Extreme-ultraviolet light source device

The present invention relates to an extreme ultraviolet (EUV) light source device used as a light source for an exposure device.

In recent years, the miniaturization of optical lithography has been rapidly progressing with the miniaturization of semiconductor processes, and in the next generation, microfabrication of 100 to 70 nm and further microfabrication of 50 nm or less will be 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 with a wavelength of about 13 nm and reduced projection reflective optics.

EUV light sources include 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 a discharge. There are three types: a DPP (discharge produced plasma) light source that uses the generated plasma, and an SR (synchrotron radiation) light source that uses orbital radiation. Among these, the LPP light source can increase the plasma density considerably, so that extremely high brightness close to blackbody radiation can be obtained, and by selecting the target material, it is possible to emit light only in the required wavelength band, which is almost isotropic. Since it is a point light source with a typical angle distribution, there are no structures such as electrodes around the light source, and it is possible to secure an extremely large collection solid angle of 2π plasmadian, so power of several tens of watts or more can be obtained. It is considered to be a promising light source for the required EUV lithography.

Here, the principle of EUV light generation by the LPP method is shown in the figure of Patent Document 1.<u style="single">14</u>Will be explained with reference to. A substance (target substance) that is excited by being irradiated with a laser beam to be turned into plasma is supplied from the target nozzle 101. This target substance is in the state of continuous flow of liquid or gas (target jet) or in the form of droplets.<u style="single">Voice (state)</u>Droplet target)<u style="single">Or</u>, Supplied in the form of a granular solid. Such a target substance is irradiated with a laser beam emitted from a laser device (driving laser) 102 and focused by a condenser lens 103. As a result, the target substance is excited to generate plasma 104, from which various wavelength components including EUV light are emitted. On the other hand, on the reflective surface of the EUV condensing mirror 105, for example, a film (Mo / Si multilayer film) in which molybdenum and silicon are alternately laminated in order to selectively reflect a predetermined wavelength component (for example, around 13.5 nm). ) Is formed. The EUV condensing mirror 105 reflects and condenses a predetermined wavelength component (EUV light) emitted from the plasma 104, and outputs the light to an exposure apparatus or the like.

In such an LPP type EUV light source device, the influence of high-speed ions and high-speed neutral particles emitted from plasma has become a problem. Because the EUV focusing mirror is installed near the plasma, such particles sputter and damage the reflective surface of the mirror. However, EUV condensing mirrors are very expensive because they require high surface flatness of, for example, about 0.2 nm (rms) in order to maintain high reflectance. Therefore, from the viewpoint of reducing the operating cost of the EUV exposure system (exposure system that uses EUV light as a light source) and reducing the maintenance time, it is desired to extend the life of the EUV condensing mirror. Debris from plasma containing fast ions and neutral particles and debris of target substances are called debris.

In order to solve such a problem, Patent Document 1 describes a target supply unit that supplies a target substance, a laser unit that generates plasma by irradiating the target with a laser beam, and extreme ultraviolet light emitted from the plasma. It includes a condensing optical system that condenses and emits light, and a light source generator that generates a magnetic field in the condensing optical system when a current is supplied to trap the charged particles emitted from the plasma. Extreme ultraviolet light source devices are disclosed. That is, in Patent Document 1, high-speed ions emitted from the plasma are trapped by the action of a magnetic field to prevent collision with the EUV condensing mirror. Further, Patent Document 1 also discloses that neutral particles are ionized by irradiation with ultraviolet rays or the like in order to similarly trap uncharged neutral particles.

Further, Patent Document 2 describes a chamber in which extreme ultraviolet light is generated, a target supply means for supplying a target substance into the chamber, and a laser light source that generates plasma by irradiating the target with a laser beam. A condensing optical system that collects extreme ultraviolet light emitted from the plasma, an ionization means that ionizes the neutral particles contained in the particles emitted from the plasma into charged particles, and at least an ionization means. An extreme ultraviolet light source device is disclosed that includes a magnet that forms a magnetic field in the chamber to trap the neutral particles ionized by. Further, Patent Document 2 discloses that the neutral particles are ionized by colliding the neutral particles with plasma (plasma for ionization), and as a method for generating the plasma for ionization, microwaves are used for electrons. It is mentioned that irradiation causes electron cyclotron resonance (ECR) (paragraphs 0037 to 0040).<patcit num="1"><text>U.S. Patent US6,987,279B2 (Page 1)</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2006-80255 (pages 2, 8 and 9)</text></patcit>

<p> By the way, in an LPP type EUV light source device, laser oscillation is usually performed by a pulse operation in which the pulse width is about several n seconds to several tens of n seconds and the repetition frequency of continuous pulses is about 1 kHz to 10 kHz from the viewpoint of EUV conversion efficiency and the like. Is generated by performing the above. Also, in the DPP type EUV light source device, plasma is generated by discharging at a repeating frequency of about 1 kHz to 10 kHz. However, the above-mentioned Patent Document 2 does not describe at all the characteristics and generation timing of microwaves used to generate ECR.</p><p> Here, after the plasma is generated, the neutral particles emitted from the plasma are scattered for about several microseconds. Therefore, when microwaves are continuously emitted, most of the microwave energy is not utilized for ionization of neutral particles by ECR, and is finally released as thermal energy into the chamber of the EUV light source device. Therefore, there is a problem from the viewpoint of effective use of energy. In addition, when thermal energy is released into the chamber, it causes disturbance to the generation of fine target jets and droplet targets, and the target state becomes unstable. In particular, targets liquefied by cooling a gaseous substance at room temperature (liquefied xenon jets and liquefied xenon droplet targets), such as xenon (Xe), are sensitive to changes in ambient temperature. Such instability of the target causes problems such as a decrease in the output of the generated EUV light and a decrease in the stability of the EUV pulse energy, and further, a decrease in the exposure performance in the EUV exposure system and an exposure processing capacity. It will lead to a decline.</p><p> Another problem with the continuous emission of microwaves is the generation of X-rays. That is, when a so-called mass limiting target containing a metal material or a droplet target is used as the target substance, the residual gas pressure in the chamber becomes low. Therefore, the ionization of neutral particles by ECR occurs efficiently only in a short time of several μs in a region with a relatively high particle density near the EUV plasma. However, even after that, the electrons that generated ECR continue to absorb microwave energy without colliding with neutral particles. As a result, the electrons obtain extremely large kinetic energy, and finally, synchrotron radiation (X-rays) is generated by the swirling motion. The generation of such X-rays has an adverse effect on the human body and the environment, and is a major problem.</p><p> Therefore, in view of the above points, it is an object of the present invention to efficiently ionize neutral particles emitted from plasma in an extreme ultraviolet light source device that discharges debris containing high-speed ions and neutral particles by the action of a magnetic field. And.</p>

<p> In order to solve the above problems, the extreme ultraviolet light source device according to one aspect of the present invention is<u style="single">In the chamber</u>Radiates extreme ultraviolet light<u style="single">for</u>A plasma generation means for generating plasma by pulse operation, a condensing optical system for condensing extreme ultraviolet light emitted from the plasma, and<u style="single">It has a magnetic field forming means that forms a magnetic field in the chamber and causes at least the electrons emitted from the plasma to perform a cyclotron motion, and a frequency corresponding to the rotation frequency of the cyclotron motion of the electrons.</u>Microwave<u style="single">To the electron by pulse operation</u>By irradiating to generate electron cyclotron resonance<u style="single">Accelerate the electrons</u>, Neutral particles emitted from the plasma<u style="single">By collision with accelerated electrons</u>Ionization<u style="single">And trap in the magnetic field formed by the magnetic field forming means</u>With microwave radiation means<u style="single">, Small</u>At least the above plasma generation means<u style="single">Operation timing and</u>The above microwave radiation means<u style="single">Operation timing and</u>same<u style="single">Period system</u>It is equipped with a control means to control.</p>

<p> According to the present invention, microwaves for causing electron cyclotron resonance are radiated in a pulsed manner in synchronization with the generation of plasma, so that the utilization efficiency of microwave energy in the ionization of neutral particles can be improved. It will be possible.</p>

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same components are given the same reference numbers, and the description thereof will be omitted. FIG. 1 is a diagram showing a configuration of an extreme ultraviolet (EUV) light source device according to a first embodiment of the present invention. Further, FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. The EUV light source device according to the present embodiment employs a laser excitation plasma (LPP) method that generates EUV light by irradiating a target substance with a laser beam to excite it. As shown in FIG. 1, this EUV light source device includes a chamber 10 in which EUV light is generated, a target supply device 11, a target nozzle 12, a prepulse laser device 13, a main pulse laser device 15, and a main pulse laser device 15. It includes condensing lenses 14 and 16, an EUV condensing mirror 17, and a target recovery cylinder 18. Further, the EUV light source device according to the present embodiment includes electromagnet coils 19a and 19b, a microwave generator 20, a microwave waveguide 21, a microwave antenna 22, a target recovery pipe 23, an ion discharge pipe 24, and the like. It further includes a target exhaust pipe 25, a target circulation device 26, a target supply pipe 27, a target synchronization monitor 28 (FIG. 2), and a synchronization controller 29.

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

The state of the target substance may be any of gas, liquid, and solid. For example, when a gas target substance at room 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 contrary, when a solid substance at room temperature is used as a liquid target such as tin, the liquefied tin is supplied to the target nozzle 12 by heating the tin in the target supply device 11.

The target nozzle 12 injects the target substance supplied from the target supply device 11 and supplies it into the chamber 10. Further, the target nozzle 12 is provided with a vibration mechanism such as a piezo element in order to generate a droplet target (droplet target) 1. Here, according to Rayleigh's theory of micro-disturbance stability, when a target jet with a diameter d flowing at a velocity v is disturbed by vibrating at a frequency f, the wavelength λ (λ = λ =) of the vibration generated in the target jet. When v / f) satisfies a predetermined condition (for example, λ / d = 4.51), jets of uniform size are repeatedly formed at the frequency f. The frequency f at that time is called the Rayleigh frequency.

Both the pre-pulse laser device 13 and the main pulse laser device 15 are laser light sources capable of pulse oscillation at a high repetition frequency (for example, a pulse width of about several n seconds to several tens of n seconds and a frequency of about 1 kHz to 10 kHz). is there. Further, the condenser lenses 14 and 16 focus the laser beams 2 and 3 emitted from the laser devices 13 and 15, respectively, so that the target substance 1 ejected from the target nozzle 12 is irradiated at a predetermined position. Instead of the condenser lenses 14 and 16, other condenser optical components or a condenser optical system in which a plurality of optical components are combined may be used.

The main pulse laser device 15 emits a laser beam (main pulse) 3 for making plasma by irradiating the target substance 1. Further, the pre-pulse laser device 13 emits a laser beam (pre-pulse) 2 to be pre-irradiated to the target substance 1 so that the density of the target substance 1 is in an appropriate state when the main pulse 3 is irradiated. ..

Here, since the target substance 1 is injected from the inside of the high pressure (for example, about 15 MPa) target nozzle 12 into the low pressure (for example, about 0.1 Pa) chamber 10, even if it is a liquid at the moment of injection. After that, the temperature drops sharply due to adiabatic expansion and solidifies. However, the density of the solidified target material may be too high to generate EUV plasma. In such a case, by irradiating the target substance 1 with the pre-pulse 2 in advance to reduce the density, EUV light can be generated more efficiently when the main pulse 3 is irradiated. The intensity of the pre-pulse 2 and the time from the irradiation of the pre-pulse 2 to the irradiation of the main pulse are determined so that the target density is appropriate at the time of irradiation of the main pulse within the range where the target substance 1 does not become plasma. To.

By irradiating such a target substance 1 with the main pulse 3, plasma 4 is generated, and various wavelength components are emitted from the plasma 4. The EUV condensing mirror 17 is a condensing optical system that condenses a predetermined wavelength component (for example, EUV light near 13.5 nm) from various wavelength components radiated from the plasma 4. The EUV condensing mirror 17 has a concave reflecting surface, for example, a molybdenum (Mo) / silicon (Si) multilayer film that selectively reflects EUV light having a wavelength of around 13.5 nm. It is formed. The EUV condensing mirror 17 reflects and condenses the EUV light in a predetermined direction (minus Y direction in FIG. 1), and outputs the EUV light to, for example, an exposure apparatus. The condensing optical system for EUV light is not limited to the condensing mirror as shown in FIG. 1, and may be configured by using a plurality of optical components, but a reflective optical system may be used to suppress absorption of EUV light. It is necessary to.

The target recovery cylinder 18 is arranged at a position facing the target nozzle 12 with the plasma emission point (position at which the target substance 1 is irradiated with the main beam 3). The target recovery cylinder 18 recovers the target substance that has not been turned into plasma without being irradiated with the laser beam even though it is ejected from the target nozzle 12. This prevents unnecessary target substances from scattering and contaminating the EUV condensing mirror 17 and the like, and also prevents a decrease in the degree of vacuum in the chamber.

The electromagnet coils 19a and 19b form a magnetic field in the chamber 10 for causing electron cyclotron resonance, which will be described later, and for discharging charged particles by the action of a magnetic field. These electromagnet coils 19a and 19b are arranged parallel to each other or parallel to each other and facing each other so that the centers of the openings of the coils coincide with each other. Further, wiring and a power supply device for supplying a current to the coils are connected to the electromagnet coils 19a and 19b. Here, since the electromagnet coils 19a and 19b are used in the high vacuum chamber 10, the coil winding and its cooling mechanism are housed in a closed container formed of a non-magnetic metal such as stainless steel or ceramics. Has been done. As a result, components such as coil windings are separated from the vacuum space in the chamber 10, so that the release of contaminants is prevented and the degree of vacuum in the chamber 10 is maintained.

By generating magnetic fields of equal strength and direction from each of these electromagnet coils 19a and 19b, a mirror magnetic field having a high magnetic flux density in the vicinity of each coil and a low magnetic flux density is formed in the middle of the coils. Will be done. In such a magnetic field, charged particles (for example, high-speed ions emitted from plasma 4 and ionized neutral particles) rotate in a plane perpendicular to the magnetic flux line by receiving Lorentz force. Since it draws and moves, it is trapped near the Z axis. Further, when such a charged particle has a velocity component in the Z direction, it moves while drawing a spiral trajectory along the Z axis and is discharged to the outside of the electromagnet coils 19a and 19b. As a result, it is possible to prevent charged particles from flying near the EUV condensing mirror 17 and contaminating or damaging the mirror.

Further, by changing the strength of the magnetic field generated by the two electromagnet coils 19a and 19b with each other, the central axis of the magnetic flux line is shown as shown in the magnetic flux line 6 of FIG.<u style="single">When</u>straight<u style="single">Fellowship</u>An asymmetric magnetic field is formed with respect to the surface. Note that FIG. 1 shows a case where the magnetic field on the electromagnet coil 19a side is stronger than the magnetic field on the electromagnet coil 19b side. Further, in order to change the strength of the magnetic field generated by each of the electromagnet coils 19a and 19b, the strength of the current flowing through the electromagnet coils 19a and 19b can be changed, or the number of turns of the coils of the electromagnet coils 19a and 19b can be changed. The diameters may be changed from each other. Charged particles trapped in such an asymmetric magnetic field tend to be guided in the direction of low magnetic flux density (minus Z direction in FIG. 1). Therefore, the target recovery cylinder 18 and ion discharge do not cause charged particles to stay near the plasma emission point.<u style="single">Tube 2</u>It becomes possible to actively guide in four directions.

For details on the mirror magnetic field and the discharge action of charged particles by the magnetic field, see Patent Documents 1 and 2 and Dwight R. Nicholson, "Introduction to Plasma Theory" (John. See Chapter 2, Section 6 of Johon Wiley &amp; Sons, Inc. Further, in the present embodiment, the electromagnet coil is used to form the magnetic field, but instead, a superconducting magnet or a permanent magnet may be used.

The microwave generators 20 to 22 generate electron cyclotron resonance (ECR) by radiating microwaves to ionize neutral particles (neutral debris) emitted from plasma 4. Here, the principle of ionization of neutral particles by ECR will be described with reference to FIG.

The moving charged particle 100 receives a Lorentz force F expressed by the following equation (1) in a direction always perpendicular to the direction of motion due to a magnetic field. In equation (1), q (C) is the charge of the charged particle 100, v (m / s) is the velocity of the charged particle 100, and B (T) is the magnetic flux density of the magnetic field. F = q (v × B) ... (1)

Since the Lorentz force F acts in a direction orthogonal to the moving direction of the charged particle 100, the charged particle 100 makes a swirling motion so as to wind around the magnetic field line as shown in FIG. 3 (a). This turning motion is called a cyclotron motion. The rotation frequency f (cyclotron frequency) of the cyclotron motion is constant regardless of the speed of the charged particle 100, and is expressed by the following equation (2). In equation (2), m (kg) is the mass of the charged particle 100. f = qB / (2πm) ... (2)

By applying an electric field (microwave) that changes at the same frequency as this frequency f to the charged particle 100, the charged particle 100 can efficiently obtain energy from the electric field. This is called cyclotron resonance. Since the charged particle 100 is constantly accelerating in the cyclotron resonance state, the charged particle 100 moves in a spiral orbit as shown in FIG. 3 (b).

Here, assuming that the charged particle 100 is an electron, q / 2πm is about 2.8 × 10.¹⁰It becomes (C / kg). Therefore, from Eq. (2), the cyclotron frequency f is expressed as follows. f (Hz) = 2.8 × 10¹⁰B Will be. For example, if the magnetic flux density B is 0.5 (T), the cyclotron frequency f is in the microwave band of 14 (GHz).

In the region where such magnetic flux density and microwaves are applied, electrons are accelerated by obtaining a large amount of kinetic energy. On the other hand, in a neutral gas (gas of neutral particles) with appropriate pressure, when the kinetic energy of the electrons is larger than the ionization energy of the atoms that make up the neutral particles, the electrons collide with the neutral particles. Ionize it. In addition, the electrons that have lost energy by ionizing the neutral particles obtain energy from the microwave again, and repeatedly collide with the neutral particles and ionize. Therefore, as shown in FIG. 1, the neutral particles emitted from the plasma 4 can be ionized by forming a magnetic field near the plasma emission point and irradiating with microwaves. The particles ionized by ECR in this way are trapped near the Z axis by the action of the magnetic field formed by the electromagnet coils 19a and 19b, and are discharged to the outside of the electromagnet coils 19a and 10b.

The microwave generator 20 shown in FIG. 1 includes a general microwave generator such as a magnetron, a klystron, a Gunn diode, and a transistor, and emits a microwave having a predetermined frequency to generate an ECR into a predetermined pulse. It is generated by operating in a width (for example, several μs to several tens of μs).

Further, the microwave waveguide 21 guides the microwave generated in the microwave generator 20 into the vacuum chamber 10. As the microwave waveguide 21, a metal waveguide, a dielectric waveguide, a microwave transfer cable on a coaxial cable, or the like is used depending on the frequency of the microwave.

Further, the microwave antenna 22 has an open end extending like a horn, and radiates microwaves propagated through the microwave waveguide 21 into the chamber 10. The microwave antenna 22 may be provided with a separate member at the tip of the microwave waveguide 21, or the microwave antenna 22 is formed by gradually expanding the tip of the microwave waveguide 21 into a horn shape. You may. A microwave amplifier may be provided in the subsequent stage of the microwave generator 20 or in the middle of the microwave waveguide 21.

The target recovery pipe 23 conveys the target substance recovered by the target recovery cylinder 18 to the target circulation device 26. The ion discharge tube 24 is installed so that its opening is connected to the central opening of the electromagnet coil 19b, and collects charged particles radiated from the plasma 4 and led out to the outside of the electromagnet coil 19b by the action of a magnetic field. Then, it is transported to the target circulation device 26.

The target exhaust pipe 25 is a passage for discharging the target substance remaining in the chamber 10 to the outside of the chamber 10. The target circulation device 26 is a device for reusing the residual target substance and ions recovered through the target recovery pipe 23, the ion discharge pipe 24, and the target exhaust pipe 25, and is a suction power source (suction pump). It is equipped with a purification mechanism for the target substance and a pumping power source (pumping pump). The target circulation device 26 purifies the target substance or the like recovered from the chamber 10 in the purification mechanism, and pumps it to the target supply device 11 via the target supply pipe 27. An exhaust pump may be separately provided in the target recovery pipe 23, the ion discharge pipe 24, or the target exhaust pipe 25 in order to assist the pumping action by the target circulation device 26.

As shown in FIG. 2, the target synchronization monitor 28 includes a CCD camera or a linearly arranged photosensor array, and outputs a signal indicating the time when the target substance 1 passes a predetermined position. .. The position monitored by the target synchronization monitor 28 may be the laser irradiation position (that is, the plasma emission point) or any other position, and the correlation with the time when the target substance 1 passes through the laser irradiation position. Any position is sufficient. For example, if the target substance 1 is in orbit, the time when the target substance 1 passes the laser irradiation position can be calculated based on the distance between the monitor position and the laser irradiation position and the velocity of the target substance 1.

The synchronization controller 29 synchronously controls the operation timing of the pre-pulse laser device 13, the main pulse laser device 15, and the microwave generator 20 based on the output signal of the target synchronization monitor 28. Here, from the viewpoint of improving the EUV conversion efficiency, the EUV light source device generates EUV light by, for example, irradiating a laser (main pulse 3) with a pulse width of about several n seconds to several tens of n seconds. Therefore, in the synchronization controller 29, optimization of the target density (irradiation of pre-pulse 2) and microwave irradiation for ionizing neutral particles by ECR are performed at appropriate timings based on the pulse operation of the main pulse 3. As such, set the synchronization and delay times for those devices.

Specifically, the synchronization controller 29 sets the drive timing of the main pulse laser device 15 so that the main pulse 3 is irradiated when the target substance 1 passes through the plasma emission point. Further, the synchronization controller 29 sets the drive timing of the pre-pulse laser device 13 so that the target substance 1 is irradiated with the pre-pulse 2 before a predetermined time when the main pulse 3 is irradiated.

Further, the synchronization controller 29 controls the operation of the microwave generator 20 as follows. That is, plasma 4 is generated by irradiating the target substance 1 with the main pulse 3, and neutral particles are emitted and diffused from the plasma 4, but the microwave irradiation range emitted from the microwave antenna 22 is appropriate. The density (gas pressure) is only a short time. In order to efficiently ionize the neutral particles, it is necessary that an electron avalanche due to ECR occurs at that time. Here, electron avalanche is a phenomenon in which electrons ionize neutral particles to emit another electron (secondary electron), and the secondary electron is accelerated by ECR to ionize another neutral particle. Is a phenomenon in which a large amount of electrons are generated as a result of chain formation. Therefore, the synchronization controller 29 sets the operation start timing of the microwave generator 20 so that an electron avalanche occurs when the gas pressure becomes an appropriate state. On the other hand, since the inside of the chamber 10 is kept in a high vacuum to suppress the absorption of EUV light, the mean free path until the electrons collide with the neutral particles is relatively long. Therefore, if microwaves are continuously emitted for a long time, the electrons obtain extremely large kinetic energy by ECR, and finally synchrotron radiation (X-rays) is generated by swirling motion. In order to prevent such a phenomenon, the synchronization controller 29 uses the microwave after a predetermined time (for example, while the microwave irradiation range is at an appropriate gas pressure) after the irradiation of the main pulse 3 is performed. Stop the operation of the generator 20.

FIG. 4 shows a specific example of the timing chart of the control signal output from the synchronization controller 29 to each device. In FIG. 4, the uppermost stage shows the output signal (monitor signal) of the target synchronization monitor 28, and the rising edge of the output signal represents the timing at which the droplet-shaped target substance 1 is ejected from the target nozzle 12. .. The second stage shows the control signal output to the microwave generator 20, and the microwave generator 20 radiates microwaves while the control signal is at a high level. Further, the third and fourth stages show the control signals for the pre-pulse laser device 13 and the main pulse laser device 15, respectively, and the laser devices 13 and 15 are lasers while the control signals are at a high level. Emit a beam.

In FIG. 4, each device is synchronously controlled so that the irradiation timing of the microwave is earlier than the irradiation timing of the pre-pulse 2 or the irradiation timing of the main pulse 3. As a result, it is possible to make the time when the microwave irradiation range becomes an appropriate gas pressure and the time when the electron avalanche due to ECR occurs almost coincide with each other. As a result, neutral particles can be efficiently ionized.

As described above, according to the present embodiment, since the pulse emission timing of the microwave is controlled in synchronization with the plasma generation timing, most of the microwave energy of the neutral particles (debris) emitted from the EUV plasma is controlled. It can be used for ionization. In particular, when the microwave emission is started earlier than the pre-pulse or main pulse irradiation of the target material, the utilization efficiency of the microwave energy can be further improved, and the unnecessary energy emitted into the chamber 10 can be significantly increased. It becomes possible to reduce to. As a result, the stability of the microjet target and the droplet target is improved, so that it is possible to increase the output of EUV light and improve the stability of EUV pulse energy. Further, since the electrons do not absorb the excessive microwave energy, it is possible to avoid the generation of X-rays due to the high-speed swirling motion of the electrons, and it is possible to improve the safety.

In addition, since the particles ionized in this way can be quickly discharged to the outside of the EUV condensing mirror by the action of the magnetic field, contamination and damage of the EUV condensing mirror can be suppressed, and the reflectance of the EUV condensing mirror can be reduced. It is possible to extend the life of the mirror while preventing the mirror. In addition, debris retention near the plasma emission point can be suppressed. As a result, the EUV light utilization efficiency is improved and the frequency of replacement of the EUV condensing mirror is reduced, so that it is possible to reduce the operating cost of the EUV light source device and improve the operating rate. Further, the exposure performance of the exposure system using the EUV light source device can be stabilized, the operating rate can be improved, and the exposure processing capacity can be improved, so that the productivity of the semiconductor device can be improved.

Next, the EUV light source device according to the second embodiment of the present invention will be described with reference to FIG. As shown in FIG. 5, the EUV light source device according to the present embodiment is obtained by further adding an electron supply device 31 and an electron supply controller 32 to the EUV light source device shown in FIG.

The electron supply device 31 is a device that supplies electrons to the inside of the chamber 10. The electron supply device 31 may be installed anywhere in the chamber 10 as long as the electrons 7 emitted from the electron supply device 31 can reach the region where ECR is generated (that is, near the plasma emission point). .. In the present embodiment, the electron supply device 31 is installed near the central opening of the electromagnet coil 19a. The electrons 7 emitted at such positions are guided to the vicinity of the plasma emission point along the magnetic flux line 6 by the action of the magnetic field formed by the electromagnet coils 19a and 19b. The electronic supply controller 32 includes a power supply device and controls the operation of the electronic supply device 31.

Here, when microwaves are radiated with a pulse width of several μs to several tens of μs, in order to efficiently proceed with the ionization of neutral particles by ECR, the ionization is steep at the initial stage of microwave radiation. It is necessary to generate an early rise, that is, an electron avalanche. However, it is difficult to synchronize with the pulse operation of the microwave generator 20 because the initial electrons that trigger the generation of electron avalanche usually appear accidentally from an ionization source existing in the natural environment like cosmic rays. Is. Another problem is that the number of electrons generated from such an ionization source and the number of electrons existing in the background are small.

Therefore, in the present embodiment, a sufficient number of initial electrons are introduced into the chamber 10 by providing the electron supply device 31 in order to generate an electron avalanche quickly and surely. As a result, according to the present embodiment, it is possible to reliably and efficiently proceed with the ionization of neutral particles by ECR.

Next, the EUV light source device according to the third embodiment of the present invention will be described with reference to FIG. As shown in FIG. 6, the EUV light source device according to the present embodiment is an EUV light source device having an electron supply device 31 and an electron supply controller 32, and their operations are controlled by a synchronization controller 29. .. Other configurations are the same as those shown in FIG.

In the present embodiment, the operation of the electron supply controller 32 is controlled so as to perform a pulse operation based on the microwave radiation start timing. As a result, the timing at which the initial electrons 7 reach the microwave irradiation range and the microwave radiation start timing can be matched, so that electron avalanche by ECR can be reliably generated at an appropriate timing. Further, since the minimum number of electrons 7 is introduced into the chamber 10, it is possible to suppress a decrease in the degree of vacuum in the chamber 10 and damage to parts in the chamber 10 due to unnecessary electrons.

FIG. 7 shows a specific example of the timing chart of the control signal output from the synchronization controller 29 to each device. The uppermost stage shows the output signal of the target synchronization monitor 28, and the rising edge of the output signal represents the timing at which the droplet-shaped target substance 1 is ejected from the target nozzle 12. Further, the second stage shows a control signal output to the electron supply controller 32, and the electron supply device 31 emits electrons 7 while the control signal is at a high level. The third stage shows the control signal output to the microwave generator 20, which emits microwaves while the control signal is at a high level. Further, the 4th and 5th stages show the control signals output to the pre-pulse laser device 13 and the main pulse laser device 15, respectively, and the control signals of these laser devices 13 and 15 are at a high level. It emits a laser beam while it is.

As shown in FIG. 7, the timing at which the initial electrons are emitted by the pulse operation and the timing at which the microwave emission is started are matched, and those timings are set from the irradiation timing of the prepulse 2 or the irradiation timing of the main pulse 3. Synchronously control each device so that the speed is increased. Thereby, when the neutral particles emitted from the plasma 4 have an appropriate particle density in the microwave irradiation range, electron avalanche by ECR can be surely generated. As a result, it is possible to suppress the influence of electrons on the parts in the chamber 10 and efficiently ionize the neutral particles by a large amount of electrons accelerated at high speed. The timing at which the supply of initial electrons is terminated may be earlier than the timing at which the emission of microwaves is terminated. This is because once an electron avalanche is generated, the ECR continues without supplying new electrons.

In the second and third embodiments described above, for example, an electron gun is applied as the electron supply device 31. As the electron gun, either a thermionic radiation type or a field emission type electron gun may be used. FIG. 8 is a diagram for explaining the electron generation principle of the thermionic radiation type electron gun. As shown in FIG. 8, by heating the filament 33b with the heating power source 33a, thermoelectrons are generated from the tip of the filament 33b. These thermions are accelerated and emitted by the accelerating electrode (anode) 33c.

Further, FIG. 9 is a diagram for explaining the electron generation principle of the field emission electron gun. As shown in FIG. 9, by forming a strong electric field by the extraction electrode (anode) 34a, electrons are generated from the tip of the emitter (anode) 34b. These electrons are accelerated and emitted by the accelerating electrode (anode) 34c.

Next, the EUV light source device according to the fourth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 10, the EUV light source device according to the present embodiment has an ultraviolet ionizer 35 and an electronic supply controller 36 instead of the electronic supply device 31 and the electronic supply controller 32 shown in FIG. , Supply initial electrons 7 by the principle of ultraviolet ionization. Other configurations are the same as those shown in FIG.

FIG. 11 is a diagram for explaining the principle of electron supply by ultraviolet ionization. The ultraviolet ionizer 35 has a set of discharge electrodes 35a arranged so as to face each other. Further, the electronic supply controller 36 includes a high voltage supply circuit. When a pulse discharge is generated by applying a high voltage to the discharge electrode 35a by the electron supply controller 36, ultraviolet rays 8 are generated at that time. When the residual gas existing in the vicinity is irradiated by the ultraviolet rays 8, the residual gas is ionized and electrons 7 are generated. If residual gas is also present between the discharge electrodes 35a, the residual gas is ionized by pulse discharge to generate electrons 7. The electrons 7 generated in this way are guided to the vicinity of the plasma emission point along the magnetic flux line 6 by the action of the magnetic field formed by the electromagnet coils 19a and 19b (FIG. 10), and are used as initial electrons in the ECR.

The operation of the electronic supply controller 36 is controlled by the synchronous controller 29 so that the pulse operation is performed based on the microwave radiation start timing. Desirably, the voltage is supplied by the electron supply controller 35 to start the discharge before the irradiation timing of the prepulse 2 or the main pulse 3 as described with reference to FIG. 7.

Next, the EUV light source device according to the fifth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 12, the EUV light source device according to the present embodiment has an electron supply laser device 37, a condenser lens 38, and an electron instead of the electron supply device 31 and the electron supply controller 32 shown in FIG. It has a supply target 39 and supplies initial electrons 7 into the chamber 10 by the principle of laser-generated plasma. Other configurations are the same as those shown in FIG.

As the electron supply target 39, it is desirable to use a material that generates as little debris as possible in order to suppress contamination and damage to the parts in the chamber 10 and a decrease in the degree of vacuum. Examples of such a target include a metal rotation target such as a tungsten (W) material, an argon (Ar) gas jet target, a helium (He) gas jet target, and the like. The laser beam emitted from the electron supply laser device 37 is focused and irradiated on the electron supply target 39 by the condenser lens 38. As a result, the electron supply target 39 is excited to generate plasma. The electrons 7 emitted from this plasma are guided to the vicinity of the plasma emission point along the magnetic flux line 6 by the action of the magnetic field formed by the electromagnet coils 19a and 19b, and are used as initial electrons in the ECR.

Also in this embodiment, the operation of the electron supply laser device 37 is controlled by the synchronization controller 29 so as to perform a pulse operation based on the microwave radiation start timing. Desirably, the operation of the microwave generator 20 and the electron supply laser device 37 is started before the irradiation timing of the pre-pulse 2 or the main pulse 3 as described with reference to FIG. 7.

Next, the EUV light source device according to the sixth embodiment of the present invention will be described with reference to FIG. As shown in FIG. 13, the EUV light source device according to the present embodiment has a photoelectron generation target 40 instead of the electron supply target 39 shown in FIG. 12, and is in the chamber 10 according to the principle of photoelectron generation. Supply initial electron 7. Further, in the present embodiment, since it is not necessary to condense the laser beam emitted from the electron supply laser device 37, the condensing lens 38 (FIG. 12) is not provided. Other configurations are the same as those shown in FIG.

As the photoelectron generation target 40, it is desirable to use a material that has a small work function of photoelectron generation and that generates as little debris as possible in order to suppress contamination and damage to the parts in the chamber 10 and a decrease in the degree of vacuum. .. Examples of such a target include a cesium (Cs) metal plate or an alloy plate target containing cesium, a magnesium (Mg) metal plate or an alloy plate target containing magnesium, a tungsten (W) metal plate target, and the like. .. By irradiating such a photoelectron generation target 40 with a laser beam emitted from an electron supply target 39, the photoelectron generation target 40 is excited and electrons 7 are emitted from its surface. The electron 7 is guided to the vicinity of the plasma emission point along the magnetic flux line 6 by the action of the magnetic field formed by the electromagnet coils 19a and 19b, and is used as the initial electron in the ECR.

Also in this embodiment, the operation of the electron supply laser device 37 is controlled by the synchronization controller 29 so as to perform a pulse operation based on the microwave radiation start timing. Desirably, the operation of the microwave generator 20 and the electron supply laser device 37 is started before the irradiation timing of the pre-pulse 2 or the main pulse 3 as described with reference to FIG. 7.

Next, the EUV light source device according to the seventh embodiment of the present invention will be described with reference to FIG. As shown in FIG. 14, the EUV light source device according to the present embodiment is provided with a microwave height directional device 41 in place of the microwave antenna 22 shown in FIG. 6 or in addition to the microwave antenna 22. is there. Other configurations are the same as those shown in FIG.

Here, referring to FIG. 15, normally, the microwave 9 radiated from the horn-shaped aperture antenna (horn antenna) diverges in the chamber 10. On the other hand, in the region where microwave 9 should be irradiated in order to ionize neutral particles by ECR, assuming that the expansion rate of plasma 4 is about several km / s, plasma 4 takes several n seconds to several tens of n seconds. It stays in the range of 1 cm to several cm that expands. Therefore, of the microwave energy radiated into the chamber 10, the ratio actually used for ionization by ECR is very small. That is, the intensity of the microwave is insufficient in the region where the irradiation of the microwave is required, and unnecessary microwave energy is supplied into the chamber 10.

On the other hand, in the present embodiment, since the microwave height directional device 41 is provided, the microwave 9 can be intensively irradiated to a region of about 1 cm to several cm centered on the plasma emission point. As a result, it is possible to effectively utilize the microwave energy and to prevent the stability of droplet target generation from being impaired by unnecessary microwave energy.

Next, the specific configuration of the microwave height directional device 41 shown in FIG. 14 will be described with reference to FIGS. 16 to 18. FIG. 16 shows an example of forming a microwave height directional device by a microwave parabolic mirror 42. In this case, the microwave propagating through the microwave waveguide 21 is incident on the microwave parabolic mirror 42. Here, since the incident wave incident on the parabolic surface is reflected in a predetermined direction regardless of the incident angle, it is possible to form the microwave 9 propagating in parallel.

FIG. 17 shows an example of forming a microwave height directional device by the microwave rotating ellipsoidal mirror 43. In this case, the microwave rotating ellipsoidal mirror 43 is installed so that its first focus is located near the end of the microwave waveguide 21 and its second focus is located near the plasma emission point. , Microwaves are incident on the reflecting surface. Here, the incident wave incident on the spheroidal surface through the first focal point of the spheroidal mirror is reflected in the direction passing through the second focal point of the spheroidal surface, so that the microwave 9 is focused near the plasma emission point. Can be made to.

FIG. 18 shows an example in which a microwave height directional device is formed by arranging a dielectric microwave lens (focusing lens) 44 in front of the microwave antenna 22. Here, the dielectric microwave lens 44 is a microwave lens formed of a dielectric such as ceramic or Teflon (registered trademark), and acts on microwaves in the same manner as the action of an optical lens on light. .. In this case, the dielectric microwave lens 44 is installed so that its focal point is located near the plasma emission point. As a result, the microwave 9 emitted from the microwave antenna 22 can be focused near the plasma emission point. As described above, according to the present embodiment, since the directivity of the microwave is increased, it is possible to intensively irradiate the range in which the plasma is expanded within a predetermined time with the microwave having sufficient intensity. Become.

In the first to seventh embodiments of the present invention described above, the LPP method is used as the plasma generation method in the EUV light source device, but the discharge generation plasma (DPP) method may be used instead. Here, the DPP method is a method of generating plasma by applying discharge energy to a plasma-producing substance (discharge luminescent gas). In the DPP method, a discharge section in which a counter electrode is formed is installed in the chamber, a plasma generating substance such as xenon gas is supplied to the discharge section, and a voltage is applied between the electrodes by pulse operation. The method of condensing EUV light from the generated plasma is the same as in the LPP method.

For such a DPP type EUV light source device, magnetic field forming means (electromagnet coils 19a and 19b), microwave emitting means (microwave generator 20 to microwave antenna 22, and microwave height directional device 41) and the like. , Synchronous control means (synchronous controller 29), electron supply means (electron supply device 31 to photoelectron generation target 40), etc. are additionally provided to efficiently ionize neutral debris generated from plasma by ECR. Due to the action of the magnetic field, it can be quickly discharged to the outside of the EUV condensing mirror.

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

<figref num="1">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 1st Embodiment of this invention.</figref><figref num="2">It is a figure which shows the cross section in II-II of FIG.</figref><figref num="3">It is a figure for demonstrating the principle of electron cyclotron resonance (ECR).</figref><figref num="4">It is a timing chart of the control signal output from the synchronization controller shown in FIG.</figref><figref num="5">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 2nd Embodiment of this invention.</figref><figref num="6">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 3rd Embodiment of this invention.</figref><figref num="7">It is a timing chart of the control signal output from the synchronization controller shown in FIG.</figref><figref num="8">It is a figure for demonstrating the electron generation principle of a thermionic radiation type electron gun.</figref><figref num="9">It is a figure for demonstrating the electron generation principle of a field emission electron gun.</figref><figref num="10">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 4th Embodiment of this invention.</figref><figref num="11">It is a figure for demonstrating the principle of electron supply by ultraviolet ionization shown in FIG.</figref><figref num="12">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 5th Embodiment of this invention.</figref><figref num="13">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 6th Embodiment of this invention.</figref><figref num="14">It is a figure which shows the structure of the extreme ultraviolet light source apparatus which concerns on 7th Embodiment of this invention.</figref><figref num="15">It is a figure which shows the radiation range of the microwave radiated from the microwave antenna.</figref><figref num="16">It is a figure which shows the example which forms the microwave height directional device by the microwave parabolic mirror.</figref><figref num="17">It is a figure which shows the example which forms the microwave height directional device by the microwave rotating ellipsoidal mirror.</figref><figref num="18">It is a figure which shows the example which forms the microwave high directional device by the dielectric microwave lens.</figref>

Code description

1 ... target substance (droplet target), 2 ... laser light (prepulse), 3 ... laser light (main pulse), 4 ... plasma, 5 ... EUV light, 6 ... Magnetic flux lines, 7 ... electrons (initial electrons), 8 ... ultraviolet rays, 9 ... microwaves, 10 ... chambers, 11 ... target feeders, 12 ... target nozzles, 13. .Prepulse laser device, 14, 16 ... condensing lens, 15 ... main pulse laser device, 17 ... EUV condensing mirror, 18 ... target recovery tube, 19a, 19b ... electromagnet Coil, 20 ... microwave generator, 21 ... microwave waveguide, 22 ... microwave antenna, 23 ... target recovery pipe, 24 ... ion discharge pipe, 25 ... target exhaust Tube, 26 ... Target Circulator, 27 ... Target Supply Tube, 28 ... Target Sync Monitor, 29 ... Sync Controller, 31 ... Electronic Supply Device, 32, 36 ... For Electronic Supply Controller, 33a ... Heating power supply, 33b ... Filament, 33c ... Acceleration electrode (anodole), 34a ... Extraction electrode (anodole), 34b ... Emitter (anodole), 34c ... Acceleration electrode (anodide), 35 ... EUV ionizer, 37 ... Laser device for electron supply, 38 ... Condensing lens, 39 ... Electron supply target, 40 ... Photoelectron generation target , 41 ... Microwave High Direction Device, 42 ... Microwave Pneumatic Mirror, 43 ... Microwave Rotating Elliptical Mirror, 44 ... Dielectric Microwave Lens, 100 ... Charged Particles