Discharge lamp

Abstract

To provide a discharge lamp including an electrode having excellent heat dissipation characteristics, high reliability, and long lifetime.SOLUTION: The present invention relates to a discharge lamp in which a pair of electrodes are disposed to face each other in a light-emitting tube, at least one of the pair of electrodes including: a main body made of a refractory metal; a sintered body formed by sintering a plurality of particles mainly composed of ceramics and covering at least a part of a first outer surface of the main body; and a covering body mainly composed of a refractory metal and covering at least a part of a second outer surface of the sintered body.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] The present invention relates to a discharge lamp. [Background technology]

[0002] For example, discharge lamps (particularly "short arc discharge lamps") are used as light sources in exposure devices used in the manufacturing processes of semiconductor elements, liquid crystal display elements, etc., and in various projectors. These discharge lamps are configured such that an anode and a cathode are arranged opposite each other within an arc tube, and a luminous substance such as mercury or xenon gas is sealed within the arc tube.

[0003] In such discharge lamps, the thermal load on the anode is high when the lamp is lit, which causes evaporation of the electrode material due to overheating of the anode, and this evaporation deposits on the inner wall of the arc tube, resulting in a decrease in light transmittance, known as blackening.

[0004] To solve such problems, a technology is known in which a heat dissipation layer is formed on the surface of the electrode to suppress the temperature rise of the electrode, and Patent Document 1 below discloses a discharge lamp in which a heat dissipation layer containing at least one type of metal oxide is formed on the outer surface of the electrode except near the tip. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-259639 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a heat dissipation layer is formed on the outer surface of the electrode as in the discharge lamp described in Patent Document 1, cracks may occur in the heat dissipation layer due to rapid thermal expansion caused by a temperature rise during lighting. When a crack occurs in the heat dissipation layer, the cracks gradually spread as the lamp is repeatedly lit, and there is a risk that the heat dissipation layer will eventually peel off from the outer surface of the electrode.

[0007] The peeled-off heat dissipation layer remains inside the arc tube of the discharge lamp, hindering the progress of light generated inside the arc tube and affecting the reliability and lifespan of the discharge lamp itself.

[0008] In view of the above problems, an object of the present invention is to provide a discharge lamp having electrodes with excellent heat dissipation characteristics, high reliability, and long life. [Means for solving the problem]

[0009] The discharge lamp according to the present invention comprises: A discharge lamp in which a pair of electrodes are arranged opposite each other in an arc tube, At least one of the pair of electrodes is a main body made of a high melting point metal; a sintered body covering at least a portion of a first outer surface of the main body portion and formed by sintering a plurality of particles whose main component is ceramic; and a coating body whose main component is a high-melting-point metal, the coating body covering at least a portion of the second outer surface of the sintered body.

[0010] In this specification, the term "major component" is used to refer to a component whose content is 50% or more.

[0011] In this specification, the term "covering the outer surface" refers to a state in which the material adheres to the target outer surface in a conformal manner, and is used to distinguish it from a state in which particulate matter simply adheres to the surface. The term "coated body" in this specification refers to a body that can be interpreted as a "film," "layer," "sheet," etc., along the outer surface, and also to bodies that extend in any direction along the target outer surface, regardless of length, and that can be interpreted as "string-like," "linear," "spheroidal," etc., and that have shapes that are generally distinguishable from particulate (spherical) shapes when their individual shapes are discernible (e.g., when viewed with an SEM image). The "coated body" may also be formed between multiple particles that make up the sintered body, covering the outer surfaces of each particle and connecting these particles to each other. Specific examples of the shape of the coated body are described in the "Description of the Invention" section with reference to the drawings.

[0012] As mentioned above, ceramics undergo rapid thermal expansion when the temperature rises, so sintered bodies made by sintering particles whose main component is ceramic may crack or break due to the heat generated when the discharge lamp is turned on.In contrast, metals, especially high-melting-point metals with melting points higher than 2000°C, such as tungsten (W) and molybdenum (Mo), have smaller thermal expansion due to temperature rises than ceramics, and are less likely to crack or break due to thermal expansion.

[0013] Therefore, in the discharge lamp having the above configuration, even if a sudden thermal expansion occurs in the sintered body constituting the heat dissipation layer, causing a crack, the coating material functions like an adhesive to seal the crack. In other words, the discharge lamp having the above configuration prevents the sintered body from cracking due to sudden thermal expansion, and further prevents the sintered body from peeling off from the first outer surface of the main body due to the expansion of the crack.

[0014] In the discharge lamp, The coating may be formed so as to straddle two or more of the particles that make up the sintered body.

[0015] Cracks in a sintered body tend to occur at the joints between ceramic-based particles that make up the sintered body. Therefore, in order to prevent cracks from occurring in the sintered body, it is preferable to form a coating of high-melting-point metal across multiple particles to connect them together.

[0016] The term "particle" as used herein refers to a component of the sintered body that is identified as an independent object in appearance due to gaps, cracks, etc. when observing the sintered body attached to the first outer surface of the main body in an image obtained by photographing the electrode surface with a microscope, etc.

[0017] In the discharge lamp, The sintered body may be a sintered body obtained by sintering particles whose main component is zirconia.

[0018] Zirconia has higher toughness than other ceramic materials, so that the discharge lamp having the above-described structure is relatively resistant to cracks and fractures in the sintered body.

[0019] In the discharge lamp, The coating may be composed mainly of tungsten.

[0020] Furthermore, in the discharge lamp, The coating may be mainly composed of pure tungsten.

[0021] As is common in the technical field of discharge lamps, "pure tungsten" refers to a material with a tungsten purity of 99% or more.

[0022] Tungsten has a melting point of approximately 3400° C. under normal pressure, making it a suitable material as a high-melting-point metal for forming the electrodes of discharge lamps.

[0023] The discharge lamp is The coverage of the first outer surface of the sintered body with the coating may be 5% to 50%.

[0024] In this specification, the term "coverage rate by the coating" refers to the ratio of the area of ​​the area covered by the coating to the area of ​​the entire curved surface when the area where the sintered body is formed when viewed radially of the electrode is considered to be a surface along the first outer surface of the main body.

[0025] In order to dissipate heat generated in the main body, it is preferable that the sintered body has a part of its outer surface exposed rather than being entirely covered with a coating. Specifically, it is preferable that heat dissipation occurs over an area larger than half of the entire sintered body, and it is preferable that the area of ​​the region where the second outer surface of the sintered body is exposed is larger than 50% of the entire area of ​​the second outer surface of the sintered body. In other words, it is preferable that the coverage rate of the second outer surface of the sintered body with the coating is 50% or less.

[0026] However, if the area of ​​the coating is made too small in an attempt to ensure that the outer surface is exposed, the coating will not be able to achieve the expected function of suppressing cracks, breakage, peeling, etc. of the sintered body. For this reason, the coverage rate of the coating on the second outer surface of the sintered body is preferably 5% or more.

[0027] From the above, it is preferable that the coverage of the first outer surface of the sintered body with the coating body is 5% to 50%.

[0028] In the discharge lamp, The coverage of the first outer surface of the sintered body with the coating may be relatively smaller on the side opposite to the tip of the electrode than on the tip side of the electrode.

[0029] When a discharge lamp is lit, the electrodes tend to become hotter the closer they are to the tip where electrons are emitted or collide, meaning that cracks, breaks, and peeling of the sintered body are more likely to occur closer to the tip of the electrode.

[0030] Therefore, by adopting the above-described configuration, cracks, breaks, and peeling of the sintered body are suppressed on the tip side of the electrode, and sufficient heat dissipation characteristics are ensured on the side opposite the tip of the electrode. [Effects of the Invention]

[0031] According to the present invention, a discharge lamp having electrodes with excellent heat dissipation characteristics, high reliability, and long life is realized. [Brief explanation of the drawings]

[0032] [Figure 1] 2 is a diagram schematically illustrating an embodiment of a discharge lamp when viewed in the Z direction. [Figure 2A] FIG. 2 is an enlarged view of a region P1 of the discharge lamp shown in FIG. [Figure 2B] 2B is a diagram showing a state in which a heat sink is removed from the anode 4 shown in FIG. 2A. [Figure 3A] 3 is a schematic enlarged view of an anode and a heat sink formed on the outer surface of the anode. FIG. [Figure 3B] 2 is a cross-sectional view of an anode and a schematic enlarged view of the vicinity of the outer surface in the cross-section. FIG. [Figure 3C] 1 is an enlarged photograph (SEM image) of a heat sink formed on the outer surface of an anode. [Figure 3D] 1 is an enlarged photograph (SEM image) of a heat sink formed on the outer surface of an anode. [Figure 3E] 1 is an enlarged photograph (SEM image) of a heat sink formed on the outer surface of an anode. [Figure 4] 1 is a diagram schematically showing a cathode on which a heating layer is formed. [Figure 5] FIG. 10 is an enlarged view of a region P1 in another embodiment of the discharge lamp. DETAILED DESCRIPTION OF THE INVENTION

[0033] The discharge lamp of the present invention will be described below with reference to the drawings. Note that the drawings are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily match the actual dimensional ratios and numbers.

[0034] Fig. 1 is a diagram showing a schematic view of one embodiment of a discharge lamp 1 as viewed in the Z direction. As shown in Fig. 1, the discharge lamp 1 of this embodiment includes an arc tube 2 and a pair of electrodes arranged opposite each other within the arc tube 2. The pair of electrodes includes an anode 4 supported by a lead rod 3a and a cathode 5 supported by a lead rod 3b.

[0035] In the following description, as shown in FIG. 1, the direction in which the anode 4 and the cathode 5 face each other is referred to as the X direction, as will be described later, the direction in which the tip portion 2c formed on the tube wall 2b is located as viewed from the axis 2a of the arc tube 2 is referred to as the Y direction, and the direction perpendicular to the X direction and the Y direction is referred to as the Z direction.

[0036] As described above, in this specification, when expressing a direction, if a distinction is made between positive and negative directions, the direction is described with a positive or negative sign, such as "+Z direction" or "-Z direction." When expressing a direction without distinguishing between positive and negative directions, the direction is simply described as "Z direction."

[0037] The discharge lamp 1 is a short arc type discharge lamp in which the distance in the X direction between the tip of the anode 4 and the tip of the cathode 5 (at room temperature without thermal expansion) is 40 mm or less. The short arc type discharge lamp is a discharge lamp in which the luminous material sealed inside the arc tube 2, the power to be input, etc. are selected according to the intended use. Note that the discharge lamp 1 to which the present invention is applied is not limited to a short arc type discharge lamp.

[0038] The discharge lamp 1 of this embodiment will be described on the assumption that it is a large-sized discharge lamp used in an exposure device or the like used in the manufacturing process of semiconductor elements, liquid crystal display elements, etc. A specific example of a large-sized discharge lamp is a discharge lamp with a rated input power in the range of 2 kW to 35 kW.

[0039] The light-emitting tube 2 is a tubular body that is transparent to the light generated inside when power is applied and is made of a highly heat-resistant material, and has a shape that is bulged out at the center compared to both ends in the X direction.

[0040] Here, being transmissive to light generated inside means that the transmittance is 80% or more for light of a wavelength that shows at least an intensity peak in the intensity spectrum of light generated inside the arc tube 2. Note that the light generated inside the arc tube 2 may be any of ultraviolet light, visible light, and infrared light, depending on the luminescent material sealed inside the arc tube 2.

[0041] Furthermore, high heat resistance is intended to mean a material that has heat resistance to the extent that it does not melt due to the heat generated when the lamp is lit, and specifically, a melting point of 1400° C. or higher is preferred.

[0042] The material of the arc tube 2 in this embodiment is quartz glass, but other materials such as translucent ceramics may also be used. The arc tube 2 in this embodiment is filled with mercury as a light-emitting material, and when lit, emits light whose intensity spectrum has a wavelength showing an intensity peak that belongs to the wavelength band of ultraviolet light.

[0043] When the lamp is not lit, the mercury inside the arc tube 2 is liquid, but when the lamp is lit, it vaporizes due to the heat generated inside the arc tube 2 and spreads inside the arc tube 2 .

[0044] In addition to mercury as the light-emitting material, a starting-assist buffer gas such as argon gas or xenon gas may be enclosed inside the light-emitting tube 2. Furthermore, the light-emitting material may be argon gas or xenon gas.

[0045] A tip portion 2c is formed on the tube wall 2b of the arc tube 2 on the +Y side as viewed from the axis 2a. The tip portion 2c is a protruding portion formed when closing the portion of the arc tube 2 where mercury is placed during the manufacturing process of the discharge lamp 1. In a typical discharge lamp 1, the tip portion 2c remains on the tube wall 2b of the arc tube 2, but the discharge lamp 1 does not necessarily need to have the tip portion 2c formed.

[0046] The lead rods (3a, 3b) are cylindrical members provided at both ends in the X direction of the light emitting tube 2. An anode 4 is connected to the end of the lead rod 3a, and a cathode 5 is connected to the end of the lead rod 3b. The lead rods (3a, 3b) support the anode 4 and the cathode 5, respectively, in the center of the light emitting tube 2 so that the anode 4 and the cathode 5 are arranged opposite each other in the X direction.

[0047] The ends of the lead rods (3a, 3b) located on both ends in the X direction of the arc tube 2 are electrically connected to the bases (6, 6) via molybdenum conductive foils (not shown) mounted on the stems, respectively. With this configuration, when power is supplied via power supply wires connected to the bases (6, 6) or via electrodes of a device in which the discharge lamp 1 is mounted, a discharge occurs between the anode 4 and the cathode 5, and light is emitted.

[0048] The anode 4 is an electrode into which electrons flow from the discharge plasma when the lamp is lit, and is larger than the cathode 5. Note that, as a mere example, the anode 4 in this embodiment is an electrode formed so that the length in the X direction is 60 mm and the diameter of the thickest part as viewed in the X direction is 40 mm.

[0049] The cathode 5 is an electrode that emits electrons when lit, and is an electrode having a cross-sectional shape that gradually decreases in diameter toward the anode 4 when cut along a plane (YZ plane) perpendicular to the X direction.

[0050] Fig. 2A is an enlarged view of region P1 of the discharge lamp 1 shown in Fig. 1, and Fig. 2B is a view showing a state in which the heat sink 10 has been removed from the anode 4 shown in Fig. 2A. The heat sink 10 is formed on the outer surface (first outer surface) of the main body 11 of the anode 4. Note that in Fig. 2A, for convenience of illustration, the detailed structure of the heat sink 10 is omitted and shown by hatching.

[0051] Here, the outer surface of the anode 4 refers to the outer surface excluding the tip surface 4a facing the cathode 5. Since the temperature of the tip surface 4a of the anode 4 may rise to or exceed the melting point of the heat sink 10 when the discharge lamp 1 is turned on, in this embodiment, the tip surface 4a of the anode 4 is not provided with the heat sink 10.

[0052] In this embodiment, the heat sink 10 is provided on the outer peripheral surface 4b of the cylindrical body centered on the axis 2a among the outer surfaces of the anode 4, but the heat sink 10 may also be provided on the tapered surface 4c located between the outer peripheral surface 4b and the tip surface 4a. Furthermore, the heat sink 10 may also be provided on the rear tapered surface 4d located on the -X side of the outer peripheral surface 4b of the anode 4.

[0053] Fig. 3A is a schematic enlarged view of the anode 4 and the heat sink 10 formed on the outer surface of the anode 4, and Fig. 3B is a schematic enlarged view of a cross section of the anode 4 and the vicinity of the outer surface in the cross section. As shown in Figs. 3A and 3B, the heat sink 10 includes a sintered body 12 formed by sintering a plurality of granules 12a, and a coating 13 that covers at least a portion of the outer surface (second outer surface) of the sintered body 12.

[0054] Although the sintered body 12 in this embodiment is formed by sintering a plurality of particles 12a whose main component is zirconia (ZrO2), it may also be formed by sintering particles 12a whose main component is something other than zirconia. The main component of the particles 12a may be ceramic, and examples of the materials that can be used include oxides such as alumina (Al2O3) and titania (TiO2), nitrides such as silicon nitride (Si3N4) and aluminum nitride (AlN), and carbides such as silicon carbide (SiC).

[0055] The sintered body 12 in this embodiment is formed by adding particles 12a, the main component of which is zirconia having a particle size of 10 μm or less, to a solvent consisting of nitrocellulose and butyl acetate, mixing them well, applying the mixture to the outer surface of the anode 4 with a brush, drying the mixture at 150°C for 30 minutes, and then sintering the particles 12a by performing a heat treatment at 1900°C for 120 minutes in a vacuum atmosphere.

[0056] The coating 13 in this embodiment is mainly composed of tungsten, and is formed so as to cover the outer surface of the sintered body 12 and to straddle two or more of the plurality of grains 12a.

[0057] The coating 13 may be formed of a material mainly composed of a high-melting-point metal other than tungsten, such as molybdenum. The coating 13 may also be formed so as to anchor each of the particles 12a on the outer surface of each particle 12a, rather than spanning multiple particles 12a. As described above, when an SEM image is acquired and the sintered body 12 attached to the first outer surface of the main body 11 is observed, the particles 12a are identified as independent particles due to gaps, cracks, and the like, and are components of the sintered body 12.

[0058] The coating 13 is formed by, for example, metal vapor deposition or thermal spraying onto the sintered body 12, but may be formed by other methods.

[0059] 3C and 3D are enlarged photographs (SEM images) of the heat sink 10 formed on the outer surface of the anode 4. FIG. 3C is an SEM image at 1000x magnification, and FIG. 3D is an SEM image at 2500x magnification. In FIGS. 3C and 3D, the white portion is the region of the coating 13. FIG. 3D shows an independent object in the SEM image, i.e., an object determined to be a particle 12a.

[0060] 3E is an enlarged photograph (SEM image) of a heat sink 10 formed on the outer surface of the anode 4, different from those in FIGS. 3C and 3D. Note that the shapes shown in FIGS. 3C to 3E are merely examples, but the coating 13 is different from particulate matter attached to the outer surface of the sintered body 12 and is an object that is formed along the outer surface of the sintered body 12 and can be read as a "film," "layer," "sheet," etc., and furthermore, an object that extends in any direction along the target outer surface, regardless of its length, and can be read as a "string-like," "linear," "spheroidal," etc.

[0061] The coverage rate of the coating 13 on the outer surface of the sintered body 12 is arbitrary, but is preferably 5% to 50% in order to balance the adhesiveness of the particles 12a that make up the sintered body 12 and the heat dissipation characteristics of the sintered body 12.

[0062] Here, the "coverage rate by the coating material" refers to the ratio of the area of ​​the area covered by the coating 13 to the area of ​​the entire curved surface when the area where the sintered body 12 is formed when viewed in the radial direction (direction perpendicular to the X direction) of the electrode (anode 4) is regarded as a surface along the first outer surface of the main body 11, as described above.

[0063] More specifically, the ratio of the area of ​​the region where the coating 13 is formed to the area of ​​the curved surface along the surface of the main body 11 on which the sintered body 12 is formed, passing through the part where the film thickness of the sintered body 12 is at its maximum, is the "coverage rate by the coating material."

[0064] As just one example, the coverage rate is derived by acquiring images such as those shown in Figures 3C to 3E over the entire area of ​​the electrode (anode 4) where the heat sink 10 is formed, calculating the area of ​​the entire heat sink 10 and the area of ​​the area where the coating 13 is formed, and then calculating these.

[0065] Furthermore, although the above description has been given in connection with an embodiment in which heat sink 10 is formed on the outer surface of anode 4, the heat sink layer may be formed on the outer surface of cathode 5. Fig. 4 is a diagram schematically illustrating cathode 5 on which heat sink 50 is formed.

[0066] Here, the outer surface of the cathode 5 refers to the outer surface of the main body excluding the tip 51 containing the emitter material, which faces the anode 4. The tip 51 of the cathode 5 is not provided with the heat sink 10 because the temperature of the tip 51 may rise to or exceed the melting point of the heat sink 50 when the discharge lamp 1 is turned on.

[0067] In this embodiment, the heat sink 10 is provided on the outer surface of the cathode 5, on the outer peripheral surface 5b of the cylindrical body centered on the axis 2a, but the heat sink 50 may also be provided on the tapered surface 5c located between the outer peripheral surface 5b and the tip portion 51.

[0068] The main body of the cathode 5 is a member made of pure tungsten and formed so as to have a length in the X direction of 35 mm and a diameter of 20 mm at its thickest part when viewed in the X direction. The size and shape of the main body are arbitrary.

[0069] The material for the main body of the cathode 5 may be any high-melting-point metal, such as molybdenum (Mo). However, pure tungsten is preferred because of its high melting point and because thoriated tungsten is considered to be the preferred material for the tip 51, as will be described later.

[0070] The tip portion 51 is a member that extends from the main body portion toward the anode 4 side (-X side), and has a cross section that, when cut in the YZ plane, gradually decreases in diameter toward the anode 4 side.

[0071] The material of the tip portion 51 may be a high-melting-point metal containing an emitter material. Examples of the emitter material include thorium oxide (ThO2) and lanthanum oxide (La2O3). Examples of the high-melting-point metal include molybdenum (Mo) and tungsten (W).

[0072] However, from the viewpoints of electron emission occurring at low energy, i.e., having a low work function and being resistant to evaporation and melting at high temperatures, it is preferable to use thoriated tungsten (sometimes called "thoriated tungsten"), which is made by dispersing thorium oxide (ThO2), an emitter material, in pure tungsten, a high-melting-point metal, for the tip 51 of the cathode 5. The concentration of thorium oxide in the tip 51 is about several percent (e.g., 3%).

[0073] The structure of the heat sink 50 formed on the outer surface of the cathode 5, and the structures and materials of the sintered body and coating body that constitute the heat sink 50, are the same as those of the heat sink 10 formed on the outer surface of the anode 4, and the sintered body 12 and coating body 13 that constitute the heat sink 10.

[0074] In the discharge lamp 1 having the above configuration, even if a sudden thermal expansion occurs in the sintered body 12 constituting the heat sink 10, causing a crack, the covering body 13 functions like an adhesive to seal the crack. In other words, the discharge lamp 1 having the above configuration is prevented from cracking the sintered body 12 due to sudden thermal expansion, and furthermore, from peeling off the sintered body 12 from the outer surface of the main body 11 due to the expansion of the crack, resulting in a discharge lamp 1 having electrodes with excellent heat dissipation characteristics, high reliability, and a long life.

[0075] [Another embodiment] Another embodiment will be described below.

[0076] <1> Fig. 5 is an enlarged view of a region P1 in another embodiment of the discharge lamp 1. In the anode 4 in this embodiment, when the outer peripheral surface 4b is divided into a first outer peripheral surface 4b1 located on the tip end side (+X side) from the center in the X direction and a second outer peripheral surface 4b2 located on the opposite side (-X side) from the tip end (tip end surface 4a), the heat sink 10 is formed so that the coverage of the outer surface of the sintered body 12 with the coating 13 differs between the first heat sink 10a formed on the first outer peripheral surface 4b1 and the second heat sink 10b formed on the second outer peripheral surface 4b2, both of which are not shown. More specifically, the coverage of the second heat sink 10b is adjusted to be relatively smaller than the coverage of the first heat sink 10a.

[0077] The coverage of the coating 13 on the sintered body 12 can be adjusted, for example, by spraying a high-melting point metal, which is the material of the coating 13, onto the outer peripheral surface (4b1, 4b2) of the sintered body 12 so as to achieve the desired coverage.

[0078] According to the above configuration, cracks, breaks, and peeling of the sintered body 12 are suppressed on the +X side of the anode 4, and sufficient heat dissipation characteristics are ensured on the −X side of the anode 4.

[0079] <2> The configuration of the discharge lamp 1 described above is merely an example, and the present invention is not limited to the configurations shown in the drawings. [Explanation of symbols]

[0080] 1: Discharge lamp 2: Arc tube 2a : Axis 2b: Pipe wall 2c: Tip part 3a: lead stick 3b: lead stick 4: Anode 4a: Tip surface 4b: Outer surface 4b1: First outer peripheral surface 4b2: Second outer peripheral surface 4c: Tapered surface 4d: Rear tapered surface 5 : Cathode 5b: Outer surface 5c: Tapered surface 6: nozzle 10: Heat sink 10a: first part 10b : Second part 11: Main body 12: Sintered body 12a: Granules 13 : Covering body 50: Heat sink 51: Tip P1: Area

Claims

1. A discharge lamp in which a pair of electrodes are arranged opposite each other in an arc tube, At least one of the pair of electrodes is a main body made of a high melting point metal; a sintered body covering at least a portion of a first outer surface of the main body portion and formed by sintering a plurality of particles whose main component is ceramic; a coating whose main component is a high-melting-point metal, said coating covering at least a portion of a second outer surface of said sintered body.

2. 2. The discharge lamp according to claim 1, wherein the coating is formed so as to straddle two or more of the plurality of particles that constitute the sintered body.

3. 2. The discharge lamp according to claim 1, wherein the sintered body is formed by sintering a plurality of particles whose main component is zirconia.

4. 2. The discharge lamp according to claim 1, wherein the coating is mainly composed of tungsten.

5. 5. The discharge lamp according to claim 1, wherein the coating has a coverage of 5% to 50% of the first outer surface of the sintered body.

6. A discharge lamp as described in any one of claims 1 to 4, characterized in that the coverage rate of the first outer surface of the sintered body by the covering body is relatively smaller on the side opposite the tip of the electrode than on the tip side of the electrode.

Images