JP4513031B2 - Short arc type high pressure discharge lamp - Google Patents

Description

  The present invention relates to a short arc type high pressure discharge lamp, and more particularly to a structure of an electrode of a short arc type high pressure discharge lamp.

  In recent years, short arc type high-pressure discharge lamps have been used as a light source in a photolithography process, for example, a liquid crystal color filter manufacturing process. The emitted light at this time has a strong emission line spectrum at wavelengths of 365 nm and 436 nm. Is called. On the other hand, the market demands a larger color filter and shorter exposure time, and the amount of radiant light from the short arc type high-pressure discharge lamp is also required to increase. In particular, the amount of radiant light near 365 nm is strongly increased. It is desired.

  It has been conventionally known that the amount of radiation of a short arc type high-pressure discharge lamp is proportional to the electric input to the discharge lamp. That is, the amount of radiation can be increased by increasing the electrical input to the discharge lamp. Here, the following methods exist for increasing the electrical input to the discharge lamp. First, increase the distance between the electrodes to increase the light emission length of the short arc type high-pressure discharge lamp, and second, increase the amount of mercury enclosed in the discharge lamp, and turn on the lamp at a higher pressure. Third, increase the input current to the discharge lamp.

  However, the various methods described above have problems. The first method is to increase the light emission length, and the light emitting part becomes larger than the point light source lamp that is normally used. When using as a light source in an exposure apparatus for photolithography, a point light source is desired in relation to the irradiation optical system, and thus extending the light emission length is not suitable as a light source for the exposure apparatus. Thus, even if the amount of radiated light is improved, it cannot be actually used.

  The second method has a problem in terms of mechanical strength of the arc tube because the internal pressure of the short arc type high-pressure discharge lamp increases. Conventional short arc type high-pressure discharge lamps are often designed with the vapor pressure at the time of lighting of mercury enclosed in the lamp being close to the upper limit of the internal pressure intensity of the lamp. The high-pressure discharge lamp will be destroyed. In other words, a method of increasing the amount of mercury enclosed in the conventional short arc type high-pressure discharge lamp and lighting at an ultra-high pressure cannot be used to improve the radiation amount.

  In the third method, when the lamp current increases, the tip of the anode is heated by the increase of the electron current, and the temperature of the anode increases. Usually, heat generated at the anode is radiated to the outside by heat conduction of the anode, and heat radiated from the surface of the anode to the outside by radiation. However, in the method of increasing the lamp current, the heat released to the outside is insufficient as compared with the heating by increasing the electron current. As a result, the thermal evaporation of the anode member accompanying the temperature rise of the anode is promoted, and the arc tube There are problems such as blackening the inner wall of the lamp and shortening the lamp life.

  In order to solve this problem, a method for improving the efficiency of heat radiation from the anode and lowering the temperature of the anode has been proposed. For example, Japanese Patent Publication No. 39-11128 discloses providing a V-shaped groove on the side surface of the anode. Specifically, a cooling groove having a depth of about 1 mm to 3 mm and an opening angle of 90 ° is provided, and the surface of the anode is sintered by sintering tantalum carbide on the surface of the cooling groove. It is described that the heat radiation from can be further increased. However, this method has a problem that carbon is liberated depending on the temperature of the anode, and the arc tube of the short arc type high-pressure discharge lamp is blackened, or the carbon moves to the tip of the electrode and the electrode is melted.

  Further, JP-A-9-231946 discloses that tungsten powder is sintered on the side surface of the anode to improve the thermal emissivity of the electrode surface. FIG. 9 shows this structure, and a particulate tungsten sintered layer 91 is formed in a predetermined surface region of the anode 90. The tungsten fine particles have a particle size of about 0.1 to 100 μm, and the surface area of the tungsten fine particles is increased by providing the sintered fine particles on the anode surface. With such a structure, the temperature of the electrode is lowered by increasing the amount of heat radiation from the electrode surface. However, this structure can increase the heat radiation from the electrode as compared with the case where the tungsten powder is not applied, but when the electric input to the discharge lamp is made higher, the cooling of the electrode becomes insufficient. As a result, there is a problem that heat radiation from the electrode becomes insufficient.

  The problem to be solved by the present invention is that, in a short arc type high pressure discharge lamp in which the input power to the lamp is increased in order to increase the amount of radiated light, the heat radiation characteristic from the electrode is improved and the temperature of the electrode is efficiently increased. Is to lower. And, by efficiently lowering the electrode temperature, it is possible to suppress or mitigate evaporation of the electrode constituent material from the anode tip, and to reduce wear and thermal deformation of the electrode tip, as a result. An object of the present invention is to maintain light emission of a discharge lamp stably for a long time.

In order to solve the above problems, a short arc type high pressure discharge lamp of the present invention is a short arc type high pressure discharge lamp having a pair of tungsten electrodes in an arc tube, wherein at least one tungsten electrode of the tungsten electrodes has a side surface. It is characterized by having a groove part in which the pitch between adjacent top parts formed by laser processing is at least 150 μm to 500 μm and the depth is 2 to 3 times the pitch .

As described above, in the short arc type discharge lamp of the present invention, the pitch (P) between adjacent apexes formed by laser processing on at least a part of the side surface of at least one tungsten electrode is 150 μm to 500 μm. And since the groove part whose depth is 2 to 3 times the pitch is formed, the thermal emissivity from the electrode can be increased, and even if the input power of the discharge lamp is increased, it is efficient. Since heat radiation is possible, the amount of radiation can be increased.

  FIG. 1 shows an overall view of a short arc type high pressure discharge lamp. The discharge lamp 10 is composed of an arc tube portion 11 and a sealing tube portion 12, and an anode 20 and a cathode 30 made of tungsten are arranged opposite to each other with a tip distance of about 10 mm in the arc tube portion 11. The anode 20 and the cathode 30 are each embedded in the sealing tube portion 12 and electrically connected to the external terminal 13. The arc tube 11 is filled with a sealing gas composed of a rare gas such as xenon, argon, krypton, or a mixture thereof, and a luminescent material such as mercury. The pressure of the sealed gas is, for example, 0.1 to 10 atmospheres at the time of sealing, and the mercury filling amount is 10 to 60 mg / cc in terms of the weight per inner volume of the arc tube portion 11. For example, the discharge lamp is lit at a rating of 50 V and a rating of 5 kW.

  2A and 2B are enlarged views of the anode 20, wherein FIG. 2A is a side view showing the shape of the anode 20, and FIGS. 2B and 2C are enlarged cross-sectional views of grooves formed on the anode side surface.

  In FIG. 2A, the anode 20 includes a tip portion 21, a cone portion 22, and a body portion 23. The tip portion 21 is planar and faces the cathode. The cone portion 22 is provided with a taper connecting the tip portion 21 and the body portion 23. The body portion 23 is formed with a V-shaped groove portion 24 which is even formed by laser processing on the side surface thereof. As for numerical values of the anode, the body portion 23 has a diameter of 25 mm and a length of 45 mm, the cone portion 22 has an opening angle of 120 °, and the tip portion 21 has a diameter of 8 mm.

  In (b), the groove portion 24 is formed in a V shape from the convex portion 25 and the concave portion 26, a top portion 27 is formed at the apex of the convex portion 25, and a bottom portion 28 is formed at the bottom of the concave portion 26. Further, the distance between the top portions 27 of the adjacent convex portions 25 forms the groove pitch P, and the depth from the top portion 27 to the bottom portion 28 forms the groove depth D. In the structure shown in the figure, the top portion 27 of the convex portion 25 and the bottom portion 28 of the concave portion 26 are formed to be sharp, and constitute a complete V-shaped structure as a whole. The advantage of such a V-shaped groove structure is that the base is thick and stable in shape, and no change in shape occurs. As a numerical example, the pitch P of the groove structure is, for example, 0.5 mm, the groove depth D is, for example, 1.5 mm, and 80 grooves are formed in the range of the side surface of the anode 20 of 40 mm. (C) shows the enlarged view of the groove part of the trunk | drum 23 similarly, but unlike (b), the top part 33 and the bottom part 34 are not sharp but are formed in the curved surface form. An advantage of such a structure is that, as will be described later, electric field concentration at the start of lighting can be prevented.

  Here, the structure of the groove provided in the anode is not limited to that shown in FIG. 3A to 3E illustrate another embodiment of the groove structure. (A) is that the groove direction of the groove part 24 provided in the body part 23 of the anode 20 is formed not in the circumferential direction of the anode 20 but in the direction in which the anode 20 extends. In (b), the groove portion 24 is formed not in the body portion 23 but in the cone portion 22. Moreover, the groove part 24 can also be provided in both the cone part 22 and the trunk | drum 23. FIG. In (c), the groove direction of the groove part 24 provided in the body part 23 is spiral, and the groove is formed continuously. In (d), the groove 20 provided in the body part 23 is formed in a mesh shape. In addition, the direction of a groove | channel is not limited to what is shown in a figure, Moreover, you may combine with the groove | channel structure shown to (a), (b). Furthermore, a net-like groove can be formed by providing two spiral grooves shown in (c). (E) is one in which the groove portions 20 are randomly formed in the body portion 23. These laser beams are randomly drawn to form irregular grooves in the body part 23 as a result. Therefore, the laser irradiation is irradiated irregularly in the direction with respect to the surface of the body portion 23.

  In the present invention, the “side surface” of the electrode means not only the body portion but also the cone portion. In the above-described embodiments (FIGS. 2A, 3A, 3C, D, and E), the groove portion 24 is provided in the front portion of the body portion 23, but the body portion 23 is provided. It can also be formed over the entire side surface of the film, or can be provided in a specific part. Further, the cone portion is not limited to a truncated cone shape, and includes a curved shape. Moreover, although the said Example illustrated about the case where the groove part 24 is provided in the anode 20, the same groove part can also be provided in a cathode. Furthermore, in an AC-lighted discharge lamp, one or both of the above-described portions can be provided. Further, the groove structure of the present invention is not limited to the above structure, and includes other structures.

The short arc type discharge lamp of the present invention improves the thermal emissivity from the electrode by providing the groove structure as described above to the electrode. Defining the relationship further improves this effect. Hereinafter, this point will be described. Here, a model in which the shape of the electrode is not cylindrical but a groove structure is formed on a flat plate is considered. In FIG. 4, a groove 41 having the same structure as that shown in FIG. In this case, the relationship between the pitch P and depth D of the groove 41 and the thermal emissivity ε can be expressed by the following equation.
ε = ε0 / [1- (1-ε0) {1-sin (α / 2)}] (Expression 1)
Here, “ε0” is an emissivity specific to the material, and is about 0.4 when tungsten is used as the electrode material, for example. “Α” is an angle formed at the top or bottom of the groove. Effectively, the smaller α is, the larger the emissivity ε is, and the smaller value of α is that the ratio of the pitch P to the groove depth D, that is, the case where D / P is large. Focused on what it meant.

  FIG. 5 shows the relationship between the angle and the thermal emissivity in the groove structure shown in FIG. 2, and shows a calculation result obtained approximately by the flat plate structure shown in FIG. The groove angle (top and bottom) is changed to 10 °, 20 °, 30 °, 40 °, 50 °, 60 °, 70 °, 80 °, 90 °, 180 °, and the groove pitch is the same. Then, the groove depth D and the pitch ratio D / P are obtained, and the thermal emissivity of each is obtained from the above equation 1.

  Here, the angle 180 ° of the V-groove means a planar state without a groove. As a result of this calculation, it is shown that the emissivity of the structure provided with the V-groove is higher than that of the structure not provided with the V-groove. It can also be seen that when the angle of the V-groove is 30 ° or less, the emissivity in the groove is as high as 0.7 or more.

  Next, in order to verify the prediction based on the above calculation, an experiment for measuring thermal radiation at the electrode of the discharge lamp was performed. In the experiment, for a cylindrical tungsten having a diameter of 20 mm and a total length of 40 mm, the groove pitch P is changed to 0.5 mm, and the groove depth D is changed to 0.5 mm, 0.75 mm, 1.0 mm, and 1.5 mm. Four types of electrodes were prepared. And these four electrodes were heated up to about 2000 degreeC by the high frequency heating, and the thermal emissivity with respect to each electrode was measured. The measurement was performed using a thermopyrometer having a wavelength λ = 0.68 μm.

  Although the experimental results are shown in FIG. 6, the relationship between the groove depth D and the pitch P indicates that the emissivity is 0.7 when P / D ≧ 2, and the effect is obtained as compared with the case where no groove is provided. I understand that. Further, when the thermal emissivity of the electrode coated with the tungsten fine particles shown in FIG. 9 described in the prior art was measured in the same manner, the emissivity was about 0.6. That is, it can be seen that, by adopting a configuration of P / D ≧ 2 in the groove structure of the present invention, the thermal emissivity can be increased to 0.7, which is superior to the case of applying conventional tungsten fine particles. . Also, even when the groove portion is provided, depending on the angle of the groove, the effect may be inferior to that when the tungsten fine particles are applied (for example, when P / D = 1). It is shown that pitch and depth are extremely important.

  The method of processing the groove is a method of irradiating laser light. In particular, when the groove pitch is about 150 μm to 500 μm and the groove depth is about 2 to 3 times the pitch, laser processing using a pulse laser or the like is suitable. In this case, the curved surface formed at the bottom of the groove as shown in FIG. 2C can be processed by appropriately selecting the focal point of the laser beam.

  Next, the life characteristics of the short arc type high-pressure discharge lamp having the electrode of the present invention will be described. The relationship between lighting time and illuminance was measured for the discharge lamp having the groove structure of the present invention and the discharge lamp having an electrode coated with tungsten powder. The discharge lamp of the present invention is a lamp having a rated input of 12 KW, a rated current of 120 A, a mercury filling amount of 24 mg / cc, and using xenon as a buffer gas. The anode has a cylindrical shape with a diameter of 29 mm and a total length of 60 mm. A part having a diameter of 10 mm and an opening angle of the cone part of 120 ° was used. The groove structure is formed by laser processing and has a groove pitch of 200 μm and a groove depth of 600 μm, which is the structure shown in FIG. Moreover, the same discharge lamp was employ | adopted as the discharge lamp for a comparison except having apply | coated the tungsten powder instead of forming a groove part in an anode.

  FIG. 7 shows the experimental results. The vertical axis represents the illuminance ratio with respect to the illuminance at the start of lighting, and the horizontal axis represents the elapsed lighting time. As shown in the figure, the short arc type high-pressure discharge lamp of the present invention is markedly improved in terms of the illuminance maintenance rate as compared with the conventional short arc type high-pressure discharge lamp. That is, while the conventional short arc type high pressure discharge lamp attenuates the illuminance maintenance rate to 85% or less after lighting for 200 hours, the short arc type high pressure discharge lamp of the present invention can be operated for about 800 hours. The illuminance maintenance rate is maintained at a value close to 90%. This means that the heat emissivity from the anode surface is improved due to the groove structure applied to the electrode, and the heat generated by the lamp lighting is radiated efficiently. As a result, it can be understood that high illuminance can be maintained for a long time by preventing the tungsten from being scattered and evaporated.

  As described above, by forming an electrode having a predetermined groove depth and groove pitch, it is possible to remarkably increase the heat radiation from the electrode. However, depending on the groove structure, a substantial disconnection of the electrode may occur. It was confirmed that the area was reduced, and the heat release probability due to heat conduction from the electrode through the molybdenum foil or the external lead was reduced. Generally, the heat release due to heat conduction is proportional to the cross-sectional area of the electrode, and even if the groove structure is formed as in the present invention, if the groove depth with respect to the electrode diameter becomes too large, the electrode It was confirmed that the thermal radiation characteristics from Specifically, in the groove structure, when the groove depth is deeper than 12% with respect to the diameter of the electrode, the heat conduction is hindered due to the reduction of the cross-sectional area, and the temperature of the electrode is reduced. It turned out that it cannot be lowered effectively.

  In addition, the short arc type discharge lamp having the groove structure of the present invention is effective in terms of the temperature drop of the electrode and the resulting illuminance maintenance rate. Occasionally, there was a problem that a good lamp could not be lit. FIG. 8 shows the depth of the groove and the occurrence of abnormal discharge. It can be seen that the occurrence of abnormal discharge becomes more pronounced as the depth of the groove increases. This is considered to be because when the apex, which is the tip of the groove, has an acute angle, the electric field tends to concentrate and a corona discharge formed at the beginning of lighting is formed at the apex of the tip. Further, when the bottom of the groove has an acute angle, it is considered that corona discharge is likely to occur due to the hollow effect.

  In the present invention, in order to reduce the occurrence of such abnormal discharge, it is preferable to form a curved surface instead of sharpening the top or bottom of the groove as shown in FIG. Such a curved surface shape may have a curvature radius of about 5 μm, for example. And since such a curved surface shape is meaningful in eliminating the pointed tip, it can be similarly formed on the electrodes of some embodiments of FIG.

  The curved surface provided in such a groove is processed by, for example, buffing an acute angle portion on the outer peripheral surface and then performing electrolytic polishing in a caustic soda solution having a concentration of 10%. Moreover, it can form in the bottom part of a groove | channel by making the front-end | tip shape, such as a diamond cutting grindstone etc. which process a groove part into the shape which carried out the round beforehand. It can also be formed by heat treatment at a high temperature in a vacuum. Specifically, the V-shaped groove can be curved by heat-treating at 2000 ° C. for 120 minutes.

  The groove structure of the present invention is particularly effective in a lamp having a high electric input, and specifically, is effective in a short arc type discharge lamp having an input current to the discharge lamp of 100 amperes or more.

An overall view of a short arc type high pressure discharge lamp is shown. The enlarged view of the anode of the short arc type high pressure discharge lamp of this invention is shown. 1 shows an embodiment of an anode of a short arc type high-pressure discharge lamp of the present invention. The drawing for demonstrating the effect of the groove structure of this invention is shown. The effect of the groove structure of this invention is shown. The effect of the groove structure of this invention is shown. The effect of the groove structure of this invention is shown. The effect of the groove structure of this invention is shown. Shows conventional electrode structure

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Short arc type high pressure discharge lamp 11 Light emission tube part 12 Sealing tube part 13 Metal foil 14 External lead 20 Anode 21 Tip part 22 Cone part 23 Body part 24 Groove part 25 Convex part 26 Concave part 27 Top part 28 Bottom part 30 Cathode P Groove pitch D Groove depth

Claims (1)

In a short arc type high pressure discharge lamp having a set of tungsten electrodes in the arc tube,
At least one tungsten electrode among the tungsten electrodes has a pitch between adjacent top portions formed by laser processing on at least a part of a side surface of 150 μm to 500 μm and a depth of 2 to 3 times the pitch. A short arc type high-pressure discharge lamp having a V-shaped groove.

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