Short arc type discharge lamp and manufacturing method of the short arc type discharge lamp

Abstract

To provide a short arc type discharge lamp which has a characteristic that is similar to the short arc type discharge lamp into which a mixed gas having a conventional xenon gas or a xenon gas as a main component is sealed, and which can be replaced.SOLUTION: A short arc type discharge lamp 10 seals a mixed gas to which a xenon gas having an ionization energy is higher than that of mercury by using an argon gas of which the ionization energy is higher than that of a xenon gas as a main component with mercury into an electric discharge tube 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a short arc type discharge lamp (mercury lamp), and in particular to a discharge gas sealed in a discharge tube. [Background technology]

[0002] In a short arc type discharge lamp, a pair of electrodes (anode, cathode) are placed opposite each other inside a discharge tube, and discharge gas is enclosed inside. An arc discharge is generated by applying a voltage between the pair of electrodes, and light in the ultraviolet wavelength range, including i-lines, is emitted as continuous spectrum light. Such short arc type discharge lamps are used in the exposure process of semiconductor manufacturing, and are capable of emitting high-power ultraviolet light.

[0003] In order to improve the starting performance of the lamp and to obtain a heat retention effect for the gas and the discharge tube, xenon (Xe) gas or a mixed gas mainly composed of xenon gas is usually sealed inside the discharge tube (see, for example, Patent Document 1).

[0004] Meanwhile, focusing on the fact that argon gas, krypton gas, and neon (Ne) gas have a higher thermal conductivity than mercury, a short-arc type discharge lamp has been proposed in which at least one of these rare gases is enclosed in the discharge tube (see Patent Document 2). In this lamp, the tip of the cathode is configured with a protrusion formed on the tip surface of a truncated cone shape to prevent deformation and wear of the tip of the cathode. It is also described that the influence of disturbances from the outside (such as cold wind) is prevented by adding xenon gas, which has a lower thermal conductivity than mercury, to argon gas, krypton gas, and neon gas, which have a higher thermal conductivity than mercury. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-151501 A [Patent Document 2] JP 2003-257364 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional short arc discharge lamps that contain xenon gas or a mixed gas mainly composed of rare gases have good lamp starting properties, heat retention, etc. If argon gas or krypton gas is filled in the discharge tube instead of the xenon gas as a buffer gas, the amount of ultraviolet radiation increases, but it also leads to unstable arc discharge, reduced illuminance, and non-uniformity. In other words, the advantages of conventional short arc discharge lamps that contain xenon gas or a mixed gas mainly composed of xenon gas are lost.

[0007] An object of the present invention is to provide a short arc type discharge lamp which has the same characteristics as, and can replace, a conventional short arc type discharge lamp filled with xenon gas or a mixed gas containing xenon gas as a main component. [Means for solving the problem]

[0008] The present invention is a short arc type discharge lamp (mercury lamp) having a discharge tube and a pair of electrodes arranged in the discharge tube, in which a mixed gas containing argon gas and at least one rare gas having a lower ionization energy than argon gas is enclosed. For example, the discharge lamp can be started by a breakdown voltage lower than the breakdown voltage when only xenon is enclosed in the discharge tube.

[0009] As the rare gas, xenon gas or krypton gas can be used. Alternatively, both gases may be rare gases. The mixed gas can be filled with argon gas and at least one rare gas. For example, a mixed gas of argon gas and xenon gas is filled.

[0010] In the present invention, the mixing ratio of at least one rare gas to the mixed gas is equal to or lower than the mixing ratio of argon gas. Mixed gases containing argon gas as the main component and mixed gases rich in argon gas are included in gases that satisfy the above-mentioned mixing ratio conditions. The mixing ratio can be expressed as a ratio of gas concentration (molar concentration), and the ratio of the charging pressures can be regarded as the mixing ratio.

[0011] For example, at room temperature (20°C±15°C), the mixing ratio of at least one kind of rare gas to the mixed gas can be in the range of 10% to 50%. When the filling pressure is high, for example, 1 atmosphere or more, the mixing ratio of at least one kind of rare gas to the mixed gas can be in the range of 10% to 30%. On the other hand, when the filling pressure is low, for example, less than 1 atmosphere, the mixing ratio of at least one kind of rare gas to the mixed gas can be in the range of 30% to 50%.

[0012] For example, the discharge tube may be a bulb-type discharge tube, and at least a portion of the anode in the pair of electrodes may be configured to be located at the maximum diameter portion of the discharge tube along the lamp axis.

[0013] A manufacturing method of a short arc type discharge lamp, which is another aspect of the present invention, includes the steps of forming a discharge tube, welding a pre-assembled mounting part to a sealing tube, and sealing argon gas at a predetermined ratio from an exhaust tube provided in the discharge tube, and after sealing in argon gas, sealing in xenon gas so that the xenon gas is mixed in the same ratio as or lower than the argon gas. Effect of the Invention

[0014] According to the present invention, it is possible to provide a short arc type discharge lamp that has the same characteristics as a conventional short arc type discharge lamp filled with xenon gas or a mixed gas containing xenon gas as a main component, and can be used as an alternative. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic plan view of a discharge lamp according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The short arc type discharge lamp 10 is a mercury lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (light emitting tube) 12 made of transparent quartz glass. A pair of electrodes 20, 30 made of, for example, tungsten are arranged facing each other (coaxially) within the discharge tube 12. On both sides of the discharge tube 12, sealing tubes 13A, 13B made of quartz glass are connected to the discharge tube 12 and formed integrally with it. Here, the discharge tube 12 is bulb-shaped, and mercury and a rare gas, which will be described later, are sealed in a discharge space DS within the discharge tube 12.

[0017] The cathode electrode 20 is supported by an electrode support rod 17A. Sealed in the sealed tube 13A are a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A that connects to an external power source, and a metal foil 16A that connects the electrode support rod 17A and the lead rod 15A. Similarly, the anode electrode 30 is sealed with mounting parts such as a glass tube (not shown) through which the electrode support rod 17B is inserted, a metal foil 16B, and a lead rod 15B. Furthermore, caps 19A and 19B are attached to the ends of the sealed tubes 13A and 13B, respectively.

[0018] When a voltage is applied to the pair of electrodes 20, 30, an arc discharge occurs between the electrodes 20, 30, and light is emitted toward the outside of the discharge tube 12. Here, the short arc type discharge lamp is configured as a high-output discharge lamp, and a power of 1 kW or more is input. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

[0019] In this embodiment, the rare gas sealed in the discharge tube 12 is a mixed gas containing argon (Ar) gas as a main component and xenon (Xe) gas as an additive, which can be said to be a mixed gas rich in argon gas.

[0020] In the periodic table, the ionization energy of an element is lower as it is written in the lower left and higher as it is written in the upper right. In terms of rare gases, the ionization energy is highest in the following order: helium (He) gas, neon (Ne) gas, argon gas, krypton (Kr) gas, and xenon gas. The ionization energy of mercury (Hg) is also lower than that of xenon gas.

[0021] In this embodiment, a mixed gas containing argon gas, which has a higher ionization energy than xenon gas, as a main component, and xenon gas, which has a higher ionization energy than mercury, is sealed inside discharge tube 12. The mixed gas is sealed inside discharge tube 12 so that the mixing ratio of xenon gas at the time of sealing is the same as or lower than the mixing ratio of argon gas.

[0022] When the pressure of the mixed gas is set to 1 atmosphere or more at room temperature (5°C or more and 35°C or less as specified in JIS Z8703), the mixing ratio of xenon gas is set to 10% to 30%. Here, the mixing ratio refers to the concentration ratio of the mixed gas filled in the discharge space DS, and the ratio can be adjusted by adjusting the filling pressure of each gas.

[0023] Furthermore, when the pressure of the mixed gas is equal to or less than 1 atmosphere at room temperature, or less than 1 atmosphere, the mixing ratio of xenon gas is set to 30% to 50%.

[0024] By thus sealing a mixed gas containing argon gas as the main component (rich state) inside the discharge tube 12, it is possible to obtain characteristics similar to those of a conventional short arc type discharge lamp containing xenon gas or a mixed gas containing xenon gas as the main component.

[0025] That is, when argon gas alone is enclosed in the discharge tube as the rare gas, the ultraviolet light intensity does not vary significantly compared to when conventional xenon gas or a rare gas mainly composed of xenon gas is enclosed in the discharge tube 12. However, since the ionization energy is high, it becomes difficult to transition to an arc discharge (main discharge) after lighting starts. Therefore, abnormal discharge is likely to occur after lighting starts, and in some cases, an arc may jump and cause distortion in the light-emitting tube.

[0026] On the other hand, xenon gas has a low ionization energy and is therefore prone to arc discharge. Therefore, by sealing a mixed gas of argon gas and xenon gas in discharge tube 12 at a mixing ratio in which argon gas is the main component, it is possible to radiate ultraviolet light with the same intensity as in the past while suppressing the occurrence of abnormal discharge.

[0027] In addition, in terms of starting the lamp, by filling discharge tube 12 with a mixed gas containing argon gas as the main component (rich state), which has a lower dielectric breakdown voltage than when xenon gas or a mixed gas containing xenon gas as the main component is filled, the starting performance can be improved or at least made equal.

[0028] The electrode 20, which is a cathode, and the electrode 30, which is an anode, are coaxially arranged along the lamp axis in the discharge tube 12, with their tips positioned at approximately the same distance from the center (middle) of the discharge tube 12, but an offset arrangement is also possible. Specifically, the tip of the electrode 30 can be configured to be located at the maximum diameter of the bulb-shaped discharge tube 12 along the lamp axis C. This makes it difficult for the flying arc to reach the discharge tube 12, and in combination with the inclusion of a mixed gas, it is possible to reliably suppress distortion of the discharge tube 12.

[0029] As described above, the short arc type discharge lamp of the present embodiment has the same characteristics as the conventional short arc type discharge lamp, and therefore can be substituted for the conventional discharge lamp. In addition, it is not only possible to simply substitute for the conventional discharge lamp, but also has economic advantages.

[0030] That is, argon gas is much cheaper and easier to obtain than xenon gas, so even if the economic situation makes the supply of xenon gas unstable, it will be possible to continue to provide short arc discharge lamps with the same functions as before.

[0031] Such a short arc type discharge lamp can be manufactured, for example, by the following manufacturing method.

[0032] First, the discharge tube is formed by a conventional method, and the mounting parts that have been assembled in advance are welded to the sealed tube. At this time, the position of the tip of the electrode that becomes the anode can be adjusted along the lamp axis and welded. Then, mercury and rare gas are sealed in through an exhaust tube (not shown) provided in the discharge tube. The rare gas is sealed in a predetermined ratio starting from argon gas, which is the main component, and then xenon gas is sealed in so that the mixture ratio is the same as or lower than that of argon gas. Note that a mixed gas adjusted to a predetermined mixture ratio may be sealed in from the beginning, or xenon gas may be sealed in first. It is also possible to seal krypton gas instead of xenon gas. Krypton gas also has a lower ionization energy than argon gas, and can obtain an effect similar to that of xenon gas.

[0033] A process of mixing (agitating) the gas may be provided, but the gas sealed in the discharge space DS can be caused to circulate and mix by going through a conventional lighting test (aging) that is well known in the art. EXAMPLES

[0034] The short arc type discharge lamp of this embodiment will be described below.

[0035] The short arc type discharge lamp of this embodiment is a discharge lamp corresponding to the short arc type discharge lamp of this embodiment, and is configured as a plurality of short arc type discharge lamps in which the mixture ratio of argon gas and xenon gas is changed.

[0036] Mercury was enclosed in the bulb-shaped discharge tube 12, and a mixed gas consisting mainly of argon gas with added xenon gas was enclosed at room temperature of about 15°C and 1 atmosphere. At this time, short arc type discharge lamps were created in which the mixture ratio of argon gas was enclosed as shown in Table 1. Then, an experiment was carried out in which a voltage of 8 kW was applied, the lamp was turned on and off repeatedly, and the occurrence and number of abnormal discharges, as well as the ultraviolet ray intensity, were measured.

[0037] As a comparison example, a short arc type discharge lamp filled with only xenon gas was also created, and experiments were conducted to confirm the discharge state and ultraviolet ray intensity by lighting it. However, in all short arc type discharge lamps, the cathode and anode were positioned so that the tip of the anode was at the maximum diameter position of the discharge tube along the lamp axis. The experimental results are shown in Table 1 below. However, the ultraviolet ray illuminance is expressed as a relative value when xenon gas only (100 percent Xe) is set to 100.

[0038] [Table 1]

[0039] As shown in Table 1, it was confirmed that the occurrence of abnormal discharge was suppressed by sealing a mixed gas containing argon gas as the main component, that is, a mixture ratio of 50% or more, inside the discharge tube.

[0040] On the other hand, it was confirmed that the ultraviolet ray intensity was approximately the same as that of a conventional short arc type discharge lamp filled with only xenon gas.

[0041] Furthermore, the breakdown voltage was measured for the short arc type discharge lamp of this embodiment, which contains mixed gas (Ar90%:Xe10%), mixed gas (Ar70%:Xe30%), and mixed gas (Ar50%:Xe50%), as well as the short arc type discharge lamp of the comparative example, which contains only xenon gas.

[0042] In the case of a short arc type discharge lamp with mixed gas (Ar90%:Xe10%), the breakdown voltage was 2.7 kV, in the case of a short arc type discharge lamp with mixed gas (Ar70%:Xe30%), the breakdown voltage was 2.8 kV, and in the case of a short arc type discharge lamp with mixed gas (Ar50%:Xe50%), the breakdown voltage was 3.4 kV. On the other hand, in the case of a short arc type discharge lamp filled with only xenon gas, the breakdown voltage was 4.5 kV, and the improvement in the lighting startability of the short arc type discharge lamp of this embodiment was confirmed.

[0043] As described above, it has been confirmed that the short arc type discharge lamp of this embodiment has the same characteristics as the conventional short arc type discharge lamp in which rare gas consisting of only xenon gas is enclosed, and is a short arc type discharge lamp with good lighting starting properties. [Explanation of symbols]

[0044] 10. Discharge Lamp 20 electrode (cathode) 30 electrode (anode)

Claims

1. A discharge tube; A pair of electrodes is disposed in the discharge tube, A short arc type discharge lamp characterized in that the gas sealed in the discharge tube is a mixed gas containing argon (Ar) gas and at least one rare gas having a lower ionization energy than argon gas, and the mixing ratio of the at least one rare gas to the mixed gas is the same as or lower than the mixing ratio of the argon gas.

2. 2. The short arc type discharge lamp according to claim 1, wherein the mixing ratio of said at least one rare gas to said mixed gas is in the range of 10% to 50%.

3. 2. The short arc type discharge lamp according to claim 1, wherein the mixing ratio of said at least one rare gas to said mixed gas is in the range of 10% to 30%.

4. 2. The short arc type discharge lamp according to claim 1, wherein the mixing ratio of said at least one kind of rare gas to said mixed gas is in the range of 30% to 50%.

5. 2. The short arc type discharge lamp according to claim 1, wherein the at least one rare gas is xenon (Xe) gas.

6. The discharge tube is a bulb-type discharge tube, 2. The short arc type discharge lamp according to claim 1, wherein at least a part of the anode of the pair of electrodes is located at a maximum diameter portion of the discharge tube along the lamp axis.

7. 7. The short arc type discharge lamp according to claim 1, wherein lighting is started by a breakdown voltage lower than the breakdown voltage when only xenon is enclosed in said discharge tube.

8. The discharge tube is molded, and the pre-assembled mounting parts are welded to the sealing tube. a step of filling the discharge tube with argon gas at a predetermined ratio through an exhaust pipe provided in the discharge tube; After the argon gas is charged, xenon gas is charged so that the xenon gas is mixed at a ratio equal to or lower than that of the argon gas. A method for manufacturing a short arc type discharge lamp, comprising:

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