JP3553927B2 - Fluorine gas generator and electrolytic bath liquid level control method thereof - Google Patents

Description

  The present invention relates to a fluorine gas generator, and more particularly, to a fluorine gas generator that generates a high-purity fluorine gas containing extremely few impurities used in a manufacturing process of a semiconductor or the like.

Conventionally, fluorine gas has been an essential gas indispensable in, for example, the semiconductor manufacturing field. In some cases, nitrogen trifluoride gas (hereinafter referred to as NF ₃ gas) or the like is synthesized based on fluorine gas, and used as a cleaning gas for semiconductors or a gas for dry etching. The demand is growing rapidly. Further, neon fluoride gas (hereinafter, referred to as NeF gas), argon fluoride gas (hereinafter, referred to as ArF gas), krypton fluoride gas (hereinafter, referred to as KrF gas), or the like is used for patterning a semiconductor integrated circuit. Excimer laser oscillation gas is used, and a mixed gas of a rare gas and a fluorine gas is frequently used as a raw material thereof.

Fluorine gas and NF ₃ gas used in the production of semiconductors and the like are required to be high-purity gases with few impurities. Also, in a manufacturing site for semiconductors and the like, a required amount of gas is extracted from a gas cylinder filled with fluorine gas and used. For this reason, it is very important to control the storage location of gas cylinders, ensuring gas safety and maintaining purity. Furthermore, since the demand for NF ₃ gas has been rapidly increasing recently, there is a problem in the supply side, and there is also a problem that a certain amount of stock must be held. As an environment that replaces NF ₃ with fluorine as a countermeasure against global warming and the ozone hole, considering these factors, an on-demand, on-site fluorine gas generator is more effective than treating high-pressure fluorine gas packed in cylinders. Is preferably installed at a place where it is used.

Usually, fluorine gas is generated by an electrolytic cell as shown in FIG. The material of the electrolytic cell body 201 is usually Ni, Monel, carbon steel, or the like. Further, when the electrolytic cell main body 201 also serves as a cathode, a bottom plate 212 made of a material having electrical insulation and corrosion resistance such as polytetrafluoroethylene for preventing the generated hydrogen gas and fluorine gas from being mixed with each other is provided at the bottom thereof. Is attached. The electrolytic bath body 201 is filled with a mixed molten salt of potassium fluoride-hydrogen fluoride (hereinafter, referred to as KF-HF) as an electrolytic bath 202. The anode chamber 210 and the cathode chamber 211 are separated by a skirt 209 formed of Monel or the like. A voltage is applied between the carbon or nickel (hereinafter referred to as Ni) anode 203 housed in the anode chamber 210 and the cathode 204 made of Ni or iron housed in the cathode chamber 211, and the fluorine gas is applied by electrolysis. Is occurring. The fluorine gas generated in the anode chamber 210 is released from the generation port 208, and the hydrogen gas generated in the cathode chamber 211 is released from the generation port 207 (for example, see Patent Document 1).
Japanese Patent Publication No. 9-505853

  However, in the conventional fluorine gas generator, when the electrolysis is stopped, the supply of current between the anode 203 and the cathode 204 is stopped, and the fluorine gas remaining in the anode chamber 210 is adsorbed by the anode 203, so that the pressure in the anode chamber 210 is reduced. Decreases. This phenomenon is particularly noticeable when the anode 203 is made of carbon. When the pressure in the anode chamber 210 decreases, the level of the electrolytic bath in the anode chamber 210 rises, and the level of the electrolytic bath in the cathode chamber 211 decreases, and the state of the liquid level is uneven between the anode chamber 210 and the cathode chamber 211. In the worst case, the generated gas passes through the partition wall 209 and mixes with fluorine and hydrogen, causing an explosion.

  The present invention has been made in view of the above problems, and an object thereof is to close a gas generation port of a fluorine gas provided in an anode chamber of a fluorine gas generator, and to suspend the generation of the fluorine gas when the gas generation is stopped. Another object of the present invention is to provide a fluorine gas generator capable of controlling the position of the electrolytic bath liquid level in the electrolytic cell.

Means and effects for solving the problem

A fluorine gas generator of the present invention for solving the above problems is a fluorine gas generator for electrolyzing an electrolytic bath made of a mixed molten salt containing hydrogen fluoride to generate fluorine gas, wherein a partition wall is used. A pressure detecting means for detecting pressures in the anode chamber and the cathode chamber, and at least one of the anode chamber and the cathode chamber when fluorine gas generation is stopped Pressure adjusting means interlocked with the pressure detecting means for controlling the electrolyte surface height of , the pressure detecting means, by applying an appropriate current to the anode, to adjust the pressure in the anode chamber, The liquid level difference between the anode chamber and the cathode chamber is adjusted .
According to this configuration, when the generation of fluorine gas from the fluorine gas generator is stopped, that is, when the application of current between the anode and the cathode is stopped and the gas generation port of the fluorine gas provided in the anode chamber of the electrolytic cell is closed. In addition, even if fluorine gas remaining in the electrolytic cell is absorbed into the pores of the carbon anode and the level of the electrolytic bath rises due to a decrease in the pressure in the anode chamber, this phenomenon can be controlled. Can be stabilized. As a result, the generated gas does not pass through the partition, so that an explosion generated by mixing fluorine and hydrogen can be prevented.
In this specification, when the generation of fluorine gas is stopped (when the generation of fluorine gas is stopped), when there is no need to generate and release the fluorine gas, the main voltage applied between both the anode and the cathode is referred to. This refers to a state in which the supply of the electrolytic current is stopped and the fluorine gas generating port provided in the anode chamber of the electrolytic cell is closed.

In addition, according to the above configuration, it is possible to accurately detect a change in the height of the electrolytic bath liquid level by directly or indirectly detecting a pressure change in the anode chamber, which is one of the causes of the electrolytic bath liquid level difference. It becomes. As a result, the gas outlet of the fluorine gas provided in the anode chamber of the electrolytic cell of the fluorine gas generator is closed, and even when the generation of fluorine gas is stopped, the difference in the electrolytic bath liquid level between the positive and negative electrode chambers of the electrolytic cell is reduced. The electrolysis conditions can be stabilized at the time of resuming the electrolysis because the control can be performed and the difference in the electrolytic bath liquid level can be controlled. As a result, the generated gas does not pass through the partition, so that an explosion generated by mixing fluorine and hydrogen can be prevented.

Further, according to the above configuration, the gas generating port of the fluorine gas provided in the anode chamber of the electrolytic cell of the fluorine gas generating device is closed, so that the pressure can be easily adjusted even when the generation of the fluorine gas is stopped. The current applied between the positive and negative electrodes in the present invention is preferably 0.1 to 5 A / dm ² in terms of current density, and more preferably 0.5 to ^{2 A} / dm ^2. . The current applied at this time may be transmitted from the main electrolytic power supply or may be transmitted from a separately provided auxiliary power supply.

The electrolytic bath liquid level control method of the fluorine gas generator of the present invention includes an anode chamber and a cathode chamber separated by a partition wall, and electrolyzes an electrolytic bath made of a mixed molten salt containing hydrogen fluoride to convert fluorine gas. A method for controlling a liquid level of an electrolytic bath of a fluorine gas generator for generating, wherein at the time of stoppage of generation of fluorine gas, pressure of at least one of the anode chamber and the cathode chamber is detected by pressure detection means, and the pressure is detected. A means for supplying a weak current between the cathode and the cathode according to the detection result of the detection means and adjusting the pressure of the anode chamber by generating a small amount of fluorine gas, thereby controlling a liquid level difference between the anode chamber and the cathode chamber. It is.
According to this configuration, since the pressure change in the anode chamber, which is the cause of the difference in the electrolytic bath liquid level, is detected directly or indirectly, it is possible to detect the difference in the electrolytic bath liquid level between the positive and negative electrodes. Even when the fluorine gas generator stops electrolysis, the height of the electrolytic bath liquid level in the electrolytic cell can be controlled, and the electrolysis conditions at the time of restarting the electrolysis can be stabilized. As a result, the generated gas does not pass through the partition, so that an explosion generated by mixing fluorine and hydrogen can be prevented.

  Hereinafter, an example of an embodiment of a fluorine gas generator according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view of a main part of the fluorine gas generator of the present embodiment. In FIG. 1, 1 is an electrolytic bath, 2 is an electrolytic bath made of a KF-HF-based mixed molten salt, 3 is an anode room, 4 is a cathode room, and 5 is a liquid level of the electrolytic bath 2 of the anode room 3 in five steps. The first liquid level detecting means 6 for detecting, and the second liquid level detecting means 6 for detecting the liquid level of the cathode chamber 4 in five stages. Reference numeral 7 denotes a pressure gauge for measuring the pressure in the anode chamber 3, and reference numeral 8 denotes a pressure gauge for measuring the pressure in the cathode chamber 4. Reference numerals 9 and 10 denote automatic valves that open and close in conjunction with the pressures of the pressure gauges 7 and 8. Reference numeral 11 denotes a thermometer for measuring the temperature of the electrolytic bath 2, and reference numeral 12 denotes a hot water heating device which operates in response to a signal from the thermometer 11 and controls a hot water jacket 13 provided on the side and bottom of the electrolytic cell 1. . Reference numeral 14 denotes a removal tower for removing HF from a mixed gas of hydrogen and HF released from the cathode chamber 4, and 15 denotes a removal tower for removing HF gas from a mixed gas of F ₂ and HF released from the anode chamber 3. HF removal tower filled with NaF or the like that releases only high-purity fluorine gas. 51 is an anode and 52 is a cathode.

  The electrolytic cell 1 is formed of a metal or alloy such as Ni, Monel, pure iron, and stainless steel. The electrolytic cell 1 is separated into an anode chamber 3 and a cathode chamber 4 by a partition 16 made of Monel. An anode 51 is disposed in the anode chamber 3. The cathode chamber 4 is provided with a cathode 52. In addition, it is preferable to use a low-polarization carbon electrode for the anode 51. The cathode 52 is made of Ni, iron, or the like. In the upper lid 17 of the electrolytic cell 1, purge gas inlets and outlets 21 and 20 from gas lines 18 and 19, which are one of pressure maintaining means for maintaining the insides of the anode chamber 3 and the cathode chamber 4 at atmospheric pressure, and a gas generated from the anode chamber 3. A gas outlet 22 for fluorine gas and a gas outlet 23 for hydrogen gas generated from the cathode chamber 4 are provided. The upper lid 17 has an HF inlet 25 from an HF supply line 24 for supplying HF, first liquid level detecting means 5 for detecting the liquid level of the anode chamber 3 and the liquid level of the cathode chamber 4, and a second liquid level detecting means. A surface detecting means 6 and pressure gauges 7 and 8 are provided.

  The electrolytic cell 1 is provided with a temperature adjusting means for heating the inside of the electrolytic cell 1. The temperature adjusting means includes a hot water jacket 13 provided in close contact with the periphery of the electrolytic cell 1 main body, a hot water heating device 12 connected to the hot water jacket 13 and capable of performing general PID control, an anode chamber 3 or And a thermometer 11 such as a thermocouple provided in one of the cathode chambers 4 to control the temperature in the electrolytic cell 1. Although not shown, a heat insulating material is provided around the hot water jacket 13. The shape of the warm water jacket 13 is not particularly limited, but is preferably a shape that covers the entire circumference of the electrolytic cell 1.

  The pressure maintaining means for maintaining the pressure in the anode chamber 3 and the cathode chamber 4 at a target value is obtained by measuring the gas from the pressurizing cylinder with pressure gauges 7 and 8 for measuring the pressure in the anode chamber 3 and the cathode chamber 4. Automatic valves 9 and 10 that open and close in response to the results, and open and close according to the result of detection of the liquid level of the electrolytic bath 2 by the first liquid level detecting means 5 and the second liquid level detecting means 6. Automatic valves 31 to 34 for supplying or exhausting gas to the anode chamber 3 and the cathode chamber 4 respectively, manual valves 64 to 67 for opening and closing the gas lines 18 and 19 of the pressure maintaining means, and pass through the gas lines. And flow meters 68 to 71 that can set the gas flow rate to be set to a predetermined flow rate in advance. As the automatic valves 31 to 34, it is preferable to use an air actuator type that generates almost no operating heat. As a result, heat generation during operation can be reduced, and corrosion of the automatic valve body can be suppressed, so that the influence on the gas line can be reduced. Since the pressure in the anode chamber 3 and the cathode chamber 4 is maintained at the target value by the pressure maintaining means, the liquid level between the positive and negative electrodes is controlled. Therefore, stable electrolysis can be performed with little change in electrolysis conditions. Further, fluorine gas and hydrogen gas generated by the electrolysis are released from the respective generation ports 22 and 23.

  The gas supplied into the electrolytic cell 1 connected to the pressure maintaining means is not particularly limited as long as it is an inert gas. For example, when one or more rare gases such as Ar gas, Ne gas, Kr gas, and Xe gas are used, a mixed gas of fluorine gas and these rare gases can be easily obtained at an arbitrary mixing ratio. This makes it possible, for example, to use it as a radiation source for excimer laser oscillation for patterning integrated circuits in the semiconductor manufacturing field, and by disposing the fluorine gas generator according to the present invention on a manufacturing line in the semiconductor manufacturing field, A mixed gas of a fluorine gas and a rare gas can be appropriately supplied on-site when needed.

  The HF removal tower 14 for removing HF gas in the hydrogen gas released from the cathode chamber 4 has a first removal tower 14a and a second removal tower 14b provided in parallel. These first removal tower 14a and second removal tower 14b can be used simultaneously or one of them can be used. The removal tower 14 is preferably formed of a material having corrosion resistance to HF. For example, the removal tower 14 is formed of stainless steel, Monel, Ni, or the like, and is loaded with soda lime, sodium fluoride, or the like inside. HF in hydrogen gas is removed.

  This HF removal tower 14 is arranged downstream of the automatic valve 10 which is one of the pressure maintaining means. A vacuum generator 26 is provided between the automatic valve 10 and the HF removal tower 14. The vacuum generator 26 reduces the pressure in the gas line 28 by the ejector effect of the gas passing through the gas line 27.

  The HF removal tower 15 for removing HF in the fluorine gas released from the anode chamber 3 is provided with a first removal tower 15a and a second removal tower 15b in parallel, like the HF removal tower 14 described above. . Then, the inside is filled with NaF, and HF contained in the released fluorine gas is removed. Like the HF removal tower 14, the HF removal tower 15 is preferably formed of a material having corrosion resistance to fluorine gas and HF, and examples thereof include stainless steel, Monel, and Ni.

  On the upstream or downstream side of the HF removal tower 15, a valve which constitutes a pressure maintaining means, for example, an automatic valve 9 is provided. The gas generated from the anode chamber 3 is a severe environment in which HF gas and electrolytic bath splash are generated simultaneously with fluorine gas. When the automatic valve 9 is located upstream of the HF removal tower 15, it is easy to control the internal pressure of the electrolytic cell. Particularly in an environment where fluorine gas and HF are mixed, a strong oxidizing atmosphere is created. For this reason, by providing the automatic valve 9 on the downstream side of the HF removal tower 15, only the fluorine gas from which HF has been removed can be brought into contact, and the opening and closing operation can be performed without being affected by the HF gas. Become. The position where the automatic valve 9 is provided can be appropriately selected according to the specifications. The HF removal tower 14 and the HF removal tower 15 are provided with pressure gauges 30 and 29, respectively, so that clogging inside can be detected. The automatic valves 9 and 10 are not particularly limited, and examples thereof include a piezo valve and a mass flow controller.

  It is preferable that the fluorine gas generator including the electrolytic cell 1 is provided in a cabinet having a single casing (not shown). By exhausting the inside of the cabinet, even if a gas leak occurs in the apparatus or the peripheral piping, the gas can be treated in the cabinet, so that the on-demand and on-site use becomes easy. Further, it is preferable that the cabinet is formed of a material that does not easily react with fluorine gas. For example, a metal such as stainless steel can be used.

  Although not shown, a storage means such as a buffer tank is preferably provided on the downstream side from which high-purity fluorine gas is released. As a result, a desired amount of fluorine gas can be provided when needed, and an on-line fluorine gas generator can be easily installed on a production line of a semiconductor production facility.

  The anode 51 has a pressure adjusting function for generating a slight amount of fluorine gas by supplying a weak current in conjunction with the pressure gauge 7. Further, when the gas generating port is closed and the voltage is completely cut off when the generation of fluorine gas is stopped, the polarities of the anode 51 and the cathode 52 are reversed and the cathode 52 is melted. Continue applying voltage in between. At this time, the applied current may be transmitted from the main electrolytic power supply or may be transmitted from a separately provided auxiliary power supply.

  Next, the operation of the fluorine gas generator of the present embodiment when the gas generation port is closed and the generation of fluorine gas is stopped will be described with reference to FIG. FIG. 2 is a flowchart showing the electrolytic bath liquid level control method of the fluorine gas generator according to the present embodiment.

  Normally, in a state in which electrolysis for generating fluorine gas is performed, the inside of the electrolytic cell 1 is maintained at the atmospheric pressure, and the heights of the electrolytic baths 2 in the anode chamber 3 and the cathode chamber 4 are the same. It becomes the bath liquid level position. When the generation of fluorine gas is stopped at night or the like, the current supplied between the positive and negative electrodes is stopped, and the gas generation port 22 provided in the anode chamber 3 is closed (step 1). The fluorine gas generated in the anode chamber 3 and staying in the anode chamber 3 is adsorbed inside the pores of the carbon electrode used as the anode 51. As a result, the pressure in the anode chamber 3 decreases, and the electrolytic bath surface position in the anode chamber 3 rises and the electrolytic bath surface position in the cathode chamber 4 drops in balance with the pressure in the cathode chamber 4. Thereafter, the process proceeds to step S2, and this pressure change is detected by the pressure gauge 7 for controlling the electrolytic bath liquid level, which measures the pressure in the anode chamber 3. Here, it is preferable that the pressure change detection standard of the anode chamber 3 is adjusted to be about 0 to −10 kPa of the pressure when the fluorine gas is generated. While the pressure gauge 7 does not detect a pressure change in the anode chamber 3 (S2: NO), the determination in step S2 is continued. When the pressure change of the anode chamber 3 is detected by the pressure gauge 7 (S2: YES), the process proceeds to step S3, and in conjunction therewith, a very small amount of fluorine gas is generated again by supplying a weak current between the positive and negative electrodes. Thereafter, the process proceeds to step S4, where the weak current is continuously supplied until the pressure in the anode chamber 3 returns to the original level, and the pressure gauge 7 detects that the pressure in the anode chamber 3 has returned to normal. Unless the normal pressure in the anode chamber 3 is detected by the pressure gauge 7 (S4: NO), the determination in step S4 is continued. When the normal pressure of the anode chamber 3 is detected by the pressure gauge 7 (S4: YES), the process proceeds to step S5, and the supply of the weak current flowing between the positive and negative electrodes is stopped.

  As described above, the fluorine gas generating apparatus according to the present embodiment supplies fluorine gas by supplying a weak current between the positive electrode and the negative electrode when the pressure change of the anode chamber is detected by the pressure gauge during the stop of the fluorine gas generation. When the pressure in the anode chamber returns to normal, the supply of the weak current between the positive and negative electrodes is stopped. Thus, a minute change in the electrolytic bath liquid level can be detected by a change in pressure, and accurate electrolytic bath liquid surface position control can be performed. Therefore, the electrolysis for generating fluorine gas can be easily restarted, and at the same time, the condition in the anode chamber can be monitored, and safe operation can be performed.

  The fluorine gas generator of the present invention is not limited to the above-described embodiment, and may be, for example, the following.

  Instead of directly detecting the pressure change in the anode chamber, the pressure change in the anode chamber may be indirectly detected by detecting the pressure change in the cathode chamber. Alternatively, instead of the pressure gauge, a sensor such as a non-contact type distance meter that directly detects the electrolytic bath liquid level may be used. In addition, the gas generation port of the anode chamber is closed, and as a control method of the electrolytic bath liquid level in the electrolytic cell when the generation of fluorine gas is stopped, a threshold value is set for the pressure in the anode chamber, and the current value supplied to the anode is also controlled. The on / off control may be simply set in advance, or the deviation due to the pressure change may be monitored, and the amount of current supplied to the anode may be changed according to the deviation amount.

  The present invention can be changed in design without departing from the scope of the claims, and is not limited to the above embodiment.

It is a schematic diagram of the principal part of the fluorine gas generator of the present invention. It is a flowchart figure which shows the electrolytic bath surface position control method of the fluorine gas generator of this invention. It is a schematic diagram of the fluorine gas generator used conventionally.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Electrolyzer 2 Electrolyte bath 3 Anode chamber 4 Cathode chamber 5 1st liquid level detection means 6 2nd liquid level detection means 7, 8 Pressure gauge 9, 10, 31-34 Automatic valve 11 Thermometer 12 Hot water heating device 13 Hot water jacket 14, 15 HF removal tower 16 Partition wall 17 Upper lid 18, 19 Gas line 20, 21 Purge gas inlet / outlet 22, 23 Gas generating port 24 HF supply line 25 HF inlet 26 Vacuum generator 27, 28 Gas line 29, 30 Pressure gauge 35 to 38 Pressure reducing valve 64 to 67 Manual valve 68 to 71 Flow meter 51 Anode 52 Cathode

Claims (2)

A fluorine gas generator for electrolyzing an electrolytic bath made of a mixed molten salt containing hydrogen fluoride to generate fluorine gas,
It has an anode compartment and a cathode compartment separated by a partition,
Pressure sensing means for sensing the pressures of the anode chamber and the cathode chamber, and interlocking with the pressure sensing means for controlling the level of the electrolytic solution surface of at least one of the anode chamber and the cathode chamber when fluorine gas generation is stopped Pressure adjusting means,
A fluorine gas generator wherein the pressure detecting means adjusts the pressure in the anode chamber by applying an appropriate current to the anode to adjust a liquid level difference between the anode chamber and the cathode chamber . An electrolytic bath liquid level control method for a fluorine gas generator for generating an fluorine gas by electrolyzing an electrolytic bath made of a mixed molten salt containing hydrogen fluoride, comprising an anode chamber and a cathode chamber separated by a partition wall. So,
When the generation of fluorine gas is stopped, the pressure of at least one of the anode chamber and the cathode chamber is detected by pressure detection means, and a weak current is supplied between the positive and negative electrodes according to the detection result of the pressure detection means, and a very small amount of fluorine An electrolytic bath liquid level control method for a fluorine gas generator, wherein a pressure in the anode chamber is adjusted by generating gas to control a liquid level difference between the anode chamber and the cathode chamber.

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