JP2002279932A - Discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp, having a high illuminance maintenance factor on an irradiation surface, when used being built in a converging mirror while suppressing the distortion of glass induced by the irradiation of ultraviolet rays, to prevent the destruction of an arc tube and efficiently emitting light in a wide region from a vacuum ultraviolet region to an infrared region with high radiation intensity by suppressing the cloudiness of the arc tube. SOLUTION: In this discharge lamp, a pair of electrodes are arranged mutually facing in the arc tube formed of silica glass, and rare gas is sealed in the arc tube. At the center part of the arc tube, where at least the emission degree of ultraviolet rays is a maximum, when setting the thickness of the arc tube as d (μm), and the distance from the inner surface of the arc tube as x (μm), the average OH base concentration n of a region 0<=x<=20 (μm) is 10 ppm<=n<=190 ppm, and the average OH base concentration n of a region 20 (μm)<=x<=200 (μm) is 200 ppm<=n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp for use in a projection field such as a projector and a discharge lamp for satisfactorily emitting ultraviolet rays used in a photochemical industry, a semiconductor manufacturing field and the like.

[0002]

2. Description of the Related Art Conventionally, a discharge lamp has a pair of electrodes 2 inside an arc tube 1 forming a discharge space as shown in FIG.
Are arranged facing each other, and the rare gas alone or the rare gas and mercury are sealed in the arc tube 1. Specifically, xenon, krypton, and argon are used as the rare gas. In particular, in a short arc discharge lamp, a rare gas such as xenon, krypton, or argon, or a rare gas obtained by combining several kinds of these gases is sealed in the arc tube 1 as a buffer gas, so that the lamp emits light. It improves efficiency, arc stability, and arc concentration.

When a voltage is applied to the pair of electrodes 2, light is emitted when the rare gas or mercury present in the arc tube 1 returns from the excited state to the ground state or returns from the excited state to the metastable state. Alternatively, light is emitted by the recombination of free electrons and ions, or the rare gas atoms are excited to instantaneously enter an excimer state and generate excimer light when returning from this excimer state to the ground state. All these lights are summed up to emit a wide range of light from the vacuum ultraviolet region to the infrared region. The arc tube 1 is made of silica glass to transmit a wide range of light from the vacuum ultraviolet region to the infrared region.

In particular, in a discharge lamp which emits ultraviolet rays, it is desired to emit high-energy vacuum ultraviolet rays as strongly as possible in addition to the emission of ultraviolet rays by mercury.

[0005] Among the above-mentioned lights from this viewpoint, the excimer light due to the rare gas atoms is vacuum ultraviolet light having a wavelength of 200 nm or less. The emission wavelength of an excimer is 146 nm in a typical example, and the emission wavelength of an argon excimer is 126 nm in a typical example. It is desired that such vacuum ultraviolet light be radiated well.

However, the silica glass as the arc tube 1 is
Usually, as a result of having a property of absorbing light of less than 180 nm, a part of the vacuum ultraviolet light is absorbed, so that the absorption of the vacuum ultraviolet light is minimized and the vacuum ultraviolet light is transmitted efficiently. In order to shorten the optical path of the vacuum ultraviolet light transmitted through the arc tube 1, the arc tube 1 is thinned.

However, when the arc tube 1 is thinned, the intensity of the arc tube 1 is weakened, and the exhaust tube 3 shown in FIG. 1 is broken from the root while the lamp is lit, or the light output emitted from the arc tube 1 is reduced. When the electric input is increased in order to increase the power, there is a problem that the exhaust pipe 3 is cracked in a short time.

The destruction or cracking of the exhaust pipe 3 is partly due to a high gas pressure load caused by a rise in the gas temperature in the arc tube 1 when the lamp is turned on. However, the distortion of the glass induced by the irradiation of ultraviolet rays is large. It is a factor. This UV-induced strain causes stress concentration in the exhaust pipe 3 which is structurally deformed, and furthermore, when the lamp is lit for a long time, the synergistic action of the stress concentration and the high gas pressure load overlap, and the vicinity of the mounting portion of the exhaust pipe 3 There is a problem that the arc tube 1 is broken starting from the point. In particular, in a discharge lamp that emits ultraviolet light, the above-described ultraviolet light from mercury and vacuum ultraviolet light that is excimer light of a rare gas cause
There is a problem that a large ultraviolet light-induced strain occurs and the arc tube 1 is easily broken.

As described above, when a rare gas is used as the buffer gas, the luminous efficiency of the lamp, arc stability,
The arc concentration can be improved, but on the other hand, the arc tube 1 is easily clouded, the radiation intensity is reduced, and a problem that light in the vacuum ultraviolet region to the infrared region is not efficiently emitted may occur.

It has been found that the clouding phenomenon of the arc tube 1 is caused by the deposition of silica particles. In particular, argon excimer light,
Krypton excimer light emits light of higher energy than the absorption edge of silica glass. It is presumed that this light emission breaks the bond of Si—O of the silica glass, sublimes the silica glass, and deposits silica particles on the inner surface of the arc tube 1.

In order to avoid such ultraviolet ray-induced distortion and white turbidity of the arc tube, Japanese Patent Application Laid-Open No. H11-33716 discloses an OH tube in the thickness direction of silica glass.
Focusing on the base concentration distribution, a high concentration of OH groups is present in a region very close to the inner surface of the arc tube, and a specific O
An H group concentration distribution was provided.

[0012]

Incidentally, such a short arc type discharge lamp is used for a device which is condensed by a converging mirror which is usually an elliptical mirror. In such an apparatus, the illuminance of the irradiated surface is such that light from the light-emitting portion at the cathode tip is large, so that a change in the shape of the cathode tip greatly affects the illuminance value of the irradiated surface.

In a region very close to the inner surface of the arc tube, a high concentration of O
In a discharge lamp in which an H group is present, there is a problem that the illuminance on the irradiation surface is rapidly deteriorated. According to the inventor's intensive studies, when a high concentration of OH groups is present in a region very close to the inner surface of the arc tube, the arc tube becomes high in temperature at the start of the discharge lamp and at the start of the lamp, and the OH groups are released from the inner surface. I do. Normal,
A getter such as tantalum or zirconium is attached to the electrode of the arc tube, and when the OH group is released into the arc tube at a speed exceeding the getter capability, the released OH group becomes H ₂ O and enters the arc tube. Diffuses and reacts with electrodes and the like to form low melting point metal oxides. Since the tip of the electrode operates at a high temperature, it changes the shape of the tip of the cathode, lowers the brightness of the arc, and further reduces the light-collecting efficiency due to the spread of the arc. Is thought to cause a rapid decline in

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress distortion of glass induced by irradiation of ultraviolet rays and prevent breakage of an arc tube.
By suppressing white turbidity of the arc tube, light from the vacuum ultraviolet region to the infrared region can be efficiently emitted with high radiation intensity,
It is an object of the present invention to provide a discharge lamp having a high illuminance maintenance ratio on an irradiation surface when used by being incorporated in a condenser mirror.

[0015]

According to a first aspect of the present invention, there is provided a discharge lamp in which a pair of electrodes are opposed to each other in an arc tube made of silica glass and a rare gas is sealed in the arc tube. When the thickness of the arc tube is d (μm) and the distance from the inner surface of the arc tube is x (μm), at least at the center portion of the arc tube where the degree of ultraviolet radiation is maximum, 0 ≦ x ≦ 20 (μm) Average OH group concentration n in the region
Is 10 ppm ≦ n ≦ 190 ppm, and 20 (μ
m) ≦ x ≦ 200 (μm)
200 ppm ≦ n.

[0016] The discharge lamp according to claim 2 is a silica lamp.
A pair of electrodes are arranged opposite to each other in an arc tube made of glass.
Discharge lamp with rare gas and mercury sealed in the arc tube
Wherein the noble gas is argon and / or krypton;
Xenon, the partial pressure of argon and the partial pressure of krypton.
The pressure is the partial pressure of argon, PA (Pa), krypton
When the pressure is PK (Pa), PA + PK ≧ 1.0 ×
10⁵(Pa).
Non partial pressure is 2.0 × 10⁵(Pa)
And the mercury is 0.1 mg / cm³Less than
Upper 7mg / cm ³It is enclosed so that it is as follows
The arc tube that has at least the maximum UV emission of the arc tube
In the central part, the thickness of the arc tube is d (μm), and the arc tube
When the distance from the inner surface is x (μm), 0 ≦ x ≦ 2
The average OH group concentration n in the region of 0 (μm) is 10 ppm ≦
n ≦ 190 ppm and 20 (μm) ≦ x ≦ 200
(Μm), the average OH group concentration n is 200 ppm ≦
n.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The discharge lamp of the present invention has the same outer shape as the discharge lamp of FIG. 1 described in the prior art, and will be described with reference to FIG. This is a short arc type discharge lamp in which a pair of electrodes 2 are arranged opposite to each other inside an arc tube 1 forming a discharge space, and xenon is sealed in the arc tube 1 as a rare gas.

The specific specification is that the distance between the electrodes is 4.5 m
m, the pressure of the enclosed xenon is 3 in 300K conversion
× 10 ⁵ Pa, output 2 KW. In addition, xenon was sealed in the arc tube at a pressure of 3 × 10 ⁵ Pa in terms of 300K. However, other than xenon, argon or krypton may be used, or a mixed gas thereof may be used. Unless the total pressure is 0.1 × 10 ⁵ Pa or more, sufficient ultraviolet light emission efficiency cannot be obtained by the rare gas.

The arc tube 1 is made of silica glass. The central portion of the arc tube where the degree of emission of ultraviolet rays in this specification is maximum is, as shown in FIG.
, A portion where a virtual line Y orthogonal to the axis X between the electrodes 2 intersects the arc tube 1 is defined as the center portion of the arc tube where the degree of ultraviolet radiation is maximum, and the thickness of the arc tube at this portion is d ( μm)
Fig. 3 shows the average OH group concentration at a predetermined depth of the arc tube when
This is like the lamp 2 shown in FIG. The specific value is 20 μm from the inner surface of the arc tube.
The average OH group concentration from 20 to 200 μm from the inner surface of the arc tube is 200 ppm.
pm, the average OH group concentration from the inner surface of the arc tube to 200 to d-600 μm is 5 ppm.

Then, a total of five discharge lamps for comparison with the discharge lamp of the present invention including the above-described discharge lamp of the present invention were prepared, and each discharge lamp was lit so that only the OH group concentration of the arc tube was different. FIG. 3 shows experimental data obtained by observing deformation of the tip of the cathode 50 hours later and checking for the presence or absence of white turbidity in the arc tube, and further confirming the state of distortion of the arc tube 400 hours after lighting. In all the discharge lamps, the distance between the electrodes was 4.5 mm, the pressure of the enclosed xenon was 3 × 10 ⁵ Pa in terms of 300 K, and the output was 2 KW.
The average OH group concentration of the arc tube of each discharge lamp is as shown in FIG.

As shown in FIG. 3, a method for changing the average OH concentration in the depth direction of the arc tube is to introduce an appropriate amount of water vapor into the silica glass of the original tube to be the arc tube and heat the silica glass from the outside.
A secondary tube is manufactured, and the primary tube is processed into an arc tube as it is, or the primary tube is further heated in vacuum to produce a secondary tube, and the secondary tube is processed into an arc tube. As a result, the average OH group concentration of the arc tube is appropriately changed in a predetermined depth direction of the arc tube.

As can be seen from the experimental data shown in FIG. 3, the discharge lamps of the present invention, Lamp 2, Lamp 3, Lamp 4
When the thickness of the arc tube is d (μm) and the distance from the inner surface of the arc tube is x (μm) at the center of the arc tube where the degree of ultraviolet emission of the arc tube is maximum, 0 ≦ x ≦ 20 ( μ
The average OH group concentration n in the region m) is 10 ppm ≦ n ≦ 19
0 ppm, 20 (μm) ≦ x ≦ 200 (μ
The average OH group concentration n in the region of m) is n ≧ 200 ppm, the average OH group concentration n in the region of 200 (μm) ≦ x ≦ d-600 (μm) is n ≦ 800 ppm,
As a result, there is no deformation of the tip of the cathode, the distortion of the arc tube is small enough, the arc tube can be prevented from exploding due to the distortion, and the arc tube has no cloudiness. Which is a discharge lamp.

On the other hand, lamp 1 as a comparative discharge lamp
In the lamp 5, the average OH group concentration is out of the average OH group concentration range of the present invention in the central portion of the arc tube where the emission degree of ultraviolet light of the arc tube is maximum, and in the lamp 1, the arc tube becomes cloudy and distortion occurs. There is a sufficient risk that the arc tube may burst due to some influence due to the pressure of the gas inside the arc tube, and the lamp 5 has a defect such as deformation of the cathode tip.

From the above experimental data, it can be seen that the discharge lamp of the present invention reduces the concentration of OH groups in the region extremely near the inner surface of the arc tube, thereby reducing the amount of OH groups released into the arc tube when the lamp is started. And the clouding of the arc tube can be suppressed, and the deformation of the cathode can be prevented. Furthermore, by increasing the OH group concentration at the center in the depth direction of the arc tube, the OH groups can be constantly supplied to the inner surface of the arc tube by the concentration diffusion of the OH groups during lamp operation. The presence of a high concentration of OH groups from the center to the vicinity of the inner surface can suppress the influence of distortion due to ultraviolet rays.

In addition, the deformation of the tip of the cathode is as follows.
The difference in the deformation from the initial stage was visually inspected by enlarging with a double magnification projector.

The measurement of the average OH group concentration of the arc tube was performed as follows. Perform absorption measurement in the IR (infrared) region,
The OH group concentration was determined from the infrared absorption intensity at a wavelength of 3673 cm ^-1 . The concentration in a specific region in the depth direction of the arc tube is determined by chemically polishing (HF / H
Etching with a mixed acid of ₂ SO ₄ ) was performed, and the degree of IR absorption before and after the polishing was compared to calculate the average OH group concentration contained in the polished region.

The distortion of the arc tube due to ultraviolet rays is measured by arranging an arc tube and a polarizing plate as a sample in a crossed Nicols relationship, illuminating diffused light, and obtaining the intensity of light transmitted through the sample by birefringence. (Photoelasticity measurement), the measurement site is the arc tube glass part located almost horizontally and horizontally at the tip of the cathode when the discharge lamp is vertical (the part where the emission of ultraviolet radiation is maximum: see FIG. 2). It was performed about.

Next, the lamps 2, 3, and 4 as the discharge lamps of the present invention and the lamps 1 and 5 as the discharge lamps for comparison are continuously turned on. The change of the illuminance maintenance rate with the passage of time when the value of the light having a wavelength of 365 nm at the initial stage of lighting on the irradiation surface condensed by the method was defined as 1 was examined. FIG. 4 shows the results. As can be seen from FIG. 4, the lamps 2, 3 and 4 of the present invention remain 90 hours after being turned on for 1500 hours.
It can be seen that the illuminance maintenance rate of% can be maintained.
This is because the arc tube is not clouded and the cathode is not deformed. On the other hand, lamp 1 which is a discharge lamp for comparison
And the lamp 5 has a sharp decrease in the illuminance maintenance ratio immediately after lighting, and particularly, the lamp 1 has a 50% illuminance maintenance ratio after lighting for 300 hours.
After lighting the lamp 5 for 1500 hours, the illuminance maintenance ratio was reduced to 65%. This is because clouding of the arc tube occurs, and the biggest factor is deformation of the cathode.

Next, mercury, argon and / or krypton as a rare gas, and xenon were sealed in the lamp 2 as the discharge lamp of the present invention. The partial pressure of argon is represented by PA (Pa), and the partial pressure of krypton is represented by PK (Pa), and PA + PK ≧ 1.0 × 10 ⁵ (Pa). In addition, xenon is 2.0 × 10 ⁵ (Pa) Enclosed in the following range, mercury is 0.1 mg / cm ³ or more and 7 mg / c
m ³ was prepared discharge lamp of the present invention encapsulating following.

The discharge lamp of the present invention suppresses clouding of the arc tube and does not deform the tip of the cathode, similarly to the other discharge lamps of the present invention, such as the lamps 2, 3, and 4. Distortion due to ultraviolet rays is also suppressed, and the illuminance maintenance ratio on the irradiation surface is high even when the lamp is turned on for a long time.

As described above, the partial pressure of argon is defined as PA and the partial pressure of krypton is defined as PK + PAK ≧ 1.0 × 10 ⁵ (P
By defining a), the intensity of the ultraviolet light having a wavelength of 365 nm can be increased. Further, when the xenon regulates the partial pressure to 2.0 × 10 ⁵ (Pa) or less, it is possible to effectively obtain an ultraviolet intensity of a wavelength of 365 nm.
If the partial pressure of xenon is less than 0.13 × 10 ⁵ (Pa), a clouding phenomenon may occur in the discharge vessel.

The amount of mercury enclosed was 0.1 mg /
cm ³ or more 7mg / cm ³ or less reason, 0.1m
If it is less than g / cm ³ , it is impossible to effectively obtain an ultraviolet intensity of 365 nm wavelength, and if it exceeds 7 mg / cm ³ , the spectrum width of the emission of 365 nm wavelength will be widened.

[0033]

As described above, according to the discharge lamp of the present invention, the distortion of the glass induced by the irradiation of ultraviolet rays can be suppressed, and the destruction of the arc tube can be prevented. Accordingly, light in the vacuum ultraviolet region to the infrared region can be efficiently radiated with high radiation intensity, and when used in a condensing mirror, a discharge lamp having a high illuminance maintenance ratio on an irradiation surface is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a discharge lamp.

FIG. 2 is an explanatory diagram of a central portion of an arc tube in which the degree of ultraviolet radiation is maximum.

FIG. 3 is an explanatory diagram of experimental data for confirming deformation of a cathode tip, opacity of an arc tube, and distortion of an arc tube of a discharge lamp of the present invention and a comparative discharge lamp.

FIG. 4 is an explanatory diagram of experimental data of the illuminance maintenance ratio of the discharge lamp of the present invention and a discharge lamp for comparison.

[Explanation of symbols]

 1 arc tube 2 electrode 3 exhaust tube

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C015 PP03 PP04 PP05 PP07 PP08 5C039 HH02 HH15 5C043 AA03 CC02 CC05 CD01 DD03 EB15 EC06

Claims (2)

[Claims] 1. A discharge lamp in which a pair of electrodes are opposed to each other in an arc tube made of silica glass, and a rare gas is sealed in the arc tube. In the above, when the thickness of the arc tube is d (μm) and the distance from the inner surface of the arc tube is x (μm), 0 ≦ x ≦
The average OH group concentration n in the region of 20 (μm) is 10 ppm
≦ n ≦ 190 ppm, and 20 (μm) ≦ x ≦ 200
(Μm), the average OH group concentration n is 200 ppm ≦
n. A discharge lamp, wherein n is n. 2. A discharge lamp in which a pair of electrodes are arranged opposite to each other in an arc tube made of silica glass and a rare gas and mercury are sealed in the arc tube, wherein the rare gas is argon and / or krypton and xenon. The partial pressure of argon and the partial pressure of krypton are expressed as follows: the partial pressure of argon is PA (Pa), and the partial pressure of krypton is PK (Pa).
In this case, PA + PK ≧ 1.0 × 10 ⁵ (Pa), and the xenon partial pressure is 2.0 × 10 ⁵ (Pa) or less. The mercury is sealed so as to be 0.1 mg / cm ³ or more and 7 mg / cm ³ or less, and the thickness of the arc tube is at least at the central portion of the arc tube where the degree of ultraviolet radiation is maximum. Where d (μm) is the distance and x (μm) is the distance from the inner surface of the arc tube, 0 ≦ x ≦
The average OH group concentration n in the region of 20 (μm) is 10 ppm
≦ n ≦ 190 ppm, and 20 (μm) ≦ x ≦ 200
(Μm), the average OH group concentration n is 200 ppm ≦
n. A discharge lamp, wherein n is n.