excimer lamp

Abstract

The objective of this invention is to provide an excimer lamp that suppresses both the ultraviolet distortion of the discharge capacitor and the deviation in illuminance maintenance rate corresponding to the location of the discharge capacitor. The excimer lamp of the solution comprises a long strip-shaped discharge capacitor containing fluorine-doped quartz glass and encapsulating a luminescent gas inside, and a pair of electrodes to which a discharge voltage is applied to the interior of the discharge capacitor. Within the effective luminescent area of ​​the discharge capacitor, the virtual temperature T[°C] of each measurement site, consisting of a pair of end portions along the long side and a plurality of intermediate portions obtained by substantially equally dividing the area between the pair of end portions along the long side, satisfies the following equations (1) and (2) when the intermediate value of the virtual temperature T[°C] of each measurement site is set as Ta[°C].

Description

Excimer lamp The present invention relates to an excimer lamp, and in particular to an excimer lamp in which a discharge vessel is doped with fluorine. An excimer lamp that emits ultraviolet light has a discharge vessel made of quartz glass filled with a specific luminescent gas. When an excimer lamp is continuously lit, the ultraviolet light generated within the discharge space transmits through the quartz glass forming the discharge vessel, causing deformation and sometimes breakage of the glass. This problem is particularly pronounced in excimer lamps, which emit ultraviolet light in the short-wavelength range (also known as vacuum ultraviolet light) with a peak wavelength of less than 200 nm. Furthermore, even if the glass itself does not break, the absorption of ultraviolet light by quartz glass can cause structural defects in the molecules that make up the glass, which can increase the amount of ultraviolet light absorbed. This can result in a decrease in the transmittance of the discharge vessel itself, sometimes leading to a decrease in illuminance. In view of this situation, it is important to suppress ultraviolet deformation as much as possible in the discharge vessel of the excimer lamp, and several technologies have been proposed so far. One of the factors that causes UV absorption bands in quartz glass is unstable structures within the glass, specifically three-membered ring structures and four-membered ring structures. These unstable structures have weaker binding energy than normal structures, so the more unstable structures there are, the lower the UV transmittance. It is known that this unstable structure depends on the virtual temperature of the quartz glass. Lowering the virtual temperature further reduces the amount of unstable structure generated. Heat treatment in a furnace is a known method for changing the virtual temperature of quartz glass. Lowering the virtual temperature of quartz glass can be achieved by heat treatment at low temperatures. However, when the desired virtual temperature is low, long heat treatment times are often required. From the perspective of industrial excimer lamp production, extremely long heat treatment times are not ideal. For example, if the virtual temperature is set to around 500°C, the heat treatment time could exceed one month. It is also known that when fluorine (F) is contained in quartz glass, Si-F bonds are formed, thereby having the effect of alleviating the above-mentioned unstable structure. In other words, by introducing fluorine into quartz glass, the heat treatment time can be relatively shortened while reducing the amount of unstable structure generated. The present applicant has previously proposed an excimer lamp using synthetic quartz glass with a fluorine content of 7000 wt.ppm to 30000 wt.ppm and a virtual temperature of 750°C to 1000°C as a discharge vessel (see Patent Document 1). [Prior Art] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-192351 [Problems to be solved by the invention] The present inventors have conducted extensive research and have newly discovered that when an excimer lamp using fluorine-containing quartz glass as a discharge vessel is operated for a long period of time, the illumination intensity varies depending on the location of the discharge vessel. In other words, the present inventors have newly discovered that in an excimer lamp using fluorine-containing quartz glass as a discharge vessel, the illumination maintenance rate varies depending on the location of the discharge vessel. The present invention has been developed in view of the above-mentioned problems, and its object is to provide an excimer lamp that suppresses both ultraviolet distortion of a discharge container and variations in the illuminance maintenance rate depending on the location of the discharge container. [Means for Solving the Problem] The excimer lamp of the present invention is characterized by comprising: a long strip-shaped discharge vessel comprising fluorine-doped quartz glass and enclosing a luminescent gas therein; and a pair of electrodes for applying a discharge voltage to the interior of the discharge vessel; wherein, within an effective luminescent region of the discharge vessel, the virtual temperature T[°C] of each measurement location, consisting of a pair of end locations in the longitudinal direction and a plurality of intermediate locations obtained by dividing the region between the pair of end locations into a predetermined number of substantially equal portions in the longitudinal direction, satisfies the following equations (1) and (2) when the intermediate value of the virtual temperature T[°C] of each measurement location is defined as Ta[°C]: Through intensive research by the present inventors, it was found that the reason why the illumination maintenance rate varies depending on the location of the discharge vessel is due to variations in the virtual temperature of the discharge vessel during the manufacturing process. As mentioned above, when ultraviolet light generated in the discharge space of an excimer lamp passes through the quartz glass forming the discharge vessel, it can cause deformation of the quartz glass. It is known that this problem can be solved by slowing down the cooling rate during excimer lamp manufacturing to lower the virtual temperature of the quartz glass. However, this method has another problem in that the manufacturing time is too long when manufacturing excimer lamps for industrial use. Therefore, from the perspective of achieving a relatively fast cooling rate and easily lowering the virtual temperature of the quartz glass, a method using fluorine-doped quartz glass as a discharge vessel has been developed, as described in Patent Document 1. However, cooling quartz glass at an accelerated cooling rate tends to cause the virtual temperature of the quartz glass to become non-uniform. Specifically, while fluorine doping tends to lower the virtual temperature of the quartz glass for the same cooling time, another problem becomes apparent: the virtual temperature tends to vary at various locations within the manufactured discharge vessel. In particular, when an excimer lamp has a long discharge vessel, the virtual temperature tends to vary depending on the position along the longitudinal direction. This variation in virtual temperature causes variations in the illumination maintenance rate at each location after prolonged operation. In other words, prolonged operation can easily cause variations in brightness depending on the location of the discharge vessel. This problem is particularly pronounced in excimer lamps with discharge vessels exceeding 1 meter in length along the longitudinal direction. Excimer lamps are primarily used in industrial applications. For example, by enclosing a luminescent gas primarily composed of Xe, excimer lamps produce vacuum ultraviolet light sources with a peak wavelength near 172nm. Such lamps are used, for example, for surface modification and cleaning of wafers. If brightness variations occur in different locations within the discharge vessel due to prolonged operation, this can affect the degree of treatment of the object being treated. Therefore, in excimer lamps, it is sometimes desirable to minimize variations in the illumination maintenance factor regardless of the location within the discharge vessel. However, suppressing variations in the virtual temperature, which is one of the causes of variations in the illumination maintenance factor, requires an extremely slow cooling rate. As mentioned above, this approach is difficult to adopt for industrial production. In contrast, an excimer lamp that satisfies equations (1) and (2) can tolerate variations in the virtual temperature to a certain extent while suppressing variations in the illuminance maintenance rate. Consequently, the manufacturing time required for the excimer lamp is not significantly prolonged, and variations in brightness after long-term operation can be suppressed. Details are described later in the "Implementation Methods" section. The maximum value and the minimum value of the virtual temperature T at each measurement location of the excimer lamp system may differ by 10° C. or more. [Effects of the Invention] According to the present invention, an excimer lamp that suppresses both ultraviolet deformation of a discharge vessel and variations in the illuminance maintenance rate depending on the location of the discharge vessel can be realized without significantly increasing production cycle time. The embodiments of the excimer lamp of the present invention will be described with reference to the drawings as appropriate. Note that the following drawings are schematic illustrations, and the dimensional ratios in the drawings are not necessarily consistent with the actual dimensional ratios. Furthermore, the dimensional ratios in the drawings are not necessarily consistent. FIG1 is a top view schematically showing the structure of an excimer lamp 1 according to this embodiment. The excimer lamp 1 comprises a long discharge vessel 10 primarily made of fluorine-doped quartz glass and bases (31, 32) disposed at both ends of the discharge vessel 10. The bases (31, 32) are provided to secure the ends of the discharge vessel 10, but are not essential for the present invention. In the following description, the XYZ coordinate system shown in FIG1 is referenced as appropriate. When expressing a direction, a positive or negative sign is added, such as "+X direction" or "-X direction." When expressing a direction without distinguishing between positive and negative directions, the direction is simply expressed as "X direction." In the excimer lamp 1 of this embodiment, the length of the discharge vessel 10 in the X direction is 1 m or longer. However, the present invention can also be applied to an excimer lamp 1 in which the length of the discharge vessel 10 in the X direction is less than 1 m. It is known that the transmittance of ultraviolet light in quartz glass is affected by the concentration of OH groups contained in the quartz glass. Specifically, when the concentration of OH groups in the quartz glass is high, the transmittance for short-wavelength light is low. Conversely, when the concentration of OH groups is low, the transmittance for short-wavelength light is high. In the present invention, the concentration of OH groups contained in the quartz glass constituting the discharge vessel 10 is arbitrary, but from the viewpoint of improving the efficiency of extracting ultraviolet rays generated in the discharge vessel 10 to the outside of the discharge vessel 10, the OH group concentration is preferably lower. When the concentration of OH groups in the quartz glass is high, the durability of the quartz glass improves. However, by introducing fluorine into the quartz glass, structural instability can be eliminated and the durability of the quartz glass can be increased. In other words, when fluorine is doped into the quartz glass, even if the concentration of OH groups in the quartz glass is reduced, quartz glass exhibiting high durability can be achieved. From this perspective, the OH group concentration in the quartz glass constituting the discharge vessel 10 is preferably 10 wt.ppm to 450 wt.ppm. In the present invention, the fluorine concentration doped in the quartz glass constituting the discharge vessel 10 is arbitrary. However, if the fluorine concentration is too high, the ultraviolet rays generated in the excimer lamp 1 may cause oxygen-deficient defects in the quartz glass constituting the discharge vessel 10. On the other hand, if the fluorine concentration is too low, the effect of lowering the virtual temperature of the quartz glass is substantially negligible. From this perspective, the fluorine concentration in the quartz glass constituting the discharge vessel 10 is preferably 10 wt.ppm to 3000 wt.ppm. The concentration of OH groups in quartz glass can be determined by measuring infrared absorption spectra at a wavelength of 3670 cm -1As a specific example of the method, the following method can be cited: (1) performing IR absorption measurement on the measurement object, (2) then scraping off the measurement object portion (surface layer) of the measurement object and further performing IR absorption measurement, and (3) calculating the concentration of the scraped portion (surface layer) based on the difference between the measurement values ​​before and after the scraping treatment of the obtained surface layer. The concentration of fluorine contained in quartz glass can be measured by, for example, ion chromatography, EPMA (Electron Probe Micro-Analysis), fluorescent X-ray spectroscopy, SIMS (Secondary Ion Mass Spectrometry), or the like. Fig. 2A is a schematic cross-sectional view of the excimer lamp 1 of Fig. 1 taken along the XZ plane. However, in Fig. 2A , the bases (31, 32) are not shown. 1 and 2A , the excimer lamp 1 of this embodiment is configured to emit ultraviolet light L1 in the Z direction with the X direction being the longitudinal direction. A discharge space 11 in which a luminescent gas is sealed is formed inside a discharge vessel 10 . The excimer lamp 1 includes a pair of electrodes (21, 22) for applying a discharge voltage to the discharge space 11. More specifically, the excimer lamp 1 of this embodiment includes an electrode 21 formed on the outer wall of the discharge vessel 10 on the +Z side, and an electrode 22 formed on the -Z side. In this example, the electrodes 21 and 22 are arranged in a grid pattern, and ultraviolet light L1 is emitted through the gaps between the electrodes 21 and the gaps between the electrodes 22. Both electrodes 21 and 22 are preferably formed of a highly corrosion-resistant material such as gold (Au). Alternatively, the electrodes 21 and 22 may be arranged in a plurality of separated lines. Alternatively, as shown in Figure 2B , electrode 22 may be formed into a film. In this case, if the excimer lamp 1 is intended to emit ultraviolet light L1 in the +Z direction, as shown in Figure 2B , electrode 22 is preferably formed from a material containing a metal that reflects ultraviolet light L1. Gold, an example of a highly corrosion-resistant material, exhibits high reflectivity to ultraviolet light L1 and can therefore also be used as the material for electrode 22 in Figure 2B . In addition, when it is planned to emit the ultraviolet rays L1 not only in the +Z direction but also in the -Z direction, the electrode 22 on the -Z side may be formed in a grid shape or a line shape. FIG1 corresponds to a plan view of the excimer lamp 1 as viewed from the +Z side, and therefore, illustration of the electrode 22 disposed on the −Z side of the discharge vessel 10 is omitted. A luminescent gas that forms excimers through discharge is enclosed within the discharge vessel 10. The luminescent gas is arbitrary; for example, one primarily composed of xenon (Xe) can be used. When a high-frequency AC voltage of approximately 1 kHz to 5 MHz is applied between electrodes 21 and 22, this voltage is applied to the luminescent gas via the discharge vessel 10, generating plasma within the discharge space 11. This excitation excites atoms in the luminescent gas into an excimer state, which then emits excimer light as they transition to the ground state. When a gas containing xenon (Xe) is used as the luminescent gas, this excimer light emission produces ultraviolet light L1 with a peak wavelength of approximately 172 nm. Furthermore, the wavelength of ultraviolet light L1 can be varied by varying the substance used as the luminescent gas. Examples of combinations of luminescent gas and peak wavelength include ArBr (165 nm), ArF (193 nm), KrBr (207 nm), and KrCl (222 nm). As described above, by applying a voltage between the electrodes 21 and 22, the luminescent gas within the discharge space 11 undergoes excimer luminescence, emitting ultraviolet light L1. Consequently, the excimer lamp 1 emits strong light in the region where the electrodes 21 and 22 face each other within the discharge space 11. Furthermore, as shown in FIG2A , when both the electrodes 21 and 22 form a grid pattern, the excimer lamp 1 emits strong light in the region where the electrode 21 is arranged on the outer wall of the discharge vessel 10 on the +Z side and the electrode 22 is arranged on the outer wall of the discharge vessel 10 on the -Z side, facing each other within the discharge space 11. In this specification, the region within the discharge space 11 that emits relatively intense light is referred to as the "effective light-emitting region." More specifically, the effective light-emitting region refers to the region within the discharge space 11 where light of 60% or more of the peak value is emitted in the light intensity distribution along the longitudinal direction (X direction) of the discharge vessel. In FIG. 2A and subsequent figures, the reference numeral 5 denotes the effective light-emitting region. The excimer lamp 1 has the following characteristics regarding the virtual temperature at each location along the longitudinal direction (X direction) of the discharge vessel 10. This will be explained with reference to FIG3 . FIG3 corresponds to a top view of the excimer lamp 1 illustrated in the same manner as FIG1 , with the effective light-emitting region 5 and measurement locations (4, 4, ...) additionally indicated. The measurement locations (4, 4, ...) will be described later. The measurement locations (4, 4, ...) are locations where the virtual temperature of the discharge vessel 10 is measured. Specifically, the measurement locations (4, 4, ...) are obtained by dividing the area within the effective light-emitting region 5 of the discharge vessel 10 into a predetermined number of substantially equal portions in the longitudinal direction (X direction). In the example of FIG3 , the area within the effective light-emitting region 5 of the discharge vessel 10 is substantially divided into four equal portions in the X direction, indicating a total of five measurement locations (4, 4, ...). The X coordinate positions of each measurement location (4, 4, ...) correspond to X1, X2, X3, X4, and X5. In the example of FIG3 , the measurement locations 4 corresponding to locations X1 and X5 correspond to a pair of end locations, while the measurement locations 4 corresponding to locations X2, X3, and X4 correspond to a middle location. The measurement locations (4, 4, ...) are provided to measure the degree of variation (uniformity) of the virtual temperature in the longitudinal direction (X direction) of the discharge vessel 10. Therefore, if the plurality of measurement locations (4, 4, ...) are offset toward the ends on the -X side, toward the ends on the +X side, or toward the center in the X direction, verification of the variation of the virtual temperature in the X direction of the discharge vessel 10 cannot be said to be effective. That is, in this specification, "substantially equally divided" means that the measurement locations (4, 4, ...) are dispersed in the X direction to such an extent that the deviation of the virtual temperature in the X direction of the discharge vessel 10 can be verified. Within the range that achieves this purpose, the separation distances between the measurement locations (4, 4, ...) are allowed to vary. As an example, the maximum separation distance between the measurement locations (4, 4, ...) may be no greater than twice the average value of the aforementioned separation distances. In the discharge vessel 10 of the excimer lamp 1 , the virtual temperature T [° C.] of each measurement location ( 4 , 4 , . . . ) set as described above and the median value Ta [° C.] of all virtual temperatures T satisfy the following equations (1) and (2). In other words, each virtual temperature T [° C.] and the median value Ta [° C.] of all virtual temperatures T are in a relationship that is located within the noisy region of the graph of FIG. 4 . The virtual temperature T of each measurement location (4, 4, ...) can be obtained by infrared absorption spectroscopy or Raman spectroscopy. Infrared absorption spectroscopy is the method of measuring the peak value (2260 cm) representing the stretching vibration of Si-O bond in quartz glass. -1 Specifically, it is known that a method is used to calculate the virtual temperature of quartz glass by a simple calculation based on the following formula (3), according to the peak wave number ν2 [cm -1 ]Calculate the virtual temperature T f method. Raman spectroscopy is a method that uses the ω-wavelength vibration of Si-O-Si bonds in quartz glass to 1(at 440cm -1 Specifically, it is known that a method is used to calculate the offset of the line of the peak appearing near the Raman signal of quartz glass by a simple calculation based on the following formula (4). 1 to calculate the virtual temperature T f method. The virtual temperature T of each measurement location (4, 4, ...) is measured using the aforementioned infrared absorption spectroscopy, Raman spectroscopy, etc. Hereinafter, the virtual temperature of each position Xi (i=1, 2, ...) of each measurement location (4, 4, ...) is denoted as Ti. The intermediate value Ta is a value located exactly in the middle between the maximum value and the minimum value of the virtual temperature Ti at each position Xi. As described above, when excimer lamps are manufactured for industrial use, variations in the virtual temperature of the discharge vessel are unavoidable. Meanwhile, during discharge vessel manufacturing, heating and cooling curves are set so that the virtual temperature reaches a certain target value. Specifically, when the virtual temperature of each measurement location in a discharge vessel manufactured using conventional methods is measured, the target virtual temperature during manufacturing generally coincides with the median value of the virtual temperatures at each measurement location, and exhibits a tendency to fluctuate based on this median value depending on the measurement location. The graph in FIG4 indicates that the permissible range of the deviation of the virtual temperature at each measurement location (4, 4, ...) changes depending on the intermediate value Ta of the virtual temperature, in other words, the value of the virtual temperature targeted during manufacturing (target value). Specific numerical examples are listed below. When the intermediate value Ta (i.e., target value) of the virtual temperature is 920°C, the permissible range of variation of all virtual temperatures Ti at each location Xi is 193.4°C within the range of 823.3°C to 1016.7°C. As another example, when the intermediate value Ta (i.e., target value) of the virtual temperature is 960°C, the permissible range of variation of all virtual temperatures Ti at each location Xi is 121.4°C within the range of 899.3°C to 1020.7°C. As another example, when the intermediate value Ta (i.e., target value) of the virtual temperature is 980°C, the permissible range of variation of all virtual temperatures Ti at each location Xi is 85.4°C within the range of 937.3°C to 1022.7°C. That is, as the virtual temperature intermediate value Ta approaches 1000°C, the permissible fluctuation range of the virtual temperature Ti at each measurement location (4, 4, ...) decreases. If the virtual temperature Ti at each measurement location (4, 4, ...) deviates beyond this permissible fluctuation range, the illumination maintenance rate after the excimer lamp is illuminated for a long period of time will vary significantly. In contrast, as in the excimer lamp 1 of this embodiment, if the permissible fluctuation range of the virtual temperature Ti at each measurement location (4, 4, ...) is controlled within the shaded area of ​​the graph in FIG. 4 , the difference in illumination maintenance rate at each location after 3000 hours can be kept below 15%. This point will be described in further detail. Samples #1 to #3 of ideal excimer lamps were prepared, which suppressed the variation of virtual temperature Ti at each location in the X direction. All of these samples #1 to #3 were excimer lamps with a peak wavelength of 172 nm and Xe gas sealed in a discharge vessel as the luminescent gas. Samples #1-#3 were manufactured by heating under highly precise control along a carefully defined temperature profile during manufacturing, and then cooling extremely slowly, a process that would not be considered efficient in manufacturing industrial excimer lamps. Samples #1-#3 were manufactured with different target virtual temperatures (target values). The target virtual temperatures for each of Samples #1-#3 are shown in Table 1 below. Furthermore, to be on the safe side, the virtual temperature Ti of each measurement location (4, 4, ...) of samples #1 to #3 was measured, and the results confirmed that in any sample #1 to #3, the virtual temperature Ti converged within the range of ±5°C relative to the target value (i.e., the intermediate value Ta). The time variation of the illuminance maintenance rate of these samples #1 to #3 was measured. Specifically, after lighting for a predetermined time, the illuminance of the ultraviolet rays from each sample #1 to #3 was measured using an illuminance meter, and the relative value relative to the initial illuminance was calculated. When measuring the illuminance, an ultraviolet integrating light meter (UIT-250) and a separate light receiver (VUV-S172) manufactured by Ushio Electric Co., Ltd. were used. The relationship between the illuminance maintenance rate and the lighting time of each sample #1 to #3 was obtained, as shown in Figure 5. Furthermore, the results obtained in Figure 5 were redrawn by expressing the horizontal axis in logarithmic terms. This figure is shown in Figure 6. Using a linear regression model, we applied linear approximation to the data obtained in Figure 6, thereby deriving the relationship between the illuminance maintenance rate y and the lighting time [Log(h)]x for each sample #1 to #3. The linear approximation and the coefficient of determination R2 are as follows. Sample #1: Linear approximation y = -4.2999 × x + 100, coefficient of determination R 2=0.8931 Sample #2: Linear approximation y=-4.9565×x+100, coefficient of determination R 2 =0.8998 Sample #3: Linear approximation y=-7.6343×x+100, coefficient of determination R 2 =0.9541 In any of samples #1 to #3, since the coefficient of determination of the approximate formula is close to 1, it can be understood that the correlation between the approximate formula and the obtained data is high. Next, the relationship between the virtual temperature (the target value, also the intermediate value Ta) for each of Samples #1 to #3 and the slope of the aforementioned linear approximation equation is plotted in a graph. This graph is shown in Figure 7. Hereinafter, the slope of the linear approximation equation will be referred to as the "illuminance maintenance rate reduction coefficient," corresponding to the "coefficient" plotted on the vertical axis of the graph in Figure 7. The results in Figure 7 show that the change in the illuminance maintenance rate reduction coefficient between Sample #1 (949°C) and Sample #2 (987°C) is greater than the difference in the illuminance maintenance rate reduction coefficient between Sample #2 (987°C) and Sample #3 (997°C). The results in Figure 7 approximate the relationship between the virtual temperature and the illuminance maintenance rate reduction coefficient using two straight lines, m1 and m2. Specifically, within the range of virtual temperatures below 987°C, the relationship between the virtual temperature x and the illuminance maintenance rate reduction coefficient y is approximated by the straight line m1: y = -0.0159*x + 10.786. Furthermore, within the range of virtual temperatures above 987°C, the relationship between the virtual temperature x and the illuminance maintenance rate reduction coefficient y is approximated by the straight line m2: y = -0.2651*x + 256.69. In other words, straight lines m1 and m2 represent the relationship between the virtual temperature and the illuminance maintenance rate reduction coefficient. Hereinafter, it is simply expressed as "relational expression α". Here, in the excimer lamp 1, the uniformity U[%] of the illuminance maintenance rate at each measurement location (4, 4, ...) is defined by the following formula (5) using the maximum illuminance maintenance rate Imax and the minimum virtual temperature Imin. The results in Figures 5 and 6 show that the higher the virtual temperature of the discharge vessel, the lower the illumination maintenance factor. Specifically, when measuring the illumination maintenance factor of an excimer lamp at each location within the discharge vessel, the virtual temperature at the location with the maximum illumination maintenance factor Imax, or in other words, the lowest virtual temperature T1, is defined by T1 = x, assuming the median value (target value) of the virtual temperature is x and the temperature difference between the median value and the location is a. Conversely, the virtual temperature at the location with the minimum illumination maintenance factor Imin, or in other words, the highest virtual temperature T2, is defined by T2 = x + a. When the coefficient of the above relational expression α at the position of the lowest virtual temperature T1 is k1, the intercept is k1′, and the lighting time is τ [h], the illuminance maintenance rate Imax at the portion representing the virtual temperature T1 is defined by the following equation (6). Similarly, when the coefficient of the above-mentioned relational expression α at the position of the highest virtual temperature T2 is set to k2, the intercept is k2', and the lighting time is τ [h], the illumination maintenance rate Imin of the portion representing the virtual temperature T2 is defined by the following equation (7). When the above equations (6) and (7) are substituted into equation (5) and transformed into a mathematical formula for calculating the temperature difference a between the virtual temperature and the intermediate value, the following equation (8) is obtained. In an excimer lamp, if the difference in the illuminance maintenance rate at each location in the discharge vessel 10 after 3000 hours of lighting is controlled to less than 15%, the problem of use is reduced. Therefore, in the above formula (8), τ = 3000 and U = 15 are substituted. In addition, the coefficient k1 and intercept k1' of the above-mentioned relationship α at the position of the lowest virtual temperature T1, and the coefficient k2 and intercept k2' of the above-mentioned relationship a at the position of the highest virtual temperature T2 are all based on the relationship a shown in Figure 7 and are uniquely determined according to the value of the virtual temperature. That is, the target virtual temperature (intermediate value) x is sequentially changed to obtain the allowable temperature difference a, and the allowable upper limit and allowable lower limit are calculated by calculation. The calculation process is shown in Table 2 below. The relationship between the intermediate value x and the allowable lower limit (xa), and the relationship between the intermediate value x and the allowable upper limit (x+a), obtained in this manner, are plotted in a graph, and the region within the range of the intermediate value x and the allowable upper limit (x+a) is shaded, resulting in the graph of FIG4 . Thus, by manufacturing the excimer lamp 1 so that the intermediate value Ta of the virtual temperature and the virtual temperature Ti at each measurement location are present within the shaded region shown in FIG4 , the variation in the illuminance maintenance rate at each location in the discharge vessel 10 after 3000 hours of lighting can be suppressed to 15% or less. Hereinafter, the verification results performed using Examples and Comparative Examples will be described. (Example 1) Using fluorine-doped quartz glass, a plurality of samples of excimer lamps 1 were produced as Example 1, with the target value of the virtual temperature set to 983°C under a specific temperature curve. For one of the plurality of samples produced, the virtual temperatures of five measurement locations (X1, X2, ..., X5) were measured, as shown schematically in FIG3 . Specifically, the measurement was performed using the following method. First, glass chips were obtained by crushing the five locations within the effective light-emitting region 5 of the discharge vessel 10. Then, the infrared absorption spectrum of the obtained glass chips was measured using a projection method, and calculations were performed based on the above formula (3). The values ​​obtained by the calculations were used as the virtual temperatures Ti (i=1, 2, ..., 5) of the measurement locations (X1, X2, ..., X5) corresponding to the positions of the respective chips. In Example 1, the relationship of the above formula (2) holds true between the virtual temperature T of each measurement location and the intermediate value Ta of the virtual temperatures. Next, the undamaged sample of the excimer lamp 1 of Example 1 was continuously lit for 3000 hours. Then, the illuminance maintenance rate of each measurement location (X1, X2, ..., X5) after the 3000-hour lighting was measured. Figure 8 schematically illustrates the method for measuring the illuminance maintenance rate at each measurement location. Specifically, after the excimer lamp 1 has been lit for 3000 hours, a light meter 41 is placed near each measurement location (X1, X2, ..., X5) and adjusted so that only the ultraviolet light L1 at that location is received. The illuminance maintenance rate at each measurement location (X1, X2, ..., X5) is then calculated by calculating the ratio of the illuminance measured at each location to the initial illuminance. The measurements were performed using a Ushio Electric Co., Ltd. ultraviolet integrating light meter (UIT-250) and a separate light receiver (VUV-S172) as described above. (Comparative Example 1) Verification was conducted using the same method as in Example 1, except that the target value of the virtual temperature was set to 983°C, similar to Example 1, and the temperature profile during manufacturing was changed compared to Example 1. In Comparative Example 1, the relationship of equation (2) above did not hold between the virtual temperature T at each measurement location and the intermediate value Ta of the virtual temperature. (Example 2) Verification was conducted using the same method as in Example 1, except that the target value of the virtual temperature was set to 909°C and the temperature profile during manufacturing was changed compared to Example 1. In Example 2, the relationship of equation (2) above also holds between the virtual temperature T at each measurement location and the intermediate value Ta of the virtual temperature. (Comparative Example 2) Verification was conducted using the same method as in Example 2, except that the target value of the virtual temperature was set to 909°C, similar to Example 2, and the temperature profile during manufacturing was changed compared to Example 2. In Comparative Example 2, the relationship of equation (2) above did not hold between the virtual temperature T at each measurement location and the intermediate value Ta of the virtual temperature. The verification results are shown in the following Table 3 and Figures 9A to 12B. The uniformity in the following Table 3 is a value calculated based on the above formula (5). The above results show that in Examples 1 and 2, where the virtual temperatures Ti (i = 1, 2, ..., 5) at each measurement location (X1, X2, ..., X5) were kept within the allowable range, the uniformity (variation) of the illuminance maintenance rate after 3000 hours of lighting was less than 6%, significantly below the allowable range of 15%. In contrast, in Comparative Examples 1 and 2, where the virtual temperatures Ti (i = 1, 2, ..., 5) at each measurement location (X1, X2, ..., X5) partially exceeded the allowable range, the uniformity (variation) of the illuminance maintenance rate after 3000 hours of lighting significantly exceeded 15%. In the present invention, the shape of the discharge vessel 10 included in the excimer lamp 1 is not limited. For example, the discharge vessel 10 may have a double-tube structure comprising an outer tube and an inner tube disposed inside the outer tube, with the outer and inner tubes sealed at both ends in the tube axial direction. With this structure, in the excimer lamp 1, the space between the inner and outer tubes forms the discharge space 11, and a luminescent gas is enclosed within this discharge space 11. 1: Excimer lamp 4: Measurement site 5: Effective light emitting area 10: Discharge container 11: Discharge space 21: Electrode 22: Electrode 31: Base 32: Base 41: Light meter L1: Ultraviolet light X1: X-coordinate position of the measurement site X2: X-coordinate position of the measurement site X3: X-coordinate position of the measurement site X4: X-coordinate position of the measurement site X5: X-coordinate position of the measurement site [Figure 1] A top view schematically showing the structure of one embodiment of the excimer lamp of the present invention. [Figure 2A] Another schematic cross-sectional view of the excimer lamp of Figure 1 cut along the XZ plane, omitting the base. [Figure 2B] Another schematic cross-sectional view of the excimer lamp of Figure 1 cut along the XZ plane, omitting the base. [Figure 3] A diagram showing the effective light-emitting area and the measurement location in the top view of the excimer lamp shown in Figure 1. [Figure 4] A graph for illustrating the contents of equations (1) and (2). [Figure 5] A graph showing the relationship between the illuminance maintenance rate and the lighting time of each lamp sample #1 to #3. [Figure 6] A graph showing the horizontal axis of the graph of Figure 5 expressed logarithmically. [Figure 7] A graph showing the relationship between the virtual temperature of each lamp sample #1 to #3 and the slope of the linear approximation. [Figure 8] A diagram schematically showing a method for measuring the illuminance maintenance rate of the excimer lamp at each measurement location. [Figure 9A] A graph showing the value of the virtual temperature at each measurement location in the excimer lamp of Example 1. [Figure 9B] A graph showing the value of the illuminance maintenance rate at each measurement location in the excimer lamp of Example 1. [Figure 10A] A graph showing the value of the virtual temperature at each measurement location in the excimer lamp of Comparative Example 1. [Figure 10B] A graph showing the value of the illuminance maintenance rate at each measurement location in the excimer lamp of Comparative Example 1. [Figure 11A] A graph showing the value of the virtual temperature at each measurement location in the excimer lamp of Example 2. [Figure 11B] A graph showing the value of the illuminance maintenance rate at each measurement location in the excimer lamp of Example 1. [Figure 12A] A graph showing the value of the virtual temperature at each measurement location in the excimer lamp of Comparative Example 2. [Figure 12B] A graph showing the value of the illuminance maintenance rate at each measurement location in the excimer lamp of Comparative Example 2.

Claims

1. An excimer lamp, characterized by comprising: a strip-shaped discharge capacitor comprising fluorine-doped quartz glass and encapsulating a luminescent gas inside; and a pair of electrodes for applying a discharge voltage to the interior of the discharge capacitor, wherein the virtual temperature T[°C] of each measuring portion of the discharge capacitor within the effective luminescent area is formed by a pair of end portions in the long side direction and a plurality of intermediate portions obtained by substantially equally dividing the area between the pair of end portions in the long side direction, and when the intermediate value of the virtual temperature T[°C] of each measuring portion is set as Ta[°C], the following equations (1) and (2) are satisfied.

2. The excimer lamp as described in claim 1, wherein, The maximum and minimum values ​​of the aforementioned virtual temperature T at each measurement site differ by more than 10°C.

3. The excimer lamp as described in claim 1 or 2, wherein, The length of the aforementioned discharge capacitor in the aforementioned long side direction exceeds 1m.

Images