JP5303890B2 - Excimer lamp - Google Patents

Description

  The present invention relates to an excimer lamp including a discharge vessel made of silica glass and having a pair of electrodes provided in a state where the silica glass forming the discharge vessel is interposed to generate excimer discharge inside the discharge vessel.

  In recent years, for example, by irradiating a vacuum ultraviolet light having a wavelength of 200 nm or less onto a target object made of metal, glass and other materials, the target object 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, an excimer molecule is formed by excimer discharge, and an excimer lamp using light emitted from the excimer molecule is used as a light source. In the excimer lamp, many attempts have been made to efficiently radiate higher-intensity ultraviolet rays.
Specifically, for example, referring to FIG. 6, a discharge vessel (51) made of silica glass that transmits ultraviolet rays is provided, and electrodes (55, 56) are provided inside and outside the discharge vessel (51), respectively. In the excimer lamp (50) provided with the above, it is described that an ultraviolet reflective film (20) is formed on the surface exposed to the discharge space (S) of the discharge vessel (51). Examples of the material include those composed only of silica particles and those composed only of alumina particles (see Patent Document 1).
In this excimer lamp (50), a light emitting portion (58) that emits ultraviolet rays generated in the discharge space (S) because the ultraviolet reflecting film (20) is not formed on a part of the discharge vessel (51). ) Is formed.

  According to the excimer lamp (50) having such a configuration, the ultraviolet reflective film is provided on the surface of the discharge vessel (51) that is exposed to the discharge space (S), whereby the ultraviolet reflective film is provided. In the region, the ultraviolet rays generated in the discharge space (S) are reflected by the ultraviolet reflecting film, so that the ultraviolet rays pass through the silica glass in the region constituting the light emitting part (58) without entering the silica glass. Therefore, basically, the ultraviolet rays generated in the discharge space (S) can be used effectively, and the silica constituting the region other than the light emitting portion (58) can be used. It is said that damage due to ultraviolet distortion of glass can be suppressed to a small extent, and the occurrence of cracks can be prevented.

Japanese Patent No. 3580233

  However, it has been found that the excimer lamp having the above-described configuration has a problem that the reflectance of the ultraviolet reflecting film is lowered and that the ultraviolet reflecting film is peeled off when it is lit for a long time.

  The present invention has been made based on the circumstances as described above, and even when the lamp is lit for a long time, the degree of decrease in the reflectance of the ultraviolet reflecting film is suppressed to a small extent, and the ultraviolet reflecting film is peeled off. Therefore, an object of the present invention is to provide an excimer lamp that can efficiently emit vacuum ultraviolet light.

The excimer lamp of the present invention includes a discharge vessel made of silica glass having a discharge space, a pair of electrodes is provided in a state where the silica glass forming the discharge vessel is interposed , and xenon gas is sealed in the discharge space. It becomes Te, when the tube wall loading of the discharge vessel with b [W / cm ^2], tube wall loading b is 0.5 W / cm ² or more, is illuminated in a condition to be 1.4 W / cm ² or less, the discharge An excimer lamp that generates excimer discharge in the discharge space of the vessel,
An ultraviolet reflective film made of silica particles and alumina particles is formed on the surface of the discharge vessel exposed to the discharge space, and the ultraviolet reflective film is formed of alumina particles in the surface layer portion exposed to the discharge space. Is (10b-4) wt% or more and 70 wt% or less.

  According to the excimer lamp of the present invention, the ultraviolet reflecting film is composed of silica particles and alumina particles, and the alumina particles are contained at an appropriate ratio, so that even when the lamp is lit for a long time, Since the grain boundaries are maintained without disappearance, vacuum ultraviolet light can be efficiently diffusely reflected, the degree of reflectivity can be suppressed, and ultraviolet reflection due to the mixing of alumina particles. The binding property of the film to the discharge container is not significantly reduced, and the ultraviolet reflective film can be reliably prevented from being peeled off from the discharge container, and thus vacuum ultraviolet light can be emitted efficiently.

FIG. 1 is an explanatory cross-sectional view showing an outline of the configuration of an example of an excimer lamp according to the present invention, wherein (a) a cross-sectional view showing a cross section along the longitudinal direction of a discharge vessel, and (b) in (a). It is AA sectional view.
This excimer lamp 10 includes a hollow discharge vessel 11 having a rectangular cross section in which both ends are hermetically sealed and a discharge space S is formed therein. As the discharge gas, for example, xenon gas or a mixed gas of argon and chlorine is enclosed.
The discharge vessel 11 is made of silica glass, for example, synthetic quartz glass, which transmits vacuum ultraviolet light well, and has a function as a dielectric.

On the outer surface of the long side surface of the discharge vessel 11, a pair of grid-like electrodes, that is, one electrode 15 functioning as a high-voltage power supply electrode and the other electrode 16 functioning as a ground electrode extend in a long direction. Thus, the discharge vessel 11 functioning as a dielectric is interposed between the pair of electrodes 15 and 16.
Such an electrode can be formed, for example, by applying an electrode material made of metal to the discharge vessel 11 or by printing.

  In this excimer lamp 10, when lighting power is supplied to one electrode 15, a discharge is generated between both electrodes 15 and 16 through the wall of the discharge vessel 11 functioning as a dielectric, and thereby excimer molecules Excimer discharge in which vacuum ultraviolet light is radiated from the excimer molecule is generated. In order to efficiently use the vacuum ultraviolet light generated by the excimer discharge, silica particles and silica particles are formed on the inner surface of the discharge vessel 11. An ultraviolet reflecting film 20 made of alumina particles is provided. Here, when xenon gas is used as the discharge gas, vacuum ultraviolet light having a peak at a wavelength of 172 nm is emitted, and when gas mixed with argon and chlorine is used as the discharge gas, the peak is at a wavelength of 175 nm. A vacuum ultraviolet ray having is emitted.

The ultraviolet reflecting film 20 is, for example, an inner surface region corresponding to one electrode 15 functioning as a high-voltage power supply electrode on the long side surface of the discharge vessel 11 and a part of the inner surface region of the short side surface continuing to this region. The light emitting portion (aperture portion) 18 is formed by the absence of the ultraviolet reflecting film 20 in the inner surface region corresponding to the other electrode 16 that functions as the ground electrode on the long side surface of the discharge vessel 11. Is configured.
The film thickness of the ultraviolet reflecting film 20 is preferably 10 to 100 μm, for example.

The ultraviolet reflecting film 20 is at least a surface layer portion exposed to the discharge space S, that is, a portion where the disappearance of the grain boundary may occur due to the influence of the plasma generated by the excimer discharge, for example, the depth. In the range of about 2 μm, alumina particles are mixed with silica particles, and for example, it can be constituted by a deposit of silica particles and alumina particles.
Since the ultraviolet reflecting film 20 has a vacuum ultraviolet light transmission property in which the silica particles and the alumina particles themselves have a high refractive index, a part of the vacuum ultraviolet light reaching the silica particles or the alumina particles is the surface of the particles. And the other part is refracted and incident on the inside of the particle, and much of the light incident on the inside of the particle is transmitted (partially absorbed) and refracted when it is emitted again. It has a function of “diffuse reflection” in which such reflection and refraction occur repeatedly.
Further, since the ultraviolet reflecting film 20 is composed of silica particles and alumina particles, that is, ceramics, the ultraviolet reflecting film 20 does not generate an impure gas and has a characteristic that can withstand discharge.

As the silica particles constituting the ultraviolet reflective film 20, for example, silica glass made into fine powder particles can be used.
The silica particles have a particle size defined as follows within a range of 0.01 to 20 μm, for example, and the center particle size (peak value of the number average particle size) is, for example, 0.1 to 10 μm. Is preferable, and more preferably 0.3 to 3 μm.
Moreover, it is preferable that the ratio of the silica particle which has a center particle diameter is 50% or more.

The alumina particles constituting the ultraviolet reflecting film 20 have a particle diameter defined as follows within a range of 0.1 to 10 μm, for example, and have a center particle diameter (peak value of number average particle diameter). For example, it is preferably 0.1 to 3 [mu] m, more preferably 0.3 to 1 [mu] m.
Moreover, it is preferable that the ratio of the alumina particle which has a center particle diameter is 50% or more.

The “particle diameter” of the silica particles and the alumina particles constituting the ultraviolet reflecting film 20 refers to an approximately intermediate position in the thickness direction on the fracture surface when the ultraviolet reflecting film 20 is broken in the direction perpendicular to the surface. As a range, a magnified projection image is acquired by a scanning electron microscope (SEM), and a ferret (Feret) that is an interval between the parallel lines when arbitrary particles in the magnified projection image are sandwiched between two parallel lines in a certain direction. ) The diameter.
Specifically, as shown in FIG. 2A, when particles such as substantially spherical particles A and particles B having a pulverized particle shape are present alone, the particles are moved in a certain direction (for example, ultraviolet rays). The interval between the parallel lines when sandwiched between two parallel lines extending in the thickness direction (Y-axis direction) of the reflective film 20 is defined as particle diameters DA and DB.
In addition, for the particles C having a shape in which the particles of the starting material are melted and joined, as shown in FIG. 2 (b), for each of the spherical portions in the portion distinguished from the particles C1 and C2 that are the starting materials, The distance between the parallel lines when measured between two parallel lines extending in a certain direction (for example, the thickness direction (Y-axis direction) of the ultraviolet reflecting film 20) is measured, and these are set as the particle diameters DC1 and DC2. .

  The “center particle diameter” of the silica particles and alumina particles constituting the ultraviolet reflecting film 20 is a range of particle diameters between the maximum value and the minimum value of the particle diameter of each particle obtained as described above, for example, 0. A center value of a section having a maximum number of particles (frequency) belonging to each section divided into a plurality of sections, for example, about 15 sections within a range of 1 μm.

  Since the silica particles and the alumina particles have a particle diameter in the above range, which is approximately the same as the wavelength of vacuum ultraviolet light, it is possible to efficiently diffuse and reflect vacuum ultraviolet light.

In the above, the ratio of the alumina particles contained in the ultraviolet reflective film 20 in the excimer lamp 10 is (10b-4) wt% or more when the tube wall load of the discharge vessel 11 is b [W / cm ² ]. 70 wt% or less.
In an excimer lamp, the frequency of plasma generation increases as the potential difference between the electrodes increases, so the greater the input power, that is, the greater the load on the tube wall, the more frequently the UV reflective film is exposed to the plasma. It will be used under severe conditions. However, as also shown in the results of the experimental examples described later, the lower limit value of the content ratio of the alumina particles is set in relation to the tube wall load of the discharge vessel 11, so that the reflectivity of the ultraviolet reflecting film 20 can be reduced. The degree of reduction can be suppressed small.

Such an ultraviolet reflective film 20 can be formed by a method called “flow-down method”, for example. That is, a dispersion vessel is prepared by mixing silica particles and alumina particles in a solvent having a combination of water and PEO resin (polyethylene oxide), and then pouring this dispersion into the discharge vessel formation material to form a discharge vessel. After adhering to a predetermined region on the inner surface of the material, the ultraviolet reflecting film 20 can be formed by evaporating water and the PEO resin by drying and baking.
For the production of the silica particles and the alumina particles used for forming the ultraviolet reflective film 20, any of a solid phase method, a liquid phase method, and a gas phase method can be used. Of these, submicron, A gas phase method, particularly chemical vapor deposition (CVD) is preferred because micron-sized particles can be obtained reliably.
Specifically, for example, silica particles are synthesized by reacting silicon chloride and oxygen at 900 to 1000 ° C., and alumina particles are synthesized by heating and reacting raw material aluminum chloride and oxygen at 1000 to 1200 ° C. The particle size can be adjusted by controlling the raw material concentration, the pressure in the reaction field, and the reaction temperature.

In general, in an excimer lamp, it is known that plasma is generated by excimer discharge. However, in the excimer lamp having the above-described configuration, the plasma is incident at a substantially right angle with respect to the ultraviolet reflection film. Therefore, if the temperature of the ultraviolet reflection film is locally rapidly increased and the ultraviolet reflection film is made of only silica particles, for example, the silica particles are melted by the heat of the plasma and the grain boundaries are Since it disappears, the vacuum ultraviolet light cannot be diffusely reflected and the reflectivity decreases.
However, since the ultraviolet reflective film 20 is composed of silica particles and alumina particles, and the alumina particles are contained in an appropriate ratio, the excimer lamp 10 having the above configuration is exposed to heat from plasma. In this case, since the alumina particles having a melting point higher than that of the silica particles are not melted, the adjacent silica particles and alumina particles are prevented from being bonded to each other, and the grain boundary is maintained. Even when the lamp is lit for a long time, it is possible to efficiently diffuse and reflect the vacuum ultraviolet light, maintain the initial reflectance, and the ultraviolet reflecting film 20 by mixing the alumina particles. Since the binding property to the discharge vessel 11 is not significantly lowered, it is possible to reliably suppress the ultraviolet reflective film 20 from being peeled off from the discharge vessel 11. It can, therefore, can be emitted efficiently vacuum ultraviolet light.
In addition, since alumina particles have a higher refractive index than silica particles, it is possible to obtain a higher reflectance than an ultraviolet reflective film made only of silica particles.

  In addition, since the ultraviolet reflecting film 20 is formed on the inner surface of the discharge vessel 11 exposed to the discharge space S where excimer emission occurs, the silica glass in the region other than the light emitting portion 18 is exposed to vacuum ultraviolet rays in the discharge space S. Damage due to ultraviolet distortion caused by being incident on can be reduced, and the occurrence of cracks can be prevented.

Examples of experiments conducted to confirm the effects of the present invention will be described below.
<Experimental example 1>
According to the configuration shown in FIG. 1, seven types of excimers having the same configuration except that the content of alumina particles contained in a film thickness of 2 μm from the surface of the ultraviolet reflective film is changed in the range of 0 to 50 wt%. An excimer lamp having the same configuration except that the lamp was not manufactured and the ultraviolet reflecting film was not provided was manufactured. Here, the content of alumina particles and the proportion of silica particles contained in a film thickness of 2 μm from the surface of the ultraviolet reflection film are as follows. It is obtained by performing quantitative analysis using an energy dispersive X-ray analyzer while observing, and the content of alumina particles is expressed as alumina particle mass / (silica particle mass + alumina particle mass) × 100 ”. wt% ”, and the content of silica particles is expressed as silica particle mass / (silica particle mass + alumina particle mass) × 100“ wt% ”.

[Configuration of excimer lamp]
The dimensions of the discharge vessel were 10 × 42 × 150 mm and the wall thickness was 2.5 mm, and xenon gas was enclosed in the discharge vessel as a discharge gas in an amount of 40 kPa.
The dimensions of the high voltage supply electrode and the ground electrode are 30 × 100 mm.
The silica particles constituting the ultraviolet reflecting film have a particle diameter in the range of 0.3 to 1.0 μm, a center particle diameter of 0.5 μm, and a ratio of particles having the center particle diameter of 50%. .
The alumina particles constituting the ultraviolet reflecting film have a particle diameter in the range of 0.2 to 0.7 μm, a center particle diameter of 0.4 μm, and a ratio of particles having the center particle diameter of 50%. .
The particle diameters of silica particles and alumina particles are measured using Hitachi field emission scanning electron microscope “S4100”, the acceleration voltage is 20 kV, and the observation magnification in the enlarged projection image is 0.1 to 1 μm. The particle size was 20000 times, and the particle size of 1 to 10 μm was 2000 times.
The ultraviolet reflecting film was obtained by a flow-down method at a firing temperature of 1100 ° C., and the film thickness was 30 μm.

For each excimer lamp, wall loading b of the discharge vessel is ^{0.5W / cm 2, 0.7W / cm} 2, 1.0W / cm 2, are turned under the condition that a 1.4 W / cm ^2, and after lighting Measure the illuminance of xenon excimer light with a wavelength of 172 nm after 500 hours of continuous lighting with a constant tube wall load, and change the illuminance due to a decrease in reflectance (relative to the initial illuminance), that is, [(lighting for 500 hours Later luminescence intensity) / (luminescence intensity immediately after lighting)] was calculated. The results are shown in Table 1 below.
As shown in FIG. 3, the illuminance measurement is performed by fixing the excimer lamp 10 on a ceramic support 31 disposed inside the aluminum container 30 and at a position 1 mm away from the surface of the excimer lamp 10. In a state where the ultraviolet illuminance meter 35 is fixed so as to face the excimer lamp 10 and the inner atmosphere of the aluminum container 30 is replaced with nitrogen, an AC high voltage is applied between the electrodes 15 and 16 of the excimer lamp 10 to discharge. A discharge was generated inside the container 11 and the illuminance of xenon excimer light emitted through the mesh of the other electrode (ground electrode) 16 was measured.

From the above results, in the excimer lamp that does not have an ultraviolet reflecting film, since the illuminance change with time does not substantially occur, the decrease in illuminance is caused by the decrease in the reflectance of the ultraviolet reflecting film. You can see that
For example, since a maintenance rate of 80% or more may be required as a product standard, when the change in illuminance is 0.8 or more, the determination standard is alumina whose illuminance change is maintained at 0.8 or more. The content ratio of the particles is 1 wt% or more when the tube wall load is 0.5 W / cm ² , 3 wt% or more when the tube wall load is 0.7 W / cm ² , and the tube wall load is 1.0 W / cm ^2. In this case, it is confirmed that it is necessary to be 6 wt% or more, and when the tube wall load is 1.4 W / cm ² , it is necessary to be 10 wt% or more. As shown in FIG. If the alumina content y when maintained is an amount in the region above the approximate straight line L indicated by y = 10b-4 in relation to the tube wall load b, the ultraviolet reflection film is used for the desired reflection characteristics. Can be configured as having illuminance It was confirmed that it is possible to reduce suppress the degree below.

<Experimental example 2>
Each of the six types of excimer lamps having the same basic configuration as that used in Experimental Example 1 except that the content ratio of silica particles and alumina particles constituting the ultraviolet reflecting film was changed according to Table 2 below. Each of the excimer lamps was prepared, and the presence or absence of peeling of the ultraviolet reflecting film was visually observed. The results are shown in Table 2 below.

  From the above results, it was confirmed that peeling of the ultraviolet reflective film did not occur when the content of alumina particles in the ultraviolet reflective film was 70 wt% or less.

Therefore, from the results shown in Experimental Example 1 and Experimental Example 2, the content ratio of alumina particles in the ultraviolet reflecting film is (10b-4) wt% or more (b: tube wall load [W / cm ² ] of the discharge vessel). 70 wt% or less, it is possible to obtain an excimer lamp that maintains the initial reflectivity of the ultraviolet reflecting film and does not cause peeling of the ultraviolet reflecting film even when the lamp is lit for a long time. confirmed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment, A various change can be added.
The present invention is not limited to the excimer lamp having the above-described configuration, and is also applicable to a so-called “square” excimer lamp as shown in FIG. 5 and a double-tube structure excimer lamp as shown in FIG. Can be applied.
An excimer lamp 40 shown in FIG. 5 includes a discharge vessel 41 having a rectangular cross section made of, for example, synthetic silica glass. A pair of outer electrodes 45, 45 made of metal are disposed on the outer surfaces of the discharge vessel 41 facing each other. The discharge vessel 41 is filled with, for example, a xenon gas that is a discharge gas. In FIG. 5, reference numeral 42 denotes an exhaust pipe, and reference numeral 43 denotes a getter made of, for example, barium.
In the excimer lamp 40 having such a configuration, the ultraviolet reflective film 20 is provided on the inner surface of the discharge vessel 41 over a region corresponding to each of the outer electrodes 45 and 45 and one inner surface region continuous with these regions. In addition, the light emitting portion 44 is formed by not providing the ultraviolet reflecting film 20.

An excimer lamp 50 shown in FIG. 6 has a cylindrical outer tube 52 made of silica glass, and an outer diameter smaller than the inner diameter of the outer tube 52 arranged along the tube axis in the outer tube 52. A cylindrical inner tube 53 made of, for example, silica glass, the outer tube 52 and the inner tube 53 are melt-bonded at both ends, and an annular discharge space S is formed between the outer tube 52 and the inner tube 53. A discharge vessel 51 having a double tube structure formed, and one electrode (high voltage supply electrode) 55 made of, for example, metal is provided in close contact with the inner peripheral surface of the inner tube 53; The other electrode 56 made of a conductive material such as a wire mesh is provided in close contact with the outer peripheral surface of the outer tube 52 and forms excimer molecules in the discharge space S by excimer discharge such as xenon gas. Vinegar is filled, it is configured.
In the excimer lamp 50 having such a configuration, for example, the ultraviolet reflecting film 20 is provided over the entire inner surface of the inner tube 53 of the discharge vessel 51, and a light emitting portion 58 is formed on the inner surface of the outer tube 52. An ultraviolet reflecting film 20 made of silica particles and alumina particles is provided except for a part of the region.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing for description which shows the outline of the 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 sectional view in (a) FIG. It is explanatory drawing for demonstrating the definition of the particle diameter of a silica particle and an alumina particle. It is sectional drawing for demonstrating the measuring method of the illumination intensity of the excimer lamp in an experiment example. It is a graph which shows the relationship between the tube wall load of a discharge vessel and the alumina content in an ultraviolet reflective film when the illumination intensity change of an excimer lamp is maintained at 0.8 or more. It is sectional drawing for description which shows the outline of the structure in the other 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) It is perpendicular | vertical to the paper surface of (a). It is sectional drawing which shows the cross section by a simple plane. It is sectional drawing for description which shows the outline of the structure in the further another example of the excimer lamp of this invention, Comprising: (a) The cross-sectional view which shows the cross section along the longitudinal direction of a discharge vessel, (b) A in (a) FIG.

Explanation of symbols

10 Excimer lamp 11 Discharge vessel 15 One electrode (high voltage supply electrode)
16 The other electrode (ground electrode)
18 Light emitting part (aperture part)
20 UV reflecting film 30 Aluminum container 31 Support base 35 UV illuminometer 40 Excimer lamp 41 Discharge container 42 Exhaust pipe 43 Getter 44 Light emitting part 45 Outer electrode 50 Excimer lamp 51 Discharge container 52 Outer tube 53 Inner tube 55 One electrode ( High voltage supply electrode)
56 Other electrode 58 Light emitting portion S Discharge space

Claims (1)

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 xenon gas is sealed in the discharge space. when the wall load b [W / cm ^2], tube wall loading b is 0.5 W / cm ² or more, it is illuminated in a condition to be 1.4 W / cm ² or less, an excimer in the discharge space of the discharge vessel An excimer lamp for generating discharge,
An ultraviolet reflective film made of silica particles and alumina particles is formed on the surface of the discharge vessel exposed to the discharge space, and the ultraviolet reflective film is formed of alumina particles in the surface layer portion exposed to the discharge space. Is contained in a proportion of (10b-4) wt% or more and 70 wt% or less.

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