JP2005187312A - Removal method of silicon tetrafluoride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of reducing silicon tetrafluoride contained in carbonyl difluoride to a quantity as low as it will not affect in judging the end point of cleaning. <P>SOLUTION: In this refining method of carbony difluoride, silicon tetrafluoride is removed by contacting a gas mixture containing the silicon tetrafluoride and the carbony difluoride with a metal fluoride in a gaseous state or a supercritical state at 60-250°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to carbonyl difluoride having a reduced content of silicon tetrafluoride, particularly carbonyl difluoride suitable for use as a cleaning gas.

  The present invention also relates to a method for removing carbonyl difluoride from carbonyl difluoride and purifying carbonyl difluoride. More specifically, the present invention relates to a method for purifying carbonyl difluoride used as a cleaning gas, particularly for semiconductor manufacturing.

  Carbonyl difluoride is useful as a cleaning gas during semiconductor production. Silicon tetrafluoride is exhausted as a product together with unreacted cleaning gas when the CVD chamber is cleaned with carbonyl difluoride or the like. In general, the end point of cleaning is determined from the amount of silicon tetrafluoride discharged. However, if silicon tetrafluoride is included in the cleaning gas in advance, it is difficult to determine the end point.

For example, to clean the CVD chamber, O ₂ in addition to COF ₂ is also performed normally be flowed simultaneously, further, the exhaust gas from the chamber, in general, be evacuated with a dry pump (diaphragm pump), this Sometimes the exhaust gas is diluted with a large amount of N ₂ . Thereafter, the concentration of SiF ₄ is analyzed by FTIR or the like. If the amount of SiF ₄ derived from the raw material is, for example, 100 ppm or more in the exhaust gas after dilution, it becomes difficult to confirm the end point of cleaning, and the cleaning is completed. The cleaning process is performed for a longer time than necessary.

  Therefore, it is desirable that the amount of silicon tetrafluoride in the cleaning gas is such that it does not affect this determination. Therefore, it is necessary to remove silicon tetrafluoride from carbonyl difluoride.

Conventionally, carbonyl difluoride has been obtained as a by-product when a perfluoroolefin having a double bond at its terminal, such as hexafluoropropylene, is oxidized with oxygen and converted to an epoxy compound such as hexafluoropropylene oxide. In addition, SiF ₄ is contained together with carbonyl difluoride derived from a silicon compound such as SiO ₂ or glass or the like compounded to suppress decomposition / dislocation of the epoxy compound (Patent Documents 1 and 2). ). SiF ₄ was produced together with carbonyl difluoride produced as a by-product, and the content of SiF ₄ was considerably large, and at least 0.1 mol% or more was contained.

Further, Patent Document 3 discloses a method of removing HCl and HF by bringing COF ₂ and NaF into contact with each other, but does not show that silicon tetrafluoride is removed. Further, some examples contain 1 mol% of SiF ₄ even after contact with NaF, and it is impossible to predict that SiF ₄ can be removed by NaF from the literature.

Non-Patent Document 1 describes that, in the section of chemical characteristics of silicon tetrafluoride, silicon tetrafluoride and NaF react with each other to produce sodium silicate hydrofluoride (Na ₂ SiF ₆ ). No mention is made of conditions or removal of silicon tetrafluoride in carbonyl difluoride.
JP-A-6-247950 US3639429 US2836622 GAS DATA BOOK Sixth Edition Matheson, 636-639

  An object of the present invention is to treat a mixed gas containing silicon tetrafluoride and carbonyl difluoride to reduce the amount of silicon tetrafluoride to an amount that does not affect the determination of the end point of cleaning.

  As a result of repeated studies in view of the above problems, the present inventor made a reaction by reacting a mixed gas containing silicon tetrafluoride and carbonyl difluoride with an alkali metal fluoride or an alkaline earth metal fluoride in a specific temperature range. It was found that silicon fluoride was removed and high-purity carbonyl difluoride was obtained.

The present invention provides the following carbonyl difluoride and a purification method thereof.
1. Carbonyl difluoride, wherein the content of silicon tetrafluoride in the carbonyl difluoride is 0.05 mol% (500 ppm) or less.
2. Item 2. The carbonyl difluoride according to Item 1, wherein the content of silicon tetrafluoride is 0.01 mol% (100 ppm) or less.
3. Item 3. The carbonyl difluoride according to Item 1 or 2, wherein the content of silicon tetrafluoride is 0.005 mol% (50 ppm) or less.
4). Item 4. The carbonyl difluoride according to any one of Items 1 to 3, which is used as a chamber cleaning gas for a semiconductor manufacturing apparatus.
5). Silicon tetrafluoride is removed by bringing a mixed gas containing silicon tetrafluoride and carbonyl difluoride into contact with a metal fluoride at 60 ° C. to 250 ° C. in a gas state or a supercritical state. Method for purifying carbonyl.
6). The content of silicon tetrafluoride in carbonyl difluoride before purification is 0.1 mol% (1000 ppm) or more, and the content of silicon tetrafluoride in carbonyl difluoride after purification is 0.05 mol% ( Item 6. The method according to Item 5, which is 500 ppm or less.
7). Item 7. The method according to Item 6, wherein the content of silicon tetrafluoride in the carbonyl difluoride after purification is 0.01 mol% (100 ppm) or less.
8). Item 8. The method according to Item 7, wherein the content of silicon tetrafluoride in the carbonyl difluoride after purification is 0.005 mol% (50 ppm) or less.
9. Item 9. The method according to any one of Items 5 to 8, wherein the metal fluoride is at least one selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides.
10. Item 5-9, wherein when the mixed gas containing silicon tetrafluoride and carbonyl difluoride is brought into contact with the metal fluoride, the gas and / or metal fluoride is heated to remove silicon tetrafluoride. The method according to any one.
11. Item 11. The method according to any one of Items 5 to 10, wherein the temperature at which the mixed gas containing silicon tetrafluoride and carbonyl difluoride is brought into contact with the metal fluoride is 80 ° C to 250 ° C.
12 Item 12. The method according to any one of Items 5 to 11, wherein the metal fluoride is an alkali metal fluoride.
13. Item 13. The metal gas fluoride is brought into contact with the metal fluoride by causing a gas mixture containing silicon tetrafluoride and carbonyl difluoride to flow through the container containing the metal fluoride. the method of.

Hereinafter, the present invention will be described in more detail.

  The mixed gas containing silicon tetrafluoride and carbonyl difluoride can be obtained as an object or a by-product according to the methods described in Patent Documents 1 to 3, for example.

The ratio of the mixed gas containing silicon tetrafluoride and carbonyl difluoride before purification to which the method of the present invention is applied is COF ₂ : SiF ₄ = 99.9 to 90 mol%: 0.1 to 10 mol%. . If there is too much SiF ₄ in the mixed gas, it will be difficult to separate high-purity COF ₂ gas that can be used as a cleaning gas during semiconductor manufacturing. If there is too little SiF ₄ , the need for separation and purification will be reduced. It is.

The mixed gas of carbonyl difluoride and SiF ₄ contains HFC such as CHF ₃ , PFC such as CF ₄ and C ₂ F ₆ , acidic gas such as HF, CO ₂ , N ₂ , O _{2 and the} like up to about 10 mol%. You may do it.

The ratio of SiF ₄ in the purified carbonyl difluoride obtained in the present invention is usually 0.05 mol% (500 ppm) or less, preferably 0.01 mol% (100 ppm) or less, more preferably 0.005 mol% (50 ppm) or less. It is. If the ratio of SiF ₄ exceeds 0.05 mol% (500 ppm), it becomes difficult to determine the end point of cleaning. This is due to the following reasons.

That is, for cleaning the CVD chamber, in addition to COF ₂ , O ₂ is allowed to flow at the same time, and exhaust gas from the chamber is generally exhausted using a dry pump (diaphragm pump). It is diluted with N _2. Thereafter, when the concentration of SiF ₄ is analyzed by FTIR, the typical flow rate ratio at this time is about 1: 0.5: 10 to 20 for COF ₂ : O ₂ : N ₂ , and about COF ₂ is about Dilute 10-20 times. Therefore, SiF ₄ originally contained in COF _{2 is} also diluted 10 to 20 times.

The SiF ₄ concentration used for determining the end point varies from case to case, but is at most about 0.04 mol% (400 ppm) or less, usually about 0.01 mol% (100 ppm) or less. If the initial concentration of SiF _{4 in} COF ₂ used for the cleaning gas is 0.1 mol% (1000 ppm), the exhaust gas contains 0.005 to 0.01 mol% (50 to 100 ppm) of SiF _4. Thus, when the determination of the end point is SiF ₄ concentration 0.01 mol% (100 ppm), it is difficult to determine the end point.

Next, when the SiF ₄ initial concentration in the COF ₂ used for the cleaning gas is 0.05 mol% (500 ppm), the SiF ₄ concentration in the exhaust gas becomes 0.0025 mol to 0.005 mol% (25 to 50 ppm), The end point can be roughly determined. When the initial concentration of SiF _{4 in} COF ₂ used for the cleaning gas is 0.01 mol% (100 ppm), the concentration of SiF _{4 in} the exhaust gas is 0.0005 to 0.001 mol% (5 to 10 ppm), and there is almost no problem. I can judge. When the initial concentration of SiF _{4 in} COF ₂ used for the cleaning gas is 0.005 mol% (50 ppm), the concentration of SiF _{4 in} the exhaust gas is 0.00025 to 0.0005 mol% (2.5 to 5 ppm), which is a problem. There will be no level.

Preferred examples of the metal fluoride used for removing silicon tetrafluoride include alkali metal fluorides and alkaline earth metal fluorides. Examples of the alkali metal fluoride include LiF, NaF, KF, and CsF, and examples of the alkaline earth metal fluoride include CaF ₂ , MgF ₂ , BaF ₂ , and SrF ₂ . As the alkali metal fluoride, LiF, NaF, KF, and CsF which are alkali metal fluorides are particularly preferable. Further, NaF is most preferable from the viewpoint of availability. These metal fluorides are preferably selected from pellets, granules and powders. If the pellet is too large, the removal efficiency of silicon tetrafluoride is deteriorated. If the powder is too small, it is difficult to remove the powder. Therefore, the pellet is preferably smaller than 10 mm in diameter and about 10 mm in height. A diameter larger than about 100 μm is selected. Metal fluoride, and immediately after the removal of the SiF4, it can be removed by such as a filter, etc. when filling in a bomb or to transfer the COF ₂ removal of the SiF ₄ to the storage tank.

  Before being used, the metal fluoride can remove adsorbed or absorbed moisture by heating at an appropriate temperature of about 100 ° C. to 300 ° C. under a nitrogen stream or reduced pressure or both. Water is consumed by the hydrolysis of carbonyl difluoride and causes carbon dioxide and hydrogen fluoride to be generated. Carbon dioxide gas moves to the next step together with carbonyl difluoride, but a small amount of moisture is allowed because most of the hydrogen fluoride can be removed by the metal fluoride.

  As an embodiment, carbonyl difluoride containing silicon tetrafluoride is put in a storage tank containing a metal fluoride, and is left for a certain period of time or stirred with a stirring device such as a screw, and then carbonyl difluoride from the gas phase. A batch-type removal method, which is a method for extracting the carbon fluoride, and a continuous removal method, which is a method for circulating a carbonyl difluoride gas containing silicon tetrafluoride at a certain flow rate by heating a container containing a metal fluoride, are possible. When the purity of the resulting purified carbonyl difluoride gas is insufficient, the silicon tetrafluoride content may be further reduced through a container containing metal fluoride again. In order to increase the efficiency of both the batch removal method and the continuous removal method, a large amount of gas can be processed in a short time by increasing the pressure of the gas to be processed and increasing the density. Although there is no restriction | limiting in particular as a pressure at this time, Considering the pressure | voltage resistance of an apparatus, etc., it is thought that it is suitable to about 10 MPaG (G shows a gauge pressure). A preferable pressure is 0 to 10 MPaG, more preferably 0.1 to 8 MPaG, and particularly preferably 1 to 4 MPaG.

  The method of the present invention removes silicon tetrafluoride by contacting a solid metal fluoride with a mixture of carbonyl difluoride and silicon tetrafluoride in a gas state (including high density gas) or supercritical state, It is characterized by purifying carbonyl difluoride. In the case of performing purification with stirring in a batch system, it is preferable to perform the stirring with stirring of a metal fluoride solid with a stirring device such as a screw.

  The removal temperature in the batch type and the continuous type is selected from 60 ° C to 250 ° C, preferably 80 ° C to 250 ° C, more preferably 100 ° C to 200 ° C. If the temperature is too low, the removal efficiency of silicon tetrafluoride is deteriorated and the time required for the treatment becomes long, which is uneconomical. Moreover, the higher the temperature, the better the removal efficiency. However, if the temperature is too high, it will heat more than necessary, which is also uneconomical and may also cause deterioration of the equipment. The treatment time is selected from 1 minute to 480 minutes, preferably 2 minutes to 300 minutes, more preferably 3 minutes to 200 minutes. The ratio of the carbonyl difluoride to be treated and the metal fluoride varies depending on the content of silicon tetrafluoride in the carbonyl difluoride. 0.01 mol to 20 mol, preferably 0.02 mol to 10 mol, and more preferably 0.5 mol to 5 mol are selected with respect to 1 mol of carbonyl chloride. If silicon tetrafluoride exceeds 1 mol%, 1 mol to 2000 mol, preferably 2 mol to 1000 mol, and more preferably 5 mol to 500 mol are selected with respect to 1 mol of silicon tetrafluoride contained.

  The amount of silicon tetrafluoride that does not affect the determination of the end point of cleaning during semiconductor production is preferably 0.05 mol% (500 ppm) or less, more preferably 0.01 mol% (100 ppm) or less, and even more preferably 0. 0.005 mol% (50 ppm) or less. If silicon tetrafluoride is 0.05 mol% (500 ppm) or less, particularly 0.01 mol% (100 ppm) or less, the determination of the end point of cleaning is not affected.

  According to the present invention, silicon tetrafluoride contained in carbonyl difluoride can be easily reduced to an amount that does not affect the determination of the end point of cleaning.

Hereinafter, the present invention will be described in more detail based on examples (method for analyzing silicon tetrafluoride).
A gas cell with a window material of CaF ₂ and a cell length of 10 cm was evacuated to −0.1 MPaG with a gauge pressure, and then gas was introduced until it became −0.06 MPaG, followed by quantitative determination by FT-IR (manufactured by PERKIN ELMER). . Quantitation was calculated from the change from the initial value of the absorbance of approximately 1030 cm ^-1 in the silicon tetrafluoride based on the absorption of approximately 2200 cm ^-1 of carbonyl difluoride.
Example 1
Examples 1-4, Comparative Example 1
In a stainless steel container with a capacity of about 20 ml, 0.1 g of metal fluoride is put in, vacuumed while being heated to about 100 ° C., cooled with dry ice, and difluoride containing 0.4 mol% of silicon tetrafluoride. 0.24 g of carbonyl was charged. This was allowed to stand at 80 ° C. for 3 hours, and then the concentration of silicon tetrafluoride was measured by FTIR. The results are shown in Table 1.

Examples 5 to 11, Comparative Examples 2 and 3
97 g of NaF pellets (3 mmφ × 3 mm) were charged into a stainless steel reaction tube having an outer diameter of 3/4 inch. While heating the reaction tube to a predetermined temperature with a heater, a predetermined flow rate of carbonyl difluoride was passed while adjusting with a mass flow meter. The gas after distribution was sampled, and the concentration of silicon tetrafluoride was measured by FTIR. The results are shown in Table 2. The results in Table 2 are values when the concentration of silicon tetrafluoride is stabilized after sampling several times.

Claims (13)

Carbonyl difluoride, wherein the content of silicon tetrafluoride in the carbonyl difluoride is 0.05 mol% (500 ppm) or less. The carbonyl difluoride according to claim 1, wherein the content of silicon tetrafluoride is 0.01 mol% (100 ppm) or less. The carbonyl difluoride according to claim 1 or 2, wherein the content of silicon tetrafluoride is 0.005 mol% (50 ppm) or less. The carbonyl difluoride according to any one of claims 1 to 3, which is used as a chamber cleaning gas for a semiconductor manufacturing apparatus. Silicon tetrafluoride is removed by bringing a mixed gas containing silicon tetrafluoride and carbonyl difluoride into contact with a metal fluoride at 60 ° C. to 250 ° C. in a gas state or a supercritical state. Method for purifying carbonyl. The content of silicon tetrafluoride in carbonyl difluoride before purification is 0.1 mol% (1000 ppm) or more, and the content of silicon tetrafluoride in carbonyl difluoride after purification is 0.05 mol% ( The method according to claim 5, which is 500 ppm or less. The method according to claim 6, wherein the content of silicon tetrafluoride in the carbonyl difluoride after purification is 0.01 mol% (100 ppm) or less. The method according to claim 7, wherein the content of silicon tetrafluoride in the carbonyl difluoride after purification is 0.005 mol% (50 ppm) or less. The method according to claim 5, wherein the metal fluoride is at least one selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides. 10. The silicon tetrafluoride is removed by heating the gas and / or metal fluoride when the mixed gas containing silicon tetrafluoride and carbonyl difluoride is brought into contact with the metal fluoride. The method in any one of. The method according to any one of claims 5 to 10, wherein the temperature at which the mixed gas containing silicon tetrafluoride and carbonyl difluoride is brought into contact with the metal fluoride is from 80C to 250C. The method according to claim 5, wherein the metal fluoride is an alkali metal fluoride. The mixed gas and the metal fluoride are brought into contact with each other by flowing a mixed gas containing silicon tetrafluoride and carbonyl difluoride through a container containing the metal fluoride. The method described.