JP2002363115A - Recycling method of perfluoro compound by low temperature purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient low-temperature purifying system suppressing an energy load for recycling components useful as perfluoro compounds(PFC) for a semiconductor production process from a PFC mixture containing an inert low-boiling component. SOLUTION: This method for recycling comprises prefeeding a high-boiling fluoride (5) into a rectifying device, thereby reducing energy required for cooling, isolating the useful PFC components in the PFC mixture with the recrifying device, filling the components in containers (10), (11) and (12) for each component so as to be feedable for reutilizing as the PFC for the semiconductor production process when the recovered PFC mixture is separated with the rectifying device provided with a condenser (9), a separating tank (4), a heater (6) and a connecting pipe (7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing CF ₄ (methane tetrafluoride) and C ₂ as useful components from a gas mixture containing various PFCs (perfluoro compounds) discharged from a semiconductor manufacturing process or the like. The present invention relates to a PFC recycling method using a low-temperature purification system, which enables F ₆ (ethane hexafluoride) to be efficiently isolated and supplied as a recycled PFC.

[0002]

2. Description of the Related Art Various PFCs have been used as an etching agent in an etching step for manufacturing semiconductors or the like, or as a plasma cleaning agent in a CVD step or the like. Exhaust gas discharged from such a process is generally composed of a large amount of nitrogen or other inert gas, used unreacted gas, acidic gas (HF, SiF ₄ , COF _2, etc.) generated by the reaction, and oxidizing gas. (O ₃ , F _2, etc.).
The release of acidic gases into the atmosphere causes air pollution such as acid rain, destruction of the ozone layer by chlorofluorocarbons, so-called perfluorocarbons and hydrofluorocarbons (HFCs),
It is necessary to treat these exhaust gases from the viewpoint of global warming due to SF ₆ or the like.

Conventionally, the acidic gas and the oxidizing gas in the mixed gas discharged as described above have been treated by a method using a predetermined chemical, a method using a predetermined apparatus, or the like. However, the exhaust gas after removing the acidic gas and the oxidizing gas is in a state in which PFC and HFC are diluted with a large amount of nitrogen and the like, and it is not possible to isolate useful PFC components from the exhaust gas for reuse. Have difficulty. Techniques such as membrane separation and adsorption separation have been reported as methods for collecting and concentrating PFC or HFC and nitrogen from the exhaust gas.
In these conventional techniques, PFC and HFC and nitrogen can be separated and concentrated, but separation into a single component gas is difficult, and is not always satisfactory for reuse in a semiconductor manufacturing process. That is the fact.

[0004] Recently, a technique has been reported in which PFC and HFC are absorbed in a cleaning solution at a low temperature and rectification is performed therefrom (see Japanese Patent Application Laid-Open No. 11-142053). Although this technique has a high recovery rate and a high enrichment rate, it is expected that there are many problems in terms of cost due to the large size of the apparatus to be installed adjacent to a semiconductor factory. In order to separate a mixed gas of PFC and HFC to a high purity state for each gas component, rectification at a low temperature is a known fact. However, rectification utilizes a difference in boiling points between components. Very large equipment is required to isolate the components approaching. P
Many FCs and HFCs have a low boiling point, and rectification of PFCs usually requires cooling by a refrigerator or liquid nitrogen. However, the larger the equipment, the higher the cost and the more difficult it is to commercialize.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a high-efficiency low-temperature purification system in which a PFC mixture containing an inert low-boiling component is treated with a high-efficiency low-temperature purification system in view of the above-mentioned problems related to the prior art. Another object of the present invention is to provide a method for efficiently isolating useful PFC components in the PFC mixture and supplying the PFC components as recycled PFC by low-temperature purification of PFC.

[0006]

In order to achieve the above object, the present inventors have developed a rectification method which has been conventionally performed, and have effectively combined other methods to carry out a wide variety of tests. The research and development were completed, and the present invention was completed.

That is, the present invention has achieved the above object by providing the following PFC recycling method. The purification system having a condensing section, a separating section, a heating section, and a connecting section connecting the condensing section and the separating section has a PFC.
(Perfluoro Compound) Specific PFC from mixture
A method of recycling a PFC in which components can be isolated and supplied for reuse, comprising: 1) introducing a high-boiling fluoride into the purification system and pre-cooling the purification system; Feeding the PFC mixture into the purification system; 3) discharging the gaseous inert low-boiling component from the condensing section; 4) isolating a specific PFC component by the condensing section; A method of filling each separated PFC component into a container so that the PFC component can be supplied as a recycled PFC.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a PFC recycling method of the present invention will be described with reference to the drawings. PFC of the present invention
As a purification system for carrying out the recycling method of the present invention, specifically, for example, as shown in FIG.
A separation tank (4), a heater (6) for heating the separation tank (4),
In addition, a rectification column composed of a connecting pipe (7) connecting the condenser (9) and the separation tank (4) is used.

In carrying out the PFC recycling method of the present invention using the above rectification column as a purification system,
First, a high boiling point fluoride (5) is introduced into the rectification column, and the inside of the rectification column is pre-cooled.

[0010] Exhaust gas (PFC mixture) is sent directly to the rectification tower
Once it enters, it is necessary for the gaseous state to be liquefied.
Energy required to cool the rectification tower
A large amount of liquid nitrogen is needed for the condenser (9). So
Here, the temperature range existing in the liquid state in the rectification column is wide
High boiling point fluoride (5) is introduced in advance and the high boiling point fluoride
By storing (5) in a liquid state in the separation tank (4),
It pre-cools the inside of the rectification column. Thus the rectification tower
High boiling point introduced into the rectification column by pre-cooling the inside
Fluoride (5) can reduce the sensible heat of exhaust gas
The amount of liquid nitrogen required for cooling
Less than half of what would have been done without
Can be. High-boiling fluoride (5) introduced into the rectification column
Is propane octafluoride (C_ThreeF₈), Octafluorocyclo
Butane (C_FourF₈), Ethylene difluorochloride (C_TwoHC
IF _Two) Is used, and among these,
(C_ThreeF₈Is preferred.

[0011] The pre-cooled rectification column is charged with PF
Feed in the C mixture. The PFC mixture is a flow controller
It is fed into the connecting pipe (7) of the rectification column via the introduction pipe (1) provided with (2).

As the PFC mixture, a gas mixture containing various PFCs recovered from exhaust gas discharged from a semiconductor manufacturing process (such as an etching step or a CVD step) is used. Since the gas mixture uses an inert low-boiling component such as nitrogen as a purge gas and a carrier gas in a semiconductor manufacturing process, the gas mixture contains such an inert low-boiling component.

Before the PFC mixture is sent to the rectification column, the acidic gas (HF, S
iF ₄ , COF _2, etc.) and oxidizing gases (O ₃ , F _2, etc.) are removed, and PFC is further concentrated. The PFC is concentrated to a certain degree (PFC concentration is preferably 50 to 100%, more preferably (90 to 100%). As a method for removing these acidic gases and oxidizing gases, there are a scrubber method using a chemical solution, a removal method using a solid adsorbent, a heat oxidation removal method, a thermal decomposition removal method, and the like, and a removal method using a solid adsorbent is particularly preferable. . Also,
Examples of the PFC concentration method include a concentration method by membrane separation, a concentration method by adsorption, and the like, and a concentration method by membrane separation is preferable.

The gas mixture containing various PFCs recovered from the exhaust gas discharged from the semiconductor manufacturing process includes CHF ₃ , SF ₆ , NF in addition to CF ₄ and C ₂ F _6.
3 , C ₂ F _{4 and} other gases. The boiling points of CF ₄ and NF ₃ are close to each other, and C ₂ F ₆ and CHF
₃ , SF ₆ and C ₂ F ₄ also have close boiling points. Main PF
The boiling point of C is shown in Table 1 below. The gas mixture is C
F ₄ , C ₂ F ₆ and inert low-boiling components (N ₂ ) make up the majority, while other PFC gases are in small amounts. However, since these small amounts of PFC become impurities and hinder recycling, it is preferable to remove them before sending them to the rectification column. Known methods for removing these substances include removal by thermal decomposition, removal using a catalytic reaction,
Although there are removal by adsorption, etc., the main components CF ₄ and C ₂
In view of the fact that F ₆ is selectively removed without being decomposed, it is preferable to remove by thermal decomposition, and it is preferable to further fill the inside with a drug in order to further increase thermal efficiency and remove decomposition products. It is desirable to use activated carbon or soda lime. When activated carbon is used as a drug, it is preferably 500 to 800 ° C, more preferably 600 to 70 ° C.
The gas mixture is preferably brought into contact with activated carbon at 0 ° C., and when soda lime is used as a drug, preferably 300 to 600 ° C., more preferably 400 to 500 ° C.
The gas mixture and the soda lime are preferably brought into contact with each other.
When PFC as the impurity is removed, CF ₄ , C ₂
There are three types of gas, F ₆ and an inert low-boiling component (N ₂ ), which are sent to a rectification column.

[0015]

[Table 1]

Since the rectifying operation uses a gas-liquid equilibrium state utilizing a boiling point difference, the PFC components (CF ₄ , C ₂ F ₆ ), which are the target components of the PFC mixture for recycling, are separated.
(4) It is liquefied inside, and inert low-boiling components such as nitrogen in the PFC mixture are discharged out of the system. That is, the PFC mixture sent into the connection pipe (7) of the rectification tower is connected to the connection pipe (7).
To the condenser (9), and the PFC components (CF ₄ , C ₂ F ₆ ) which are the target components for recycling in the PFC mixture
Is liquefied in the condenser (9) and stored in the separation tank (4),
The inert low-boiling component (N ₂ ) in the PFC mixture is discharged out of the system without being liquefied in the condenser (9).

The connecting pipe (7) is preferably filled with a filler (8) for enhancing gas-liquid contact, whereby the rectification efficiency can be improved and the energy efficiency can be improved. As the packing material (8), a packing material used in a normal rectification step can be used, but the corrosion resistance and the gas-liquid contact efficiency (filling height, inner diameter of the column, etc.) can be improved. In consideration of the above, it is preferable to use an ordered packing made of metal. Further, the material is particularly preferably SUS316L, and the shape is a structure having a regular space such as a wire mesh inside. It is desirable that the outer shape is cylindrical according to the diameter.

The removal of the inert low-boiling components can be carried out after all the PFC mixtures have been received, provided that the amount of the inert low-boiling components in the PFC mixture is small. Since a considerable amount of inert low-boiling components are contained therein, it is preferable to discharge the inert low-boiling components while receiving the PFC mixture in the rectification column. At this time, since some PFC components are discharged out of the system together with the inert low-boiling components, such PF
It is preferable that the C component is separated and recovered by, for example, a membrane separation device (3), and then sent back to the rectification column. As the membrane separation device (3), a device using a polymer membrane and / or a carbon membrane is preferable because the PFC component can be efficiently separated and recovered. As the polymer film and the carbon film, known polymer films and carbon films can be used.

The PFC component (C) stored in the separation tank (4)
F ₄ , C ₂ F ₆ ) are isolated by the condenser (9).

Further, for each isolated specific component, for example,
Methane tetrafluoride is filled in the CF ₄ storage tank (10), and ethane hexafluoride is filled in the C ₂ F ₆ storage tank (12), so that they can be supplied as recycled PFC for the semiconductor manufacturing process. At the switching point between CF ₄ and C ₂ F ₆ , CF ₄ and C ₂
Since the mixed gas is distilled out in a mixed state with F ₆ , the mixed gas is stored in a dedicated mixed gas storage tank (11). The CF ₄ and C ₂ F ₆ stored in the storage tanks are of a purity that can be supplied to the semiconductor manufacturing process, and are each in a dedicated container.
(14) is filled by the pump (13).

[0021]

EXAMPLES Examples for clarifying the energy effect and rectification effect of the method of the present invention are shown below, but the present invention is not limited to the following examples.

Example 1 <Application of Recovered Gas> As a PFC mixture, one recovered from an actually operating semiconductor manufacturing process was prepared. Table 2 below shows the composition of the PFC mixture.

[0023]

[Table 2]

<Pretreatment for purification>
And C_ThreeF₈Is introduced into the rectification column,
Although it can not be a thing, SF₆, CHF_ThreeAnd C_TwoF_FourIs large
C occupying part_TwoF ₆Impurities near the boiling point
Can be Therefore, SF₆, CHF_ThreeAnd C_TwoF
_FourWas removed before entering the rectification column. Removal, pyrolysis
The method was implemented. Soda lime as a chemical inside the digester
Fill and select by heating the temperature to 500 ℃
SF₆, CHF_ThreeAnd C_TwoF_FourWas disassembled. Removal
Check the gas chromatograph mass spectrometer (HEWLETT PACKA
RD HP5973) and Fourier transform infrared spectrophotometer (MIDAC
IGA2000). Table 3 below shows the pretreatment for purification.
Shows the composition of the PFC mixture obtained (analysis confirmed
Used).

[0025]

[Table 3]

<Precooling of the rectification column> C ₃ F ₈ was fed into the rectification column through an inlet pipe. Before the feed, since the rectification column is at room temperature, the condenser is cooled to −50 ° C. with liquid nitrogen, and C ₃ F
₈ was liquefied and placed in a separation tank.

<Acceptance to the rectification column>
After cooling with liquid nitrogen to ℃, the PFC mixture which had been subjected to the pretreatment for purification was fed to the rectification column. The composition of N ₂ was confirmed by gas chromatography, and only the amount of N ₂ was discharged out of the system without being liquefied by the condenser at the upper part of the purifier. The target components, CF ₄ and C ₂ F ₆ , reached the condenser through the filler, where they were liquefied and stored in the separation tank. Since the PFC mixture to be treated is sent from the vessel to the rectification column via the pre-purification treatment, it is switched to the next vessel when the residual gas in the vessel falls below 0.05 MPa, and the same operation is performed. Was carried out.
In this example, when the remaining gas amount in all the prepared containers was lower than 0.05 MPa, the P
The reception of the FC mixture was terminated. In Table 4 below, C ₃ F
₈ shows changes in the amount of liquid nitrogen used when pre-cooling was performed according to Fig. 8 and when gas was supplied without pre-cooling.

[0028]

[Table 4]

<Recovery of Exhausted PFC> The concentration of PFC that goes out of the system together with N ₂ discharged from the upper part of the refining apparatus was about 4%. In order to recover this, PFC was recovered using a membrane separation device using a carbon membrane.
0.1MPa, 0.3MPa pressure to feed into carbon membrane
a, 0.5 MPa, the higher the pressure, the higher the PF
Since C permeates the carbon membrane and PFC discharged out of the system together with N ₂ increases, the recovery rate decreases. 0.1MPa pressure and 30SLM flow rate
(Standard Liter Minute), 97.5% of PFC could be recovered with 10% of PFC entrained in the gas to be sent. The results are shown in Table 5 below. The recovered PFC is
It was sent back to the purification device through the inlet tube.

[0030]

[Table 5]

<Purification of PFC> Purification was carried out at 50 kPa.
It was performed at a rolling pressure. CF received in separation tank_Four, C _Two
F₆Is gasified by a heater and filled with filler.
Through the connecting pipe to reach the condenser. Set temperature of condenser
Is -140 ° C, and the gas liquefies in the condenser and passes through the connecting pipe.
Return to the separation tank. By repeating this, CF having a low boiling point_Four
To the storage tank, and then set the condenser temperature to -100 ° C.
Raise C_TwoF₆Distilled. CF_FourIs in the separation tank
When it runs out, C_TwoF₆Is mixed, so this
Accepted in a mixed gas storage tank. Stored in each storage tank
CF_Four, C_TwoF₆Are 47L and 10L containers
Was filled.

<Confirmation of gas composition>
The charged gas is analyzed by a gas chromatograph mass spectrometer
Confirmation of gas composition using d-transform infrared spectrophotometer
The results are shown. CF_Four, C _TwoF₆Both have small amounts of impurities
High-purity products can be obtained, compared to commercially available gases
Products that can be reused in semiconductor manufacturing processes.
It turned out to be a product. In addition, inductive coupling
Mass spectrometry also analyzes metal components in gas.
As a result, no metal component was detected.

[0033]

[Table 6]

[0034]

According to the method of the present invention, a PFC mixture containing an inert low-boiling component can be treated by a high-efficiency low-temperature purification system with reduced energy load, and useful PFC in the PFC mixture can be treated. The components can be efficiently isolated and supplied as recycled PFC.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a purification system for carrying out the method of the present invention.

[Explanation of symbols]

1 inlet pipe 2 flow regulator 3 membrane separator 4 separation tank 5 high boiling fluoride 6 heater 7 connecting pipe 8 filler 9 condenser 10 CF ₄ for storage tank 11 mixed gas storage tank 12 C ₂ F ₆ for tank 13 filled Pump 14 filling container

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C07C 17/38 C07C 17/38 17/395 17/395 19/08 19/08 F25J 3/02 F25J 3 / 02 A (72) Inventor Kozo Oya 1-5-13 Nishi-Shimbashi, Minato-ku, Tokyo 8th Oriental Maritime Building 8F PFC collection and reuse project room (72) Inventor Katsato Ezawa 1-5-13 Shimbashi 8th Toyo Kaiji Building 8F PFC Collection and Reuse Project Room (72) Inventor Shuji Nagano 1-5-13 Nishishinbashi 1-chome, Minato-ku, Tokyo 8th Toyo Maritime Building 8F PFC Collection and Reuse Project Room (72) Inventor Akihiko Nitta 1-5-13 Nishi-Shimbashi, Minato-ku, Tokyo 8th Toyo Maritime Building 8F PFC Collection and Reuse Project Room (72) Person Takefumi Manabe 1-5-13 Nishi-Shimbashi, Minato-ku, Tokyo 8th Oriental Maritime Building 8F PFC collection and reuse project room (72) Inventor Masatoshi Goto 1-5-13 Nishi-Shimbashi, Minato-ku, Tokyo 8F Oriental Maritime Building 8F PFC collection and reuse project room F term (reference) 4D006 GA41 KA01 KB12 KB18 KD09 KD19 MC05 PA01 PB20 PB63 PC01 4D047 AA07 BA01 BA08 BB03 BB06 CA09 DA04 EA01 4G066 AA66B CA32 DA05 ABB37A DA01 EA01 EB09 EE31 FB02 4H006 AA02 AD11 AD19 AD30 BD33 BD40 BD51

Claims (11)

[Claims] 1. A purifying system comprising a condensing section, a separating section, a heating section, and a connecting section connecting the condensing section and the separating section.
Specific P from FC (perfluoro compound) mixture
A method for recycling a PFC in which an FC component can be isolated and supplied for reuse, comprising: 1) a step of introducing a high-boiling fluoride into the purification system and pre-cooling the purification system; 2) Pre-cooling the purification system. Feeding the PFC mixture into the purification system; 3) discharging gaseous inert low-boiling components from the condensing section; 4) isolating specific PFC components by the condensing section; and 5). A process of filling each isolated PFC component into a container so that it can be supplied as recycled PFC. 2. A gaseous inert low-boiling component discharged from the condensing section is fed into a membrane separation device, and a PFC component present in the inert low-boiling component is separated and recovered, and the purification is performed. The recycling method according to claim 1, wherein the recycling method is performed again. 3. The recycling method according to claim 2, wherein the membrane separation device is configured using a polymer membrane and / or a carbon membrane. 4. The recycling method according to claim 1, wherein said high-boiling fluoride is propane octafluoride. 5. The PFC mixture comprises PFC recovered from a semiconductor manufacturing process and an inert low-boiling component, and the isolated PFC component can be supplied as a recycled PFC for a semiconductor manufacturing process. 5. The recycling method according to any one of items 1 to 4. 6. The recycling method according to claim 1, wherein the PFC mixture is brought into contact with activated carbon or soda lime before being sent to the purification system. 7. The recycling method according to claim 6, wherein the PFC mixture after contacting with the activated carbon or soda lime comprises methane tetrafluoride and / or ethane hexafluoride and an inert low-boiling component. 8. The recycling method according to claim 1, wherein the isolated PFC component is methane tetrafluoride or ethane hexafluoride. 9. The recycling method according to claim 1, wherein the inert low-boiling component is nitrogen. 10. The recycling method according to claim 1, wherein the connecting portion is filled with a filler for enhancing gas-liquid contact. 11. The recycling method according to claim 10, wherein the filler is a metal structured packing.