FIG. 10 is a diagram for explaining the principle of the RF accelerator. The RF accelerator includes a plurality of cylindrical acceleration cavities 211 to 216 formed of copper or the like. These accelerating cavities 211 to 216 are connected in common to the RF power supply device 217 every other wiring. Further, the lengths of the acceleration cavities 211 to 216 are designed to gradually increase in accordance with the speed of the charged particles 210 introduced from the acceleration cavity 211 side. The RF power supply device 217 applies an AC voltage to each of the acceleration cavities 211 to 216 in synchronization with the timing when the charged particle 210 passes through the acceleration cavities 211 to 216. FIG. 10A shows the state of the electric field at a certain moment, and FIG. 10B shows the state of the electric field at another moment. For example, when the charged particle 210 has a negative charge, the voltage application timing is adjusted so that the charged particle 210 moves from the negative acceleration cavity toward the positive acceleration cavity when passing through a certain gap. Thereby, the charged particle 210 is accelerated little by little every time it passes through the gap.

  FIG. 11 is a diagram for explaining the principle of the vandegraph type electrostatic acceleration device. The van de graph type electrostatic acceleration device includes an acceleration tube 221, a direct-current high-voltage power supply 222, a charge transport unit 223, and a cap 224 that accumulates charges. The charge transport unit 223 is, for example, a belt conveyor formed of an insulating material, and transports the charge supplied from the DC high voltage power supply 222 to the cap 224. As a result, a high voltage (for example, several hundred kilos to several megavolts) is generated between the cap 224 and the ground potential, and the charged particles 220 are accelerated in the acceleration tube 221 using this as an acceleration electric field.

Next, an extreme ultraviolet light source apparatus according to the second embodiment of the present invention will be described with reference to FIG.
The extreme ultraviolet light source device according to the present embodiment further includes an auxiliary magnetic field forming device 31 with respect to the extreme ultraviolet light source device shown in FIG. Other configurations are the same as those shown in FIG.

Here, in the magnetic field formed by the electromagnets 19a and 19b, the magnetic flux lines diverge as the distance from the electromagnet 19a increases. Moreover, when the yoke 19c is provided in the electromagnets 19a and 19b, the magnetic flux lines are more likely to diverge. Therefore, in the present embodiment, by providing the auxiliary magnetic field forming device 31, the magnetic flux lines are substantially linear and substantially parallel to the entry direction of the target material 1 in a wider area. Thereby, the fluctuation of the trajectory of the target material 1 is more reliably prevented.
The arrangement of the auxiliary magnetic field forming device 31 is not limited below the acceleration device 18 and may be anywhere between the charge supply device 17 and the electromagnet 19a.

Next, an extreme ultraviolet light source apparatus according to the third embodiment of the present invention will be described with reference to FIG.
The extreme ultraviolet light source device according to this embodiment is obtained by further adding an auxiliary magnetic field forming device 32 above the acceleration device 18 to the extreme ultraviolet light source device shown in FIG.
Here, the target material 1 is affected by the magnetic field as soon as the charge is supplied by the charge supply device 17. Therefore, in the present embodiment, by providing the auxiliary magnetic field forming device 32, the region in which the magnetic flux lines 6 are substantially linear and substantially parallel to the entry direction of the target material 1 is further expanded. Thereby, the trajectory of the charged target material 1 can be stabilized more reliably. As the auxiliary magnetic field forming device 32, an electromagnet, a superconducting magnet, or a permanent magnet is used.

  Next, an extreme ultraviolet light source apparatus according to the fourth embodiment of the present invention will be described. FIG. 14 is a diagram showing the configuration of the extreme ultraviolet light source apparatus according to this embodiment, and FIG. 15 is a cross-sectional view taken along XV-XV shown in FIG. The extreme ultraviolet light source apparatus according to the present embodiment further includes a target position adjusting device 41, a target position controller 42, and a target position monitor 43 with respect to the extreme ultraviolet light source apparatus shown in FIG. Other configurations are the same as those shown in FIG.

  The target position adjusting device 41 adjusts the position of the target material 1 so that the target material 1 supplied with charge passes through the center of the magnetic field (that is, on the axis of the plasma emission point) under the control of the target position controller 42. adjust. As the target position adjusting device 41, a device that exerts a mechanical action on the charged target material 1, such as an electric field or a magnetic field, is used.

The target position controller 42 controls the operation of the target position adjustment device 41 based on the detection signal output from the target position monitor 43.
As shown in FIG. 15, the target position monitor 43 includes an image sensor such as a CCD camera or a linearly arranged photosensor array, and detects the position of the target material 1 with respect to the laser irradiation position (plasma emission point). . The position where the target position monitor 43 is installed may be a position that directly faces the laser irradiation position, or any other position that has a correlation with the position of the target material 1 with respect to the laser irradiation position. Further, as shown in FIG. 15, the position detection accuracy of the target material 1 can be improved by arranging a plurality of target position monitors 43 so that the target material 1 faces from a plurality of different directions.

  According to the present embodiment, the position of the charged target material 1 is adjusted, and the magnetic flux lines of the mirror magnetic field are accurately input into the region where the magnetic field lines are substantially linear. Can be suppressed.

Next, a specific configuration of the target position adjusting device 41 shown in FIG. 14 will be described.
The extreme ultraviolet light source device shown in FIG. 16 has a voltage generator 51 and two pairs of electrodes 52 and 53 as a target position adjusting device, and adjusts the position of the target material 1 by the action of an electric field.

The voltage generator 51 supplies a pulsed or continuous high voltage to the electrode pairs 52 and 53 under the control of the target position controller 42.
Each of the electrode pairs 52 and 53 includes two electrode plates arranged to face each other so as to be parallel to each other across the trajectory of the target material 1. The electrode pair 52 is arranged so that an electric field in the X direction is formed between the two electrode plates, and the electrode pair 53 is arranged so that an electric field in the Y direction is formed between the two electrode plates. Yes.

  In this way, the position of the target material 1 is adjusted two-dimensionally by passing the charged target material 1 through regions where electric fields in two different directions are formed by the electrode pairs 52 and 53, respectively. . The amount of displacement of the target material 1 in the X direction and the Y direction is controlled by the voltage value supplied from the voltage generator 51 to the electrode pairs 52 and 53.

The extreme ultraviolet light source device shown in FIG. 17 includes a power supply device 61 and an electromagnet unit 62 as a target position adjusting device, and adjusts the position of the target material 1 by the action of a magnetic field.
The power supply device 61 supplies current to the electromagnet unit 62 in a pulsed or continuous manner under the control of the target position controller 42.

  FIG. 18 is a plan view showing the electromagnet portion 62. As shown in FIG. 18, the electromagnet portion 62 includes two pairs of electromagnets arranged to face each other so as to be parallel to each other with the trajectory of the target material 1 interposed therebetween. In these electromagnets, the direction of current is determined so that the same magnetic poles face each other, whereby a magnetic field represented by magnetic flux lines 7 is formed between the four electromagnets. In addition, these electromagnets have the center of the magnetic field (in other words, the position where the magnetic fields formed by the four electromagnets cancel each other) on the axis of the plasma emission point (that is, the magnetic field formed by the electromagnets 19a and 19b). (On the central axis).

  As shown in FIG. 18, the charged target material 1 passes through the center of the magnetic field formed by the electromagnet unit 62 in a direction perpendicular to the plane including the magnetic flux lines 7 (for example, the direction from the front surface to the back surface of the paper). In this case, the target material 1 does not cross the magnetic flux line 7. Therefore, the target material 1 goes straight without being affected by the magnetic field. On the other hand, when the position of the target material 1 is deviated from the center of the magnetic field, the target material 1 crosses the magnetic flux lines 7. Therefore, the charged target material 1 receives a Lorentz force and is pushed back toward the center. As shown in FIG. 18, the magnetic flux lines 7 are gradually becoming denser from the center toward the periphery, so that the target material 1 has more magnetic flux lines 7 as the passing position of the target material 1 approaches the periphery. Will be pushed back toward the center with greater force. Eventually, the charged target material 1 receives a force in the direction in which the magnetic flux density is small (that is, the direction of the magnetic field center), and the position converges to the magnetic field center.

  In addition, in order to align the center of the magnetic field formed by the electromagnet part 62 on the axis of the plasma emission point, it may be performed by adjusting the strengths of the currents supplied to the four electromagnets. This may be done by adjusting the position. In FIG. 17, the position of the target material 1 may be adjusted by the same principle using a permanent magnet instead of the electromagnet.

  In the above description, the position of the target material is adjusted by the action of either the electric field or the magnetic field, but both actions may be used. For example, as the target position adjusting device 41 shown in FIG. 14, the electrode pairs 52 and 53 shown in FIG. 16 are provided downstream of the charge supply device 17, and the electromagnet unit 62 shown in FIG. Thereby, after adjusting the trajectory of the target material 1 by the action of the electric field, the trajectory of the target material 1 can be converged on the axis of the plasma emission point by the action of the magnetic field. As a result, the position of the target material 1 can be adjusted with higher accuracy.

  Here, in the present embodiment, the target position adjusting device 41 is provided to adjust the position of the target material 1 that is input to the magnetic field, but the target position adjusting device 41 is used for other purposes. May be.

  Here, the frequency f at which the droplet target material 1 is generated is not necessarily the same as the repetitive operation frequency f ′ at which the laser device 13 (FIG. 14) oscillates the laser beam 2. For example, in the case where a repetitive operation frequency f ′ of a YAG laser generally used in an LPP type EUV light source device is about 10 kHz, a droplet having a diameter of about 60 μm is formed at a speed of about 30 m / s. The frequency f of vibration for generating is about 110 kHz. Thus, normally, the droplet generation frequency f is several times to several tens of times the repetition frequency f ′. In such a case, the target material 1 ejected from the target nozzle 12 is irradiated with the laser beam 2 at several intervals. Therefore, the target material 1 that is not irradiated with the laser beam 2 is also introduced around the EUV collector mirror 15, but such a state is not preferable from the viewpoint of debris generation. That is, plasma is generated by irradiating a certain target material 1 with the laser beam 2, but the adjacent target material 1 is evaporated by the heat energy generated thereby. For this reason, the nearby target material does not contribute to the generation of EUV light, but causes contamination in the vacuum chamber 10.

  Therefore, the target position adjusting device 41 can be used to thin out the target material 1 of the droplets. That is, as shown in FIG. 19, the trajectory of a predetermined target material 1 ′ from the target material 1 injected from the target nozzle 12 (FIG. 14) is moved along the traveling direction ( The direction is different from the direction toward the plasma emission point. Thereby, only the target material 1 that matches the irradiation timing of the laser beam 2 can be injected into the plasma emission point. Further, the target material 1 ′ whose trajectory has been changed may be recovered, for example, guided in the direction of the target discharge pipe 24. Thereafter, the target material 1 may be purified by the target circulation device 25 and reused.

  Thus, by thinning out the unnecessary target material 1, the amount of evaporation of the target material 1 in the vicinity of the plasma emission point can be reduced, so that a decrease in the degree of vacuum (pressure increase) in the vacuum chamber 10 can be prevented, Contamination of components in the vacuum chamber 10 such as the EUV collector mirror 15 can be suppressed.

  The fourth embodiment of the present invention described above is provided with a target position adjusting device for the extreme ultraviolet light source device shown in FIG. 1, but is similar to the extreme ultraviolet light source device shown in FIGS. An apparatus may be provided. Thereby, the accuracy of the trajectory of the target material 1 can be further increased.

  The present invention can be used in an extreme ultraviolet light source device used as a light source of an exposure apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Target material (droplet target), 2 ... Laser beam, 3 ... Plasma, 4 ... EUV light, 6, 7 ... Magnetic flux line, 10 ... Vacuum chamber, 11 ... Target supply apparatus, 12 ... Target nozzle, 13 ... Laser Device: 14 ... Condenser lens, 15 ... EUV collector mirror, 16 ... Target recovery cylinder, 17 ... Charge supply device, 18 ... Accelerator, 19a, 19b ... Electromagnet, 19c ... Yoke, 20 ... Synchronous controller, 21 ... Target Monitor, 22 ... Target recovery pipe, 23 ... Ion discharge pipe, 24 ... Target discharge pipe, 25 ... Target circulation apparatus, 26 ... Target supply pipe, 31, 32 ... Auxiliary magnetic field forming apparatus, 41 ... Target position adjustment apparatus, 42 ... Target position controller 43 ... Target position monitor 51 ... Voltage generator 52, 53 ... Electrode , 61 ... power supply device, 62 ... electromagnet unit, 101 ... heating power source, 102 ... filament, 103, 113 ... acceleration electrode, 111 ... emitter, 112, 126 ... extraction electrode, 121, 131, 141 ... discharge chamber, 122 DESCRIPTION OF SYMBOLS 133 ... Electromagnet, 123, 134, 143 ... Microwave generator, 124, 136, 144 ... Microwave waveguide, 125, 132, 142 ... Orifice, 127, 152 ... High voltage power supply device, 200, 210, 220 ... Charged particle, 136, 145 ... window, 151 ... electrode, 201 ... conductor, 202 ... magnetic body, 203 ... wiring, 204 ... gap, 211-216 ... acceleration cavity, 217 ... RF power supply

Claims (5)

An extreme ultraviolet light source device that generates extreme ultraviolet light by irradiating a target material with laser light output from a laser light source to plasma the target material,
A chamber in which extreme ultraviolet light is generated,
A target nozzle for injecting a target material into the chamber;
A charge supply device for charging a target material ejected from the target nozzle;
One of an electromagnet, a superconducting magnet, and a permanent magnet, a pair of magnets for forming a mirror magnetic field in the chamber, and a magnetic flux line of the mirror magnetic field in a trajectory of the target material is substantially linear and the target A magnetic field forming device including at least one auxiliary magnetic field forming device that forms an auxiliary magnetic field so as to be substantially parallel to the direction of entry of the substance;
An extreme ultraviolet light source device comprising: The magnetic field forming device is
A set of electromagnets for forming a mirror magnetic field in the chamber;
The magnetic flux lines of the mirror magnetic field formed by the one set of electromagnets are supplied to the one set of electromagnets so as to be substantially linear in the trajectory of the target material and substantially parallel to the entry direction of the target material. A control unit for controlling the current;
The extreme ultraviolet light source device according to claim 1, comprising:   The extreme ultraviolet light source device according to claim 1, further comprising an acceleration device for accelerating a target material charged by the charge supply device.   The extreme according to claim 3, wherein the at least one auxiliary magnetic field forming device is arranged between the acceleration device and the set of magnets and / or between the charge supply device and the acceleration device. Ultraviolet light source device. Further comprising a target collection cylinder arranged in pairs toward the target nozzle, extreme ultraviolet light source device according to claim 1 or 2, wherein.

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