JP5652179B2 - Method for producing semiconductor gas - Google Patents

Description

The present invention relates to a process for producing monofluoromethane (CH ₃ F, HFC-41), and more particularly to a process involving purification by contact with a liquid.

Monofluoromethane is used as an etching agent and a cleaning agent in thin film manufacturing processes such as semiconductor industry.
As a method for producing fluorinated methane such as trifluoromethane (CHF ₃ , HFC-23), a method in which the corresponding chlorinated methane is fluorinated with hydrogen fluoride in the presence of a catalyst is industrially implemented. A method for producing methane is also known (for example, Patent Document 1). The reaction products obtained by this method generally contain hydrogen chloride, hydrogen fluoride, unreacted methyl chloride, as well as polyfluorinated products generated by fluorination or disproportionation, and increase the selectivity. For this purpose, the conversion rate is often sacrificed, and in the example of Patent Document 1, the yield is only about 20%. In addition, purification of organic components is usually performed by distillation, and Patent Document 1 shows a similar example.

  As a production method different from the halogen exchange method using hydrogen fluoride for such a halogenated hydrocarbon, a method using a decomposition / fluorination reaction of a compound having a methyl group is known. For example, methyl iodide is converted to tetra-n-butylammonium. A method of fluorinating with a fluorine salt of has been reported. It is also known that monofluoromethane is produced as a by-product when 1-methoxy-1,1,2,2-tetrafluoroethane is contacted with a catalyst to synthesize difluoroacetic acid fluoride or difluoroacetic acid ester. (Patent Literature 3, Patent Literature 4). However, in any method, purification is usually indispensable for producing monofluoromethane for the semiconductor industry, but separation of organic components other than distillation or adsorption to a solid as disclosed in Patent Document 1 is required. The method is not known.

  In this way, distillation is indispensable in any conventional method for producing monofluoromethane, and trifluoromethane, difluoromethane, etc. are produced as by-products by any method, Since trifluoromethane is relatively stable, it is easy to produce, and its boiling point (−82.1 ° C.) is close to monofluoromethane (boiling point, −78.2 ° C.), so that distillation separation is difficult.

Trifluoromethane is known as a trifluoromethylating agent in the field of organic chemistry (Non-patent Document 1, Patent Document 5, etc.), but the reactivity difference between CH ₃ F and CHF ₃ and CH ₃ F There is no description about the separation and removal method of CHF _{3 in the} medium.

WO2005 / 026090 JP 2006-111611 A JP-A-8-92162 JP 2010-064999 U.S. Patent No. 6355849

J. Org. Chem. 1991, 56 (1), 2-4

  Monofluoromethane produced or processed in the gas phase may be accompanied by trifluoromethane due to equilibrium, fluorination or disproportionation reactions, but their boiling points are close and cannot be separated efficiently by distillation. .

  Then, it replaces with distillation and provides the industrially applicable method which can manufacture the monofluoromethane which does not contain trifluoromethane substantially.

  The present inventors diligently studied a method for producing high-purity monofluoromethane, and found that trifluoromethane can be easily removed by contacting monofluoromethane containing trifluoromethane with a mixture of amide and base. The present invention has been completed.

  That is, the present invention is as follows.

[Invention 1]
A method for producing purified monofluoromethane, comprising a step of bringing a monofluoromethane composition containing at least trifluoromethane into contact with a trifluoromethane treatment liquid containing an amide and a base represented by the following general formula (1).

(Wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group, and may be bonded to each other to form a ring, and the ring carbon is substituted with an oxygen atom, a nitrogen atom or a sulfur atom) You may do it.)
[Invention 2]
Amide is formamide, N, N-dimethylformamide, N, N-diethylformamide, N, N-dipropylformamide, N, N′-dimethylethyleneurea, N, N′-dimethylpropyleneurea, N-formylmorpholine, Invention 1 which is at least one amine selected from N-formylpyrrolidine, N-formylpiperidine, acetamide, N, N-dimethylacetamide, N, N-diethylacetamide, and N, N-dipropylacetamide.

[Invention 3]
Invention 1 or 2 wherein the base is a metal alkoxide, metal hydride or silylamine compound.

[Invention 4]
Inventions 1 to 3 wherein the trifluoromethane treatment liquid is a trifluoromethane treatment liquid further containing an anion scavenger.

[Invention 5]
Invention 4 wherein the anion scavenger is a carbonyl compound, a thiocarbonyl compound, a disulfide compound or a diselenide compound.

[Invention 6]
Inventions 1 to 5 wherein the trifluoromethane treatment liquid is a trifluoromethane treatment liquid further containing a solvent inert under the treatment conditions.

[Invention 7]
The gas composition for semiconductors containing the monofluoromethane obtained with the manufacturing method of the refinement | purification monofluoromethane in any one of invention 1-6.

  The production method of the present invention can easily produce high-purity monofluoromethane substantially free of trifluoromethane. The production method of the present invention is sufficient with a simple operation and can be stably produced on an industrial scale. Furthermore, the monofluoromethane obtained by this reaction has a performance equal to or higher than that of a commercially available product as an etching agent, and can be used as a semiconductor gas.

(A) shows the cross-sectional schematic diagram of the sample for etching used in Example 11 and Comparative Example 1, and (b) shows the cross-sectional schematic diagram after etching. It is a schematic sectional drawing of the remote plasma apparatus used in Example 11 and Comparative Example 1. FIG. 11 is a schematic view of an apparatus used in Example 10.

  The present invention relates to a monofluoromethane composition (herein referred to as “crude monofluoromethane”) containing at least trifluoromethane and a composition containing an amide and a base (herein referred to as “trifluoromethane treatment liquid”). Or simply referred to as “treatment liquid”.), A process for producing purified monofluoromethane. Purified monofluoromethane refers to a monofluoromethane composition having a lower trifluoromethane content than before treatment, and is a concept that includes high-purity monofluoromethane used in the semiconductor industry.

According to Non-Patent Document 1, the reaction according to the method of the present invention is presumed that the adduct I is formed by adding the CF ₃ anion generated from trifluoromethane to the carbonyl carbon of the amide activated by the base. The Although the adduct I and the adduct II described later each have an enantiomer, these structural drawings are not intended to specify one of the enantiomers.

[Rough monofluoromethane containing at least trifluoromethane]
The crude monofluoromethane containing at least trifluoromethane used in the present invention may be obtained by any method, for example, fluorination of methane or methanol with hydrogen fluoride in the presence of a catalyst. A method in which monochloromethane is halogen-exchanged with hydrogen fluoride in the presence of a catalyst, a method in which fluorinated methane such as methane or difluoromethane is disproportionated in the presence of a catalyst, 1-methoxy-1,1,2, , 2-tetrafluoroethane may be exemplified by a method of catalytic pyrolysis to obtain with difluoroacetic acid fluoride. Even if it manufactures by any method, although a by-product is accompanied, before applying the processing method concerning this invention, it is preferable to remove components other than trifluoromethane previously. In particular, acidic components such as hydrogen fluoride, hydrogen chloride, and difluoroacetic acid fluoride increase the necessary amount of base used in the method of the present invention, and therefore should be removed before application of the method of the present invention. preferable.

  Such pre-purification performed in advance is not particularly limited and varies depending on each production method for producing monofluoromethane, but any known technique may be applied with the knowledge of those skilled in the art. For example, when the monofluoromethane obtained by the production method contains a hydrocarbon halide such as trifluoromethane and an acidic component such as hydrogen chloride or hydrogen fluoride, it is brought into contact with water or / and an alkaline aqueous solution, Then, it is preferably dried, and the content other than trifluoromethane is preferably reduced as much as possible by distillation as necessary. Here, when components other than trifluoromethane cannot be sufficiently removed by distillation, it can be distilled again after removing trifluoromethane by the treatment method according to the present invention.

  Further, monofluoromethane obtained by catalytic pyrolysis of 1-methoxy-1,1,2,2-tetrafluoroethane contains an equimolar amount of difluoroacetic acid fluoride. When this mixed gas (pyrolysis gas) is cooled, the difluoroacetic acid fluoride is condensed and easily separated into gas and liquid from monofluoromethane. Further, when the mixed gas is brought into contact with an active hydrogen compound such as water or alcohol, difluoroacetic acid fluoride is converted into high-boiling difluoroacetic acid or difluoroacetic acid ester to obtain gaseous monofluoromethane. In such treatment, normally, monofluoromethane is not subjected to decomposition or the like. When the unreacted 1-methoxy-1,1,2,2-tetrafluoroethane is contained in the crude monofluoromethane, it stays in the treatment liquid, so that the treatment such as gas-liquid separation is performed in advance or It is preferable to remove it by distillation.

  The crude monofluoromethane obtained by the pre-purification treatment may contain components other than carbon compounds such as air, but the composition is displayed excluding air and the like unless otherwise noted. The content of trifluoromethane contained in the crude monofluoromethane is not particularly limited, but is 50 mol% or less, preferably 10 mol% or less, and more preferably 5 mol% or less. Even if it exceeds 50 mol%, it can be applied, but in the case of a high content, preliminary purification by distillation or the like is efficient as a method for producing monofluoromethane.

[Trifluoromethane treatment solution]
The trifluoromethane treatment liquid is a liquid containing at least an amide and a base, and optionally contains an anion scavenger. Further, the trifluoromethane treatment liquid may contain a solvent inert under the treatment conditions.

  The amide used in the method of the present invention is an amide represented by the general formula (1). The amide may be cyclic (lactam).

In the formula, each of R ¹ , R ² and R ³ independently represents a hydrogen atom or an alkyl group, and may combine with each other to form a ring, and the ring carbon is substituted with an oxygen atom, a nitrogen atom or a sulfur atom. May be.

The alkyl group is preferably a linear, branched or cyclic alkyl group having 1 to 4 carbon atoms. Specific examples include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, an s-butyl group, and a t-butyl group. Examples of the ring formed by bonding to each other with or without an oxygen atom, nitrogen atom or sulfur atom include a pyrrolidine ring, a pyrrolidone ring, and a morpholine ring. Specific examples of such amides include formamide (H ₂ NCOH), N, N-dimethylformamide (DMF), N, N-diethylformamide, N, N-dipropylformamide, N, N′-dimethylethyleneurea. (DMEU), N, N′-dimethylpropyleneurea (DMPU), N-formylmorpholine, pyrrolidine-1-carbaldehyde (N-formylpyrrolidine), piperidine-1-carbaldehyde (N-formylpiperidine), acetamide, N , N-dimethylacetamide, N, N-diethylacetamide, N, N-dipropylacetamide, and the like. Mixtures of these can also be used. An amide such as formamide that is solid at room temperature is preferably used together with the amide that is liquid at the treatment temperature or a solvent described later. Of these amides, N, N-dimethylformamide is particularly preferable because it is easily available and easy to handle.

  The amide functions as a catalyst and a solvent in the trifluoromethane treatment liquid. Therefore, the amide can occupy 1 to 99 parts by weight out of 100 parts by weight of the treatment liquid, preferably 5 to 90 parts, and more preferably 10 to 80 parts. If the amount is less than 1 part by weight, the amount of crude monofluoromethane treated per unit volume of the processing liquid is small, leading to an increase in the size of the apparatus. Absent.

  Although the base used by the method of this invention is not specifically limited, A metal alkoxide, a metal hydride, a silylamine compound, etc. are mentioned. The metal of the metal alkoxide and metal hydride is preferably an alkali metal or alkaline earth metal, and may be a composite alkoxide or metal hydride containing an alkali metal or alkaline earth metal.

  The alkali metal or alkaline earth metal alkoxide is represented by ROM, where R represents an alkyl group, and M represents an alkali metal or an alkaline earth metal. R is a linear, branched or cyclic alkyl group having 1 to 8 carbon atoms, specifically, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i- Examples thereof include a butyl group, a s-butyl group, a t-butyl group, a hexyl group, a peptyl group, an octyl group and isomers thereof, a cyclohexyl group, and a cyclopentyl group. M is lithium, sodium, potassium, calcium, or magnesium. Specifically, potassium methoxide, potassium ethoxide, potassium isoproxide, potassium t-butoxide, sodium methoxide, sodium ethoxide, sodium isoproxide, sodium t-butoxide and the like can be exemplified. Specific examples of the alkali metal hydride include sodium hydride and potassium hydride. Two or more of these alkoxides or hydrides can be used in combination. The alkali metal hydride can be used together with alcohol. In that case, it is considered that an alkali metal alkoxide is generated in the treatment liquid. Commercially available alkoxides can be used, but it is also preferable that the alkali metal alkoxide is prepared in situ as described above.

As the silylamine compound, tris (trimethylsilyl) amine ((TMS) ₃ N), potassium bis (trimethylsilyl) ((TMS) ₂ NK), (TMS) ₂ NNa, or the like can be used. These trimethylsilylamines can also be used in combination with the alkali metal alkoxide described above. (TMS) ₃ N can be used together with tetramethylammonium fluoride ((CH ₃ ) ₄ NF), the alkali metal or alkaline earth metal alkoxide or fluoride. Examples of the fluoride include cesium fluoride and potassium fluoride.

  As the base, an alkali metal or alkaline earth metal alkoxide is preferable, and potassium t-butoxide is particularly preferable in view of safety, handleability, and availability.

  The base requires a number of moles equal to the number of moles of trifluoromethane fixed in the process of the invention. Therefore, it is preferable to adjust the amount of the base contained in the treatment liquid by the treatment amount of the crude monofluoromethane, but it is 0.1 to 30 parts by weight with respect to 100 parts by weight of the treatment liquid, and 0.5 to 20 parts by weight. 1 to 10 parts by weight is more preferable. Less than 0.1 parts by weight is not preferable because the contact efficiency is low and the absorption rate of trifluoromethane is small. When the solubility exceeds 30 parts by weight, it is possible to add to the saturated solubility, but it is difficult to recover the amide from the treatment liquid after use, and it is not preferable to exceed 30 parts by weight. Those with low solubility can be used at concentrations below their saturation solubility.

[Anion scavenger]
As shown in Scheme 1 above, trifluoromethane can form adduct I in the treatment liquid and fix trifluoromethane in the crude monofluoromethane with an equimolar amount of amide. Thus, trifluoromethane may not be sufficiently removed even in the presence of an excessive amount of amide and base. However, more trifluoromethane can be fixed by adding an anion scavenger to the treatment liquid used in the method of the present invention. Monofluoromethane blown into the treatment liquid is captured by an amide and a base as shown in Scheme 1 to form adduct I, and is captured by the treatment liquid. In Non-Patent Document 1, the adduct I is an intermediate having a high solubility because the trifluoromethyl anion apparently moves to the anion scavenger when an electrophilic agent such as the carbonyl compound is present in the treatment liquid as an anion scavenger. Presumed to be Body II. As an example, the reaction when a carbonyl compound is used as an anion scavenger is illustrated in Scheme 2.

  The anion scavenger refers to a compound having an atom to which a trifluoromethyl anion can be nucleophilically added under the reaction conditions according to the present invention. The anion scavenger may be a compound having a site capable of accepting a fluoromethyl anion as a nucleophile, and a carbonyl compound, a thiocarbonyl compound, a disulfide compound, a diselenide compound, or the like can be used. Among these, a carbonyl compound represented by the following general formula (2) is preferable because it is easy to handle.

R ^X and R ^Y in the formula each independently and independently represent a hydrogen atom, an aromatic group having or not having a substituent, or an aliphatic group having or not having a substituent, and bonded to each other to form a ring. It may be formed. Aromatic groups with or without substituents include phenyl, o-, m- or p-tolyl, o-, m- or p-ethylphenyl, o-, m- or p-fluorophenyl. Group, o-, m- or p-chlorophenyl group, o-, m- or p-methoxyphenyl group, p-phenylphenyl group and the like. Examples of the aliphatic group having or not having a substituent include alkyl groups such as methyl group, ethyl group, n-propyl group and i-propyl group, ethenyl group, propenyl group, isopropenyl group, 2-phenylethynyl group, An alkylene group such as a 3-phenylpropenyl group and an alkyne group such as an ethynyl group can be mentioned.

  Specifically, the following can be exemplified, but not limited thereto.

  Among these, a compound having no hydrogen atom on the carbon adjacent to the carbonyl group (α carbon) is preferable because of its high reactivity with the trifluoromethyl anion.

  Benzophenone or benzaldehyde is preferred as the anion scavenger, and benzophenone is particularly preferred.

Examples of the thiocarbonyl compound used as the anion scavenger include those obtained by replacing the carbonyl oxygen atom of the carbonyl compound with a sulfur atom. The disulfide compound is a compound represented by the general formula (R—S—) ₂ , and examples of R include a linear, branched or cyclic alkyl group or an aromatic ring. Examples of the alkyl group include straight-chain alkyl groups having about 1 to 20 carbon atoms. As the aromatic ring, a phenyl group or a phenyl group is substituted with a substituent (such as a methyl group, an ethyl group, a propyl group, or an isopropyl group). Can be exemplified. Examples of the diselenide compound include those obtained by replacing the sulfur atom of the disulfide compound with a selenium atom.

[solvent]
In the method of the present invention, a solvent that is inert under the processing conditions (referring to a solvent that does not form a chemical bond with the processing solution component) can be used. For example, aliphatic or aromatic hydrocarbon solvents, ether solvents and the like can be suitably used. Diethyl ether, tetrahydrofuran, 1,4-dioxane, methyl t-butyl ether, toluene, benzene, xylene, pentane, hexane, heptane , Cyclohexane, cyclopentane and the like. The solvent is preferably used when a solid reagent such as formamide is used. Since the use of a solvent lowers the amide and base concentrations, the solvent is preferably used in an amount of less than 50 parts by weight with respect to 100 parts by weight of the treatment liquid, and usually not used.

  The reagents such as amine, base, solvent, and anion scavenger described above do not have to be particularly high in purity, and may be commercially available. These are preferably dehydrated in advance.

[Processing temperature and pressure]
In the method of the present invention, the treatment temperature is -78 to + 50 ° C, preferably -20 ° C to 0 ° C. When the temperature is −78 ° C. or lower, cooling is costly and viscosity of the amide, the treatment liquid or the like becomes high or may solidify, which is not preferable. Furthermore, since monofluoromethane is liquefied at such a low temperature, operations such as swinging the pressure and temperature to recover from the processing liquid are required, and there is a disadvantage that handling becomes complicated. When the treatment temperature exceeds + 50 ° C., the solubility of the intermediate I is lowered and the amount of trifluoromethane treated is reduced, which is not preferable. Since the reaction shown in Scheme 1 or 2 does not depend on pressure, the treatment pressure may be arbitrary, and can be operated under a pressure of about 0.01 to 1 MPa or under reduced pressure. Convenient and preferred.

[Contact method]
The method of the present invention is carried out by bringing crude monofluoromethane, which is usually supplied as a gas, into contact with the treatment liquid. For contacting the monofluoromethane with the treatment liquid, a known gas-liquid contact means can be used. For example, a submerged blow type, a droplet gas contact type, or the like can be used. The apparatus for performing the contact is not particularly limited, but a counter-current or co-current gas-liquid contact apparatus such as an empty tower or a gas cleaning tower using a packed tower with a packing inside, a scrubber apparatus, etc. A bubbling device by blowing can be exemplified. Further, as a contact method, a combination of using a bubbling device after treating in a gas washing tower in advance is also effective. In the case of the bubbling method, the processing efficiency can be increased by using an apparatus that generates fine bubbles such as microbubbles and nanobubbles.

  As the container used for the contact, a normal chemical reaction container made of glass, glass lining, fluororesin, fluororesin lining, stainless steel, or the like can be used.

  The case where the method of this invention is performed in a tank type is demonstrated. Cool the vessel containing the trifluoromethane treatment liquid prepared by mixing amide and base in advance or mixing after charging to a predetermined temperature, and then introduce crude monofluoromethane from the blowing tube into the gas-liquid contact. The treated monofluoromethane is distilled from the vessel. A solvent that is inert under the processing conditions other than amide can be added to the processing solution. The anion scavenger can be added together with the amide, base and optionally a solvent before the treatment operation, but can be added intermittently or continuously with the progress of the treatment, or the treatment liquid is taken out to the outside. It can also be added in a separate container. The purified purified monofluoromethane is collected by drying, and other purification treatments such as distillation and air removal can be performed as necessary.

[Usage]
Monofluoromethane obtained by the method of the present invention has high purity and can be used as a gas for semiconductors such as an etching agent and a cleaning agent in a thin film manufacturing process in the semiconductor industry. In use, oxygen, ozone, carbon monoxide, carbon dioxide, fluorine, chlorine, bromine, iodine, nitrogen trifluoride, chlorine trifluoride, It can be used as a semiconductor gas composition in which gases such as argon, nitrogen, helium, hydrogen fluoride, hydrogen chloride, nitric oxide, ammonia, and hydrogen are mixed.

  Analysis of organic substances such as monofluoromethane was performed by a gas chromatograph (GC, FID detector), and the composition was expressed in area%.

[Example 1]
N, N-dimethylformamide (DMF, 70 ml) in a 100 ml three-necked glass container equipped with a dry ice condenser sealed with nitrogen on the atmosphere side, a blow pipe with a ball filter, a thermometer, and a soda lime pipe at the outlet, Potassium t-butoxide (t-BuOK, 5.0 g) and benzaldehyde (1.5 g) were charged to prepare a treatment liquid, which was cooled in an ice-water bath with stirring. While maintaining the temperature of the treatment liquid at −5 to 0 ° C., a mixed gas of monofluoromethane (CH ₃ F): 98.890 area% and trifluoromethane (CHF ₃ ): 1.110 area% was introduced from the blowing tube ( The gas sampled at the outlet of the soda lime tube was subjected to gas chromatographic analysis every predetermined time. The results are shown in Table 1. In the treated monofluoromethane, a trace amount of isobutylene ((CH ₃ ) ₂ C═CH ₂ ) was detected, but the other components contained trifluoromethane that had not been removed.

[Example 2-9]
Table 1 shows the results of experiments similar to Example 1 performed under the conditions shown in Table 1.

[Example 10]
The apparatus shown in the schematic diagram of FIG. 3 was used. A flow rate of 1 g / min of 1-methoxy-1,1,2,2-tetrafluoroethane in a stainless steel reaction tube with an inner diameter of 37 mm and a length of 500 mm filled with 300 ml of alumina fluorinated with hydrogen fluoride and maintained at 180 ° C. The reaction tube outlet gas (pyrolysis product) was discharged from the bypass pipe to the exhaust gas treatment device. After the composition of the pyrolysis product was stabilized after 2 hours, an absorption liquid prepared by dissolving 50 g of potassium hydroxide in 250 ml of ethanol was charged, immersed in a -30 ° C. constant temperature bath, and cooled with a 1 L PFA first The reaction tube outlet gas was blown into the gas washing bottle, then the outlet gas from the washing bottle was blown into a 1 L PFA second gas washing bottle charged with 200 ml of DMF, and the outlet gas was passed through the first soda lime pipe. . After 6 hours from the start of blowing into the absorbent, the gas that passed through the first soda lime pipe was introduced into the trifluoromethane treatment tank through the blow pipe. Gas chromatograph analysis of the gas obtained at the sampling port A provided immediately after the outlet of the first soda lime tube revealed that methane: 0.004 area%, ethylene: 0.048 area%, CHF ₃ : 0.111 area%, CH ₃ F: 99.781 area%, propylene: 0.057 area%.

  The trifluoromethane treatment tank is a 1 L glass washing bottle charged with a treatment solution prepared by dissolving 15 g of t-BuOK and benzophenone 25 in 250 ml of DMF, and equipped with a stirrer inside and cooled with an ice bath from the outside. Is equipped with a glass ball filter blow tube, a gas outlet leading to a cold finger cooled outside with dry ice grains, and a thermometer. The effluent gas from the first soda lime pipe is contacted with the treatment liquid at -5 to 0 ° C. in the trifluoromethane treatment tank, and after passing through the cold finger and the second soda lime pipe, the stainless steel trap cooled with liquid nitrogen Cooled and collected with a tube. A balloon was provided at the exit of the trap tube to keep the system at atmospheric pressure and shut it off from the outside air.

When the gas obtained at the sampling port B provided immediately after the outlet of the second soda lime tube was analyzed by gas chromatography, methane: 0.004 area%, ethylene: 0.049 area%, CHF ₃ : not detected, CH ₃ F: 99.935 area%, propylene: 0.012 area%.

Two hours after the start of the treatment operation, the trifluoromethane treatment solution was treated with a 2N aqueous hydrochloric acid solution and analyzed by ¹⁹ FNMR. As a result, 1,1-diphenyl-2,2,2-trifluoroethanol (Ph-C (CF ₃ ) ( OH) -Ph) it was detected, but 1,1-diphenyl-2-fluoro-ethanol _{(Ph-C (CH 2 F} ) (OH) -Ph) was detected.

[Reference Example 1]
A pure monofluoromethane commercial product (100.000 area%) was used in place of the crude monofluoromethane under the same conditions as in Example 10. When analyzed after 125 minutes, it was 100.000 area%. The solution (treatment liquid) in the gas washing bottle was treated with 2N aqueous hydrochloric acid and analyzed by ¹⁹ FNMR. As a result, 1,1-diphenyl-2,2,2-trifluoroethanol (Ph—C (CF ₃ ) (OH ) -Ph) and 1,1-diphenyl-2-fluoro-ethanol _{(Ph-C (CH 2 F} ) (OH) -Ph) were detected both.

[Example 11]
In Example 10, monofluoromethane (CH ₃ F) collected in a trap tube cooled with liquid nitrogen was evacuated, heated and melted, and degassed by solidification with liquid nitrogen was repeated five times. The interlayer insulating film (SiO ₂ ) was etched by contact hole processing using this gas. FIG. 1 schematically shows a cross section of a sample before etching (a) and after etching (b). An SiO ₂ interlayer insulating film 2 was formed on the single crystal silicon wafer 1, and a resist mask 3 having an opening as an etching mask was formed on the SiO ₂ film.

FIG. 2 shows a schematic diagram of the apparatus used in the experiment. The gas (monofluoromethane): 50 SCCM was introduced from the first gas inlet 4 and Ar: 20 SCCM was introduced from the second gas inlet 5, respectively, and the high frequency power source 3 ( The generated active species were excited into the chamber by a gas flow, and the sample 12 fixed to the sample holder 10 was etched. Each etching gas was introduced through a mass flow controller (not shown). The substrate (sample holder 11) temperature was 25 ° C., the pressure was 2.67 Pa (0.02 torr), and the RF power density was set to 2.2 W / cm ² . The results of etching are shown in Table 2. The relative etching rate was obtained when the area of SiF ₃ (mass number 85) obtained by analyzing the exhaust gas of the reaction chamber 1 with a mass spectrometer (MS) and a commercially available CH ₃ F were used (Comparative Example 1). It was determined as an area ratio between the area of SiF ₃ below). The relative etching rate of monofluoromethane obtained in Example 10 was 1.000.

[Comparative Example 1]
An etching test was performed on commercially available semiconductor grade (pure value in product test result sheet: 99.99% by volume) under the same conditions as in Example 11. The results are shown in Table 2. The monofluoromethane obtained in Example 10 had almost the same etching performance as commercially available monofluoromethane.

  Monofluoromethane obtained by the method of the present invention is useful as a gas for a semiconductor (dry etching agent, cleaning agent).

1: Chamber 2: Earth 3: High-frequency power supply 4: First gas inlet 5: Second gas inlet 6: Third gas inlet 7: Sapphire tube 8: Induction coil 9: Electronic pressure gauge 10 Exhaust gas line 11 : Sample holder 12: Sample 21: Silicon wafer 22: SiO ₂ interlayer insulating film 23: Resist mask 24: Shoulder dropping part 31 .. Reaction tube 32 .. Bypass tube 33 .. First gas cleaning bottle 34 .. Second gas Washing bottle 35 ・ ・ First soda lime pipe 36 ・ ・ Sampling port A 37 ・ ・ Trifluoromethane treatment tank 38 ・ ・ Stirrer 39 ・ ・ Cold finger 40 ・ ・ Second soda lime pipe 41 ・ ・ Sampling port B 42 ・ ・Trap tube 43 ... Balloon

Claims (6)

A method for producing purified monofluoromethane, comprising a step of bringing a monofluoromethane composition containing at least trifluoromethane into contact with a trifluoromethane treatment liquid containing an amide and a base represented by the following general formula (1).

(Wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group, and may be bonded to each other to form a ring, and the ring carbon is substituted with an oxygen atom, a nitrogen atom or a sulfur atom) You may do it.) Amide is formamide, N, N-dimethylformamide, N, N-diethylformamide, N, N-dipropylformamide, N, N′-dimethylethyleneurea, N, N′-dimethylpropyleneurea, N-formylmorpholine, 2. The purified monoester according to claim 1, which is one or more amines selected from N-formylpyrrolidine, N-formylpiperidine, acetamide, N, N-dimethylacetamide, N, N-diethylacetamide, and N, N-dipropylacetamide. A method for producing fluoromethane. The method for producing purified monofluoromethane according to claim 1 or 2, wherein the base is a metal alkoxide, a metal hydride, or a silylamine compound. The method for producing purified monofluoromethane according to any one of claims 1 to 3, wherein the trifluoromethane treatment liquid is a trifluoromethane treatment liquid further containing an anion scavenger. The method for producing purified monofluoromethane according to claim 4, wherein the anion scavenger is a carbonyl compound, a thiocarbonyl compound, a disulfide compound or a diselenide compound. The method for producing purified monofluoromethane according to any one of claims 1 to 5, wherein the trifluoromethane treatment liquid is a trifluoromethane treatment liquid further containing a solvent inert under the treatment conditions.