JP3905433B2 - Fluorine gas generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluorine gas generator, and more particularly to a fluorine gas generator disposed in a gas supply system of a semiconductor processing system. Here, the semiconductor processing means that a semiconductor device, an insulating layer, a conductive layer, etc. are formed in a predetermined pattern on a substrate to be processed such as a semiconductor wafer or an LCD substrate. The various processes performed in order to manufacture the structure containing the wiring connected to a semiconductor device, an electrode, etc. are meant.
[0002]
[Prior art]
In the manufacture of semiconductor devices, various types of semiconductor processing such as film formation, etching, and diffusion are performed on a substrate to be processed, such as a semiconductor wafer or an LCD substrate. In a semiconductor processing system that performs such processing, for example, a fluorine-based gas is used as a processing gas for various purposes such as etching a silicon film or a silicon oxide film or cleaning a processing chamber. Fluorine gas is attracting attention as a new etching gas and cleaning gas, but it is not common to generate fluorine at the manufacturing site of semiconductor devices because the problem has not been completely solved in terms of safety and reliability. Is not done.
[0003]
On the other hand, an apparatus using an electrolytic cell is known as an apparatus for generating fluorine gas in a gas manufacturing factory. For example, JP-A-9-505853 discloses this type of fluorine gas generator. 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 from above into the molten salt. A pair of probes that terminate at different heights are disposed in the anode chamber. The pair of probes function as a level gauge for controlling on / off of the 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 apparatus 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 the intermediate capacitor 116 through the 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 studies by the present inventors, in the case of the fluorine gas generator shown in FIG. 3, when the operation time is long, some problems may occur in terms of safety and reliability as will be described later. Has been found. If such a problem is not solved, it becomes practically difficult to incorporate and use the 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 prior art, and an object of the present invention is to provide a fluorine gas generation device capable of operating with high safety and reliability even during long-time operation. . In particular, an object of the present invention is to provide an apparatus for generating fluorine gas on-site and on-demand. Here, on-site means that the fluorine gas generation apparatus is combined with a predetermined main processing apparatus, for example, a main processing apparatus of a semiconductor processing system. On-demand means that gas can be supplied at the timing according to the request from the main processing apparatus and with necessary component adjustment.
[0007]
[Means for Solving the Problems]
A first 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 the first gas phase portion on the anode side, and second on the cathode side. An electrolytic cell for generating a by-product gas mainly composed of hydrogen gas in the gas phase portion;
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt;
First piping for deriving the product gas from the first gas phase portion;
A second pipe for deriving 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 the opening of the first flow control valve based on the measurement result of the first pressure gauge so that the pressure of the first gas phase portion is maintained at a first set value;
Based on the measurement result of the second pressure gauge, the opening of the second flow rate control valve is adjusted 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 be adjusted;
It is characterized by comprising.
[0008]
According to a second aspect of the present invention, in the first viewpoint device, 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 disposed 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 apparatus according to the third aspect, the second pipe is connected to a second suction unit that sucks the second pipe downstream from the second flow rate control valve. It is arranged in that.
[0011]
According to a fifth aspect of the present invention, in any one of the first to fourth viewpoints,
A switching valve disposed in the raw material piping;
A current accumulator that integrates 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 the replenishment of the hydrogen fluoride into the molten salt based on the measurement result by the current accumulator;
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 piping 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 a pipe for supplying nitrogen gas to the raw material pipe downstream from the switching valve is connected, and the hydrogen fluoride gas is supplied into the molten salt in a state of being 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 the first gas phase portion on the anode side, and second on the cathode side. An electrolytic cell for generating a by-product gas mainly composed of hydrogen gas in the gas phase portion;
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt;
First piping for deriving the product gas from the first gas phase portion;
A second pipe for deriving the by-product gas from the second gas phase portion;
A switching valve disposed in the raw material piping;
A current accumulator that integrates 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 the replenishment of the hydrogen fluoride into the molten salt based on the measurement result by the current accumulator;
It is characterized by comprising.
[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 piping is a gas.
[0016]
According to a tenth aspect of the present invention, in the apparatus according to the ninth 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 a pipe for supplying nitrogen gas to the raw material pipe downstream from the switching valve is connected, and the hydrogen fluoride gas is supplied into the molten salt in a state of being added to the nitrogen gas. Features.
[0017]
Further, the embodiments of the present invention include various stages of the invention, 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 shown in the embodiment, when the extracted invention is carried out, the omitted part is appropriately supplemented by a well-known common technique. It is what is said.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the course of the development of the present invention, the present inventors have studied the problems of safety and reliability in the conventional fluorine gas generation apparatus as described with reference to FIG. As a result, the present inventors have obtained knowledge as described below.
[0019]
In the case of the apparatus shown in FIG. 3, 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, a large pressure fluctuation occurs in the fluorine gas pipe 120, whereby mist-like molten salt accumulates at the inlet of the pipe 120 and causes the pipe 120 to be blocked. In addition, since the valve 122 is frequently opened and closed, the seat 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 exhaust system pipe 121, is normally diluted below the regulation value, and is discharged outside the system. At this time, the pressure of the discharge system is expected to change depending on the installation environment. For example, if 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 rises accordingly. In this case, the liquid level largely fluctuates, and the molten salt is dragged into the hydrogen gas pipe 121 side, causing the pipe 121 to be blocked.
[0021]
When the molten salt is solidified 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. A further problem 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 greatly disrupted, there is a risk that fluorine gas and hydrogen gas will come into contact with each other 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 function and configuration are denoted by the same reference numerals, and redundant description will be given 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. The 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 disposed. An upper electrode 16 is also disposed in the processing chamber 12 so as to face the mounting table 14. By applying RF power from an RF (high frequency) power source 15 between both 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 the lower portion of the processing chamber 12. A gas supply system 20 for supplying a processing gas is connected to the 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 placement table (support member) 14 for placing 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 the lower portion of the processing chamber 12. A remote plasma chamber 13 for generating plasma is connected to the 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 source 15 to the coil antenna 17, an induction electric field for converting the processing gas into plasma is formed in the remote plasma chamber 13. A gas supply system 20 for supplying a processing gas is connected to the upper part of the remote plasma chamber 13.
[0026]
The fluorine gas generation apparatus according to the embodiment of the present invention can also be applied to a case where a cleaning gas or the like is supplied to a semiconductor processing apparatus that does not use plasma, such as a thermal CVD apparatus.
[0027]
Returning to FIG. 1, the gas supply system 20 is selectively switched between a predetermined gas in the processing chamber 12, for example, a processing gas for performing semiconductor processing and a processing gas for cleaning the processing chamber 12. A flow management unit 22 for supplying at a flow rate of 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]
A fluorine gas generation device 30 according to an embodiment of the present invention is detachably connected to the flow management unit 22 and the gas generation unit 26. That is, the generation device 30 is used to supply the fluorine gas directly to the flow management unit 22 or to supply the fluorine gas raw material to the gas generation unit 26 (the 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 production | generation apparatus 30 has the airtight electrolytic vessel 32 which accommodates the electrolytic bath which consists of 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 from above into the molten salt. In the anode chamber 34 and the cathode chamber 36, a carbon electrode (anode) 42 and a nickel electrode (cathode) 44 are respectively immersed in the molten salt. 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 accumulator 40 for integrating the supply current.
[0030]
During the electrolytic treatment, the electrolytic cell 32 is heated and kept at 80 to 90 ° C. by the accompanying heater 33. By electrolyzing hydrogen fluoride in the electrolytic bath, fluorine gas (F ₂ ) Is generated as a main component, and a by-product gas mainly including hydrogen gas is generated in the gas phase portion of the cathode chamber 36. In each of the product gas and the by-product gas, hydrogen fluoride gas is mixed by the vapor pressure of the 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 in each gas phase portion.
[0031]
Connected to the anode chamber 34 is 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. In the first pipe 52, 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 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 first pipe 52 being sucked 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. This hydrogen fluoride is removed when the product gas passes through the adsorption cartridge 56. For this reason, an adsorbent that traps 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 is made of an adsorbent whose adsorption capacity varies with temperature, such as sodium fluoride (NaF). A temperature adjustment jacket (heater) 57 for adjusting the temperature of the cartridge 56 is disposed around the cartridge 56.
[0033]
A pressure gauge 65 is disposed in the main buffer tank 64, and the pressure in the tank 64 is continuously measured. This measurement result is transmitted to the 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 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 and generation of fluorine gas is started. 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. The Thereby, 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 to, for example, atmospheric pressure to atmospheric pressure + 0.18 Mpa.
[0034]
On the other hand, the second piping 72 for deriving byproduct 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 rate 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 the second piping 72 being sucked by the exhaust system 78, passes through the abatement part 76, and then enters 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 broken due to various factors, and the liquid level is likely to change in the electrolytic bath 32. Further, even during other than the electrolytic treatment, for example, in the electrolytic bath 32 immediately after the gas switching step, such as the purge in the electrolytic bath 32 with nitrogen gas, the nitrogen purge step after the supply of the raw material hydrogen fluoride gas, etc. Liquid level fluctuations are likely to occur. These cause damage to the safety and reliability of the fluorine gas generator.
[0036]
On the other hand, in the fluorine gas generator shown in FIG. 1, the pressures in 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 the first and second control members 55 and 75 associated with the first and second flow control valves 54 and 74, respectively. Based on the transmitted measurement results, the first and second control members 55 and 75 set the first and second set values so that the pressures in the 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 degree 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 associated therewith.
[0037]
As described above, the pressures in the anode chamber 34 and the cathode chamber 36 are always constantly measured and controlled independently, so that the state of the molten salt liquid level in the anode chamber 34 and the cathode chamber 36 is maintained uniformly. In other words, with this configuration, the electrolytic cell 32 allows the fluorine generation state, the state in the first and second pipes 52 and 72, the operating state of the compressor 62 and the exhaust system 78 of the semiconductor manufacturing factory, and other environments. Protects against adverse effects of fluctuations. For this reason, damage to the expensive electrode or the like, for example, the anodic effect can be avoided in advance, and the process can be advanced safely and without suddenly stopping the electrolysis. Further, since the molten salt does not solidify at the inlets of the first and second pipes 52 and 72 and 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 preferably set to atmospheric pressure to 820 Torr, and more preferably set to atmospheric pressure to 770 Torr. Further, in order to stabilize the pressure in the anode chamber 34 and the cathode chamber 36, the first and second flow rate control valves 54 and 74 need to be able to continuously adjust the opening degree with high responsiveness. From this point of view, a piezo valve is desirably used as the first and second flow control valves 54 and 74.
[0039]
Returning to FIG. 1 again, the cathode chamber 36 of the electrolytic cell 32 is provided with a raw material pipe 82 immersed in the molten salt in order to supply hydrogen fluoride gas as a consumed raw material in 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 between a closed state and an open state of the pipe 93 is disposed in the pipe 93 on the nitrogen source 94 side. When the fluorine gas generator 30 is in operation, 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 hydrogen fluoride gas of 1 to 50 L / min. Since nitrogen gas hardly dissolves in the molten salt, it passes through the molten salt to the cathode side and is discharged.
[0041]
On the other hand, a switching valve 86 for switching between a closed state and an open state of the pipe 83 is disposed in the pipe 83 on the hydrogen fluoride source 84 side. The switching valve 86 is opened and closed under the control of the control member 87 associated therewith. During the electrolytic treatment, the current supplied between the anode 42 and the cathode 44 is integrated by the current accumulator 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 hydrogen fluoride gas into the molten salt (mixing hydrogen fluoride gas into 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]
The supply of hydrogen fluoride (HF) gas to the electrolytic cell 32 is controlled by integrating the supply current based on the following theory. That is, fluorine in electrolysis (F ₂ ) The amount of generation is proportional to the amount of electricity according to Faraday's law. This law holds regardless of the electrolysis conditions such as temperature, concentration, and electrode type. 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 represents a fluorine generation flow rate (cc / min), and X represents an electric quantity (here, electrolysis current value (A)).
[0044]
For example, in the initial state, the hydrogen fluoride concentration 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 hydrogen fluoride concentration falls below the lower limit of the concentration, the melting point of the molten salt increases, and in the worst case, the molten salt may solidify and 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 in fluorine also increases. In this case, there arises a problem that a burden on an adsorbent (for example, sodium fluoride (NaF)) that traps hydrogen fluoride by adsorption in the adsorption cartridge 56 increases. Therefore, it is necessary to keep the hydrogen fluoride concentration within the above range, for example, within the range of 41 to 39%. Equation (2) below shows the relationship between the amount of hydrogen fluoride gas consumed and the amount of fluorine gas generated. Here, 2 moles of hydrogen fluoride are required to generate 1 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 necessary for generating 1 mol of fluorine (cc / min), and the first 0.05Z is a flow rate of hydrogen fluoride accompanying 1 mol of fluorine (cc / min). min), the second 0.05Z is the flow rate of hydrogen fluoride accompanying one mole of hydrogen (cc / min), t is the generation time (min), and T is the amount of hydrogen fluoride consumed (L). Show.
[0046]
Substituting 6.8X for Z in equation (2) based on equation (1) yields equation (3) below.
[0047]
0.01428X × t = T (3)
In Equation (3), X represents the amount of electricity (A), t represents the generation time (min), and T represents the amount of hydrogen fluoride consumed (L).
[0048]
The amount of hydrogen fluoride that can be consumed depends on the amount of molten salt introduced into the electrolytic cell 32. Since the concentration of hydrogen fluoride in the molten salt before starting electrolysis is 41%, if the amount of 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 formula (4). Therefore, the maximum amount of hydrogen fluoride that can be consumed and consumed is represented by the following formula (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 in Expression (3) is substituted into HFc in Expression (5), the following Expression (7) is obtained through the following Expression (6).
[0051]
0.01428X × t = 0.033C (6)
X × t = 2.3C (7)
In the formulas (6) and (7), X represents the amount 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) charged into the electrolytic cell 32 is determined in advance, the relationship between the amount of electricity X corresponding to the usage range of hydrogen fluoride concentration 41 to 39% and the fluorine generation time t is determined. be able to. Here, the timing of replenishment of hydrogen fluoride gas (the lower limit of the use range) can be specified by a value obtained by integrating the amount of electricity along the time axis, so 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 National Patent Publication No. 9-505853 (hereinafter referred to as' 853 Publication) detects a level of an electrolyte in an electrolytic cell, and starts supplying current in accordance with a signal from the control sensor means. Alternatively, a fluorine cell is disclosed that includes current supply means responsive to the signal to stop. That is, the generation of fluorine is continued until reaching a preset position so that a drop in liquid level generates a signal. Since the device for controlling the electrolysis in response to this signal stops the current supply to the cell, the electrolysis is stopped and the decrease in the electrolyte level is also stopped.
[0055]
That is, in the technique disclosed in this publication, current on / off control is intentionally performed using the liquid level fluctuation, and there is no idea of suppressing the fluctuation. However, in electrolysis, in order to continuously generate fluorine gas while maintaining a steady state, it is necessary to minimize the liquid level fluctuation.
[0056]
The '853 publication specifies that the anode chamber in the electrolytic cell is a fluorine storage. However, in an actual fluorine generator for semiconductor processing, it is difficult to match the amount of fluorine generated with the demand, so a capacitor and a compressor having a certain size are required. The technology disclosed in this publication cannot cope with such changes in the external environment.
[0057]
Therefore, a commercially available fluorine generation system corresponding to this publication includes a capacitor having a capacity of several liters and a bellows compressor. This system stores fluorine in the buffer tank intermittently by an on / off opening / closing valve. By using such a method, it is possible to continuously generate fluorine without stopping generation of fluorine. In this case, although the gas can be generated constantly, it has actually been experienced that the following problems occur due to long-term generation.
[0058]
Fine molten salt mist accompanying the fluorine enters the capacitor existing between the pipe or the electrolytic cell and the compressor. Since the mist has a melting point near 80 ° C., it exists as a solid in the pipe. As the amount of mist increases, problems such as (1) piping blockage or (2) damage to the valve seat in the on / off valve occur.
[0059]
In the former case, the electrolysis is immediately stopped, and it is necessary to remove the salt clogged in the pipe. Since the reactive gas fluorine is also present in the tube, the removal work is accompanied by the latest attention and danger. In the latter case, since leakage occurs in the valve, electrolysis is also stopped. In addition, since the ON / OFF operation frequently repeats the operation, the valve life is immediately reached.
[0060]
Further, in such a control method, a change in the liquid level in the anode is unavoidable to some extent, and the contact area between the electrode surface and the liquid always changes. For this reason, it becomes difficult to ensure a stable amount of fluorine generation due to a change in current efficiency during electrolysis. In addition, there arises a problem that the electrode (3) electrode (carbon is usually used for the anode electrode) needs to be replaced due to the anode effect.
[0061]
If the control of the amount of fluorine generated depends on the on / off of the power source by the control sensor as in the '853 publication, it cannot cope with the surrounding environmental change (in this case, the connection with the compressor). That is, it is necessary to use a compressor in an electrolytic bath 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 point of view, the control method of the '853 publication is not suitable for semiconductor processing and is not practical.
[0062]
An important point in the above-described embodiment of the present invention is that it is possible to always generate stable fluorine without being affected by environmental changes 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 connected to the buffer tank at the rear stage of the compressor is linked to the current source, and when the pressure decreases to a certain pressure, the power is turned on and fluorine is generated. When the pressure increases to a certain point, the power is turned off. When such a method is employed, electrolysis can be stopped without causing a difference in liquid level as in the '853 publication.
[0064]
In view of safety, the '853 publication recommends that the cathode side outlet pressure is always operated at atmospheric pressure (or a pressure slightly exceeding atmospheric pressure). However, in an actual semiconductor factory, the pressure change in the pipe on the cathode side is large, and it is almost impossible to maintain this. This publication focuses only on the pressure change in the anode chamber, which is based on the premise that the pressure in the cathode chamber 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 control. However, the actual liquid level is not known from the pressure. Therefore, for the purpose of improving safety, it is desirable that one liquid level sensor is inserted 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 into the electrolytic cell molten salt (preferably on the cathode side) by bubbling. Since AHF is absorbed by the molten salt at a very high rate, the negative pressure is instantaneously generated in the cathode chamber when supplied at a low flow rate. In this case, the molten salt rises inside the AHF feed pipe and, in the worst case, solidifies and cannot be supplied. Therefore, it is preferable that the supply flow rate of AHF is fast. However, the flow rate of AHF that can actually flow is limited.
[0067]
Therefore, in the above embodiment of the present invention, for the purpose of increasing the total flow rate during AHF, AHF is mixed with nitrogen gas and supplied when AHF is supplied. Since nitrogen gas hardly dissolves in the molten salt, it passes through the molten salt to the cathode side and is discharged. Nitrogen gas always flows into the cathode chamber with or without 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-described embodiment, the fluorine gas generation device 30 is detachably incorporated in the semiconductor processing system, but may be fixedly installed in the system. In addition, some members in the fluorine gas generation device 30, for example, the compressor 62, the main buffer tank 64, the abatement part 76, and the like can be those installed on the semiconductor manufacturing factory side. The fluorine gas is alternatively supplied to the flow management unit 22 or the gas generation unit 26. However, this gas may be supplied directly to the processing chamber 12 separately from other processing gases. Further, the gas generation unit 26 may be configured to generate other fluorine-based processing gas instead of the interhalogen fluorine compound gas.
[0069]
In addition, in the category of the idea of the present invention, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications 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 generation apparatus that can operate 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 generation device according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a modified example of a semiconductor processing apparatus used in combination with the gas supply system shown in FIG.
FIG. 3 is a schematic view showing a conventional fluorine gas generator.
[Explanation of symbols]
10, 10x ... Semiconductor processing equipment
12 ... Processing chamber
18 ... Exhaust system
20 ... Gas supply system
22 ... Flow management department
24 ... Gas storage
26 ... Gas generator
30 ... Gas generator
32 ... Electrolysis tank
34 ... Anode chamber
36 ... Cathode chamber
38 ... Current source
40 ... Current accumulator
42 ... Anode
44 ... Cathode
46, 48 ... Pressure gauge
52, 72 ... Piping
54, 74 ... Flow control valve
55, 75 ... Control member
56 ... Adsorption cartridge
58 ... Capacitor
64 ... Buffer tank
62 ... Compressor
76 ... abatement part
78 ... exhaust system
82 ... Raw material piping
84 ... Hydrogen fluoride source
86 ... Switching valve
87 ... Control member
94 ... Nitrogen source
96 ... Switching valve

Claims (4)

An apparatus for generating fluorine gas,
An electrolytic cell for electrolyzing hydrogen fluoride in one electrolytic bath made of a molten salt containing hydrogen fluoride, and a product mainly containing fluorine gas in the first gas phase portion on the anode side on the electrolytic bath Generating a gas and generating a by-product gas mainly composed of hydrogen gas in the second gas phase portion on the cathode side ;
A raw material pipe for supplying hydrogen fluoride as a raw material into the molten salt;
First piping for deriving the product gas from the first gas phase portion;
A second pipe for deriving 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 the opening of the first flow control valve based on the measurement result of the first pressure gauge so that the pressure of the first gas phase portion is maintained at a first set value;
Based on the measurement result of the second pressure gauge, the opening of the second flow rate control valve is adjusted 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 be adjusted;
A first suction means disposed in the first pipe downstream of the first flow control valve and sucking the first pipe;
Comprising
The second pipe is connected to second suction means for sucking the second pipe downstream of the second flow control valve;
The hydrogen fluoride supplied through the raw material piping is a gas, and the raw material piping is arranged to supply the hydrogen fluoride gas into the molten salt only on the cathode side of the electrolytic cell. A pipe for supplying nitrogen gas to the raw material pipe, the hydrogen fluoride gas being supplied to the molten salt in a state of being added to the nitrogen gas, and wherein the nitrogen gas is Being set to be discharged from the electrolytic cell through the second pipe together with the by-product gas;
A fluorine gas generator characterized by the above.   The fluorine gas generator according to claim 1, wherein the first and second set values are 760 to 820 Torr. A switching valve disposed in the raw material piping;
A current accumulator that integrates 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 the replenishment of the hydrogen fluoride into the molten salt based on the measurement result by the current accumulator;
The fluorine gas generator according to claim 1 , further comprising:   The fluorine gas generation device according to claim 3, wherein the piping for supplying the nitrogen gas is connected to the raw material piping downstream of the switching valve.

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