JP5233657B2 - Discharge lamp - Google Patents

Description

  The present invention relates to a high-intensity and high-intensity discharge lamp, and more particularly to a discharge lamp characterized in that a material containing lanthanum (La) as an easily electron-emitting material is used as a cathode material.

In a discharge lamp in which mercury is sealed in a discharge space used as a light source for an exposure apparatus used for exposure processing, or in a discharge lamp in which xenon gas is sealed in a discharge space used as a light source in a projector or the like, tungsten It is known that when a cathode containing (W) as a main component contains lanthanum oxide (La ₂ O ₃ ) as an electron-emitting material, good electron emission characteristics are exhibited.

However, in a discharge lamp having a cathode containing lanthanum oxide (La ₂ O ₃ ) as an electron-emitting material, lanthanum (La) evaporates early and is depleted due to the high heat load applied to the cathode during lighting. The problem is that stable discharge cannot be maintained.
Therefore, in the technique shown in Japanese Patent Application Laid-Open No. 2006-286236, at least one kind selected from these metals is used by utilizing the characteristic that zirconium (Zr), hafnium (Hf) and the like are more easily combined with oxygen than tungsten. It is described that the presence of a metal oxide can suppress the formation of tungsten oxide. Tungsten oxide having a low melting point is suppressed from being liquid phase at about the operating temperature of the cathode, the electron-emitting material is stably supplied over a long period of time, and stable discharge is maintained for a long period of time. Will be able to.

Furthermore, it is described in the technique shown in Japanese translations of PCT publication No. 2005-519436 that it tried to achieve the improvement by adding an oxide or a carbide.
JP 2006-286236 A JP 2005-519436 Gazette

By coexisting at least one metal oxide selected from zirconium (Zr), hafnium (Hf), etc., it has been possible to prevent lanthanum (La) from evaporating early and being depleted. Lanthanum (La) is still insufficient to provide a long-life discharge lamp due to insufficient reduction of the easy-electron emitting material contained as lanthanum (La ₂ O ₃ ). When lanthanum (La) is insufficient, the area covered with lanthanum (La) on the cathode tip becomes small, the work function increases, the temperature of the cathode rises, and deformation occurs, causing flickering. is there.

The present invention has been made in order to solve the above problems, and in a discharge lamp having a cathode containing lanthanum oxide (La ₂ O ₃ ) as an electron-emitting material, lanthanum oxide (La It aims to promote the reduction of ₂ O ₃ ), increase the supply amount of lanthanum (La), and provide a long-life discharge lamp.

The first invention of the present application has an anode and a cathode disposed inside the discharge vessel so as to face each other in the tube axis direction of the discharge vessel, and in the tungsten metal substrate, lanthanum metal oxide, zirconium In a discharge lamp in which the cathode is formed of a material containing a metal oxide , the number of carbons is larger than the number of oxygens when carbon and oxygen are compared with the number of atoms in the anode. It is characterized by being added.

According to the discharge lamp according to the first invention of the present application, since not only carbon (C) but also oxygen (O) is added to the anode, carbon monoxide (CO) in which carbon (C) is combined with oxygen (O). ) To be emitted into the inner space of the arc tube, and carbon atoms (C) can be diffused into the cathode. The carbon (C) diffused inside the cathode can reduce the lanthanum oxide (La ₂ O ₃ ) contained in the cathode and maintain the state where the tip of the cathode is covered with lanthanum (La). As a result, the operating temperature of the cathode is lowered to suppress the occurrence of flickering, and the life of the discharge lamp can be extended.
Furthermore, since a large portion of the anode 4 including the anode tip can be a carbon monoxide (CO) supply source, there is no fear that carbon monoxide (CO) for reducing lanthanum oxide (La ₂ O ₃ ) will be insufficient. Further, the supply of lanthanum (La) is also maintained, and a long-life discharge lamp can be provided. Further, since the diffusion rate of carbon (C) in the tungsten base metal is slower than the diffusion rate of oxygen (O), the number of carbon atoms (C) contained in the anode is determined from the number of oxygen atoms (O). By increasing the number, the number of carbon (C) and oxygen (O) reaching the surface of the anode by diffusion approaches, so that a sufficient amount of carbon monoxide (CO) can be generated.

  FIG. 1 is an explanatory cross-sectional view showing a configuration of a discharge lamp in which mercury is sealed in a discharge space used as a light source for an exposure apparatus used for exposure processing as an example of the discharge lamp of the present invention. Only the arc tube 2 which is a part of the discharge vessel 1 is allowed to pass through to show the internal structure.

The discharge lamp is made of a light transmissive material such as quartz glass, for example, and includes a discharge vessel 1 having a substantially spherical arc tube 2 and a sealing tube 3 extending outwardly continuously at both ends thereof. Inside, an anode 4 and a cathode 5 each made of tungsten (W), for example, are arranged facing each other in the tube axis direction of the discharge vessel 1. In the internal space of the discharge vessel 1, mercury and buffer gas as a light emitting substance or start-up assisting gas are sealed in predetermined amounts. For example, xenon gas is sealed as the buffer gas. Amount of enclosed mercury, for example in the range of 1~70mg / cm ^3, for example, is a 22 mg / cm ^3, it is enclosed amount of xenon gas in the range of for example 0.05 to 0.5 MPa, for example, 0.1MPa .

  When a high voltage, for example, 20 kV is applied between the electrodes of the anode 4 and the cathode 5, electrons fly from the cathode 5 to the anode 4 to cause dielectric breakdown between the electrodes, and subsequently, a discharge arc is formed, for example, a wavelength of 365 nm. Light including i-line and g-line having a wavelength of 435 nm is emitted.

  The anode 4 contains tungsten (W) as a main component and carbon (C) and oxygen (O) are added. The cathode 5 contains tungsten as a main component and has a tungsten content of less than 98% by weight. The tungsten metal substrate of the cathode 5 contains lanthanum (La) metal oxide as an electron-emitting material and zirconium (Zr) metal oxide as a stabilizing material for stabilizing the electron-emitting material. ing.

For example, carbon (C) contained in the anode 4 is dissolved in tungsten (W) and added in a single state. Oxygen (O) contained in the anode 4 is added in the state of a metal oxide such as chromium oxide (Cr ₂ O ₃ ) or aluminum oxide (Al ₂ O ₃ ).
Note that the anode 4 does not contain an easy-electron emitting material such as lanthanum oxide (La ₂ O ₃ ). Compared with tungsten containing thorium oxide (ThW), so-called triated tungsten, tungsten containing lanthanum oxide (La ₂ O ₃ ) has a lower heat-resistant temperature. This is because there is a risk of effect.

On the other hand, lanthanum oxide (La ₂ O ₃ ) contained in the cathode 5 is an electron-emissive material, and is reduced to release oxygen, move as a lanthanum atom in tungsten, and proceed to the tip of the cathode 5. A monoatomic electron emission cathode is formed covering the tip of 5. That is, when the tip of the cathode 5 is coated with a single atomic layer of lanthanum (La), the work function of the cathode 5 is reduced, the operating temperature of the cathode 5 is lowered, and the occurrence of flickering is suppressed. Can be extended.

Zirconium oxide (ZrO ₂ ) contained in the cathode 5 is a stabilizing material that stabilizes the electron-emitting material, and it is possible to suppress liquid phase formation due to the formation of tungsten oxide and the lowering of the melting point. Is. In the absence of zirconium (Zr) or the like, oxygen (O ₂ ) generated by reducing lanthanum oxide (La ₂ O ₃ ) combines with tungsten (W) to form tungsten oxide (WO ₃ ). Generate. Tungsten oxide (WO ₃ ) forms a compound having a low melting point with lanthanum oxide (La ₂ O ₃ ), and the liquid phase makes it possible to rapidly increase the transport speed of the emitter, resulting in consumption. Cause it to occur.

Therefore, zirconium oxide (ZrO ₂ ) is added to suppress the formation of tungsten oxide (WO ₃ ) because zirconium (Zr), which is more easily combined with oxygen than tungsten (W), functions as an oxygen getter. . Since a compound having a low melting point is not formed, the liquid phase is suppressed from being about the operating temperature of the cathode 5, and lanthanum (La) can be prevented from evaporating early and depleted.

  The discharge lamp shown in FIG. 1 has been described as being filled with mercury. However, in the discharge lamp used as a light source in a projector or the like, the inclusion is replaced with mercury and only xenon gas is used. An anode to which (C) and oxygen (O) are added can also be used.

Here, when a test was performed by applying a configuration in which carbon (C) and oxygen (O) were added to the anode 4, the life of the discharge lamp was improved. As the reason for the improvement, it is presumed that the following phenomenon occurs.
FIG. 2 is a schematic diagram for explaining the reaction between carbon (C) and oxygen (O) added to the anode 4.
Since the anode 4 becomes hot during the operation of the discharge lamp, the carbon (C) added to the anode 4 acts as a reducing agent on the metal oxide contained in the anode 4 and reduces the metal oxide. To generate carbon monoxide (CO). For example, when aluminum oxide (Al ₂ O ₃ ) is contained as a metal oxide, a reaction represented by the following chemical formula occurs.
Al ₂ O ₃ + 3C ⇔ 2Al + 3CO
Carbon monoxide (CO) decomposes into carbon (C) and oxygen (O), dissolves in the tungsten base metal constituting the anode 4, and diffuses together with the carbon (C) contained in the anode 4. To reach the surface of the anode 4.

  Since the diffusion rate of carbon (C) in the tungsten base metal is slower than the diffusion rate of oxygen (O), the number of carbon atoms (C) contained in the anode 4 is the number of oxygen atoms (O). More than the number is preferred. By making the number of carbon atoms (C) contained in the anode 4 larger than the number of oxygen atoms (O), the number of carbon (C) and oxygen (O) reaching the surface of the anode 4 by diffusion approaches. This is because a sufficient amount of carbon monoxide (CO) can be generated.

  The simple carbon (C) does not evaporate because of its low vapor pressure, and the carbon (C) contained in the anode 4 is not transported to the inner space of the arc tube 2 or the cathode 5. However, by adding not only carbon (C) but also oxygen (O) to the anode 4, the carbon (C) and oxygen (C) reaching the surface of the anode 4 become carbon monoxide (CO). Then, it is discharged into the inner space of the arc tube 2.

Carbon monoxide (CO) released into the inner space of the arc tube 2 is partly transported into the arc by diffusion and convection in the discharge gas, and decomposed into carbon (C) and oxygen (O) by the high temperature of the arc. At the same time, carbon is ionized into positive ions (C ⁺ ) and oxygen is ionized into negative ions (O ⁻ ). The carbon ions (C ⁺ ) move in the arc by an electric field, reach the tip of the cathode 5, recombine with electrons emitted from the cathode 5 to become carbon atoms (C), and diffuse into the cathode 5. Go.

The carbon (C) diffused inside the cathode 5 reacts with lanthanum oxide (La ₂ O ₃ ) contained in the cathode 5 as follows to reduce lanthanum oxide (La ₂ O ₃ ).
La ₂ O ₃ + 3C ⇔ 2La + 3CO
The single lanthanum (La) produced by reduction diffuses through the crystal grain boundary of tungsten (W) and proceeds to the tip of the cathode 5. By covering the tip of the cathode 5 with a single atomic layer of lanthanum (La), the work function of the cathode 5 is reduced, the operating temperature of the cathode 5 is lowered, deformation of the tip of the cathode 5 is suppressed, and flickering occurs. The life of the cathode 5 can be extended.

The temperature of the anode 4 at the time of lighting of the discharge lamp becomes very high, and the half including the tip of the anode becomes 2000 ° C. or more including the inside. Since the reaction between carbon (C) and oxygen (O) occurs at a temperature of about 2000 ° C. or higher, by adding carbon and oxygen to the anode 4, half of the anode 4 including the anode tip is oxidized. It can be a source of carbon (CO). Since the volume of the portion serving as the supply source of carbon monoxide (CO) is large as described above, there is no fear that carbon monoxide (CO) serving as a reducing material for reducing lanthanum oxide (La ₂ O ₃ ) will be insufficient. The supply of (La) is also maintained, and a long-life discharge lamp can be provided.

In addition, when lanthanum oxide (La ₂ O ₃ ) is used as the electron-emitting material, the reduction has not progressed sufficiently so far that lanthanum (La) is insufficient and the temperature at the tip of the cathode 5 rises. It could not be used for large discharge lamps with high power. However, by adding carbon (C) and oxygen (O) to the anode 4 and diffusing the carbon (C) inside the cathode 5, it is easy to emit electrons into a large discharge lamp to which high power is applied. Even when lanthanum oxide (La ₂ O ₃ ) is adopted as a material, lanthanum (La) can be sufficiently supplied.

Then, the manufacturing method of the anode 4 which has added carbon (C) and oxygen (O) in tungsten (W) is demonstrated.
Tungsten as an anode material is formed by powder metallurgy. First, chromium (Cr) or aluminum (Al) nitrate is added to a purified ammonium paratonguenate solution, and evaporated and roasted to produce a doped tungsten oxide powder. This is reduced with hydrogen to obtain a prepared tungsten powder. Chromium (Cr) or aluminum (Al) nitrate becomes a metal oxide for adding oxygen (O).

  Then, powders having different average particle diameters are mixed so that the prepared tungsten powder has an appropriate particle size distribution, a binder such as stearic acid is added, the mold is filled, and pressure-molded to obtain a rod-shaped molded body. Subsequently, the temperature is gradually raised in hydrogen to skip the binder, and the temperature is further raised to obtain a temporary sintered body. At this time, if the dew point of hydrogen is low, the residual amount of carbon (C) derived from the binder increases. Therefore, the amount of carbon dope can be controlled by adjusting the dew point of hydrogen.

  Furthermore, a sintered rod can be obtained by conducting current sintering of the temporary sintered rod in hydrogen. During the sintering process, the amount of oxygen and carbon contained decreases. The rate of reduction varies depending on the thickness of the pre-sintered rod, the particle size distribution of the raw powder, the apparent density of the pre-sintered rod, the sintering temperature (conducting current), and the sintering time. Adjust the amount of chromium (Cr) or aluminum (Al) in the adjusted powder, and adjust the dew point of hydrogen during pre-sintering for the carbon amount. A tungsten sintered rod with a certain amount is obtained.

Next, an analysis method for verifying that carbon (C) and oxygen (O) are added to the anode material tungsten (W) will be described.
First, a method for analyzing the amount of carbon (C) added to tungsten (W) as the anode material will be described. The analysis method is tungsten / molybdenum industry association standard, tungsten and molybdenum analysis method, 16. According to the total carbon quantification method. Quantitative methods for total carbon include a) combustion-dielectric constant method, b) combustion-coulometric method, c) combustion-electric heat conduction method, d) combustion-infrared absorption method (integral method), e) combustion-infrared absorption method ( (Circulation method) is mentioned, but any may be used.
Here, a) the combustion-dielectric constant method will be described.
The cathode 5 is crushed to form a tungsten powder sample, and the sample is heated in an oxygen stream to oxidize the carbon to carbon dioxide, which is absorbed in a certain amount of sodium hydroxide solution, and the conductivity of the solution before and after absorption. By measuring the change in the carbon content, the carbon content can be determined.

It is preferable that carbon (C) is added to the anode material tungsten (W) in a range where the carbon content is 10 wtppm or more and 100 wtppm or less as an analysis result. Since the mass of carbon (C) is light, if the amount is 10 wtppm, it can be said that there is a sufficient amount for supplying carbon (C) into the cathode 5 and reducing lanthanum oxide (La ₂ O ₃ ). .
In addition, if the amount of carbon (C) added to tungsten (W) as the anode material becomes too large, the melting point of tungsten (W) as the anode material will be lowered, and it may be melted when the discharge lamp is turned on. come. Therefore, the amount of carbon (C) added to tungsten (W) as the anode material is preferably 100 wtppm or less.

  Next, a method for analyzing the amount of oxygen (O) added to the anode material tungsten (W) will be described. 15. Analysis method is tungsten / molybdenum industry association standard, tungsten and molybdenum analysis method, 15. According to oxygen determination method. Examples of the method for quantifying oxygen include a) hydrogen reduction weight method, b) oxygen weight method, and c) inert gas melting-infrared absorption method. For example, in the a) hydrogen reduction gravimetric method, oxygen can be quantified by heating a sample in a hydrogen stream to reduce it and measuring its weight.

  Tungsten (W) of the anode material so that the number of oxygen atoms (O) calculated from the amount of oxygen obtained as an analysis result is greater than the number of carbon atoms (C) calculated from the analysis result of carbon content. It is preferable that oxygen (O) is added therein. As described above, since the diffusion rate of carbon (C) in the tungsten base metal is slower than the diffusion rate of oxygen (O), the number of carbon atoms (C) contained in the anode 4 is changed to oxygen atoms (O ), The number of carbon (C) and oxygen (O) reaching the surface of the anode 4 due to diffusion approaches, so that a sufficient amount of carbon monoxide (CO) can be generated. is there.

In the above embodiment, the carbon (C) is described as being dissolved in the anode 4. However, carbon (C) can be added to the anode 4 as another form.
Another embodiment will be described with reference to FIG. As shown in the figure, the outer surface of the anode 4 is carburized to increase the amount of carbon in the carburized portion 41 formed on and around the metal surface of the anode 4. The carburizing process is performed by vacuum carburizing that is heated in a vacuum corresponding to the thickness to be carburized, and the carburized portion 41 is configured as tungsten carbide (W ₂ C).

Even when carbon (C) added to the anode 4 is in the form of tungsten carbide (W ₂ C) by carburizing treatment, the carbon (C) is in a state of carbon monoxide (CO) bonded to oxygen (O), The carbon atoms (C) can be diffused into the cathode 5 by being discharged into the inner space of the arc tube 2. The carbon (C) diffused inside the cathode 5 can reduce the lanthanum oxide (La ₂ O ₃ ) contained in the cathode 5 and maintain the state where the tip of the cathode 5 is covered with lanthanum (La). As a result, the operating temperature of the cathode 5 is lowered, and the occurrence of flickering can be suppressed and the life can be extended.

Sectional drawing for description which shows the structure in an example of the discharge lamp of this invention Sectional drawing for demonstrating the anode of the discharge lamp of this invention Sectional drawing for demonstrating the anode of the discharge lamp of this invention

Explanation of symbols

1 discharge vessel 2 arc tube 3 sealing tube 4 anode 5 cathode

Claims (1)

The discharge vessel has an anode and a cathode disposed so as to face each other in the tube axis direction of the discharge vessel, and the tungsten metal substrate contains lanthanum metal oxide and zirconium metal oxide. In a discharge lamp in which the cathode is formed of a material,
A discharge lamp, wherein carbon and oxygen are added to the anode such that the number of carbons is larger than the number of oxygens when compared in terms of the number of atoms .

Images