Patent Application
20180139830
The present invention relates to discharge electrodes for use in a light source device configured to emit light upon electric discharging, and also relates to a light source device having such discharge electrodes.
In recent years, a light source for exposure needs to emit light at a short(er) wavelength as a semiconductor integrated circuit is designed more compact and circuit integration has a higher density. As a next-generation light source for exposing a semiconductor, developed is an extreme ultraviolet (hereinafter, occasionally referred to as “EUV”) light source device that emits extreme ultraviolet light at a wavelength of, particularly, 13.5 nm.
Several methods are known to cause the EUV light source device to emit EUV light. One of such methods heats and excites an extreme ultraviolet emission seed (EUV emission seed) to generate high temperature plasma, and extracts EUV light from the high temperature plasma.
An EUV light source device that employs such method is categorized into an LPP (Laser Produced Plasma) type and a DPP (Discharge Produced Plasma) type, depending upon a method used to generate high temperature plasma.
A DPP type EUV light source device applies a high voltage across a pair of electrodes, which is supplied with a discharge gas containing an extreme ultraviolet light emission seed, to generate high-density and high-temperature plasma upon electric discharging, and uses extreme ultraviolet light emitted therefrom. For use with the DPP type EUV light source device, a method has been proposed that includes supplying a surface of each electrode, which is used to generate electric discharge, with a raw material such as Sn (tin) or Li (lithium), and irradiating the raw material with an energy beam such as a laser beam for evaporation thereof such that high-temperature plasma is generated upon electric discharging. Such method is sometimes referred to as an LDP (Laser Assisted Discharge Produced Plasma) method or an LDP type. An LDP type EUV light source device is disclosed in, for example, Patent Literature Document 1. In Patent Literature Document 1 (Japanese Patent Application Laid-Open Publication No. 2007-505460), a pair of disk-shaped rotating electrodes are used as the above-mentioned electrodes, and the paired rotating electrodes are disposed such that the peripheral edges of the two rotating electrodes face each other.
Patent Literature Document 1: Japanese Patent Application Laid-Open Publication No. 2007-505460
The output efficiency of the EUV light varies with the shape(s) of the electrode(s). Patent Literature Document 1 (Japanese Patent Application Laid-Open Publication No. 2007-505460), however, does not consider the shapes of the electrodes at all, for the purpose of obtaining desired EUV output. When the EUV light, which is emitted from plasma generated between the electrodes, is extracted from the electrodes, the electrodes having certain shapes block part of the EUV light by the end portion(s) of the electrode(s), and therefore the extraction angle of the EUV light may not become a desired angle. When the energy beam is directed to the raw material on the electrodes, the incident angle of the energy beam may be restricted depending upon the shapes of the electrodes, and therefore it may be impossible to direct the energy beam at a desired angle (the electrodes may not be irradiated with the energy beam at a desired angle).
The technology disclosed in Patent Literature Document 1, therefore, may not be able to achieve a desired extraction efficiency of the EUV light and may not be able to generate desired plasma.
Accordingly, an object of the present invention is to provide discharge electrodes, each of which has a shape that can provide a desired light output, and to provide a light source device equipped with such discharge electrodes.
In order to achieve the above-mentioned object, one aspect of the present invention provides discharge electrodes for use in a light source device. The light source device includes a pair of disc-shaped discharge electrodes disposed such that peripheries thereof oppose each other with a predetermined space left therebetween, a pulsed power supply unit that supplies pulsed power across the discharge electrodes, a raw material (source material) supply unit that supplies onto the discharge electrodes a source material to emit light, and an energy beam irradiation unit that irradiates the source material on curved surfaces of the discharge electrodes with an energy beam to vaporize the source material. At least one of the paired discharge electrodes has an inclined surface formed on a periphery of at least one of two circular surfaces thereof. The inclined surface inclines such that a thickness of the discharge electrode concerned decreases in a radially outward direction of the discharge electrode.
With this configuration, when the inclined surface is formed, for example, on the circular surface on the light extraction side, then it is possible to avoid or reduce the possibility that the light emitted from the plasma be blocked by the end of the electrode, and possible to have a large light extraction angle. When the inclined surface is formed on the circular surface on the energy beam incident side, then it is possible for the energy beam to have a large incident angle to the discharge electrode, and enhance the energy beam intensity per unit area on the discharge electrode. The incident angle of the energy beam is an angle between the energy beam incident plane and the energy beam incident direction (angle γ in
The inclined surface of the discharge electrode may have an angle of inclination corresponding to a take-off angle (extraction angle) of the light from the discharge electrodes, and may be provided on the periphery of the circular surface located on a side toward which the light is extracted from the discharge electrodes. With such configuration, it is possible to extract the light from the discharge electrodes at a desired extraction angle. Thus, it is possible to achieve a desired light extraction efficiency.
The inclined surface of the discharge electrode may have an angle of inclination corresponding to an angle of incidence of the energy beam on the curved surface of the discharge electrode, and may be provided on the periphery of the circular surface located on a side where a radiation source of the energy beam is installed. With such configuration, it is possible to cause the energy beam to be incident to the discharge electrodes at a desired angle of incidence. Thus, it is possible to generate desired plasma, and generate stable light.
The angle of inclination of the inclined surface provided on one of the two circular surfaces of the discharge electrode may be set to an angle different from the angle of inclination of the inclined surface provided on the opposite circular surface of the same discharge electrode. When the inclination angles of the inclined surfaces of the opposite circular surfaces of the discharge electrode are different from each other, it is possible to increase a degree of freedom in setting the light extraction angle and the angle of incidence of the energy beam.
The angle of inclination of the inclined surface provided on one of the two discharge electrodes may be set to an angle different from the angle of inclination of the inclined surface provided on the other of the two discharge electrodes. When the inclination angles of the inclined surfaces of the two discharge electrodes are different from each other, it is possible to have the inclined surface(s) only at a necessary position or positions. Thus, it is possible to omit unnecessary machining steps.
According to another aspect of the present invention, there is provided a light source device including any one of the above-described discharge electrodes. This light source device is able to provide a desired light output.
The light of the light source device may be extreme ultraviolet light, an X-ray, or vacuum ultraviolet light.
The present invention can have a desired take-off angle (extraction angle) of the light emitted from the plasma, which is generated upon electric discharging across the electrodes, and can generate desired plasma. Thus, the present invention can provide a desired light output.
These and other objects, aspects and advantages of the present invention will be understood by a person skilled in the art from the following detailed description of the present invention with reference to the accompanying drawings and the claims.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
An EUV light source device 100 is an apparatus that can be used as a light source for exposing semiconductor and emits extreme ultraviolet light (EUV light) at a wavelength of 13.5 nm, for example.
The EUV light source device 100 according to the present embodiment is a DPP type EUV light source device and is more specifically an LDP type EUV light source device. An LDP type EUV light source device irradiates a high-temperature-plasma source material supplied to a surface of an electrode for producing a discharge with an energy beam, such as a laser beam, to vaporize the high-temperature-plasma source material and then produces high-temperature plasma upon electric discharging.
In this light source device, vacuum ultraviolet light (10 nm to 200 nm) or X-rays (soft X-rays to hard X-rays: 10 pm to 10 nm) can also be extracted by selecting an appropriate high-temperature-plasma source material and adjusting the conditions for exciting the high-temperature-plasma source material.
As illustrated in
Two discharge electrodes 21a and 21b, which are each independently rotatable, are disposed to oppose each other with a space provided therebetween in the discharge space 11b. The discharge electrodes 21a and 21b are discharge members for heating and exciting a high-temperature-plasma source material including an EUV radiation seed.
The pressure inside the discharge space 11b is kept to a vacuum atmosphere so that the discharge for heating and exciting the high-temperature-plasma source material occurs favorably.
An EUV collector mirror (collector mirror) 12 and a debris trap 13 are disposed in the light condensing space 11c.
The EUV collector mirror 12 collects EUV light, which is radiated upon heating and exciting the high-temperature-plasma source material, and guides the EUV light, for example, to an irradiation optical system (not illustrated) of an exposure device via an EUV outlet 11d provided in the chamber 11.
The EUV collector mirror 12 is, for example, an oblique-incidence collector mirror and has a structure in which a plurality of thin concave mirrors are arranged precisely in a nested pattern. The reflective surface of each concave mirror has, for example, a shape of an ellipsoid of revolution, a shape of a paraboloid of revolution, or a Wolter shape, and each concave mirror has a shape of a body of revolution. The Wolter shape is a concave shape in which a light-incident surface is composed of a hyperboloid of revolution and an ellipsoid of revolution or composed of an ellipsoid of revolution and a hyperboloid of revolution arranged successively from the light-incoming side.
The EUV collector mirror 12 includes a plurality of concave mirrors that each have a reflective surface in the shape of an ellipsoid of revolution, the Wolter shape, or the like and that are in the shapes of bodies of revolution having different diameters. The concave mirrors of the EUV collector mirror are disposed coaxially with their axes of revolution aligned with each other so that their focal points substantially coincide with each other. As these concave mirrors are arranged precisely in a nested pattern in this manner, the EUV collector mirror 12 can favorably reflect EUV light incident obliquely thereon at approximately 25° or less and collect (condense) the EUV light at a single point.
The base material of each concave mirror is, for example, nickel (Ni) or the like. In order to reflect EUV light having a very short wavelength, the reflective surface of each concave mirror is formed into a highly smooth surface. The reflective material provided on this smooth surface is a metal film of, for example, ruthenium (Ru), molybdenum (Mo), rhodium (Rh), or the like. The reflective surface of each concave mirror is coated precisely with such metal film.
The debris trap 13 traps debris, which are generated as plasma is produced upon electric discharging, and prevents or suppresses the movement of debris into the EUV light collecting area. The debris trap 13 plays a role of trapping debris and allowing only the EUV light to pass therethrough.
The discharge electrodes 21a and 21b disposed in the discharge space 11b are disc-shaped members and are made of metal. The discharge electrodes 21a and 21b are made, for example, of a high-melting-point metal, such as tungsten, molybdenum, or tantalum. Of the two discharge electrodes 21a and 21b, one discharge electrode 21a is a cathode, and the other discharge electrode 21b is an anode.
The discharge electrode 21a is disposed such that a portion thereof is immersed in a high-temperature-plasma source material 22a received in a container 23a. A rotating shaft 25a of a motor 24a is mounted to the substantially center portion of the discharge electrode 21a. Specifically, the discharge electrode 21a rotates as the motor 24a causes the rotating shaft 25a to rotate. The driving of the motor 24a is controlled by a control unit 40.
The rotating shaft 25a extends into the chamber 11 via a mechanical seal 26a, for example. The mechanical seal 26a keeps the inside of the chamber 11 to a reduced-pressure atmosphere while allowing the rotating shaft 25a to rotate.
Similar to the discharge electrode 21a, the discharge electrode 21b is disposed such that a portion thereof is immersed in a high-temperature-plasma source material 22b received in a container 23b. A rotating shaft 25b of a motor 24b is mounted to the substantially center portion of the discharge electrode 21b. Specifically, the discharge electrode 21b rotates as the motor 24b causes the rotating shaft 25b to rotate. The driving of the motor 24b is controlled by the control unit 40.
The rotating shaft 25b extends into the chamber 11 via a mechanical seal 26b, for example. The mechanical seal 26b keeps the inside of the chamber 11 to a reduced-pressure atmosphere while allowing the rotating shaft 25b to rotate.
The liquid high-temperature-plasma source materials 22a and 22b on the surfaces of the discharge electrodes 21a and 21b are transported to a discharge region as the discharge electrodes 21a and 21b rotate.
The discharge region is a space between the electrodes 21a and 21b in which an electric discharge takes place and is an area across which the electrodes 21a and 21b are closest to each other. In the present embodiment, the discharge electrodes 21a and 21b are disposed to oppose each other such that their edge portions on the peripheries are spaced apart from each other by a predetermined distance. Therefore, the discharge region is an area across which the distance between the edge portions on the peripheries of the electrodes 21a and 21b is shortest.
A molten metal, such as liquid tin (Sn), is used as the high-temperature-plasma source materials 22a and 22b. The high-temperature-plasma source materials 22a and 22b also function as power supplying conductors for supplying power to the discharge electrodes 21a and 21b.
The containers 23a and 23b are connected to a pulsed power supply unit 27 via power introducing units 11e and 11f that can keep the inside of the chamber 11 to a reduced-pressure atmosphere. The power introducing units 11e and 11f are made from an insulating material. The containers 23a and 23b and the high-temperature-plasma source materials 22a and 22b, i.e., tin, are conductive. The discharge electrode 21a is partially immersed in the tin 22a, and the discharge electrode 21b is partially immersed in the tin 22b. Therefore, pulsed power can be supplied across the discharge electrodes 21a and 21b by supplying pulsed power across the containers 23a and 23b from the pulsed power supply unit 27.
Although not illustrated, temperature adjusting mechanisms for keeping the tin 22a and 22b in a molten state are provided in the containers 23a and 23b.
The pulsed power supply unit 27 supplies pulsed power having a short pulse duration across the containers 23a and 23b, or in other words, across the discharge electrodes 21a and 21b. The driving of the pulsed power supply unit 27 is controlled by the control unit 40.
A laser source 28 is an energy beam irradiation unit that irradiates the tin 22a on the discharge electrode 21a, which is transported to the discharge region, with a laser beam (energy beam). The laser source 28 is, for example, an Nd:YVO4 laser device (Neodymium-doped Yttrium Orthovanadate laser device). A laser beam L emitted from the laser source 28 is incident on a window portion 11g of the chamber 11 via a laser beam condensing unit and so on and is guided onto the discharge electrode 21a. The irradiation timing of the laser beam from the laser source 28 is controlled by the control unit 40.
When the high-temperature-plasma source material 22a transported to the discharge region is irradiated with a laser beam while pulsed power is being supplied to the discharge electrodes 21a and 21b by the pulsed power supply unit 27, the high-temperature-plasma source material is vaporized, and a pulsed discharge starts across the electrodes 21a and 21b. Consequently, plasma P of the high-temperature-plasma source materials 22a and 22b is formed. Then, when the plasma P is heated and excited by a large current that flows during the electric discharge and is brought to a high temperature, EUV light is radiated from this high-temperature plasma P.
As described above, since the pulsed power supply unit 27 supplies pulsed power across the discharge electrodes 21a and 21b, the electric discharge is a pulsed discharge, and the EUV light to be radiated is pulsed light.
In the present embodiment, in order to obtain a desired EUV light output, inclined surfaces (tapered surfaces) are formed at the peripheries of the circular surfaces of the discharge electrodes 21a and 21b, and each of the inclined surfaces inclines such that the thickness of the disc decreases in the radially outward direction of the disc. Hereinafter, the shape of the discharge electrodes 21a and 21b will be described more specifically.
The discharge electrode 21a includes an inclined surface 211a on the incoming side of the laser beam L and an inclined surface 212a on the radiation side of the EUV light. In this specification, the incoming side of the laser beam L is the side from which the laser beam L impinging the curved surface of the cathode (the discharge electrode 21a) is coming and is the side where the laser source 28 serving as an emission source of the laser beam L is installed. The radiation side of the EUV light is the side toward which the EUV light is radiated (extracted) from the discharge electrodes 21a and 21b. The discharge electrode 21b includes an inclined surface 211b on the incoming side and an inclined surface 212b on the radiation side. In the example illustrated in
The angles of inclination of the inclined surfaces 211a and 211b on the incoming side are determined such that the angle of incidence of the laser beam L on the discharge electrode 21a becomes a desired angle. The angles of inclination of the inclined surfaces 212a and 212b on the radiation side are determined such that the angle θ of radiation of the EUV light (take-off angle, or an extraction angle) becomes a desired angle. The angle of inclination of the inclined surface 211a on the incoming side is an angle α indicated in
The angle of inclination of the inclined surfaces 211a and 211b on the incoming side and the angle of inclination of the inclined surfaces 212a and 212b on the radiation side may be the same (α=β) or may be different (α≠β).
As described above, the electric discharge is likely to occur at a location where the two electrodes are closest to each other. In the case of the arrangement illustrated in
In the case of the arrangement illustrated in
However, in the arrangement illustrated in
In the case of the arrangement illustrated in
In contrast, in the present embodiment, the inclined surfaces 211a and 211b are formed at the ends of the discharge electrodes 21a and 21b on the incoming side.
As the inclined surface 211b is formed on the anode (discharge electrode 21b) at the end on the incoming side, the angle γ of incidence of the laser beam L on the cathode (discharge electrode 21a) can be increased correspondingly. In other words, when the angles of the axes of rotation of the discharge electrodes 21a and 21b are the same as the angles of the axes of rotation of the discharge electrodes 121a and 121b illustrated in
Thus, in the present embodiment, as illustrated in
The maximum value of the angle γ of incidence of the laser beam L with which the cathode (discharge electrode 21a) can be irradiated with the laser beam L, without the laser beam L being blocked by the anode (discharge electrode 21b) is determined by the angle of inclination (including the depth of inclination) of the inclined surface 211b formed on the anode (discharge electrode 21b). Therefore, by adjusting the angle of inclination of the inclined surface 211b, the angle γ of incidence of the laser beam L can be set to a desired angle.
By forming the inclined surface 211a on the cathode (discharge electrode 21a) at the end on the incoming side, which is similar to the anode (discharge electrode 21b), the edge portions on the ends of the electrodes can be disposed symmetrically. Therefore, the location where the electric discharge occurs can be stabilized. Thus, the fluctuation in the emission point of the EUV light can be suppressed, and a stable EUV light output can be obtained.
The inclined surfaces 212a and 212b are formed on the discharge electrodes 21a and 21b at their ends on the radiation side. Thus, when the angles of the axes of rotation of the discharge electrodes 21a and 21b are the same as the angles of the axes of rotation of the discharge electrodes 121a and 121b illustrated in
The angle θ of EUV radiation is determined by the angles of inclination (including the depth of inclination) of the inclined surfaces 212a and 212b on the discharge electrodes 21a and 21b on the radiation side. Therefore, by adjusting the angles of inclination of the inclined surfaces 212a and 212b, the angle θ of EUV radiation can be set to a desired angle.
When the angle α of inclination of the inclined surface on the incoming side is equal to the angle β of inclination of the inclined surface on the radiation side, the inclination of a cutter for cutting the discharge electrodes 21a and 21b to form the inclined surfaces needs to be set only once. Therefore, the manufacture of the discharge electrodes 21a and 21b can be facilitated.
On the other hand, when the angle α of inclination of the inclined surface on the incoming side differs from the angle β of inclination of the inclined surface on the radiation side, the inclination of the cutter needs to be set twice. This makes the manufacturing process somewhat more complex as compared to the case in which the angles α and β are equal to each other. However, the case where the angle α is different from the angle β has an advantage in that the degree of freedom in setting the angle θ of EUV radiation and setting the angle γ of incidence of the laser beam L increases.
In the above-described embodiment, the inclined surfaces are formed on the discharge electrodes 21a and 21b on both the incoming side and the radiation side. It should be noted, however, that an inclined surface may be formed on at least one of the discharge electrodes 21a and 21b on at least one of the incoming side and the radiation side.
For example, as illustrated in
Alternatively, as illustrated in
Alternatively, as illustrated in
In the above-described embodiment, the incoming side of the laser beam L is opposite to the radiation side of the EUV light across the discharge electrodes 21a and 21b. It should be noted, however, that as illustrated in
The high-temperature-plasma source materials (tin) 22a and 22b can adhere to the ends of the electrodes efficiently by the inclined surfaces 211a and 211b on the side opposite to the radiation side of the EUV light (the incoming side of the laser beam L). When the discharge electrodes 21a and 21b rotate, the centrifugal force acts also on the tin 22a and 22b adhering to the surfaces of the discharge electrodes 21a and 21b, and the tin 22a and 22b tends to move toward the peripheries of the discharge electrodes 21a and 21b. At this point in time, if the inclined surfaces are formed at the peripheries, the tin 22a and 22b flows onto the end faces of the electrodes more easily. Therefore, it is possible to cause the tin 22a and 22b to adhere appropriately to regions necessary for producing the plasma P.
In the above-described embodiment, a laser is used as an energy beam with which the high-temperature-plasma source material is irradiated. It should be noted, however, that an ion beam, an electron beam, and the like can be used in place of the laser.
In the foregoing embodiment, the EUV light source device is used as a light source for exposing semiconductor. It should be noted, however, that this is not a limiting example. For example, the EUV light source device may be used as a light source for an inspection device of an exposure mask.
When the above-described EUV light source device functions as a VUV light source device for extracting VUV (vacuum ultraviolet light), this VUV light source device can be used as a light source for reforming the surface of a substrate, a light source for producing ozone, or a light source for bonding substrates.
When the above-described EUV light source device functions as an X-ray generating device for extracting X-rays, this X-ray generating device can be used for applications such as chest X-ray photography, dental X-ray photography, and CT (Computer Tomogram) in the medical fields. In addition, this X-ray generating device can be used for applications such as non-destructive testing or non-destructive tomography testing for observing the interior of a substance in a structural body or a welded portion in the industrial fields. Furthermore, this X-ray generating device can be used for applications such as an X-ray analysis for analyzing the crystal structure of a substance or X-ray spectroscopy (fluorescence X-ray analysis) for analyzing a constituting element of a substance in the research fields.
Although specific embodiments have been described above, these embodiments are merely illustrative in nature and are not intended to limit the scope of the present invention. The device and the methods described in the present specification can be implemented in embodiments aside from those described above. In addition, omissions, substitutions, and modifications can be made, as appropriate, to the embodiments described above without departing from the scope of the present invention. An embodiment with such omissions, substitutions, and modifications is encompassed by what is described in the claims and any equivalent thereof and falls within the technical scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-078411 | Apr 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/001884 | 4/1/2016 | WO | 00 |
