KR20030060319A - a method of purifying nitrogen trifluoride by zeolite mixing - Google Patents

Abstract

PURPOSE: Provided is a method for purifying nitrogen trifluoride (NF3) gas by effectively removing N2O and CO2 contained in the nitrogen trifluoride gas by using zeolite mixture (molecular sieve 5A and molecular sieve 13X). CONSTITUTION: The method comprises the step of passing nitrogen trifluoride gas containing impurities through an adsorbent layer made out of zeolite mixture being consisted of molecular sieve 5A zeolite and molecular sieve 13X zeolite at temperature of -100-50°C.

Description

Method for purifying nitrogen trifluoride using zeolite mixing {a method of purifying nitrogen trifluoride by zeolite mixing}

The present invention relates to a method for purifying nitrogen trifluoride to remove other impurities in the manufacturing process of nitrogen trifluoride (NF ₃ ) using zeolite mixture, more specifically, Molecular 5A and Molecular 13X was mixed in one column to allow NF ₃ containing impurities such as N ₂ O and CO ₂ to pass through the adsorbed bed at an appropriate temperature so as to separate impurities from the NF ₃ gas.

In general, NF ₃ gas is used as a dry etchant for semiconductor manufacturing, CVD equipment cleaning, rocket propellant, and the like, and NF ₃ gas used in these applications is required to have high purity.

On the other hand, NF ₃ gas is produced by various manufacturing methods, for example, a method of electrolysis of molten salt of ammonium fluoride, a method of reacting ammonium fluoride with gaseous fluorine in the molten state, ammonium fluoride or acidic NH ₄ F-HF using ammonium and hydrogen fluoride as raw materials, or molten salt electrolysis in KF-NH ₄ F-HF system in which potassium fluoride or acidic potassium fluoride is added thereto.

However, in most cases of the above method, the obtained NF ₃ gas contains a large amount of impurities such as nitrous oxide (N ₂ O), carbon dioxide (CO ₂ ), dinitrogen difluoride (N ₂ F ₂ ), and has a high purity of 99.99% or more. To produce a product that requires a refining process is required.

In general, there are two methods for removing impurities in NF ₃ gas: membrane application using membrane and adsorbent use. The double electron method is difficult to apply due to the difficult regeneration and manufacturing techniques. In view of these aspects, the latter method, which can be economically used, is currently used mainly.

As the method of using the adsorbent, a method of adsorbing and removing these impurities using an adsorbent such as synthetic zeolite, activated carbon, activated alumina, and the like is generally known. In particular, the synthetic zeolite disclosed in US Pat. No. 4,156,598 provides the impurities. It is known to adsorb relatively efficiently.

However, in the case of the synthetic zeolite of the US patent, for example, Molecular Sieve 5A has a problem that the adsorption capacity of N ₂ O is high but the adsorption capacity of CO ₂ is small. Molecular Sieve 13X) has a problem that the adsorption capacity of CO ₂ is large but the adsorption capacity of N ₂ O is small.

Therefore, in order to effectively remove N ₂ O and CO ₂ in the NF ₃ gas, a method of sequentially removing each impurity by sequentially installing adsorbents having a large removal capability has been used.

The present invention is directed towards a devised in view of the conventional actual circumstances, such as the above, and an object is by using a zeolite to produce a high-purity NF ₃ gas by removing impurities such as the N ₂ O or CO ₂ contained in the NF ₃ gas effectively It is to provide a nitrogen trifluoride purification method using a zeolite mixture.

The present invention in order to attain the object of the N ₂ O, CO ₂ a NF ₃ containing impurities such as with excellent adsorption performance for the N ₂ O and CO ₂ at a suitable temperature molecular sieve 5A and molecular particulate rush 13X is mixed in one column to pass through the packed adsorption layer to separate impurities from the NF ₃ gas, which will be described in more detail below.

The present invention is a mixture of two adsorbents that selectively adsorb only specific molecules according to the selective adsorption capacity and tendency of zeolite among many adsorbents, that is, the pore structure characteristics of minerals and the shape, size and polarity of molecules. It is to maximize the adsorption characteristics.

In other words, the nitrogen trifluoride purification method of the present invention is a nitrogen trifluoride (N ₂ O) and nitrogen trifluoride (NF ₃ ) containing carbon dioxide (CO ₂ ) at a temperature of -100 ~ 50 ℃ Molecular 5A and Molecular Two zeolites of Rive 13X are passed through the adsorbent bed mixed and filled at a constant rate to remove N ₂ O and CO ₂ .

The zeolites used in the present invention are Molecular 5A and Molecular 13X in which water is completely removed, and the suitable particle size for use as the adsorbent is 1 to 100 mesh, preferably 8 to 40 mesh.

The present invention removes impurities by ventilating a nitrogen trifluoride gas containing an impurity gas in an adsorbent layer in which two zeolites of molecular 5A and molecular 13X are mixed and filled at a constant ratio at a temperature of -100 to 50 ° C. The most preferred embodiment of the present invention is to perform water removal and adsorption purification of NF ₃ gas in the same vessel.

That is, the zeolite is filled in a suitable container or column with a desired particle size distribution to form an adsorbent layer, followed by heat treatment while inert gas is blown through the adsorbent layer, and after the heat treatment, the zeolite is cooled out without leaving the vessel. followed by a method of venting the NF ₃ gas to the zeolite adsorbent layer at a temperature of -100 ~ 50 ℃ is preferred.

In the present invention, the purification of the NF ₃ gas is carried out by aeration through a zeolite adsorbent layer filled in a column or the like as described above, wherein the aeration temperature at this time is preferably 50 ° C. or lower, and aeration at 50 ° C. or higher. Not only does the content of N ₂ O in the NF ₃ gas after aeration not sufficiently decrease, but the adsorption amount of N ₂ O in the NF ₃ gas per unit volume of zeolite greatly decreases, which is not good.

Therefore, the lower the aeration temperature is preferable, but the boiling point of the NF ₃ is -129 ℃, since it is practically difficult to operate below this temperature should be carried out in the range of -100 ℃ or more.

As the material of the container or glass in which the zeolite adsorbent layer is filled in the present invention, conventional materials such as stainless steel, copper, nickel and iron can be used.

Meanwhile, in the present invention, the aeration conditions of the zeolite adsorbent layer will be described in more detail as follows.

That is, the diameter of the zeolite adsorbent layer is preferably about 1 to 50 cm, the height of the adsorbent layer is preferably about 5 cm to 2 m, the gas flow rate is about 5 to 500 ml / min, and the special limitation on the pressure of the NF ₃ gas at the time of aeration. It is preferable because the pressure of 0 ~ 10kg / cm ² -G is easy to operate.

When the NF ₃ gas intended for the present invention is purified, the impurity content in the gas can be 0 to 5 ppm of N 2 O and 0 to 5 ppm of CO 2, and these analytical values are numerical values performed by gas chromatography (DID).

Example 1

A 10 cm diameter stainless steel column is filled with 400 mm by filling a 50 mm by weight mixture of spherical zeolite molecular 5A and molecular sieve 13X each having a particle size of 8 to 12 mesh with water completely removed. At aeration temperature of 10 ° C., NF ₃ containing 2% N ₂ O and 2% CO ₂ was aerated at breakthrough time at a flow rate of 150 ml / mim.

Example 2

Under the same adsorbent bed filling conditions as in Example 1, the aeration temperature was changed to 0 ° C., and NF ₃ was vented to the adsorbent layer until the breakthrough time under the same aeration conditions as in Example 1.

Example 3

Under the same adsorbent bed filling conditions as in Example 1, the aeration temperature was changed to −10 ° C., and NF ₃ was vented to the adsorbent layer until the breakthrough time under the same aeration conditions as in Example 1.

Example 4

Under the same adsorbent bed filling conditions as in Example 1, the aeration temperature was changed to −20 ° C., and NF ₃ was vented to the adsorbent layer until the breakthrough time under the same aeration conditions as in Example 1.

The breakthrough time described above means that if the adsorbent has good adsorption ability when the gas containing impurities is adsorbed and removed by adsorbing the adsorbent layer, the impurity content in the gas immediately obtained through the gas passage is small, and is constant or gradually gradually. Although the state of increase continues, when the adsorbent loses the adsorption capacity, the impurity content starts to increase rapidly. As such, the aeration time until the adsorbent loses the adsorption capacity and the content of impurities starts to increase rapidly.

The above-described respective examples and the respective comparative examples to be described later which one was the aeration time to more than 20ppm time as the breakthrough time, N ₂ O, to the breakthrough time by the respective embodiments described above CO _2, NF of the impurity The adsorption amount of ₃ is shown in Table 1.

Example 1 Example 2 Example 3 Example 4 Aeration condition Temperature (℃) 10 0 -10 -20 Zeolite content MS-5A (wt%) 50 50 50 50 MS-13X (wt%) 50 50 50 50 Breakthrough time N ₂ O (min) 253 334 352 359 CO ₂ (min) 273 345 350 352 Adsorption amount until breakthrough time N ₂ O (ml) 759 1002 1056 1077 CO ₂ (ml) 819 1035 1050 1056 NF ₃ (ml) 0 0 0 8

As a result of purification according to each example as shown in Table 1, N ₂ O and CO ₂ in NF ₃ was removed very well, the breakthrough time was also relatively long, and the lower the aeration temperature, the better the adsorption capacity of impurities.

Comparative Example 1

Under the same adsorbent bed filling conditions as in Example 1, the aeration temperature was changed to 60 ° C., and NF ₃ was vented to the adsorbent layer until the breakthrough time under the same aeration conditions as in Example 1.

Comparative Example 2

Embodiment and first absorbent layer changes the zeolite blend ratio of the filling conditions molecular particulates to rush probe 5A 100% by weight, such as, the NF ₃ by aeration under the same conditions as in Example 1 in a state in which change in the aeration temperature was 0 ℃ the absorbent layer Aerated until breakthrough time.

Comparative Example 3

The zeolite mixing ratio in the adsorbent layer filling conditions as in Example 1 was changed to 80% by weight of molecular 5A, 20% by weight of 13X in molecular weight, and the aeration temperature was changed to 0 ° C as in Example 1. Under aeration conditions, NF ₃ was allowed to air through the adsorbent layer until the breakthrough time.

Comparative Example 4

The zeolite mixing ratio of the adsorbent layer filling conditions as in Example 1 was changed to 20% by weight of Molecular 5A, 13X 80% by weight, and the aeration temperature was changed to 0 ° C. Under aeration conditions, NF ₃ was allowed to air through the adsorbent layer until the breakthrough time.

Comparative Example 5

Embodiment and first absorbent layer changes the zeolite blend ratio of the filling conditions molecular particulates to rush probe 13X 100% by weight, such as, the NF ₃ by aeration under the same conditions as in Example 1 in a state in which change in the aeration temperature was 0 ℃ the absorbent layer Aerated until breakthrough time.

Table 2 shows the adsorption amounts of N ₂ O, CO ₂ , and NF ₃ up to the breakthrough time according to the comparative examples.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Aeration condition Temperature (℃) 60 0 0 0 0 Zeolite content MS-5A (wt%) 50 100 80 20 0 MS-13X (wt%) 50 0 20 80 100 Breakthrough time N ₂ O (min) 31 340 298 143 0 CO ₂ (min) 27 0 112 286 352 Adsorption amount until breakthrough time N ₂ O (ml) 93 1020 894 429 0 CO ₂ (ml) 81 0 336 858 1056 NF ₃ (ml) 0 0 0 0 0

As shown in Table 2 above, in Comparative Example 1 in which the aeration temperature of NF ₃ gas was changed to 60 ° C. exceeding 50 ° C. or lower, which is a proper aeration temperature, the breakthrough time was very short and the adsorption amount up to the breakthrough time was as follows. Very few lost industrial applicability.

In addition, when using Molecular 5A and Molecular 13X alone without mixing, as in Comparative Example 2 and Comparative Example 5, it was observed that only one impurity was superior to each other. If the adsorbent is used alone, a new investment cost, such as a new adsorption bed is required, causing a loss in commercial terms.

However, when the two zeolite adsorbents are used over a certain ratio as in each of the above-described Examples, Comparative Examples 3 and 4, each impurity can be easily removed because it acts on both impurities.

As described above, the present invention comprises a zeolite adsorption layer by mixing the molecular 5A and the molecular 13X, the NF ₃ containing impurities such as N ₂ O, CO ₂ in the zeolite adsorption layer at a suitable temperature Impurities can be separated from the NF ₃ gas by passing through the present invention. According to the present invention, impurities such as N ₂ O and CO ₂ can be simultaneously removed through a zeolite mixed adsorption layer packed in one column. In addition, it is possible to obtain an effect such as being able to purify a high quality NF ₃ gas at low cost.

Claims (1)

Aeration temperature of nitrogen trifluoride (NF ₃ ) containing impurity gas in the zeolite mixed adsorbent layer filled with 10 to 90% by weight of two zeolites, Molecular 5A and Molecular 13X, in which water is completely removed. Nitrogen trifluoride purification method using a zeolite mixture, characterized in that aeration at a temperature of 100 ~ 50 ℃.