JP2009295469A - Excimer lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excimer lamp provided with an ultraviolet reflecting layer, which can efficiently emit vacuum ultraviolet ray even when lighting for a long time while minimizing the degree of deterioration of illuminance. <P>SOLUTION: The excimer lamp 10 comprises the ultraviolet reflecting layer 30 formed on a portion of the inner surface of a discharge vessel 20. The ultraviolet reflecting layer 30 is composed of a deposit A31 formed in at least part of the area corresponding to one electrode 11, and a deposit B32 formed in at least part other than the area corresponding to electrodes 11 and 12. The deposit A31 includes: silica particles containing OH-group; and fine particles higher in melting point than silica. The deposit B32 includes fine particles containing the silica particles containing OH-group. The OH-group concentration in the silica particles constituting the ultraviolet reflecting layer 30 is 10 wt.ppm or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an excimer lamp used for performing surface treatment such as cleaning treatment, ashing treatment, and film formation treatment by irradiating ultraviolet rays on a workpiece.

  By irradiating an object to be processed such as a glass substrate or a semiconductor wafer of a liquid crystal display device with vacuum ultraviolet light having a wavelength of 200 nm or less, the object to be processed is processed by the action of the vacuum ultraviolet light and ozone generated thereby. Technology, for example, a cleaning processing technology for removing organic contaminants attached to the surface of the object to be processed and an oxide film forming processing technology for forming an oxide film on the surface of the object to be processed have been developed and put into practical use.

As an apparatus for irradiating vacuum ultraviolet light, for example, a discharge gas is sealed in a discharge vessel made of a dielectric, and an excimer discharge is generated by applying an alternating high voltage through the discharge vessel. An excimer lamp that emits a certain excimer emission is used. In such excimer lamps, many attempts have been made to efficiently radiate higher-intensity ultraviolet rays.
Specifically, an ultraviolet reflecting layer is formed on the inner surface of the discharge vessel of the excimer lamp, and the ultraviolet reflecting layer transmits fine particles, for example, only silica, or silica and other fine particles, For example, a technique formed by laminating alumina, magnesium fluoride, calcium fluoride, lithium fluoride, magnesium oxide, or the like is disclosed (see Patent Document 1).

  In the excimer lamp having such a configuration, the ultraviolet rays generated in the discharge vessel that are not directly emitted toward the light emitting portion are incident on the ultraviolet reflecting layer, and the surfaces of the plurality of microparticles constituting the ultraviolet reflecting layer. The light is emitted from the light emitting portion by being diffusely reflected by repeatedly performing refraction and reflection. Thereby, an ultraviolet-ray can be radiated | emitted efficiently.

  In lamps that emit ultraviolet rays, for example, silica glass is widely used as a material constituting the discharge vessel. Therefore, in order to increase the adhesion of the ultraviolet reflecting layer to the silica glass by eliminating the difference in thermal expansion coefficient from the silica glass constituting the discharge vessel or making it extremely small as the fine particles constituting the ultraviolet reflecting layer. In addition, it is preferable to include silica particles made of the same material as the discharge vessel.

  Many objects to be processed for surface treatment have a flat shape such as a glass substrate of a liquid crystal panel. For this reason, an excimer lamp having a light emitting portion that is a flat discharge vessel similar to the object to be processed can suppress the absorption of ultraviolet rays by oxygen by reducing the gap between the light emitting portion and the object to be processed. Surface treatment can be performed efficiently. As an excimer lamp composed of a discharge vessel having such a shape, for example, Patent Document 2 discloses an excimer lamp composed of a rectangular discharge vessel.

As an excimer lamp including a discharge vessel having a flat light emitting portion, there is a structure as shown in FIG. The excimer lamp 10 includes a flat rectangular discharge vessel 20 made of silica glass. The discharge vessel 20 has a structure in which an upper wall plate 21, a lower wall plate 22, a side wall plate 23, and an end wall plate 24 are connected. The discharge gas is sealed inside. Further, a high voltage supply electrode 11 is provided on the outer surface of the upper wall plate 21, and a ground electrode 12 is provided on the outer surface of the lower wall plate 22, and these electrodes 11, 12 are disposed so as to face each other. The excimer emission generated in is emitted to the outside through the lower wall plate 22 also serving as a light emitting portion.
JP 2007-335350 A JP 2004-113984 A

  However, in an excimer lamp provided with an ultraviolet reflecting layer made of fine particles containing silica particles, the illuminance maintenance factor gradually decreases over time when the lamp is lit for a long time. For this reason, for example, when performing a surface treatment such as a cleaning treatment, there is a problem in that the processing capability of the excimer lamp varies with the lighting time even if the treatment is performed with a constant illuminance.

  The present invention has been made based on the circumstances as described above, and includes an ultraviolet reflecting layer made of fine particles containing silica particles, and suppresses the degree of decrease in illuminance to a small level even when lit for a long time. An object of the present invention is to provide an excimer lamp capable of efficiently emitting vacuum ultraviolet light.

The excimer lamp of the first invention of the present application includes a discharge vessel made of silica glass having a discharge space, a pair of electrodes are provided in a state where the silica glass forming the discharge vessel is interposed, and a discharge vessel is provided in the discharge space. An excimer lamp in which a gas is sealed and an ultraviolet reflective layer is formed on a part of the inner surface of the discharge vessel, wherein the ultraviolet reflective layer is formed in at least a part of a region corresponding to one electrode. The deposited body A and the deposited body B formed in at least a part other than the region corresponding to the electrode, the deposited body A being silica particles containing OH groups, and fine particles having a melting point higher than that of silica. And consist of
The deposit B is made of fine particles containing silica particles containing OH groups, and the OH group concentration in the silica particles constituting the ultraviolet reflecting layer is 10 wtppm or more.

The second invention of the present application is the first invention of the present application, wherein the installation area of the deposit A is a (cm ² ), the installation area of the deposit B is b (cm ² ), and the specific surface area of the deposit B Is c (cm ² / g), and the inner surface area of the discharge vessel is d (cm ² ), the respective relationships are b ≧ −5.0 × 10 ⁻³ ac + 0.35a and b> 0.02d
It is characterized by satisfying.

By mixing microparticles having a melting point higher than that of silica into the ultraviolet reflective layer, it is possible to prevent the grain boundaries from being lost due to bonding between adjacent microparticles, and to suppress a decrease in the reflectance of the ultraviolet reflective layer. it can. In particular, since the deposit A formed in the region corresponding to the electrode is susceptible to the heat of plasma, it is necessary to mix the fine particles having a melting point higher than that of silica to suppress the decrease in the reflectance of the ultraviolet reflecting layer. .
Further, by including OH groups in the silica particles constituting the ultraviolet reflecting layer, it is possible to suppress the generation of internal defects in the silica particles contained in the ultraviolet reflecting layer, and to reduce the wavelength of light in the ultraviolet region by the ultraviolet reflecting layer. Absorption is prevented and the reflectivity of the ultraviolet reflecting layer is maintained, the degree of illuminance reduction of the excimer lamp is suppressed to a small level, and vacuum ultraviolet light can be emitted efficiently. In particular, by setting the OH group concentration in the silica particles constituting the ultraviolet reflective layer to 10 wtppm or more, the reflection maintenance factor and the illuminance maintenance factor can be kept high, and the illuminance maintenance when lighting for a long time is conspicuous. Exhibits excellent effects.

  When the ultraviolet reflecting layer formed on the inner surface of the discharge vessel corresponding to the position where the electrode is provided contains OH groups, it is exposed to the discharge plasma and emits an impurity gas mainly composed of water. . When the impure gas containing water as a main component is combined with the discharge gas, the illuminance of excimer emission decreases. However, by forming an ultraviolet reflecting layer on a part of the inner surface of the discharge vessel corresponding to the position where the electrode is not provided, the water is released from the ultraviolet reflecting layer in the plasma at the same time. Oxygen generated by decomposition can be adsorbed to suppress a decrease in illuminance of excimer emission. Therefore, even when the excimer lamp is lit for a long time, the degree of decrease in illuminance can be suppressed to be small, and vacuum ultraviolet light can be emitted efficiently.

Considering the specific surface area of the deposit B, the installation area of the deposit A is a (cm ² ), the installation area of the deposit B is b (cm ² ), and the specific surface area of the deposit B is c (cm ² / g). ), Where the inner surface area of the discharge vessel is d (cm ² ), the respective relationships are b ≧ −5.0 × 10 ⁻³ ac + 0.35a and b> 0.02d
By satisfying the above, the amount of impurity gas released from the deposit A does not exceed the amount of impurity gas that the deposit B can adsorb, and the impurity gas can be prevented from remaining in the discharge space. Therefore, it is possible to suppress the decrease in illuminance of excimer emission due to the oxygen atoms contained in the impure gas being combined with the discharge gas, and to suppress the decrease in illuminance even when the excimer lamp is lit for a long time. And vacuum ultraviolet light can be emitted efficiently.

FIG. 1 is an explanatory sectional view showing an outline of the configuration of an example of an excimer lamp 10 according to the present invention. (A) is sectional drawing which shows the cross section along the longitudinal direction of the discharge vessel 20, (b) is sectional drawing of the AA 'line in (a).
This excimer lamp 10 includes a discharge vessel 20 having a rectangular hollow cross-section, in which both ends are hermetically sealed and a discharge space S is formed therein. The discharge vessel 20 includes an upper wall plate 21, a lower wall plate 22 facing the upper wall plate 21, a pair of side wall plates 23 connected to the upper wall plate 21 and the lower wall plate 22, the upper wall plate 21, It consists of a pair of end wall plates 24 provided so as to seal both ends of a rectangular cylindrical body comprising a wall plate 22 and a pair of side wall plates 23. The discharge vessel 20 is formed of silica glass, for example, synthetic quartz glass, which transmits vacuum ultraviolet light well.

  A discharge gas is sealed in the discharge vessel 20 at a pressure of 10 to 80 kPa, for example. No matter which gas is selected as the discharge gas, it does not affect the temporal change of the radiation intensity, but the central wavelength of the excimer emission that is emitted differs depending on the type of the discharge gas. For example, excimer emission with a central wavelength of 172 nm occurs in an excimer lamp enclosing xenon (Xe), and excimer with a central wavelength of 175 nm in an excimer lamp enclosing a mixed gas of argon (Ar) and chlorine (Cl). In the excimer lamp in which a mixed gas of krypton (Kr) and iodine (I) is enclosed, excimer emission having a central wavelength of 191 nm is generated, and a mixed gas of argon (Ar) and fluorine (F) is enclosed. The excimer lamp emits excimer light having a wavelength of 193 nm as a central wavelength, and the excimer lamp in which a mixed gas of krypton (Kr) and bromine (Br) is sealed generates excimer light having a central wavelength of 207 nm. In an excimer lamp in which a mixed gas of chlorine (Cl) is sealed, the center wavelength is 222 nm. Excimer emission is generated, excimer light emission center wavelength of 308nm occurs in excimer lamps mixed gas is sealed xenon (Xe) and chlorine (Cl).

  A high voltage supply electrode 11 is provided on the outer surface of the upper wall plate 21 in the discharge vessel 20, and a ground electrode 12 is provided on the outer surface of the lower wall plate 22, and these electrodes 11 and 12 are arranged so as to face each other. Such electrodes 11 and 12 have a network structure, and are formed so that light can pass through between the meshes. As the material, for example, aluminum, nickel, gold, or the like is used, and for example, it is formed by means of screen printing or vacuum deposition. The electrodes 11 and 12 are connected to an appropriate high frequency power source (not shown).

In the excimer lamp 10, in order to efficiently use vacuum ultraviolet light generated by excimer discharge, an ultraviolet reflection layer 30 made of fine particles is provided on the inner surface facing the discharge space S of the discharge vessel 20. . The ultraviolet reflecting layer 30 includes a deposit A31 and a deposit B32. The deposit A31 is a part of the inner surface facing the discharge space S of the discharge vessel 20 provided with the high voltage supply electrode 11, that is, the region corresponding to the high voltage supply electrode 11 on the inner surface of the upper wall plate 21. Formed in part. Further, the deposit B32 deviates from a part of the inner surface facing the discharge space S of the discharge vessel 20 where the high voltage supply electrode 11 and the ground electrode 12 are not provided, that is, from the region corresponding to the electrodes 11 and 12. It is formed in any region of the inner surfaces of the upper wall plate 21 and the lower wall plate 22 and the inner surfaces of the side wall plate 23 and the end wall plate 24. That is, the ultraviolet reflecting layer 30 formed in the region corresponding to the high voltage supply electrode 11 on the inner surface of the upper wall plate 21 is called a deposit A31 and is formed in other regions on the inner surface of the discharge vessel 20. The ultraviolet reflecting layer 30 is referred to as a deposit B32.
On the other hand, the light emitting portion is configured by the ultraviolet reflecting layer 30 not being formed on the inner surface of the lower wall plate 22 of the discharge vessel 20 corresponding to the ground electrode 12.

  The deposit A31 has a thickness of, for example, 5 to 1000 μm, and includes silica particles and fine particles having a melting point higher than that of silica and transmitting ultraviolet rays. The fine particles having a melting point higher than that of silica and transmitting ultraviolet rays are, for example, alumina, lithium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, and the like.

When vacuum ultraviolet light is incident on such a deposit A31, a part of the light is reflected on the surface of the fine particles, a part of the light is refracted and transmitted to the inside of the particles, and is reflected or refracted again on another surface. When such reflection and refraction occur repeatedly in a plurality of fine particles, vacuum ultraviolet light is diffusely reflected.
However, the silica particles are melted by the heat of the plasma generated in the excimer lamp 10 and the grain boundary disappears, so that the vacuum ultraviolet light cannot be diffusely reflected and the reflectance may be lowered. In particular, the deposit A31 formed in the region corresponding to the high voltage supply electrode 11 is easily subjected to the heat of plasma, and the silica particles constituting the deposit A31 are easily melted. On the other hand, fine particles having a melting point higher than that of silica do not melt even when exposed to heat from plasma. Therefore, by mixing fine particles having a melting point higher than that of silica into the deposit A31, it is prevented that the fine particles adjacent to each other are bonded to each other and the grain boundary disappears, and a decrease in the reflectance of the deposit A31 is suppressed. be able to.

  The deposit B32 has a thickness of 10 to 1000 μm, for example, and is composed of fine particles containing silica particles. The fine particles constituting the deposit B32 are composed only of silica particles, but also contain insulating microparticles made of a substance that contains oxygen and transmits ultraviolet rays. For example, alumina, lithium fluoride, magnesium fluoride, calcium fluoride, or barium fluoride may be used.

  Even when the vacuum ultraviolet light is incident on the deposit B32, the vacuum ultraviolet light is diffusely reflected by the repeated reflection and refraction of the fine particles. In addition, since the deposit B32 is formed on the inner surface of the discharge vessel 20 other than the region corresponding to the electrodes 11 and 12, the deposit B32 is not easily affected by heat from plasma. Therefore, even if the deposit B32 is composed of only silica particles, the disappearance of grain boundaries due to bonding between adjacent microparticles hardly occurs.

The fine particles have a particle size defined as follows within a range of 0.01 to 20 μm, for example, and the center particle size (maximum value of the particle size distribution based on the number) is the deposit A31. For example, the thickness is preferably 0.1 to 10 μm, more preferably 0.1 to 3 μm, and the deposit B is also preferably 0.1 to 20 μm, for example.
The term “particle diameter” as used herein refers to an approximate intermediate position in the thickness direction on the fracture surface when fractured in the direction perpendicular to the surface of the ultraviolet reflective layer 30, using a scanning electron microscope (SEM). It refers to the Feret diameter, which is the interval between parallel lines obtained when an enlarged projection image is acquired and arbitrary particles in the enlarged projection image are sandwiched between two parallel lines in a fixed direction.
In addition, the “center particle size” is a particle size range between the maximum value and the minimum value of the particle size of each particle obtained as described above, for example, in a range of 0.1 μm, The center value of the section where the number of particles (frequency) belonging to each section is maximized.

In the excimer lamp 10, when lighting power is supplied to the high voltage supply electrode 12, excimer discharge is generated in the discharge space S between the electrodes 11 and 12 via the discharge vessel 20. Thereby, excimer molecules are formed and vacuum ultraviolet light is emitted from the excimer molecules. Part of the vacuum ultraviolet light generated in the discharge space S is directly emitted to the outside through the lower wall plate 22 that also serves as a light emitting part. Further, a part of the vacuum ultraviolet light is radiated in the direction of the upper wall plate 21, but is diffusely reflected by the ultraviolet reflecting layer 30 and emitted to the outside through the light emitting part.
Since the fine particles constituting the ultraviolet reflecting layer 30 have a particle diameter comparable to the wavelength of vacuum ultraviolet light, the vacuum ultraviolet light can be diffusely reflected efficiently.

However, when the excimer lamp 10 including the ultraviolet reflection layer 30 is lit for a long time, it was confirmed that the initial illuminance could not be maintained and the illuminance gradually decreased with the lighting time. The inventors examined the cause of the decrease in illuminance from all directions and thought that the reflectance of the ultraviolet reflective layer 30 that is one of the causes may have decreased.
Therefore, the reflection intensity spectrum of the ultraviolet reflection layer 30 of the excimer lamp 10 in the initial lighting stage and the reflection intensity spectrum of the ultraviolet reflection layer 30 of the excimer lamp 10 after lighting for a long time were measured, and both were comparatively analyzed. From this result, in the ultraviolet reflecting layer 30 of the excimer lamp 10 after lighting for a long time, an absorption band is generated in the ultraviolet region, and a part of the ultraviolet ray is absorbed by the ultraviolet reflecting layer 30, thereby causing a decrease in illuminance. I understood it.

  The absorption band in the ultraviolet region generated in the ultraviolet reflecting layer 30 is subjected to radiation damage due to the silica particles constituting the ultraviolet reflecting layer 30 being exposed to ultraviolet rays or plasma during discharge, and has an ultraviolet wavelength range. It is considered that diffuse reflection is suppressed by the occurrence of internal defects that absorb light and the absorption of ultraviolet rays by the internal defects. The internal defect is a Si-Si defect having an absorption edge in the vicinity of a wavelength of 163 nm, or an absorption band in the vicinity of a wavelength of 215 nm, which is generated when the Si-O-Si bond of silica particles is exposed to ultraviolet rays or plasma. E'center (Si ·).

  For the above reasons, it is silica particles that have internal defects that absorb light in the ultraviolet region, and absorption of light in the ultraviolet region that causes a decrease in illuminance depends on internal defects in the silica particles. Conceivable. Further, fine particles that transmit ultraviolet light other than silica particles made of alumina, lithium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, and the like do not cause radiation damage even when exposed to ultraviolet light or plasma. Therefore, it is considered that by preventing the internal defects from being generated in the silica particles constituting the ultraviolet reflecting layer 30, it is possible to suppress a decrease in illuminance and maintain a high illuminance maintenance rate even after lighting for a long time.

  In order to prevent internal defects from occurring in the silica particles, it is effective to contain OH groups in the silica particles. By containing the OH group, it is possible to suppress the generation of internal defects in the silica particles contained in the ultraviolet reflecting layer 30 and to prevent the reflectance of the ultraviolet reflecting layer 30 from being lowered.

  Then, the formation method of the ultraviolet reflective layer 30 which consists of microparticles | fine-particles containing the silica particle containing OH group is demonstrated. In the ultraviolet reflecting layer 30, a particle deposition layer containing silica particles is formed in a predetermined region on the inner surface of the discharge vessel forming material by, for example, a method called “flowing method”. For example, a dispersion liquid is prepared by mixing fine particles with a solvent having a viscosity obtained by combining water and a PEO resin (polyethylene oxide), and the dispersion liquid is poured into the discharge vessel forming material. And after making a dispersion liquid adhere to the predetermined | prescribed area | region in the inner surface of a discharge vessel formation material, water and PEO resin are evaporated by drying and baking, Thereby, a particle deposition layer can be formed. Here, the firing temperature is, for example, 500 ° C. to 1100 ° C.

As an example of a method for adding OH groups to silica particles, silica particles containing a large amount of OH groups are produced by heating an electric furnace (for example, 1000 ° C.) while supplying water vapor to silica particles that do not contain OH groups. There are things to do. By using such treated silica particles, it is possible to form the ultraviolet reflecting layer 30 made of fine particles containing silica particles containing OH groups.
As another method, silica particles that do not contain OH groups are attached to a predetermined region on the inner surface of the discharge vessel forming material, and then fired while supplying water vapor, whereby OH groups are added to the silica particles. It can also be included. Moreover, after baking using the silica particle which does not contain OH group and forming the ultraviolet reflective layer 30, an OH group can also be included in a silica particle by heating an electric furnace, supplying water vapor | steam again.
The silica particles that can be obtained by purchase include products containing OH groups depending on the production method, but some products have low OH group concentration. It is desirable to make it.

  The concentration of OH groups contained in the silica particles can be adjusted to an arbitrary value by selecting various warm exhaust conditions for the OH groups contained in the silica particles constituting the ultraviolet reflecting layer 30. For example, even if the holding temperature is constant, more OH groups can be removed as the holding time is increased. In consideration of the amount of OH groups previously contained in the silica particles, by adjusting the amount of OH groups to be removed by warm evacuation, an ultraviolet reflecting layer comprising fine particles containing silica particles having an arbitrary OH group concentration 30 can be formed.

A first experiment on an excimer lamp is shown.
Excimer lamps having an ultraviolet reflecting layer were produced according to the configuration shown in FIGS. 1 (a) and 1 (b).
[Basic configuration of excimer lamp]
The discharge vessel is made of silica glass and has dimensions of 15 mm × 43 mm × 350 mm and a wall thickness of 2.5 mm.
The dimensions of the high voltage supply electrode and the ground electrode are 30 mm × 300 mm.
The ultraviolet reflecting layer is composed of a mixture of silica particles having a center particle size of 1.5 μm and a component ratio of 90% by weight, and alumina particles having a center particle size of 1.5 μm being mixed by a component ratio of 10% by weight. The firing temperature was 1000 ° C.
Xenon was enclosed in a discharge vessel at 40 kPa as a discharge gas.

About the excimer lamp which has the said structure, the OH group density | concentration in a silica particle, a reflection maintenance factor, and the illumination intensity maintenance factor were measured. All the ultraviolet reflective layer was scraped from the discharge vessel and measured using a temperature programmed desorption gas analysis method to calculate the OH group concentration in the silica particles contained in the ultraviolet reflective layer. Moreover, the component ratio of the silica particle contained in the shaved ultraviolet reflective layer was calculated | required, and the weight of OH group with respect to the weight of only a silica particle was computed and calculated from the component ratio. Furthermore, using a vacuum ultraviolet light spectrometer (VUV) or an ultraviolet illuminance measuring instrument, the reflection maintenance factor and the illuminance maintenance factor of the ultraviolet reflecting layer after 500 hours of continuous lighting with respect to the initial state were measured.
The measurement results of lamps 1 to 5 are shown in Table 1.

FIG. 2 is a graph in which the values of lamps 1 to 5 are plotted with the OH group concentration in silica particles (wtppm) on the horizontal axis and the reflection maintenance ratio (%) on the vertical axis for the measurement results shown in Table 1.
FIG. 3 is a graph plotting the values of lamps 1 to 5 with the horizontal axis representing the OH group concentration (wtppm) on the horizontal axis and the illuminance maintenance rate (%) on the vertical axis for the measurement results shown in Table 1. .
The graphs shown in FIGS. 2 and 3 are semi-logarithmic graphs in which the horizontal axis is a logarithmic scale.

  From the above results, it can be seen that when the OH group concentration in the silica particles is less than 10 wtppm, the reflection maintenance ratio and the illuminance maintenance ratio remain low, and the processing capability decreases when the excimer lamp is lit for a long time. On the other hand, when the OH group concentration in the silica particles is 10 wtppm or more, the reflection maintenance ratio and the illuminance maintenance ratio are 90% or more, and it can be read that the processing capability can be maintained even if the excimer lamp is lit for a long time. As shown in FIG. 2 and FIG. 3, when the OH group concentration is less than 10 wtppm to 10 wtppm or more, the reflection maintenance ratio and the illuminance maintenance ratio increase rapidly, so the OH group concentration in the silica particles is increased to 10 wtppm or more. It was found that there was a remarkable difference in the performance of the illumination, and that the effect of maintaining illuminance when lighting for a long time was outstanding.

  However, even when the OH group concentration in the silica particles constituting the ultraviolet reflection layer 30 is 10 wtppm or more, the excimer lamp has a low illuminance of excimer emission centered at 172 nm. Further, during the lighting of the excimer lamp 10 in which xenon is enclosed as a discharge gas, the color of the discharge generated in the discharge space S may become green, and molecules (XeO) in which xenon atoms and oxygen atoms are bonded are generated. Thus, it was confirmed that green light having a center wavelength of around 550 nm was emitted from this molecule.

Further, when the OH groups contained in the silica particles constituting the ultraviolet reflecting layer 30 are exposed to the discharge plasma generated in the discharge space, the OH groups are mainly heated (H ₂ O) in the discharge space S by being heated. It is considered that impure gas as a component is released. Oxygen atoms generated by decomposing an impurity gas containing water as a main component in the plasma are released into the discharge space S from OH groups contained in silica particles constituting the ultraviolet reflecting layer 30.

  When the ultraviolet reflecting layer 30 made of fine particles is formed on the inner surface of the discharge vessel 20, since there are irregularities of the fine particles, the surface of the flat discharge vessel 20 without the ultraviolet reflecting layer 30 is formed. Increases surface area. Since the impure gas is emitted from the ultraviolet reflecting layer 30 exposed to the discharge plasma, more impure gas is generated when the ultraviolet reflecting layer 30 is formed. Further, the fine particles constituting the ultraviolet reflecting layer 30 have a smaller heat capacity than the discharge vessel 20 because the volume of one particle is small. For this reason, even if it is heated in a short time of about several tens of nanoseconds when the discharge plasma is generated, the temperature becomes high and impurities are likely to be released.

Since the deposit A31 is formed in a region corresponding to the high voltage supply electrode 11 on the inner surface of the upper wall plate 21, it is directly exposed to the discharge plasma generated between the electrodes 11 and 12, so that it is heated. Impure gas is discharged into the discharge space S.
On the other hand, the deposit B32 is either the inner surface of the upper wall plate 21 that is separated from the high voltage supply electrode 11 or the lower wall plate 22 that is separated from the ground electrode 12, or the inner surface of the side wall plate 23 or the end wall plate 24. However, the discharge space S is not directly exposed to the discharge plasma generated between the electrodes 11 and 12. Therefore, it is considered that almost no impure gas is generated from the deposit B32. On the contrary, it is considered that the deposit B32 adsorbs an impure gas, which is proved by the following experiment.

  As a second experiment object, an excimer lamp in which only the deposit B was formed on the inner surface of the discharge vessel 20 and no deposit A was formed was manufactured. Excimer lamps in which xenon was used as the discharge gas, oxygen was also mixed when the discharge gas was sealed, and oxygen was previously sealed as an impure gas were used as experimental objects. The oxygen concentration enclosed in the discharge space S was 160 wtppm, and the pressure of the discharge gas was 40 kPa. When oxygen is mixed as an impure gas, it has a great influence on the decrease in illuminance by reacting with a rare gas. Further, since light of discharge with a wavelength of 550 nm is generated, it is easily determined that oxygen is mixed in the discharge space S. it can.

  Three types of excimer lamps provided with the deposit B having different component ratios of the particles constituting the fine particles were prepared on the inner surface of the discharge vessel. The lamp 1 includes a deposit B made of only silica particles, the lamp 2 includes a deposit B made of silica particles and alumina particles, and the lamp 3 includes a deposit B made of silica particles and calcium fluoride particles. As a comparative example, a lamp 4 on which no deposit B was formed was prepared. For each lamp, the emission intensity at 550 nm after 15 minutes of continuous lighting until the excimer discharge became stable was measured, and this was designated as “550 nm emission intensity lighting initial stage”. Thereafter, the excimer lamp was continuously turned on, and the 550 nm emission intensity after 5 hours of continuous lighting was measured, which was defined as “550 nm emission intensity after 5 hours”.

  The results of the second experiment are shown in Table 2. The value of “after 550 nm emission intensity lighting 5 hours” is expressed as a relative value when the value of “550 nm emission intensity lighting initial stage” is 100. In the lamps 1 to 3 provided with the deposit B, the value after 5 hours of lighting at 550 nm is decreased to 100 or less, and the number of molecules (XeO) in which xenon atoms and oxygen atoms are bonded compared to the initial lighting time. Is decreasing. That is, the oxygen previously mixed in the discharge space is reduced. On the other hand, in the lamp 4 in which the deposit B is not formed, the value after 5 hours of lighting at 550 nm is maintained as 100, and it can be seen that there is no change in the amount of oxygen previously mixed in the discharge space. From this, it is confirmed that the light of 550 nm is reduced by providing the deposit B on the inner surface of the discharge vessel of the excimer lamp, and oxygen is adsorbed by the deposit B. Moreover, since the deposit B is not exposed to the discharge plasma, it is considered that the adsorbed impure gas is not released into the discharge space.

  Subsequently, a third experiment was performed in order to confirm whether or not the phenomenon that the oxygen confirmed in the second experiment was adsorbed by the deposit B was caused by the lighting of the excimer lamp. Lamps 5 to 7 having the same configuration as the lamps 1 to 3 as the second experiment object were set as the third experiment object. Moreover, the lamp | ramp 8 in which the deposit B is not formed was prepared as a comparative example. For each lamp, the emission intensity at 550 nm after 15 minutes of continuous lighting was measured, and this was set as “550 nm emission intensity lighting initial stage”. Thereafter, the light was left unlit for 48 hours, lighted after being left, and the luminescence intensity at 550 nm after 15 minutes of continuous lighting was measured. Thereafter, the excimer lamp was continuously turned on, and the 550 nm emission intensity after 5 hours of continuous lighting was measured, which was defined as “after 5 hours of lighting after 48 hours of 550 nm emission intensity”.

The results of the third experiment are shown in Table 3. The values of “550 nm emission intensity after 48 hours” and “550 nm emission intensity lighting after 48 hours after lighting” are expressed as relative values when the value of “550 nm emission intensity lighting initial stage” is 100. Yes. In the lamps 5 to 7 including the deposit B, the value after 48 hours of 550 nm emission intensity is 100, whereas the value after 5 hours of lighting after 48 hours of 550 nm emission intensity is reduced to 10-11. It turns out that oxygen is reduced only when the excimer lamp is turned on. As a principle of adsorbing oxygen on the deposit B, it is considered that chemical adsorption is caused on the surface of the fine particles of the deposit B, in which oxygen is adsorbed by causing a chemical reaction by ultraviolet light generated by lighting.
On the other hand, in the lamp 8 in which the deposit B is not formed, the value remains 100 after the 550 nm emission intensity 48 hours has elapsed and after the 550 nm emission intensity 48 hours has elapsed, so that the value remains 100. It can be seen that there is no change in the amount of oxygen mixed.

  Since the fine particles constituting the deposit B adsorb impure gas on the surface exposed to the discharge space, the larger the surface area facing the discharge space, the more impure gas can be adsorbed. Therefore, the larger the “specific surface area”, that is, the total surface area of all the particles contained in the unit weight of the powder, the more impure gas is adsorbed. The specific surface area is measured using, for example, a measurement method called a BET method in which a molecular gas (for example, nitrogen) having a known occupation area is adsorbed on the surface of a fine particle in advance and the specific surface area is obtained from the amount. When measuring the specific surface area of the fine particles constituting the deposit B, the surface of the deposit B exposed to the discharge space is exposed to a molecular gas and adsorbed, and the specific surface area is determined from the amount.

Below, the 4th experiment conducted in order to confirm the effect of this invention is shown.
<Target of experiment>
Excimer lamps including a deposit A and a deposit B were manufactured according to the configuration shown in FIGS.
[Basic configuration of excimer lamp]
The discharge vessel is made of silica glass and has dimensions of 15 mm × 43 mm × 540 mm and a wall thickness of 2.5 mm.
The dimensions of the high voltage supply electrode and the ground electrode are 32 mm × 500 mm.
The size of the light emitting portion corresponding to the region where the deposit B is not formed on the lower wall plate is 2 mm larger than the ground electrode, and is 36 mm × 504 mm.
The deposit A and the deposit B were formed by a flow-down method, respectively, and the firing temperature was 1000 ° C.
After performing hot evacuation at 800 ° C. for 1 hour (time after the temperature rise), xenon was sealed in the discharge vessel. The enclosed amount is 40 kPa.
The OH group content of the deposited body A of the manufactured lamp is 500 wtppm.

As shown in Table 4, four types of configuration (1-1), configuration (1-2), configuration (1-3), and configuration (1-4) were prepared for the deposit A. Each of the four types has the same material, particle size, center particle size, and component ratio, but the installation area of the deposit A formed in the region corresponding to the high voltage supply electrode on the inner surface of the upper wall plate is 160 cm. ² , 128 cm ² , 107 cm ² , and 40 cm ² . Since the amount of impure gas released into the discharge space depends on the installation area of the deposit A, the larger the install area of the deposit A as in the configuration (1-1), the greater the amount of impure gas. As (1-4), the smaller the installation area of the deposit A, the smaller the amount of impure gas. Further, in the configuration (1-2), the configuration (1-3), and the configuration (1-4), the installation area where the deposit A is formed is 160 cm ² where the high voltage supply electrode is formed. Since it is smaller, the deposit A is formed not in the entire region of the inner surface of the discharge vessel provided with the high voltage supply electrode but in a part thereof.

Moreover, as shown in Table 5, also about the structure of the deposit B, four types, the structure (2-1), the structure (2-2), the structure (2-3), and the structure (2-4), were prepared. . Configuration (2-1), Configuration (2-2), and Configuration (2-3) consist only of silica particles, and Configuration (2-4) consists of silica particles and alumina particles. In the configuration (2-1), the configuration (2-2), and the configuration (2-3), the specific surface area is changed to 16 × 10 ⁻⁴ cm ² / g and 4 × 10 ⁻⁴ by changing the particle diameter of the silica particles. cm ² / g, it is to 1 × ¹⁰ -4 ^cm 2 / g and different. Moreover, the specific surface area of a structure (2-4) is 4 * 10 < ^-4 > cm < ² > / g. Since the larger the specific surface area of the deposit B, the more impure gas is adsorbed, the larger the specific surface area of the deposit B as in the configuration (2-1), the larger the surface area facing the discharge space. As the specific surface area of the deposit B is smaller as in the configuration (2-3), the amount of impure gas mixed in the electric space decreases with the lighting. .

In contrast to the deposit (A) having the configuration (1-1), the deposit (B) having the configurations (2-1) to (2-4) was prepared as an experiment target. In addition, five types with different installation areas of the deposits B were prepared for each combination. Similarly, the deposit B is composed of the configurations (2-1) to (2-) with respect to the deposit (A) having the configuration (1-2), the configuration (1-3), and the configuration (1-4). 3) was prepared.
For such each excimer lamp configured in the tube wall loading of the discharge vessel is lit under the condition that a 0.6 W / cm ^2, the wavelength range of 150nm~200nm after continuous lighting 15 minutes of xenon excimer light The illuminance and the illuminance of xenon excimer light in the wavelength range of 150 nm to 200 nm after continuous lighting for 500 hours with a constant tube wall load were measured. The illuminance after 15 minutes of continuous lighting is the initial illuminance, the illuminance after 500 hours of continuous lighting is the relative value of the initial illuminance, and the illuminance maintenance rate is “500 hours illuminance maintenance rate”. ) / (Illuminance immediately after lighting)] (%). The reason for the 500 hours is as follows. Although the illuminance decrease due to the impure gas continues until 500 hours, the illuminance after that does not decrease, so it is considered that all the impure gas contained in the ultraviolet reflecting layer is released up to 500 hours and not released thereafter. It is.
As a product standard, it may be required to maintain an illuminance of 80% or more. Therefore, when the 500-hour illuminance maintenance rate is 80% or more as a judgment, “◯” is given, and the 500-hour illuminance maintenance rate is 80% or less. When it becomes, it was set as "x".

  As shown in FIG. 4, the illuminance measurement is performed by fixing the excimer lamp 10 on the ceramic support base 41 disposed inside the aluminum container 40 and at a position 1 mm away from the surface of the excimer lamp 10. An ultraviolet illuminance measuring device 42 is fixed so as to face the excimer lamp 10, and an alternating high voltage of 5.0 kV is applied between the electrodes 11 and 12 of the excimer lamp 10 in a state where the inner atmosphere of the aluminum container 40 is replaced with nitrogen. As a result, a discharge was generated inside the discharge vessel 20, and the illuminance of vacuum ultraviolet light emitted through the mesh of the ground electrode 12 was measured.

The experimental results are shown in FIGS. From this result, in each combination of the configuration of the deposit A and the configuration of the deposit B, the combination with the smallest installation area of the deposit B is extracted from the excimer lamps in which the 500-hour illuminance maintenance rate is 80% or more. did. For example, the lamp 3 corresponds to the combination in which the configuration of the deposit A is “configuration (1-1)” and the configuration of the deposit B is “configuration (2-1)”. Similarly, the lamp 8, the lamp 13, the lamp 18, and the like are applicable.
Table 6 shows the combinations extracted in this way, listing the configuration of the deposit A, the configuration of the deposit B, the specific surface area of the deposit B, and the installation area of the deposit B.

FIG. 7 is a graph showing the results of Table 6. The horizontal axis is the specific surface area (× 10 ⁻⁴ cm ² / g) of the deposit B, the vertical axis is the installation area (cm ² ) of the deposit B, and the values are plotted for each configuration of the deposit A.
Table 6 and FIG. 7 show that the larger the specific surface area, the smaller the installation area necessary for suppressing the decrease in illuminance. For each configuration of the deposit A, that is, the configuration (1-1), the configuration (1-2), and the configuration (1-3), the installation area is proportional to the specific surface area. However, in the excimer lamp having the configuration (1-4) as the deposit A, the installation area did not become lower than 10 cm ² even if the specific surface area increased.

In the excimer lamp having the configuration (1-4) as the deposit A, the installation area of the deposit B is too small with respect to the internal volume of the discharge vessel, so that the impure gas diffusing in the discharge space is accumulated in the deposit B. This is considered to be because the probability of reaching the temperature becomes low and the effect of adsorption does not appear. That is, it can be said that there is a minimum necessary area of the deposit B with respect to the size of the discharge space. When the size of the discharge space is expressed by the inner surface area of the discharge vessel, in this case, the inner surface area is approximately 500 cm ² , whereas the installation area of the deposit B is 10 cm ² . Therefore, the minimum required installation area of the deposit B is 0.02 times the inner surface area of the discharge vessel.

  Next, the respective inclinations and intercepts of the approximate lines of the respective configurations of the deposit A in FIG. 7, that is, the configuration (1-1), the configuration (1-2), and the configuration (1-3) were derived. The results are listed of the configuration of the deposit A, the installation area of the deposit A, the slope of the relationship between the specific surface area and the installation area of the deposit B, and the intercept of the relationship between the specific surface area and the installation area of the deposit B Is shown in Table 7.

FIG. 8 shows the results of Table 7, where the horizontal axis is the installation area (cm ² ) of the deposit A, and the vertical axis is the slope (× 10 ⁻⁴ g) of the relationship between the specific surface area of the deposit B and the installation area. The values are plotted.
From the graph, it can be seen that the slope of the relationship between the specific surface area of the deposit B and the installation area is proportional to the installation area (cm ² ) of the deposit A having a negative slope. When the installation area of the deposit A is a (cm ² ), the slope of the relationship between the specific surface area of the deposit B and the installation area can be expressed as −5.0 × 10 ⁻³ × a.

FIG. 9 plots the values for the results in Table 7 with the horizontal axis as the installation area (cm ² ) of the deposit A and the vertical axis as the intercept (cm ² ) of the relationship between the specific surface area of the deposit B and the installation area. It is a thing.
From the graph, it can be seen that the intercept of the relationship between the specific surface area and the installation area of the deposit B is in a proportional relationship having a positive slope with respect to the installation area (cm ² ) of the deposit A. When the installation area of the deposit A is a (cm ² ), the intercept of the relationship between the specific surface area of the deposit B and the installation area can be expressed as 0.35 × a.

From FIG. 7, the installation area of the deposit B is “the slope of the relationship between the specific surface area of the deposit B and the installation area” with respect to the specific surface area of the deposit B, It can be said that there is a proportional relationship that is “intercept of the relationship with the installation area”. From this, the relationship between the installation area of the deposit B and the specific surface area of the deposit B in FIG. 5 is that the installation area of the deposit B is b (cm ² ) and the specific surface area of the deposit B is c (cm ² / g). )
b = (inclination of the relationship between the specific surface area of the deposit B and the installation area) × c + (intercept of the relationship between the specific surface area of the deposit B and the installation area)
It can be expressed as.

Further, from the results of FIGS. 8 and 9, when the installation area of the deposit A is a (cm ² ), the slope of the relationship between the specific surface area of the deposit B and the installation area is −5.0 × 10 ^−3. Since the intercept of the relationship between the specific surface area of the deposit B and the installation area can be expressed as 0.35 × a, the ratio of the installation area of the deposit B to the deposit B in FIG. The relationship with the surface area can be shown as follows.
b = −5.0 × 10 ⁻³ ac + 0.35a

5 and 6, if the installation area b of the deposit B is larger than the amount shown in the relationship between the installation area of the deposit B and the specific surface area of the deposit B in FIG. It can be read that the illuminance maintenance ratio is 80% or more and the determination is “good”.
From the above results, it was found that in the excimer lamp provided with the deposit A containing the OH group, the installation area of the deposit B only needs to satisfy the following relationship in order to suppress a decrease in illuminance.
When the installation area of the deposit A is a (cm ² ), the installation area of the deposit B is b (cm ² ), and the specific surface area of the deposit B is c (cm ² / g),
b ≧ −5.0 × 10 ⁻³ ac + 0.35a.

Further, in FIG. 7, in the excimer lamp having the configuration (1-4) as the deposit A, even if the specific surface area of the deposit B is increased, the installation area of the deposit B is not lower than 10 cm ² . The relationship between the specific surface area of the deposit B and the installation area did not become as in the case where the deposit (A) includes the configuration (1-1), the configuration (1-2), and the configuration (1-3). Therefore, in Table 7, FIG. 8, and FIG. 9, the case where the structure (1-4) is provided as the deposit A is not considered. That is, the condition that the installation area of the deposit B should satisfy is the case where the configuration (1-4) is provided as the deposit A. Therefore, the case where the configuration (1-4) is provided as the deposit A under the condition that the installation area of the deposit B should satisfy must be excluded.

The case where the configuration (1-4) is provided as the deposit A is a case where the effect of adsorption is not exhibited because the installation area of the deposit B is too small with respect to the internal volume of the discharge vessel. That is, the installation area of the deposit B is about 0.02 times the inner surface area of the discharge vessel. Therefore, regarding the relationship of the installation area b (cm ² ) of the deposit B for suppressing the decrease in illuminance, the following conditions must be satisfied when the inner surface area of the discharge vessel is d (cm ² ).
b> 0.02d

From the above results, it was found that in the excimer lamp provided with the deposit A containing the OH group, the configuration of the deposit B needs to satisfy the following relationship in order to suppress the decrease in illuminance. The installation area of the deposit A is a (cm ² ), the installation area of the deposit B is b (cm ² ), the specific surface area of the deposit B is c (cm ² / g), and the inner surface area of the discharge vessel is d (cm ² )
b ≧ −5.0 × 10 ⁻³ ac + 0.35a and b> 0.02d
It is necessary to satisfy.

  By satisfying the above relationship, the amount of impurity gas released from the deposit A does not exceed the amount of impurity gas that can be absorbed by the deposit B, and the impurity gas can be prevented from remaining in the discharge space. Therefore, it is possible to suppress the decrease in illuminance of excimer emission due to the oxygen atoms contained in the impure gas being combined with the discharge gas, and to suppress the decrease in illuminance even when the excimer lamp is lit for a long time. And vacuum ultraviolet light can be emitted efficiently.

Incidentally, the installation area a of the stack A (cm ²⁾ and stack footprint b (cm ²⁾ of the B is without considering the unevenness of fine particles, is deposited body A or the surface of the deposited body B to be smooth This is the value measured assuming it. The inner surface area d (cm ² ) of the discharge vessel is also a value measured on the assumption that the surface is smooth.

It is sectional drawing for description which shows the outline of a structure in an example of the excimer lamp of this invention, Comprising: (a) Sectional drawing which shows the cross section along the longitudinal direction of a discharge vessel, (b) AA 'line | wire in (a) It is sectional drawing. It is an experimental result of an excimer lamp. It is an experimental result of an excimer lamp. It is sectional drawing for demonstrating the measuring method of the illumination intensity of the excimer lamp in an experiment example. It is an experimental result of an excimer lamp. It is an experimental result of an excimer lamp. It is an experimental result of an excimer lamp. It is an experimental result of an excimer lamp. It is an experimental result of an excimer lamp. It is an explanatory perspective view which shows the outline of a structure of the conventional excimer lamp.

Explanation of symbols

10 Excimer lamp 11 High voltage supply electrode 12 Ground electrode 20 Discharge vessel 21 Upper wall plate 22 Lower wall plate 23 Side wall plate 24 End wall plate 30 Ultraviolet reflection layer 31 Deposit A
32 Deposit B
40 Aluminum container 41 Support base 42 UV illuminance measuring device S Discharge space

Claims (2)

A discharge vessel made of silica glass having a discharge space is provided, and a pair of electrodes is provided in a state where the silica glass forming the discharge vessel is interposed, and a discharge gas is enclosed in the discharge space, and the discharge vessel An excimer lamp having an ultraviolet reflecting layer formed on a part of its inner surface,
The ultraviolet reflecting layer is composed of a deposit A formed in at least a part of a region corresponding to one electrode, and a deposit B formed in at least a part other than a region corresponding to the electrode,
The deposit A is composed of silica particles containing OH groups and fine particles having a melting point higher than that of silica.
The deposit B consists of fine particles containing silica particles containing OH groups,
An excimer lamp, wherein an OH group concentration in silica particles constituting the ultraviolet reflecting layer is 10 wtppm or more. The installation area of the deposit A is a (cm ² ), the installation area of the deposit B is b (cm ² ), the specific surface area of the deposit B is c (cm ² / g), and the inner surface area of the discharge vessel is d (Cm ² ), the respective relations are b ≧ −5.0 × 10 ⁻³ ac + 0.35a and b> 0.02d.
The excimer lamp according to claim 1, wherein:

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