JPH04301352A - low pressure mercury discharge lamp - Google Patents

Abstract

PURPOSE:To decrease self absorbing action of ultraviolet rays so as to improve an output of the ultraviolet rays by forming a section of at least discharge space of a luminous tube into a non-circular shape. CONSTITUTION:In a luminous tube 2, its section is formed into noncircular shape, for instance, into almost flat quadrangle shape, and ratio x/y of a minor side (x) to a major side (y) is formed to about 0.2 to 0.8. The tube 2 is sealed with rare gas of mercury and argon or the like so as to generate a 0.7 to 13Pa vapor pressure of mercury during lighting and a 13 to 133Pa seal pressure of argon gas during lighting. In this way, also a discharge space provides a flat quadrangle to reduce a thickness of a mercury vapor layer. Accordingly, since absorption of ultraviolet rays by the mercury vapor layer is suppressed to reduce an optical obstacle, self absorption of the ultraviolet rays is decreased even when the mercury vapor pressure is increased, and even in the case of increasing current density to a range of exceeding a saturation region in the past, an ultraviolet ray output can be improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure mercury discharge lamp used as a light source for ultraviolet photochemical reactions.

0002

[Prior Art] Electrodes are sealed at both ends of an arc tube made of quartz glass or the like that transmits ultraviolet rays, and mercury and rare gas are sealed inside the arc tube, and when the electrodes are energized, a discharge is generated within the arc tube. A low-pressure mercury vapor discharge lamp, which emits ultraviolet light mainly at 185 nm and 254 nm resonance lines of mercury by ionizing and exciting mercury atoms, is used as an ultraviolet light source for photochemical reaction devices and the like.

[0003] That is, the above-mentioned low-pressure mercury vapor discharge lamp is, for example, a photo-CVD (Chemical Vapor Depth)
It is an indispensable ultraviolet light source for semiconductor manufacturing-related applications such as the synthesis of Si thin films using the photoposition method, photocuring of resists, photoashing, and photocleaning. It is also widely used as a light source that irradiates short-wavelength ultraviolet rays in sterilization treatments.

[0004] Recently, there has been a growing demand for high-speed photochemical processing, and there is a demand for an improvement in the output of ultraviolet rays emitted from low-pressure mercury discharge lamps.

[0005]

A conventional low-pressure mercury vapor discharge lamp has an arc input of about 5 W/cm and a lamp capacity of about 500 W. In this case, the arc tube has an inner diameter of 2
It has a circular cross-section of about 4 mm (cross-sectional area = about 4.5
cm2), the discharge current is 7A (current density 1.6A/cm
2) specifications.

In order to increase the ultraviolet output in such a low-pressure mercury discharge lamp, it is necessary to increase the discharge current, but in the conventional case, the current density is 1.6 A, as shown by the broken line in FIG. /cm2 or less, the lamp input increases as the discharge current increases, and the ultraviolet output increases; however, in the area where the current density is 1.6 to 2A/cm2, the output reaches its maximum and reaches saturation, and then Above 2 A/cm2, the UV output decreases even though the lamp input increases.

The cause of this is not clear, but when the current flowing through the discharge path is increased, the current density in the arc increases, and the vaporized mercury atoms are excessively ionized, which causes the excited atoms that contribute to light emission to become This is thought to be due to a shortage.

[0008] In order to compensate for the amount of excited atoms, it is necessary to increase the mercury vapor pressure, but as the mercury vapor pressure increases, 2
It is widely known that self-absorption of 54 nm ultraviolet rays occurs, and the emitted 254 nm ultraviolet rays are absorbed by mercury vapor in the arc, resulting in a decrease in ultraviolet output.

The present invention was made based on the above circumstances, and its purpose is to provide a low-pressure mercury discharge lamp that has less self-absorption of ultraviolet rays and can increase the output of ultraviolet rays. It is.

0010

[Means for Solving the Problems] In the present invention, electrodes are sealed at both ends of an arc tube, and mercury and rare gas are sealed in the arc tube, and the lamp is lit at a current density in the range of 1 to 6 A/cm2. The low-pressure mercury discharge lamp is characterized in that at least the discharge space of the arc tube has a non-circular cross-sectional shape.

[0011]

[Operation] According to the present invention, since the cross-sectional shape of the discharge space of the arc tube is made non-circular, the optical thickness of the mercury vapor layer within the arc tube is reduced, which means that self-absorption of ultraviolet rays by mercury vapor is suppressed. Therefore, it is considered that the ultraviolet output is improved even when the current density is increased to a range that is conventionally considered to exceed the saturation region.

0012

Embodiment The present invention will be explained below based on an embodiment shown in FIGS. 1 and 2. In FIG. 1, reference numeral 1 denotes a low-pressure mercury discharge lamp, and this discharge lamp 1 is equipped with an arc tube 2 made of synthetic quartz and bent into a substantially U-shape.

Stems 3, 3 are sealed to both ends of the arc tube 2, and an anode 4 and a hot cathode 5 are supported on these stems 3, 3, respectively. Each anode 4 is arranged in front of the hot cathode 5 in the discharge space, and the anode 4 is formed by a circular coil, a cylinder, or an annular plate, and the hot cathode 5 is formed by a filament coil.

The arc tube 2 has a non-circular cross section, for example, as shown in FIG.
As shown in Figure (b), it has a substantially flat rectangular shape, and the ratio x/y of the short side x to the long side y is about 0.2 to 0.8. In this embodiment, the short side x is 15 mm, the long side y is 30 mm, and the cross-sectional area of the arc tube 2 is about 4.5 cm2, which is substantially the same as the conventional one.

The arc tube 2 is filled with mercury and a rare gas such as argon. In this case, the vapor pressure of mercury is 0.7 to 13 Pa during lighting, and the sealing pressure of argon gas is 1.
It is sealed so as to have a pressure of 3 to 133 Pa.

This low pressure mercury discharge lamp 1 has a lighting circuit device 1.
0 to the AC power supply. Lighting circuit device 1
0 is, for example, a step-up transformer 11 and a heater transformer 12.
, 12, the step-up transformer 11 is connected to the anodes 4, 4 of the lamp 1, and the heater transformer 1
2 and 12 are connected to hot cathodes 4 and 4, respectively. Therefore, the hot cathodes 4, 4 always generate heat and emit thermoelectrons.

Note that 13 and 13 are diodes.

The lighting circuit device 10 is configured to supply, for example, a commercial power supply with an input of 500 W to the low pressure mercury discharge lamp 1, so that a discharge current of 7 A flows through the low pressure mercury discharge lamp 1 during discharge. Current density is 1-6A/cm2
It is designed so that

Furthermore, the peak value of the discharge current is 1 of its effective value.
．． It is set to be 2 times or less. This means that in low-pressure mercury discharge lamps that are lit at a high current density of 1A/cm2 or more, the ultraviolet output increases when the peak value of the discharge current is set to 1.2 times or less of its effective value. This is because the present inventors have confirmed that.

In the low pressure mercury discharge lamp 1 having such a configuration, when 500 W of power is applied from the power supply through the lighting circuit device 10, the hot cathodes 5, 5 are connected to the heater transformer 12.
, 12 to an AC power source, these cathodes 5, 5 constantly generate heat and emit thermoelectrons. Then, power is applied from the step-up transformer 11 between each anode 4 and the hot cathode 5.

Therefore, in the low-pressure mercury discharge lamp 1, a half-wave current flows between the anode 4 at one end and the hot cathode 5 at the other end, a discharge occurs between them, and then the heat at the one end flows. A reverse half-wave current flows between the cathode 5 and the anode 4 at the other end, and discharge occurs between them. In this way, each anode 4 and hot cathode 5 alternately repeat discharge each time the polarity is reversed, thereby continuing lighting.

[0022] Such a discharge excites mercury-based vapor, and therefore the mercury resonance lines 185 nm and 254 nm
Light in the short wavelength ultraviolet range including nanometers is emitted.

In such a low-pressure mercury discharge lamp, the flat surface of the arc tube bulb 2 is directed toward the irradiated surface, that is, in order to effectively utilize the irradiation in the direction of the arrow in FIG. 1(b). use In the case of such a lamp, since the cross-sectional shape of the arc tube bulb 2 is a flat square, the discharge space also becomes a flat square, and the thickness of the mercury vapor layer is reduced. Therefore, absorption of ultraviolet rays by the mercury vapor layer is suppressed, and optical disturbances are reduced. Therefore, even if the mercury vapor pressure is increased, self-absorption of ultraviolet rays is small, so it is possible to increase the current density and increase the ultraviolet output.

In other words, if the current density in the arc is increased by increasing the current flowing through the discharge path, the vaporized mercury atoms will be excessively ionized, resulting in a shortage of excited atoms contributing to light emission. As the current density is increased, the mercury vapor pressure increases and the mercury atomic weight is compensated for, resulting in active excitation and increased UV output at 185 nm and 254 nm.

Furthermore, since the wide flat surface faces the irradiated surface, the wide light emitting surface can be effectively utilized, increasing the amount of ultraviolet rays irradiated.

The above effect has also been confirmed through experiments, and the characteristic B shown by the solid line in FIG. 2 is the case of the above embodiment. In this characteristic B, when the current density is from 1.6 A/cm2 to 6 A/cm2, the lamp input increases and the ultraviolet output increases as the discharge current increases. Therefore, compared to the conventional characteristic A, it is confirmed that the ultraviolet output can be significantly improved by increasing the current density.

When the current density is further increased, it is preferable to increase the heat capacity of the electrode, especially the anode, in order to prevent the electrode from scattering. In this case, for example, as shown in FIG. The anode 4 may be supported via a metal cylinder 6 attached around the periphery of the anode.

In the arc tube 2 shown in FIG. 1, the U-shaped bent portion is formed into a substantially rectangular shape, but an arc tube with such a structure is formed by bending a single long glass tube. This is even more difficult in the case of quartz glass. Therefore, a manufacturing method as shown in FIG. 4 may be adopted.

That is, in FIG. 4(a), a quartz glass tube made of quartz glass and having a flat cross section is cut into three parts 2a, 2b, and 2c. This cutting line is set at 45°. The three parts 2a, 2b cut in this way,
As shown in FIG. 4(b), 2c is made to face each other with their respective cutting lines butted against each other. In this case, the parts 2a and 2c on both sides are arranged at substantially right angles to the central part 2b. The abutting surfaces of these parts 2a, 2b, 2c are heated and welded using a burner 20, etc.

As a result, the arc tube 2 having the shape shown in FIG. 1 can be easily produced.

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

That is, although the arc tube 2 of the above embodiment has a flat rectangular cross-section, the present invention is not limited to this, and may have a cross-sectional shape as shown in FIG. 5, for example.

That is, FIG. 5(a) is an example of a valve 30 having an elliptical cross-section, FIG. 5(b) is an example of a valve 40 having a wedge-shaped cross-section, and FIG. 5(c) is an example of a valve 40 having a cross-section. valve 50,
FIG. 5D shows the case of a three-radial valve 60 in cross section.

In particular, in the case of the shapes shown in FIGS. 5(c) and 5(d), when immersed in a liquid and used as a light source to promote a photochemical reaction, the surface area increases and the reaction process is performed. Since the contact area of the liquid is increased, the processing performance is improved.

Also, regarding the cross section of the arc tube in the tube axis direction, for example, as shown in FIG. 5(e), the end portion 70 of the arc tube
If it is made into a cylindrical shape and the discharge space 80 is made into a non-circular shape,
This is preferable because the electrodes can be sealed well. Furthermore, in this case, as shown in the figure, if the arc tube axis of the discharge space 80 and the central axis of the arc tube end are deviated so that one irradiation surface becomes a flat surface, This is suitable for forcibly cooling the arc tube by bringing it into contact with another structure such as a cooling block.

Further, in the above embodiments, a U-shaped lamp is used, but the lamp may have a bent shape such as a W-shape or an annular shape, or a straight tube-shaped lamp.

Furthermore, the lamp is not limited to a lamp having a cathode and an anode at each end, and the cathode and anode discharge each other each time the polarity is reversed.

[0038]

[Effects of the Invention] As explained above, according to the present invention, since the cross-sectional shape of the arc tube is made non-circular, the optical thickness of the mercury vapor layer within the arc tube is reduced, and self-absorption of ultraviolet rays by mercury vapor is suppressed. Therefore, even when the current density is increased to a range that is conventionally considered to exceed the saturation region, the ultraviolet output is improved.

[Brief explanation of drawings]

1 shows an embodiment of the present invention, (a) is a configuration diagram showing a lighting structure of a low-pressure mercury discharge lamp, and (b) is a cross-sectional view taken along line II in (a).

FIG. 2 is a characteristic diagram showing ultraviolet output.

FIG. 3 is a diagram showing an anode support structure according to another embodiment of the present invention;

FIG. 4 shows an example of a method for manufacturing an arc tube, and FIG. 4(a) and FIG. 4(b) are explanatory diagrams of the steps.

FIG. 5 (a) to (d) are diagrams showing the cross-sectional shape of the arc tube of other embodiments of the present invention, and (e) is a diagram showing the cross-sectional shape of the arc tube in the axial direction of another embodiment. Figure shown.

[Explanation of symbols]

1...Low pressure mercury discharge lamp, 2...Earth tube bulb, 4...Anode, 5
...Hot cathode, 10...Lighting circuit device.

Claims (2)

[Claims] 1. A low-pressure mercury discharge lamp in which electrodes are sealed at both ends of the arc tube, mercury and a rare gas are sealed in the arc tube, and the lamp is operated at a current density of 1 to 6 A/cm2. A low-pressure mercury discharge lamp characterized in that the cross-sectional shape of at least the discharge space of the arc tube is non-circular. 2. The vapor pressure of mercury sealed in the arc tube is 0.7 to 13 Pa at room temperature, and the pressure of the rare gas sealed is 13 Pa at room temperature.
The low-pressure mercury discharge lamp according to claim 1, characterized in that the pressure is 133 Pa to 133 Pa.