Method for measuring fluorine gas concentration contained in halogen fluoride-containing gas by ultraviolet spectroscopy

Abstract

To provide a highly accurate measurement method for measuring a concentration of fluorine gas contained in a halogen fluoride-containing gas using an ultraviolet spectrophotometer, by reducing measurement errors caused by fluorine gas generated by photolysis of halogen fluoride.SOLUTION: The present invention is a method for measuring a fluorine gas concentration, which comprises: irradiating a halogen fluoride-containing gas with ultraviolet light such that a ratio (WX / WF) of a maximum ultraviolet light intensity (WX) in a wavelength region less than 250 nm to an ultraviolet light intensity (WF) at a wavelength of 285 nm is 1 / 10 or less; measuring an absorbance at a wavelength of 285 nm; and acquiring a fluorine gas concentration contained in the halogen fluoride-containing gas.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for measuring the concentration of fluorine gas contained in a halogen fluoride-containing gas. [Background technology]

[0002] Halogen fluorides are used in etching gases, cleaning gases, etc. in semiconductor manufacturing processes. In recent years, semiconductors have become increasingly finer, and high-purity gases are required for the etching gases, cleaning gases, etc. used in the semiconductor manufacturing process. In order to prepare high-purity gases, a method for accurately measuring the concentration of fluorine gas, which is an impurity contained in etching gases, cleaning gases, etc., is required.

[0003] As a method for measuring fluorine gas concentration, for example, Patent Document 1 discloses a method for measuring the concentration of fluorine gas contained in gas such as exhaust gas discharged from electronic device manufacturing equipment such as semiconductor manufacturing equipment using an ultraviolet spectrophotometer and a Fourier transform infrared spectrophotometer. Patent Document 2 discloses a method for measuring the fluorine concentration in exhaust gas discharged from semiconductor process equipment using an ultraviolet spectrophotometer and a Fourier transform infrared spectrophotometer. Patent Document 3 discloses a method for analyzing halogen gas generated from a semiconductor manufacturing process by ultraviolet-visible absorption spectroscopy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5221881 [Patent Document 2] JP 2010-203855 A [Patent Document 3] U.S. Patent No. 6,686,594 Summary of the Invention [Problem to be solved by the invention]

[0005] When measuring the fluorine gas concentration in a halogen fluoride-containing gas by ultraviolet spectroscopy, a part of the halogen fluoride is photodecomposed to generate fluorine molecules and fluorine radicals because the halogen fluoride mainly absorbs light with a wavelength of less than 250 nm. Therefore, when measuring the fluorine gas concentration in the halogen fluoride, there is a problem that measurement errors occur due to the fluorine and fluorine radicals generated by photolysis.

[0006] Therefore, an object of the present invention is to provide a highly accurate measurement method for measuring the concentration of fluorine gas contained in a halogen fluoride-containing gas using an ultraviolet spectrophotometer, by reducing measurement errors caused by fluorine gas generated by photolysis of halogen fluoride. [Means for solving the problem]

[0007] As a result of intensive research to solve the above problems, the present inventors have found that when measuring the concentration of fluorine gas contained in a halogen fluoride-containing gas by irradiating ultraviolet light, highly accurate measurement can be achieved by suppressing irradiation of ultraviolet light with a wavelength of less than 250 nm, and have completed the present invention. That is, the present invention includes the following [1] to [8].

[0008] [1] Ultraviolet light intensity (W F ) vs. the maximum ultraviolet light intensity in the wavelength range below 250 nm (W X ) ratio (W X / W F A method for measuring fluorine gas concentration by irradiating ultraviolet light at a wavelength of 285 nm so that the absorbance at that wavelength is 1 / 10 or less, and measuring the absorbance at a wavelength of 285 nm to obtain the fluorine gas concentration contained in a halogen fluoride-containing gas. [2] The method for measuring a fluorine gas concentration according to [1], wherein the halogen fluoride-containing gas is irradiated with ultraviolet light having a wavelength of 250 nm or more using a means for suppressing irradiation of ultraviolet light having a wavelength of less than 250 nm from a light source. [3] The method for measuring a fluorine gas concentration according to [1] or [2], wherein the means irradiates the halogen fluoride-containing gas with ultraviolet light from the light source through a filter that blocks 50% or more of ultraviolet light with a wavelength of less than 250 nm and transmits 90% or more of ultraviolet light with a wavelength of 280 to 290 nm. [4] The method for measuring a fluorine gas concentration according to any one of [1] to [3], wherein the halogen fluoride is any one gas selected from the group consisting of chlorine trifluoride, bromine pentafluoride, iodine heptafluoride, bromine trifluoride, and iodine pentafluoride. [5] The method for measuring a fluorine gas concentration according to any one of [1] to [4], wherein the halogen fluoride is iodine heptafluoride. [6] The halogen fluoride is bromine pentafluoride, and the maximum ultraviolet light intensity (W X ) is the maximum value of ultraviolet light intensity in a wavelength region of less than 225 nm. [7] The halogen fluoride is chlorine trifluoride, and the maximum ultraviolet light intensity (W X ) is the maximum value of ultraviolet light intensity in a wavelength region of less than 215 nm. [8] The method for measuring a fluorine gas concentration according to any one of [1] to [7], comprising subtracting an absorption spectrum measured by irradiating a reference gas with the ultraviolet light from an absorption spectrum measured by irradiating the halogen fluoride-containing gas with the ultraviolet light, and obtaining a fluorine gas concentration from an absorbance at a wavelength of 285 nm of the obtained absorption spectrum. Effect of the Invention

[0009] According to the present invention, the concentration of fluorine gas contained in a halogen fluoride-containing gas can be measured with high accuracy. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a schematic diagram of an example of an analytical device used in measuring the concentration of fluorine gas in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below, if necessary, with reference to Fig. 1. The analysis device used in the present invention is not limited to the analysis device shown in Fig. 1. The present invention provides a method for treating a halogen fluoride-containing gas by applying ultraviolet light having a wavelength of 285 nm (W F ) vs. the maximum ultraviolet light intensity in the wavelength range below 250 nm (W X ) ratio (W X / W F This relates to a method for measuring a fluorine gas concentration, which comprises irradiating a gas containing halogen fluoride with ultraviolet light such that the absorbance at a wavelength of 285 nm is 1 / 10 or less, and measuring the absorbance at a wavelength of 285 nm to obtain the fluorine gas concentration contained in the gas containing halogen fluoride.

[0012] <Measurement gases and equipment used to measure fluorine gas concentration> (Halogen fluoride-containing gas) The halogen fluoride contained in the halogen fluoride-containing gas used in one embodiment of the present invention is a fluorine compound containing halogen such as chlorine, bromine and iodine as a constituent element. Examples of halogen fluorides include chlorine fluoride, chlorine trifluoride, bromine fluoride, bromine trifluoride, bromine pentafluoride, iodine fluoride, iodine trifluoride, iodine pentafluoride, and iodine heptafluoride. Among these, from the viewpoint of etching performance and cleaning performance, chlorine trifluoride, bromine trifluoride, bromine pentafluoride, iodine pentafluoride, and iodine heptafluoride are preferred, and chlorine trifluoride, iodine heptafluoride, and bromine pentafluoride are more preferred and can be applied to the present invention. The halogen fluoride-containing gas may contain one kind of halogen fluoride alone or multiple kinds.

[0013] The halogen fluoride-containing gas may contain the fluorine gas to be measured and impurity gas other than fluorine gas. The impurity gas may include, for example, helium, argon, oxygen gas (O2), nitrogen gas (N2), carbon dioxide and carbon tetrafluoride. The halogen fluoride-containing gas may contain one or more impurity gases, and the content is not particularly limited.

[0014] In addition, the halogen fluoride-containing gas may contain a diluent gas. The diluent gas is a gas that is inert to the halogen fluoride, the fluorine-containing gas and the impurity gas. Examples of the diluent gas include helium, argon, nitrogen gas (N2), carbon dioxide and carbon tetrafluoride. The halogen fluoride-containing gas may contain one or more diluent gases, and the content is not particularly limited.

[0015] The halogen fluoride-containing gas is introduced from the halogen fluoride-containing gas supply source 10 through the valve 14 into the gas cell 22 described later. The halogen fluoride-containing gas supply source 10 is not particularly limited in terms of the supply method, shape, size, etc., as long as it can supply the halogen fluoride-containing gas to the gas cell 22. For example, the halogen fluoride-containing gas may be supplied to the gas cell 22 through the valve 14 from a branch pipe branched from a supply pipe of the halogen fluoride-containing gas connected to an etching device in a semiconductor manufacturing process, or may be supplied to the gas cell 22 from a container such as a gas cylinder in which the same halogen fluoride-containing gas as the gas supplied to the etching device is stored.

[0016] (Reference gas) When the halogen fluoride-containing gas is irradiated with ultraviolet light by a method described later to measure the absorption spectrum, it is preferable to use a reference gas as a blank and measure the absorption spectrum of the reference gas in a gas cell 22 described later. The reference gas is not particularly limited as long as it does not contain a component that absorbs wavelengths around 285 nm. Examples of the reference gas include nitrogen gas (N2) and helium gas.

[0017] The reference gas is introduced from the reference gas supply source 12 to the gas cell 22 via the valve 16. The reference gas supply source 12 is not particularly limited in terms of the supply method, shape, size, etc., as long as it can supply the reference gas to the gas cell 22. For example, the reference gas may be supplied to the gas cell 22 from a container such as a gas cylinder in which the reference gas is stored.

[0018] (Light source 18) The light source 18 used in one embodiment of the present invention is used to irradiate the halogen fluoride-containing gas and the reference gas with ultraviolet light. The light source 18 is not particularly limited as long as it emits ultraviolet light including a wavelength of 285 nm, and for example, a deuterium lamp, a xenon lamp, a mercury lamp (low pressure, high pressure), a metal halide lamp, a fluorescent lamp, a black light (blue lamp), etc. can be used, and a light beam with a small amount of light components with a wavelength of less than 250 nm can also be used.

[0019] (Filter 20) In one embodiment of the present invention, when using a means for suppressing irradiation of ultraviolet light with a wavelength of less than 250 nm, it is preferable to irradiate the ultraviolet light irradiated from the light source 18 to the halogen fluoride through the filter 20, since this can efficiently suppress the photodecomposition of the halogen fluoride. The filter 20 is not particularly limited as long as it can sufficiently block ultraviolet light with a wavelength of less than 250 nm, but it is preferable to use one that can block 50% or more, more preferably 60% or more, and even more preferably 70% or more. By irradiating ultraviolet light through the filter 20, it is possible to suppress the decrease in measurement accuracy caused by fluorine gas, etc., generated by the photodecomposition of halogen fluoride having a maximum absorption wavelength in the wavelength region of less than 250 nm.

[0020] For the filter 20, it is preferable to use a filter that sufficiently transmits ultraviolet light including the wavelength of 285 nm, which is the maximum absorption wavelength of fluorine, in order to enable highly accurate measurement, and it is preferable that the filter transmits preferably 90% or more, more preferably 95% or more, of ultraviolet light having a wavelength of 280 to 290 nm. The filter 20 is not particularly limited as long as it has the above-mentioned performance, and for example, a commercially available filter such as a short wavelength cut filter manufactured by Asahi Spectroscopic Co., Ltd. can be used.

[0021] (Gas Cell 22) The gas cell 22 is used to irradiate ultraviolet light by sealing or passing the halogen fluoride-containing gas and the reference gas. The gas cell 22 is provided with a gas inlet, a gas exhaust port connected to the exhaust port 26, an entrance window, an exit window, etc., in the gas cell body. The material of the gas cell 22 body other than the entrance window and the exit window is not particularly limited as long as it shows corrosion resistance against the components contained in the halogen fluoride-containing gas and fluorine gas, and for example, stainless steel, nickel, Inconel, and Monel can be used.

[0022] Furthermore, the material for the entrance window and exit window is not particularly limited as long as it does not absorb light with a wavelength around 285 nm and exhibits corrosion resistance against halogen fluoride-containing gases and fluorine-containing gases. For example, calcium fluoride and barium fluoride can be used.

[0023] (Spectrometer 24) The spectroscope 24 measures the absorption spectrum of the wavelength of the ultraviolet light emitted from the exit window of the gas cell 22. The spectroscope 24 is not particularly limited as long as it can measure the absorption spectrum of ultraviolet light, and for example, an ultraviolet spectrophotometer that is commonly used in the field of the present invention can be used.

[0024] (others) In order to efficiently capture the light from the light source 18 into the gas cell 22 , a lens or the like may be provided between the emission end of the light source 18 and the entrance window of the gas cell 22 .

[0025] <Method of measuring fluorine gas concentration> The method for measuring a fluorine gas concentration according to the present invention using the above-mentioned measurement gas and instruments will now be described. (1) Measurement of reference gas In order to measure the fluorine gas concentration contained in the halogen fluoride-containing gas of the present invention, it is preferable to measure the absorption spectrum of the reference gas in advance. In order to measure the absorption spectrum of the reference gas, the valve 14 is closed to prevent the halogen fluoride-containing gas from being supplied from the halogen fluoride-containing gas supply source 10, and the valve 16 is opened to introduce the reference gas from the reference gas supply source 12 into the gas cell 22. When introducing the reference gas, the exhaust port 26 may be left open so that the reference gas flows through the gas cell 22, or the exhaust port 26 may be closed so that the reference gas is sealed in the gas cell 22.

[0026] The reference gas in the gas cell 22 is irradiated with ultraviolet light emitted from the light source 18 from an entrance window of the gas cell 22, preferably via a filter 20. At this time, the ultraviolet light from the light source 18 may be irradiated to the entrance window of the gas cell 22 via an optical fiber. In addition, since short-wavelength ultraviolet light may generate ozone from oxygen in the air and affect the measurement, it is preferable to flow a purge gas such as nitrogen near the entrance window or to make the structure airtight so that oxygen, air, etc. do not enter through the entrance window and exit window.

[0027] The ultraviolet light intensity (W F ) vs. the maximum ultraviolet light intensity in the wavelength range below 250 nm (W X ) ratio (W X / W F ) (hereinafter also referred to as "ultraviolet light intensity ratio") must be 1 / 10 or less. This makes it possible to suppress the deterioration of measurement accuracy due to the fluorine gas that is generated as a result of photolysis of halogen fluorides by irradiation with ultraviolet light having a wavelength of less than 250 nm. X / W FIt is more preferable that W is 1 / 15 or less. The maximum value of the ultraviolet light intensity in the wavelength region of less than 250 nm is, in other words, the intensity of the ultraviolet light having the highest intensity among the ultraviolet light having wavelengths of less than 250 nm. F and W X can be measured by the spectrometer 24. The ultraviolet light intensity ratio can be adjusted by the light source 18 and the filter 20.

[0028] The ultraviolet light intensity ratio may be appropriately set according to the absorption wavelength of the halogen fluoride within the above range. For example, the maximum absorption wavelength of bromine pentafluoride is 217 nm, and the ultraviolet light intensity in the wavelength region shorter than this maximum absorption wavelength plus 7 to 9 nm, for example, the maximum value of the ultraviolet light intensity in the wavelength region less than 225 nm, may be set as W X This may be used to calculate the ultraviolet light intensity ratio.

[0029] Similarly, the maximum absorption wavelength of chlorine trifluoride is 207 nm, so for example, the maximum value of the ultraviolet light intensity in the wavelength region below 215 nm is W X The maximum absorption wavelength of iodine heptafluoride is 241 nm, so for example, the maximum value of the ultraviolet light intensity in the wavelength region less than 250 nm can be calculated as W X This may be used to calculate the ultraviolet light intensity ratio.

[0030] The ultraviolet light emitted from the exit window of the gas cell 22 is measured by a spectroscope. The ultraviolet light emitted from the exit window may be introduced into the spectroscope via an optical fiber. When using the spectroscope, for example, the absorption spectrum of the reference gas is measured by operating it according to the manual that comes with the product. For example, high-purity nitrogen gas is used as the reference gas, and the reference gas is irradiated with ultraviolet light using a filter so that the ultraviolet light intensity ratio falls within the range described above. Since there is no absorption by nitrogen or halogen fluorides in the wavelength region of less than 250 nm, the absorption spectrum can be blanked.

[0031] (2) Measurement of the absorbance of halogen fluoride-containing gases at a wavelength of 285 nm The valve 16 is closed, the valve 14 is opened, and the halogen fluoride-containing gas is introduced from the halogen fluoride-containing gas supply source 10 into the gas cell 22, and the absorption spectrum of the halogen fluoride-containing gas is measured in the same manner as the reference gas. At this time, the halogen fluoride-containing gas diluted with a diluent gas such as helium, argon, nitrogen, carbon dioxide, or carbon tetrafluoride may be introduced into the gas cell 22. From the absorption spectrum, the absorbance at a wavelength of 285 nm, which is the maximum absorption wavelength of fluorine, is measured, and the fluorine gas concentration is obtained by absorptiometry.

[0032] In addition, it is preferable to subtract the absorption spectrum of the reference gas from the absorption spectrum of the halogen fluoride-containing gas, measure the absorbance at a wavelength of 285 nm from the obtained absorption spectrum, and obtain the fluorine gas concentration by absorptiometry, in terms of enabling highly accurate measurement.

[0033] (3) Measurement conditions The temperature in the gas cell 22 during the above measurement is not particularly limited as long as it is equal to or higher than the temperature at which the halogen fluoride-containing gas and the reference gas are liquefied and solidified, but is preferably 20 to 150° C., and more preferably 50 to 120° C. If the temperature is higher than this range, the reaction of the halogen fluoride with the gas cell, the entrance window, and the exit window may proceed, or the decomposition of the halogen fluoride may proceed, which is not preferable.

[0034] In addition, the pressure in the gas cell 22 when the halogen fluoride-containing gas and the reference gas are sealed in the gas cell 22 and measurements are performed is not particularly limited, but is preferably 0.01 to 0.2 MPaA, and more preferably 0.05 to 0.15 MPaA. If the pressure is lower than this range, the gas concentration may decrease and the sensitivity may decrease, and if the pressure is higher than this range, the device may be damaged. EXAMPLES

[0035] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0036] [Example 1] Bromine pentafluoride gas was used as the halogen fluoride-containing gas, and the fluorine gas concentration contained in the bromine pentafluoride gas was measured according to the measurement method of the present invention using the analyzer shown in Figure 1. The gas cell 22 used had a body made of SUS316 and entrance and exit windows made of calcium fluoride.

[0037] First, nitrogen gas was used as the reference gas, and nitrogen gas was introduced into the gas cell 22 from a high-purity nitrogen gas cylinder, which is the reference gas supply source 12. The maximum value of the ultraviolet light intensity in the wavelength region of less than 225 nm was measured by measuring the wavelength of the reference gas from a deuterium lamp (product name: L10290, manufactured by Hamamatsu Photonics K.K.) as the light source 18 through a short-wavelength cut filter (product name: LU0250, manufactured by Asahi Spectroscopy Co., Ltd.) as the filter 20. X And W X / W F = 1 / 20 ultraviolet light was irradiated onto the nitrogen gas in the gas cell 22. The absorption spectrum of the ultraviolet light emitted from the gas cell 22 was measured using a multichannel spectrometer (product name: FLAME-S, manufactured by Ocean Optics) as the spectrometer 24. The temperature in the gas cell was 50°C, and the pressure was 0.1 MPaA.

[0038] Next, the nitrogen gas in the gas cell 22 is exhausted from the exhaust port 26, and then bromine pentafluoride gas is introduced from the halogen fluoride-containing gas supply source 10 into the gas cell 22. W is then introduced from the light source through the filter under the same temperature and pressure conditions as those for the reference gas measurement. X / W F The bromine pentafluoride gas in the gas cell 22 was irradiated with ultraviolet light having a wavelength of 1 / 20 of the wavelength of the bromine pentafluoride gas. The absorption spectrum of the ultraviolet light emitted from the gas cell 22 was measured by the above-mentioned spectrometer. The absorption spectrum of the nitrogen gas was subtracted from the absorption spectrum of the bromine pentafluoride gas obtained to determine the fluorine gas concentration contained in the bromine pentafluoride gas. As a result, the fluorine concentration was 2 ppm by volume.

[0039] [Example 2] Using iodine heptafluoride gas instead of bromine pentafluoride gas as the halogen fluoride-containing gas, the maximum ultraviolet light intensity in the wavelength range below 250 nm is set to W X And W X / W F Except for irradiating the iodine heptafluoride gas with ultraviolet light of 1 / 18, the fluorine gas concentration in the iodine heptafluoride gas was determined in the same manner as in Example 1. As a result, the fluorine concentration was 3 ppm by volume.

[0040] [Example 3] Chlorine trifluoride gas was used instead of bromine pentafluoride gas as the halogen fluoride-containing gas, and the maximum ultraviolet light intensity in the wavelength range below 215 nm was set to W X Except for the above, the fluorine gas concentration in the chlorine trifluoride gas was determined in the same manner as in Example 1. As a result, the fluorine concentration was 5 ppm by volume.

[0041] [Comparative Example 1] Without using a filter, X / W F The fluorine gas concentration in the bromine pentafluoride gas was determined in the same manner as in Example 1, except that the ultraviolet light used was irradiated at 1 / 5 of the wavelength of the ultraviolet light used in Example 1. As a result, the fluorine concentration was 20 ppm by volume, and it was confirmed that the decomposition reaction of bromine pentafluoride had progressed.

[0042] [Comparative Example 2] Without using a filter, X / W F The fluorine gas concentration in the iodine heptafluoride gas was determined in the same manner as in Example 2, except that the ultraviolet light was irradiated at 1 / 5 of the wavelength of the ultraviolet light. As a result, the fluorine concentration was 24 ppm by volume, and it was confirmed that the decomposition reaction of iodine heptafluoride had progressed.

[0043] [Comparative Example 3] Without using a filter, X / W F The fluorine gas concentration contained in the chlorine trifluoride gas was determined in the same manner as in Example 3, except that the ultraviolet light of 1 / 5 was irradiated. As a result, the fluorine concentration was 18 ppm by volume, and it was confirmed that the decomposition reaction of chlorine trifluoride had progressed.

[0044] The conditions and results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

[0045] [Table 1] [Explanation of symbols]

[0046] 10. Halogen fluoride-containing gas supply source 12. Reference gas supply source 14. Valve 16. Valve 18...Light source 20 Filter 22 Gas cell 24...Spectrometer 26...Exhaust port

Claims

1. For halogen fluoride-containing gas, ultraviolet light intensity (W F ) vs. the maximum ultraviolet light intensity in the wavelength region less than 250 nm (W X ) ratio (W X / W F ) is 1 / 10 or less, and the absorbance at a wavelength of 285 nm is measured to obtain the fluorine gas concentration contained in the halogen fluoride-containing gas.

2. 2. The method for measuring a fluorine gas concentration according to claim 1, wherein the halogen fluoride-containing gas is irradiated with ultraviolet light having a wavelength of 250 nm or more using a means for suppressing irradiation of ultraviolet light having a wavelength of less than 250 nm from a light source.

3. 3. The method for measuring a fluorine gas concentration according to claim 1 or 2, wherein the means irradiates the halogen fluoride-containing gas with ultraviolet light from the light source through a filter that blocks 50% or more of ultraviolet light with a wavelength of less than 250 nm and transmits 90% or more of ultraviolet light with a wavelength of 280 to 290 nm.

4. The method for measuring a fluorine gas concentration according to any one of claims 1 to 3, wherein the halogen fluoride is any one gas selected from the group consisting of chlorine trifluoride, bromine pentafluoride, iodine heptafluoride, bromine trifluoride, and iodine pentafluoride.

5. 5. The method for measuring a fluorine gas concentration according to claim 1, wherein the halogen fluoride is iodine heptafluoride.

6. The halogen fluoride is bromine pentafluoride, and the maximum value of the ultraviolet light intensity in the wavelength region less than 250 nm (W X 5. The method for measuring a fluorine gas concentration according to claim 1, wherein the maximum ultraviolet light intensity is in a wavelength region of less than 225 nm.

7. The halogen fluoride is chlorine trifluoride, and the maximum value of the ultraviolet light intensity in the wavelength region less than 250 nm (W X 5. The method for measuring a fluorine gas concentration according to claim 1, wherein the maximum ultraviolet light intensity is in a wavelength region of less than 215 nm.

8. The method for measuring a fluorine gas concentration according to any one of claims 1 to 7, comprising subtracting an absorption spectrum measured by irradiating a reference gas with the ultraviolet light from an absorption spectrum measured by irradiating the halogen fluoride-containing gas with the ultraviolet light, and obtaining a fluorine gas concentration from an absorbance at a wavelength of 285 nm of the obtained absorption spectrum.

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