JP4483591B2 - Flash discharge lamp - Google Patents

Description

  The present invention relates to a flash discharge lamp. In particular, the present invention relates to a flash discharge lamp having a single crystal alumina arc tube.

Flash discharge lamps are used as light sources in rapid thermal processing of semiconductor manufacturing processes. This is because light with high radiation intensity can be obtained with high efficiency.
This type of flash discharge lamp has an extremely short time required for one light emission, and the temperature inside the arc tube reaches a high temperature of, for example, 1000 ° C. For this reason, attention is paid to single crystal alumina (sapphire) as a material of the arc tube. This is because it is superior in heat resistance to quartz glass.

  However, although the arc tube made of sapphire is excellent in heat resistance, there is a problem that the service life cannot be sufficiently obtained. This is because the thermal expansion coefficient of sapphire is larger than the thermal expansion coefficient of quartz glass, and a large stress is generated inside the arc tube every time flash light is emitted, and the arc tube is broken by the repetition.

In order to solve the above-mentioned problem, for example, Japanese Patent Application Laid-Open No. 2003-109537 introduces a technique for providing a thermal expansion buffer recess in the arc tube. This is because the recesses avoid or suppress the generation of stress by absorbing thermal expansion.
However, even if this technology is applied to the sapphire arc tube, the generation of stress cannot be sufficiently suppressed, and in some cases, the arc tube breaks at the same level as when the thermal expansion buffer recess is not formed. May occur.
In particular, the above-mentioned prior art document covers a wide range of ceramics such as polycrystalline alumina, and although a certain degree of effect can be obtained with polycrystalline ceramics, a sufficient effect cannot be obtained with single crystal alumina. could not.
JP 2003-109537 A

  The problem to be solved by the present invention is that, in a flash discharge lamp composed of a single crystal alumina (sapphire) arc tube, the influence of stress due to thermal expansion is reliably suppressed, and as a result, the arc tube is prevented from being damaged. Or it is providing the structure which can be suppressed.

In order to solve the above problems, a flash discharge lamp according to the present invention comprises a light emitting tube made of single crystal alumina and encloses a pair of electrodes and a discharge gas inside, and on the inner surface of the light emitting tube, A concave portion extending in a direction crossing the C axis of the single crystal alumina constituting the arc tube is formed.
Further, the recess is characterized by extending so as to be orthogonal to the C-axis of the single crystal alumina constituting the arc tube.
The arc tube may be a straight tube, and the recess may be formed in a circular shape on the inner peripheral surface of the arc tube.
The concave portion has an average roughness of 0.1 μm to 1 μm.

With the above configuration, even an arc tube made of single crystal alumina can suppress the occurrence of stress due to thermal expansion and avoid breakage of the arc tube.
In particular, the present invention focuses on the crystal axis having the largest thermal expansion coefficient (for example, the C-axis direction for sapphire) in a single crystal having a different thermal expansion coefficient with respect to the crystal axis direction, and the direction in which the recess extends. Thus, a structure that reduces the influence of stress due to thermal expansion can be achieved.

FIG. 1 shows a flash discharge lamp (hereinafter also referred to as “flash lamp”) according to the present invention.
The flash discharge lamp 10 has a straight tube arc tube 11. Inside the arc tube 11, a pair of electrodes 12 are supported by the electrode rods 13 and arranged to face each other. A cylindrical sealing member 14 made of a polycrystalline alumina sintered body is inserted into both ends of the arc tube 11. The arc tube 11 and the sealing member 14 are hermetically sealed with a sealing glass 15. An electrode rod 13 is provided through the sealing member 14 so as to extend in the axial direction of the arc tube 11. The electrode rod 13 and the sealing member 14 are also hermetically sealed by the sealing glass 15.
The inside of the arc tube 11 forms a discharge space and, for example, xenon gas is enclosed as a discharge gas.

The arc tube 11 is made of single crystal alumina (sapphire). A single crystal is superior in light transmittance, mechanical strength, heat resistance, plasma resistance, and the like as compared with a polycrystal. Considering physical properties required as a lamp material, excellent characteristics can be obtained by using sapphire, which is a single crystal of aluminum oxide.
Although not shown, a trigger wire is provided on the outer surface of the arc tube 11.

FIG. 2 shows an enlarged view of a part P of the arc tube 11 shown in FIG. A part P of the arc tube 11 has a hollow cylindrical shape, and the longitudinal direction of the arc tube 11 shown in FIG. 1 is replaced with a vertical direction in FIG. FIG. 2 also shows a form in which a part P ′ of the part P of the arc tube is further enlarged.
A circular recess (groove) 20 is formed on the inner wall of the arc tube 11 in the circumferential direction. The direction in which the recess 20 extends is formed in a direction orthogonal to the C axis (direction indicated by X in the figure) of the single crystal alumina constituting the arc tube.

FIG. 3 shows a cross-sectional structure of a part P of the arc tube 11 shown in FIG.
The recess 20 is formed continuously over the entire length of the arc tube 11. This is because the suppression of stress can be expected over the entire length of the arc tube. Moreover, it is desirable to form it at least in the effective light emitting region of the arc tube, although it is not the full length. This is because the effective light emitting region is susceptible to thermal expansion. In this case, the effective light emitting region refers to a region formed between the tips of both electrodes.
Further, the concave portion 20 can be partially formed on the inner wall of the arc tube as long as the influence of stress can be substantially avoided.

The present invention is characterized in that the direction in which the recess (groove) extends is defined in relation to the C-axis direction of the single crystal alumina. This is because single crystal alumina has a different coefficient of thermal expansion depending on the crystal direction, and the direction of the generated thermal stress is also different.
Specifically, it is about 4.5 × 10 ⁻⁶ (1 / K) in the vertical direction with respect to the C axis of the single crystal alumina, and is about 5.3 × 10 ⁻⁶ (1 / K) in the parallel direction. It is. This numerical value is an example at 25 ° C.

Furthermore, in comparison with polycrystal, the arc tube is made of a polycrystalline material. As a result, since the C-axis direction of each crystal exists as various directions, the inner wall of the arc tube is appropriately formed. Even if the recesses are formed, the C-axis of some crystals among many crystals is established in an optimal relationship with the direction in which the recesses extend. Therefore, in the case where the arc tube is made of polycrystal, even if the concave portions are formed without any regularity, there is an effect that stress can be suppressed or avoided not a little.
On the other hand, in the case of a single crystal, the C-axis direction is determined to be one, so that the stress suppressing effect is not produced at all depending on the formation direction of the recess.
Based on such knowledge, the present invention has found that when a single crystal arc tube is used, it is effective to define the direction in which the recess extends in relation to the C-axis direction of the crystal. . That is, in the single crystal alumina having anisotropy in the crystal structure and different thermal expansion coefficients depending on the direction, the direction in which the recess is formed is defined by the relationship with the C-axis direction of the crystal.
Accordingly, any single crystal material can be applied to other materials without being limited to sapphire, but sapphire is practically used as a material suitable for the arc tube of the lamp.

Here, the direction in which the concave portion is formed is most preferably orthogonal to the C-axis of the arc tube, but is not necessarily limited to the orthogonal direction, and is effective even if the relationship intersects at a predetermined angle. Have
Therefore, when the arc tube has a straight tube shape and the C-axis of the crystal is formed in the longitudinal direction, the concave portion is formed in a circular shape or a spiral shape on the inner wall of the arc tube.

  Here, coordinate axes are taken along the sides corresponding to the vertical, horizontal, and height of the basic solid constituting the crystal lattice, and these crystal axes are referred to as an A axis, a B axis, and a C axis, respectively. The C-axis of the crystal can be detected by, for example, a crystal orientation measurement method called a back reflection Laue method, and performing X-ray diffraction analysis on single crystal alumina.

The depth Ra of the recess is an arithmetic average roughness according to JIS standard, and a numerical value selected from a range of 0.1 μm to 1.0 μm is preferable, and a range of 0.3 μm to 1.0 μm is particularly preferable.
If it is smaller than 0.1 μm, the stress caused by the thermal expansion of the arc tube cannot be sufficiently suppressed, and a crack occurs on the inner surface of the arc tube. On the other hand, when the thickness exceeds 1.0 μm, the mechanical strength of the arc tube is lowered. The thickness of the lamp is usually about 0.5 to 2 mm, and if the depth of the recess exceeds 1.0 μm within that range, there is a problem.
The depth Ra is the arithmetic average roughness published in the JIS standard, and the cutoff value is 2.5 mm.

The present invention is also suitable for a flash discharge lamp that is lit at a high load. This is because the arc tube causes thermal expansion because it is lit at a high load.
Specifically, the structure of the present invention is effective when flash lighting is performed under the condition that the tube wall load WL is 4 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ) or more. Here, the tube wall load WL is a value obtained by dividing the input energy (J) of the lamp by the inner surface area of the arc tube, and the inner surface area of the arc tube is not the total area of the inside of the arc tube, but between the tips of a pair of electrodes. It is the part formed by the above, that is, the area of the effective light emitting region. Also, τ means the half width (FWHM) of the current waveform.
This is because when the tube wall load WL is less than 4 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ), the impact on the lamp is small, so that the thermal expansion of the arc tube does not matter regardless of the presence or absence of the recess. .
If the tube wall load WL is 4 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ) or more, there is no upper limit from the technical point of view of suppressing thermal expansion. Therefore, it is generally limited to 18 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ) or less.
Therefore, the present invention is effective when the tube wall load WL is in the range of 4 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ) to 18 × (τ × 10 ⁴ ) ^0.5 (J / cm ² ).

  The method of forming the concave portion on the inner surface of the arc tube is, for example, a method of cutting from a single crystal alumina in a lump shape by machining, a method of cutting machining or chemical etching after forming a cylindrical arc tube, and There is a method of adjusting the pulling condition in the pulling method.

As for numerical examples of the flash lamp, the inner diameter of the arc tube is selected from the range of φ8 to 20 mm, for example, 10 mm, and the length of the arc tube is selected from the range of 100 to 600 mm, for example, 300 mm.
The amount of sealed xenon gas is selected from the range of 200 to 1500 torr, for example, 500 torr. The main light emitting component is not limited to xenon gas, and argon or krypton gas can be used instead. In addition to xenon gas, other substances such as mercury can be added.
An electrode is an electrode which has tungsten as a main component, Comprising: A size is selected from the range whose outer diameter is 4-18 mm, for example, is selected from the range whose length is 5 mm and 5-9 mm, for example, is 7 mm. The distance between the electrodes is selected from the range of 50 to 550 mm, for example, 280 mm. In addition, barium oxide (BaO), calcium oxide (CaO), strontium oxide (SrO), alumina (Al2O3), lanthanum oxide (La2O3), thorium oxide (ThO2), and the like are mixed in the cathode as an emitter.
Furthermore, the trigger electrode is in the form of a wire formed of nickel or tungsten and is in contact with the arc tube.

As for numerical examples of flash lamp emission, the light emission cycle is repeated, for example, 0.5 to 6 times per minute, specifically, once, and the emission energy of each flash lamp is 24 to 17000 J. For example, 850J is selected from the range.
There may be a case where a plurality of flash lamps are arranged to emit light at the same time. Specifically, 5 to 40 flash lamps are selected, for example, 30 are arranged. Light intensity on the irradiated surface as the range of the total number of flash lamps 5 to 40, are selected from 2~50J / cm ² range, for example, a 20 J / cm ^2.

Next, an experiment for confirming the effect of the present invention will be described.
1 is a straight tube arc tube, and a flash discharge lamp having a C axis in the longitudinal direction of the arc tube as shown in FIG. Four types of lamps of 0 ° (parallel to the C axis), 30 °, 60 °, and 90 ° were prepared.
Each lamp has basically the same structure except that the direction of formation of the recess is different. The inner diameter is 10.4 mm, the outer diameter is 13 mm, the total length is 300 mm, the depth of the recess is 0.3 μm, and the effective light emission length (distance between electrodes) is 250 mm. The sealing gas was xenon and 450 Torr. Further, flash lighting was repeated at a tube wall load WL of 15 J / cm ² and a half-value width of 100 μsec.

When the lamp was lit approximately 1000 times under the above conditions, the lamp having the recess formed at 0 ° with respect to the C axis and the lamp formed at 30 ° with respect to the axis caused many fine cracks on the inner surface of the arc tube. In addition, the lamp in which the concave portion was formed at 60 ° with respect to the C-axis generated fine cracks, though only slightly. On the other hand, it was confirmed that the lamp in which the concave portion was formed at 90 ° with respect to the C axis hardly caused cracks, and the light output was not different from that at the start of lighting.
As a result, it can be seen that the concave portion has an effect of suppressing the generation of cracks against thermal expansion in the range of 60 to 90 ° with respect to the C-axis of the crystal, and particularly has an excellent effect at 90 °.

  Since the sealing member 14 attached to the end of the arc tube 11 is inexpensive and hardly affected by thermal expansion, a sintered body of polycrystalline alumina is used, but other materials are used. Is also possible. In particular, when the electrode rod 13 is short and the effective light emitting region is long, it is advantageous to provide single crystal alumina when the end of the arc tube 11 is also affected by thermal expansion.

  In the above embodiment, a flash discharge lamp having a straight tube-shaped arc tube having an inner diameter of about 10 mm and a total length of 200 mm or more was used. However, it is not limited to such a straight tube-shaped arc tube.

  In the structure shown in the figure, the dimensional relationship is not accurately expressed for convenience of explanation. In particular, the relationship between the depth of the recess and the inner diameter of the arc tube is exaggerated.

1 shows a flash discharge lamp according to the present invention. 2 shows a part of a flash discharge lamp according to the present invention. 2 shows a part of a flash discharge lamp according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Flash discharge lamp 11 Arc tube 12 Electrode 13 Electrode rod 14 Sealing member 15 Sealing glass 20 Recessed part

Claims (3)

In a flash discharge lamp comprising an arc tube made of single crystal alumina and having a pair of electrodes and a discharge gas enclosed therein,
On the inner surface of the arc tube, a recess extending in a direction intersecting with the C axis of the single crystal alumina constituting the arc tube is formed, and the recess has an average roughness of 0.1 μm to 1.0 μm. Features a flash discharge lamp.   2. The flash discharge lamp according to claim 1, wherein the recess extends so as to be orthogonal to the C axis of single crystal alumina constituting the arc tube.   2. The flash discharge lamp according to claim 1, wherein the arc tube is a straight tube, and the recess is formed in a circular shape or a spiral shape on an inner peripheral surface of the arc tube.

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