KR101025074B1 - Method for producing high purity liquid chlorine - Google Patents

Abstract

An object of the present invention is to provide a method for mass production of high purity liquid chlorine containing almost no hydrogen chloride, water and carbon dioxide with excellent production efficiency.

In order to solve the above problems, the present invention is to distill the liquid chlorine under pressure, to separate the outflow gas into a liquefied component and a gaseous substance in the cooler, and to transfer some or all of the liquefied component as a liquid chlorine to the product receiving tank. A method of producing high-purity liquid chlorine comprising: providing a bypass in the middle of a pipe connecting a liquid outlet port of the cooler and a liquid chlorine tank, and placing a part of the liquefied component in an infrared absorbance measurement flow cell installed in the bypass. By collecting and measuring the impurity concentration in the liquefied component, it provides a method for producing high purity liquid chlorine characterized in that the liquefied component whose impurity concentration reaches the target value is transferred to the product storage tank. According to this, high purity liquid chlorine of 2 ppm or less of water, 5 ppm or less of hydrogen chloride and 2 ppm or less of carbon dioxide can be easily obtained, and such high purity liquid chlorine is very suitable for the semiconductor manufacturing process.

Description

Manufacturing Method of High Purity Liquid Chlorine {METHOD FOR PRODUCING HIGH PURITY LIQUID CHLORINE}

The present invention relates to a high purity liquid chlorine having a very low content of impurities used for removing hydroxy groups in the manufacture of semiconductors, for example, etching of single crystal silicon films and the like, and the manufacture of optical fiber materials, and a method for producing the same. In the high purity liquid chlorine of the present invention, only very small amounts of impurities such as hydrogen chloride, water and carbon dioxide, as well as molecular oxygen and molecular hydrogen, are contained. Moreover, the manufacturing method of this invention employ | adopts distillation means.

In addition, in the following description, molecular oxygen, molecular hydrogen, etc. may be called oxygen gas, hydrogen gas, etc., and molecular chlorine may be called simply chlorine.

Chlorine gas is produced together with casein soda by electrolysis of saline solution, whereby crude chlorine gas containing relatively large amounts of water, oxygen gas and hydrogen gas is obtained. Such crude chlorine gas is removed from water by, for example, contact with concentrated sulfuric acid, and then purified by chlorine gas or liquid chlorine having a purity of about 99% by various methods. The crude chlorine gas after the removal of water usually contains 2 to several% of oxygen gas, 0.1 to 0.2% of hydrogen gas, and 0.4 to 0.6% of carbon dioxide gas. The method of removing it in the process of making it into liquid chlorine once and then vaporizing is common (for example, refer patent document 1).

As another purification method for crude chlorine gas, chlorine in crude chlorine gas is dissolved in low temperature water to form a chlorine hydrate crystal and separated from gas other than chlorine, and then the crystal is warmed to obtain high purity chlorine. The method of obtaining a gas is also known (refer patent document 2).

In addition, Patent Literature 3 discloses the content of supplying crude liquid chlorine to a distillation column and driving off oxygen gas and the like by heating in the distillation column. Further, in Patent Document 4, crude chlorine gas is adsorbed to an adsorbent such as zeolite or activated carbon by a pressure swing adsorption method, and impurities other than chlorine and chlorine are separated by their adsorptive difference, and then the boiling point is distilled. A purification method for removing low gas is disclosed.

On the other hand, the chlorine gas used as a dry etching agent in a semiconductor manufacturing process is very few impurities. In particular, since hydrogen chloride, water, oxygen gas, and carbon dioxide adversely affect the single crystal silicon film, in the case of chlorine gas used for this purpose, the content of such impurities at the ppm level becomes a problem.

For example, oxygen gas, hydrogen chloride, and water have a problem of oxidizing a semiconductor wafer surface, and may also cause corrosion of gas piping and etching apparatus. Or, there was a problem that carbon dioxide is also contaminated by solid carbon that forms the wafer surface. Therefore, the chlorine gas for a semiconductor manufacturing process should be what refine | purified the chlorine gas or liquid chlorine obtained by the above-mentioned refinement | purification method further, As the purification method for this, the following method was employ | adopted.

That is, Patent Document 5 proposes to pass chlorine gas through a purification apparatus filled with an acid-treated zeolite to remove impurities in the gas, and to use the chlorine gas obtained through this for etching in a semiconductor manufacturing process. have.

In addition, Patent Document 6 discloses a method of removing hydrogen chloride and water in chlorine gas by bringing chlorine gas into contact with a molded body containing iron oxide as a main component. However, in the case of the adsorption method described above, deterioration of the function of the adsorbent is inevitable, and as compared with, for example, distillation method, the adsorption method is not cost-effective as a means for purifying a large amount of chlorine.

[Patent Document 1] Japanese Patent Application Laid-open No. S50-128696 (claims)

[Patent Document 2] Japanese Patent Laid-Open No. S53-31593 (claims and bottom right section of page 2)

[Patent Document 3] Japanese Patent Laid-Open No. 2002-316804 (claims and paragraphs [0003] to [0008] of the second page)

[Patent Document 4] Japanese Patent Laid-Open No. H9-132401 (paragraph 6 on page 6 and FIG. 10 on page 12)

[Patent Document 5] Japanese Patent Application Laid-open No. S52-65194 (claims)

[Patent Document 6] Japanese Patent Application Laid-open No. H8-119604 (claims)

The present invention aims to provide a method for mass-producing high purity liquid chlorine containing almost no impurities, particularly hydrogen chloride, water and carbon dioxide, which can be used, for example, in a semiconductor manufacturing process.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, the technical means which was not employ | adopted in the refinement | purification of the conventional chlorine, ie, chlorine distilled liquid chlorine and gasified again in the condenser, and at this time, By means of removal to the outside of the system, the inventors have found that high-purity liquid chlorine can be efficiently produced in large quantities, and have completed the present invention.

That is, the present invention is a high-purity liquid consisting of distilling liquid chlorine under pressure, separating outflow gas into a liquefied component and a gaseous substance in a cooler, and transferring some or all of the liquefied component as liquid chlorine to a product receiving tank. As a method for producing chlorine, a bypass is provided in the middle of a pipe connecting the liquid outlet port of the cooler and a part of the liquefied component is collected in an infrared absorbance measurement flow cell installed in the bypass. It is a manufacturing method of high purity liquid chlorine characterized by measuring the impurity density | concentration in a liquefied component, and conveying the liquefied component whose impurity concentration reached the target value to the product storage tank.

(Effects of the Invention)

According to the present invention, high purity liquid chlorine of 2 ppm or less of water, 5 ppm or less of hydrogen chloride, and 2 ppm or less of carbon dioxide can be easily produced, and water and hydrogen chloride contained in the liquid chlorine to be produced are appropriately selected by distillation conditions in the present invention. Or content of carbon dioxide etc. can also be changed according to the objective.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of one Embodiment of the distillation apparatus in this invention, and the infrared absorbance measurement flow cell built in it.

2 is an example of an absorption spectrum in which infrared absorbance is measured for high purity liquid chlorine obtained in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

1: rectification tower

2: condenser

3: non-condensing gas discharge pipe

4: infrared absorbance measurement flow cell

5: product tank

6: flow meter

7: initial oil discharge pipe

8: liquid chlorine supply pipe

9: hot water supply pipe

10: hot water discharge pipe

11: cold water supply pipe

12: cold water discharge pipe

Hereinafter, the present invention will be described in more detail. Purification of the liquid chlorine in the present invention is basically performed by distillation. In the present invention, a distillation column, a condenser, and a product holding tank are required as the equipment for the distillation. In order to measure the concentration, an infrared spectrophotometer and an infrared absorbance measuring flow cell need to be embedded in the distillation system.

There is no restriction | limiting in particular about a distillation method, Any method of batch distillation or continuous distillation may be used, and either distillation or rectification may be sufficient. What is necessary is just to select these suitably according to the high and low degree of production amount, or the purity of the liquid chlorine made into the objective.

EMBODIMENT OF THE INVENTION Below, this invention is demonstrated using FIG. 1 which shows one Embodiment of this invention. In Fig. 1, a rectifying column 1 is used as the distillation column. As the rectifying column, a filling type filled with a glass filler is preferable in that metal impurities are not easily mixed in chlorine, but a general lathe type can be used. The theoretical theoretical stage of a rectification tower is two or more stages. It is preferable that the heating of the liquid chlorine supplied to the bottom of the rectification column is performed by hot water at about 35 to 40 ° C supplied from a hot water tank (not shown). In addition, the pressure inside the column is preferably 1.1 to 2.0 MPa.

The vaporized component passes through the condenser (2). As the condenser, a multi-tube condenser having a plurality of tubes in a cylindrical container, for example, a refrigerant is allowed to flow into the tube, a cooled gas is flowed into the cylindrical container, and heat exchanged is preferable. In the present invention, a discharge port 3 (non-condensing gas discharge pipe) for removing the non-condensable gas from the condenser 2 is attached, and the gas which is not condensed in the condenser 2 is removed from the system through this. The main components contained in the non-condensable gas are oxygen gas, carbon dioxide, nitrogen gas, and the like. In addition, most of the moisture contained in liquid chlorine as an impurity is converted into hydrogen chloride by reaction with chlorine during rectification in a rectifying column.

The number of inner tubes in the multi-tube condenser is not particularly limited, but usually about 20 to 20 are sufficient. As a refrigerant | coolant, cold water of 10 degrees C or less is preferable.

The oil fraction liquefied in the condenser 2 is monitored by an infrared absorbance measurement flow cell 4 provided immediately after the condenser 2 and an infrared spectrophotometer (not shown). The infrared absorbance measurement flow cell 4 is arranged and connected with a pipe branched from a pipe constituting the distillation system, that is, a bypass, so that the oil can be collected into the flow cell without being in contact with the outside air. The oil content sealed in the flow cell is measured by an infrared spectrophotometer, and the concentration of impurities inherent in the infrared absorption is measured from the absorbance at a specific wave number in the spectrum. As an infrared spectrophotometer, although the thing used for general use can be used, the measuring device of a Fourier transform system is preferable at the point which can measure a high sensitivity in a short time. For example, the MAGNA750 type infrared spectrophotometer manufactured by Nikolesa Co., Ltd. which can measure the absorbance to 0.0001 with an S / N ratio of 4000-2000 cm <^-1> wavenumber is 1: 10000 or more.

As a flow cell, it is preferable that it is a material which does not corrode easily with respect to chlorine, and has some pressure resistance. It is preferable that the internal pressure of a flow cell withstands the pressure of 1.5-2.0 MPa. Moreover, as an infrared transmission window board, calcium fluoride, sapphire, or quartz which is high in hardness and excellent in pressure resistance, without penetrating into chlorine is preferable. Although the material of a cell body is not specifically limited, It is preferable that it is excellent in corrosion resistance, such as stainless or Hastelloy. The length of the optical path of the cell is preferably 5 to 40 mm, and may be appropriately selected according to the performance of the infrared spectrophotometer and the lower limit of quantification required.

The oil content coming out of the said capacitor | condenser 2 is selected as the whereabouts are few with few impurities contained in it. That is, part of it is usually returned to the distillation column as reflux, and the remainder is sent to the product storage tank 5 as liquid chlorine which has been purified entirely. In the case of batch rectification, during the period from the start of the rectification to the end time, the flow is converted at the start, and the water in the liquid chlorine is reacted with chlorine to convert the water into hydrogen chloride, while the oil from the condenser 2 Monitor with infrared spectrophotometer. After confirming that the impurity concentration in the oil is stabilized, a portion of the oil is further refluxed to the distillation column, and the other oil is discharged out of the system through the initial oil discharge pipe (7). The impurity concentration is continuously monitored while the initial oil flows out, and after confirming that the target purity is reached, the highly purified liquid chlorine oil is sent to the product reservoir.

When the single distillation is employed in the present invention, reflux is unnecessary, and the oil from the condenser is monitored by an infrared spectrophotometer, and only the cut between the initial oil and the high boiling oil is required. In any case of short distillation or rectification, when the purity of the oil from the condenser 2 is low, the oil may be discharged out of the system through the initial oil discharge pipe 7 as necessary.

In the case of continuous distillation, a long time after the start of distillation, a washing operation to the inside of the apparatus is performed, and at this time, it is preferable to remove the oil from the condenser through the initial oil discharge pipe (7). Thereafter, while distilling the non-condensable gas out of the system continuously, distillation conditions can be selected so as to obtain the desired purity of liquid chlorine, thereby allowing continuous distillation.

As an impurity monitored by an infrared spectrophotometer, water, hydrogen chloride, or carbon dioxide is preferable. For the measurement of the concentration of water, hydrogen chloride or carbon dioxide, it is preferable to use infrared absorption of the wave number of water 3710 cm ^-1 hydrogen chloride 2830 cm ^-1 carbon dioxide 2340 cm ^-1 . In addition, an example of the infrared absorption spectrum measured with respect to the high purity liquid chlorine manufactured by the method of this invention is as showing in FIG. Impurity concentration is calculated | required by a conventional method from the infrared absorption in the wave number corresponding to each impurity.

The molar extinction coefficient of each impurity component necessary for converting the absorbance measured for the impurity measurement into the concentration can be obtained by a method generally used in the absorbance photometric method. That is, the unit optical path length or the absorbance per unit molar concentration may be obtained by using a standard sample in which a certain amount of the impurities are dissolved in a substance having a solvent characteristic similar to liquid chlorine, such as carbon tetrachloride.

The concentration of oxygen gas or nitrogen gas in the high purity liquid chlorine obtained by the present invention can be measured by gas chromatography or the like, but usually all are reduced to below the detection lower limit. In the present invention, it is preferable to select distillation conditions so that high purity liquid chlorine of 2 ppm or less of water, 5 ppm or less of hydrogen chloride, or 2 ppm or less of carbon dioxide can be obtained which can be used very suitably for semiconductor production. Furthermore, it is more preferable if it is high purity liquid chlorine of 0.4 ppm or less of water, 1 ppm or less of hydrogen chloride, and 1 ppm or less of carbon dioxide.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Chlorine (hereinafter, referred to as `` raw material chlorine '') in which chlorine (liquefied chlorine) is liquefied by air pressurization of chlorine produced and dried in an electrolytic cell of salt (1) is a packed column type rectification tower in a distillation apparatus as shown in FIG. 300 kg). According to a separate infrared absorption spectrum analysis, the raw material liquid chlorine contained impurities of 2.1 ppm of water and 1.9 ppm of hydrogen chloride.

The distillation machine was heated to 40 degreeC, commutation operation was started, and the infrared absorption spectrum measurement of the oil introduced into the flow cell was carried out, carrying out switching flow. Three hours after commencement of the conversion, the water was reduced to 0.8 ppm and the hydrogen chloride was increased to 8.9 ppm. In the meantime, it is assumed that water in liquid chlorine reacted with chlorine and changed to hydrogen chloride.

Subsequently, after removing 30 kg of the initial oils in the discharge pipe 7 at the reflux ratio 2, the amount of impurities in the effluent was measured, and the water content was reduced to 0.4 ppm of water and 1.3 ppm of hydrogen chloride. Subsequently, the total amount of the effluent was introduced into the product container 5 as the main oil. The recovered liquid chlorine had a yield of 260 kg and a yield of 87%. As a result of measuring the infrared absorption spectrum with respect to the obtained high purity liquid chlorine, water, hydrogen chloride, and carbon dioxide content were 0.33 ppm, 0.95 ppm, and 0.51 ppm, respectively.

In addition, the infrared absorption spectrum measurement conditions used for the measurement of the impurity concentration in liquid chlorine in the above example are as follows.

○ Measurement condition

   Apparatus: MAGNA750 type Fourier transform infrared spectrophotometer manufactured by Nikolesa

Wave range of measurement: 4000 to 2100 cm ^-1

Resolution: 4cm ^-1

   Total number of times: 128 times

Parameters used for quantitative calculations: molar extinction coefficient water 35M ^-1 cm ^-1 (3710cm ^-1 )

Molar extinction coefficient: Hydrogen chloride 12M ^-1 cm ^-1 (2830cm ^-1 )

Molar extinction coefficient: CO2 120M ^-1 cm ^-1 (2340cm ^-1 )

   Specific gravity of liquid chlorine: 1.44

○ flow cell

   Material of cell body: Hastelloy

   Material of infrared transmission window: Sapphire (Effective light receiving surface: Diameter 15mm)

   Inner volume of cell: 1ml

   Light path length: 1cm

The high purity liquid chlorine obtained by the present invention has a very low concentration of moisture and hydrogen chloride, and is very suitable for the manufacture of a dry etchant for a semiconductor wafer or an optical fiber material.

Claims (4)

The liquid chlorine is distilled under pressurization, the outflowing gas is separated into a liquefied component and a gaseous substance in a cooler, and a part or all of the liquefied component is transferred to the product receiving tank as liquid chlorine. In the manufacturing method, a bypass is provided in the middle of the pipe connecting the liquid outlet port of the cooler and the liquid chlorine tank, and a part of the liquefied component is collected in an infrared absorbance measurement flow cell installed in the bypass. The method for producing high purity liquid chlorine, wherein the impurity concentration in the liquid is measured and the liquefied component whose impurity concentration reaches the target value is transferred to the product storage tank. The method for producing high purity liquid chlorine according to claim 1, wherein one or two or more kinds of water, hydrogen chloride or carbon dioxide are selected from the impurities of the liquefied component and the concentration thereof is measured. A method for producing high purity liquid chlorine, wherein the concentrations of water, hydrogen chloride and carbon dioxide are measured by the method according to claim 1 or 2, wherein the concentration of water, hydrogen chloride and carbon dioxide is 2 ppm or less, 5 ppm or less, and 2 ppm or less, of carbon dioxide. A method for producing high purity liquid chlorine, wherein the concentrations of water, hydrogen chloride and carbon dioxide are measured by the method according to claim 1 or 2 to make 0.4 ppm or less of water, 1 ppm or less of hydrogen chloride, and 1 ppm or less of carbon dioxide.

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