JP2001135274A - Short-arc type discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high emission efficiency and satisfactory stability of illuminance for the purpose of extending lifetime of short-arc type discharge lamps used for exposure apparatus for IC and the like. SOLUTION: A race gas is sealed in an interior 21 of a light-emitting tube 1 is such a race gas with relatively high molecular weight such as Xe, Kr or Ar and the like mixed with such a race gas with relatively low molecular weight as He or Ne and the like at 5 to 40%, and it is sealed at above 2 atmospheric pressure or so. Also, its anode consists of a cylindrical trunk portion 14, a taper portion 13 and a tip flat portion 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp, in particular, to a high stability used in an exposure apparatus such as a semiconductor integrated circuit (IC).
Also, the present invention relates to a short arc discharge lamp having a long life.

[0002]

2. Description of the Related Art Various techniques are required for an IC manufacturing process. One of them is exposure technology. A desired pattern is formed on a semiconductor substrate (substrate) using a resin (resin) that is cured by irradiation with a light beam such as ultraviolet rays. In general, a short arc discharge lamp is used for an exposure apparatus used in a manufacturing process of such an electronic device. Among them, with the recent high integration of IC devices, a discharge lamp that efficiently generates an i-line having a short emission wavelength of about 365 nm has become mainstream.

Since the progress of IC technology is extremely rapid, IC
Manufacturing requires large capital investment and price competition is extremely intense. Therefore, controlling the manufacturing cost is indispensable for the success of the IC maker, and one of the consumables used in the IC manufacturing process.
As for the short arc type discharge lamp, which is one of them, there is a severe demand for cost reduction by extending the life. In the conventional short arc type discharge lamp, as a method of extending the life, the reduction of the illuminance maintenance rate (illuminance reduction rate with respect to the lighting time) by the shape of components or members constituting the discharge lamp such as electrodes and various treatments, It has been practiced to extend the usable time substantially by improving the luminous efficiency of the i-line and increasing the illuminance on the exposed surface.

A short arc type discharge lamp used in an IC exposure apparatus using i-line is used in an exposure apparatus for a liquid crystal display panel (LDP) or a printed circuit board (PCB) in order to increase the luminous efficiency of i-line. Compared to a commonly used short arc discharge lamp, the amount of enclosed mercury is reduced by half.
It is generally carried out to about 1/10. As a result, the internal pressure of the discharge tube during lighting is reduced, and the radiance is reduced. Therefore, a method of increasing the pressure of the rare gas sealed as the buffer gas to compensate for this is adopted.
On the other hand, it is known that this has an effect of suppressing the consumption of the electrode and suppressing a decrease in the illuminance maintenance ratio.

In an exposure apparatus, a part of the emitted i-ray is used not only for exposure but also for focus adjustment at the time of exposure. Therefore, high illuminance stability is required. However, recently, a light source having a shorter exposure wavelength, such as an excimer laser, is used in combination. As a result, the technology of exposing while scanning on the semiconductor substrate becomes effective,
Higher illuminance stability is required.

[0006]

However, it has not been possible to sufficiently meet the above-mentioned demand for extending the life of the light source for an exposure apparatus. Therefore, an object of the present invention is to meet the above-mentioned requirements,
An object of the present invention is to provide a short arc discharge lamp having high luminous efficiency and good illuminance stability.

[0007]

Means for Solving the Problems To overcome the above-mentioned problems,
In order to achieve the above object, according to the short arc discharge lamp of the present invention, as the rare gas sealed inside the arc tube in which the cathode and the anode are arranged to face each other, 2
A rare gas having a high molecular weight such as xenon (Xe), krypton (Kr), or argon (Ar) at a pressure higher than atmospheric pressure;
A gas mixed with a low molecular weight rare gas such as 0% helium (He) or neon (Ne) is used.

The anode is composed of a substantially cylindrical body, a tapered part, and a flat end. The distance L (mm) from the tip of the anode at which the current density of the anode is 0.3 A per 1 mm ² is 0.05 when the discharge current is I (A).
It is assumed that I <L <0.08I. The flat end of the anode
The diameter should be less than twice the distance between the cathode and the anode. The current density of the anode is set to 3.5 A or less per 1 mm ² .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a preferred embodiment of a short arc discharge lamp according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a preferred embodiment of a short arc discharge lamp according to the present invention. A short arc type discharge lamp 20 shown in FIG. 1 includes an arc tube 1, a cathode 2, an anode 3, internal lead rods 4 and 5 of these electrodes 2, 3, an arc tube.
It is constituted by metal foils 8 and 9 for connecting the sealing portions 6 and 7 of the first, the outer lead bars 10 and 11 and the inner lead bars 4 and 5 to the outer lead bars 10 and 11, respectively. And the internal space of the arc tube 1
A rare gas having a high thermal conductivity, that is, a rare gas having a low molecular weight, is sealed in 21.

FIG. 2 is an enlarged view of the anode 3 of the short arc discharge lamp 20 shown in FIG. As shown in FIG. 2, the anode 3 is composed of a flat tip portion 12 facing the cathode 2, a chamfered conical portion, that is, a tapered portion 13, and a substantially cylindrical body portion.

Next, referring to FIGS. 1 and 2, detailed specifications of the short arc type discharge lamp of the present invention will be described. The arc tube 1 is made of light transmissive glass such as quartz glass having an outer diameter of 70 mm, for example. The cathode 2 is made of, for example, tungsten containing about 2% by weight of thorium, and has a diameter of about 10%.
mm. The tip facing the anode 3 is formed at an acute angle, and faces the tip flat portion 12 of the anode 3 at an interval of about 4.5 mm. On the other hand, the anode 3 has a diameter of about 7 mm,
It has a flat portion 12 with a current density of about 0.3 A per ² and a body portion 14 having a diameter of about 25 mm. The flat tip 12 of the anode 3 where the current density of the anode 3 is 0.3 A per 1 mm ²
The distance L (mm) from is approximately 3.5 mm. Also,
About 4.5 mg of mercury per cc is sealed in the interior 21 of the arc tube 1.

First, the results of a preliminary experiment for confirming the improvement in illuminance by the high-pressure rare gas sealed inside the arc tube 1 will be described. Xenon (Xe) as a rare gas,
A relatively high molecular weight rare gas such as krypton (Kr) or argon (Ar) was sealed. A total of 18 types of discharge lamps were manufactured, each having a different sealing pressure at room temperature. And
The illuminance on the exposure surface of the IC exposure apparatus and the illuminance stability were compared. These discharge lamps all turned on at 2500W. The discharge current of the discharge lamp in this case was 100A. Table 1 shows the experimental results.

[Table 1]

As is apparent from Table 1, the filling pressure of each of the rare gases Xe, Kr and Ar is set to 1.
Experiments were performed at 0, 2.0, 4.0, 7.0, 10.0 and 13.0 atmospheres. The illuminance was measured five times for each sealed pressure, and the average of these measurements was taken as the illuminance of the discharge lamp.
Since the illuminance difference between these five illuminance measurements was 0.02, it can be said that the rare gas sealing pressure for improving the illuminance by at least 0.02 or more is 2.0 atm or more. The illuminance stability is a value obtained by dividing the difference between the maximum value and the minimum value of illuminance during continuous illuminance measurement for 25 seconds by the average illuminance for 25 seconds. Furthermore, this is an average value obtained by performing this measurement five times, and it was confirmed that the illuminance stability was reduced when the sealing pressure was increased.

Next, a description will be given of a mixing experiment of a rare gas filled in the internal space 21 of the arc tube 1 of the short arc discharge lamp according to the present invention. A discharge lamp in which Xe, Kr and Ar are sealed as a rare gas at 2 atm and 7 atm, respectively, and neon (Ne) and helium (He) which are relatively low molecular weight rare gases are mixed at a volume ratio of 5% to 40%. A total of 28 types were manufactured, and the illuminance on the exposure surface of the IC exposure apparatus and the illuminance stability were compared. Table 2 shows the results of this experiment. Illuminance stability
It is a range of five measurements and has a value of about 0.2. Here, superiority was shown in all discharge lamps in which Ne or He was sealed. Also, no decrease in illuminance was observed.

[Table 2]

[0016] When the sealing pressure of a plurality of rare gases at room temperature is 2 atm or more, setting the volume ratio of Ne and He to 40% or more with respect to other rare gases is difficult due to the problem of the sealing method. It could not be sealed at a stable rate. Therefore, in order to improve the illuminance and improve the illuminance stability by mixing and encapsulating Ne or He with Xe, Kr or Ar, it is necessary to set Ne or He at a normal temperature of more than 2 atmospheres. Or Xe, Kr or Ar of He
Is effective when the volume ratio to is 5% to 40%. This is because the thermal conductivity of relatively low molecular weight Ne and He causes the rare gas to be mixed, X
e, higher than Kr or Ar.
From this, it is apparent that the same effect can be obtained even when a gas containing a mixture of rare gases of Ne and He is sealed. Further, X, which is the rare gas to be mixed,
It is clear that a similar effect can be obtained when e, Kr and Ar are mixed.

Next, an experiment on the current density of the anode 3 and the life of the discharge lamp will be described. The current density is a value obtained by dividing the discharge current by the sectional area of the anode 3. As for the life, the initial illuminance was set to 100%, and the illuminance after continuous lighting for 1500 hours was compared as an illuminance maintenance ratio. Here, the shape of the anode 3 is shown in FIG.
The experiment was performed by changing the length or distance L (mm) from the flat end portion 12 of the anode 3 to the cylindrical body portion 14 as a parameter from 3 mm to 10 mm in 1 mm units.

First, as a rare gas, 10% by volume of Ne is used.
7 atm is sealed at room temperature, and a flat portion at the tip of the anode 3
For a discharge lamp having a diameter of 12 mm of 7 mm, the distance L (m) from the flat end portion 12 of the anode 3 to the cylindrical body portion 14 described above.
Eight types of discharge lamps were prepared using m) as a parameter, and the illuminance and the illuminance maintenance ratio were obtained by experiments. Other specifications of the discharge lamp 20 are the same as described above. Table 3 shows the results of these experiments.

[Table 3]

When the distance L from the flat end portion 12 of the anode 3 to the body portion 14 was 4 mm or less, a decrease in illuminance was observed. It is considered that this is because the anode 3 itself blocks light emission, and as a result, the illuminance is reduced. The anode 3
The distance L from the flat end portion 12 to the cylindrical body portion 14 is 9
In the case of not less than mm, a decrease in the illuminance maintenance ratio was observed. This is because the current density in the flat end portion 12 of the anode 3 is high,
It is considered that this is because the temperature of the tip of the anode 3 is high, and the consumption of the tip of the anode due to the heat generated by the collision of electrons and ions due to the discharge is promoted. As a result of observing these discharge lamps in which the experiment of illuminance maintenance rate was performed, a crater-like deep hole was observed at the tip of the anode.

Next, as a rare gas, 10% by volume of Ne is used.
7 atm at room temperature, and the distance L (mm) from the flat end 12 of the anode 3 to the cylindrical body 14 at which the current density of the anode 3 becomes 0.3 A per 1 mm ² is set to 5 mm and 8 mm. Using the diameter of the flat end portion 12 of the anode 3 as a parameter, 16 types of discharge lamps were manufactured, and the illuminance and the illuminance maintenance ratio were compared. Other specifications of the discharge lamp are the same as described above. Table 4 shows the results of this experiment.

[Table 4]

The distance L (mm) at which the current density becomes 0.3 A per mm ² from the flat end portion 12 of the anode 3 is 5 mm.
In both cases of 8 mm and 8 mm, when the diameter of the flat end portion 12 of the anode 3 was 10 mm or more, the illuminance was clearly reduced. This is considered that the illuminance is reduced as a result of the anode 3 itself blocking the light emission, as in the case described above. In this discharge lamp, since the distance (interval) between the cathode 2 and the anode 3 is 4.5 mm, it is shown that this problem occurs when the diameter is more than twice this distance. Further, when the diameter of the flat end portion 12 of the anode 3 was 5.5 mm or less, a decrease in the illuminance maintenance ratio was observed. Again, as in the case above,
It is considered that the high temperature at the tip of the anode 3 promoted the consumption of the anode 3 due to the heat generated by the collision of electrons and ions due to the discharge. Observation of a sample of each discharge lamp after completion of the experiment on the illuminance maintenance ratio revealed that this discharge lamp also had a deep crater formed at the tip of the anode.

Therefore, in order to obtain a sufficient life in these discharge lamps, when the discharge current is I (A), the anode 3
The distance L (mm) from the flat end portion 12 of the anode 3 to the cylindrical body portion 14 at which the current density of the anode 3 becomes 0.3 A per 1 mm ² is:
0.05I to 0.08I.
It has been shown that it is effective to have an average current density of 3.5 A or less per mm ² and a diameter of twice or less the distance between the cathode 2 and the anode 3.

The preferred embodiment of the short arc discharge lamp according to the present invention has been described above in detail. However, it should be understood by those skilled in the art that the present invention should not be limited to only such specific embodiments, and that various modifications can be made without departing from the spirit of the present invention.

[0024]

As will be understood from the above description, according to the short arc type discharge lamp of the present invention, the rare gas sealed in the discharge tube is a relatively high molecular weight rare gas such as Xe, Kr or Ar. The mixed gas of these rare gases contains N
a relatively low molecular weight rare gas such as e or He
Mix 40%. Then, the pressure of these mixed rare gases at normal temperature is set to 2 atm or more. As a result, an effect that the illuminance and the illuminance maintenance ratio can be improved can be obtained.

The discharge current of the short arc type discharge lamp is defined as I (A), and the distance L from the flat end portion 12 of the anode 3 to the cylindrical body portion 14 at which the current density is 0.3 A per 1 mm ² is obtained. (mm) is in the range 0.05I <L <0.08I given by:, 2 times or less the diameter of the distance between the anode tip flat portion cathode and anode and a current density is 1 mm ² per 3, By setting the area to be equal to or more than 0.5 A, it is possible to obtain a short arc discharge lamp having high luminous efficiency and good illuminance stability that meets the demand for a long life of the light source.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a preferred embodiment of a short arc discharge lamp according to the present invention;

FIG. 2 is an enlarged view of an anode used in the short arc discharge lamp of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc tube 2 Cathode 3 Anode 12 Flat part of anode tip 13 Tapered part 14 Body of anode 20 Short arc type discharge lamp 21 Discharge space

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akiyoshi Fujimori 3-34-1, Chofugaoka, Chofu-shi, Tokyo F-term in Oak Manufacturing Co., Ltd. (Reference) 5C015 JJ06 JJ08 PP01 PP02 PP03 PP04 PP05 PP07 PP08

Claims (7)

[Claims] 1. A short arc type discharge lamp in which a cathode and an anode are arranged opposite to each other in an arc tube and a rare gas is sealed in a space in the arc tube. About 40%
A short-arc discharge lamp characterized in that a low molecular weight rare gas is sealed at room temperature at a pressure of 2 atm or more. 2. The short arc discharge lamp according to claim 1, wherein xenon, krypton, argon or a mixed gas thereof is used as the high molecular weight rare gas. 3. The short arc discharge lamp according to claim 1, wherein helium, neon, or a mixed gas thereof is used as the low molecular weight rare gas. 4. The anode according to claim 1, wherein the anode has a substantially cylindrical body portion, a tapered portion on the cathode side of the body portion, and a flat portion at a front end of the tapered portion. Short arc type discharge lamp. 5. The anode according to claim 1, wherein said anode has a current density of 0.2 / mm ² .
2. The short arc according to claim 1, wherein a distance L (mm) from the front end of the anode, which is 3 A, satisfies 0.05I <L <0.08I when a discharge current is I (A). 3. Type discharge lamp. 6. The short arc type discharge lamp according to claim 5, wherein the diameter of the flat portion at the tip of the anode is not more than twice the distance between the cathode and the anode. 7. The short arc type discharge lamp according to claim 4, wherein an area of the flat end portion of the anode has a current density of 3.5 A or less per 1 mm ² .