JP5258473B2 - Short arc type discharge lamp - Google Patents

Description

  The present invention relates to a short arc type discharge lamp used as a light source in an exposure apparatus or the like, and more particularly to a lamp structure that suppresses fluctuation (illuminance fluctuation).

  In the short arc type discharge lamp, the anode and the cathode are held in the vicinity of the arc tube, and by applying a voltage, an arc discharge is generated between the electrodes, and light of a specific wavelength such as ultraviolet light is emitted. Since the short-arc discharge lamp has a short distance between the electrodes, it can be regarded as a point light source, and light with high radiance can be obtained. For example, when used in an exposure apparatus that forms a wiring pattern on a substrate, light emitted outside the lamp is converted into parallel light through a lens, a mirror, and the like, and irradiated onto the substrate.

  While the lamp is on, the electrode is in a high temperature state. For this reason, arc discharge becomes unstable due to, for example, the consumption of the electrode tip, and the bright spot of the arc moves or the light emission length changes. As a result, no light is emitted as a point light source, resulting in illuminance reduction and illuminance fluctuation. In an exposure apparatus or the like, it is necessary to maintain illuminance uniformity over the entire exposure surface, and illuminance fluctuations must be suppressed.

As a lamp structure that suppresses fluctuations in illuminance, a discharge lamp is known in which an electrode tip is disposed on or on a plane including the maximum diameter portion of the arc tube (see Patent Document 1). Alternatively, a part of the cathode body is formed in a taper shape, and a protrusion is provided on the taper portion to suppress the contraction and movement of the arc bright spot (see Patent Document 2).
Japanese Patent Laid-Open No. 10-269990 JP 2003-132837 A

  While the discharge lamp is lit, the cooling air is applied to the discharge lamp (especially a high-temperature sealed tube) to cool the lamp. However, when the cooling air hits the sealing tube and further the arc tube, the arc tube is partially cooled. As a result, the temperature distribution inside the arc tube is non-uniform and convection occurs inside the arc tube, and this convection causes movement and fluctuation of the arc bright spot. It is a problem to prevent such fluctuations of the discharge lamp due to lamp cooling.

  The short arc type discharge lamp of the present invention is a lamp that stably emits light without being affected by lamp cooling. For example, the short arc type discharge lamp is used in an illumination device of an exposure apparatus, and is cooled by a cooling device that cools the short arc type discharge lamp. Irradiate light while being cooled. The discharge lamp includes an arc tube having an anode and a cathode facing each other, and a sealing tube connected to the arc tube and supporting the anode and the cathode. For example, the cathode and the anode are arranged such that the electrode axis is along the vertical direction.

  In the present invention, the thickness of the arc tube shoulder is 5 mm or more. However, the arc tube shoulder corresponds to the arc tube portion between the arc tube maximum diameter portion and the connection portion of the sealing tube, and the plane including the tip when the tip of the cathode is used as a reference. Corresponds to the arc tube portion with an angle from about 60 degrees. When the electrodes are arranged in the vertical direction, it corresponds to the vicinity in the latitudinal direction 60. Or it corresponds to the arc tube portion outside the region of the light emission range.

  In the conventional lamp structure that suppresses fluctuations in illumination and fluctuations, the influence (disturbance) from other than the lighting device is not considered, and in particular, the influence of the cooling air due to the lamp cooling is not considered. In particular, it has not been found that the thickness of a part of the arc tube (not the total thickness) affects fluctuations. In the present invention, the thickness of the arc tube shoulder is set to 5 mm or more, which is much thicker than that of the conventional lamp, in order to suppress the occurrence of fluctuations due to the influence of the cooling air. As a result, the fluctuation (illuminance fluctuation) is minimized, and the illuminance fluctuation can be suppressed.

  When manufacturing a discharge lamp made of a glass tube or the like, the arc tube is expanded by being softened by heating. Considering the lamp manufacturing method, it is difficult to maintain the entire arc tube with a large thickness. For this reason, it is desirable to make the arc tube thickness near the maximum diameter portion of the arc tube smaller than the thickness of the arc tube shoulder, rather than making the entire arc tube uniform with the same thickness.

  In particular, in order not to affect the light transmission, it is preferable to reduce the thickness of the arc tube near the maximum diameter portion. In addition, it is desirable to maintain a constant illuminance by making the arc tube thickness in the light emission range substantially constant.

  On the other hand, if the sealing tube is made too thick, there is a risk of lamp breakage due to the arc tube rupture. That is, when a crack occurs inside the sealing tube, the crack may be transmitted to the arc tube first because it is difficult to break due to the thickness of the sealing tube. Therefore, it is desirable to make the thickness of the sealing tube smaller than the thickness of the arc tube shoulder.

  In order to suppress the fluctuation more effectively, it is desirable that the tip surface of the anode is located on a plane along the maximum diameter portion of the arc tube. On the other hand, when the radius of curvature of the connecting portion between the arc tube and the sealing tube is larger than 2 mm, the connecting portion between the sealing tube and the arc tube is bent gently, and stress concentration is avoided.

  According to the present invention, it is possible to suppress lamp fluctuation and illuminance fluctuation due to cooling, and maintain stable lamp lighting.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view schematically showing an exposure apparatus that uses the short arc type discharge lamp of this embodiment as a light source of an illumination apparatus.

  The exposure apparatus 100 includes an illumination device 120 and a DMD (Digital Micro-mirror Device) 140 and forms a pattern on the drawing table 180. The lighting device 120 includes a short arc type discharge lamp (not shown here), and light emitted from the discharge lamp 10 is guided to the DMD 140. While the discharge lamp 10 is lit, the cooling device 140 provided near the discharge lamp 10 blows cooling air toward a base (not shown here) of the discharge lamp 10.

  FIG. 2 is a schematic cross-sectional view of the short arc type discharge lamp 10. FIG. 3 is a diagram showing a light distribution (illuminance distribution) of the lamp.

  The short arc type discharge lamp 10 in the lighting device 120 includes a light emitting tube 12 made of transparent quartz glass, and a cathode 20 and an anode 30 in the light emitting tube 12, and the cathode 20 and the anode 30 are arranged to face each other with a predetermined interval L. Is done. On both sides of the spherical arc tube 12, sealing tubes 13A and 13B made of quartz glass facing each other are connected to the arc tube 12 and integrally formed. The discharge lamp 10 is arranged so that the anode 30 is on the upper side, the cathode 20 is on the lower side, and the electrode axis E is along the vertical direction.

  Inside the sealing tubes 13A and 13B, conductive electrode support rods 17A and 17B for supporting the cathode 20 and the anode 30 are arranged, and the conductive electrodes are provided via the metal rings 18A and 18B and the metal foils 16A and 16B. Connected to the lead bars 15A and 15B, respectively. Both ends of the sealing tubes 13A and 13B are closed by the caps 19A and 19B. Further, the sealing tubes 13A and 13B are welded to the glass tubes 21A and 21B and the glass rods 23A and 23B provided inside, thereby sealing the discharge space in the arc tube 12. Mercury and a rare gas are enclosed in the arc tube 12.

  The lead rods 15A and 15B are connected to an external power source (not shown), and the cathodes are connected to the lead rods 15A and 15B, the metal foils 16A and 16B, the metal rings 18A and 18B, and the electrode support rods 17A and 17B. 20, power is supplied to the anode 30. When a voltage is applied between the cathode 20 and the anode 30, an arc discharge is generated between the electrodes, and light from mercury is radiated out of the arc tube 12.

  The cathode 20 is formed with a conical tip portion 20A, and the tip surface is configured as a discharge surface. On the other hand, a conical tip 30A is also formed on the anode 30, and the tip surface is configured as a discharge surface. When arc discharge occurs between the tip surfaces of the cathode 20 and the anode 30, light is emitted in all directions. A light emission center (hereinafter referred to as a bright spot) H when the discharge lamp 10 is used as a point light source is defined on the front end face of the cathode front end portion 20A, and it can be considered that light is emitted from the bright spot H.

  The light distribution shown in FIG. 3 is obtained by measuring the irradiance in the vertical direction, that is, the latitudinal direction in the emitted light. The vertical axis represents the illuminance. When the illuminance on the reference plane (± 0 °) is 100%, the illuminance along the latitude is represented by the ratio. However, a horizontal plane F (see FIG. 2) perpendicular to the electrode axis E and along the tip 20A of the cathode 20 is defined as a reference plane (0 degree), and a positive latitude and a negative cathode side are defined from the reference plane to the anode side. To do.

  The radiation range RK of the discharge lamp 10 is determined according to the arrangement, size and shape of the cathode 20 and the anode 30 and the distance between the cathode 20 and the anode 30. Here, the radiation range on the anode side is defined as a range from 0 degree to about 30 degrees due to the influence of the shape of the anode tip portion 30A and the distance between the electrodes. On the other hand, the radiation range on the cathode side extends to about -60 degrees.

  In the present embodiment, the thickness of the arc tube 12 is not uniform overall, and the thickness (thickness) T1 near the arc tube shoulder 12T is larger than the thickness T2 near the arc tube maximum diameter portion 12S. Here, the arc tube shoulder 12T is an arc tube portion close to the connection portion 12V with the sealing tubes 13A and 13B, and indicates an arc tube portion corresponding to the vicinity of +60 degrees in the latitude direction on the anode side.

  On the other hand, the arc tube maximum diameter portion 12S indicates a light emission portion where the diameter of the arc tube 12 is maximum, and here is an arc tube portion corresponding to a plane G along the tip surface 31A of the anode tip portion 30A. The thickness T2 in the vicinity of the maximum diameter portion 12S is less than 5 mm, and is set in the range of 3 mm to 3.5 mm, for example. On the other hand, the thickness T1 in the vicinity of the arc tube shoulder 12T is set to 5 mm or more (for example, 5.3 mm to 5.5 mm).

  The arc tube portion corresponding to the radiation range RK (see FIG. 3) of the arc tube 12 has a substantially constant thickness and a thickness T2 of the maximum diameter portion 12S. Further, the thickness T1 of the arc tube shoulder 12T is substantially unchanged up to the vicinity of the connection portion 12V with the sealing tubes 13A and 13B. On the other hand, the thickness T3 of the sealing tubes 13A and 13B is smaller than the thickness T1 of the arc tube shoulder 12T. Further, the radius of curvature R1 at the connecting portion 12V between the sealing tubes 13A and 13B and the arc tube 12 is set to 2 mm or more (for example, 10 mm).

  As shown in FIG. 2, during the lamp lighting, the cooling air from the cooling device 140 is blown mainly toward the caps 19A and 19B. This air blowing direction is to prevent the temperature fluctuation in the arc tube 12 from occurring due to cooling to the inside of the arc tube 12 at that time when the overheating state inside the sealing tubes 13A and 13B is prevented. The cooling air cools the inside of the sealing tubes 13A and 13B that are in a high temperature state, thereby suppressing the high temperature state.

  The structural portion of the lamp 10 that is directly affected by the cooling air is not limited to the sealing tubes 13A and 13B, but extends to the connection portion 12V of the arc tube 12 near the sealing tubes 13A and 13B and the vicinity of the shoulder portion 12T. However, since the thickness T1 of the arc tube shoulder 12T is sufficiently thicker than usual (about 3.0 mm), the influence of the cooling air does not reach the inside 12 of the arc tube or the effect is very small. As a result, even if the inside of the sealing tubes 13A and 13B is cooled, it is not cooled to the inside of the arc tube 12, the temperature distribution in the arc tube 12 is kept uniform, and the convection in the tube that causes fluctuation is suppressed.

  On the other hand, the production of the arc tube 12 usually involves an operation in which a quartz tube as a material is heated by a burner or the like and softened and expanded. In order to reduce the thickness T2 of the arc tube maximum diameter portion 12S, the arc tube 12 can be manufactured more easily than when the entire arc tube thickness is maintained at the thickness T1 of the arc tube shoulder 12T. In addition, the permeability is prevented from being affected by the thickness.

  Furthermore, the change in the thickness of the arc tube 12 occurs outside the range of the radiation range RK, and the arc tube thickness is maintained substantially constant within the radiation range RK. Therefore, the transparency becomes uniform in the entire device, and the illuminance uniformity can be maintained.

  Further, the fluctuation G is suppressed by matching the plane G along the tip surface 31A of the anode tip portion 30A with the plane passing through the maximum diameter portion 12S.

  On the other hand, the sealing tubes 13A and 13B cannot be made thicker than necessary in order to prevent lamp damage due to cracks or the like. When the thickness T3 of the sealing tubes 13A and 132B is increased, if cracks occur in the sealing tubes 13A and 13B, it takes time until the sealing tubes 13A and 13B crack and break. There is a risk that the crack will propagate first and cause a lamp burst. Therefore, the thickness T3 of the sealing tube 13A is set smaller than the thickness of the arc tube shoulder 12T.

  Since the thickness T1 of the arc tube shoulder 12T is increased and the thickness T3 of the sealing tubes 13A and 13B is different from the thickness T1 of the arc tube shoulder 12T, the arc tube connection portion Stress concentration tends to be applied to 12V. However, the curvature radius R1 of the connecting portion 12V is set to be as small as 2 mm or more. Therefore, stress concentration can be prevented.

  Since the fluctuation due to the influence of the cooling air is related to the thickness of the arc tube shoulder 12T, the thickness of the arc tube 12 may be entirely matched with the thickness T1 of the shoulder 12T. It is also possible to define and specify the arc tube shoulder based on the arrangement direction and position of the anode and electrode. A short arc type discharge lamp may be used in addition to the exposure apparatus.

  In order to confirm the effectiveness of the above configuration, the fluctuation (illuminance fluctuation) inside the arc tube 12 was measured while changing the thickness of the arc tube shoulder 12S and the strength of the cooling air. The discharge lamp having the above-described configuration was arranged along the vertical direction, and was lit while the cooling air was blown toward the base. The arc tube thickness of about 60 degrees from the reference plane F is the thickness T1 of the arc tube shoulder 12T.

  FIG. 4 is a graph showing the magnitude of fluctuation with respect to the thickness of the arc tube shoulder.

  The horizontal axis represents the thickness T1 (mm) of the arc tube shoulder 12T, and the vertical axis represents the magnitude of fluctuation. Fluctuations were measured as illuminance fluctuations, and illuminance was measured with an illuminometer having a sensitivity region near a wavelength of 350 nm in the latitude direction +30 degrees. Then, averaging was performed every 5 seconds, and a fluctuation value R was obtained by “(maximum value−minimum value) ÷ average value”. It is also possible to calculate the magnitude of fluctuation as the illuminance fluctuation rate.

  The cooling air has three stages: “strong” when the arc tube shoulder 12S is supercooled, “medium” where the cooling air to the arc tube shoulder 12S is weak, and “weak” where the cooling air does not hit the arc tube shoulder 12S. The temperatures of the arc tube shoulder 12S in “strong”, “medium”, and “weak” are about 470 ° C., about 700 ° C., and about 800 ° C., respectively.

  Preparing a plurality of discharge lamps having a thickness T1 of the arc tube shoulder 12T in a range of about 3.0 mm to about 5.5 mm (particularly, a range of 3.5 to 4.0 mm and 5.3 mm or more); The fluctuation R was measured while changing the strength of the cooling air. Then, based on the measurement plot, curves W1 to W3 indicating the correlation between the thickness T1 and the fluctuation R are defined (see FIG. 4). Curves W1, W2, and W3 correspond to “strong”, “medium”, and “weak” cooling, respectively.

  As can be seen from FIG. 4, when the thickness T1 of the arc tube shoulder 12T is 5.0 mm or more, the fluctuation R is almost within the minimum value (around 65), and the thickness T1 is 3.0 mm to 5.0 mm. Compared to the range, the illuminance fluctuation is small and stable. In particular, in the thickness range of 3.0 mm to 5.0 mm, variation occurs depending on the cooling air level. However, when the thickness T1 is 5.0 mm or more, the fluctuation R does not vary and is low regardless of the level of the cooling air. The value is suppressed.

It is the perspective view which showed typically the exposure apparatus which uses the short arc type discharge lamp of this embodiment as an illuminating device. It is a schematic sectional drawing of a short arc type discharge lamp. It is the figure which showed the light distribution (illuminance distribution) of the lamp | ramp. It is the graph which showed the magnitude | size of the fluctuation | variation with respect to the thickness of an arc tube shoulder part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Short arc type discharge lamp 12 Arc tube 12S Arc tube maximum diameter part 12T Arc tube shoulder part 13A, 13B Sealing tube RK Radiation range F Reference plane (plane including cathode tip)
G Plane including anode tip

Claims (7)

An arc tube provided with an opposing anode and cathode inside;
A sealing tube connected to the arc tube and supporting the anode and the cathode;
Relative to the distal end portion of the cathode, and perpendicular to the electrode axis, the thickness of the arc tube shoulder near the angle 60 degrees from the plane including the tip state, and are more 5 mm,
The arc tube thickness near the maximum diameter portion of the arc tube is smaller than the thickness of the arc tube shoulder,
The thickness of the arc tube portion corresponding to the light emission range is substantially constant,
A short arc discharge lamp characterized in that the change in thickness of the arc tube portion occurs outside the light emission range . The arc tube thickness near the maximum diameter portion of the arc tube is determined in the range of 3 to 3.5 mm,
The short arc type discharge lamp according to claim 1, wherein a thickness of the arc tube shoulder is set in a range of 5.3 to 5.5 mm . 2. The short arc type discharge lamp according to claim 1 , wherein the electrode axis is disposed along the vertical direction .   The short arc type discharge lamp according to any one of claims 1 to 3, wherein a thickness of the sealing tube is smaller than a thickness of a shoulder portion of the arc tube.   The short arc type discharge lamp according to any one of claims 1 to 4, wherein a radius of curvature of a connection portion between the arc tube and the sealing tube is larger than 2 mm. An illumination device having the short arc type discharge lamp according to any one of claims 1 to 5,
An exposure apparatus comprising: a cooling device that cools the short arc discharge lamp. An arc tube provided with an opposing anode and cathode inside;
A sealing tube connected to the arc tube and supporting the anode and the cathode;
The thickness of the shoulder of the arc tube that is between the connecting portion with the sealing tube and the maximum diameter portion of the arc tube and is outside the light emission range is 5 mm or more ,
The arc tube thickness near the maximum diameter portion of the arc tube is smaller than the thickness of the arc tube shoulder,
The thickness of the arc tube portion corresponding to the light emission range is substantially constant,
A short arc discharge lamp characterized in that the change in thickness of the arc tube portion occurs outside the light emission range .

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