JP2004043885A - Fluorine gas-generating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine gas-generating apparatus which is operated with a high degree of safety and reliability even for a long time of operation. <P>SOLUTION: The fluorine gas-generating apparatus 30 has an electrolytic cell 32 which generates a byproduct gas mainly containing a hydrogen gas in a section of a second gas phase in a cathode side, along with generating a product gas mainly containing a fluorine gas in a section of a first gas phase in an anode side. In order to measure pressures in the sections of the first and the second gas phases, a first and a second pressure gauges 46 and 48 are arranged. In order to extract the product gas and the byproduct gas, a first and a second pipes 52 and 72 are arranged. In the first and the second pipes 52 and 72, a first and a second flow control valves are arranged. Degrees of openings of the first and the second flow control valve are adjusted on the basis of measured results in the first and the second pressure gauges 46 and 48, so as to keep pressures in sections of the first and the second gas phases to the first and the second set values which are substantially equal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fluorine gas generator, and more particularly to a fluorine gas generator provided in a gas supply system of a semiconductor processing system. Here, the semiconductor processing means that a semiconductor layer, an insulating layer, a conductive layer, and the like are formed in a predetermined pattern on a substrate to be processed such as a semiconductor wafer or an LCD substrate, so that a semiconductor device or the like is formed on the substrate to be processed. Means various processes performed for manufacturing a structure including wirings, electrodes, and the like connected to a semiconductor device.
[0002]
[Prior art]
In the manufacture of semiconductor devices, various semiconductor processes such as film formation, etching, and diffusion are performed on a substrate to be processed, for example, a semiconductor wafer or an LCD substrate. In a semiconductor processing system that performs such processing, a fluorine-based gas is used as a processing gas for various uses, for example, when etching a silicon film or a silicon oxide film, or when cleaning a processing chamber. Fluorine gas is attracting attention as a new etching gas and cleaning gas.However, since problems in terms of safety and reliability have not been completely solved, it is common to produce fluorine in the field of semiconductor device manufacturing. Has not been done.
[0003]
On the other hand, as a device for generating fluorine gas in a gas manufacturing plant, a device using an electrolytic cell is known. For example, Japanese Patent Publication No. 9-505853 discloses a fluorine gas generator of this type. In the apparatus disclosed in this publication, the inside of the electrolytic cell is partitioned into a central anode chamber and a surrounding cathode chamber by a partition plate extending into the molten salt from above. A pair of probes terminating at different heights are disposed in the anode chamber. The pair of probes function as a liquid level gauge for controlling on / off of a current supplied between the anode and the cathode. That is, this apparatus controls the generation of fluorine gas by detecting the liquid level of the molten salt.
[0004]
FIG. 3 is a schematic view showing another conventional fluorine gas generator. This device has an improved mechanism for controlling the supply of fluorine gas from the electrolytic cell. In the case of this apparatus, fluorine gas generated on the anode 114 side of the electrolytic cell 112 is continuously supplied to an intermediate capacitor 116 through a pipe 120 and temporarily stored therein. When the capacitor 116 reaches a certain pressure, the on-off valve 122 disposed between the compressor 118 and the capacitor 116 is temporarily opened, and a certain amount of fluorine gas is sucked into the compressor 118. The operation of the valve 122 is repeated many times, and the pressure in the secondary buffer tank 124 is increased to a predetermined value.
[0005]
[Problems to be solved by the invention]
According to the study of the present inventors, in the case of the fluorine gas generator shown in FIG. 3, if the operation time is long, as described later, some problems may occur in terms of safety and reliability. Have been found. Unless such a problem is solved, it is practically difficult to incorporate and use a fluorine gas generator in an automated production system, for example, a semiconductor device manufacturing system.
[0006]
The present invention has been made in view of the problems of the related art, and has as its object to provide a fluorine gas generation device that can operate with high safety and reliability even during long-time operation. . In particular, an object of the present invention is to provide an apparatus that generates fluorine gas on-site and on demand. Here, "on-site" means that the fluorine gas generation device is combined with a predetermined main processing device, for example, a main processing device of a semiconductor processing system. On-demand means that gas can be supplied at a timing according to a request from the main processing unit and with necessary component adjustment.
[0007]
[Means for Solving the Problems]
A first aspect of the present invention is an apparatus for generating a fluorine gas,
By electrolyzing hydrogen fluoride in an electrolytic bath made of a molten salt containing hydrogen fluoride, a product gas containing fluorine gas as a main component is generated in a first gas phase portion on the anode side, and a second gas on the cathode side is generated. An electrolytic cell that generates a by-product gas containing hydrogen gas as a main component in a gas phase portion,
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt,
A first pipe for leading the product gas from the first gas phase portion;
A second pipe for leading the by-product gas from the second gas phase portion;
A first pressure gauge for continuously measuring the pressure of the first gas phase portion;
A second pressure gauge for continuously measuring the pressure of the second gas phase portion;
A first flow control valve disposed in the first pipe;
A second flow control valve disposed in the second pipe;
A first control member that adjusts an opening degree of a first flow control valve based on a measurement result of the first pressure gauge so that a pressure of the first gas phase portion is maintained at a first set value;
The opening of the second flow control valve is adjusted based on the measurement result of the second pressure gauge so that the pressure of the second gas phase portion is maintained at a second set value substantially equal to the first set value. A second control member to adjust;
It is characterized by having.
[0008]
According to a second aspect of the present invention, in the apparatus according to the first aspect, the first and second set values are 760 to 820 Torr.
[0009]
According to a third aspect of the present invention, in the apparatus according to the first or second aspect, the first suction means is provided in the first pipe downstream of the first flow control valve, and sucks the first pipe. Is further provided.
[0010]
According to a fourth aspect of the present invention, in the device according to the third aspect, the second pipe is connected to a second suction unit that suctions the second pipe downstream of the second flow control valve. It is characterized by being arranged in.
[0011]
According to a fifth aspect of the present invention, in any one of the first to fourth aspects,
A switching valve disposed on the raw material pipe,
A current integrator for integrating the current supplied between the anode-side electrode and the cathode-side electrode of the electrolytic cell,
A control member that opens and closes the switching valve so as to control replenishment of the hydrogen fluoride into the molten salt based on a measurement result obtained by the current integrator,
Is further provided.
[0012]
According to a sixth aspect of the present invention, in the apparatus according to the fifth aspect, the hydrogen fluoride supplied through the raw material pipe is a gas.
[0013]
According to a seventh aspect of the present invention, in the apparatus according to the sixth aspect, the raw material pipe is disposed on the cathode side of the electrolytic cell so as to supply the hydrogen fluoride gas into the molten salt. And that a pipe for supplying nitrogen gas to the raw material pipe downstream of the switching valve is connected, and the hydrogen fluoride gas is supplied to the molten salt in a state where the gas is added to the nitrogen gas. Features.
[0014]
An eighth aspect of the present invention is an apparatus for generating fluorine gas,
By electrolyzing hydrogen fluoride in an electrolytic bath made of a molten salt containing hydrogen fluoride, a product gas containing fluorine gas as a main component is generated in a first gas phase portion on the anode side, and a second gas on the cathode side is generated. An electrolytic cell that generates a by-product gas containing hydrogen gas as a main component in a gas phase portion,
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt,
A first pipe for leading the product gas from the first gas phase portion;
A second pipe for leading the by-product gas from the second gas phase portion;
A switching valve disposed on the raw material pipe,
A current integrator for integrating the current supplied between the anode-side electrode and the cathode-side electrode of the electrolytic cell,
A control member that opens and closes the switching valve so as to control replenishment of the hydrogen fluoride into the molten salt based on a measurement result obtained by the current integrator,
It is characterized by having.
[0015]
According to a ninth aspect of the present invention, in the apparatus according to the eighth aspect, the hydrogen fluoride supplied through the raw material pipe is a gas.
[0016]
A tenth aspect of the present invention is the device according to the ninth aspect, wherein the raw material pipe is disposed on the cathode side of the electrolytic cell so as to supply the hydrogen fluoride gas into the molten salt. And that a pipe for supplying nitrogen gas to the raw material pipe downstream of the switching valve is connected, and the hydrogen fluoride gas is supplied to the molten salt in a state where the gas is added to the nitrogen gas. Features.
[0017]
Furthermore, the embodiments of the present invention include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, when an invention is extracted by omitting some constituent elements from all the constituent elements described in the embodiment, when implementing the extracted invention, the omitted part is appropriately supplemented by well-known conventional techniques. It is something to be done.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In the course of the development of the present invention, the present inventors have studied the safety and reliability issues of the conventional fluorine gas generator as described with reference to FIG. As a result, the present inventors have obtained the following knowledge.
[0019]
In the case of the apparatus shown in FIG. 3, an operation is performed in which the valve 122 is opened at the upper limit of the pressure of the capacitor 116 and the valve 122 is closed at the lower limit of the pressure. For this reason, large pressure fluctuations occur in the fluorine gas pipe 120, whereby mist-like molten salt accumulates at the inlet of the pipe 120, causing the pipe 120 to be blocked. Further, since the valve 122 is repeatedly opened and closed frequently, the sheet of the valve 122 is easily damaged by the mechanical action of the solidified molten salt particles and the chemical action of the fluorine gas.
[0020]
Further, the hydrogen gas generated from the cathode side passes through the piping 121 of the exhaust system, is usually diluted to a regulated value or less, and is discharged out of the system. At this time, it is expected that the pressure of the discharge system changes depending on the installation environment. For example, when the suction capacity of the exhaust system is high, the pressure on the cathode side naturally becomes a negative pressure, and the molten salt level on the cathode side increases accordingly. In this case, the liquid level greatly fluctuates, and the molten salt is drawn into the pipe 121 side of the hydrogen gas, which causes the pipe 121 to be blocked.
[0021]
When the molten salt solidifies in the pipes 120 and 121, it is necessary to stop the apparatus and perform a maintenance operation, which results in downtime of the entire system to which the apparatus is related. What is more problematic is that the pressure balance in the electrolytic cell 112 is lost even if either the fluorine gas pipe 120 or the hydrogen gas pipe 121 is closed. If the pressure balance in the electrolytic cell 112 is largely disturbed, the fluorine gas and the hydrogen gas may come into contact in the electrolytic layer 112 and cause an explosion.
[0022]
Hereinafter, an embodiment of the present invention configured based on such knowledge will be described with reference to the drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and repeated description will be made only when necessary.
[0023]
FIG. 1 is a schematic diagram showing a semiconductor processing system incorporating a fluorine gas generator according to an embodiment of the present invention. This semiconductor processing system includes a semiconductor processing apparatus 10 that performs processing such as film formation, etching, or diffusion on a substrate to be processed such as a semiconductor wafer or an LCD substrate.
[0024]
The semiconductor processing apparatus 10 includes a processing chamber 12 for storing a substrate to be processed and performing semiconductor processing. In the processing chamber 12, a lower electrode and mounting table (supporting member) 14 for mounting a substrate to be processed is provided. An upper electrode 16 is provided in the processing chamber 12 so as to face the mounting table 14. By applying an RF power from an RF (high frequency) power supply 15 between the electrodes 14 and 16, an RF electric field for converting the processing gas into plasma is formed in the processing chamber 12. An exhaust system 18 for exhausting the inside and setting a vacuum is connected to a lower portion of the processing chamber 12. Further, a gas supply system 20 for supplying a processing gas is connected to an upper portion of the processing chamber 12.
[0025]
FIG. 2 is a schematic view showing a modified example 10x of the semiconductor processing apparatus used in combination with the gas supply system 20 shown in FIG. The semiconductor processing apparatus 10x includes a processing chamber 12 for storing a substrate to be processed and performing semiconductor processing. A mounting table (supporting member) 14 for mounting a substrate to be processed is disposed in the processing chamber 12. An exhaust system 18 for exhausting the inside and setting a vacuum is connected to a lower portion of the processing chamber 12. A remote plasma chamber 13 for generating plasma is connected to an upper portion of the processing chamber 12. A coil antenna 17 is wound around the remote plasma chamber 13. By applying RF power from the RF (high frequency) power supply 15 to the coil antenna 17, an induced electric field for converting the processing gas into plasma is formed in the remote plasma chamber 13. Further, a gas supply system 20 for supplying a processing gas is connected to an upper portion of the remote plasma chamber 13.
[0026]
The fluorine gas generator according to the embodiment of the present invention can be applied to a case where a cleaning gas or the like is supplied to a semiconductor processing apparatus that does not use plasma, for example, a thermal CVD apparatus.
[0027]
Returning to FIG. 1, the gas supply system 20 selectively switches an arbitrary gas into the processing chamber 12, for example, a processing gas for performing semiconductor processing or a processing gas for cleaning the inside of the processing chamber 12. A flow management unit 22 for supplying at a flow rate is provided. A gas storage unit 24 having a plurality of gas sources for storing various active gases and inert gases is connected to the flow management unit 22. The flow management unit 22 is also connected to a gas generation unit 26 that generates a fluorine gas-based processing gas by a reaction process.
[0028]
The fluorine management unit 30 according to the embodiment of the present invention is detachably connected to the flow management unit 22 and the gas generation unit 26. That is, the generating device 30 is used to directly supply the fluorine gas to the flow management unit 22 or to supply the fluorine gas raw material to the gas generating unit 26 (a switching valve is not shown). In the gas generation unit 26, for example, an interhalogen fluorine compound gas is generated by reacting a fluorine gas raw material with another halogen gas such as Cl.
[0029]
The generator 30 has an airtight electrolytic tank 32 that houses an electrolytic bath made of a molten salt containing hydrogen fluoride. The molten salt is composed of a mixture of potassium fluoride (KF) and hydrogen fluoride (HF) (KF / 2HF) or a mixture of Fremy's salt and hydrogen fluoride. The electrolytic cell 32 is divided into an anode chamber 34 and a cathode chamber 36 by a partition plate 35 extending into the molten salt from above. In the anode chamber 34 and the cathode chamber 36, a carbon electrode (anode) 42 and a nickel electrode (cathode) 44 are immersed in the molten salt, respectively. The electrolytic cell 32 is provided with a current source 38 for supplying a current between the anode 42 and the cathode 44 and a current integrator 40 for integrating the supplied current.
[0030]
During the electrolytic treatment, the electrolytic bath 32 is heated and kept at 80 to 90 ° C. by the accompanying heater 33. By electrolyzing hydrogen fluoride in the electrolytic bath, a fluorine gas (F ₂ ) Is generated, and a by-product gas mainly containing hydrogen gas is generated in the gas phase of the cathode chamber 36. Hydrogen fluoride gas is mixed into each of the product gas and the by-product gas by the vapor pressure of hydrogen fluoride gas in the molten salt of the raw material (for example, 5%). First and second pressure gauges 46 and 48 are disposed in the anode chamber 34 and the cathode chamber 36 in order to continuously measure the pressure of each gas phase.
[0031]
A first pipe 52 for extracting the product gas and sending it to the flow management unit 22 and the gas generation unit 26 of the gas supply system 20 is connected to the anode chamber 34. A first flow control valve 54, an adsorption cartridge 56, a mini-buffer tank 58, a compressor (suction means) 62, a main buffer tank 64, and the like are arranged in the first pipe 52 in this order from the upstream side. The product gas generated in the anode chamber 34 is forcibly extracted from the anode chamber 34 by the suction of the first pipe 52 by the compressor 62 and stored in the main buffer tank 64. In FIG. 1, reference numeral 66 denotes a line filter.
[0032]
As described above, several percent (for example, 5%) of hydrogen fluoride is mixed in the product gas. The hydrogen fluoride is removed when the product gas passes through the adsorption cartridge 56. Therefore, an adsorbent that captures hydrogen fluoride by adsorption is built in the cartridge 56. The adsorbent is composed of a large number of pellets filled in the cartridge 56 in consideration of handling and pressure loss. The adsorbent comprises, for example, an adsorbent whose adsorption capacity changes with temperature, such as sodium fluoride (NaF). Around the cartridge 56, a temperature adjusting jacket (heater) 57 for adjusting the temperature of the cartridge 56 is provided.
[0033]
A pressure gauge 65 is provided in the main buffer tank 64, and the pressure in the tank 64 is continuously measured. This measurement result is transmitted to a control member 39 associated with the current source 38. The control member 39 turns on / off the current source 38 based on the transmitted measurement result, and controls the supply of the current to the electrolytic cell 32. That is, when the pressure in the tank 64 decreases to a certain pressure, the current source 38 is turned on to start generation of fluorine gas, and when the pressure in the tank 64 increases to a certain pressure, the current source 38 is turned off and generation of fluorine gas is stopped. You. Thus, electrolysis can be stopped without making a difference in the liquid level of the molten salt between the anode chamber 34 and the cathode chamber 36 in the electrolytic cell 32. The pressure in the tank 64 is set, for example, from atmospheric pressure to atmospheric pressure + 0.18 Mpa.
[0034]
On the other hand, a second pipe 72 for extracting the by-product gas is connected to the cathode chamber 36. The second pipe 72 is detachably connected to, for example, a pipe of an exhaust system (suction unit) 78 of a semiconductor manufacturing factory. The second pipe 72 is provided with a second flow control valve 74, an abatement part 76, and the like. The by-product gas generated in the cathode chamber 36 is forcibly extracted from the cathode chamber 36 by being sucked into the second pipe 72 by the exhaust system 78, passes through the abatement unit 76, and then passes to the exhaust system 78. Sent.
[0035]
As described above, during the electrolytic treatment, the pressure balance between the anode chamber 34 and the cathode chamber 36 is lost due to various factors, and the liquid level fluctuates easily in the electrolytic tank 32. In addition, even during the electrolysis process, for example, immediately after the gas switching step, such as a purge in the electrolysis tank 32 by nitrogen gas, a nitrogen purge step after the end of supply of the raw material hydrogen fluoride gas, or the like, Fluid level fluctuation is likely to occur. These cause the safety and reliability of the fluorine gas generator to be impaired.
[0036]
On the other hand, in the fluorine gas generator shown in FIG. 1, the pressures of the gas phase portions of the anode chamber 34 and the cathode chamber 36 are continuously measured by the first and second pressure gauges 46 and 48. These measurement results are transmitted to first and second control members 55 and 75 associated with the first and second flow control valves 54 and 74, respectively. The first and second control members 55 and 75, based on the transmitted measurement result, set the first and second set values where the pressures of the respective gas phase portions of the anode chamber 34 and the cathode chamber 36 are substantially equal to each other. The opening degree of the first and second flow control valves 54 and 74 is adjusted so as to be maintained. That is, the opening of the first and second flow control valves 54 and 74 is continuously adjusted under the control of the first and second control members 55 and 75 respectively attached thereto.
[0037]
As described above, since the pressures in the anode chamber 34 and the cathode chamber 36 are independently and constantly measured and controlled independently, the state of the liquid level of the molten salt in the anode chamber 34 and the cathode chamber 36 is maintained uniformly. In other words, according to this configuration, the electrolytic cell 32 causes the state of generation of fluorine, the state in the first and second pipes 52 and 72, the operation state of the compressor 62 and the exhaust system 78 of the semiconductor manufacturing plant, and other environments. Protected from the adverse effects of fluctuations. For this reason, damage to expensive electrodes and the like, for example, the anodic effect can be avoided beforehand, and the process can proceed safely and without sudden stopping of electrolysis. Further, since the molten salt does not solidify at the inlets of the first and second pipes 52 and 72 to block them, there is no need for frequent maintenance.
[0038]
The first and second set values of the gas phase portions of the anode chamber 34 and the cathode chamber 36 are desirably set at atmospheric pressure to 820 Torr, more desirably, atmospheric pressure to 770 Torr. In addition, in order to stabilize the pressure in the anode chamber 34 and the cathode chamber 36, the first and second flow control valves 54 and 74 need to be able to continuously adjust their opening with good responsiveness. From such a viewpoint, a piezo valve is desirably used as the first and second flow control valves 54 and 74.
[0039]
Returning to FIG. 1 again, the raw material pipe 82 is disposed in the cathode chamber 36 of the electrolytic cell 32 in a state where the raw material pipe 82 is immersed in the molten salt in order to supply hydrogen fluoride gas, which is a raw material to be consumed, into the molten salt. . A hydrogen fluoride source 84 and a nitrogen source 94 are detachably connected to the raw material pipe 82 via pipes 83 and 93.
[0040]
A switching valve 96 for switching the pipe 93 between a closed state and an open state is provided in the pipe 93 on the nitrogen source 94 side. During the operation of the fluorine gas generator 30, the switching valve 96 is always open, and nitrogen gas is constantly supplied into the molten salt in the electrolytic cell 32. The flow rate of the nitrogen gas is set to be 0.2 to 50 L / min, preferably 2 to 10 L / min with respect to the flow rate of the hydrogen fluoride gas being 1 to 50 L / min. Since the nitrogen gas hardly dissolves in the molten salt, the nitrogen gas is discharged through the molten salt to the cathode side.
[0041]
On the other hand, a switching valve 86 for switching the pipe 83 between a closed state and an open state is provided in the pipe 83 on the hydrogen fluoride source 84 side. The switching valve 86 is opened and closed under the control of a control member 87 associated therewith. During the electrolysis, the current supplied between the anode 42 and the cathode 44 is integrated by the current integrator 40 and transmitted to the control member 87. The control member 87 opens and closes the switching valve 86 so as to control replenishment of the hydrogen fluoride gas into the molten salt (mixing of the hydrogen fluoride gas into the nitrogen gas) based on the transmitted measurement result. . Here, the set value of the control member 87 is set so that, for example, the concentration of hydrogen fluoride in the molten salt is maintained in a range of 41 to 39%.
[0042]
Replenishment of the hydrogen fluoride (HF) gas to the electrolytic cell 32 is controlled by integrating the supply current based on the following theory. That is, fluorine (F ₂ ) The amount of generation is proportional to the amount of electricity according to Faraday's law. This rule is satisfied irrespective of the electrolysis conditions such as temperature, concentration, and type of electrode. In the electrolytic cell 32 according to the present embodiment, the approximate amount of fluorine gas generated is determined according to the following equation (1) from the relationship of current efficiency.
[0043]
Z = 6.8X (1)
In the formula (1), Z indicates a fluorine generation flow rate (cc / min), and X indicates an electric quantity (here, an electrolytic current value (A)).
[0044]
For example, in the initial state, the concentration of hydrogen fluoride in the molten salt is set to 41%. The supply timing of the raw material hydrogen fluoride gas is performed before the concentration of hydrogen fluoride in the molten salt decreases from the initial concentration of 41% to reach the lower concentration limit, for example, 39%. If the concentration of hydrogen fluoride is lower than the lower limit of the concentration, the melting point of the molten salt increases, and in the worst case, the molten salt may be solidified and the electrolysis may not be performed. On the other hand, when the hydrogen fluoride concentration exceeds the initial concentration, the vapor pressure of hydrogen fluoride in the molten salt increases, and the concentration of hydrogen fluoride mixed with fluorine also increases. In this case, there is a problem that a load on the adsorbent (for example, sodium fluoride (NaF)) that captures hydrogen fluoride by adsorption in the adsorption cartridge 56 increases. Therefore, it is necessary to keep the hydrogen fluoride concentration in the above range, for example, in the range of 41 to 39%. The following equation (2) shows the relationship between the amount of hydrogen fluoride gas consumed and the amount of generated fluorine gas. Here, two moles of hydrogen fluoride are required to generate one mole of fluorine.
[0045]
(2Z + 0.05Z + 0.05Z) t / 1000 = T (2)
In the formula (2), 2Z is a flow rate of hydrogen fluoride (cc / min) necessary to generate 1 mole of fluorine, and the first 0.05Z is a flow rate of hydrogen fluoride (cc / min) entrained in 1 mole of fluorine. min), the second 0.05Z is the hydrogen fluoride flow rate (cc / min) entrained in 1 mole of hydrogen, t is the generation time (min), and T is the amount of hydrogen fluoride consumed (L), respectively. Show.
[0046]
By substituting 6.8X for Z in equation (2) based on equation (1), the following equation (3) is obtained.
[0047]
0.01428X × t = T (3)
In the formula (3), X indicates the amount of electricity (A), t indicates the generation time (min), and T indicates the amount of hydrogen fluoride consumed (L).
[0048]
The amount of hydrogen fluoride that can be consumed depends on the amount of molten salt charged into the electrolytic cell 32. Since the concentration of hydrogen fluoride in the molten salt before starting the electrolysis is 41%, if the amount of the molten salt is C, the amount of hydrogen fluoride in the electrolytic bath 32 is 0.41C. When the electrolytic bath 32 is used in a hydrogen fluoride concentration range of 41 to 39%, the relationship between the hydrogen fluoride concentration in the molten salt and the amount of hydrogen fluoride consumed is expressed by the following equation (4). Therefore, the maximum amount of hydrogen fluoride that can be consumed and consumed is represented by the following equation (5).
[0049]
(0.41C-HFc) / (C-HFc) = 0.39 (4)
HFc = 0.033C (5)
In the formulas (4) and (5), C represents the weight of the molten salt, and HFc represents the amount of hydrogen fluoride consumed.
[0050]
Therefore, when T of equation (3) is substituted for HFc of equation (5), the following equation (7) is obtained through the following equation (6).
[0051]
0.01428X × t = 0.033C (6)
X × t = 2.3C (7)
In the formulas (6) and (7), X represents the quantity of electricity (A), t represents the generation time (min), and C represents the weight of the molten salt.
[0052]
That is, if the weight C of the molten salt (KF / 2HF) to be charged into the electrolytic cell 32 is determined in advance, the relationship between the amount of electricity X corresponding to the usage range of the hydrogen fluoride concentration of 41 to 39% and the fluorine generation time t is determined. be able to. Here, the timing of replenishment of the hydrogen fluoride gas (the lower limit of the range of use) can be specified by a value obtained by integrating the amount of electricity along the time axis, so that the amount of electricity X does not necessarily need to be fixed.
[0053]
Next, advantages of the above embodiment of the present invention will be described.
[0054]
Japanese Unexamined Patent Application Publication No. 9-505853 (hereinafter referred to as' 853) discloses a control sensor for detecting the level of an electrolyte in an electrolytic cell, and starts supplying a current in response to a signal from the control sensor. Alternatively, a fluorine cell including a current supply unit responsive to the signal to stop the operation is disclosed. That is, the generation of fluorine is continued until a decrease in the liquid level reaches a position set in advance to generate a signal. Since the device controlling the electrolysis in response to this signal stops the current supply to the cell, the electrolysis is stopped and the lowering of the electrolyte level is also stopped.
[0055]
In other words, in the technology disclosed in this publication, the on / off control of the current is performed by intentionally using the liquid level fluctuation, and there is no idea to suppress the fluctuation. However, in order to continuously generate fluorine gas while maintaining a steady state in electrolysis, it is necessary to minimize the liquid level fluctuation.
[0056]
Further, '853 discloses that an anode chamber in an electrolytic cell is a fluorine storage. However, in an actual fluorine generator for semiconductor processing, it is difficult to match the amount of generated fluorine with demand, so that a capacitor and a compressor having a certain size are required. The technology disclosed in this publication cannot cope with such a change in the external environment.
[0057]
Therefore, a commercially available fluorine generation system corresponding to this publication is provided with a capacitor having a capacity of several liters and a bellows compressor. This system stores fluorine intermittently in a buffer tank by an on / off opening / closing valve. By using such a method, it is possible to continuously generate fluorine without stopping the generation. In this case, the gas can be generated constantly, but the following problems are actually caused by long-term generation.
[0058]
Fine molten salt mist entrained by fluorine penetrates the capacitor existing between the pipe or the electrolytic cell and the compressor. Since the mist has a melting point of around 80 ° C., it exists as a solid in the pipe. As the amount of mist increases, problems such as (1) blockage of the pipe or (2) damage to a valve seat in the on / off valve occur.
[0059]
In the former case, the electrolysis is immediately stopped, and it is necessary to remove salt clogged in the piping. The removal operation involves the latest caution and danger because the reactive gas fluorine is also present in the tube. In the latter case, electrolysis is stopped because the valve leaks. In addition, the operation is frequently repeated on / off, so that the valve life comes soon.
[0060]
Further, in such a control method, the liquid level in the anode cannot be avoided to some extent, and the contact area between the electrode surface and the liquid always changes. For this reason, it becomes difficult to secure a stable amount of fuchse generation due to a change in current efficiency during electrolysis. In addition, there arises a problem that the electrode (3) needs to be replaced (usually carbon is used for the anode electrode) due to the anode effect.
[0061]
If the control of the amount of generated fluorine relies on the turning on / off of the power by a control sensor as in the '853 publication, it cannot cope with a change in the surrounding environment (in this case, connection with the compressor). That is, it is necessary to use a compressor for the electrolytic cell for semiconductor processing. On the other hand, it is essential that the generation of fluorine is not affected by the downstream side after the electrolytic cell. From this viewpoint, the control system disclosed in the '853 publication is not suitable for semiconductor processing and is not practical.
[0062]
An important point in the above embodiment of the present invention is that the hook can be constantly generated stably without being affected by a change in the environment after the electrolytic cell. This fluorine supply device is designed for semiconductor processing. That is, it is basically assumed that a suction device such as a compressor is used.
[0063]
The pressure gauge and the current source connected to the buffer tank at the subsequent stage of the compressor are linked, and when the pressure decreases to a certain level, the power is turned on and fluorine is generated. When the pressure increases to a certain point, the power is turned off. By adopting such a method, it is possible to stop electrolysis without making a difference in liquid level as in the '853 publication.
[0064]
'853 discloses that it is preferable that the pressure at the cathode side outlet always operates at atmospheric pressure (or slightly higher than atmospheric pressure) in consideration of safety. However, in an actual semiconductor factory, it is almost impossible to maintain the pressure change in the cathode side pipe because the pressure change is large. Also, this publication focuses only on the pressure change in the anode compartment, but this is based on the assumption that the pressure in the cathode compartment is always atmospheric pressure.
[0065]
In the above embodiment of the present invention, the pressure in the bipolar chamber in the electrolytic cell is always kept constant by maintaining the pressure by independent flow rate control. However, the actual liquid level is not known from the pressure. Therefore, for the purpose of enhancing safety, it is a desirable embodiment to insert one liquid level sensor on the anode side or the cathode side, preferably on the cathode side.
[0066]
Anhydrous hydrogen fluoride (AHF) as a raw material is usually a gas, and is supplied by bubbling into a molten salt in an electrolytic cell (preferably on the cathode side). Since AHF is absorbed at a very high rate by the molten salt, a negative pressure is instantaneously applied to the cathode chamber when the AHF is supplied at a low flow rate. In this case, the molten salt rises inside the AHF feed tube, and in the worst case, solidifies and cannot be supplied. Therefore, it is preferable that the supply flow rate of AHF is high. However, there is a limit to the flow rate of AHF that can actually flow.
[0067]
Therefore, in the above embodiment of the present invention, AHF is mixed with nitrogen gas and supplied at the time of AHF supply in order to increase the total flow rate during AHF. Since the nitrogen gas hardly dissolves in the molten salt, the nitrogen gas is discharged through the molten salt to the cathode side. Nitrogen gas always flows to the cathode compartment regardless of the presence or absence of electrolysis. For this reason, during electrolysis, hydrogen generated from the cathode side is diluted, and even if fluorine gas enters the cathode side due to unexpected sudden liquid level fluctuation, it is possible to keep the state outside the explosion limit. Become. The flow rate of nitrogen is optimally adjusted depending on the size of the electrolytic cell.
[0068]
In the above embodiment, the fluorine gas generation device 30 is detachably incorporated in the semiconductor processing system, but may be fixedly installed in the semiconductor processing system. Some members in the fluorine gas generator 30, for example, the compressor 62, the main buffer tank 64, the abatement part 76, etc., may be those provided on the semiconductor manufacturing factory side. The fluorine gas is alternatively supplied to the flow management unit 22 or the gas generation unit 26, but this gas may be supplied directly to the processing chamber 12 separately from other processing gases. Further, the gas generator 26 may be configured to generate another fluorine-based processing gas instead of the inter-halogen fluorine compound gas.
[0069]
In addition, within the scope of the concept of the present invention, those skilled in the art can come up with various modified examples and modified examples, and it is understood that these modified examples and modified examples also belong to the scope of the present invention. .
[0070]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a fluorine gas generator capable of operating with high safety and reliability even during long-time operation.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a semiconductor processing system incorporating a fluorine gas generator according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing a modified example of the semiconductor processing apparatus used in combination with the gas supply system shown in FIG. 1;
FIG. 3 is a schematic diagram showing a conventional fluorine gas generator.
[Explanation of symbols]
10, 10x ... semiconductor processing device
12 Processing room
18 Exhaust system
20 ... Gas supply system
22 ... Flow management unit
24 ... Gas storage unit
26 ... Gas generator
30 ... Gas generator
32 ... Electrolyzer
34… Anode chamber
36 ... Cathode room
38 Current source
40 ... current integrator
42… Anode
44 ... Cathode
46, 48 ... Pressure gauge
52, 72… Piping
54, 74: Flow control valve
55, 75 ... control members
56 ... Suction cartridge
58 ... Capacitor
64 ... buffer tank
62 ... Compressor
76 ... Elimination unit
78 ... Exhaust system
82 ... Raw material piping
84 ... hydrogen fluoride source
86 ... Switching valve
87 ... Control member
94 ... Nitrogen source
96 ... Switching valve

Claims (10)

An apparatus for generating fluorine gas,
By electrolyzing hydrogen fluoride in an electrolytic bath made of a molten salt containing hydrogen fluoride, a product gas containing fluorine gas as a main component is generated in a first gas phase portion on the anode side, and a second gas on the cathode side is generated. An electrolytic cell that generates a by-product gas containing hydrogen gas as a main component in a gas phase portion,
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt,
A first pipe for leading the product gas from the first gas phase portion;
A second pipe for leading the by-product gas from the second gas phase portion;
A first pressure gauge for continuously measuring the pressure of the first gas phase portion;
A second pressure gauge for continuously measuring the pressure of the second gas phase portion;
A first flow control valve disposed in the first pipe;
A second flow control valve disposed in the second pipe;
A first control member that adjusts an opening degree of a first flow control valve based on a measurement result of the first pressure gauge so that a pressure of the first gas phase portion is maintained at a first set value;
The opening of the second flow control valve is adjusted based on the measurement result of the second pressure gauge so that the pressure of the second gas phase portion is maintained at a second set value substantially equal to the first set value. A second control member to adjust;
A fluorine gas generator, comprising: The fluorine gas generator according to claim 1, wherein the first and second set values are 760 to 820 Torr. The fluorine gas generation apparatus according to claim 1, further comprising a first suction unit disposed on the first pipe downstream of the first flow control valve and suctioning the first pipe. apparatus. The fluorine according to claim 3, wherein the second pipe is disposed downstream of the second flow control valve so as to be connected to a second suction unit that suctions the second pipe. Gas generator. A switching valve disposed on the raw material pipe,
A current integrator for integrating the current supplied between the anode-side electrode and the cathode-side electrode of the electrolytic cell,
A control member that opens and closes the switching valve so as to control replenishment of the hydrogen fluoride into the molten salt based on a measurement result obtained by the current integrator,
The fluorine gas generator according to any one of claims 1 to 4, further comprising: The fluorine gas generator according to claim 5, wherein the hydrogen fluoride supplied through the raw material pipe is a gas. The raw material pipe is disposed on the cathode side of the electrolytic cell so as to supply the hydrogen fluoride gas into the molten salt, and a nitrogen gas is supplied to the raw material pipe downstream of the switching valve. The fluorine gas generator according to claim 6, wherein a supply pipe is connected, and the hydrogen fluoride gas is supplied into the molten salt in a state where the hydrogen fluoride gas is added to the nitrogen gas. An apparatus for generating fluorine gas,
By electrolyzing hydrogen fluoride in an electrolytic bath made of a molten salt containing hydrogen fluoride, a product gas containing fluorine gas as a main component is generated in a first gas phase portion on the anode side, and a second gas on the cathode side is generated. An electrolytic cell that generates a by-product gas containing hydrogen gas as a main component in a gas phase portion,
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt,
A first pipe for leading the product gas from the first gas phase portion;
A second pipe for leading the by-product gas from the second gas phase portion;
A switching valve disposed on the raw material pipe,
A current integrator for integrating the current supplied between the anode-side electrode and the cathode-side electrode of the electrolytic cell,
A control member that opens and closes the switching valve so as to control replenishment of the hydrogen fluoride into the molten salt based on a measurement result obtained by the current integrator,
A fluorine gas generator, comprising: The fluorine gas generator according to claim 8, wherein the hydrogen fluoride supplied through the raw material pipe is a gas. The raw material pipe is disposed on the cathode side of the electrolytic cell so as to supply the hydrogen fluoride gas into the molten salt, and a nitrogen gas is supplied to the raw material pipe downstream of the switching valve. The fluorine gas generator according to claim 9, wherein a supply pipe is connected, and the hydrogen fluoride gas is supplied into the molten salt in a state where the hydrogen fluoride gas is added to the nitrogen gas.

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