Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2002-09-12
2004-11-09
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S132000
Reexamination Certificate
active
06815568
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for purifying an octafluorocyclobutane, a process for preparing a high-purity octafluorocyclobutane, a high-purity octafluorocyclobutane, and uses thereof.
BACKGROUND ART
Heretofore, in the process of producing semiconductor devices, a gas etching for partially removing a thin-film material is performed for forming a circuit pattern which constitutes a semiconductor circuit. At the same time, removal of deposits using a cleaning gas is performed to remove a thin-film starting material deposited to the inside of a reactor during the thin film formation. One of useful etching or cleaning gases conventional for the production process of a semiconductor device is octafluorocyclobutane (hereinafter referred to as “FC-C318”).
On the other hand, to keep up with recent tendency toward higher performance, smaller size, higher density wiring of electrical or electronic equipment, the circuit patterns are becoming finer and in order to form a higher-precision circuit pattern by etching, use of a high-purity etching gas from which impurities are eliminated as much as possible is demanded. When an etching gas contains an impurity even a small amount, this may cause generation of a large width line during the formation of a fine pattern and increase of defects in the product having a high density integrated circuit.
Also in the process of removing adeposits using a cleaning gas, residual impurities in the production process of a semiconductor device after cleaning must be reduced as much as possible so as to provide a high-purity and high-quality device. For this purpose, a high-purity cleaning gas containing substantially no impurity is demanded.
With respect to the production process of FC-C318, for example, a method of purifying FC-C318 obtained as a by-product in the production of tetrafluoroethylene (hereinafter sometimes referred to as “FC-1114”) or hexafluoropropene (hereinafter sometimes referred to as “FC-1216”) is known.
However, these FC-1114 and FC-1216 each is produced by thermally decomposing chlorodifluoromethane (hereinafter sometimes referred to as “HCFC-22”) as described, for example, in EP451793 and many kinds of substances are produced by this thermal decomposition. The reaction product also contains unreacted HCFC-22 and many chlorine-containing compounds.
The boiling points of FC-C318 and respective compounds contained as impurities after the thermal decomposition of HCFC-22 are shown in Table 1. Among these, FC-1114 and FC-1216 as objective products and unreacted HCFC-22 can be mostly separated by distillation.
However, chlorofluorocarbons, particularly, 2-chloro-1,1,1,2,3,3,3-heptafluoropropane (hereinafter sometimes referred to as “CFC-217ba”), 1-chloro-1,1,2,2,3,3,3-heptafluoropropane (hereinafter sometimes referred to as “CFC-217ca”), 2-chloro-1,1,1,2-tetrafluoroethane (hereinafter sometimes referred to as “HCFC-124”), 1-chloro-1,1,2,2-tetrafluoroethane (hereinafter sometimes referred to as “HCFC-124a”), 1,2-dichlorotetrafluoroethane (hereinafter sometimes referred to as “CFC-114”), FC-1216 and 1H-heptafluoropropane (hereinafter referred to as “HFC-227ca”), have a boiling point close to the boiling point of FC-C318 and therefore, FC-C318 having an impurity concentration of 1 ppm by mass or less can be hardly obtained through separation by distillation.
TABLE 1
Boiling
Structural
Point
Compound Name
Formula
(° C.)
Octafluorocyclobutane (FC-C318)
c-CF
2
CF
2
CF
2
CF
2
—
−6
Chlorodifluoromethane (HCFC-22)
CHClF
2
−41
Hexafluoropropene (FC-1216)
CF
3
CF═CF
2
−31
2-Chloro-1,1,1,2,3,3,3-
CF
3
CClFCF
3
−2
heptafluoropropane (CFC-217ba)
1-Chloro-1,1,2,2,3,3,3-
CClF
2
CF
2
CF
3
−2 to −1
heptafluoropropane (CFC-217ca)
2-Chloro-1,1,1,2-
CF
3
CHClF
−12
tetrafluoroethane (HCFC-124)
1-Chloro-1,1,2,2-
CClF
2
CHF
2
−10.2
tetrafluoroethane (HCFC-124a)
1H-Heptafluoropropane
CHF
2
CF
2
CF
3
−19
(HFC-227ca)
1,2-Dichlorotetrafluoroethane
CClF
2
CClF
2
−3.8
(CFC-114)
Therefore, a purification method other than the separation by distillation, such as extractive distillation, membrane separation and adsorption separation, is being attempted.
However, the extractive distillation method has a problem in that the equipment costs highly and the process is cumbersome. The membrane separation method has a problem in that an appropriate and practical membrane having properties necessary for separating FC-C318 from impurities is not known, and purification to high purity, for example, such that the content of impurities in FC-C318 is 1 ppm by mass or less, is difficult.
Also, as shown in Table 2, there is almost no difference in the molecular size (calculated value at stable state structure) between FC-C318 and the impurity compounds, there is only a small difference in the boiling point between FC-C318 and impurity compounds as described above, and FC-C318 and impurities are approximated in the structure and physical properties. Therefore, separation of FC-C318 from impurity compounds to obtain a high-purity FC-C318 can be hardly attained by an adsorption separation method using a known adsorbent such as activated carbon, silica gel, zeolite (molecular sieves) and molecular sieving carbon (hereinafter referred to as “MSC”).
TABLE 2
Molecular Size
Compound Name
(calculated value)
Octafluorocyclobutane (FC-C318)
5.2 to 5.8 Å
2-Chloro-1,1,1,2,3,3,3-Heptafluoropropane
4.0 to 6.2 Å
(CFC-217ba)
1-Chloro-1,1,2,2,3,3,3-Heptafluoropropane
3.9 to 6.1 Å
(CFC-217ca)
2-Chloro-1,1,1,2-tetrafluoroethane
4.3 to 5.6 Å
(HCFC-124)
1-Chloro-1,1,2,2-tetrafluoroethane
4.3 to 5.6 Å
(HCFC-124a)
1,2-Dichlorotetrafluoroethane (CFC-114)
4.8 to 5.6 Å
Hexafluoropropene (FC-1216)
4.9 to 5.9 Å
1H-Heptafluoropropane (HFC-227ca)
4.3 to 6.2 Å
Among these, activated carbon is effective to adsorb and thereby remove FC-1216, which is one of impurities, but all other impurities including chlorine compounds cannot be separated.
Accordingly, in conventional purification methods, it is difficult to obtain FC-C318 reduced in the concentration of fluorocarbon impurities, particularly CFC-217ba, to 1 ppm by mass or less.
As a result of extensive investigations to solve these problems, the present inventors have found that when crude octafluorocyclobutane containing impurities such as fluorocarbon is contacted with an impurity decomposing agent containing an iron oxide and an alkaline earth metal compound and then with an adsorbent, these impurities can be substantially removed with ease.
More specifically, the present inventors have found a purification process of FC-C318, where FC-C318 containing fluorocarbon impurities such as CFC-217ba, CFC-217ca, HCFC-124, HCFC-124a, CFC-114, FC-1216 and HFC-227ca, particularly CFC-217ba, in a concentration of 10 to 10,000 ppm by mass is contacted with an impurity decomposing agent and further with an adsorbent and thereby these impurities can be reduced to less than 1 ppm by mass. The present invention has been accomplished based on this finding.
OBJECT OF THE INVENTION
An object of the present invention is to solve the above-described problems in conventional techniques and provide a process for purifying an octafluorocyclobutane, where impurities can be substantially removed from a crude octafluorocyclobutane containing impurities. More specifically, an another object of the present invention is to provide a purification process capable of effectively removing CFC-217ba, which has been difficult to remove by conventional purification processes, and reducing the impurities such as fluorocarbon to less than 1 ppm by mass.
A further object of the present invention is to provide a process for preparing an octafluorocyclobutane, comprising the above-described purification steps, and also provide a high-purity octafluorocyclobutane and uses thereof.
SUMMARY OF THE INVENTION
The process for purifying an octafluorocyclobutane according to the present invention comprises the step of contacting a crude octafluorocyclobutane containing im
Horiba Minako
Suzuki Yasuhiro
Shippen Michael L.
Showa Denko K.K.
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