Method for producing high-purity phosphorus trifluoride

Abstract

The present invention produces phosphorus trifluoride at a high yield by using readily available raw materials (phosphorus trichloride and hydrogen fluoride), and produces a high-purity phosphorus trifluoride by purifying an obtained product gas containing phosphorus trifluoride by using a method suitable for mass production.　The present invention pertains to: a method for producing phosphorus trifluoride, the method comprising (a) a step for reacting phosphorus trichloride with hydrogen fluoride to produce a product gas, and (b) a step for removing hydrogen chloride from the product gas; and a high-purity phosphorus trifluoride obtained by said method.

Description

Manufacturing method for high-purity phosphorus trifluoride

[0001] The present invention relates to a method for producing high-purity phosphorus trifluoride, and to high-purity phosphorus trifluoride obtained by this method.

[0002] The reaction of phosphorus trifluoride from phosphorus trichloride and hydrogen fluoride is represented by the following formula: ３　 + 3HF → PF ３　 + 3HCl

[0003] Patent Document 1 describes a method for producing phosphorus trifluoride by reacting phosphorus trichloride with hydrogen fluoride using activated carbon as a catalyst. Patent Document 2 relates to a method for producing electronic-grade phosphorus trifluoride, and describes a method in which phosphorus trichloride (liquid) is placed in a reactor at 40 to 60°C and stirred for 20 to 50 minutes, and then hydrogen fluoride is gradually introduced to recover phosphorus trifluoride, which is then purified by distillation to obtain phosphorus trifluoride with a purity of 99.99% (4N). Patent Document 3 describes a method for producing phosphorus trifluoride by reacting phosphorus trichloride with a metal fluoride.

[0004] International Publication No. 2023 / 168597 Chinese Patent Publication No. CN117228643A Chinese Patent Publication No. CN101955173A

[0005] However, none of the prior art documents mentions PF ３ There have been no reports on the difficulty of separating low-concentration hydrogen halides, especially low-concentration HCl, when purifying PF 2 for semiconductor manufacturing. ３When using a process using a phosphorus trifluoride, trace amounts of impurities can also be a problem. According to the method of Patent Document 3, metal halides are produced as by-products instead of hydrogen halides, and therefore removing the hydrogen halides is not considered to be an issue. However, this method has a slow reaction rate and produces metal halides as by-products, which require careful handling, making it unsuitable for mass production of phosphorus trifluoride. Furthermore, since phosphorus trichloride and hydrogen fluoride contain trace amounts of water, in production methods using these raw materials, hydrogen halides such as hydrogen chloride and hydrogen fluoride are contaminated in the product gas due to the reaction of the raw materials or product with water. Therefore, an object of the present invention is to produce phosphorus trifluoride in a high yield using easily available raw materials (phosphorus trichloride and hydrogen fluoride), and to purify the resulting product gas containing phosphorus trifluoride by a method suitable for mass production, thereby producing high-purity phosphorus trifluoride. To achieve this object, it is important to remove the by-product hydrogen chloride by a method suitable for mass production.

[0006] According to the present invention, the following are provided: [1] A method for producing phosphorus trifluoride, comprising: (a) reacting phosphorus trichloride with hydrogen fluoride to produce a product gas; and (b) removing hydrogen chloride from the product gas. [2] The method according to [1], wherein the product gas after the (b) step has a total content of hydrogen chloride and water of less than 100 ppm by volume. [3] The method according to [1], wherein the product gas after the (b) step has a total content of metal components of less than 1 ppm by weight. [4] The method according to [1], wherein the reaction is carried out in a reactor filled with a packing material. [5] The method according to [4], wherein the packing material is composed of at least one material selected from alumina, activated carbon, silicon carbide, boron nitride, zirconia, titanium oxide, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (PFA), stainless steel, nickel, and copper. [6] The method according to any one of [1] to [5], wherein the step (b) of removing hydrogen chloride comprises at least one selected from the group consisting of distilling the product gas, passing the product gas through a solid adsorbent, and passing the product gas through a liquid absorbent. [7] The method according to [6], wherein the solid adsorbent comprises at least one selected from a metal fluoride and activated carbon. [8] The method according to [6], wherein the liquid absorbent comprises water. [9] The method according to [6], wherein the step (b) of removing hydrogen chloride comprises passing the product gas through a liquid absorbent containing water, and comprises, after step (b), a step of removing water from the product gas using molecular sieves.

[10] The method according to any one of [1] to [5], wherein the reaction temperature of phosphorus trichloride and hydrogen fluoride is 120°C to 250°C.

[11] The method according to any one of [1] to [5], wherein the molar ratio of hydrogen fluoride to phosphorus trichloride is 1 to 20.

[12] Phosphorus trifluoride having a hydrogen chloride content of less than 50 ppm by volume.

[13] Phosphorus trifluoride having a water content of less than 50 ppm by volume.

[14] Phosphorus trifluoride having a total metal component content of less than 1 ppm by weight.

[15] The phosphorus trifluoride according to any one of

[12] to

[14] , characterized in that the purity is 99.99% by volume or more.

[0007] According to the present invention, phosphorus trifluoride can be produced in high yield using easily available raw materials (phosphorus trichloride and hydrogen fluoride), and the resulting product gas containing phosphorus trifluoride can be purified by a method suitable for mass production to produce high-purity phosphorus trifluoride. In particular, according to the present invention, by-product hydrogen chloride can be efficiently removed by a method suitable for mass production.

[0008] 1 shows a test apparatus used in Example 1 to examine step (a) and Example 2 to examine step (b).

[0009] [Function] The method for producing phosphorus trifluoride of the present invention includes (a) a step of reacting phosphorus trichloride with hydrogen fluoride to produce a product gas, and (b) a step of removing hydrogen chloride from the product gas. Phosphorus trichloride and hydrogen fluoride are both the most readily available raw materials for producing phosphorus trifluoride, and the target phosphorus trifluoride can be produced by reacting them in a single step. However, although hydrogen chloride is produced as a by-product in step (a), there was a reason that high purity was not required for the target phosphorus trifluoride, and therefore removal of the by-product was not an issue. In recent years, demand for high-purity phosphorus trifluoride for semiconductor manufacturing applications has increased, creating a need for simple and efficient removal of the by-product hydrogen chloride. In the method of the present invention, hydrogen chloride is removed in step (b), and high-purity phosphorus trifluoride can be successfully provided at a mass production level. Specific embodiments of step (b) include at least one selected from (i) distilling the product gas, (ii) passing the product gas through a solid adsorbent, and (iii) passing the product gas through a liquid absorbent. Furthermore, since the presence of moisture affects the purity, a step of removing water from the product gas may also be necessary to produce high-purity phosphorus trifluoride. When the method of the present invention is carried out in this manner, phosphorus trifluoride characterized by a hydrogen chloride (HCl) content of less than 50 ppm by volume, a water content of less than 50 ppm by volume, and a total content of metal components of less than 1 ppm by weight can be obtained, and the purity of these phosphorus trifluorides can achieve 99.99% by volume or more.

[0010] [(a) Phosphorus trichloride (PCl ３) and hydrogen fluoride (HF) to produce a product gas. In this step, for example, phosphorus trichloride (boiling point: 74-78°C) and HF gas (boiling point: 19.5°C, optionally gasified by heating) are mixed before entering a cylindrical reactor packed with a filler / catalyst as shown in Figure 1, and the mixture is passed through the cylindrical reactor. In Figure 1, the reactor is set up vertically, and the raw material gases (phosphorus trichloride gas and HF gas) are passed from the upper inlet to the lower outlet to carry out the reaction. A mantle heater is installed on the side of the reactor so that the temperature inside the reactor can be adjusted.

[0011] Filler / Catalyst: The reactor can be filled with a filler. The filler has the effect of efficiently transferring heat within the reactor. The reaction proceeds even in an empty reactor (empty column) without a filler. However, to improve the thermal efficiency within the reactor, a filler that does not inhibit the reaction may be used. The reactor can also be filled with a catalyst as a filler. Examples of fillers include alumina, activated carbon, silicon carbide, boron nitride, zirconia, titanium oxide, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (PFA), stainless steel, nickel, and copper. In the present invention, catalytically active metal fluorides can be used alone as a filler or supported on the filler. Examples of metal fluorides include alkali metal fluorides (NaF, KF, etc.), CrF ３ , AlF ３ The amount of metal fluoride supported in the filler is 1 to 30% by weight, preferably 1 to 20% by weight, and particularly 1 to 15% by weight, per 100% by weight of the supported filler. The shape of the filler may be powder, granules, spheres, pellets, etc. The size of the filler in the case of granules, spheres, or pellets is 0.1 mm to 30 mm, preferably 0.1 mm to 20 mm, and particularly 0.2 mm to 15 mm, in terms of diameter or major axis.

[0012] Raw material gas: Phosphorus trichloride (PCl３ The molar ratio of hydrogen fluoride (HF) to phosphorus trifluoride (PF) is preferably an amount that replaces all chlorine bound to phosphorus with fluorine, and is preferably 3 or more. However, if there is too much hydrogen fluoride, it will be wasted, so it is usually 1 to 20, preferably 3 to 10, and particularly 3 to 6. The raw material gas is passed through the reactor while being maintained in a gaseous state by heating the pipes so that the temperature is equal to or higher than the boiling points of hydrogen fluoride and phosphorus trichloride. In particular, in the present invention, the product gas (phosphorus trifluoride (PF)) is ３ ) and hydrogen chloride (HCl) ３ The boiling point of PCl is high, and even if any raw material remains after the reaction, it is easy to recover and reuse. ３ The molar ratio of HF to PCl is less than 3 and unreacted PCl ３ Even if PCl is left behind, it is possible to avoid unreacted HF remaining after the reaction, and ３ This has the advantage that priority can be given to the collection of waste.

[0013] Reaction temperature: In the method of the present invention, the boiling point of the produced phosphorus trifluoride is -101.8°C, and the boiling point of the by-product hydrogen chloride is -85°C, so the product gas can be circulated through the reactor at any reaction temperature at which the raw material gas can be maintained in a gaseous state. The reaction temperature is usually set to 80°C to 300°C, preferably 100°C to 250°C, and particularly 120°C to 200°C.

[0014] The total content of hydrogen chloride and water in the product gas obtained in this step is preferably less than 100 ppm by volume after step (b).

[0015] [(b) Step of Removing Hydrogen Halide from Product Gas] This step is a step of obtaining high-purity phosphorus trifluoride by removing hydrogen halide from the product gas obtained in step (a). In the present invention, the hydrogen halide to be removed is at least one selected from hydrogen chloride (HCl) as a by-product and hydrogen fluoride (HF) as an unreacted raw material. In this step, to remove this hydrogen halide, at least one method selected from the following is carried out: (i) distilling the product gas, (ii) passing the product gas through a solid adsorbent, and (iii) passing the product gas through a liquid absorbent.

[0016] (i) Distilling the product gas: Preferred distillation conditions are as follows: Type of column packing: Helipak No. 1, Helipak No. 2 Number of distillation plates: preferably 10 to 45, more preferably 20 to 45, more preferably 30 to 45, particularly preferably 30 to 35 Pot temperature: preferably −105° C. to −50° C., more preferably −105° C. to −75° C. Condenser temperature: preferably −110° C. to −90° C.

[0017] (ii) Passing the product gas through a solid adsorbent: Examples of the solid adsorbent include metal fluorides, activated carbon, alumina, magnesia, etc. Examples of the metal fluorides include sodium fluoride, magnesium fluoride, aluminum fluoride, potassium fluoride, calcium fluoride, etc.

[0018] (iii) Passing the product gas through a liquid absorbent: Examples of liquid absorbents include water. While tap water can be used, it is preferable to use distilled water, deionized water, purified water, ultrapure water, etc., from the viewpoint of minimizing the incorporation of metal ions into the product. When the liquid absorbent contains a trace amount of metal, it is conceivable that trace amounts of metal (Ca, K, Na, Mg, etc.) will be entrained with the product gas by passing the gas through the liquid absorbent. However, these can be removed by a subsequent drying step (passing the gas through a desiccant (e.g., molecular sieves)) or a distillation step. When water is used as the liquid absorbent, this step should be carried out at a low temperature (below 10°C) at which the water does not solidify, in order to ensure the absorption of hydrogen chloride and the PF ３It is also suitable for suppressing the decomposition of HCl. The optimal conditions for the temperature and acid concentration of the liquid absorbent vary depending on the flow rate of the product gas and the amount of HCl contained in the product gas, but they can be adjusted so that the HCl content in the product gas is less than 50 ppm by volume. When water is used as the liquid absorbent, the water temperature is typically in the range of 0 to 40°C, preferably 0 to 20°C, and more preferably 0 to 10°C, and it is desirable to use a constant amount of water that can mitigate the effect of the heat of dissolution of HCl and maintain the water temperature. The liquid absorbent is typically used assuming an acid concentration (HCl concentration) of 0 to 30% by weight, preferably 0 to 20% by weight, and more preferably 0 to 10% by weight.

[0019] [Step of Removing Water from Product Gas] In order to produce high-purity phosphorus trifluoride for semiconductor manufacturing, it is necessary to keep the water content low. In this step, water is removed using molecular sieves. Examples of molecular sieves include 3A, 4A, 5A, 10X, and 13X. When the liquid absorbent used in step (b) contains water, it is preferable to remove the water in this step.

[0020] [High-Purity Phosphorus Trifluoride] The present invention provides high-purity phosphorus trifluoride. This high-purity phosphorus trifluoride is particularly useful for semiconductor manufacturing applications. Specifically, the high-purity phosphorus trifluoride of the present invention is characterized by having an HCl content of less than 50 ppm by volume, preferably less than 10 ppm by volume, and particularly less than 5 ppm by volume; a water content of less than 50 ppm by volume, preferably less than 10 ppm by volume, and particularly less than 5 ppm by volume; a total metal content of less than 1 ppm by weight, particularly the total content of Na, K, Mg, Ca, Al, Fe, Cr, Ni, As, Co, Mn, Mo, Zn, Li, Cd, Pb, Ti, and W of less than 1 ppm by weight; and a purity of 99.99% by volume or more, preferably 99.995% by volume or more, and particularly 99.999% by volume or more. The reason why the total content of the metal components Na, K, Mg, Ca, Al, Fe, Cr, Ni, and As in the phosphorus trifluoride of the present invention is preferably less than 1 ppm by weight is that when water is used as the liquid absorbent in step (b), metals such as Na, K, Mg, and Ca contained in the water may be mixed into the product gas; when a metal fluoride catalyst is used in step (a), metals such as Na, K, Al, and Cr may be mixed into the product gas; when SUS or Ni is used for the reaction vessel and piping, metals such as Fe, Cr, and Ni may be mixed into the product gas; the raw material HF may be contaminated with As compounds that form an azeotropic point with HF; and other metal species (Co, Mn, Mo, Zn, Li, Cd, Pb, Ti, and W) may be mixed in because they are contained in the raw materials or originate from the reaction apparatus, and therefore, when used for semiconductor applications, it is necessary to limit the content of these metals.

[0021] The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples. In the following description, the following abbreviations may be used: MFC: Mass flow controller TIC: Temperature indicator / controller TI: Temperature sensor MS column: Molecular sieve packed column eq: PC1 ３ Molar equivalent of HF to

[0022] Example 1: Reaction test of step (a) Using the reactor shown in Figure 1, phosphorus trifluoride was produced by carrying out a gas phase reaction between phosphorus trichloride and hydrogen fluoride according to the following formula. It was expected that hydrogen chloride would be produced as a by-product according to the following formula: PCl ３　 + 3HF → PF ３　 + 3HCl

[0023] The schematic of the apparatus of FIG. 1 is as follows: ３ is released from a syringe pump (labeled "pump" in Figure 1) at a rate of 46.5 μL per minute (liquid volume), vaporized through a heated pipe (heated line indicated by a thick line in Figure 1), and supplied to the reactor at a rate of 11.9 mL per minute (gas flow rate). HF is supplied to the reactor from a cylinder via an MFC through the heated pipe at a rate of 47.8 mL per minute (R-1 to R-4) (gas flow rate). The pipe extending from the syringe pump to the reactor and the pipe extending from the cylinder to the reactor merge just before the reactor inlet, so that the two raw gases enter the reactor in a mixed state. The reactor is a SUS cylindrical reactor (inner diameter 10 mm x length 60 cm) installed vertically, with the inlet at the top and the outlet at the bottom. A mantle heater is installed on the outer side of the reactor, allowing the reactor temperature to be adjusted externally while being detected by TI and TIC. The reactor is filled with filler (particle diameter of filler is 4-5 mm) in an amount that occupies almost 100% of the reactor's internal volume. When the raw material gas comes into contact with the filler, the target PF ３ The product gas containing the by-product HCl is released from the outlet at the bottom of the reactor. ３ The yields are shown in Table 1. An example was also carried out in which no filler was used (R-1).

[0024]

[0025] From the test results in Table 1, if the amount of HF is slightly more than the required amount, the following can be achieved: empty tower (no packing), activated carbon, activated carbon supported by metal fluoride (KF), Al ２ O ３(alumina) were found to have practical yields of 70% or more. The yields were calculated using a gas chromatograph (GC-TCD) ３ This was done by quantitative analysis.

[0026] (Example 2) Testing the Effect of Step (b) Using the reactor shown in Figure 2, a gas phase reaction between phosphorus trichloride and hydrogen fluoride was carried out according to the following formula, and high purity phosphorus trifluoride was produced by removing the by-product HCl from the product gas using water as a liquid absorbent. It was expected that hydrogen chloride would be produced as a by-product according to the following formula: PCl ３　 + 3HF → PF ３　 + 3HCl

[0027] 2, the liquid PC1 in the storage vessel is ３ is released from the metallore pump (labeled "pump" in Figure 2) at a rate of 1781 μL per minute (liquid volume), vaporized through a heated pipe (heated line indicated by a thick line in Figure 2), and supplied to the reactor at a rate of 458 mL per minute (gas flow rate). HF is supplied to the reactor from a cylinder via an MFC through a heated pipe at a rate of 1757 mL per minute (gas flow rate) (flow rate is for R-6 in Table 2). The pipe extending from the metallore pump to the reactor and the pipe extending from the cylinder to the reactor merge just before the reactor inlet, so that the two raw gases enter the reactor in a mixed state. The reactor is a Ni cylindrical reactor (inner diameter 2 inches x length 100 cm) installed vertically with the inlet at the top and the outlet at the bottom. A mantle heater is installed on the outer side of the reactor, allowing the reactor temperature to be adjusted externally while being detected by TI and TIC. The reactor is filled with a filler (type: activated carbon; filler particle diameter: 4 mm) as a reaction catalyst, taking up almost 100% of the reactor's internal volume. When the raw material gas comes into contact with the filler, the target PF ３The product gas containing the by-product HCl is released from the outlet at the bottom of the reactor. The product gas leaving the reactor outlet is passed through an empty bottle for recovering raw materials, then through water in a PFA bottle to remove HCl (hereinafter sometimes referred to as "water washing"). The product gas is then passed through an MS column to remove moisture, resulting in high-purity phosphorus trifluoride from which moisture has been removed, which is then collected in a collection vessel cooled with liquid nitrogen. The outlet of the MS column is connected to a piping leading to the collection vessel, as well as to a gas chromatograph (GC-TCD) and an infrared absorption spectrometer (FT-IR) for gas analysis. Although not shown in FIG. 2 , as an optional additional step, the high-purity phosphorus trifluoride collected in the collection vessel was further purified by distillation in a distillation column (distillation conditions: packing material (Helipak No. 2); number of distillation columns: 31). After distillation and purification, the phosphorus trifluoride recovered in the collection vessel was analyzed by a TDLAS (Typical Dew Point Atomic Energy Analyzer) and an inductively coupled plasma atomic emission spectroscopy (ICP-AES). Table 2 shows the reaction conditions, and Table 3 shows the analysis results for the purity of high-purity phosphorus trifluoride obtained when step (b) was performed. Table 4 shows the composition of the product gas used in the test and the distillation conditions. The product gas for R-5 was used in the method without water washing, and the product gas for R-6 was used in the method with water washing. For water washing, tap water containing metal components (Na, K, Mg, Ca, Al, Fe, Cr, Ni, and As) in amounts of 100 to 200 ppm by weight was used. In the tables below, values ​​marked with "<" indicate values ​​below the lower limit of quantitation of the analytical instrument. For impurities below the lower limit of quantitation, the total impurities were calculated assuming the lower limit of quantitation was included. GC area % was calculated as vol%.

[0028]

[0029]

[0030]

[0031] From the results in the first row of Table 3, immediately after the gas phase reaction of phosphorus trichloride and hydrogen fluoride, hydrogen chloride is produced in an amount three times the molar equivalent of phosphorus trifluoride. Therefore, the ratio of these in the product gas is PF ３　27.6% by volume of hydrogen chloride and 72.3% by volume of HCl. From the results in the second row of Table 3, when this product gas was purified by distillation, most of the hydrogen chloride was removed and HCl was not detected in terms of GC area ratio, but FT-IR analysis revealed that it contained 6,876 ppm by volume or more of HCl and less than 18 ppm by volume (trace amount) of HF. It was found that while a GC area ratio of 99% by volume or more can be achieved by simply purifying the product gas by distillation, this is not sufficient for producing high-purity phosphorus trifluoride for semiconductor manufacturing. The results in the third row of Table 3 show that when this product gas was passed through water (liquid absorbent), decomposition of phosphorus trifluoride occurred and the purity of phosphorus trifluoride temporarily decreased, but unexpectedly, most of the hydrogen chloride was removed and HCl was not detected in terms of GC area ratio, but FT-IR analysis showed that the product contained less than 26 ppm by volume of HCl (trace amount) and less than 18 ppm by volume of HF (trace amount).The results in the fourth row of Table 3 show that when this product gas was passed through water (liquid absorbent) and further purified by distillation, most of the hydrogen chloride was removed and HCl was not detected in terms of GC area ratio, but FT-IR analysis showed that the product contained less than 26 ppm by volume of HCl (trace amount) and less than 18 ppm by volume of HF (trace amount). From the above results, it was found that although a small amount of decomposition of phosphorus trifluoride occurred when the product gas was passed through water (liquid absorbent) (water washing), hydrogen chloride could be sufficiently removed before distillation purification, and by subsequently carrying out distillation purification, high-purity phosphorus trifluoride of 99.9% by volume or more could be obtained.

[0032] The results in Table 3 can be further summarized as follows: In step (b), high-purity phosphorus trifluoride with a purity of 99.99% by volume or more, i.e., high-purity phosphorus trifluoride suitable for semiconductor manufacturing, can be obtained by passing the product gas through water (liquid absorbent) (water washing), removing water by MS (drying), and purifying by distillation. Furthermore, the content of metal components was low at 0.0085 ppm by weight, and high-purity phosphorus trifluoride could be obtained even when tap water was used for washing, demonstrating that the method of the present invention is suitable for mass production of high-purity phosphorus trifluoride.

[0033] (Footnote: H２ The O content was analyzed by FT-IR when the water washing and drying process was performed, and by TDLAS when the water washing, drying, and distillation process was performed. In the FT-IR analysis, the values ​​for both the water washing and drying process and the water washing, drying, and distillation process were both <105, and no difference was confirmed between the two.

Claims

1. A method for producing phosphorus trifluoride, comprising: (a) reacting phosphorus trichloride with hydrogen fluoride to produce a product gas; and (b) removing hydrogen chloride from the product gas.

2. The method of claim 1, wherein the combined hydrogen chloride and water content of the product gas after step (b) is less than 100 ppm by volume.

3. The method of claim 1, wherein the total content of metal components in the product gas after step (b) is less than 1 ppm by weight.

4. The method according to claim 1, wherein the reaction is carried out in a reactor filled with a packing material.

5. The method according to claim 4, wherein the filler is composed of at least one material selected from the group consisting of alumina, activated carbon, silicon carbide, boron nitride, zirconia, titanium oxide, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (PFA), stainless steel, nickel, and copper.

6. The method according to any one of claims 1 to 5, wherein (b) the step of removing hydrogen chloride comprises at least one selected from the group consisting of distilling the product gas, passing the product gas through a solid adsorbent, and passing the product gas through a liquid absorbent.

7. The method of claim 6, wherein the solid adsorbent comprises at least one selected from metal fluorides and activated carbon.

8. The method of claim 6, wherein the liquid absorbent comprises water.

9. The method of claim 6, wherein (b) the step of removing hydrogen chloride comprises passing the product gas through a liquid absorbent containing water, and further comprising, after step (b), removing water from the product gas using molecular sieves.

10. The method according to any one of claims 1 to 5, wherein the reaction temperature of phosphorus trichloride and hydrogen fluoride is 120°C to 250°C.

11. The method according to any one of claims 1 to 5, wherein the molar ratio of hydrogen fluoride to phosphorus trichloride is 1 to 20.

12. Phosphorus trifluoride characterized by having a hydrogen chloride content of less than 50 ppm by volume.

13. Phosphorus trifluoride having a water content of less than 50 ppm by volume.

14. Phosphorus trifluoride characterized by having a total content of metal components of less than 1 ppm by weight.

15. Phosphorus trifluoride according to any one of claims 12 to 14, characterized in that the purity is 99.99% by volume or more.

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