JPH01261207A - Method for purifying nitrogen trifluoride gas - Google Patents

Abstract

PURPOSE:To efficiently, safely and economically remove dinitrogen difluoride which is an impurity contained in nitrogen trifluoride gas, by heating the nitrogen trifluoride gas in a metallic vessel having the inner wall lined with a solid fluoride at a specific temperature. CONSTITUTION:Nitrogen trifluoride gas containing dinitrogen difluoride as at least an impurity is heated at 150-600 deg.C temperature in a metallic vessel having the inner wall lined with a solid fluoride. The above-mentioned vessel is preferably a cylindrical shape. The afore-mentioned solid fluoride preferably has >600 deg.C melting point and, e.g., fluorides (e.g., LiF or NaF) of group IA metals, fluorides (e.g., BeF2 or MgF2) of group IIA metals and fluorides (e.g., AlF3 or GaF3) of group IIIA metals of the periodic table, are cited.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for purifying nitrogen trifluoride gas.

More specifically, the present invention relates to a method for removing dinitrogen difluoride from nitrogen trifluoride gas.

[Prior art and problems to be solved by the invention] Nitrogen trifluoride (Nh) gas is used as a dry etching agent for semiconductors and CV
Nitrogen trifluoride gas, which has recently attracted attention as a cleaning gas for D equipment, is required to be as pure as possible for use in these applications.

Nitrogen trifluoride (NF) gas is produced by various methods, but in most cases, the gas obtained by any of the methods is nitrous oxide (N,0), carbon dioxide (COz), or difluoride. Since it contains a relatively large amount of impurities such as dinitrogen (N2Fz), purification is required to obtain high-purity NF3 gas for the above-mentioned use.

As a 49M method for removing these impurities from NF3 gas, the method of adsorbing and removing impurities using an adsorbent such as zeolite is well known as one of the most efficient and simple methods [Chemical Enjuang (Ch
em, Eng,) 84.116. (1977), etc.], however, in this adsorption purification method, NF
The presence of N and F in Yugas causes the following adverse effects. That is, 1) If NzFz exists, the ability to adsorb other impurities such as co2, N, and O becomes extremely small.

2) The presence of NzF2 also makes it easier for NF3 to be adsorbed by the adsorbent, thus causing loss of NF3 gas.

3) N2F2 that has been adsorbed and concentrated on the adsorbent is likely to decompose and generate heat, causing an explosion in severe cases.

Therefore, NF using adsorbents such as zeolites.

When employing a method of adsorbing and removing impurities in the gas, it is necessary to remove Nth in advance.

As a method for removing N2Fz from NF3 residue, a method is conventionally known in which Kl, old, Na2S, NazSzOa, Na25O, etc. are reacted with NJz in a reaction tank. J, Massone+
Chemie Ingénuelle Technique (CheIIl)
, Ing, Techn, ) 41. (12),
695. (1969)). However, this method requires a relatively long time to completely remove N2F2 and therefore only requires a considerably larger reactor:
It also requires large amounts of drugs.

Another method for removing N2 is to use NF gas containing N and F2 on heated stainless steel,
Fill a reaction vessel with metal pieces or nets such as carbon steel, copper, aluminum, zinc, lead, nickel, iron, etc. to form a catalyst packed layer, and bring NF and gas into contact with the charged IJtFi by aerating them. A method is also known in which a metal piece or net is used as a catalyst to cause reaction and decomposition on the surface of the metal piece or net (Japanese Patent Publication No. 15081/1981). However, according to our study, this method is difficult to use when metal pieces and NzF
z tends to react and form metal fluoride on the surface of the metal piece or net. In many cases, the generated metal fluoride peels off from the surface of the metal piece and becomes powder, causing a problem of clogging the inside of the packed bed and the piping of the refining device.

However, according to our study, when nickel is used as a metal piece, the nickel piece only forms a fluoride film on its surface, and this film is relatively difficult to peel off.
Although the above-mentioned problem of pipe blockage can be prevented for the time being, the nickel piece whose surface is covered with fluoride no longer reacts with HtFz and naturally loses its activity as a catalyst.
It is necessary to periodically stop the operation, replace it with a new nickel piece, and refill the catalyst layer, which is not only extremely complicated, but also causes a considerable cost increase due to the high price of nickel. .

Furthermore, in order to increase the removal efficiency of N and F, when the heating temperature of the packed bed of metal pieces is increased, NFff, which is the main component, also reacts considerably with the metal pieces at temperatures of 200 °C or higher. There is also the problem that decomposition occurs and the yield of NF decreases accordingly.

(Means for solving the problem) The inventors of the present invention have conducted intensive studies on methods for removing NF, N and F2 contained in gas, and have surprisingly found that NJ
NF containing z, just by heating the gas to a specific temperature, N
We have obtained the knowledge that 2F2 is efficiently decomposed into nitrogen (N gas) and fluorine (F2) gas.Also, if the above heating is carried out in a specific container, even if heated to a temperature of 200"C or higher, the main component will not remain. We have also obtained the knowledge that certain NFs do not decompose, which is advantageous, and that this allows us to efficiently, safely, and economically remove NF and NZFK from gas. This study was made based on new findings discovered by the authors.

That is, the present invention allows nitrogen trifluoride gas containing dinitrogen difluoride as an impurity to be mixed in a metal container, preferably a cylindrical container, whose inner wall is lined with a solid fluoride.
This is a method for producing I# using nitrogen trifluoride gas, which is characterized by heating to a temperature of 0°C to 600°C.

[Detailed disclosure of the invention]

The present invention will be explained in detail below.

First, to explain the equipment such as containers used in the present invention, NF and gas are subject to the High Pressure Gas Control Law. Therefore, the manufacturing equipment must be a high-pressure gas manufacturing equipment, and the outside of the manufacturing equipment generally needs to be made of metal.

For the above reasons, the container used in the present invention, preferably a cylindrical container, must be made of metal such as iron or stainless steel.

In the following explanation, a cylindrical container, which is the easiest to manufacture, will be used as a representative container shape, but as is clear from the description of the first claim, this is based on Patent Law No. 70.
Other than cylindrical containers within the technical scope of the present invention as defined in Article 1.
It should be clearly understood that this is not intended to exclude container shapes such as square, box, conical, double tube, etc.

The metal cylindrical container used in the present invention (hereinafter simply referred to as cylindrical container) is preferably equipped with an inlet pipe and an outlet pipe for NF3 gas, and whose inner wall is lined with solid fluoride. is desirable.

In the present invention, Nh gas is heated at a maximum of 600° in the above cylindrical container.
Since the solid fluoride lining the inner wall is heated to about 600°C, it is preferable that the melting point exceeds 600°C. Examples of such solid fluorides include lithium fluoride (TiF), sodium fluoride (NaF),
Potassium fluoride (KF), rubidium fluoride (RbF)
, metal fluorides listed in Periodic Table IA such as cesium fluoride (CsF); beryllium fluoride (BeFz), magnesium fluoride (MgFz), calcium fluoride (CaF), strontium fluoride (Srh), and fluoride. Metal fluorides of the nA group such as barium (BaF z); aluminum fluoride (AffiF
t), gallium fluoride (Gaps), insidium fluoride (
Examples include metal fluorides of the nlA group such as InF3); reheating materials such as sodium aluminum fluoride (Na, A e F, ). A mixture of these may also be used.

For example, even if a solid fluoride other than those mentioned above has a melting point of 600°C or less, as long as it has a melting point of about 350°C or more, the present invention can be carried out at a temperature below that melting point. Needless to say.

In the present invention, the shape of the container for heating Nh does not necessarily have to be cylindrical, but it is easy to manufacture the container itself and process the lining with solid fluoride, and the strength of the lining layer is maintained during use. A cylindrical shape is preferable in order to prevent cracks from forming in the lining layer. There is no particular limit to the thickness of the lining layer, but if it is too thin, it will be technically difficult to process the lining, and there is also a risk that the inner wall of the cylindrical container will not be completely lined and a portion of the metal surface of the cylindrical container will be exposed. . On the other hand, if it becomes too thick, the cylindrical container is heated by a heater or the like from outside the cylindrical container in the present invention, so the heat transfer efficiency during heating will decrease and thermal energy will be lost, so it is preferable. Therefore, the thickness of the lining layer is approximately 1 to 5 mm.

As a method for lining the inner wall of a cylindrical container with a solid fluoride, when using a fluoride of an element of group IA, which has a relatively low melting point among the solid fluorides exemplified above, for example,
A sintering method can be adopted.

That is, as shown in FIG. 1, an inner tube 3 having an outer diameter slightly smaller than the inner diameter of the cylindrical container 1 is inserted into the cylindrical container 1 so as to be concentric. Next, after filling the gap between the cylindrical container 1 and the inner tube 3 with powdered solid fluoride 4, a load is applied to the press-fit tube 5 to compress and mold the solid fluoride 4. This filling and compression molding of the solid fluoride 4 is repeated to form a compression molded layer of the solid fluoride 4 on the entire inner wall of the cylindrical container 1. After that, inner cylinder 1
Slowly pull out the cylindrical container 1 and fill it with nitrogen (N2).
The inner wall of the cylindrical container 1 can be easily lined with the solid fluoride 4 by gradually raising the temperature to the softening point of the solid fluoride 4 under an inert gas atmosphere such as helium (He), and then slowly cooling it. can.

In this case, it is preferable that the solid fluoride contains 2 to 3% by weight of water, since the above-mentioned compression molding is easier. This also applies to the case of lining by the high-pressure press method described later.

Incidentally, it is preferable to apply a lubricant to the surface of the cylindrical container 3 in advance, since this makes it easier to pull out the inner cylinder 3 after the compression-molded layer of the solid fluoride 4 is formed on the surface of the cylindrical container 1.

When lining the inner wall of a cylindrical container with a solid fluoride having a relatively high melting point, a high-pressure press method is suitable. That is,
As in the case of the sintering method, after filling the gap between the cylindrical container l and the inner tube 3 shown in FIG. 1 with the solid fluoride 4, a load is applied to the press-fit tube 5 and compression molding of the solid fluoride 4 is repeated. This can be carried out by forming a lining layer of the solid fluoride 4 on the entire inner wall of the cylindrical container 1 and then slowly pulling out the inner cylinder 3.

In this case, in order to form a strong lining layer,
The load during compression molding is preferably 2t/c+a or more. Furthermore, as in the case of the sintering method, if a lubricant is applied to the surface of the inner cylinder 3 in advance, the inner cylinder 3 can be easily pulled out after the solid fluoride lining layer is formed on the inner surface of the cylindrical container 1. This is desirable because it is easy. However, in this case, the lubricant must be removed by evaporation by heating or the like after the solid fluoride lining layer is formed.

Furthermore, in the present invention, as a method for lining the inner wall of a cylindrical container with a solid fluoride, in addition to the above method, after flowing a molten solid fluoride into the gap between the cylindrical container 1 and the inner tube 3 in FIG. It is also possible to employ methods such as cooling and solidifying.

In the present invention, the NF3 gas to be purified is thus heated and decomposed in a cylindrical container whose inner surface is lined with solid fluoride. The NF3 is heated by preparing in advance a cylindrical container whose inner surface is lined with a solid fluoride as described above, keeping it in a heated state, and heating the NF3 containing N, F,
Preferred is a method in which gas is vented into the cylindrical container. Heating of the cylindrical container can be easily carried out by heating the outside of the cylindrical container with a heater or the like.

In the present invention, the heating temperature of NF and gas containing N2F2 is 1
It is carried out at 50-600°C, preferably 250-350°C. If the ventilation temperature is less than 150°C, almost no N2F2 can be decomposed and removed. Conversely, at temperatures exceeding 600″C, N and F are used.

Although it can be almost completely removed, it is disadvantageous because the lining layer of the cylindrical container may crack due to the difference in coefficient of thermal expansion. It also leads to loss of thermal energy.

Note that at the above heating temperature, the decomposition rate of NzFz is very fast, so NF is ventilated.

The residence time of the gas in the container (the ratio of the reactor volume to the gas volume velocity) may be short, but it is usually carried out within a range of about 5 to 1000 seconds.

In the present invention, the NF and gas to be vented into the cylindrical container may be supplied alone, but may also be diluted with an inert gas such as Nz or He. There are no particular restrictions on the pressure of the ventilation gas, but it is usually between O and 5k.
A pressure of g/cm''-G is preferred because it is easy to operate.

[Effects of the Invention] As described in detail above, the present invention
The method for removing Fz is a very simple method of heating NF and gas to a specific temperature in a cylindrical container whose inner wall is lined with solid fluoride, so it is an extremely economical method. In addition, as shown in the examples to be described later, N2
Since the removal rate of F is excellent, if the NF3 gas purified by the method of the present invention is repurified using a conventionally known purification method, for example, using an adsorbent such as the above-mentioned zeolite, Reference Example 1 can be obtained.
As shown in the figure above, it has a remarkable effect in that it is possible to easily obtain high-purity NF and gas suitable as raw materials for semiconductor dry etching. Furthermore, the method of the present invention allows NF and gas to be obtained in high yield with almost no loss of NF3, and is also a safe method.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that % and ppm in Examples, Comparative Examples, and Reference Examples represent jump capacity standards unless otherwise specified.

Examples 1 to 3 A stainless steel cylindrical container (column) 1 with an inner diameter of 10 mm and a length of 300 mm was coated with stearic acid as a lubricant on the surface as shown in FIG. 1, and the outer diameter was 5 mm.

After inserting the inner tube 3 with a length of 400 mm into the column 1, the water content is 3% by weight in the gap between the column 1 and the inner tube 3.
After gradually filling powder 4, which is a mixture of 5% by weight of cesium fluoride powder into lithium fluoride powder, a press-fit tube 5 with an outer diameter of 9.6 mm and an inner diameter of 6.5 mm is inserted into the above-mentioned gap. The mixed powder 4 was compression molded by applying a load of It/c. The operations of inserting the mixed powder 4 and compression molding were repeated to form a compression molded body of the mixed powder 4 on the entire inner wall of the column 1, and then the inner tube 3 was slowly pulled out.

Next, this column 1 was heated to 850°C at a heating rate of 200°C/h in an electric furnace under a N2 gas atmosphere.
After being maintained at a temperature of 50°C for 1 hour, it was cooled down to room temperature by natural cooling in an electric furnace to obtain a column 1 whose inner wall was entirely lined with a solid fluoride layer having a thickness of 21 cm.

NF gas containing NzFz was diluted with approximately the same volume of He gas and then aerated into this column 1 under the conditions shown in Table 1. The gas after ventilation is potassium iodide (K[) with a concentration of 1%.
After bubbling into the aqueous solution, it was introduced into a collection pump cooled with liquid nitrogen to liquefy and collect the NF*. After stopping the ventilation of NF and gas, the inside was evacuated to the above-mentioned NF3 collection pump to remove IleHe gas.

The composition of NF and gas before ventilation and the composition of NF in the collection pump after ventilation were analyzed by gas chromatography. As shown in Table 1, NJ2 had a high removal rate. In addition, there was almost no disappearance of Nh.

The fact that the N2 gas content is higher after ventilation in Table 1 is considered to be because N2F2 was decomposed into N2 and F2 due to heating.

In addition, in Example 3, column 1 after NF3 gas ventilation
The condition of the lining surface was observed, and no abnormalities such as cracks or damage were observed.

Examples 4-6 Same inner diameter 10 mm and length 3 as used in Examples 1-3
00mm stainless steel column 1 and outer diameter 6I, length 4
Using the 00-open inner cylinder 3, the first
Into the gap between the column 1 shown in the figure and the inner cylinder 3 whose surface is coated with stearic acid as a lubricant, a powder of solid fluoride 4 of the type shown in Table 2 with a moisture content of 3% by weight in Table 1 is added little by little. After filling, fill the above gap with an outer diameter of 9.8 mm.
A load of 2 t/c+fl was applied to the press-fit tube 5 having an inner diameter of 6.2 mm to compress the powder of the solid fluoride 4. This solid fluoride powder 4 was repeatedly filled and compressed to form a lining layer of solid fluoride powder on the entire inner wall of the column 1, and then the inner cylinder 3 was slowly extracted.

Next, this column 1 was placed in an electric furnace in a N2 gas atmosphere for 2 hours.
By raising the temperature to 300°C at a heating rate of 00°C/h,
After holding the stearic acid at a temperature of 00°C for 1 hour to remove the stearic acid 7 times, the column 1 was cooled to room temperature by natural cooling in an electric furnace, and the inner wall was lined entirely with solid fluoride with a thickness of 2 mm. I got it.

Column 1 obtained by
The NFS gas containing 2 was diluted with almost the same volume of He gas as in Examples 1 to 3, and the gas after aeration was 1% Kl water as in Examples 1 to 3. After bubbling into the liquid, the NF3 was introduced into a collection cylinder cooled with liquid nitrogen to liquefy and collect the NF3.

Table 2 After stopping the gas ventilation, the inside of the NF3 collection cylinder was evacuated to remove the tleHe gas.

The composition of NF and gas before ventilation and the composition of NF3 in the tili collection cylinder after ventilation were analyzed by gas chromatography. As shown in Table 2, the results showed that NzFz had a high removal rate. Furthermore, there was almost no disappearance of NF.

In addition, in Table 2, the content of N2 gas is higher after ventilation, which is considered to be because 82F was decomposed into N2 and F2 by heating.

Furthermore, the condition of the lining surface of the column 1 after the NF3 gas ventilation was observed, but no abnormality such as cracks or damage was observed.

Comparative Examples 1 to 3 Cylindrical containers (columns) made of the materials shown in Table 3 (dimensions are inner diameter 6
m111, length 300v++) was used as it was without lining with solid fluoride, and approximately the same volume of NF3 gas containing N2h was added to this column under the conditions shown in Table 3 as in Examples 1 to 3. The mixture was diluted with He gas and vented. The gas after ventilation has a concentration of 1% as in Examples 1 to 3.
After bubbling into the aqueous solution, the NF3 was introduced into a collection pump cooled with liquid nitrogen to liquefy and collect the NF3 in the same manner as in Examples 1 to 3.

After stopping the ventilation of the NF gas, the inside of the NF collection cylinder was evacuated to remove the He gas.

The composition of NF and gas before ventilation and the composition of NF3 in the collection cylinder after ventilation were analyzed by gas chromatography. The results are shown in Table 3, and it can be seen that although 82F2 is removed, the yield of NF is also poor.

Reference Example 1 A stainless steel column with an inner diameter of 110 mm and a length of 300 mm was filled with commercially available zeolite (pore size: 5) (granular product of 24 to 48 mesh) (packed bed: 250 mm). The NF obtained in Example 3 from which N2F2 was removed, the gas was aerated, the temperature was room temperature (approximately 20"C), and the NF3 gas flow was N2ONrnl/
The insufflation pressure was 60 Torr.

The composition of the NF3 gas after ventilation was analyzed by gas chromatography. The result is a combination of impurities 3
The surface amount is very small, less than 20 ppm of NJz, less than 20 ppm of NzO, and less than 220 ppm of CCo, and NtF! If the NF3 gas from which the
It is understood that this can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a state in which the inner wall of a cylindrical container (column) is lined with solid fluoride in an example. In the figure, 1.--.-- Metal cylindrical container (column),
2-...------N F 3 Gas outlet pipe, 3...-
---Inner tube, 4------Solid fluoride, 5-1--Press-fit tube, 6---11111 auxiliary cylindrical tube, 7 −−−−・Indicates a fixed board.

Claims (2)

[Claims] (1) Nitrogen trifluoride gas containing at least dinitrogen difluoride as an impurity is heated to a temperature of 150 to 600°C in a metal container whose inner wall is lined with solid fluoride. A method for purifying nitrogen trifluoride gas. (2) The method according to claim 1, wherein the metal container is a cylindrical container.