JPH025359A - Short arc electric discharge lamp - Google Patents

Abstract

PURPOSE:To increase a total efficiency as an optical system by providing a specific condition among a lamp voltage immediately after start, a lamp voltage at the time for stable lighting-up, a distance between electrodes, a bulb inside diameter at the central part and a lamp electric power at the time for stable lighting-up. CONSTITUTION:Assuming that a lamp voltage immediately after start is VSL(V), a lamp voltage at the time for stable lighting-up, VL(V), a distance between electrodes, l(mm), an inside diameter at a place positioned at the central part of a distance between electrodes of light emitting tube bulb, D(cm) and a lamp electric power at the time for stable lighting-up, WL(kW), they are controlled by (VL-VSL)/l=510(V/mm) D/WL=1.8-3.5(cm/kW). When(VL-VSL)/l is less than 5, the distance between electrodes lmay be too large or the lamp voltage at the time for stable lighting-up may be too low, so that a function as a point source light is lost, and when it is larger than 10, the inside pressure of the bulb during lighting-up increases with the result that its reliability is decreased. When D/WL is less than 1.8, even if the diameter of an arc is narrowed down, the temperature of the bulb tube wall becomes too high until and when D/WL exceeds 3.5, narrowing-down of the arc is lost with the result that no improvement of a total efficiency will be recognized.

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-ac discharge lamps.

(Prior art) In general, short arc discharge lamps such as ultra-high pressure mercury lamps and xenon-mercury lamps are ultraviolet lamps with small arcs and are close to point light sources. Used in industrial equipment.

For example, an exposure apparatus used for printing circuit patterns of semiconductor electronic circuits is also described in Japanese Patent Application Laid-Open No. 60-57930, and as shown in FIG. is installed 17 at approximately the focal point of a reflecting mirror 21 consisting of a rotating quadratic curved surface, the light emitted from this short arc discharge lamp 1 is focused by the reflecting mirror 21, and this reflected light is directed to a plane reflecting mirror 22 in the direction of irradiation with C. The light is further condensed by the condensing lens 23 and then passes through the photomask 24 to the irradiated surface 25,
For example, the surface of a semiconductor wafer coated with an ultraviolet-sensitive resin 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.

The short arc mercury lamp 1 used as a light source is
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.
Install and configure.

Electrode support rods 5.6 are sealed at both ends of the arc tube bulb 2, and since direct current lighting is the mainstream, an anode 7 and a cathode (
cathode) 8 is formed. 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 shape of the arc tube bulb 2 is such that the central portion thereof is swollen in the shape of a sphere or an ellipsoid to improve the pressure resistance.

Incidentally, in recent industrial fields, the precision of micromachining is increasing year by year, and higher performance machining precision is required, and higher efficiency is also being demanded from the perspective of improving productivity. For example, in the field of semiconductor manufacturing mentioned above, ultra LSI
As the integration of semiconductor devices continues to increase, there is a demand for higher exposure efficiency.

As a means for increasing exposure efficiency, it is desirable to increase the light intensity, that is, to improve the brightness on the irradiated surface 25.

In order to increase the brightness of the irradiated surface 25, it is possible to improve the light collecting ability of the reflecting mirror 21 and the lens 23 to increase the efficiency of the device, and to improve the output of the lamp as a light source.

Various efforts have been made to improve instrument efficiency, and it is recognized that a certain level of technology has already been reached.

On the other hand, there is still plenty of room for improvement in lamps.

In other words, in order to increase exposure efficiency from the perspective of the lamp, conventionally it was thought that increasing the luminous intensity was sufficient, but attention has been paid to the development and use of lamps with excellent luminous efficiency and large light output. It was broken.

However, in general, when trying to increase the output of a lamp, the wattage tends to increase, and in such a case, the lamp necessarily tends to increase in size.

(Problems to be Solved by the Invention) That is, when the lamp input is increased in order to increase the light emission output of the lamp, the bulb shape becomes larger and the arc diameter becomes thicker.

According to the research of the present inventors, even if an attempt is made to increase the amount of light emitted by increasing the lamp power and making the arc larger, when this lamp is installed at the focal position of the reflector 21, the arc will protrude from the focal position. In other words, the arc does not become a point light source, the light focusing ability by the reflection 1!21 and the condensing lens 23 decreases, the light is diffused on the irradiated surface 25, and the light intensity on the irradiated surface 25 increases. It was found that there may be a decrease in

On the other hand, if the arc is made smaller and closer to a point light source, even if the light emission output of the lamp decreases slightly, the arc will be placed at the focal point of the reflector 21 with high precision, and the arc will be more accurately positioned at the focal point of the reflector 21 and the condenser lens 23. It has been found that there are cases where the light condensing property is improved and the light intensity on the irradiated surface 25 is increased.

In addition, increasing the size of the lamp causes an increase in radiant heat and requires cooling measures for the lighting device, which leads to the device becoming larger and more sophisticated, leading to problems such as making existing devices unusable.

The present invention provides a short arc discharge lamp that improves the total efficiency when combined with an optical system such as a reflector by reducing the spread of the arc, even though the efficiency of the lamp itself may deteriorate slightly. That is.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, an arc tube is used as the light source in an optical system that focuses light emitted from a light source onto a surface to be illuminated via a reflecting mirror and a lens. In a short arc discharge lamp in which a pair of electrodes is provided inside the bulb and mercury and rare gas are sealed in the arc tube bulb, the lamp voltage immediately after starting is VSL (V), and the lamp voltage during stable lighting is VSL.
1 (V), the distance between the electrodes is I! (mm), and the inner diameter of the arc tube bulb at the center of the distance between the electrodes is D (cm).
L, when the lamp power during stable lighting is WL (KW), it is characterized by being regulated to (1) L-''' = 5 to 10 (V/m+s)a.

(Function) As described above, the present invention reduces the spread of the arc.
Even if the light emission output of the lamp decreases slightly, it is better to move closer to the point C light source because the arc is placed at the focal point of the reflector with high precision, which improves the ability of the reflector and lens to condense light, and improves the ability to focus the light on the irradiated surface. This was done by paying attention to the fact that the light intensity of the arc may increase in some cases, and was the result of considering how much the arc should be made smaller.

In other words, according to the research and experiments conducted by the present inventors, if the distance between the electrodes is made the same as before, the potential gradient is lowered, and the inner diameter of the arc tube bulb is made smaller, the luminous intensity will decrease slightly, but the arc length will be the same as before. , the arc diameter becomes smaller,
Close to a point light source.

Therefore, in the present invention, when such a lamp is used in combination with a reflector and a lens, the range in which the total efficiency is improved compared to the conventional one is numerically regulated using the potential gradient and the inner diameter of the arc tube bulb as parameters. It is something.

(Example) The present invention will be described below based on an example not shown in FIG.

The short arc mercury lamp shown in Figure 1 has a lamp input of 500
In the figure, 10 is an arc tube bulb made of quartz glass. Both ends of this arc tube bulb 10 are hermetically closed, and caps 3 are attached to both ends as in the conventional case.
．． 4 is installed.

Electrode support rods 5.6 are sealed at both ends of the arc tube bulb 10, and a relatively large anode 11 and a smaller cathode 12 are formed at the tips of these electrode support rods 5.6. has been done. The anode 11 is made of pure tungsten, and the cathode 12 is made by winding a coil 12a made of pure tungsten around the electrode support rod 6 made of tungsten containing, for example, 2% thoria.
A Th O2 emitter is applied between the coils 2a.

These anode 11 and cathode 12 are placed opposite each other at a very small distance in the center of the arc tube bulb 10, and in this embodiment, the distance between the electrodes is 2.5 square meters.

The arc tube bulb 10 is formed into an ellipsoidal shape, and the diameter of the center portion between the electrodes is set to D-1.4 cm.

Inside the arc tube bulb 10, a starting rare gas consisting of a predetermined amount of mercury and argon gas is sealed. Mercury Hg is sealed in an amount such that the lamp voltage is 36 (V), and argon gas is sealed at 0.5 (atmosphere).

In this case, the mercury vapor pressure during lighting is 30 (atm), and the argon gas pressure is 4 atm, resulting in a total of 34 atm.

In addition, the voltage drop due to electrode loss Vdrop-1, 2 (
V), and in this example, the degree of influence of argon gas on the lamp voltage can be considered to be 0 (■).

Therefore, the lamp voltage immediately after starting VS L ”' V dr
op-1, 2V.

On the other hand, the following table shows general divisor values of the same 500W according to the conventional design in comparison with the present invention.

In the above table, No. 5 is a conventional lamp, Nos. 2 to 4 are lamps corresponding to the present invention, and No. 1 and No. 6.7 are lamps that were determined to be outside the scope of the present invention by experiment.

The lamps (Nos. 2 to 4) according to the present invention have a smaller distance between the electrodes than the conventional lamp No. 5, and even though they are closer to a point light source, the amount of mercury filled is reduced and the pressure inside the lamp is lower than that of the conventional lamp. It's almost the same (2 atmospheres less, to be exact).

Therefore, in the lamps of the present invention (Nos. 2 to 4), the illuminance of the lamp body decreases by about 29 to 15%.

However, in the present invention, since D/W L is set to a smaller value than the conventional one, the spread of the arc can be reduced, that is, the arc diameter can be narrowed down, and as a result, the lamp No. 5 of the conventional example can be reduced. Compared to this, due to the effects of both the short gap and arc spread reduction, the arc approaches a point light source, making it easier to place the arc at the focal position of the reflecting mirror 21 with high precision, and increasing the light collection efficiency in the light quantity Y system. As a result, it can be seen that the total efficiency when used in combination with the reflecting mirror 2 and the lens 23 is improved by 1 to 18% compared to conventional example No. 5.

On the other hand, in conventional example No. 6, in order to obtain the same total efficiency as the present invention, the conventional example No. This lamp corresponds to the lamp voltage, but in this case the pressure during lighting is 8 atm (2 atm) compared to the present invention.
4%), making it unsuitable in terms of compressive strength.

In addition, the lamp of Conventional Example No. 7 has an arc tube bulb 1 having a shape close to a sphere, a short inter-electrode distance equivalent to that of the present invention,
j? (mm) and a lamp voltage equivalent to that of the present invention, but in this case, both lamp illuminance and light collection efficiency were poor, and the total efficiency was the worst.

Lamps No. 2 to 4, which correspond to the present invention, both exhibited good results, and this was due to suppressing the spread of the arc shape with respect to the optical system.

Conventional thinking has always been that the bulb diameter increases to match the size of the lamp. For example, in the conventional case, D/
WL (cm/KW) = 4 to 6 is common, and as the wattage increases, it may exceed this value.

This is because the pressure inside the bulb during lighting is to be as large as possible to get as close as possible to the pressure limit of the bulb. This is because it was thought that the value should be higher than the required value.

However, in the present invention, we focused on the fact that the total efficiency can be increased without setting the internal pressure of the bulb so high during lighting, and decided that the bulb shape does not necessarily have to be spherical. . In other words, the valve shape is made into a slightly elongated spindle shape so that even if the pressure resistance is slightly degraded, the strength required to withstand use can be obtained.In fact, by making the valve shape elongated and spindle-shaped, it is possible to suppress the spread of the arc. Therefore, the effect of reducing the arc diameter is large, that is, the overall efficiency including the instrument efficiency can be improved.

Now, let's go back to the basics and examine the characteristics of the Nyoto arc discharge lamp.

Generally, the pressure P inside the arc tube bulb during lighting depends on the distance between the electrodes, e, the amount of 11 g of mercury enclosed, and the pressure of the rare gas. Increasing the amount of fill will increase the lamp voltage VL.

The lamp voltage V1 is expressed as the sum of the electrode loss Vdrop and the arc voltage VarQ that adds power to the arc. That is, V L = V drop + V arc
-(1) The amount of light Φ emitted from the lamp is proportional to the arc voltage V are, and Φ oe Varc ” ~1
2).

Therefore, in order to increase the light intensity Φ of the lamp, the arc voltage v arc is increased.

The arc voltage v arc is proportional to the amount of 11 g of mercury and the pressure of the rare gas. In the case of short-arc mercury lamps, argon or xenon is used as the rare gas. In this type of short-arc mercury lamp, the purpose of using the rare gas is to lower the starting voltage due to the Penning effect during starting, and to reduce the electrode constituent materials during starting. Since the purpose is to suppress the scattering of gas, the sealing pressure p gas of the rare gas is low, and is suppressed to 1 atmosphere or less.

In contrast, short-arc xenon-mercury lamps use xenon as a rare gas, and in this case, in addition to the above-mentioned effect of preventing the electrodes from scattering, the purpose of the xenon is to utilize the light emitted by xenon during lighting. For,
The sealing pressure of xenon is high, and is 5 atm above 1 atm.
In some cases, it is sealed at ~6 atmospheres. These become 4 to 5 times the pressure during lighting.

However, the normally sealed rare gas has a smaller effect on the lamp voltage than the sealed mercury, and the lamp voltage Vs, - immediately after starting is V SL -V drop+ V gas -
(3), and in this case, V gas is only about a few volts even if the rare gas filling pressure at room temperature is 5 to 6 atmospheres.

The aforementioned arc voltage varc depends on the filler gas pressure v
It is expressed as the sum of gas and Vllg, which depends on the amount of mercury enclosed, and is expressed as: V arc −V gas + V Ilg
-(4), so in the case of a short arc discharge lamp,
V arc = V Hg - (5
).

Here, Vlg is the enclosed mercuryff1M (n+g)
, 71X distance between poles, e (m11), arc tube volume A (c
When c), the following relationship is generally known. Therefore, (6)
The expression can be replaced with .

The pressure P inside the arc tube bulb during lighting depends on the average temperature inside the arc tube bulb, but if the temperature is constant, P ccPgas =
4J3), P-M
...(9), and the sealing pressure of the rare gas p g
The larger as is, and the larger the amount of mercury enclosed, the higher the valve internal pressure P becomes.

That is, from the above equation (6), when the lamp voltage V L is the same, if the distance between r and h is decreased, the mercury mM
If you try to increase the light amount Φ by increasing the arc voltage Vare, then equation (2) and (
7) From the equation, is it necessary to increase mercury ff1M?

On the other hand, in order to increase the arc voltage v arc with the same lamp power WL, increasing the lamp voltage VL also increases the arc voltage by 1ff.
However, as shown in equation (7), doing this will increase the mercury m Pvl and increase the pressure P during lighting.

I, as the pressure P in one lamp increases, the pressure resistance of the arc tube bulb increases t
This will reduce the margin for W, making it more likely that the lamp will be damaged during lighting.

Further, the arc voltage v arc is increased and tN F'5.
L! It is possible to increase the output without increasing the pressure during lighting by increasing the jJ distance and e, but this would reduce the point light source element of this lamp, and the optical system would need to be This results in a decrease in light collection efficiency when combined, resulting in a reduction in total efficiency.

Furthermore, means for increasing the pressure of mercury Hg may also cause the following malfunctions. In other words, increasing the light output by increasing the mercury 11g pressure has the disadvantage of causing a broadening of the entire arc, resulting in an increase in the output in a continuous part of the spectrum, and the output in the originally desirable UV region is not necessarily proportional. Does not increase.

In other words, the optical output was increased in the form of an increase in the output of unnecessary parts, and there were some parts that could not be said to be a true improvement in efficiency.

For this reason, as described above, the present invention makes the valve shape slightly elongated and spindle-shaped so that even if the pressure resistance is slightly degraded, the strength necessary to withstand use can be obtained. The elongated shape suppresses the spread of the arc and reduces the arc diameter, thereby improving overall efficiency including instrument efficiency.

This represents the slope, and since it is related to the distance between the electrodes, it is related to the point light source, and also ([i) (
As can be seen from equations 7) and (9), it is also related to mercury vapor pressure, and from the table of experimental results above, it is 5 to 10 (V/m
u) is desirable.

If the distance 7e is too large, or the lamp voltage VL when the lamp is stably lit is too small, it will lose its function as a point light source, or the illuminance decrease will be too large and the total efficiency will be reduced only by suppressing the arc spread. Therefore, the object of the present invention cannot be achieved.

Since the internal pressure of the bulb increases during lighting and impairs reliability, it is desirable to keep the pressure to 10 or less in the range where quartz bulbs are used.

It is necessary to set D,/WL (am/KW) to 1.8 to 3.5.

If D/WL was less than 1.8, even if the arc diameter was narrowed, the quartz tube wall temperature would rise more than necessary, the pressure resistance of the bulb would decrease, and devitrification would occur during the life of the bulb. .

Furthermore, if D/WL exceeds 3.5, no improvement in total efficiency will be recognized compared to the conventional technology.

In addition, the current should be set to satisfy the lamp power per unit length (WL m, /), but as a short arc high pressure discharge lamp, even if the wattage increases, the point light source property should be considered important. . From that point of view, as in this example (
It can be said that it is preferable to set WL/, f') to 0.17 or more.

The present invention aims to suppress internal pressure during lighting and increase total efficiency, (WL/))
Although it is not affected by
In addition, it can be said that a large wattage bulb, whose pressure resistance is somewhat lower than a small wattage bulb, is more effective.

In other words, the present invention has been explained using 500 W, but whether it is IKW or 2 KW, as the wattage increases, the bulb withstand voltage tends to decrease within the membrane, so the advantage of the present invention can be realized in that a lamp with a smaller interelectrode distance can be manufactured. .

According to this embodiment, the distance between the electrodes is shortened, the arc length is shortened, and the diameter of the arc tube bulb is narrowed to narrow down the arc diameter, so the arc approaches a point light source.
Since the light gathering ability is improved, the total efficiency in combination with the optical system is improved.

Moreover, in this case, the lamp efficiency is rather suppressed by lowering the potential gradient, so the lamp voltage does not increase.
The pressure does not increase during lighting, and the reliability of the lamp strength can be maintained.

Also, since the lamp power does not increase, the lamp heats up and
The heat capacity of the electrodes does not increase in size, and the entire lighting device is prevented from increasing in size, so that the cooling device, power supply, and optical system do not increase in size or cost.

In the examples described above, the rare gas was below 1 atm, but when using xenon using cannon gas at above 1 atm,
Needless to say, a mercury lamp has a similar effect.

Further, the present invention is not limited to being applied to an exposure apparatus for printing circuit patterns of semiconductor electronic circuits, but can also be applied to UV spot curing and the like.

[Effects of the Invention] As explained above, according to the present invention, the distance between the electrodes is shortened, so the arc length is shortened, and the diameter of the arc tube bulb is narrowed to narrow the arc diameter, so the arc becomes a point light source. As time approaches, the efficiency of a single lamp may deteriorate slightly, but if used in combination with a reflector or lens, the light gathering ability will improve and the total efficiency will increase. Moreover, in this case, since the potential gradient is lowered and the lamp efficiency is rather suppressed, the lamp voltage does not increase, the pressure during lighting does not increase, and the reliability of the lamp intensity can be maintained.

Also, since the lamp power does not increase, the lamp heats up and
There is an advantage that the heat capacity of the electrodes does not increase, the overall size of the lighting device is prevented, and the cooling device, power supply, and optical system do not increase in size or cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a short arc mercury lamp showing an embodiment of the present invention, Figs. 2 and 3 explain the conventional technology, and Fig. 2 shows an exposure apparatus for printing circuit patterns of semiconductor electronic circuits. FIG. 3 is a schematic diagram showing the configuration of a conventional short arc mercury lamp. 10... Arc tube bulb, 11... Anode, 12...
Cathode, 21...Reflector, 23...Condensing lens, 25
...Irradiated surface. Figure 1 Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] Used as the light source in an optical system that focuses light emitted from a light source onto a surface to be illuminated via a reflecting mirror and a lens,
In a short arc discharge lamp in which a pair of electrodes is placed inside the arc tube bulb and mercury and rare gas are filled in the arc tube bulb, the lamp voltage immediately after starting is VSL (V), and the lamp voltage during stable operation is VSL (V). is VL (V), the distance between the electrodes is l (mm), the inner diameter at the center of the distance between the electrodes of the arc tube bulb is D (cm), and the lamp power during stable lighting is WL (KW). In the case, [V_L-V_S_L/l]=5~10(V/mm)P
A short arc discharge lamp characterized in that /W_L=1.8 to 3.5 (cm/KW).