JPH025357A - Short arc electric discharge lamp - Google Patents

Abstract

PURPOSE:To decrease the diameter of an arc and increase the intensity of spectral line of gamma ray by sealing mercury and rare gas and additionally a specific quantity of hydrogen, and further sealing one of such elements as gadolinium, etc., in a specific quantity in a light emitting tube. CONSTITUTION:In a short arc electric discharge lamp where a pair of electrodes 7 and 8 are installed in a light emitting tube, halogen in addition to mercury and rare gas is sealed within the range from 3.5X10<-5> to 3.5X10<-3> at a sealing molar ratio to mercury. Halogen has electron affinity so that it is bonded to electron to decrease the electron number in an arc; therefore, the arc is positioned at the shortest section between an anode 7 and a cathode 8, and the arc diameter is decreased. A light emitting region becomes small and nears to a point source light and luminance increases. When at least one of gadolinium, praseodymium, samarium, lanthanum, yttrium, terbium and europium is further sealed in addition to halogen, the emission spectrum of gamma ray (436nm) increases and it becomes possible to further increase an optical output.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is used as a light source for an illumination optical system such as an exposure device or UV spot cure for printing circuit patterns of semiconductor electronic circuits. This invention relates to short arc discharge lamps.

(Prior Art) For example, an exposure apparatus used for printing a circuit pattern of a semiconductor electronic circuit is also described in Japanese Patent Application Laid-open No. 60-57930, but as shown in FIG. A short arc mercury lamp 1 as shown in FIG.
The irradiation direction of this reflected light is changed by a plane reflector 22, and the light is passed through a condenser lens 23, and the light further condensed by this condenser lens 23 is passed through a photomask 24 to an irradiated surface 25, such as an ultraviolet-sensitive resin. The surface of the coated semiconductor wafer is irradiated.

Therefore, a pattern corresponding to the photomask 24 is printed on the surface of the semiconductor wafer 25 by the ultraviolet rays emitted from the short arc mercury lamp 1.

A short arc mercury lamp 1 used as a light source has a first
As shown in the figure, both ends of an arc tube bulb 2 made of quartz glass are hermetically closed, and caps 3 and 4 are attached to these ends, respectively.
It is configured by installing.

Electrode support rods 5.6 are sealed at both ends within the arc tube bulb 2, and an anode 7 and a cathode 8 are formed at the tips of these electrode support rods 5.6.

These anode 7 and cathode 8 are opposed to each other at the center of the arc tube bulb 2 with a slight distance therebetween. Since a short arc is discharged between the anode 7 and the cathode 8, the arc tube bulb 2 has a structure in which the central portion thereof swells into a spherical or ellipsoidal shape.

Incidentally, in recent years, the integration of VLSIs has been progressing even further, and as a result, there has been a demand for higher exposure accuracy and shorter exposure time.

As a means to improve exposure accuracy, it is possible to make the light source smaller, and it is required to make the light source as close to a point as possible, that is, to make it a so-called point light source. In other words, if the light source is made as small as possible, it will be easier to install it at the focal position of the reflecting mirror 21 with high precision, and the light collection efficiency of the entire optical system including the lens 23 can be increased, so that spot light can be obtained. It becomes easier.

However, there are limits to the miniaturization of lamps due to restrictions on the lamp structure.

On the other hand, in order to shorten the exposure time, a lamp with a large light emission output is advantageous, and it may be considered to change to a lamp with a large lamp input. That is, an attempt is made to shorten the exposure time to 1/2 by using an ultra-high pressure mercury discharge lamp with a lamp power of IKW compared to an ultra-high pressure mercury discharge lamp with a lamp power of 500 W.

However, doubling the lamp input does not simply double the light emission output, and furthermore, in such a case, there is always the problem of increasing the size of the lamp.

(Problem to be solved by the invention) In other words, if the lamp input is increased in order to increase the light emission output of the lamp, the bulb shape will become larger and the arc diameter will become thicker, which not only causes a decrease in light emission efficiency (brightness). In such a case, the light source will not become a point light source and the arc will protrude from the focal position of the reflecting mirror 21, so the light focusing ability of the reflecting mirror 21 and the condensing lens 23 will be reduced, and the light will not be reflected on the irradiated surface 25. There is a problem that the exposure accuracy decreases due to the diffusion of light.

In addition, increasing the size of the lamp causes an increase in radiant heat, which requires cooling measures for the lighting device, resulting in disadvantages such as the overall complexity of the lighting device.

The present invention aims to provide a short arc discharge lamp in which the arc is thinned and the brightness of the arc is increased without increasing the size of the bulb or the lamp input, and the exposure efficiency is improved.

[Structure of the Invention] (Means for Solving the Problem) The first aspect of the present invention is to use the light source as the light source in an optical system that focuses the light emitted from the light source onto the irradiated surface via a reflecting mirror and a lens, In a short arc discharge lamp in which a pair of electrodes are provided in the arc tube, a halogen is sealed in addition to mercury and a rare gas in the arc tube, and the amount of halogen is filled in at a molar ratio of 3.5 x 10- to mercury. 5-3.
It is characterized by being 5×10 −3 .

The second aspect of the present invention is that, in addition to the above-mentioned mercury, rare gases, and halogens, at least one of gadolinium, praseodymium, samarium, lanthanum, indolium, 1-nonium, terbium, and europium is sealed in the arc tube. Features.

(Function) In the case of a conventional short arc mercury lamp, a rare gas consisting of mercury and argon is sealed in the arc tube. Conventionally, it was thought that the higher the purity of argon gas, the better in order to achieve smooth startup and stable discharge. When halogen is mixed into such argon gas, halogen has a high electron affinity and combines with electrons to reduce the number of electrons in the arc, so the arc is located at the shortest distance between the anode and cathode, which have a high electron density. As a result, a phenomenon in which the arc diameter is narrowed down can be seen. In long arc discharge lamps, the distance between the electrodes is long, which causes the arc to swing and become unstable, causing the lamp to go out, and has been disliked as a cause of malfunctions.

In contrast, the present invention is a short arc discharge lamp with a short distance between electrodes, so in this case, the arc is narrowed down, so the light emitting area is smaller and closer to a point light source, and the brightness is high. It turned out to be true.

The first aspect of the present invention is to utilize this principle to fill an arc tube with halogen in addition to mercury and a rare gas, and to adjust the amount of halogen so that the arc is narrowed and the brightness is high, while also preventing fading. By controlling the amount to such an extent that it does not occur, the initial objective can be achieved.

According to the second aspect of the present invention, in addition to halogen, at least one of gadolinium, praseodymium, samarium, lanthanum, yttrium, rhenium, terbium, and europium is sealed, so that G-line (436
nm) emission spectrum is increased, making it possible to further increase the light output.

(Example) The present invention will be explained in detail below.

Note that the lamp structure of the present invention may be the same as the conventional structure, so the description of the conventional structure using FIGS. 1 and 2 will also be used to explain the present invention, and the explanation here will be omitted.

Lamp voltage 50V, rated lamp cuff 50W.

In the short arc mercury lamp 1 with an inter-electrode distance of 3■,
1.7X10-4 (mol) of mercury was placed inside the arc tube bulb 2.
/cc) and argon gas at 500 Torr at room temperature to prevent the electrode material from scattering.

In addition, iodine is sealed in the arc tube bulb 2 as a nitrogen gas, and the amount of iodine sealed is regulated at a molar ratio of 3.5 x 10''5 to 3.5 x 10-3 with respect to mercury. It is.

Furthermore, in addition to the above halogen, inside the arc tube bulb 2,
Samarium is sealed in an amount equivalent to the chemical equivalent of halogen.

In the short arc mercury lamp 1 having such a configuration,
During lighting, mercury vapor, argon gas, and iodine and samarium vapors as halogens are present in the discharge space.

Halogens such as iodine have high electron affinity and bond with electrons to reduce the number of electrons. As a result, the arc comes to be located on the shortest distance between the anode 7 and the cathode 8, which have a high electron density, and the arc diameter is narrowed down. In other words, the arc becomes thinner over the shortest distance between the anode 7 and the cathode 8.

In this case, since the distance between the electrodes is short and the amount of halogen enclosed is appropriately regulated, arc fluctuations and instability do not occur, and the lamp does not go out.

Since the arc is narrowed in this manner, the light emitting area becomes smaller and approaches a point light source, and the light emitting efficiency improves, resulting in higher brightness.

Therefore, since the light source becomes small, it becomes easy to install it at the focal position of the reflecting mirror 21 with high precision, and the lens 23
It is possible to improve the light collection efficiency of the entire optical system including the above, and from this, it is possible to obtain a highly accurate spot light.

Furthermore, since the arc becomes thinner, the brightness increases and the emission intensity improves. Therefore, the exposure time can be shortened and the exposure efficiency can be improved.

Iodine has the above-mentioned effect, but samarium encapsulated together with iodine enhances the emission spectrum of the G-line (436 nm), which further increases the emission spectrum of 436 nm compared to when only iodine is encapsulated. It becomes possible to improve the optical output.

In order to achieve the above effects, the amount of halogen enclosed must be regulated to an optimum amount. For this reason, the inventors of the present invention conducted experiments regarding the amount of halogen enclosed to find the optimum range.

Table 1 shows the molar ratio and the change in light intensity when the amount of iodine enclosed with the mercury enclosed was varied in the short arc mercury lamp 1 with a rated lamp and cuff of 50 W.

Note that the light intensity ratio is based on the G line (436
This is a comparison of the intensity of the conventional lamp (nm), with the intensity of the conventional lamp set as 100. Further, in this case, samarium is not sealed.

From the above experimental results, the amount of iodine enclosed (molar ratio) is 3.5X1
If it is less than 0''5, the amount of iodine enclosed is so small that no improvement in light intensity can be expected, and the initial purpose of iodine inclusion cannot be achieved.However, in this case, the arc is thick and stable discharge is maintained.

Furthermore, if the amount of iodine enclosed (molar ratio) exceeds 3.5X10-3, the light intensity will be excellent, but the arc will become too thin and unstable, causing stagnation due to shaking, etc. Can be seen.

For this reason, the amount of iodine enclosed needs to be regulated in the molar ratio to the amount of mercury in the range of 3.5X10-' to 3.5X10-3, and particularly preferably 3.5X10-3.
A range of 4 to 2.0 x 10-3 is good.

Next, we investigated how the light intensity changes when samarium is added to the halogen. The results are shown in Table 2, and the amount of samarium included is the same as that of chemical iodine. Note that the light intensity ratio in this case is also the G line (4
36nffl) compared with the conventional lamp as 100.

As you can see from Table 2, No. 2 without adding samarium
The intensity of the G line (436011) is increased in cases No. 6 and No. 7, in which samarium is added, compared to cases in Nos. and 3, and therefore they are more effective in shortening the exposure time.

Note that the present invention is not limited to the above embodiments.

In other words, the rated lamp input of a short arc mercury lamp is 7
In addition to 50W, other lamp powers can be used.

In addition, the halogen may be bromine, fluorine, chlorine, etc. in addition to iodine, and these may be used alone or in combination, such as umium Gd, praseodymium Pr, and lanthanum. La, yttrium Y lunium Re,
Terbium Tb.

Europium Eu may be used, and these may be used alone or in combination.

These metals such as samarium react with halogen to form halides when the lamp is turned off, and are separated from the halogen while the lamp is on. Therefore, metals such as samarium and halogens can be previously converted into halides outside the lamp and brought into the arc tube bulb in this form.

Furthermore, the present invention is not limited to application to an exposure apparatus for printing circuit patterns of semiconductor electronic circuits;
It is also applicable to UV spot curing.

[Effects of the Invention] As explained above, according to the first aspect of the present invention, the halogen sealed in the arc tube has the effect of narrowing the arc and increasing the brightness, so that the light gathering ability is enhanced and the exposure accuracy is improved. This makes it possible to increase light output, shorten exposure time, and improve exposure performance.

Further, according to the second aspect of the present invention, since metal such as samarium increases the spectral intensity of the G-line, it is possible to further improve the light intensity.

[Brief explanation of the drawing]

Figures 1 and 2 are commonly used to explain one embodiment of the present invention and the conventional structure. Figure 1 is a configuration diagram of a short arc mercury lamp, and Figure 2 is a semiconductor electronic circuit. 1 is a schematic configuration diagram showing an exposure apparatus for printing circuit patterns. 1... Short arc mercury lamp, 2... Arc tube bulb,
7...Anode, 8...Cathode, 21...Reflector, 23...Lens, 25...Irradiated surface. Applicant's agent Patent attorney Takehiko Suzue Figure 12

Claims (1)

[Scope of Claims] (1) A short arc that is used as the light source in an optical system that focuses light emitted from a light source onto a surface to be irradiated via a reflecting mirror and a lens, and that has a pair of electrodes disposed within an arc tube. In a discharge lamp, a halogen is sealed in addition to mercury and a rare gas in the arc tube, and the amount of halogen sealed is in a molar ratio of 3.5 x 10^-^5 to 3.5 x 10 with respect to mercury. A short arc discharge lamp characterized by ^-^3. (2) The arc tube is filled with at least one of gadolinium, praseodymium, samarium, lanthanum, yttrium, rhenium, terbium, and europium in addition to mercury, a rare gas, and halogen. A short arc discharge lamp as described in Scope 1.