JPH01261210A - 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 filling a solid fluoride in a metallic vessel having the inner wall lined with the solid fluoride and heating the nitrogen trifluoride gas at a specific temperature in the packed layer of the solid fluoride. CONSTITUTION:A solid fluoride is filled in a metallic vessel having the inner wall lined with a solid fluoride and nitrogen trifluoride gas containing dinitrogen difluoride as at least an impurity is heated at 150-600 deg.C temperature in the packed layer of the solid fluoride. The above-mentioned metallic vessel is preferably a cylindrical shape. A solid fluoride having >=600 deg.C melting point is preferred as the solid fluoride for lining 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. The same solid fluoride as that for lining can be suitably used as the solid fluoride filled in the cylindrical vessel.

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 (NFs) gas is used as a dry etching agent for semiconductors and carbon dioxide.
Nitrogen trifluoride gas, which has recently attracted attention as a cleaning gas for vD devices, 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 these methods contains nitrous oxide (Neo), carbon dioxide (COz), and difluoride. Since it contains a relatively large amount of impurities such as nitrogen (NJz), purification is required to obtain high purity NF and gas for the above-mentioned uses.

As a purification method for removing these impurities from NF and gas, the method of adsorbing and removing impurities using an adsorbent such as zeolite is the most efficient (well-known as one of the simple methods). Chemical Engineering (Che
+a, Eng,) 84.116. (1977) etc.]. However, in this adsorption purification method, NF
, the presence of NzFz in the gas causes the following problems. That is, 1) N! When F exists, the ability to adsorb other impurities such as Cot and Neo becomes extremely small.

2) When N2F2 is present, NF3 is also likely to be adsorbed by the adsorbent, thus causing loss of NF and gas.

3) N and Ft adsorbed and concentrated on the adsorbent tend to decompose and generate heat, causing an explosion in severe cases.

Therefore, when adopting a method of adsorbing and removing impurities in NFa gas using an adsorbent such as zeolite, it is necessary to remove Nzh in advance.

As a method for removing NIFg from NF3 gas, a method is conventionally known in which an aqueous solution of Kl, NazS, NazSzOn, Na, SO, etc. is reacted with NJz in a reaction tank (J. Massonne, et al. chemistry
・Chem, Ing
, Techn, ) 41. (12), 695.
(1969) ), while this method reduces N
Complete removal of Jz requires a relatively long time and thus requires not only a fairly large reaction vessel but also a large amount of chemical.

In addition, as another method for removing N2F2, NF and gas containing NJz are heated and metal pieces such as stainless steel, carbon steel, copper, aluminum, zinc, lead, nickel, iron, etc.7) are placed in a reaction vessel. There is also a known method in which NF and gas are brought into contact with each other by aeration of the packed bed, and the metal pieces or net are used as catalysts to react and decompose on the surface of the metal pieces or net. There is (
(Special Publication No. 59-15081). However, according to our study, in this method, the metal pieces and NJz tend to react and form metal fluorides on the surfaces of the metal pieces and the net.

In many cases, the generated metal fluoride peels off from the surface of the metal piece and turns into powder, causing a problem of clogging the inside of the packed bed and the pipes of the stacking and conditioning equipment.

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, the nickel piece whose surface is covered with fluoride no longer reacts with N2Fz 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 N2FZ, when the heating temperature of the packed bed of metal pieces is increased, the main component NF3 also reacts considerably with the metal pieces at temperatures of 200°C or higher, causing decomposition. There is also the problem that the yield of NF decreases accordingly.

(Means for Solving the Problem) As a result of intensive studies by the present inventors on a method for removing 82F contained in NFz gas, surprisingly, N=
By simply heating NF and gas containing Fz to a specific temperature,
We have obtained the knowledge that N2F2 is efficiently decomposed into nitrogen (N2) gas and fluorine (F2) gas. In addition, it is convenient to carry out the above heating in a specific container because the main component, NF, does not decompose even if heated to a temperature of 200°C or higher. If you keep it,
Furthermore, we also obtained the knowledge that NJz can be decomposed efficiently and that NJz in Nh gas can be removed safely and economically. The present invention has been made based on the novel knowledge discovered by us.

That is, in the present invention, a metal container, preferably a cylindrical container, whose inner wall is lined with a solid fluoride is filled with a solid fluoride, and at least dinitrogen difluoride is contained as an impurity in the packed bed of the solid fluoride. Nitrogen trifluoride gas containing 150 to 6
This is a method for purifying nitrogen trifluoride gas, which is characterized by heating to a temperature of 00°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 must 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 NFI gas, and whose inner wall is lined with solid fluoride. is desirable.

In the present invention, the NFff gas is Jfft in the above-mentioned cylindrical container.
Since it is heated to about 600°C, it is preferable that the solid fluoride lining the inner wall has a melting point of over 600°C. Examples of such solid fluorides include lithium fluoride (TiF) and sodium fluoride (NaF).
), potassium fluoride (KF), rubidium fluoride (Rb
F) Metal fluorides in Group IA of the periodic table such as cesium fluoride (CsF); beryllium fluoride (BeFz), magnesium fluoride (MgFz), calcium fluoride (CaFi), strontium fluoride (SrF2), fluoride Barium chloride (BaF
Metal fluorides of the HA group such as aluminum fluoride, (A
Metal fluorides of the 11A group such as IF, ), gallium fluoride (GaF3), and insidium fluoride (InF3); and double salts such as sodium aluminum fluoride (Na sA I F &). A mixture of these may also be used.

In addition, even if there is a solid fluoride other than the above, for example, with a melting point of 600° C. or lower, as long as it has a melting point of about 350° C. or higher, the present invention can be carried out at a temperature below that melting point. Not even.

In the present invention, the shape of the container for heating NF does not necessarily have to be cylindrical, but the container itself is easy to manufacture and the solid fluoride lining process is easy.
A cylindrical shape is preferable in terms of the strength of the lining layer and the prevention of cracks in the lining layer during use.There is no particular limitation on the thickness of the lining layer, but if it is too thin, the lining processing may be difficult. This is difficult, and it is common for the inner wall of the cylindrical container to not be completely lined, leaving a portion of the metal surface of the cylindrical container exposed. On the other hand, if it becomes too thick,
In the present invention, the cylindrical container is heated from outside the cylindrical container using a heater or the like, which is not preferable because the heat transfer efficiency during heating decreases and thermal energy is lost. The thickness is approximately 1 to 5 IIIn.

As a method for lining the inner wall of a cylindrical container with a solid fluoride, when using a fluoride of an element of the IA group, 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 cylinder 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 flush with each other. 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 for the solid fluoride to contain 2 to 3% water, since the above-mentioned compression molding is easier. This also applies to the case of lining by the high-pressure pressing method described later.

Further, 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.

If water is contained in the solid fluoride, when the NF is aerated, the water reacts with the NF and forms nitrogen oxide (N2).
The water contained in this solid fluoride layer, which is undesirable because it produces o), is evaporated and removed together with the lubricant adhering to the solid fluoride layer by the heating of the solid fluoride layer.

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 1 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 the above compression molding is preferably 2 t/cd or more, and if the surface of the inner cylinder 3 is coated with lubricant in advance, as in the case of the sintering method, the inner surface of the cylindrical container 1 can be This is desirable because it is easy to pull out the inner cylinder 3 after forming the solid fluoride lining layer.

In this case, the moisture contained in the solid fluoride must be removed by evaporation together with the lubricant adhering to the lining by heating or the like after the solid fluoride lining layer is formed for the same reason as described above.

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 shown in FIG. It is also possible to employ methods such as cooling and solidifying.

Next, the solid fluoride to be filled into the cylindrical container will be explained.

The solid fluoride used in the present invention, like the solid fluoride used for lining the inner wall of a cylindrical container, preferably has a melting point of 600'C or higher, but even if the melting point is less than 600°C, It is sufficient that the NFs is solid at the temperature at which it is heated, and for example, those having a melting point of about 350° C. or higher can be used in the present invention at temperatures below that melting point.

Therefore, the same solid fluorides as those listed above as examples for lining the inner wall of a cylindrical container are preferably used.

The shape of the solid fluoride to be filled into the cylindrical container is preferably granular, and its size is not particularly limited and is determined by the size of the reactor, ease of handling, etc. Furthermore, even if the solid fluoride is in powder form, it can be suitably used by forming it into tablets using a tablet machine or the like.

In addition, if the solid fluoride mentioned above contains water, when it comes into contact with Nh gas, the water reacts with Nh and forms nitrogen monoxide (
Therefore, it is desirable to dry the solid fluoride in advance to sufficiently remove moisture.

In the present invention, heating of NF3 gas containing N2F2 is carried out by filling a cylindrical container whose inner wall is lined with solid fluoride with solid fluoride, heating the cylindrical container, and heating the NF3 gas containing N2F2.
A preferred method is to ventilate NF Yugas containing 2 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 NF3 gas to be purified is heated and decomposed in a packed bed filled with the solid fluoride in a cylindrical container whose inner surface is lined with a solid fluoride as described above. To heat the NF, prepare in advance a cylindrical container whose inner surface is lined with solid fluoride as described above, fill it with solid fluoride, and then leave it in a heated state.
A method of venting Nh gas containing zh into the cylindrical container is preferred, and 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 NF3 gas containing N2Ft is 1
It is carried out at a temperature of 50 to 600°C, preferably 250 to 350°C. If the ventilation temperature is less than 150°C, almost no NtFz can be decomposed and removed. On the other hand, at temperatures exceeding 600℃, NzFz
Although it can be almost completely removed, it is disadvantageous because the lining layer of a cylindrical container tends to crack due to the difference in coefficient of thermal expansion. It also leads to loss of thermal energy.

In addition, at the above heating temperature, the decomposition rate of NJz is very fast, so the residence time (
The reaction time (ratio of reactor volume to 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 ventilated into the cylindrical container may be supplied alone, or may be diluted with an inert gas such as N2 or He. There are no particular restrictions on the pressure of ventilation gas, but it is usually 0 to 5 kg.
A pressure of /cm''-G is preferred because it is easy to operate.

〔Effect of the invention〕

As explained in detail above, the present invention
A very simple method for removing Fz is to fill a cylindrical container whose inner wall is lined with solid fluoride with solid fluoride and heat Nh gas to a specific temperature in the solid fluoride layer. , is an extremely economical method. Furthermore, as shown in the Examples described later, the removal rate of NJz is excellent, so the Nh gas purified by the method of the present invention can be repurified using a conventionally known purification method, for example, using an adsorbent such as the above-mentioned zeolite. For example, as shown in Reference Example 1, it has a remarkable effect in that highly purified NF and gas suitable as raw materials for semiconductor dry etching agents can be easily obtained. In the present invention, since the container is filled with solid fluoride, the removal rate of Nzh is further improved than simply heating NF in the container. Furthermore, the method of the present invention produces NF, in high yield, with almost no loss of NFS.
It is a method that provides gas and is also safe.

(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 capacity standards unless otherwise specified.

Examples 1 to 3 A cylindrical container (column) 1 made of stainless steel 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. After inserting the inner tube 3 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 the lithium fluoride powder with 5% by weight of cesium fluoride powder 4, a press-fit tube 5 with an outer diameter of 9.6 mm and an inner diameter of 6.5 mm was inserted into the gap. A load of Lt/cffl was applied to the press-fit tube 5 to compression mold the mixed powder 4. 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 N gas atmosphere.
The column was maintained at a temperature of .degree. C. for 1 hour and then cooled to room temperature by natural cooling in an electric furnace to obtain a column 1 whose inner wall was entirely lined with a 2 m-thick solid fluoride layer. It should be noted that the above heating also evaporated and removed the water contained in the lithium fluoride and cesium fluoride and the lubricant used in forming the lining layer.

After that, this column 1 was filled with granular calcium fluoride (CaFz) having a particle size of 24 to 32 mesh (filling height 25
0mm) L, N heated to a temperature of 200°C,
Vent gas at a flow rate of 100cc/win for 1 hour,
Water in CaFz was removed.

Next, approximately the same volume of Nh gas containing 82Fg was added to column 1 filled with this CaFt under the conditions shown in Table 1.
It was diluted with e-gas and vented. The gas after the ventilation was bubbled into an aqueous solution of potassium iodide (H) having a concentration of 1% by weight, and then introduced into a collection cylinder cooled with liquid nitrogen to liquefy and collect NFj. After stopping the supply of NF and gas, the inside of the Nh collection pump was evacuated to remove the lleHe gas.

Composition of NF3 gas before ventilation and collection pump number after ventilation
1 The composition of NF in the table was analyzed by gas chromatography. As shown in Table 1, NJz 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 NJz was decomposed into N2 and F2 due to heating.

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

Examples 4 to 6 Using the same stainless steel cylindrical container (column) 1 with an inner diameter of 10 mm+ and a length of 300 mm as used in Examples 1 to 3 and an inner cylinder 3 with an outer diameter of 6 vs. and a length of 400 mm, Examples were carried out. Similarly to 1 to 3, a solid fluoride of the type shown in Table 2 with a water content of 1% by weight was placed in the gap between the column 1 shown in Figure 1 and the inner cylinder 3 whose surface was coated with stearic acid as a lubricant. After filling the powder in Step 4 little by little, the above gap was filled with an outer diameter of 9.8 mm.
Applying a load of 2 t/d to the press-fit tube 5 with an inner diameter of 6.21 mm,
The powder of solid fluoride 4 was subjected to a second compaction. The solid fluoride powder 4 was repeatedly filled and compressed to form a lining layer of the 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℃ at a heating rate of 00℃/h, 300℃
℃ for 1 hour to evaporate and remove the water contained in the solid fluoride layer and the stearic acid attached to the solid fluoride layer, and then cooled to room temperature by natural cooling in an electric furnace. As a result, a column 1 whose inner wall was entirely lined with solid fluoride having a thickness of 2IIIL was obtained.

The column 1 thus obtained had a particle size of 24 to 24 as shown in Table 2.
32 meshes of solid fluoride were filled in the same volume as in Examples 1 to 3, and the solid fluoride was dried to remove water under the same conditions as in Examples 1 to 3.

This column 1 contains N*h under the conditions shown in Table 2.
The F1N1 gas was diluted with approximately the same volume of He gas as in Examples 1 to 3 and aerated. The gas after 0 ventilation was bubbled into a Kl aqueous solution with a concentration of 1% by weight as in Examples 1 to 3. The NF was introduced into a collection pump cooled with liquid nitrogen, where it was liquefied and collected. NF, after gas ventilation is stopped, use the above N
The inside of the collection bomb was evacuated to remove He 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 2, the results showed that NtFz had a high removal rate. In addition, there was almost no disappearance of Nh.

Furthermore, in Table 2, the content of N2 gas is higher after ventilation, which is considered to be because N2F2 was decomposed into N2 and F2 due to heating.

In addition, the condition of the lining surface of the column 1 after the Nh gas ventilation was observed, and 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
IIIm, length 300+nm) was used as it was without lining with solid fluoride, and the column was filled with type 3 shown in Table 3 having a particle size of 24 to 32 mesh.
Filled with metal particles shown in the table (filling height 250 mm) Example 1 NFI gas containing N and F was applied under the conditions shown in Table 3
As in ~3, approximately the same volume of lleHe gas was added and vented. The gas after ventilation has a concentration of 1fi as in Examples 1 to 3.
After bubbling into a Kl aqueous solution of fi%, Example 1
NF3 was liquefied and collected by introducing it into a collection cylinder cooled with liquid nitrogen in the same manner as in 3. After stopping the ventilation of Nh gas, the inside of the NF collection pump was evacuated to remove 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 Nih is removed, the yield of NF2 is poor.

Reference Example 1 A stainless steel cylindrical container (column) with an inner diameter of 10 and a loading length of 300 + nrl was filled with commercially available zeolite (a granular product with a pore size of 5 and a particle size of 24 to 48 mesh) (packed bed of 25
0 mm), then the NF obtained in Example 3 from which NJz was removed and gas were bubbled through the zeolite layer. The ventilation conditions are room temperature (approximately 20℃) and Nh gas flow rate of 2ON.
rd/min, and the ventilation pressure of the cuff was 60 Torr.

The composition of the NF3 gas after ventilation was analyzed by gas chromatography. The result is that the impurity content is Nth
1 Qppm or less, N, Q loppm or less, Co,
The amount of 82F is as small as 10 ppm or less, and if NF and gas from which 82F has been removed in advance by the method of the present invention are purified using a conventionally known adsorbent, impurities other than NzFz, such as N, O, and CO□, can be removed at an extremely high rate. It is understood that highly purified NF is obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a state in which the four walls of a cylindrical container (column) are lined with solid fluoride in an example. In the figure, 1-...--metal cylindrical container (column), 2
・−・・−−NF, gas outlet pipe, total−・・・・−・
・Inner cylinder, 4-...--One solid fluoride, 5--...--Press-fit tube, 6------Auxiliary cylindrical tube, 7-... Fixed board, indicates.

Claims (2)

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