Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2002-10-07
2004-11-16
Valentine, Donald R. (Department: 1742)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S246000, C204S247000, C204S264000, C204S292000
Reexamination Certificate
active
06818105
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fluorine gas generating apparatus, and more particularly, to a fluorine gas generating apparatus for producing high purity fluorine gas extremely low in impurity content for the manufacturing process of semiconductors and the like, in particular.
BACKGROUND
Fluorine gas has been used hitherto as an essential gas in the semiconductor manufacturing field, for example. While the fluorine gas may be used alone, the demand for nitrogen trifluoride gas (hereinafter it is called NF
3
gas) synthetically prepared based on the fluorine gas, for the use as a semiconductor cleaning gas or a dry etching gas has been rapidly increased. Neon fluorine gas (hereinafter it is called NeF gas), Argon fluoride gas (hereinafter it is called ArF gas), Krypton fluoride gas (hereinafter it is called KrF gas) and the like are excimer laser oscillation gases used for patterning of a semiconductor integrated circuit. Mixed gas of noble gas and fluorine gas is very often used as raw material of the excimer laser oscillation gas.
The fluorine gas and the NF
3
gas used for manufacturing semiconductors and the like are required to be high purity gas containing minute amounts of impurities. In the manufacturing site of semiconductor and the like, it is a common usage that a necessary amount of gas is taken out of a gas container filled with the fluorine gas. Accordingly, it is very important to pay attention to the place to keep the gas cylinder, the assurance of the safety of gas and the preservation of the purity of gas. Further, as the demand for the NF
3
gas has been rapidly increased recently, the problem occurs with the supply-side, thus arising the problem that some stock must be backlogged. When considering these problems, it is preferable to place an on-demand or on-site fluorine gas generating apparatus in the location to use it, rather than to treat a high-pressure fluorine gas.
The fluorine gas is usually produced in an electrolytic cell as shown in FIG.
9
. Ni, monel, carbon steel and the like are usually used as material of an electrolytic cell body
201
. Further, a base plate
212
formed of polytetrafluoroethylene and the like is attached to the bottom of the cell, to prevent hydrogen gas generated and fluorine gas from being mixed with each other. Mixed molten-salt of potassium fluoride-hydrogen fluoride series (hereinafter it is called KF—HF systems) is filled in the electrolytic cell body
201
in the form of an electrolytic bath
202
. The electrolytic cell body is separated into an anode chamber
210
and a cathode chamber
211
by a skirt
209
formed of monel and the like. By the application of a voltage between a carbon or nickel (hereinafter it is called Ni) anode
203
contained in the anode chamber
210
and a Ni cathode
204
contained in the cathode chamber
211
, the fluorine gas is produced electrolytically. The fluorine gas produced is discharged from a generation port
208
and the hydrogen gas produced at the cathode side is discharged from a hydrogen gas discharge port
207
. However, since carbon tetrafluoride gas (hereinafter it is called CF
4
gas) produced and hydrogen fluoride gas (hereinafter it is called HF gas) evaporated from the electrolytic bath and the like during the electrolysis come to be mixed in the fluorine gas, it is hard to obtain the fluorine gas of high purity.
Therefore, it is the object to the present invention to provide a fluorine gas generating apparatus that can produce high purity fluorine gas stably.
DISCLOSURE OF THE INVENTION
To solve the problems mentioned above, the present invention provides a fluorine gas generating apparatus for generating fluorine gas of high purity by electrolysis of a mixed molten-salt comprising hydrogen fluoride, the fluorine gas generating apparatus comprising an electrolytic cell which is separated into an anode chamber and a cathode chamber by a partition wall, and pressure keeping means for supplying gas to the anode chamber and the cathode chamber, respectively, to keep an interior of the anode chamber and an interior of the cathode chamber at a certain pressure.
The pressure keeping means permits the anode chamber and the cathode chamber to be always kept at a constant pressure. This permits quick realization of a prescribed concentration and rate of flow of fluorine by introduction of a noble gas of a carrier gas to the fluorine gas. Particularly, this can put the gas in the usable condition quickly from the start up of electrolytic cell. Also, since the interior of the anode chamber and the interior of the cathode chamber are kept at a certain pressure, the prevention of the air and the like from coming into the chambers from outside can be provided, and as such can permit the fluorine gas of high purity to be generated stably. It should be noted that the phrase of “being kept at a certain pressure” as referred to in the present invention is intended to include the condition of no differential pressure between the internal environment and the external environment (e.g. the use under atmospheric pressure).
The present invention provides a fluorine gas generating apparatus for generating fluorine gas of high purity by electrolysis of a mixed molten-salt comprising hydrogen fluoride, the fluorine gas generating apparatus comprising an electrolytic cell which is separated into an anode chamber and a cathode chamber by a partition wall, pressure keeping means for supplying gas to the anode chamber and the cathode chamber, respectively, to keep an interior of the anode chamber and an interior of the cathode chamber at a certain pressure, a cabinet in which the electrolytic cell is contained and which can provide a controlled atmosphere, and a filter, contained in the cabinet, for filtering out particles in the fluorine gas generated from the electrolytic cell.
This can provide controlled atmosphere around the electrolytic cell, and as such can surely prevent carbon dioxide gas and the like from coming into the electrolytic cell. As a result of this, the generation of CF
4
gas produced by reaction of the fluorine gas with the carbon dioxide gas can be suppressed to obtain the fluorine gas of high purity. Also, even if leakage of the fluorine gas from the electrolytic cell occurs, there is no fear of the fluorine gas being leaked outside. In addition, the particles produced by the entrainment from the electrolytic bath during the electrolysis can be surely filtered out by the filter. It is to be noted that the filter preferably has corrosion resistance against the fluorine gas. For example, sintered monel, sintered Hastelloy and the like can be used for the filter. The cabinet for containing the electrolytic cell preferably has corrosion resistance against the fluorine gas. The cabinet is preferably formed, for example, of metal such as carbon steel or polyvinyl chloride.
In the fluorine gas generating apparatus of the present invention, at least one of the anode chamber and the cathode chamber of the electrolytic cell is provided with liquid level detecting means for detecting an upper level and a lower level of liquid level fluctuation of the molten-salt.
This permits the liquid level of the electrolytic bath contained in the electrolytic cell to be grasped even when the interior of the electrolytic cell cannot be visually inspected. This permits the electrolytic bath to be constantly kept at a constant liquid level, and as such can prevent possible back flow of the electrolytic bath. By association of the liquid level detecting means and the power source control means for the electrodes, the electrolysis can be halted whenever the abnormal liquid level of the electrolytic bath is detected.
In the fluorine gas generating apparatus of the present invention, the pressure keeping means is provided with a solenoid valve that is opened and closed based on detection results of the liquid level detecting mean, so as to supply or discharge the gas to and from the interior of the anode chamber and the interior of the cathode chamber.
This permits the automatic supply
Hiraiwa Jiro
Tada Yoshitomi
Takebayashi Hitoshi
Tojo Tetsuro
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyo Tanso Co., Ltd.
Valentine Donald R.
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