Short arc discharge lamp

Abstract

The present invention provides a short-arc discharge lamp having a pair of electrodes disposed oppositely within a light-emitting tube, with a coating formed on the outer surface of at least one of the pair of electrodes. This short-arc discharge lamp has excellent heat dissipation, reduces blackening of the inner wall of the light-emitting tube, and has a long life. In the short-arc discharge lamp having a pair of electrodes disposed oppositely within the light-emitting tube, the pair of electrodes are formed of tungsten, and a coating composed of ceramic is formed on the outer surface of at least one of the pair of electrodes, with tungsten particles attached to a portion of the outer surface of the coating.

Description

Technical Field

[0001] The present invention relates to a short arc discharge lamp. Background Art

[0002] For example, exposure equipment used in the manufacturing processes of semiconductor devices, liquid crystal display devices, and various projectors use short-arc discharge lamps (hereinafter referred to as "lamps") as light sources. These short-arc discharge lamps have an anode and a cathode facing each other within a light-emitting tube, and a luminescent substance such as mercury or xenon gas is enclosed within the tube.

[0003] In such short arc discharge lamps, a high heat load is applied to the anode during lighting, which causes evaporation of electrode material due to overheating of the anode. This evaporated material adheres to the inner wall of the arc tube, reducing light transmittance, which is known as blackening.

[0004] To solve this problem, a technique is known in which a heat dissipation layer is formed on the surface of an electrode to suppress the temperature rise of the electrode. Patent Document 1 below discloses a lamp having a heat dissipation layer containing at least one metal oxide formed on the outer surface of an electrode except near the tip.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-259639 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, even if the temperature rise of the electrodes is appropriately suppressed, as in the lamp described in Patent Document 1, evaporation of the electrode material persists. Tungsten, the electrode material, gradually evaporates, gradually blackening the inner wall of the arc tube. In recent years, demands for longer lamp life have necessitated further improvements in reducing the blackening of the inner wall of the arc tube.

[0010] In view of the above-mentioned problems, the present invention provides a short-arc discharge lamp having a pair of electrodes disposed opposite to each other inside a light-emitting tube, and a coating formed on the outer surface of at least one of the pair of electrodes. This short-arc discharge lamp has excellent heat dissipation, reduces blackening of the inner wall of the light-emitting tube, and has a long life.

[0011] Technical solutions to problems

[0012] The short arc discharge lamp of the present invention has a pair of electrodes disposed opposite to each other inside the arc tube.

[0013] The pair of electrodes are formed of tungsten,

[0014] A coating made of ceramic is formed on the outer surface of at least one of the pair of electrodes, and tungsten particles are attached to a portion of the outer surface of the coating.

[0015] This structure, with a ceramic coating formed on the outer surface of the electrode, provides excellent radiation. Furthermore, since tungsten particles adhere to a portion of the outer surface of the coating, tungsten evaporated from the electrode during lamp operation adheres to the tungsten particles on the outer surface of the coating. This reduces the amount of tungsten evaporated from the electrode that reaches the inner wall of the arc tube due to convection, resulting in less blackening. Consequently, the short-arc discharge lamp of the present invention exhibits excellent heat dissipation, minimizes blackening of the inner wall of the arc tube, and prolongs its life.

[0016] The short arc discharge lamp of the present invention may be configured such that the lighting posture is vertical, a ceramic coating is formed on the outer surface of the upper electrode of the pair of electrodes, and tungsten particles are attached to a portion of the outer surface of the coating.

[0017] According to this configuration, tungsten evaporated from the electrodes adheres to tungsten particles on the outer surface of the coating of the upper electrode of the pair of electrodes, thereby more efficiently reducing the amount of tungsten reaching the inner wall of the arc tube by convection.

[0018] In the short arc discharge lamp of the present invention, the electrode located above may be an anode.

[0019] With this configuration, tungsten evaporated from the electrode adheres to tungsten particles on the outer surface of the anode film having a larger surface area than the cathode. This effectively reduces the amount of tungsten reaching the inner wall of the arc tube by convection.

[0020] In the short arc discharge lamp of the present invention, the coverage rate of the tungsten particles with respect to the outer surface of the coating may be 3% to 40%.

[0021] This structure ensures excellent radiation performance of the coating while efficiently adhering tungsten evaporated from the electrode to the tungsten particles on the outer surface of the coating. The "coverage" mentioned here can be, for example, the ratio of the total area of the tungsten particles to the area of the coating.

[0022] In the short arc discharge lamp of the present invention, the ceramic may include at least one of metal oxide, metal carbide, metal boride, metal silicide, and metal nitride.

[0023] According to this structure, the coating can exhibit excellent radiation properties as a high radiation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is an explanatory diagram showing the structure of the short arc discharge lamp according to the present embodiment.

[0025] Figure 2 yes Figure 1 The enlarged view of the P area of the short arc discharge lamp is shown.

[0026] Figure 3A This is an enlarged view of the outer surface of the anode (surface view).

[0027] Figure 3B It is an enlarged view (cross-sectional view) of the outer surface of the anode.

[0028] Figure 3C This is an enlarged photograph (SEM image) of the outer surface of the anode.

[0029] Figure 4 This diagram explains the evaporation of tungsten contained in the electrode and its adhesion to the inner wall of the arc tube. DETAILED DESCRIPTION

[0030] Embodiments of the short arc discharge lamp according to the present invention will be described with reference to the accompanying drawings. The following drawings are schematic illustrations, and the dimensional ratios in the drawings may not necessarily match the actual dimensional ratios, nor may the dimensional ratios between the drawings necessarily match.

[0031] The following description will refer to the XYZ coordinate system as appropriate. Furthermore, in this specification, when expressing directions, if there is a distinction between positive and negative directions, the directions are indicated with positive and negative signs, such as "+X direction" and "-X direction." Furthermore, when expressing directions without distinguishing between positive and negative directions, the directions are simply referred to as "X direction." That is, in this specification, when simply referring to "X direction," both the "+X direction" and the "-X direction" are included. The same applies to the Y and Z directions.

[0032] Figure 1 This diagram illustrates the structure of a short-arc discharge lamp according to this embodiment. The short-arc discharge lamp 100 (hereinafter referred to as "lamp 100") includes: a light-emitting tube 1; an anode 2 and a cathode 3 disposed opposite each other within the light-emitting tube 1; and lead rods 4 supporting the anode 2 and cathode 3.

[0033] The lamp 100 of the present embodiment is a large lamp used in exposure equipment used in the manufacturing process of semiconductor elements, liquid crystal display elements, etc., and has a rated power of, for example, 2 kW to 35 kW.

[0034] The arc tube 1 is formed by bulging the center of a glass tube. The arc tube 1 is a region of the glass tube whose inner diameter increases from both ends in the X direction toward the center. The outer shape of the arc tube 1 is a sphere or an ellipsoid.

[0035] The arc tube 1 has a pair of sealed tube parts 11 extending continuously in opposite directions from both ends of the arc tube 1 in the X direction. The arc tube 1 and the sealed tube parts 11 are formed integrally with each other, for example, from quartz glass. The central axes of the pair of sealed tube parts 11 overlap with each other. Figure 1 The axis X1 represents.

[0036] A light-emitting space S1 is formed inside the light-emitting tube 1. In addition to a light-emitting substance such as mercury, a buffer gas for assisting starting, such as argon or xenon, is appropriately sealed in the light-emitting space S1.

[0037] Inside the arc tube 1, the anode 2 and cathode 3 are arranged facing each other along the X direction. In this embodiment, the so-called short-arc discharge lamp is a discharge lamp in which the anode 2 and cathode 3 are arranged facing each other with a distance of less than 40 mm (the value at room temperature when no thermal expansion occurs). In this embodiment, the anode 2 is formed of tungsten, and the cathode 3 is formed of thoriated tungsten.

[0038] Lead rods 4 are connected to anode 2 and cathode 3 and extend in the X direction within sealed tube 11. Anode 2 and cathode 3 are fixed to the ends of lead rods 4. The central axis of lead rods 4 preferably overlaps axis X1. Lead rods 4 are made of a material containing a high-melting-point metal, such as tungsten.

[0039] The lamp cap 7 covers the side of the sealed tube portion 11 away from the anode 2 and the cathode 3. The lamp cap 7 is electrically connected to the lead bar 4.

[0040] Figure 2 yes Figure 1 An enlarged view of the P region of the lamp 100 shown. A coating 5 comprising ceramic is formed on the outer surface of the anode 2. Here, the outer surface of the anode 2 refers to the outer surface excluding the front end face 2a facing the cathode 3. When the lamp 100 is lit, the temperature of the front end face 2a of the anode 2 sometimes rises to above the melting point of the coating 5. Therefore, in this embodiment, the coating 5 is not provided on the front end face 2a of the anode 2. In this embodiment, the coating 5 is provided on the outer peripheral surface 2b of the cylindrical main body portion centered on the axis X1 on the outer surface of the anode 2, but the coating 5 may also be provided on the tapered surface 2c located between the outer peripheral surface 2b and the front end face 2a. Furthermore, the coating 5 may also be provided on the rear tapered surface 2d located on the +X side of the outer peripheral surface 2b of the anode 2.

[0041] The material of the film 5 is important in terms of melting point, vapor pressure, emissivity, thermal expansion coefficient, etc. To reduce the temperature of the anode 2, the film 5 is preferably made of a material with high emissivity to increase the amount of heat dissipated.

[0042] Coating 5 comprises ceramic. The ceramic comprises at least one of a metal oxide, a metal carbide, a metal boride, a metal silicide, and a metal nitride. Coating 5 preferably comprises a material having a melting point of 2000°C or higher, such as aluminum oxide, zirconium oxide, zirconium carbide, zirconium boride, tantalum silicide, and zirconium nitride.

[0043] The coating 5 is formed, for example, by dispersing particles of the material constituting the coating 5 (e.g., zirconium oxide particles with a particle size of 10 μm or less) in a solvent (e.g., a solvent composed of nitrocellulose and butyl acetate), applying the dispersion to the outer peripheral surface 2 b of the anode 2 with a pen, drying at 150° C. for 30 minutes, and then heat-treating the coating 5 at 1900° C. for 120 minutes in a vacuum atmosphere. The coating 5 preferably has a thickness of 5 μm to 200 μm. If the coating 5 is too thin, sufficient emissivity cannot be achieved, while if the coating 5 is too thick, it is easily peeled off.

[0044] Figure 3A 、 Figure 3B is an enlarged view of the outer surface of the anode 2, Figure 3A It is a surface diagram. Figure 3B is a cross-sectional view. Figure 3C This is an enlarged photograph (SEM image) of the outer surface of the anode 2 .

[0045] like Figure 3B 、 Figure 3C As shown, a coating 5 is formed on the outer surface of the anode 2 made of tungsten, and tungsten particles W are attached to a portion of the outer surface of the coating 5. The tungsten particles W are Figure 3A The tungsten particles W appear as white spots in the image and are scattered so as to cover a portion of the outer surface of the coating 5. The particle size of the tungsten particles W is 0.1 μm to 10 μm.

[0046] The coverage of the outer surface of the coating 5 by the tungsten particles W is preferably 3% to 40%. The coverage here refers to the ratio of the total area of the tungsten particles W to the area of the coating 5.

[0047] Tungsten particles W are formed on the outer surface of coating 5 by vacuum deposition. For example, in the process of sintering the zirconium oxide applied to the electrode, after the electrode is placed in a furnace, the furnace is vacuumed and current is applied to tungsten, which acts as a heater, to raise the furnace temperature and heat the electrode. This is equivalent to resistive heating vacuum deposition. Alternatively, it can be said that tungsten particles W are deposited on the outer surface of coating 5 by electrically heating the tungsten as the deposition material.

[0048] Alternatively, after sintering the zirconium oxide, vacuum deposition of tungsten by electrical heating may be performed separately. By performing tungsten deposition separately from sintering the zirconium oxide, the coverage of the tungsten particles W can be easily adjusted.

[0049] Here, refer to Figure 4 , the blackening of the inner wall of the light-emitting tube is explained. Figure 4 In FIG. 1 , the arrows indicated by the dotted lines represent arc discharge when the lamp is lit. In addition, the arrows indicated by the solid lines represent the flow (convection) of the luminous gas.

[0050] The arc is extremely hot, causing a portion of the electrodes (anode 2 and cathode 3) to evaporate. The evaporated electrode component (tungsten) migrates with the flow of the luminous gas. Furthermore, as it migrates with the luminous gas flow, the evaporated tungsten adheres to the inner wall of the arc tube 1, among other things. Tungsten adhering to the inner wall of the arc tube 1 is a black substance that obstructs light transmission.

[0051] like Figure 4 As shown, the luminous gas flows upward along the anode 2, collides with the inner wall of the arc tube 1, changes direction, and circulates. Therefore, the evaporated tungsten usually adheres to the side surfaces of the electrode in addition to the inner wall of the arc tube 1.

[0052] However, when a film 5 mainly composed of ceramic is provided on the electrode surface, evaporated tungsten is less likely to adhere to the film 5. This is because tungsten forms a metallic bond, while ceramic forms a covalent bond, and metal and ceramic do not form a chemical bond.

[0053] On the other hand, the coating 5 in the lamp 100 of the present invention has tungsten particles W attached to its outer surface. The tungsten particles W attached to the outer surface of the coating 5 serve as nuclei, absorbing evaporated tungsten and causing crystal growth. Consequently, less tungsten reaches the inner wall of the arc tube 1, reducing the amount of blackening of the arc tube 1.

[0054] However, tungsten covers a portion of the outer surface of coating 5, which reduces the emissivity accordingly. This means that the electrode tip temperature is higher than in the absence of tungsten coverage, and the electrode material is more likely to evaporate. Therefore, the tungsten coverage must be adjusted so that the amount of evaporated electrode material captured exceeds the amount of electrode material evaporated due to the reduced emissivity.

[0055] In the lamp 100 of this embodiment, the coverage of the outer surface of the coating 5 by the tungsten particles W is set to 3% to 40%. This ensures excellent emissivity of the coating 5, and the tungsten particles W on the outer surface of the coating 5 can effectively capture tungsten evaporated from the electrode.

[0056] With the above structure, the lamp 100 of the present invention has excellent heat dissipation performance, can reduce the blackening of the inner wall of the light-emitting tube 1, and extend the service life of the lamp 100.

[0057] [Example]

[0058] Hereinafter, embodiments and the like that specifically illustrate the configuration and effects of the present invention will be described.

[0059] The coating with tungsten particles is formed as follows. Zirconium oxide with a particle size of 10 μm or less is added to a solvent consisting of nitrocellulose and butyl acetate, mixed thoroughly, and then applied to the outer surface of the anode with a brush. The coating is then dried at 150°C for 30 minutes. The coating is then heat-treated at 1900°C for 120 minutes in a vacuum atmosphere along with tungsten to form a tungsten-coated coating.

[0060] The effect of reducing the amount of blackening of the arc tube was confirmed using lamps having different coverage ratios of tungsten particles on the outer surface of the zirconium-containing coating (coverage ratios of 0%, 3%, 10%, 40%, and 50%).

[0061] The coverage of tungsten particles was calculated by surface analysis using a scanning electron microscope equipped with an energy dispersive X-ray device (EDS) and mapping observation of tungsten. EDS was used to map a 20 μm x 20 μm area, and the coverage was calculated as the ratio of the tungsten area to the area of the area.

[0062] The reduction in blackening of the light-emitting tube is evaluated by measuring the illuminance maintenance rate using light of a wavelength of 365 nm. The illuminance maintenance rate is the ratio of the illuminance at the start of illumination to the illuminance after an arbitrary lighting period, expressed as a percentage, with the illuminance at the start of illumination being used as the reference.

[0063] In this test, the illuminance at the start of lighting was first measured using a photodetector sensitive to a wavelength of 365 nm. Next, the illuminance after 2000 hours of continuous lighting at rated power was measured, and the ratio to the initial illuminance was calculated as the illuminance maintenance rate. The results are shown in Table 1.

[0064]

Table 1

[0065] Ceramic particle coverage 0％ 3％ 10％ 40％ 50％ Illumination maintenance rate at 2000h 90％ 92％ 94％ 92％ 90％

[0066] As shown in Table 1, when the coverage is within the range of 3-40%, the illuminance maintenance rate is improved compared to the case where no tungsten particles are attached. On the other hand, when the coverage is 50%, the illuminance maintenance rate is equivalent to the case where no tungsten particles are attached, and no improvement is achieved.

[0067] In addition, the details of the lamp specifications are as follows.

[0068] [Discharge vessel]

[0069] Material = Quartz glass, Total length = 120mm

[0070] Light-emitting tube: Maximum outer diameter = 95mm, maximum inner diameter = 85mm

[0071] [anode]

[0072] Material = Tungsten, Outer Diameter = 35mm, Total Length = 50mm

[0073] [cathode]

[0074] Material = Thoriated Tungsten, Outer Diameter = 12mm, Total Length = 35mm

[0075] [Luminous substance]

[0076] Mercury amount = 3g

[0077] [Buffer gas]

[0078] Krypton gas: Sealed pressure = 4 atmospheres

[0079] [Interpolar]

[0080] The distance between the front end of the anode and the front end of the cathode = 7mm

[0081] [Electrical characteristics]

[0082] Rated power = 4.5kW, rated voltage = 145V, rated current = 31A

[0083] [Light up pose]

[0084] Vertical lighting

[0085] While the embodiments of the present invention have been described above based on the accompanying drawings, it should be understood that the specific configuration is not limited to these embodiments. The scope of the present invention is not limited to the description of the above embodiments, but is indicated by the scope of the claims, and includes all modifications within the meaning and scope equivalent to the scope of the claims.

[0086] The structures adopted in the above-mentioned embodiments can be applied to any other embodiments. The specific structure of each part is not limited to the above-mentioned embodiments, but can be modified in various ways without departing from the scope of the present invention. In addition, one or more structures or methods involved in the various modifications described below can be arbitrarily selected and applied to the structures or methods involved in the above-mentioned embodiments.

[0087] (1) In the above embodiment, the film 5 is provided only on the outer surface of the anode 2 . However, the film 5 may also be provided on the outer surface of the cathode 3 , or may be provided only on the outer surface of the cathode 3 .

[0088] (2) In the above embodiment, the vertically lit lamp 100 is described as an example. However, even when lit horizontally, a flow of the luminous gas along the electrodes is generated, thereby achieving an effect of reducing the amount of blackening of the arc tube.

[0089] Description of labels

[0090] 1: LED

[0091] 2: Anode

[0092] 2b: Outer surface of the anode

[0093] 3: cathode

[0094] 5: Lamination

[0095] 100: Short arc discharge lamp

[0096] W: tungsten particles

Claims

1. A short arc discharge lamp having a pair of electrodes disposed opposite to each other inside a light emitting tube, characterized in that: The pair of electrodes are formed of tungsten, A coating made of ceramic is formed on the outer surface of at least one of the pair of electrodes, and tungsten particles are attached to a portion of the outer surface of the coating.

2. The short arc discharge lamp according to claim 1, wherein The short arc discharge lamp is lit in a vertical direction.

3. The short arc discharge lamp according to claim 2, characterized in that A coating made of ceramic is formed on the outer surface of the upper electrode of the pair of electrodes, and tungsten particles adhere to a portion of the outer surface of the coating.

4. The short arc discharge lamp according to claim 3, characterized in that The upper electrode is the anode.

5. The short arc discharge lamp according to claim 1, wherein The coverage rate of the tungsten particles with respect to the outer surface of the coating is 3% to 40%.

6. The short arc discharge lamp according to any one of claims 1 to 5, characterized in that The ceramic includes at least one of metal oxide, metal carbide, metal boride, metal silicide and metal nitride.

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