JP2001135272A - Extra-high pressure mercury lamp and its electrodes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extra-high pressure mercury lamp and its electrodes used for long service life and high-efficiency exposure apparatus, etc., by reducing electrode dissipation of the mercury lamp used by switching at a high frequency. SOLUTION: In AC lighting extra-high pressure mercury lamp with a pair of electrodes disposed by facing in the emitting bulb, tip part of the electrodes is manufactured in a hemisphere or such a convex surface as ellipsoid with major axis about 1.5 times the radius of the electrode tip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultra-high pressure mercury lamp,
In particular, the present invention relates to an ultra-high pressure mercury lamp that emits high-intensity ultraviolet rays and the like used as a light source of an exposure apparatus, and an electrode thereof.

[0002]

2. Description of the Related Art Semiconductor integrated circuits (ICs), liquid crystal display panels (LCDs), printed circuit boards (PCBs), etc.
Increasingly larger and denser. The manufacture of these electronic components or devices requires a short-wavelength, high-brightness light source as an exposure device. For this purpose, an ultra-high pressure mercury lamp is generally used.

[0003] A general ultra-high pressure mercury lamp has a sealed arc tube in which a pair of electrodes are arranged to face each other, and a rare gas such as argon or xenon is contained therein together with mercury. It is enclosed.

[0004] The electrode of the ultra-high pressure mercury lamp used here will be described. In a DC ignition type ultra-high pressure mercury lamp such as a short arc lamp, electrodes of different shapes are used as an anode and a cathode. On the other hand, the same pair of electrodes are used in an AC ignition type ultra-high pressure mercury lamp. The electrodes of the AC ignition type ultra-high pressure mercury lamp have different dimensions depending on the application. Generally, it has a cylindrical shape having a diameter of about 20 to 50% with respect to the inner diameter of the arc tube of about 1 to 3 mm.

[0005] During operation of such an ultra-high pressure mercury lamp, temperature rise due to arc discharge and evaporation or sputtering of electrode material due to electron collision occur. The electrode substance adhered to the inner wall of the arc tube prevents transmission of light radiated by the arc discharge, and is a factor of reducing the illuminance of the irradiated area.

Further, when exposed to a high temperature, quartz glass used as a material for an arc tube of a general ultra-high pressure mercury lamp changes its crystalline state from a metastable and transparent state to cristobalite, so-called “devitrification”. Triggers a state and loses clarity. This "devitrification" proceeds remarkably as the temperature increases. Therefore, the light that is blocked by the electrode material attached to the inner wall of the arc tube changes into heat, which raises the temperature of the arc tube, causing "devitrification" of the glass, and further lowers the illuminance.

Many exposure apparatuses using an AC-lit ultrahigh-pressure mercury lamp are used for exposing a pattern on a printed circuit board. In such applications, the lamp is generally used in a blinking manner, in which the lamp is turned on when the resist to be irradiated is exposed and the lamp is turned off when the resist is not exposed.

On the other hand, in the AC lighting type ultra-high pressure mercury lamp, when the lamp is started, that is, during the period from the start of the lamp lighting until the mercury evaporates and becomes parallel to the heat to achieve stable lighting, compared to the lamp during the stable lighting, two times. Up to three times the current flows. Therefore, the amount of electrons colliding with the electrode also increases, and the vapor pressure in the arc tube is low, so that the consumption of the electrode is accelerated as compared with during stable lighting. For this reason, a lamp used in a blinking manner has an extremely large illuminance reduction rate per integrated lighting time as compared with a lamp that is continuously lit.

FIG. 6 is a partial cross-sectional view of a typical AC-lit ultrahigh-pressure mercury lamp. This ultra-high pressure mercury lamp includes a light-transmitting light emitting tube 2 made of quartz glass or the like, stems 3a and 3b fixed to both ends of the light emitting tube 2, electrodes 1a and 1b opposed to each other inside the light emitting tube 2, and A sufficient amount of mercury 4a,
4b. Argon,
A rare gas such as xenon is sealed. Here, electrode 1
Is a flat surface as shown in FIG.

[0010]

Generally, the exposure of a resist is controlled by the integrated amount of light on the irradiation surface.
A decrease in illuminance results in an increase in exposure time and a decrease in manufacturing efficiency. Therefore, there is a need for a lamp having a high illuminance maintenance rate. In the conventional ultra-high pressure mercury lamp described above, the electric field is concentrated on the edge of the tip of the electrode, and the consumption is severe. For this reason, there has been a problem that the exposure time of an exposure apparatus using this ultrahigh-pressure mercury lamp is prolonged and the working efficiency is reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an AC-lit ultrahigh-pressure mercury lamp having a low illuminance maintenance factor and a low electrode consumption, even when used at a high frequency.

[0012]

The ultra-high pressure mercury lamp of the present invention has a pair of electrodes opposed to each other in an arc tube. Each electrode has a columnar tip portion with a radius r, and the tip portion is a convex portion in a range surrounded by a hemispherical surface centered on the tube axis direction r and an elliptic warhead surface having a major axis of approximately 1.5r in the tube axis direction. Or a convex pseudo-curved surface within a range surrounded by a pseudo-curved surface having a flat surface at the center of the tip and a radius of r / 2 at the corner and a hemisphere centered at a position in the pipe axis direction r. Is a flat surface and the corner is about 4
The convex pseudo-curved surface is chamfered at an angle of 5 degrees and has a rounded boundary.

The electrode of the ultra-high pressure mercury lamp of the AC lighting type according to the present invention is a columnar electrode having a radius of r disposed opposite to the inside of the arc tube. A gentle convex surface within a range surrounded by a hemispherical surface and an elliptical curved surface having a major axis of about 1.5r, or a pseudo-curved surface and a radius having a radius of about r / 2 with a flat central portion at the tip end and a radius of approximately r / 2. r is a convex pseudo-curved surface in a range surrounded by a hemispherical surface, or a convex pseudo-curved surface having a flat center surface at the tip and a chamfer at an angle of about 45 degrees and a rounded boundary. I do.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a preferred embodiment of an ultra-high pressure mercury lamp and its electrode according to the present invention will be described below in detail with reference to the drawings.

First, FIG. 1 shows the tip portions along the longitudinal direction of various embodiments of an electrode for an AC-lit ultrahigh-pressure mercury lamp according to the prior art and the present invention. These FIGS. 1 (a) to 1 (i)
These electrodes are arranged to face both ends of the sealed arc tube 2 of the above described AC lighting type ultra-high pressure mercury lamp of FIG. FIG. 1A shows a conventional electrode tip. Fig. 1 (b)
(D) shows the first group of electrode tips. FIG. 1 (e) to (g)
Indicates the tip of the second group of electrodes. FIGS. 1H and 1I show a third group of electrode tips.

In the present invention, experiments were conducted on various electrode tip structures as shown in FIG. Hereinafter, these various experiments will be described. The specifications of the evaluation reference lamp are as follows. A cylindrical electrode having a radius of 0.3 mm and a columnar shape is arranged opposite to an arc tube having an inner diameter of 2 mm at a lamp discharge position at a distance of 140 mm. In the arc tube, a lamp in which about 0.2 atm of xenon and mercury in an amount more than necessary and sufficient for light emission are manufactured. Hereinafter, this reference lamp is referred to as lamp A.

(Experimental Example 1) Except for the tip of the electrode 1, the specifications are the same as those of the above-mentioned reference lamp A. As shown in Table 1, the tip has a short radius of the electrode and a warhead having a long diameter of d1. Alternatively, three types of lamps B, C, and D using a first group of electrodes having a semi-elliptical shape were prepared. The electrode tip shapes of these lamps A, B, C and D are shown in FIGS. 1 (a), (b), (c) and (d), respectively.

[Table 1] In this particular example, the effective electrode diameter in Table 1 indicates the electrode diameter at a position 2 mm from the electrode tip in the tube axis direction.

These lamps A to D were housed in a cylindrical container, and turned on by supplying about 5 kVA of electric power while cooling with cooling water at a flow rate of 10 liters per minute from the outside. Reference lamp A and these three types of lamps B, C and D are
The illuminance maintenance rate according to the number of times of blinking when lit while blinking in a blinking cycle of turning on for 5 seconds and turning off for 5 seconds is shown in FIG.
Was as shown in FIG.

As is clear from the characteristic curve shown in FIG.
When the major axis of the ellipse is equal to the electrode radius r, that is, when the tip of the electrode 1 is a hemispherical shape having the radius r, the lamp B has the smallest illuminance attenuation. The longer the major axis (the lamps C and D), the greater the rate of decrease in illuminance. In particular, when the major axis is twice the effective electrode radius (lamp D), the number of blinks is 500.
At a point sufficiently less than 0 times, the illuminance drops extremely.
This indicates that as the major axis exceeds 3/2 times the minor axis and the tip of the electrode becomes sharper, the electric field is concentrated on the tip of the electrode as a cold cathode and the electrode material is more likely to evaporate.

(Experimental Example 2) Next, except for the shape of the electrode tip, the lamp A had the same specifications as the lamp A. As shown in Table 2, the tip of the electrode 1 had a corner with a radius d2 (mm). Three types of rounded lamps E, F and G were prepared. The shapes of these electrode tips are shown in FIG.
(e), (f) and (g).

[Table 2] When the lamps were lit while blinking under the same conditions as in the above-described Experimental Example 1, the lighting frequency illuminance maintenance rate (or the illuminance reduction rate) was measured, and the results shown in FIG. 3 were obtained.

As is clear from the characteristic curve in FIG. 3, the radius of the rounded corner of the tip is equal to the electrode radius, that is, when the tip of the electrode 1 is a hemisphere having a radius r (lamp E).
Has the lowest illumination attenuation. The smaller the roundness (lamp F, G), the greater the illuminance reduction rate. In particular, when the round radius is 0.1 mm (lamp G), the illuminance attenuation characteristic is close to that when a non-round electrode is used (lamp A). From this, it can be seen that, by reducing the radius of the roundness at the corner of the electrode tip, a portion of insufficient temperature is generated around the electrode tip as a cold cathode, and sputtering occurs.

(Experimental Example 3) Next, except for the shape of the electrode tip, the same specifications as those of the above-described reference lamp A were used.
As shown in FIGS. 1H and 1I, two types of lamps H and I using a third group of electrodes shown in FIGS. 1H and 1I with a chamfer of a dimension d3 (mm) at an angle of 45 degrees. A lamp was prepared. In these electrodes, each corner was rounded to about 0.03 mm in order to remove burrs generated during processing.

[Table 3]

When these lamps H and I were turned on while blinking under the same conditions as in the above-mentioned Experimental Example 1, the blinking number illuminance maintaining ratio was as shown in FIG. As is apparent from FIG. 4, even when the electrode tip portion is processed into a tapered shape instead of a pseudo-arc shape as in the above-described Experimental Examples 1 and 2, both the lamps H and I have the conventional shapes. It can be seen that the illuminance reduction rate is smaller than that of lamp A. This is considered to be an effect due to the fact that there are few portions where the temperature is insufficient at the periphery of the tip of the electrode as in Experimental Example 2. At the boundary where the surfaces intersect with each other, an angle is generated unlike the experimental example 2 described above, and the electric field is concentrated at this portion, so that the illuminance reduction rate is larger than that of the experimental example 2. Therefore, by adding a large radius to this corner, the illuminance maintenance ratio can be improved.

Next, Table 4 summarizes the illuminance maintenance ratio of the above-described reference lamp A and the lamps B to I of each of the experimental examples 1, 2 and 3 when the lamp is blinked 1000 times.

[Table 4]

FIG. 5 shows the configuration of the tip of an electrode used in an ultra-high pressure mercury lamp realizing the object of the present invention. First, in the left half of FIG. 5A, the configuration of the electrode tip portion limited to claims 1 and 4 of the present invention is shown by hatching. In the right half of FIG. 5A, the configuration of the electrode tip portion limited to claims 2 and 5 of the present invention is indicated by hatching. Further, in FIG. 5B, the configuration of the electrode tip portion limited to claims 3 and 6 of the present invention is shown by hatching.

As described above, the lamp in which the shape of the electrode tip is processed into various shapes of a convex curved surface can suppress the consumption of the electrode during lamp start-up and stable lighting as compared with the conventional lamp A. it can. Therefore, the occurrence of sputtering and "devitrification" is small, and it is possible to reduce the decrease in illuminance with the passage of the specified time of such a lamp.

The preferred embodiments of the ultra-high pressure mercury lamp and its electrode according to the present invention have 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 examples, and that various modifications can be made. For example, the electrode does not need to be cylindrical with the same radius over the entire length, and the cylindrical portion does not necessarily have to be a perfect circle.

[0028]

As will be understood from the above description, according to the ultrahigh pressure mercury lamp of the present invention and its electrode, the configuration and shape of the electrode tip are not a conventional flat shape but a hemisphere or a warhead (ellipse). By processing into a shape, it is possible to prevent concentration of an electric field and suppress consumption of electrodes during lamp startup and during stable lighting regardless of lighting conditions. As a result, there is a practically remarkable effect that the occurrence of sputtering and “devitrification” is small, and a decrease in illuminance over time can be minimized.

[Brief description of the drawings]

FIG. 1 is a view showing various electrode tip shapes for explaining the present invention;

FIG. 2 is a diagram showing a blinking number illuminance illuminance maintaining rate characteristic of an ultra-high pressure mercury lamp using a first group of electrodes;

FIG. 3 is a diagram showing a blinking number illuminance illuminance maintaining ratio characteristic of an ultra-high pressure mercury lamp using a second group of electrodes;

FIG. 4 is a diagram showing a blinking number illuminance maintaining rate characteristic of an ultra-high pressure mercury lamp using a third group of electrodes;

FIG. 5 is a diagram showing a configuration of an electrode tip portion of the present invention;

FIG. 6 is a partial cross-sectional view showing a configuration of a typical ultra-high pressure mercury lamp.

[Explanation of symbols]

 1a, 1b electrode 2 arc tube 3 stem 4a, 4b mercury r radius of columnar electrode

Claims (6)

[Claims] An ultra-high pressure mercury lamp of an AC lighting type having a pair of columnar electrodes disposed at opposite ends thereof opposed to each other and having an arc tube filled with a rare gas therein, wherein: When the radius is r, the portion from r to about 1.5r in the tube axis direction from the electrode tip is gently shaped like a warhead in a range surrounded by a hemisphere of radius r and an elliptical curved surface having a major axis of about 1.5r. An ultra-high pressure mercury lamp formed on a convex curved surface. 2. An alternating current lighting type ultra-high pressure mercury lamp having a pair of columnar electrodes at both ends facing each other and having an arc tube filled with a rare gas therein, wherein the radius of the tip of the electrode is reduced. In the case of r, the area from the electrode tip to r in the tube axis direction is surrounded by a hemisphere having a radius of r and a curved surface obtained by chamfering a center portion of the electrode tip with a flat surface and an arc having a radius of about r / 2. An ultra-high pressure mercury lamp characterized by having a convex quasi-arc curved surface within a range defined. 3. An alternating current lighting type ultra-high pressure mercury lamp having a pair of columnar electrodes at both ends facing each other and an arc tube filled with a rare gas therein, wherein the center of the electrode tip is flat. Approximately 4 corners
An ultra-high pressure mercury lamp characterized in that it is chamfered at an angle of 5 degrees and formed into a convex curved surface with a rounded boundary at each corner. 4. An electrode of an AC lighting type ultra-high pressure mercury lamp having a pair of electrodes disposed opposite to both ends of an arc tube, wherein the electrode tip has a columnar shape with a radius r. And a convex warhead in a range surrounded by a hemispherical surface having a radius of r centered on the position r in the tube axis direction and an elliptical surface of 1.5r from the tip in the tube axis direction. Electrodes for ultra-high pressure mercury lamps. 5. An electrode of an AC lighting type ultra-high pressure mercury lamp having a pair of electrodes disposed opposite to both ends of an arc tube, wherein the electrode tip portion has a columnar shape with a radius r. The center portion is a flat surface, and the corner portion is formed as a gentle convex pseudo-curved surface in a range surrounded by a rounded curved surface having a radius of about 0.5r and a hemispherical surface having a radius r. High pressure mercury lamp electrode. 6. An electrode of an alternating current lighting type ultra-high pressure mercury lamp having a pair of electrodes disposed opposite to both ends of an arc tube, wherein the electrode tip is a column having a radius r. The center is a flat surface, chamfered at an angle of about 45 degrees,
An electrode for an ultra-high pressure mercury lamp, characterized by a convex pseudo-curved surface rounded at the boundary.