Storage method for fluoro-2-butene

Abstract

This invention provides a method for storing fluoro-2-butene that minimizes the progression of isomerization reactions during storage. [Solution] General formula C4H x F y Fluoro-2-butene, represented by the general formula where x is between 0 and 7, y is between 1 and 8, and x+y is 8, may or may not contain at least one of chromium, molybdenum, iron, zinc, and aluminum as a metal impurity. This fluoro-2-butene is stored in a container with the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum (in the case where it contains these impurities) being 1000 ppb by mass or less.

Description

[Technical Field]

[0001] The present invention relates to a method for storing fluoro-2-butene. [Background Art]

[0002] Unsaturated fluorocarbons disclosed in Patent Documents 1, 2, etc. may be used as etching gases for dry etching. Among unsaturated fluorocarbons, fluoro-2-butene has attracted attention as an etching gas that can be used in the most advanced dry etching processes. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 6451810 [Patent Document 2] Japanese Patent Laid-Open Publication No. 2019-034972 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] However, fluoro-2-butene has geometric isomers of the Z-form and the E-form, and there was a risk that the isomerization reaction would proceed during long-term storage. An object of the present invention is to provide a method for storing fluoro-2-butene in which the isomerization reaction hardly proceeds during storage. [Means for Solving the Problems]

[0005] In order to solve the above problems, one aspect of the present invention is as follows [1] to [3]. [1] A method for storing fluoro-2-butene represented by the general formula C4H x F y where x in the general formula is 0 or more and 7 or less, y is 1 or more and 8 or less, and x + y is 8, A method for storing fluoro-2-butene, wherein the fluoro-2-butene contains or does not contain at least one of chromium, molybdenum, iron, zinc, and aluminum as a metal impurity, and in the case where it contains such impurities, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum is 1000 ppb by mass or less, and the fluoro-2-butene is stored in a container.

[0006] [2] A method for storing fluoro-2-butene according to [1], wherein the fluoro-2-butene is at least one selected from (Z)-1,1,1,4,4,4-hexafluoro-2-butene, (E)-1,1,1,4,4,4-hexafluoro-2-butene, (Z)-1,1,1,2,4,4,4-heptafluoro-2-butene, (E)-1,1,1,2,4,4,4-heptafluoro-2-butene, (Z)-1,1,1,2,3,4,4,4-octafluoro-2-butene, and (E)-1,1,1,2,3,4,4,4-octafluoro-2-butene. [3] The method for storing fluoro-2-butene as described in [1] or [2], which involves storing it at a temperature between -20°C and 50°C. [Effects of the Invention]

[0007] According to the present invention, the isomerization reaction of fluoro-2-butene is less likely to proceed during storage. [Modes for carrying out the invention]

[0008] One embodiment of the present invention is described below. This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention.

[0009] The storage method for fluoro-2-butene according to this embodiment is based on the general formula C4H x F yA method for storing fluoro-2-butene, which is represented by the general formula where x is between 0 and 7, y is between 1 and 8, and x+y is 8, wherein the fluoro-2-butene may or may not contain at least one of chromium (Cr), molybdenum (Mo), iron (Fe), zinc (Zn), and aluminum (Al) as a metal impurity, and in the case where it contains such impurities, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum is 1000 ppb by mass or less, and the fluoro-2-butene is stored in a container.

[0010] If fluoro-2-butene contains at least one of the following metal impurities: chromium, molybdenum, iron, zinc, and aluminum, the catalytic action of the metal impurity accelerates the isomerization reaction of fluoro-2-butene. Therefore, fluoro-2-butene containing metal impurities may undergo isomerization during storage, potentially leading to a decrease in purity.

[0011] Fluoro-2-butene stored by the storage method according to this embodiment contains no metal impurities or only small amounts of them. Therefore, isomerization reactions are less likely to occur even during long-term storage, and a decrease in purity is less likely to occur. Thus, fluoro-2-butene can be stored stably for a long period of time.

[0012] The techniques disclosed in Patent Documents 1 and 2 do not take into account the concentration of metal impurities in unsaturated fluorocarbons. Therefore, when fluoro-2-butene was stored using the techniques disclosed in Patent Documents 1 and 2, the isomerization reaction of fluoro-2-butene was sometimes accelerated by the metal impurities. As a result, the isomerization reaction of fluoro-2-butene progressed during storage, and its purity sometimes decreased.

[0013] The storage method for fluoro-2-butene according to this embodiment will be described in more detail below. [Fluoro-2-butene] The fluoro-2-butene according to this embodiment has the general formula C4H x F yIt is represented by the formula and satisfies the following three conditions: x is between 0 and 7 in the general formula, y is between 1 and 8, and x+y is 8. The type of fluoro-2-butene is not particularly limited as long as it satisfies the above requirements.

[0014] Specific examples of fluoro-2-butene include (Z)-CHF2-CF=CF-CF3, (E)-CHF2-CF=CF-CF3, (Z)-CF3-CH=CF-CF3, (E)-CF3-CH=CF-CF3, (Z)-CH2F-CF=CF-CF3, (E)-CH2F-CF=CF-CF3, (Z)-CHF2-CH=CF-CF3, (E)-CHF2-CH=CF-CF3, (Z)-CHF2-CF=CF-CHF2, (E)-CHF2-CF=CF-CHF2, (Z)-CF3-CH=CH-CF3, (E)-CF3-CH=CH-CF3, (Z)-CH3-CF=CF-CF3, (E)-CH3-CF=CF-CF3, (Z)-CH2F-CH=CF-CF3, (E)-CH2F-CH=CF-CF3, (Z)-CH2F-CF=CH-CF3, (E)-CH2F-CF=CH-CF3, (Z)-CH2F-CF=CF-CHF2, (E)-CH2F-CF=CF-CHF2, (Z)-CHF2-CH=CH-CF3, (E)-CHF2-CH=CH-CF3, (Z)-CHF2-CF=CH-CHF2, (E)-CHF2-CF=CH-CHF2, (Z)-CH3-CH=CF-CF3, (E)-CH3-CH=CF-CF3, (Z)-CH3-CF=CH-CF3, (E)-CH3-CF=CH-CF3, (Z)-CH3-CF=CF-CHF2, (E)-CH3-CF=CF-CHF2, (Z)-CH2F-CH=CH-CF3, (E)-CH2F-CH=CH-CF3, (Z)-CH2F-CH=CF-CHF2, (E)-CH2F-CH=CF-CHF2, (Z)-CH2F-CF=CH-CHF2, (E)-CH2F-CF=CH-CHF2, (Z)-CH2F-CF=CF-CH2F, (E)-CH2F-CF=CF-CH2F, (Z)-CHF2-CH=CH-CHF2, (E)-CHF2-CH=CH-CHF2, (Z)-CH3-CH=CH-CF3, (E)-CH3-CH=CH-CF3, (Z)-CH3-CH=CF-CHF2, (E)-CH3-CH=CF-CHF2, (Z)-CH3-CF=CH-CHF2, (E)-CH3-CF=CH-CHF2, (Z)-CH3-CF=CF-CH2F, (E)-CH3-CF=CF-CH2F, (Z)-CH2F-CF=CH-CH2F, (E)-CH2F-CF=CH-CH2F, (Z)-CH2F-CH=CH-CHF2,(E)-CH2F-CH=CH-CHF2, (Z)-CH3-CH=CH-CHF2, (E)-CH3-CH=CH-CHF2, (Z)-CH3-CH=CF-CH2F, (E)-CH3-CH=CF-CH2F, (Z)-CH3-CF=CH-CH2F, (E)-CH3-CF=CH-CH2F, (Z)-CH3-CF= Examples include CF-CH3, (E)-CH3-CF=CF-CH3, (Z)-CH2F-CH=CH-CH2F, (E)-CH2F-CH=CH-CH2F, (Z)-CH3-CH=CH-CH2F, (E)-CH3-CH=CH-CH2F, (Z)-CH3-CH=CF-CH3, and (E)-CH3-CH=CF-CH3. ,

[0015] These fluoro-2-butenes may be used individually or in combination of two or more. Furthermore, as described above, E / Z geometric isomers exist for the above-mentioned fluoro-2-butenes, and any of these geometric isomers of fluoro-2-butene can be used in the storage method for fluoro-2-butene according to this embodiment.

[0016] When storing fluoro-2-butene in a container, either a gas consisting solely of fluoro-2-butene may be stored in the container, or a mixed gas containing fluoro-2-butene and a diluent gas may be stored in the container. As the diluent gas, at least one selected from nitrogen gas (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used. The content of the diluent gas is preferably 90% by volume or less, and more preferably 50% by volume or less, relative to the total amount of gas stored in the container.

[0017] 〔container〕 The container for storing fluoro-2-butene is not particularly limited in shape, size, or material, as long as it can contain and seal the fluoro-2-butene. The container material can be metal, ceramic, resin, etc. Examples of metals include manganese steel, stainless steel, Hastelloy®, and Inconel®.

[0018] [Metal Impurities] The fluoro-2-butene according to this embodiment may or may not contain at least one of chromium, molybdenum, iron, zinc, and aluminum as metal impurities. However, when it contains them, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum is 1000 mass ppb or less, and it is stored in a container. Therefore, as described above, the isomerization reaction of fluoro-2-butene is less likely to be promoted. As a result, the isomerization reaction of fluoro-2-butene is less likely to proceed during storage. Here, "not containing" means a case where it cannot be quantified by an inductively coupled plasma mass spectrometer (ICP-MS).

[0019] In order to make the isomerization reaction of fluoro-2-butene less likely to proceed during storage, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum contained in fluoro-2-butene needs to be 1000 mass ppb or less, preferably 500 mass ppb or less, and more preferably 100 mass ppb or less.

[0020] In order to further suppress the progress of the isomerization reaction of fluoro-2-butene during storage, the concentrations of chromium, molybdenum, iron, zinc, and aluminum contained in fluoro-2-butene are preferably 300 mass ppb or less, and more preferably 100 mass ppb or less, respectively. However, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum contained in fluoro-2-butene is as described above.

[0021] Note that the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum contained in fluoro-2-butene may be 1 mass ppb or more. The concentrations of metal impurities such as chromium, molybdenum, iron, zinc, and aluminum in fluoro-2-butene can be quantified by an inductively coupled plasma mass spectrometer (ICP-MS).

[0022] The metal impurities mentioned above may be present in fluoro-2-butene as elemental metals, metal compounds, metal halides, or metal complexes. Of these, metal halides are known to further promote isomerization reactions. Trace amounts of hydrogen halide contained in fluoro-2-butene may react with metals in the container where fluoro-2-butene is stored, potentially generating metal halides.

[0023] Metallic impurities in fluoro-2-butene can take the form of fine particles, droplets, or gases. Chromium, molybdenum, iron, zinc, and aluminum are thought to be introduced into fluoro-2-butene from the raw materials, reactors, and purification equipment used in its synthesis.

[0024] [Method for producing fluoro-2-butene with low concentrations of metal impurities] The method for producing fluoro-2-butene with a low concentration of metal impurities is not particularly limited, but one example is a method for removing metal impurities from fluoro-2-butene with a high concentration of metal impurities. The method for removing metal impurities from fluoro-2-butene is not particularly limited, and known methods can be employed. Examples include methods using filters, methods using adsorbents, and distillation.

[0025] The material of the filter that selectively passes fluoro-2-butene gas is preferably resin, and particularly preferably polytetrafluoroethylene, in order to avoid contamination of fluoro-2-butene with metal components. The average pore size of the filter is preferably 0.01 μm to 30 μm, and more preferably 0.1 μm to 10 μm. If the average pore size is within the above range, it is possible to sufficiently remove metal impurities and ensure a sufficient flow rate of fluoro-2-butene gas to achieve high productivity.

[0026] The flow rate of fluoro-2-butene gas passing through the filter is preferably 100 mL / min or more and 5000 mL / min or less, and more preferably 300 mL / min or more and 1000 mL / min or less. Alternatively, the linear velocity of fluoro-2-butene gas passing through the filter is preferably 3 m / hr or more and 150 m / hr or less, and more preferably 9 m / hr or more and 30 m / hr or less. If the flow rate or linear velocity of fluoro-2-butene gas is within the above range, the pressure of the fluoro-2-butene gas is suppressed, the risk of leakage of fluoro-2-butene gas is reduced, and high productivity can be achieved.

[0027] [Storage pressure conditions] The storage pressure conditions in the fluoro-2-butene storage method according to this embodiment are not particularly limited as long as the fluoro-2-butene can be stored in a sealed container, but it is preferable to set the pressure to 0.05 MPa or more and 5 MPa or less, and more preferably to 0.1 MPa or more and 3 MPa or less. If the pressure conditions are within the above range, the fluoro-2-butene can be circulated without heating when the container is connected to the dry etching apparatus.

[0028] [Storage temperature conditions] The storage temperature conditions for fluoro-2-butene in the storage method according to this embodiment are not particularly limited, but it is preferably -20°C to 50°C, and more preferably 0°C to 40°C. If the storage temperature is -20°C or higher, deformation of the container is less likely to occur, so the airtightness of the container is lost and the possibility of oxygen, water, etc. entering the container is low. If oxygen, water, etc. enter, the polymerization and decomposition reactions of fluoro-2-butene may be accelerated. On the other hand, if the storage temperature is 50°C or lower, the polymerization and decomposition reactions of fluoro-2-butene are suppressed.

[0029] 〔etching〕 The fluoro-2-butene according to this embodiment can be used as an etching gas. When an etching gas containing the fluoro-2-butene according to this embodiment is used in the etching process when manufacturing a semiconductor having a silicon (Si) film, a protective film is formed on the mask and sidewalls, thereby improving the selectivity of the etching process. Furthermore, the etching gas containing fluoro-2-butene according to this embodiment can be used in both plasma etching using plasma and plasmaless etching without plasma.

[0030] Examples of plasma etching include reactive ion etching (RIE), inductively coupled plasma (ICP) etching, capacitively coupled plasma (CCP) etching, electron cyclotron resonance (ECR) plasma etching, and microwave plasma etching. Furthermore, in plasma etching, the plasma may be generated within the chamber where the workpiece to be etched is placed, or the plasma generation chamber and the chamber in which the workpiece to be etched is placed may be separated (i.e., remote plasma may be used). [Examples]

[0031] The present invention will be further described below with reference to examples and comparative examples. Fluoro-2-butene containing metal impurities at various concentrations was prepared. An example of the preparation of fluoro-2-butene is described below. (Preparation Example 1) One 10L manganese steel cylinder and four 1L manganese steel cylinders were prepared. These cylinders were referred to as Cylinder A, Cylinder B, Cylinder C, and Cylinder D, respectively. 5000g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene (boiling point: 33°C) was filled into the cylinder and liquefied by cooling to 10°C, forming a liquid phase and a gas phase at approximately 100kPa. Cylinders A, B, C, and D were then cooled to -78°C after the internal pressure was reduced to below 1kPa using a vacuum pump.

[0032] 500 g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of the cylinder where the gas phase is located, passed through a filter, and then collected in cylinder A under reduced pressure. This filter is a PTFE filter manufactured by Fluorocarbon Industries Co., Ltd., with an outer diameter of 50 mm, a thickness of 80 μm, and an average pore size of 0.3 μm. The gas flow rate through the filter was controlled to 500 mL / min by a mass flow controller. The amount of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas collected in cylinder A was 491 g.

[0033] (Z)-1,1,1,4,4,4-hexafluoro-2-butene collected in cylinder A is designated as sample 1-1. The gas of (Z)-1,1,1,4,4,4-hexafluoro-2-butene collected in cylinder A was extracted from the upper outlet, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1. The conditions for inductively coupled plasma mass spectrometry were as follows. Inductively coupled plasma mass spectrometer: Manufactured by Agilent Technologies, Inc. Agilent 7900 ICP-MS Plasma induction coil power: 1600W Sampling depth: 8mm Carrier gas flow rate: 0.7 L / min First ion lens applied voltage: +5.5V Second ion lens applied voltage: -100V Sample solution: 20% by volume nitric acid

[0034] [Table 1]

[0035] Next, cylinder A was heated to approximately 10°C to form a liquid phase and a gas phase. 100g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder A where the gas phase was present and transferred to cylinder B under reduced pressure. Furthermore, 10g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the cylinder and transferred to cylinder B under reduced pressure. Cylinder B was then heated to room temperature and allowed to stand for 24 hours. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene after standing was designated as sample 1-2. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder B where the gas phase was present after standing, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0036] Similarly, 100g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder A, where the gas phase was present, and transferred to cylinder C under reduced pressure. Furthermore, 100g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the cylinder and transferred to cylinder C under reduced pressure. Then, cylinder C was heated to room temperature and left to stand for 24 hours. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene after standing was designated as sample 1-3. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder C, where the gas phase was present, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0037] Similarly, 100g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder A, where the gas phase was present, and transferred to cylinder D under reduced pressure. Furthermore, 200g of (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the cylinder and transferred to cylinder D under reduced pressure. Then, cylinder D was heated to room temperature and left to stand for 24 hours. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene after standing was designated as sample 1-4. The (Z)-1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder D, where the gas phase was present, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0038] (Preparation Example 2) Samples 2-1 to 2-4 were prepared using the same procedure as in Preparation Example 1, except that (E)-1,1,1,4,4,4-hexafluoro-2-butene was used as the fluoro-2-butene. The concentrations of various metal impurities in each sample were then measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 2.

[0039] [Table 2]

[0040] (Preparation Example 3) Samples 3-1 to 3-4 were prepared using the same procedure as in Preparation Example 1, except that (Z)-1,1,1,2,4,4,4-heptafluoro-2-butene was used as the fluoro-2-butene. The concentrations of various metal impurities in each sample were then measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 3.

[0041] [Table 3]

[0042] (Preparation Example 4) Samples 4-1 to 4-4 were prepared using the same procedure as in Preparation Example 1, except that (E)-1,1,1,2,4,4,4-heptafluoro-2-butene was used as the fluoro-2-butene. The concentrations of various metal impurities in each sample were then measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 4.

[0043] [Table 4]

[0044] (Preparation Example 5) Samples 5-1 to 5-4 were prepared using the same procedure as in Preparation Example 1, except that (Z)-1,1,1,2,3,4,4,4-octafluoro-2-butene was used as the fluoro-2-butene. The concentrations of various metal impurities in each sample were then measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 5.

[0045] [Table 5]

[0046] (Preparation Example 6) Samples 6-1 to 6-4 were prepared using the same procedure as in Preparation Example 1, except that (E)-1,1,1,2,3,4,4,4-octafluoro-2-butene was used as the fluoro-2-butene. The concentrations of various metal impurities in each sample were then measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 6.

[0047] [Table 6]

[0048] (Example 1) After leaving cylinder A standing at 20°C for 30 days, the gas of (Z)-1,1,1,4,4,4-hexafluoro-2-butene was extracted from the gas phase of cylinder A and analyzed by gas chromatography to quantify the concentration of (E)-1,1,1,4,4,4-hexafluoro-2-butene in sample 1-1. As a result, (E)-1,1,1,4,4,4-hexafluoro-2-butene, which is the product of the isomerization reaction of (Z)-1,1,1,4,4,4-hexafluoro-2-butene, was not detected.

[0049] The measurement conditions for gas chromatography are as follows: Gas chromatograph: Shimadzu Corporation GC-2014 Column: CarbopackB phase 1% sp-1000 Injection temperature: 200℃ Column temperature: 150℃ Detector: FID Detector temperature: 200℃ Carrier gas: Helium Detection limit: 1 ppm by mass

[0050] (Examples 2-18 and Comparative Examples 1-6) Table 7 shows the analytes and analysis results for Examples 2-18 and Comparative Examples 1-6, in comparison with Example 1. That is, for items other than those shown in Table 7, the analysis was performed using the same procedure as in Example 1.

[0051] [Table 7]

Claims

1. General formula C 4 H x F y A method for storing fluoro-2-butene, which is represented by the above general formula, wherein x is between 0 and 7, y is between 1 and 8, and x + y is 8, A method for storing fluoro-2-butene, wherein the fluoro-2-butene contains or does not contain at least one of chromium, molybdenum, iron, zinc, and aluminum as a metal impurity, and in the case where it contains such impurities, the sum of the concentrations of chromium, molybdenum, iron, zinc, and aluminum is 1000 ppb by mass or less, and the fluoro-2-butene is stored in a container.

2. A method for storing fluoro-2-butene according to claim 1, wherein the fluoro-2-butene is at least one selected from (Z)-1,1,1,4,4,4-hexafluoro-2-butene, (E)-1,1,1,4,4,4-hexafluoro-2-butene, (Z)-1,1,1,2,4,4,4-heptafluoro-2-butene, (E)-1,1,1,2,4,4,4-heptafluoro-2-butene, (Z)-1,1,1,2,3,4,4,4-octafluoro-2-butene, and (E)-1,1,1,2,3,4,4,4-octafluoro-2-butene.

3. A method for storing fluoro-2-butene according to claim 1 or claim 2, wherein the fluoro-2-butene is stored at a temperature of -20°C or higher and 50°C or lower.

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