Excimer lamp

Abstract

[Project] Provides an excimer lamp that suppresses both ultraviolet deformation of the discharge vessel and deviation of the illuminance maintenance rate depending on the location of the discharge vessel. [Solution] An excimer lamp comprises a long discharge vessel containing fluorine-doped quartz glass and having a luminescent gas sealed inside, and a pair of electrodes that apply a discharge voltage inside the discharge vessel. The discharge vessel satisfies the following equations (1) and (2), wherein the virtual temperature T[°C] of each measurement location is formed by a plurality of intermediate locations obtained by dividing the area between the pair of end locations in the length direction into a predetermined number of substantially equal parts in the length direction within an effective luminescent region, and the intermediate value of the virtual temperature T[°C] of each measurement location is set to Ta[°C]. 900≤Ta≤1000 … (1) -924.7 + 1.9 × Ta ≤ T ≤ 924.7 + 0.1 × Ta … (2)

Description

Technology Field

[0001] The present invention relates to an excimer lamp, and in particular to an excimer lamp in which the discharge vessel is doped with fluorine. Background Technology

[0002] An excimer lamp that emits ultraviolet rays has a predetermined luminescent gas enclosed in a discharge vessel made of quartz glass.

[0003] When an excimer lamp is continuously lit, ultraviolet rays generated within the discharge space may cause deformation in the quartz glass forming the discharge vessel as they pass through it, potentially leading to glass breakage. In particular, this problem is significantly evident in excimer lamps that emit ultraviolet rays in the short wavelength range, such as those with a peak wavelength of 200 nm or less (also referred to as vacuum ultraviolet rays).

[0004] Furthermore, even if the glass itself does not break, the absorption of ultraviolet rays by the quartz glass causes structural defects in the molecules constituting the glass, and these defects increase the amount of ultraviolet rays absorbed. As a result, the transmittance of the discharge vessel itself decreases, which may lead to a decrease in illuminance.

[0005] Under these circumstances, it is important to suppress ultraviolet deformation as much as possible in the discharge vessel of an excimer lamp, and several techniques have been proposed to date.

[0006] One of the causes of ultraviolet absorption bands in quartz glass is unstable structures within the glass, more specifically, tricyclic or tetracyclic structures. Since these unstable structures have weaker binding energies compared to normal structures, the higher the number of unstable structures, the lower the transmittance of ultraviolet light.

[0007] It is known that this unstable structure depends on the virtual temperature of the quartz glass, and the amount of unstable structure generated can be reduced as the virtual temperature is lowered. As a means to change the virtual temperature of the quartz glass, a method of performing heat treatment inside a furnace is known. To lower the virtual temperature of the quartz glass, it can be achieved by performing heat treatment at a low temperature. However, when the intended virtual temperature is low, heat treatment for a long time is often required. From the perspective of industrial production of excimer lamps, heat treatment taking an extremely long time is undesirable. For example, if the virtual time is to be set to around 500°C, the heat treatment time may exceed one month.

[0008] It is also known that incorporating fluorine (F) into quartz glass creates Si-F bonds, which have the effect of mitigating the aforementioned unstable structure. In other words, by introducing fluorine into quartz glass, it becomes possible to reduce the occurrence of unstable structures while relatively shortening the heat treatment time.

[0009] The applicant has previously proposed an excimer lamp using synthetic quartz glass as a discharge vessel, having a fluorine content of 7,000 wt.ppm to 30,000 wt.ppm and a virtual temperature of 750°C to 1,000°C (see Patent Document 1). Prior art literature

[0010] Japanese Patent Publication No. 2008-192351 The problem to be solved

[0011] As a result of the aforementioned research, the inventors have newly discovered that when an excimer lamp with a fluorine-containing quartz glass discharge vessel is lit for a long period of time, a variation in illuminance occurs depending on the location of the discharge vessel. In other words, the inventors have newly discovered that in an excimer lamp with a fluorine-containing quartz glass discharge vessel, a variation in the illuminance maintenance rate occurs depending on the location of the discharge vessel.

[0012] The present invention aims to provide an excimer lamp that suppresses both ultraviolet deformation of the discharge vessel and deviation in the illuminance maintenance rate according to the location of the discharge vessel, in light of the above-mentioned problem. means of solving the problem

[0013] The excimer lamp according to the present invention is,

[0014] A long discharge vessel comprising fluorine-doped quartz glass and having a luminescent gas sealed inside, and

[0015] A pair of electrodes for applying a discharge voltage inside the discharge vessel is provided,

[0016] The above discharge vessel is characterized in that, within an effective light-emitting region, the virtual temperature T[°C] of each measurement location, which is formed by a plurality of intermediate locations obtained by substantially dividing the region between the pair of end locations in the length direction by a predetermined number of equal parts with respect to the length direction, satisfies the following equations (1) and (2) when the intermediate value of the virtual temperature T[°C] of each measurement location is set to Ta[°C].

[0017] 900≤Ta≤1000 … (1)

[0018] -924.7 + 1.9 × Ta ≤ T ≤ 924.7 + 0.1 × Ta … (2)

[0019] Through the inventor's research, it was discovered that the reason for the variation in the illuminance retention rate depending on the location of the discharge vessel is due to the variation in the virtual temperature of the discharge vessel during the manufacturing process.

[0020] As described above, the excimer lamp has the problem that when ultraviolet rays generated within the discharge space pass through the quartz glass forming the discharge vessel, deformation occurs in the quartz glass. It is known that this problem can be solved by slowing down the cooling rate during the manufacture of the excimer lamp to lower the virtual temperature of the quartz glass.

[0021] However, the above method has another problem in that it takes too much time to manufacture excimer lamps for industrial use. For this reason, a method was developed to use fluorine-doped quartz glass as a discharge vessel, as described in Patent Document 1, in order to make it easier to lower the virtual temperature of the quartz glass while keeping the cooling speed relatively fast.

[0022] However, cooling quartz glass at a rapid rate makes it easy for the virtual temperature of the quartz glass to become non-uniform. In other words, while doping with fluorine makes it easy for the virtual temperature of the quartz glass to decrease under the same cooling time, it has brought to the surface another problem in which the virtual temperature of the discharge vessel after manufacturing tends to become non-uniform depending on the location.

[0023] In particular, when an excimer lamp is equipped with a long discharge vessel, variations in virtual temperature are likely to occur depending on the position along the length. These variations in virtual temperature cause variations in the illumination retention rate at different locations after prolonged illumination. In other words, due to prolonged illumination, variations in brightness are likely to occur depending on the location of the discharge vessel. This problem is particularly pronounced in excimer lamps equipped with a discharge vessel with a length exceeding 1m along the length direction.

[0024] Excimer lamps are primarily used for industrial purposes. For example, by encapsulating a luminescent gas whose main component is Xe, the excimer lamp becomes a vacuum ultraviolet light source with a peak wavelength of approximately 172 nm. Such a light source is used, for instance, for wafer surface modification or cleaning. In this case, if variations in brightness occur at different locations within the discharge vessel due to prolonged illumination, effects such as uneven processing of the workpiece depending on the location are expected.

[0025] For this reason, in excimer lamps, there is a desire to suppress deviations in the illuminance retention rate as much as possible regardless of the location within the discharge vessel. However, in order to suppress deviations in virtual temperature, which is one of the causes of deviations in the illuminance retention rate, it is necessary to make the cooling speed extremely slow, and as mentioned above, this method is difficult to adopt considering industrial production.

[0026] In this regard, according to the excimer lamp satisfying the above equations (1) and (2), it is possible to suppress deviations in the illumination maintenance rate while allowing a certain degree of deviation in virtual temperature. Therefore, it is possible to suppress deviations in brightness after long-term illumination without significantly increasing the time required to manufacture the excimer lamp. More details will be described later in the section "Forms for carrying out the invention".

[0027] The above excimer lamp may be such that the maximum and minimum values ​​of the virtual temperature T at each measurement location are separated by more than 10°C. Effects of the invention

[0028] According to the present invention, an excimer lamp that suppresses both ultraviolet deformation of the discharge vessel and deviation of the illuminance maintenance rate according to the location of the discharge vessel can be realized without causing a significant increase in takt time. Brief explanation of the drawing

[0029] FIG. 1 is a plan view schematically showing the configuration of one embodiment of the excimer lamp of the present invention. FIG. 2a is a schematic cross-sectional view of the excimer lamp of FIG. 1 when cut along the XZ plane, and the base is omitted. FIG. 2b is another schematic cross-sectional view of the excimer lamp of FIG. 1 when cut along the XZ plane, with the base omitted. FIG. 3 is a plan view of the excimer lamp shown in FIG. 1, with an effective light-emitting area and a measurement location indicated. Figure 4 is a graph to explain the contents of equation (1) and equation (2). Figure 5 is a graph showing the relationship between the illuminance retention rate and the lighting time of each lamp sample #1 to #3. Figure 6 is a graph in which the horizontal axis of the graph in Figure 5 is logarithmically denoted. Figure 7 is a graph showing the relationship between the virtual temperature of each lamp sample #1 to #3 and the slope of the linear approximation. FIG. 8 is a diagram schematically illustrating a method for measuring the illuminance retention rate of an excimer lamp at each measurement location. FIG. 9a is a graph showing the virtual temperature values ​​at each measurement location in the excimer lamp of Example 1. FIG. 9b is a graph showing the value of the illuminance retention rate at each measurement location in the excimer lamp of Example 1. FIG. 10a is a graph showing the virtual temperature values ​​at each measurement location in the excimer lamp of Comparative Example 1. FIG. 10b is a graph showing the value of the illuminance retention rate at each measurement location in the excimer lamp of Comparative Example 1. FIG. 11a is a graph showing the virtual temperature values ​​at each measurement location in the excimer lamp of Example 2. FIG. 11b is a graph showing the value of the illuminance retention rate at each measurement location in the excimer lamp of Example 2. FIG. 12a is a graph showing the virtual temperature values ​​at each measurement location in the excimer lamp of Comparative Example 2. FIG. 12b is a graph showing the value of the illuminance retention rate at each measurement location in the excimer lamp of Comparative Example 2. Specific details for implementing the invention

[0030] Embodiments of an excimer lamp according to the present invention will be described with appropriate reference to the drawings. Furthermore, each of the following drawings is schematically illustrated, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios. Also, the dimensional ratios between the drawings do not necessarily correspond.

[0031] FIG. 1 is a plan view schematically showing the configuration of an excimer lamp (1) of the present embodiment. The excimer lamp (1) comprises a long discharge vessel (10) made of fluorine-doped quartz glass and bases (31, 32) installed at both ends of the discharge vessel (10). The bases (31, 32) are installed for the purpose of fixing the ends of the discharge vessel (10), but are not essential in the present invention. In the following description, the XYZ coordinate system shown in FIG. 1 is appropriately referenced. Also, when expressing a direction, if a positive or negative direction is distinguished, it is written with positive or negative signs such as "+X direction" and "-X direction," and if a direction is expressed without distinguishing between positive and negative directions, it is simply written as "X direction."

[0032] In the excimer lamp (1) of the present embodiment, the discharge vessel (10) has a length of 1m or more in the X direction. 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 1m.

[0033] 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 contained in the quartz glass is high, the transmittance for short-wavelength light is low, and conversely, when the concentration of OH groups is low, the transmittance for short-wavelength light is high.

[0034] In the present invention, the concentration of OH groups included in the quartz glass constituting the discharge vessel (10) is arbitrary, but from the perspective of increasing the efficiency of extracting ultraviolet rays generated inside the discharge vessel (10) to the outside of the discharge vessel (10), the concentration of OH groups is preferably lower.

[0035] When the concentration of OH groups contained in the quartz glass is high, the durability of the quartz glass is improved. However, by introducing fluorine into the quartz glass, structural instability is resolved, and the durability of the quartz glass can be further enhanced. That is, when fluorine is doped into the quartz glass, a quartz glass exhibiting high durability can be realized even if the concentration of OH groups contained in the quartz glass is low. From this perspective, the concentration of OH groups contained in the quartz glass constituting the discharge vessel (10) is preferably 10 wt.ppm to 450 wt.ppm.

[0036] In the present invention, the fluorine concentration doped into the quartz glass constituting the discharge vessel (10) is optional. However, if the fluorine concentration becomes excessively high, ultraviolet rays generated within the excimer lamp (1) may cause oxygen deficiency defects within the quartz glass constituting the discharge vessel (10). On the other hand, if the fluorine concentration is excessively low, the effect of lowering the virtual temperature of the quartz glass is hardly obtainable. In this regard, the fluorine concentration in the quartz glass constituting the discharge vessel (10) is preferably 10 wt.ppm to 3,000 wt.ppm.

[0037] The concentration of OH groups contained in quartz glass is, for example, at a wavelength of 3670 cm⁻¹ obtained by measuring the infrared absorption spectrum. -1 It can be calculated based on the absorbance of the surrounding area. As an example of a specific method, (1) IR absorption measurement of the object to be measured is performed, (2) then, after removing the part to be measured (surface layer) of the object to be measured, additional IR absorption measurement is performed, and (3) the concentration of the removed part (surface layer) is calculated based on the difference between the measurement values ​​before and after the removal of the surface layer obtained.

[0038] The concentration of fluorine contained in quartz glass can be measured by methods such as ion chromatography, EPMA (Electron Probe Micro-Analysis), fluorescence X-ray spectroscopy, and SIMS (Secondary Ion Mass Spectrometry).

[0039] FIG. 2a is a schematic cross-sectional view of the excimer lamp (1) of FIG. 1 when cut along the XZ plane. However, in FIG. 2a, the base (31, 32) is omitted from the illustration.

[0040] As shown in FIGS. 1 and 2a, the excimer lamp (1) of the present embodiment is configured to emit ultraviolet rays (L1) in the Z direction with the X direction as the longitudinal direction. The interior of the discharge vessel (10) forms a discharge space (11) in which a luminescent gas is sealed.

[0041] The excimer lamp (1) is provided with a pair of electrodes (21, 22) for applying a discharge voltage to a discharge space (11). More specifically, the excimer lamp (1) of the present embodiment is provided with an electrode (21) formed on the outer wall on the +Z side of the discharge vessel (10) and an electrode (22) formed on the -Z side. In this example, the electrode (21) and the electrode (22) both have a mesh shape, and ultraviolet rays (L1) are emitted through the gaps between the electrodes (21) and the gaps between the electrodes (22). It is preferable that the electrode (21) and the electrode (22) both be formed from a material with high corrosion resistance, such as gold (Au). Additionally, the electrode (21) and the electrode (22) may have a shape in which a plurality of lines are spaced apart.

[0042] Additionally, as shown in FIG. 2b, the electrode (22) may be in the shape of a film. In this case, as shown in FIG. 2b, if the excimer lamp (1) is scheduled to emit ultraviolet rays (L1) in the +Z direction, it is suitable to make the electrode (22) out of a material including a metal that exhibits reflectivity to ultraviolet rays (L1). Gold, which was described above as an example of a material with high corrosion resistance, exhibits high reflectivity to ultraviolet rays (L1), so it can also be used as the material for the electrode (22) in FIG. 2b.

[0043] In addition, if it is planned to emit ultraviolet rays (L1) in the -Z direction as well as the +Z direction, the electrode (22) on the -Z side may also be made in a mesh shape or a line shape.

[0044] Since FIG. 1 corresponds to a plan view of the excimer lamp (1) when viewed from the +Z side, the electrode (22) placed on the -Z side of the discharge vessel (10) is omitted from the illustration.

[0045] A luminescent gas that forms excimer molecules by discharge is sealed inside the discharge vessel (10). The luminescent gas is optional, but for example, a luminescent gas whose main component is xenon (Xe) can be used. When an alternating current voltage of approximately 1KHz to 5MHz is applied between the electrode (21) and the electrode (22), this voltage is applied to the luminescent gas through the discharge vessel (10), and plasma is generated within the discharge space (11). As a result, atoms of the luminescent gas are excited and become excimer, and when these atoms transition to the ground state, excimer luminescence occurs. When a gas containing the aforementioned xenon (Xe) is used as the luminescent gas, ultraviolet light (L1) with a peak wavelength of approximately 172nm is obtained through this excimer luminescence. Additionally, the wavelength of the ultraviolet light (L1) can be changed by changing the material used as the luminescent gas. Examples of combinations of luminescent gas and peak wavelength include ArBr (165 nm), ArF (193 nm), KrBr (207 nm), KrCl (222 nm).

[0046] As described above, when a voltage is applied between the electrode (21) and the electrode (22), the luminescent gas in the discharge space (11) emits excimer light and emits ultraviolet light (L1). Because of this, the excimer lamp (1) emits light strongly in the area where the electrode (21) and the electrode (22) face each other within the discharge space (11). In addition, as shown in FIG. 2a, when both the electrode (21) and the electrode (22) have a mesh shape, the excimer lamp (1) emits light strongly in the area where the electrode (21) is positioned on the outer wall on the +Z side of the discharge vessel (10) and the electrode (22) is positioned on the outer wall on the -Z side of the discharge vessel (10) face each other within the discharge space (11).

[0047] In this specification, a region that emits light relatively strongly within the discharge space (11) is referred to as an "effective light-emitting region." More specifically, the effective light-emitting region refers to a region in which 60% or more of the peak value of light is emitted in the light intensity distribution along the length direction (X-direction) of the discharge vessel in the discharge space (11). In each figure from FIG. 2a onwards, the effective light-emitting region is indicated using reference numeral 5.

[0048] 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 point will be explained with reference to FIG. 3. FIG. 3 corresponds to a plan view of the excimer lamp (1) illustrated in the same manner as FIG. 1, and shows an effective light-emitting area (5) and measurement locations (4, 4,…). The description of the measurement locations (4, 4,…) will be given later.

[0049] 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 locations obtained by substantially dividing the area within the effective light-emitting region (5) of the discharge vessel (10) into a predetermined number of equally spaced sections in the length direction (X direction). In the example of FIG. 3, the area within the effective light-emitting region (5) of the discharge vessel (10) is substantially divided into four parts in the X direction, so a total of five measurement locations (4, 4,…) are shown. The X-coordinate positions of each measurement location (4, 4,…) correspond to X1, X2, X3, X4, and X5. In the example of FIG. 3, the measurement location (4) corresponding to the positions (X1 and X5) corresponds to a “pair of end locations,” and the measurement location (4) corresponding to the positions (X2, X3 and X4) corresponds to an “intermediate location.”

[0050] Measurement points (4, 4,…) are installed to measure how uneven the virtual temperature of the discharge vessel (10) is with respect to the length direction (X direction) (uniformity). For this reason, if multiple measurement points (4, 4,…) are skewed toward the -X side end, toward the +X side end, or toward the center along the X direction, the verification of the deviation of the virtual temperature of the discharge vessel (10) with respect to the X direction cannot be considered effective.

[0051] That is, in this specification, "divided substantially equally" means to disperse in the X direction to the extent that the deviation of the virtual temperature in the X direction of the discharge vessel (10) can be verified, and within the scope of achieving this purpose, the distance between the measurement points (4, 4,…) may vary from one another. For example, the maximum value of the distance between the measurement points (4, 4,…) may be less than or equal to twice the average value of the distance between them.

[0052] The discharge vessel (10) equipped with the excimer lamp (1) satisfies the following equations (1) and (2) for the virtual temperature T[°C] at each measurement location (4, 4,…) set as above and the intermediate value Ta[°C] of all virtual temperatures T.

[0053] 900≤Ta≤1000 … (1)

[0054] -924.7 + 1.9 × Ta ≤ T ≤ 924.7 + 0.1 × Ta … (2)

[0055] In other words, each virtual temperature T[°C] and the median value Ta[°C] of all virtual temperatures T are located within the hatched area of ​​the graph in Fig. 4.

[0056] The virtual temperature T at each measurement location (4, 4,…) can be obtained using the infrared absorption spectrum method or the Raman spectrum method.

[0057] Infrared absorption spectroscopy refers to the peak (2260 cm⁻¹) representing the stretching vibration of the Si-O bond in quartz glass. -1 This is a method for calculating the virtual temperature of quartz glass from the shift amount of the (near) range. Specifically, by a simple calculation based on the following equation (3), the peak wavenumber ν2 [cm -1 Virtual temperature T from ] f A method for calculating is known.

[0058] T f = 43809.21 / (ν2-2228.64) … (3)

[0059] Raman spectroscopy is the ω1 (440 cm²) caused by the changing angle vibrations of Si-O-Si bonds in quartz glass. -1 This is a method that utilizes the shift amount of the line (peak appearing in the vicinity). Specifically, by a simple calculation based on the following equation (4), the virtual temperature T from the peak position of ω1 appearing in the Raman signal of quartz glass f A method for calculating is known.

[0060] T f = (ω1-418) / 18×10 -3 … (4)

[0061] Using the above-mentioned infrared absorption spectrum method, Raman spectrum method, etc., a virtual temperature T at each measurement location (4, 4,…) is measured. Below, the virtual temperature at each location Xi (i=1, 2,…) of each measurement location (4, 4,…) is denoted as Ti.

[0062] The median Ta is the value located exactly in the middle of the maximum and minimum values ​​of the virtual temperature Ti at each location Xi.

[0063] As described above, when manufacturing an excimer lamp for industrial use, deviations inevitably occur in the virtual temperature of the discharge vessel. Meanwhile, when manufacturing the discharge vessel, a heating and cooling profile is set so that the virtual temperature becomes a target value. That is, when the virtual temperature at each measurement point is measured for a discharge vessel manufactured by a conventional method, the value of the virtual temperature targeted during manufacturing almost coincides with the midpoint of the virtual temperatures at each measurement point, and shows a tendency to fluctuate up and down depending on the measurement point based on that midpoint value.

[0064] The graph in Fig. 4 indicates that the allowable range of deviation of the virtual temperature at each measurement location (4, 4,…) changes depending on the median value of the virtual temperature Ta, in other words, the value of the virtual temperature intended during manufacturing (target value). Specific numerical examples are as follows. When the median value of the virtual temperature Ta (i.e., target value) is 920℃, all virtual temperatures Ti at each location Xi are within the range of 823.3℃ to 1016.7℃, and the allowable variation is 193.4℃. As another example, when the median value of the virtual temperature Ta (i.e., target value) is 960℃, all virtual temperatures Ti at each location Xi are within the range of 899.3℃ to 1020.7℃, and the allowable variation is 121.4℃. As another example, when the median value of the virtual temperature Ta (i.e., the target value) is 980℃, all virtual temperatures Ti at each location Xi are within the range of 937.3℃ to 1022.7℃, and the allowable variation is 85.4℃.

[0065] That is, as the median value Ta of the virtual temperature approaches 1000℃, the allowable variation range of the virtual temperature Ti at each measurement location (4, 4,…) decreases. If the virtual temperature Ti at each measurement location (4, 4,…) becomes uneven to the extent that it exceeds this allowable variation range, a large deviation occurs in the illuminance retention rate after the excimer lamp has been lit for a long time. In contrast, as with the excimer lamp (1) of the present embodiment, if the allowable variation range of the virtual temperature Ti at each measurement location (4, 4,…) remains within the hatched region in the graph of FIG. 4, it becomes possible to maintain the difference in the illuminance retention rate at each location at 15% or less after 3000 hours. This point will be described in further detail.

[0066] Samples #1 to #3 of an ideal excimer lamp were prepared, which suppress the variation of the virtual temperature Ti at each location along the X direction. These samples #1 to #3 are all excimer lamps with a peak wavelength of 172 nm in which Xe gas is sealed in a discharge vessel as a emitting gas.

[0067] These samples #1 to #3 are manufactured by heating under high-precision control following a finely set temperature profile during manufacturing, and cooling extremely slowly, which is not efficient for manufacturing industrial excimer lamps (1). Samples #1 to #3 are lamps manufactured with different target virtual temperatures (target values). The target virtual temperatures for each sample #1 to #3 are as shown in Table 1 below.

[0068] [Table 1]

[0069]

[0070] In addition, as a precaution, the virtual temperature Ti at each measurement location (4, 4,…) for these samples #1 to #3 was measured, and it was confirmed that for any of samples #1 to #3, the virtual temperature Ti was within ±5℃ of the target value (i.e., the median value Ta).

[0071] For these samples #1 to #3, the temporal change in illuminance retention rate was measured. Specifically, after lighting for a predetermined time, the ultraviolet illuminance from each sample #1 to #3 was measured using an illuminance meter, and the relative value with respect to the initial illuminance was calculated. For the illuminance measurement, an ultraviolet integrator (UIT-250) manufactured by Ushio Electric Co., Ltd. and a separate type photodetector (VUV-S172) were used. The relationship between the illuminance retention rate and the lighting time for each sample #1 to #3 was obtained as shown in FIG. 5. Furthermore, the results obtained in FIG. 5 were re-graphed with the horizontal axis marked as a logarithm. This graph is shown in FIG. 6.

[0072] By linearly approximating each data obtained in Fig. 6 using a linear regression model, a relationship between the illuminance retention rate y and the lighting time [Log(h)] x for each sample #1 to #3 was derived. Each linear approximation equation and the coefficient of determination R 2 It is as follows.

[0073] Sample #1: Linear approximation y = -4.2999×x+100, coefficient of determination R 2 = 0.8931

[0074] Sample #2: Linear approximation y = -4.9565×x+100, coefficient of determination R 2 = 0.8998

[0075] Sample #3: Linear approximation y = -7.6343×x+100, coefficient of determination R 2 = 0.9541

[0076] In any of the samples #1 to #3, the coefficient of determination of the approximation formula is close to 1, so it is understood that the approximation formula has a high correlation with the obtained data.

[0077] Next, the relationship between the virtual temperature (which is the target value and also the median value Ta) of each of samples #1 to #3 and the slope of the linear approximation equation above was graphed. This graph is shown in FIG. 7. Hereinafter, the slope of the linear approximation equation is referred to as the "irritation retention rate reduction coefficient" and corresponds to the "coefficient" listed on the vertical axis of the graph in FIG. 7.

[0078] From the results of Figure 7, it is understood that the trend of the illuminance retention rate reduction coefficient between Sample #2, with a virtual temperature of 987°C, and Sample #3, with a virtual temperature of 997°C, shows a greater degree of change compared to the difference in the illuminance retention rate reduction coefficient between Sample #1, with a virtual temperature of 949°C, and Sample #2, with a virtual temperature of 987°C. Based on the results of Figure 7, the relationship between the virtual temperature and the illuminance retention rate reduction coefficient was approximated by two straight lines m1 and m2. That is, within the range of a virtual temperature of 987°C or lower, it can be seen that a relationship approximated by the straight line m1:y = -0.0159*x + 10.786 holds between the virtual temperature x and the illuminance retention rate reduction coefficient y. In addition, it can be seen that when the virtual temperature is within the range of 987°C or higher, a relationship approximated by the straight line m2:y = -0.2651*x + 256.69 holds between the virtual temperature x and the illuminance retention rate reduction coefficient y. That is, the straight lines m1 and m2 are the relationship between the virtual temperature and the illuminance retention rate reduction coefficient. Hereinafter, it is simply abbreviated as "Relationship α".

[0079] Here, in the excimer lamp (1), the uniformity U[%] of the illuminance retention rate at each measurement location (4, 4,…) is defined by the following equation (5) using the maximum value of the illuminance retention rate Imax and the minimum value of the virtual temperature Imin.

[0080] U[%] = (Imax-Imin) / (Imax+Imin)×100… (5)

[0081] From the results of Figures 5 and 6, it is understood that the higher the virtual temperature of the discharge vessel, the lower the value of the illuminance retention rate. That is, when the illuminance retention rate of the excimer lamp is measured at each location in the discharge vessel, the virtual temperature at the location showing the maximum value of the illuminance retention rate Imax—in other words, the lowest virtual temperature T1—is defined as T1 = xa, where x is the intermediate value (target value) of the virtual temperature and a is the temperature difference between the intermediate value and the location. Conversely, the virtual temperature at the location showing the minimum value of the illuminance retention rate Imin—in other words, the highest virtual temperature T2—is defined as T2 = x + a.

[0082] At the location of the lowest virtual temperature T1, if the coefficient of the above relationship α is k1 and the intercept is k1' and the lighting time is τ[h], the illumination retention rate Imax at the location representing the virtual temperature T1 is defined by the following equation (6).

[0083] Imax = 100+{(xa)×k1+k1'}×logτ... (6)

[0084] Likewise, if the coefficient of the above relationship α at the location of the highest virtual temperature T2 is k2 and the intercept is k2', and the lighting time is τ[h], the illumination retention rate Imin at the location representing the virtual temperature T2 is defined by the following equation (7).

[0085] Imin = 100+{(x+a)×k2+k2'}×logτ... (7)

[0086] By substituting the above equations (6) and (7) into equation (5) to transform the equation into one that calculates the temperature difference a of the virtual temperature for the intermediate value, the following equation (8) is obtained.

[0087]

[0088] In the case of an excimer lamp, it is considered that if the difference in the illuminance maintenance rate at each location of the discharge vessel (10) after 3,000 hours of lighting can be maintained at 15% or less, the problem of use is low. For this reason, τ=3000 and U=15 are substituted into the above equation (8).

[0089] Also, the coefficient k1 and intercept k1' of the relationship α at the position of the lowest virtual temperature T1, and the coefficient k2 and intercept k2' of the relationship α at the position of the highest virtual temperature T2, are all uniquely determined according to the value of the virtual temperature based on the relationship α shown in FIG. 7.

[0090] That is, by sequentially varying the target virtual temperature (intermediate value) x, the allowable temperature difference a is obtained, and as a result, the allowable upper limit and allowable lower limit are calculated by operation. This calculation process is shown in Table 2 below.

[0091] [Table 2]

[0092]

[0093] The relationship between the intermediate value x and the allowable lower limit value (xa) obtained in this way, and the relationship between the intermediate value x and the allowable upper limit value (x+a) are graphed, and the area included within the range of both is hatched, which is the graph of FIG. 4. Accordingly, by manufacturing the excimer lamp (1) such that the intermediate value Ta of the virtual temperature and the virtual temperature Ti of each measurement location exist within the hatched area shown in FIG. 4, the difference in the illuminance retention rate at each location of the discharge vessel (10) after 3000 hours of lighting can be maintained at 15% or less.

[0094] The verification results performed using the examples and comparative examples are described below.

[0095] (Example 1)

[0096] Using fluorine-doped quartz glass, multiple samples of an excimer lamp (1) were prepared under a specific temperature profile with a virtual temperature target value of 983°C, and this was designated as Example 1. For one of the multiple samples prepared, virtual temperatures at five measurement points (X1, X2, ..., X5) were measured as schematically shown in FIG. 3. Specifically, the measurements were taken in the following manner. First, glass fragments were obtained by crushing the parts at the five locations located within the effective light-emitting region (5) of the discharge vessel (10). Then, the infrared absorption spectrum of the obtained glass fragments was measured by the transmission method, and calculations were performed based on the above-described equation (3). Using the values ​​obtained from the calculations, the virtual temperatures Ti (i=1, 2, ..., 5) at the measurement points (X1, X2, ..., X5) corresponding to each fragment were set.

[0097] In Example 1, the relationship of Equation (2) above was established between the virtual temperature T of each measurement location and the intermediate value Ta of the virtual temperature.

[0098] Next, a sample of the excimer lamp (1) of Example 1 that was not destroyed was lit continuously for 3,000 hours. Then, after 3,000 hours of lighting, the illuminance retention rate of each measurement location (X1, X2, ..., X5) was measured.

[0099] FIG. 8 is a schematic diagram illustrating a method for measuring the illuminance retention rate for each measurement location. Specifically, for an excimer lamp (1) after 3,000 hours of lighting, a light meter (41) was installed near each measurement location (X1, X2, ..., X5), and the light was adjusted so that only the ultraviolet light (L1) at the location was received. Then, the illuminance retention rate for each measurement location (X1, X2, ..., X5) was calculated by calculating the ratio of the illuminance measured at each location to the initial illuminance. For the measurement, an ultraviolet integrating light meter (UIT-250) manufactured by Ushio Electric Co., Ltd. and a separate type light receiver (VUV-S172) were used, as described above.

[0100] (Comparative Example 1)

[0101] The target value of the virtual temperature was set to 983°C, the same as in Example 1, and verification was performed in the same manner as in Example 1, except that the temperature profile during manufacturing was changed from Example 1. In Comparative Example 1, the relationship of Equation (2) above did not hold between the virtual temperature T of each measurement location and the intermediate value Ta of the virtual temperature.

[0102] (Example 2)

[0103] Verification was performed in the same manner as in Example 1, except that the target value of the virtual temperature was set to 909℃ and the temperature profile during manufacturing was changed from Example 1. In Example 2 as well, the relationship of equation (2) above was established between the virtual temperature T of each measurement location and the intermediate value Ta of the virtual temperature.

[0104] (Comparative Example 2)

[0105] The target value of the virtual temperature was set to 909°C, the same as in Example 2, and verification was performed in the same manner as in Example 2, except that the temperature profile during manufacturing was changed from Example 2. In Comparative Example 2, the relationship of Equation (2) above did not hold between the virtual temperature T of each measurement location and the intermediate value Ta of the virtual temperature.

[0106] The verification results are shown in Table 3 below and Figures 9a to 12b. In addition, the uniformity in Table 3 below is a value calculated based on the above-described equation (5).

[0107] [Table 3]

[0108]

[0109] According to the above results, in Examples 1 and 2, where the virtual temperature Ti (i=1, 2,…, 5) of each measurement location (X1, X2,…, X5) is suppressed within the allowable range, it can be seen that the uniformity (degree of deviation) of the illuminance retention rate after 3,000 hours of lighting is 6% or less and falls significantly below the allowable range of 15%. In contrast, in Comparative Examples 1 and 2, where some of the virtual temperature Ti (i=1, 2,…, 5) of each measurement location (X1, X2,…, X5) exceeds the allowable range, it can be seen that the uniformity (degree of deviation) of the illuminance retention rate after 3,000 hours of lighting significantly exceeds 15%.

[0110] In addition, in the present invention, the shape of the discharge vessel (10) provided by the excimer lamp (1) is not limited. For example, the discharge vessel (10) may have a double-tube structure in which it has an outer tube and an inner tube disposed inside the outer tube, and the outer tube and the inner tube are sealed at both ends along the tube axis direction. Under this configuration, the excimer lamp (1) forms a discharge space (11) in the space sandwiched between the inner tube and the outer tube, and a luminescent gas is sealed within this discharge space (11). Explanation of the symbols

[0111] 1: Excimer lamp 4: Measurement points 5: Effective light emission area 10: Discharge vessel 11: Discharge space 21, 22: Electrodes 31, 32: Bass 41: Light meter L1: Ultraviolet rays

Claims

Claim 1 An excimer lamp comprising a long discharge vessel containing fluorine-doped quartz glass and having a luminescent gas sealed inside, and a pair of electrodes for applying a discharge voltage inside the discharge vessel, wherein the discharge vessel is characterized in that, within an effective luminescent region, the virtual temperature T [°C] of each measurement location, which is formed by a plurality of intermediate locations obtained by substantially dividing the region between the pair of end locations into a predetermined number of substantially equal parts with respect to the length direction, satisfies the following equations (1) and (2), when the intermediate value of the virtual temperature T [°C] of each measurement location is taken as Ta [°C]. Claim 2 An excimer lamp according to claim 1, characterized in that among the virtual temperatures T at each measurement location, the maximum and minimum values ​​are separated by 10°C or more. Claim 3 An excimer lamp according to claim 1 or claim 2, wherein the discharge vessel is characterized by having a length along the longitudinal direction exceeding 1m.

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