JP2014185111A - High-purity 2,2-difluorobutane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-purity 2,2-difluorobutane suitable as a gas for plasma reactions targeting semiconductors.SOLUTION: A high-purity 2,2-difluorobutane suitable as a gas for plasma reactions can be acquired past a rectifying step of purifying a crude 2,2-difluorobutane included within a crude reaction product until the purity thereof and combined contents of fluorobutenes and 2-butyne therein become 99.9 vol.% or above and 800 vol.ppm or below, respectively, a step of removing water from the purified product based on the contact thereof with an adsorbent, and a step of abating, by simple-distilling the 2,2-difluorobutane, nitrogen and oxygen concentrations within the 2,2-difluorobutane to 100 vol.ppm or below and 50 vol.ppm or below, respectively.

Description

  The present invention is a fluorine-containing alkane useful as a gas for plasma reaction such as etching, chemical vapor deposition (CVD) or the like, a fluorine-containing pharmaceutical intermediate, or a hydrofluorocarbon solvent useful in the field of manufacturing semiconductor devices. , 2-difluorobutane. Highly purified 2,2-difluorobutane is particularly suitable for plasma etching gas, CVD gas, and the like in the field of manufacturing semiconductor devices using plasma reaction.

  The miniaturization of semiconductor manufacturing technology is progressing, and the line width of 20 nm and further 10 nm generation has been adopted in the most advanced process. The technical difficulty at the time of processing is also improved with miniaturization, and technical development is advanced by approach from various fields, such as a material to be used, an apparatus, and a processing method.

Against this background, we have developed a dry etching gas that can handle the most advanced dry etching processes, and we have developed monofluoromethane, which uses saturated fluorinated hydrocarbons with a low number of fluorine atoms to etch silicon nitride films. It has been found that the performance exceeds that (Patent Document 1).
Several methods are known as methods for producing 2,2-difluorobutane. In Patent Document 2, 2-butyne and hydrogen fluoride are reacted in the presence of one or more compounds selected from the group of cyclic monoterpenes, mercaptans, or phenols, A method for producing 2-difluoroalkane is disclosed.
Patent Document 3 discloses a method for producing 2,2-difluorobutane by reacting 2-butyne and hydrogen fluoride in a nonpolar solvent.
In Patent Document 4, tetrahydrogenpentafluoride, which is a hydrogen fluoride salt, is brought into contact with 2-butyne to obtain 2,2-difluorobutane.
In Patent Document 5, when hydrogen fluoride is added to 2-butyne, a coolant such as liquid nitrogen or liquefied carbon dioxide gas is introduced into the reaction system in order to suppress polymerization of raw material alkynes accompanying heat generation. A method is disclosed.

International Publication WO2009 / 123038 Japanese Patent Laid-Open No. 5-221892 Japanese Patent Application Laid-Open No. 6-1000047 Japanese Patent Laid-Open No. 8-198784 JP 2012-144473 A

  Under such a conventional technique, the present inventor, as a gas for selectively dry-etching a silicon nitride film laminated on silicon or a silicon oxide film, has obtained 2,2- When difluorobutane was used, it was confirmed that excessive hydrocarbon-based deposits were generated and the etching itself stopped. As a result of further studies, the present inventor has found that this problem occurs when 2,2-difluorobutane contains a predetermined amount or more of fluorobutenes or 2-butyne, and has completed the present invention. It was.

Thus, according to the present invention, there is provided 2,2-difluorobutane having a purity of 99.9% by volume or more and fluorobutenes and 2-butyne being 800 ppm by volume or less in total. The 2,2-difluorobutane preferably has a nitrogen content of 100 ppm by volume and an oxygen content of 50 ppm by volume or less. The 2,2-difluorobutane preferably has a water content of 50 ppm by volume or less.
The 2,2-difluorobutane of the present invention can be used as a dry etching gas.

The 2,2-difluorobutane of the present invention has a purity of 99.9% by volume or more, and the content of fluorobutenes and 2-butyne is 800 ppm by volume or less.
In the present invention, the fluorobutenes are 2-fluoro-1-butene and 2-fluoro-2-butene ((E) -2-fluoro-2-butene and (Z) -2-fluoro-2-butene). It is a generic name and one or more fluorobutenes present in 2,2-difluorobutane are all impurities.

The 2,2-difluorobutane of the present invention is prepared by, for example, a method of adding hydrogen fluoride to 2-butyne, which is a raw material alkyne, as described in US Pat. No. 2,287,934, Organic Reaction, Vol. 34, 1 (1985), the crude 2,2-difluorobutane produced by a method of treating methyl ethyl ketone with sulfur tetrafluoride can be obtained by distillation purification.
In the present invention, the purity of 2,2-difluorobutane, the content of fluorobutenes, and the content of 2-butyne are values calculated from peak areas by gas chromatography using a flame ionization detector (FID) as a detector. It is. Fluorobutenes can be identified by gas chromatography mass spectrometry. The amount of nitrogen and oxygen in 2,2-difluorobutane is a value measured by gas chromatography using a thermal conductivity detector (TCD) as a detector. The amount of water in 2,2-difluorobutane is a value measured using FT-IR.

By subjecting crude 2,2-difluorobutane produced by the above-described method to distillation purification (rectification) or the like, organic impurities such as fluorobutenes are removed. When removing organic impurities by distillation purification, a rectifying column is used. In particular, 2,2-difluorobutane (boiling point: 31-32 ° C.), fluorobutenes: 2-fluoro-1-butene (boiling point: 24 ° C.), (E) -2-fluoro-2-butene (boiling point: In order to efficiently separate (Z) -2-fluoro-2-butene (boiling point: 26 ° C.) and 2-butyne (boiling point: 27 ° C.), a rectifying column having an appropriate number of theoretical plates is used. Used. The number of theoretical plates is usually about 10 or more and about 50, preferably 20 or more. Since these fluorobutenes and 2-butyne have a boiling point of room temperature or lower, the separation from the desired 2,2-difluorobutane is apparently deteriorated due to the vaporization phenomenon in the fraction extraction line of the rectification column. . Therefore, it is preferable that the fraction extraction line and the container for storing the initial fraction are well cooled.
In the present invention, by rectification of 2,2-difluorobutane, the amount of fluorobutenes and 2-butene is 800 ppm by volume or less, preferably 400 ppm by volume or less.

The pressure at the time of rectification is a gauge pressure, and is usually from normal pressure to 10 atm, and preferably from normal pressure to 5 atm. The ratio of the reflux amount to the withdrawal amount (hereinafter sometimes referred to as “reflux ratio”) is set to a reflux ratio of 30: 1 or more in order to efficiently separate fluorobutenes that are likely to be in a gas state. preferable. If the reflux ratio is too small, the fluorobutenes and 2-butyne are not efficiently separated, and not only the improvement in the purity of 2,2-difluorobutane is reduced, but the initial fraction is increased and recovered. The total amount of 2,2-difluorobutane is reduced. On the other hand, if the reflux ratio is too large, it takes a lot of time to recover per extraction, so that the rectification itself takes a lot of time and the productivity is poor.
For purification, either a batch system or a continuous system may be adopted, but the batch system is preferably used when the production volume is small, and when the production volume is large, a continuous system that passes several rectification towers is used. Preferably employed. Moreover, you may carry out combining the extractive distillation operation which added the extraction solvent.

  Further, although depending on the reaction applied when producing 2,2-difluorobutane, when the reaction conversion rate is low and raw material recovery is required, in distillation purification, for example, in the first distillation Stepwise distillation may be performed, for example, by separating the raw material compounds and separating the fluorobutenes and 2-butyne which are the target of impurities in the second distillation. Even in that case, the reflux ratio is preferably 40: 1 or more.

Nitrogen and oxygen in 2,2-difluorobutane are purified in an inert gas of group 0 when the above-mentioned fluorobutenes and 2-butyne are removed by rectification, or 2,2- Difluorobutane can be removed by a method such as performing simple distillation to extract a fraction. In the latter method, the amount of nitrogen and oxygen in 2,2-difluorobutane remaining in the kettle can be reduced by extracting nitrogen and oxygen together with 2,2-difluorobutane by simple distillation. it can. The amount of 2,2-difluorobutane to be extracted is preferably 20 to 50%, more preferably 30 to 40%, based on weight with respect to 2,2-difluorobutane charged in the distillation still. The extracted 2,2-difluorobutane is stored and can be recovered and reused by adding to the next batch.
In the present invention, the amount of nitrogen in 2,2-difluorobutane is preferably 100 ppm by volume or less, more preferably 80 ppm by volume or less, and the amount of oxygen is preferably 50 ppm by volume or less, more preferably 30 ppm by volume. It is as follows.

Moreover, as a method for removing water in 2,2-difluorobutane, a general method such as contacting with an adsorbent can be employed. As the adsorbent, molecular sieves, alumina, or the like can be used. As described in Japanese Patent Application No. 2012-165797, molecular sieve 3A is preferable for drying mono- or difluoro hydrocarbons such as 2-fluorobutane and 2,2-difluorobutane. When the pore size of the molecular sieves 4A and 5A is large and the 2-fluorobutane molecule is taken into the pores, the effect of reducing the moisture is lowered, and the use of molecular sieves with alkalinity is 2, Since it causes deHF reaction of 2-difluorobutane, care must be taken when using any of them. The alumina is preferably activated alumina having a low crystallinity produced by heat dehydration of alumina hydrate. Prior to contacting 2,2-difluorobutane, it is preferable to activate an adsorbent such as molecular sieve or alumina by an operation such as baking, because more water can be adsorbed. By bringing 2,2-difluorobutane into contact with the adsorbent, the amount of water in 2,2-difluorobutane can be reduced to 50 ppm by volume or less. If the amount of moisture is high, moisture will remain on the processed surface after etching the substrate, which may cause peeling of the laminated film or corrosion of the embedded wiring in the wiring formation process such as copper. It is preferable to reduce as much as possible.
From this viewpoint, the water content of 2,2-difluorobutane is preferably 50 ppm by volume or less, more preferably 20 ppm by volume or less.

  By the rectification described above, the crude 2,2-difluorobutane contained in the reaction crude product has a purity of 99.9% by volume or more, and the total of fluorobutenes and 2-butyne is 800 ppm by volume or less. Next, the step of removing moisture by contacting with an adsorbent, and the simple distillation of 2,2-difluorobutane, the concentration of nitrogen and oxygen in 2,2-difluorobutane is 100 ppm by volume. Hereinafter, high purity 2,2-difluorobutane suitable for the plasma reaction gas can be obtained through the process of reducing to 50 ppm by volume or less. By controlling the amount of impurities in this way, it becomes possible to improve the processing stability during dry etching. 2,2-Difluorobutane can be applied not only to a silicon nitride film but also to silicon nitride oxide, titanium nitride, or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited the range by the following Examples. Note that “%” represents “% by weight” unless otherwise specified.

The analysis conditions adopted below are as follows.
・ Gas chromatography analysis (GC analysis)
Apparatus: HP-6890 (manufactured by Agilent)
Column: Inert Cap-1, manufactured by GL Sciences Inc., length 60 m, inner diameter 0.25 mm, film thickness 1.5 μm
Column temperature: held at 40 ° C. for 10 minutes, then heated at 20 ° C./minute, and then held at 240 ° C. for 10 minutes Injection temperature: 200 ° C.
Carrier gas: nitrogen split ratio: 100/1
Detector: FID

・ Impurity analysis (gas chromatography mass spectrometry)
GC part: HP-6890 (manufactured by Agilent)
Column: Inert Cap-1, manufactured by GL Sciences Inc., length 60 m, inner diameter 0.25 mm, film thickness 1.5 μm
Column temperature: held at 40 ° C. for 10 minutes, then heated at 20 ° C./minute, then held at 240 ° C. for 10 minutes MS part: 5973 NETWORK made by Agilent
Detector EI type (acceleration voltage: 70eV)
¹ H and ¹⁹ F-NMR measuring apparatus: JNM-ECA-400 (manufactured by JEOL Ltd.) 400 MHz
・ Nitrogen and oxygen (gas chromatography analysis)
GC part: HP-7890 (manufactured by Agilent)
Column: HP-5 made by Agilent Co., Ltd. Length 30 m, inner diameter 0.32 mm, film thickness 0.25 μm
Column temperature: held at 40 ° C. for 5 minutes, then heated up at 5 ° C./minute, then held at 65 ° C. for 1 minute Gas sampler: 50 ° C.
Carrier gas: Helium detector: TCD + pulse discharge type, moisture measurement (FT-IR)
IG-1000 (Otsuka Electronics Co., Ltd.)
Cell length: 10m

[Production Example 1]
A pump for supplying raw materials and a hydrogen fluoride cylinder were connected to a 5 L autoclave equipped with a stirrer and a stainless steel cooling tube. The autoclave was immersed in a dry ice / ethanol bath and the temperature was kept at -70 ° C. A −30 ° C. refrigerant was circulated in the cooling pipe. 1400 g of hydrogen fluoride was supplied from a hydrogen fluoride cylinder and liquefied in an autoclave. The stirrer was started to rotate, and 1280 g of 2-butyne was dropped from the raw material container via a pump over 2 hours, and 350 g of the remaining 2-butyne was added at −30 ° C. for about 1.7 hours, and a total of 1630 g was supplied. After the completion of 2-butyne addition, the autoclave was heated to 0 ° C. and stirring was continued for about 1.5 hours. When the contents were analyzed by gas chromatography, the residual amount of 2-butyne was 0.84 area%. Separately, an aqueous solution in which 1530 g of potassium hydroxide was dissolved in 5000 g of water was placed in a glass reactor provided with stirring blades and cooled to −30 ° C. The contents in the autoclave were fed into this alkaline aqueous solution while being pressurized with nitrogen to neutralize unreacted hydrogen fluoride. After standing, the upper organic layer was separated and dried over calcium chloride. Calcium chloride was filtered and subjected to simple distillation to obtain 2045 g of crude 2,2-difluorobutane.
As a result of analyzing the obtained crude 2,2-difluorobutane by gas chromatography, the purity of 2,2-difluorobutane was 83 area%.

[Example 1]
1964 g of the crude 2,2-difluorobutane obtained in Production Example 1 was charged into a distillation kettle, and a KS type rectification column (manufactured by Toshin Seiki Co., Ltd., column length: 90 cm, packing: Helipak No. 1) was used. Distillation was performed. A 0 ° C. refrigerant was circulated through the condenser. The distillation kettle was heated to 50 ° C., and the whole system was refluxed for 1 hour to stabilize the inside of the system. Then, the fraction was extracted at a reflux ratio of 30: 1. The distillation kettle was appropriately heated from 50 ° C. and heated to 70 ° C. while observing the reflux condition in the condenser. As a result of gas chromatography analysis of the obtained fraction, 1237 g of 99.95 area (volume)% 2,2-difluorobutane was obtained, and (E) -2-fluoro-2-butene, and ( Z) -2-fluoro-2-butene and 2-butyne were included in 42 area (volume) ppm, 28 area (volume) ppm, and 216 area (volume) ppm, respectively.

Spectral data of 2,2-difluorobutane
¹ H-NMR (CDCl ₃ , TMS) δ (ppm) 0.97 (t, 3H), 1.27 (m, 3H), 1.42 (m, 2H)
¹⁹ F-NMR (CDCl ₃ , CFCl ₃ ) δ (ppm) -93.3 (m, 2F)

[Example 2]
1000 g of 2,2-difluorobutane distilled and purified in Example 1 was placed in a 5 L SUS316 container (inner surface: electrolytic polishing treatment) containing 200 g of molecular sieve 3A (manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature. Soaked for 20 hours.
Thereafter, a simple distillation apparatus equipped with a short column, a condenser, and a receiver was assembled on the top of a 1 L capacity SUS316 kettle, and cooling water at −10 ° C. was circulated through the condenser. The kettle was charged with 912 g of 2,2-difluorobutane from which water had been removed, and the kettle was heated to 80 ° C. The nitrogen and oxygen concentrations in 2,2-difluorobutane at this time were measured by gas chromatography and found to be 965 ppm by volume and 203 ppm by volume, respectively. When about 38% by weight of the charged 2,2-difluorobutane was withdrawn into the receiver, simple distillation was stopped and the kettle was cooled to room temperature. 2,5-fluorobutane in the kettle was charged into a 1 L manganese steel cylinder (inner surface roughness: 1S) with a diaphragm valve, and 549 g was charged. When nitrogen, oxygen, and water content in 2,2-difluorobutane were measured, they were 17 ppm by volume, 5 ppm by volume, and 20 ppm by volume.

[Example 3]
1245 g of crude 2,2-difluorobutane obtained by repeating the reaction of Production Example 1 was charged into a distillation kettle, and a KS type rectification tower (manufactured by Toshin Seiki Co., Ltd., column length: 60 cm, packing material: Helipak No. 1) Distillation was performed using A condenser at −10 ° C. was circulated through the condenser, and total reflux was performed for about 1 hour. The distillation kettle was heated from 45 to 70 ° C. in consideration of the temperature at the top of the column and the remaining amount inside the kettle. After total reflux, the fraction was extracted at a reflux ratio of 30: 1 to 15: 1. As a result, 634 g of 99.93 area (volume)% 2,2-difluorobutane was obtained. As impurities, (E) -2-fluoro-2-butene, (Z) -2-fluoro-2-butene, And 2-butyne were contained in 121 area (volume) ppm, 109 area (volume) ppm, and 492 area (volume) ppm, respectively.

[Example 4]
600 g of 2,2-difluorobutane obtained in Example 3 was immersed in 120 g of molecular sieve 3A (manufactured by Wako Pure Chemical Industries, Ltd.) for 24 hours at room temperature in a stainless steel container having a capacity of 1.2 L. A stainless steel container and a 1 L-capacity manganese steel cylinder were connected with a stainless steel tube, and 2,2-difluorobutane was filled into the cylinder under reduced pressure through a metal filter having a pore diameter of 0.2 μm. The cylinder was cooled with ice water, and about 120 g of 2,2-fluorobutane was extracted through a pressure controller while reducing the pressure with a vacuum pump under a pressure of 5 to 10 kPa. After returning to room temperature and allowing to stand for a while, the nitrogen, oxygen, and moisture contents in 2,2-difluorobutane were measured and found to be 28 ppm by volume, 14 ppm by volume, and 41 ppm by volume, respectively.

[Reference Example 1]
920 g of crude 2,2-difluorobutane obtained by repeating the reaction of Production Example 1 was charged into a distillation kettle, and a KS type rectification tower (manufactured by Toshin Seiki Co., Ltd., column length: 60 cm, packing material: Helipak No. 1) Distillation was performed using A condenser at −10 ° C. was circulated through the condenser, and total reflux was performed for about 1 hour. The distillation kettle was heated at 45 to 70 ° C. in consideration of the temperature at the top of the column and the remaining amount inside the kettle. After total reflux, the fraction was extracted at a reflux ratio of 10: 1. As a result, 487 g of 99.91 area% 2,2-difluorobutane was obtained, and (E) -2-fluoro-2-butene, (Z) -2-fluoro-2-butene, and 2- Butine was contained in 223 area (volume) ppm, 206 area (volume) ppm, and 639 area (volume) ppm, respectively. Thereafter, the same operation as in Example 4 was performed, and 342 g of 2,2-difluorobutane was filled in the cylinder. When nitrogen, oxygen, and water content in 2,2-difluorobutane were measured, they were 33 ppm by volume, 19 ppm by volume, and 32 ppm by volume, respectively.

[Example 6]
Dry etching evaluation: Using a wafer having a silicon nitride film formed on the surface and a wafer having a silicon oxide film formed on the surface, each wafer was etched separately. Then, the etching rates of the silicon nitride film and the silicon oxide film were measured, and the selection ratio (SiN film / SiO ₂ film) was obtained from the etching rate ratio of the silicon nitride film to the silicon oxide film based on these measurement results.
A wafer with a silicon nitride film formed on the surface and a wafer with a silicon oxide film formed on the surface were set in an etching chamber of a parallel plate plasma etching apparatus, respectively, and the system was evacuated. Etching was performed under the following etching conditions using the prepared 2-fluorobutane. The results are shown in Table 1.

Etching conditions Pressure of mixed gas: 6.7 Pa
High frequency power supply of upper electrode: 200W
High frequency power supply power of lower electrode: 100W
Distance between upper electrode and lower electrode: 50 mm
Electrode temperature: 20 ° C
Gas flow rate O ₂ gas: 60 sccm
2,2-difluorobutane: 40 sccm
Etching time: 180 seconds [Example 7]
Etching evaluation was performed in the same manner as in Example 6 except that 2,2-difluorobutane was replaced with that prepared in Example 4. The results are shown in Table 1.

[Comparative Example 1]
Etching evaluation was performed in the same manner as in Example 6 except that 2,2-difluorobutane was replaced with that prepared in Reference Example 1. The results are shown in Table 1.

Claims (4)

2,2-difluorobutane having a purity of 99.9% by volume or more and a total of 800% by volume or less of fluorobutenes and 2-butyne. The 2,2-difluorobutane according to claim 1, wherein the nitrogen content is 100 ppm by volume and the oxygen content is 50 ppm by volume or less. The 2,2-difluorobutane according to claim 1 or 2, wherein the water content is 50 ppm by volume or less. Use of 2,2-difluorobutane according to any one of claims 1 to 3 as a dry etching gas.