Discharge lamp and method of manufacturing electrodes for discharge lamp

Abstract

To increase the illuminance of light without narrowing an irradiation range of light, and prevent early disappearance of a ridge.SOLUTION: A discharge lamp includes a discharge tube, and a cathode and an anode arranged oppositely in the discharge tube, and the anode has a tip surface along the axis perpendicular direction at the tip of a reduced diameter portion, and is equipped with a ridge with a curved tip on the tip surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a discharge lamp used in an exposure device or the like, and more particularly to a short arc type discharge lamp and a method for manufacturing electrodes for a discharge lamp. [Background technology]

[0002] In short arc discharge lamps, shortening the distance between the electrodes (the distance between the tip of the anode and the tip of the cathode) is considered to increase the illuminance. However, shortening the distance between the electrodes causes the anode to block the light, resulting in a narrower irradiation range. It has been proposed to provide a cylindrical protrusion at the tip of the electrode.

[0003] For example, Patent Document 1 describes an anode shaped by sequentially stacking a cylindrical anode base 21, a truncated cone 22 at the tip of the anode base 21, and a cylinder 23 whose diameter is equal to the minor axis of the truncated cone 22. This configuration prevents the arc discharge path from shifting.

[0004] Patent Document 2 describes providing a protrusion 21, which is a portion having a lower heat capacity than other portions, on the anode 2. With this configuration, tungsten is selectively evaporated from the protrusion 21, and the evaporated tungsten is selectively returned to the protrusion 21 by the halogen cycle, so that the shape of the anode does not change over time as the lamp is lit, but is always kept constant, and the position where the discharge arc is formed does not fluctuate, making it possible to ensure illuminance maintenance over a long period of time.

[0005] Patent Document 3 describes that providing a protrusion at the tip of the cathode significantly changes the electric potential in the space in front of the protrusion, thereby increasing the electric field strength in the space in front of the protrusion. When the electric field strength in the space in front of the cathode protrusion increases, electrons emitted from the cathode tend to deviate from the electrode axis and fly toward the arc tube when the pressure inside the arc tube is low. However, this strong electric field pulls the electrons back and restrains them in front of the cathode protrusion, causing them to fly in a straight line toward the anode over the shortest distance, thereby reliably maintaining the discharge generated between the electrodes along the electrode axis. As a result, the arc generated by the discharge is formed in a state where it is reliably maintained along the electrode axis, so the arc does not approach the arc tube, preventing devitrification of the arc tube and preventing the arc tube from bursting. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 51-46441 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-265709 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-77416 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Documents 1 to 3, because a thin cylindrical protrusion is provided at the tip of the electrode, arc discharge concentrates at the protrusion, resulting in rapid electrode wear. Furthermore, the protrusions described in Patent Documents 1 and 3 may block light and reduce illuminance. Furthermore, the configurations described in Patent Documents 2 and 3, in which a thin cylindrical protrusion is provided on the tip surface of the electrode, have the problem of difficulty in ensuring the strength of the protrusion.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a discharge lamp and a method for manufacturing electrodes for a discharge lamp that can improve illuminance without causing the problems of the prior art. [Means for solving the problem]

[0009] The present invention includes a discharge tube and a cathode and an anode disposed opposite each other within the discharge tube; the anode has a tip surface at a tip of the reduced diameter portion along a direction perpendicular to the axis, The tip surface has a curved raised portion. 、 The diameter of the raised portion satisfies the following formula The discharge lamp is characterized by the above. (D - d) / 2 ≤ d where D represents the diameter of the tip surface and d represents the diameter of the raised portion, and the relationship d < D is satisfied. The present invention also provides a discharge tube, a cathode and an anode disposed opposite each other within the discharge tube; the anode has a tip surface at a tip of the reduced diameter portion along a direction perpendicular to the axis, The tip has a curved protuberance. 、 The raised portion is made of the same material as the anode and is integral with the tip surface The discharge lamp is characterized by the above. The present invention also provides a method for manufacturing an electrode for a discharge lamp, characterized in that a tip surface and a protruding portion with a curved tip are formed on the tip surface by cutting an anode member. [Effects of the Invention]

[0010] According to at least one embodiment, the curved surface can be formed, thereby avoiding the problem of arc discharge concentrating and causing rapid electrode wear. Furthermore, the illuminance can be increased without shortening the distance between the electrodes, eliminating the problem of narrowing the light irradiation range. Furthermore, compared to a configuration in which protrusions are provided, it is possible to prevent a decrease in the strength of the protrusions. The effects described herein are not necessarily limited to those described herein, and may be any of the effects described herein or effects different from those effects. [Brief explanation of the drawings]

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

[0012] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing a schematic diagram of a short arc type discharge lamp according to one embodiment. The short arc type discharge lamp 10 is a discharge lamp that can be used as a light source for an exposure device that forms a pattern, and includes a discharge tube (light emitting tube) 11 made of transparent quartz glass. A cathode 20 and an anode 30 are arranged opposite each other with a predetermined distance between them in the discharge tube 11.

[0013] Quartz glass sealed tubes 12a and 12b are integrally provided on both sides of the bulb-shaped discharge tube 11 so as to face each other, and both ends of the sealed tubes 12a and 12b are sealed by bases 13a and 13b. Conductive electrode support rods 14a and 14b supporting a metallic cathode 20 and anode 30 are disposed inside the sealed tubes 12a and 12b, respectively, and are connected to conductive lead rods 16a and 16b via metal rings (not shown) and metal foils 15a and 15b made of molybdenum or the like. The sealed tubes 12a and 12b are fused to glass tubes (not shown) provided within the sealed tubes 12a and 12b, thereby sealing the discharge space containing mercury and rare gas. The discharge lamp 10 is vertically arranged with the anode 30 on the upper side and the cathode 20 on the lower side.

[0014] The lead rods 16a, 16b are connected to an external power supply, and a voltage is applied between the cathode 20 and the anode 30 via the metal member, the metal foil, and the electrode support rods 14a, 14b. When power is supplied to the discharge lamp 10, an arc discharge occurs between the electrodes, and mercury emission lines (ultraviolet light) are emitted. Here, a power of 1 kW or more is input.

[0015] The illumination device is configured by arranging a spheroidal reflecting mirror (light-collecting mirror) (not shown) around the discharge lamp 10. When the lamp is lit, the light emitted from the discharge lamp 10 is reflected by the reflecting mirror. The reflected light is collected at a secondary focus and guided to an object to be illuminated via an illumination optical system (not shown). For example, if the illumination device is installed in an exposure tool, the light is irradiated onto the photosensitive surface of a substrate.

[0016] 2A is a cross-sectional view of an example of anode 30. Anode 30 comprises a cylindrical anode body 31 connected to electrode support rod 14B and a truncated cone-shaped anode reduced diameter portion 32, with the tip surface (annular surface) 33 of anode reduced diameter portion 32 configured as the discharge surface. Here, body 31 and anode reduced diameter portion 32 are made of a metal such as tungsten or molybdenum, or an alloy thereof. Note that the anode may also be configured by separately molding the reduced diameter portion and body and joining them by diffusion bonding or the like.

[0017] In one embodiment of the present invention, a protuberance is provided on the tip surface 33, protruding toward the cathode. The protuberance is more convex toward the cathode than the flat tip surface 33, and is smaller than the tip surface 33. In the example shown in FIG. 2A, a hemispherical protuberance 34 protruding toward the cathode is provided at approximately the center of the tip surface 33 of the anode 30. In the example shown in FIG. 2B, a protuberance 34' having a gently curved tip is provided at approximately the center of the tip surface 33. That is, in the present invention, the tip is configured to have a gently curved (hemispherical) shape rather than a sharp protrusion. In other words, the cross section of the protuberance 34, 34' in the electrode axis direction has an arc-shaped tip surface. In particular, the protuberances 34, 34' shown in FIGS. 2A and 2B are configured with a curved surface from the tip surface 33 to the apex.

[0018] An arc discharge occurs between the tip surface of the cathode 20, the tip surface 33 of the anode 30, and the tip surfaces of the raised portions 34, 34'. By providing the raised portions 34, 34', light is concentrated and the illuminance increases. In the present invention, since the raised portions 34, 34' do not protrude and have a gentle surface, the arc discharge does not locally concentrate, and premature disappearance (evaporation) of the raised portions due to excessive heating can be prevented. Further, since the raised portions 34, 34' are formed of a curved surface from the top to the bottom, the strength can be ensured as compared with a configuration in which thin columnar protrusions are provided.

[0019] The raised portions 34, 34' are formed in an arc shape and have a diameter smaller than the diameter of the tip surface 33. That is, not all of the tip surface 33 is formed of the raised portions 34, 34', and there is a tip surface (plane) along the direction perpendicular to the axis on the tip surface 33. Thereby, while providing the raised portions 34, 34', the heat capacity of the tip surface 33 serving as the discharge surface is ensured. FIG. 3 is a cross-sectional view showing an enlarged diameter-reduced portion 32 of the anode 30. As shown in FIG. 3, when the diameter of the raised portion 34 is d and the diameter of the tip surface 33 is D, and the relationship is d < D, a configuration satisfying (D - d) / 2 ≤ d is preferable. By doing so, the area of the surface (tip surface 33) receiving the arc discharge is maintained and the heat capacity does not decrease, so that an excessive temperature rise of the anode 30 can be suppressed. On the other hand, it is possible to prevent the provision of extremely small-diameter (thin) raised portions and ensure the strength of the raised portions.

[0020] Although the size of the raised portions 34, 34' is not particularly limited, the protruding height from the tip surface 33 is set to 2 mm or less, more preferably 1 mm or less, so as not to block light. FIG. 4A shows the cathode 20 and anode 30. The radiation range R of the discharge lamp 10 is determined according to the arrangement and size of the cathode 20 and anode 30, as well as the distance between the cathode 20 and anode 30. If the distance between the tip surface of the cathode 20 and the tip surface 33 of the anode 30 (inter-electrode distance) is short, the illuminance increases, but the radiation range R becomes narrow. In the present invention, the raised portions 34 are provided, so the inter-electrode distance can be shortened while maintaining the radiation range R without bringing the tip surface 33 closer to the cathode, thereby increasing the illuminance. The radiation range R refers to the radiation range in which radiated light is not blocked by the cathode 20 or anode 30 and travels directly outside the discharge lamp.

[0021] Furthermore, the protruding portion 34 is located closer to the electrode central axis X than an imaginary extended tapered surface 41, which is an extension of the tapered surface of the reduced diameter portion 32 of the anode 30. That is, the protruding portion 34 does not intersect with the imaginary extended tapered surface 41, and therefore it is possible to prevent the protruding portion 34 from blocking the emitted light. As shown in FIG. 4B , unlike the present invention, if the protruding portion 42 at the tip of the anode intersects with the imaginary extended tapered surface 41, the light would be blocked by the protruding portion 42, resulting in a problem of reduced illuminance.

[0022] The manufacturing method of the anode 30 will now be described. When the anode 30 is manufactured by cutting an anode member made of tungsten or the like, the raised portions 34, 34' are also integrally formed by cutting from the anode member and are shaped to protrude from the tip end surface. In this case, the raised portions are made of the same material as the anode. Alternatively, only the raised portions 34, 34' may be formed separately from the anode main body (anode body portion 31 and anode reduced diameter portion 32), and the raised portions and the anode main body may be diffusion-bonded to form the raised portions. In this case, the raised portions can be made of a material different from that of the anode main body.

[0023] The above-described embodiment of the present invention can increase the illuminance of light by providing the raised portions 34, 34'. Furthermore, because the raised portions 34, 34' have gentle tip surfaces, arc discharge occurs over most of the raised portions 34, 34', and does not concentrate locally, preventing premature disappearance (evaporation) of the raised portions 34, 34' due to excessive heating. Furthermore, the shape of the raised portions 34, 34' has the advantage of not narrowing the light irradiation range.

[0024] Although one embodiment of the present technology has been specifically described above, the present technology is not limited to the above-described embodiment, and various modifications based on the technical concept of the present technology are possible. For example, the protrusion of the present technology may have a cylindrical portion as long as at least the tip (the surface facing the cathode) is curved. Furthermore, while one embodiment of the present technology provides a single protrusion whose apex is located on the central axis of the electrode, multiple protrusions may be provided, or a ring-shaped protrusion may be provided surrounding the center of the electrode tip surface, as long as the area is mostly covered by the arc discharge. The present technology can also be applied to mercury-free short-arc xenon lamps and discharge lamps other than short-arc types. Furthermore, the configurations, methods, processes, shapes, materials, and values ​​described in the above-described embodiment are merely examples, and different configurations, methods, processes, shapes, materials, and values ​​may be used as necessary. [Explanation of symbols]

[0025] 10... Discharge lamp, 11... Discharge tube, 12a, 12b... Sealed tube, 13a, 13b... metal base, 14a, 14b... electrode support rod, 20... cathode, 30...Anode, 31...Anode body part, 32...Anode reduced diameter part, 34,34'...Protuberance part

Claims

1. A discharge tube; a cathode and an anode disposed opposite each other within the discharge tube; the anode has a tip surface at a tip of the reduced diameter portion along a direction perpendicular to the axis, The tip surface is provided with a raised portion having a curved tip, A discharge lamp characterized in that the diameter of the protrusion satisfies the following formula: (D−d) / 2≦d Here, D represents the diameter of the tip end surface, d represents the diameter of the protrusion, and the relationship d<D is satisfied.

2. 2. The discharge lamp according to claim 1, wherein the raised portion is formed with a curved surface from its top to its bottom.

3. 3. The discharge lamp according to claim 1, wherein the protruding portion is located closer to the central axis of the electrode than an imaginary extended tapered surface along the tapered surface formed by the reduced diameter portion.

4. A discharge tube; a cathode and an anode disposed opposite each other within the discharge tube; the anode has a tip surface at a tip of the reduced diameter portion along a direction perpendicular to the axis, The tip surface is provided with a raised portion having a curved tip, The discharge lamp is characterized in that the protrusion is made of the same material as the anode and is integral with the tip end surface.

5. A method for manufacturing an electrode for a discharge lamp, comprising cutting an anode member to form a tip surface and a protruding portion having a curved tip on the tip surface.

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