1. Field of the Invention
The present invention relates to a light source device for generating extreme ultra violet (EUV) light by applying a laser beam to a target.
2. Description of a Related Art
As semiconductor processes become finer, the photolithography has been making rapid progress to finer fabrication, and, in the next generation, microfabrication of a pattern having a width of 100 nm to 70 nm, further, microfabrication of a pattern having a width of 50 nm or less will be required. For example, in order to fulfill the requirement for microfabrication of a pattern having a width of 50 nm or less, the development of exposure equipment with a combination of an EUV light source for generating light having a wavelength of about 13 nm and a reduced projection cataoptric system is expected.
As the EUV light source, there are three kinds of an LPP (laser produced plasma) light source using plasma generated by applying a laser beam to a target, a DPP (discharge produced plasma) light source using plasma generated by discharge, an SR (synchrotron radiation) light source using orbital radiation. Among them, the LPP light source has advantages that extremely high intensity near black body radiation can be obtained because plasma density can be considerably made larger, light emission of only the necessary waveband can be performed by selecting the target material, and an extremely large collection solid angle of 2π sterad can be ensured because it is a point source having substantially isotropic angle distribution and there is no structure such as electrodes surrounding the light source, and therefore, the LPP light source is thought to be predominant as a light source for EUV lithography in which power of several tens of watts is required.
In the LPP light source, in the case where a solid material is used as a target to which a laser beam is applied for generating plasma, the heat generated by application of the laser beam is conducted to the periphery of the laser beam applied region when the laser beam application region turns into a plasma state, and the solid material is melted on the periphery thereof. The melted solid material becomes debris having a diameter of several micrometers or more, which is emitted in large quantity and causes damage to the collection mirror (specifically, to the mirror coating) and reduces the reflectance thereof. Also, in the case where a liquid material is used as the target, the flying debris causes damage to the collection mirror. On the other hand, in the case where a gas is used as the target, although debris is reduced, the conversion efficiency from the power supplied to the driving laser to the power of the EUV light is reduced.
As a related technology, Japanese Patent Publication JP-B-3433151 discloses a laser plasma X-ray source in which damage to an optical mirror due to the generated debris is prevented and the collection efficiency of X-ray is improved. According to the document, the X-ray source includes a magnetic field applying device for applying a magnetic field in a direction perpendicular to an injection direction of a target. Assuming that the traveling direction of the debris before deflected by the magnetic field is the injection direction of the target, the damage to the optical mirror can be prevented by locating the optical mirror in a direction in which ionic state debris deflected by the magnetic field do not fly.
Further, Japanese Patent Publication JP-B-2552433 discloses a removing method and device capable of radically removing debris generated from a solid target in a relative simple manner. According to the document, electric charges are provided by ultraviolet light to neutral fine particles produced with X-rays from plasma on the surface of a target material, an electromagnetic field in which an electric field and a magnetic field are mutually perpendicular is generated by a pair of mesh-form electrodes arranged along the path of X-ray and an electromagnet disposed between the pair of electrodes, and the charged fine particles are passed through the electromagnetic field such that the orbit of the charged fine particles can be bent and eliminated to the outside of the X-ray path. Thereby, an X-ray optical element provided in the X-ray path can be protected.
The present invention has been achieved in view of the above-mentioned problems. An object of the present invention is to provide an extreme ultra violet light source device capable of extending the life of a collection mirror and reducing running cost by protecting the collection mirror from debris that is considered harmful to a mirror coating.
In order to achieve the above object, an extreme ultra violet light source device according to one aspect of the present invention is a device for generating extreme ultra violet light by irradiating a laser beam to a target, and the device includes: a chamber in which extreme ultra violet light is generated; a target supplier that supplies the chamber with a material to become the target; a laser light source that irradiates a laser beam to the target so as to generate plasma; a collection optical system that collects the extreme ultra violet light emitted from the plasma; an ionizer that ionizes neutral particles included in particles emitted from the plasma into charged particles; and a magnetic field generator that generates a magnetic field within the chamber so as to trap at least the charged particles ionized by the ionizer.
According to the present invention, the neutral particles included in debris is ionized by the ionizer, and therefore, not only the charged particles included in the debris but also the neutral particles can be trapped by the magnetic field formed within the chamber. Accordingly, the debris can be efficiently collected and the collection mirror can be protected from the debris that is considered harmful to a mirror coating. As a result, the life of the collection mirror can be extended and the running cost of the EUV light source device can be reduced.
Hereinafter, preferred embodiments of the present invention will be described in detail by referring to the drawings. The same reference numerals are assigned to the same component elements and the description thereof will be omitted.
First, a basic configuration of an EUV (extreme ultra violet) light source device will be described by referring to
The EUV light source device shown in
The air within the chamber 100 is exhausted by the vacuum pump 101, and thereby, maintained at predetermined pressure.
The driving laser light source 110 generates a laser beam for providing energy to a target material for excitation. Further, the irradiation optical system 111 collects the laser beam generated from the driving laser light source 110 and introduces the beam into the chamber 100. In the embodiment, the irradiation optical system 111 is formed by a collection lens. As the collection lens, a plano-convex lens, cylindrical lens or a combination of those lenses may be used. A window 100a and an opening 102a are respectively formed in the chamber 100 and the collection mirror 102, which will be described later, and the laser beam collected by the irradiation optical system 111 passes through the window 100a and the opening 102a and applied to the target material within the chamber 100.
The target injection unit 120 supplies a target material for generating plasma to the target injection nozzle 121. As the target material, various materials may be used such as xenon (Xe), a mixture containing xenon as a principal component, argon (Ar), krypton (Kr) or a material which becomes a gas state in a low pressure condition such as water (H2O), alcohol or the like. Further, the state of the target may be any one of gas, liquid and solid. In the embodiment, liquid target jets or droplets are injected toward Z-direction (downward in the drawing) from the target injection nozzle 121 by cooling xenon under high pressure in the target injection unit.
A target material 123 is turned into plasma by applying the laser beam output from the driving laser light source 110 to the target material injected from the target injection nozzle 121. At that time, EUV light is emitted from the generated plasma. Hereinafter, the plasma is referred to as “EUV light generation plasma”.
The collection mirror 102 is used as a collection optical system for collecting the EUV light emitted from the plasma and guiding the light in a desired direction. In
The target collection tube 122 is oppositely provided to the injection tip of the target injection nozzle 121, and collects the target material that has not contribute to plasma generation of the target material 123 injected from the target injection nozzle 121 and debris produced at the time of plasma generation.
Such a chamber 100 is connected to an exposure device via a connection part 105 provided with gate valves 103 and 104. The gate valves 103 and 104 are used at the time of maintenance of the chamber 100 or the exposure device or the like. The connection part 105 is exhausted by a vacuum pump 106 and maintained at predetermined pressure. The vacuum pump 106 may be omitted in view of the vacuum pump 101. Partitions formed with apertures 107 are disposed inside of the connection part 105, and the EUV light generated in the chamber 100 enters the exposure device through the apertures 107. At that time, the gate valves 103 and 104 are held open for the EUV light to pass through.
In the embodiment, further to such an EUV light source device, magnets 130 and 131 and plural X-ray tubes 132 are provided as a mechanism for preventing the damage to the collection mirror by debris. In the embodiment, electromagnets are used as the magnets 130 and 131 and
Among debris generated from the EUV light generation plasma, charged particles (ions) are deflected because of the Lorentz force applied by the formed magnetic field. For example, as shown in
Referring to
The alternate long and short dash line in
The charged particles ionized by being applied with X-rays are trapped by the action of the magnetic field formed by the magnets 130 and 131 and collected by the target collection tube 122. The principle of trapping the charged particles is the same as has been described by referring to
Thus, according to the embodiment, since ionization is performed by applying X-rays to neutral particles, debris can be trapped with high efficiency by the action of the magnetic field formed within the chamber and collected. Therefore, the life of the collection mirror can be extended substantially by reducing the damage to the collection mirror due to debris. Thereby, the running cost of the EUV light source device can be suppressed. Further, since the gas hanging within the chamber can be reduced by collecting debris, the collection efficiency of EUV light can be raised by increasing the degree of vacuum within the chamber. Alternatively, since the exhaust ability of the vacuum chamber can be suppressed, the EUV light source device can be formed at low cost.
Although the neutral particles have been photo-ionized by using X-rays in the embodiment, other electromagnetic wave having a suitable wavelength can be used according to the kind of target material. For example, in the case of using a xenon target, the neutral particles can be photo-ionized if the light has a wavelength of about 90 nm or less. Accordingly, in that case, a light source for generating ultraviolet light having a wavelength of 90 nm or less may be used in place of X-ray tubes.
Further, as the magnets 130 and 131, electromagnets (superconducting magnets) may be used as in the embodiment, or permanent magnets may be used as long as a magnetic field with required intensity can be formed.
In the above-mentioned first and second embodiments, the optical path of the laser beam, the orbit of the target material and the arrangement of the X-ray tubes 132 have been illustrated in the same plane, however, they are not necessarily in the same plane. For example, as shown in
Next, variations in arrangement of the plural X-ray tubes and magnets in the first to third embodiments of the present invention will be described. In the present application, it is defined that the reflection surface, in which a multilayer film of Mo/Si is formed, is the front side (front surface) of the collection mirror. That is, the opposite side thereto is the backside or back surface. Further, the “outside of the collection mirror” means a position farther than the edge of the mirror.
As shown in
Here, in the above-mentioned first to third embodiments, the two magnets 130 and 131 have been provided outside of the chamber 100. As merits of the arrangement, there is no possibility that the magnets become impurity sources within the chamber in the case of using permanent magnets as the magnets 130 and 131, and there is no need to provide a cooling water pipe or current cable within the chamber in the case of using electromagnets as the magnets 130 and 131, etc. However, in the arrangement, since the distance between the magnets 130 and 131 and the EUV light generation plasma 133 becomes longer, sometimes the magnets 130 and 131 are required to be upsized for forming a sufficiently strong magnetic field around the EUV light generation plasma 133.
Thus, the arrangement of the magnets 130 and 131 can be appropriately selected according to the factors such as the kind of magnets to be used, the intensity of the necessary magnetic field, etc.
As shown in
Referring to
In the embodiment, the electron gun 140 has been used as an example of electron supply source, however, other electron supply sources may be used. Further, the metal plate 141 has been provided within the chamber 100 in order to receive the electrons emitted from the electron gun 140, however, the electrons may be received by the chamber wall surface, and metal plate 141 is not necessary to be provided in that case.
As shown in
Here, the microwave discharge occurs more easily as frequency ω of the microwave is closer to collision frequency ν of electrons with neutral particles. Contrary, in the case where the frequency ω of the microwave is larger compared to the collision frequency ν (ω>>ν), the microwave discharge becomes difficult to occur.
Alternatively, in order to cause the microwave discharge, ECR (electron cyclotron resonance) may be utilized. That is, in the magnetic field, electrons move while rotating windingly around the magnetic field lines (cyclotron motion). When an alternating current electric field is applied to the magnetic field by entering microwave having frequency ω consistent with the rotation speed, a phenomenon called electron cyclotron resonance occurs. Thereby, electrons are effectively accelerated and provide great energy, and plasma can be generated. Here, assuming that B is magnetic flux density and Me is mass of electron, electron cyclotron frequency f is expressed by f=eB/(2πMe)=2.799×106×B. For example, in the case where the magnetic flux density is about 3000 gauss, microwave having a frequency of about 9 GHz may be applied. In such ECR plasma, under pressure of 10−4 Torr to 10−2 Torr (0.0133 Pa to 1.33 Pa) , electron temperature becomes on the order of Te=5 eV to 15 eV and electron density becomes on the order of 1011 to 1012.
Furthermore, as shown in
The EUV light source device shown in
In order to generate helicon wave plasma, high-frequency wave of, for example, 13.56 MHz is applied to the antenna 220 for helicon wave excitation by the high-frequency power supply and, for example, a magnetic field of 1000 gauss or less is formed within the glass tube 201 by a magnet (electromagnet) 130 (
Thus generated plasma 203 for ionization moves to the vicinity of the EUV light generation plasma 133 by the action of the magnetic field formed by the magnets 130 and 131, collides with neutral particles flying from the EUV light generation plasma and ionizes them.
Here, gyrotron refers to a millimeter or sub-millimeter light source with “cyclotron resonance maser action” utilizing mass change of electron because of relativistic effect as an oscillation principle. Features of its operation is as follows: (1) ability of high-efficiency operation up to beam efficiency of 30% to 50%; (2) ability of high-power operation by injection of high-energy high-current electron beam; and (3) tunability of wavelength can be achieved by changing settings for cyclotron frequency. There is an advantage that plasma heating can be locally performed because electromagnetic wave can be entered into a desired position as if it were a laser beam by using high-frequency waves in an electron cyclotron wave band (millimeter wave band). Further, there is also a great advantage that an electromagnetic field generating device can be provided separately from the chamber. As to detail of the gyrotron, please refer to Japan Atomic Power Plant, Naka Institute, “Mechanism of Gyrotron”, searched on the Internet on Aug. 18, 2004, <URL:http://www.naka.jaeri.go.jp/rfkanetu/gyrotron.htm>, and Toshitaka IDEHARA, “Remote Sensing of the Atmosphere and the Environment Using a High-power Far-infrared Beam”, The Institute of Electronics, Information and Communication Engineers, searched on the Internet on Aug. 18, 2004, <URL:http://www.ieice.org/jpn/books/kaishikiji/200110/20011001-4.html>.
The EUV light source device shown in
The electromagnetic waves in the millimeter band generated in the gyrotron system 243 enter the chamber 240 via the transmission system 244 and the window 242. Plasma 203 for ionization is generated in a desired position within the chamber 240 by the electromagnetic wave 245, and neutral particles flying from the EUV light generation plasma are ionized.
By locating the plural X-ray tubes 132 in such a position, regions hidden behind the EUV light generation plasma and applied with no X-ray can be reduced. Further, by the location, the X-ray emitted from the X-ray tube 132 is reflected by the collection mirror 102 and passes through the same region again, and thereby, neutral particles can be ionized with a high rate.
Here, the EUV light generated within the chamber 100 contains various wavelength components other than a wavelength component (e.g., near 13.5 nm) to be used for exposure. Those wavelength components are diffused and attenuated without being collected by the collection mirror 102. Accordingly, in the embodiment, a wavelength component of those wavelength components that can photo-ionize neutral particles within generated debris is utilized. For example, in the case of using a xenon target, wavelength components of 90 nm or less can be utilized for ionization of neutral particles.
The EUV light source device shown in
The configuration for ionizing neutral particles by using such a reflection mirror may be combined with the above-mentioned first to eighth embodiments. Thereby, the ionization efficiency of neutral particles in other embodiments can be improved further.
In the embodiment, the gas shield device 260 is provided at the backside of the collection mirror 102, and injects the gas for shielding to the front side of the collection mirror 102 via the opening of the collection mirror 102. Thereby, the gas for shielding is introduced between the EUV light generation plasma and the collection mirror, and the collection mirror 102 is shielded from the EUV light generation plasma 133. As a result, the damage to the mirror due to collision of debris with the collection mirror 102 can be prevented.
In the embodiment, the configuration in which the gas shield device is added to the damage prevention mechanism of the collection mirror using X-ray tubes has been described, however, as explained in the second to ninth embodiments, the gas shield device can be similarly added to the other collection mirror damage prevention mechanisms using X-ray tubes or collection mirror damage prevention mechanisms using an electron gun, plasma, or reflection mirror.
In the above-mentioned first to tenth embodiments of the present invention, debris has been trapped by forming a magnetic field within the chamber, however, the arrangement of magnets and the formation of magnetic field formed thereby are not limited to those described in the embodiments. For example, a baseball magnetic field may be formed by providing an electromagnetic coil so as to wrap around the collection mirror. Further, in the case of using an electromagnet, a steady magnetic field may be generated by steadily supplying current to the coil, or a pulse magnetic field may be generated in synchronization with the operation of the driving laser light source.
The present invention can be utilized in a light source device that generates EUV light by applying a laser beam to a target. Furthermore, the present invention can be utilized in exposure equipment using such a light source device.
Number | Date | Country | Kind |
---|---|---|---|
2004-261871 | Sep 2004 | JP | national |