WO2006043125A1

WO2006043125A1 - Fluorine gas generator

Info

Publication number: WO2006043125A1
Application number: PCT/IB2004/003459
Authority: WO
Inventors: Fumihiro Honma; Jun Sonobe
Original assignee: L'air Liquide, Societe Anonyme A Directoire Et Conseil De Surveillance Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2004-10-20
Filing date: 2004-10-20
Publication date: 2006-04-27

Abstract

To provide a fluorine gas generator that is capable of very safe and highly (5) reliable operations even during long-term use. A fluorine gas generator (30) has an electrolytic cell (32) that generates product gas whose main component is fluorine gas in a first gas-phase region on the anode side and that generates by-product gas whose main component is hydrogen in a second gas-phase region on the cathode side. A first and second conduits (52, 72) are provided for withdrawal of the product and by-product gases. A first gas flow rate control valve (56) is provided in the first conduit (52); the aperture of this valve is adjusted based on information that directly or indirectly indicates the state within the electrolytic cell (32). A first cartridge (54) is disposed in the first conduit (52) upstream from the first valve (56). The first cartridge (54) holds sodium fluoride pellets that adsorb hydrogen fluoride and molten salt mist admixed in the product gas.

Description

Fluorine gas generator

This invention relates to fluorine gas generators and more particularly relates to a fluorine gas generator that is disposed in the gas feed system of a semiconductor processing system. Here, semiconductor processing refers to the various processes that are carried out in order to fabricate a semiconductor device — and/or a structure (comprising, e.g., interconnects, electrodes) that connects to a semiconductor device — on a substrate through the formation of, e.g., semiconductor, dielectric, and conductor layers in desired patterns on the substrate. This substrate can be exemplified by semiconductor wafers and LCD substrates. Various semiconductor processes, such as film formation, etching, and diffusion, are executed on substrates such as semiconductor wafers and LCD substrates during the fabrication of semiconductor devices. The semiconductor processing systems that implement such processes use, for example, fluorine (F)- type gases as process gases for various applications, such as the etching of silicon or silicon oxide films and for cleaning the interior of processing compartments. While fluorine gas has been receiving attention as a novel etching gas and cleaning gas, the production of fluorine at the site of semiconductor device fabrication is not generally practiced because issues with safety and reliability have not been completely resolved. However, research and development in this field has continued, and, for example, Patent Reference 1 discloses a semiconductor processing system in which fluorine is produced onsite and is fed to the processing compartment as a cleaning gas. Fluorine is produced as a cleaning gas in the system disclosed in this reference by the electrolysis of hydrogen fluoride (HF) by a gas generator. The cleaning gas is fed through a feed conduit that connects the gas generator to the processing compartment. A refrigerated column is provided in the feed conduit in order to remove the hydrogen fluoride (HF) in the cleaning gas by cryocondensation. On the other hand, for example, an apparatus that produces fluorine gas in a gas production plant is disclosed in Patent Reference 2. The fluorine gas generator disclosed in this reference has an electrolytic cell that holds an electrolytic bath comprising molten salt that contains potassium fluoride and hydrogen fluoride. The hydrogen fluoride in the electrolytic bath is subjected to electrolysis with the production of product gas whose main component is fluorine gas on the anode side and the production of by-product gas whose main component is hydrogen gas on the cathode side.

In the apparatus in Patent Reference 2, the feed conduit for product gas withdrawal is provided with, inter alia, a solenoid valve for liquid level control, a blank column, an absorption column, and a filter column in the given sequence considered from the upstream side. The exhaust conduit for exhaust of the by-product gas is also provided with, inter alia, a solenoid valve for liquid level control, a blank column, and an absorption column (a filter column is not present) in the given sequence considered from the upstream side. The blank column is used to remove electrolytic bath spray that is present in the product gas. The absorption column holds sodium fluoride (NaF) in order to remove hydrogen fluoride (HF) present in the product gas. Particles present in the product gas are removed by the filter column. [Patent Reference 1] Published United States Patent Application No. 2002/0074013 [Patent Reference 2]

Japanese Laid Open (Unexamined or Kokai or A) Patent Application Number 2002-339090 As a result of their research, the present inventors discovered that several problems with respect to safety and reliability occur, as described below, during longer-term operation of the prior-art apparatuses. Without a solution to these problems, use of a fluorine gas generator incorporated into an automated manufacturing system, such as a semiconductor device fabrication system, is quite problematic from a practical standpoint.

This invention was developed considering the aforementioned problems with the prior art. The object of this invention is to provide a fluorine gas generator that is capable of very safe and highly reliable operations even during long-term use. A particular object of this invention is to provide an onsite and on-demand fluorine gas generator. Here, onsite means that the fluorine gas generator is assembled or incorporated into the particular main processing equipment, for example, the main processing equipment of a semiconductor processing system. On-demand means that the gas can be supplied with the required component adjustments and at a timing that are responsive to the demands of the main processing equipment. A first aspect of the present invention is a fluorine gas generator that is characteristically provided with an electrolytic cell that effects electrolysis of hydrogen fluoride in an electrolytic bath comprising molten salt that contains potassium fluoride and hydrogen fluoride, thereby producing product gas whose main component is fluorine gas in a first gas-phase region on the anode side and producing by-product gas whose main component is hydrogen gas in a second gas-phase region on the cathode side, a first conduit that withdraws the product gas from the first gas-phase region, a second conduit that withdraws the by-product gas from the second gas-phase region, a first valve that is disposed in the first conduit and that controls the flow rate of the gas passing through the first conduit, a first control member that adjusts the aperture of the first valve based on information that directly or indirectly indicates the state within the electrolytic cell, and a first cartridge that is disposed in the first conduit upstream from the first valve and that holds sodium fluoride pellets that adsorb the hydrogen fluoride and mist of the aforementioned molten salt that are admixed in the product gas.

In a second aspect of the present invention, the fluorine gas generator according to the first aspect is characteristically also provided with a second cartridge that is disposed in the second conduit and that holds adsorbent that adsorbs mist of the aforementioned molten salt. In a third aspect of the present invention, the fluorine gas generator according to the second aspect is characterized in that the adsorbent is provided with sodium fluoride pellets. In a fourth aspect of the present invention, the fluorine gas generator according to the second or third aspect is characteristically also provided with a second valve that is disposed in the second conduit and that controls the flow rate of the gas passing through the second conduit and a second control member that adjusts the aperture of the second valve based on information that directly or indirectly indicates the state within the electrolytic cell, wherein the second cartridge is disposed upstream from the second valve.

In a fifth aspect of the present invention, the fluorine gas generator according to the fourth aspect is characteristically also provided with a first pressure gauge that measures the pressure in the first gas-phase region and a second pressure gauge that measures the pressure in the second gas-phase region, wherein the aforesaid first and second control members adjust, respectively, the apertures of the first and second valves based on the measurement results from the first and second pressure gauges so as to maintain the pressures in the first and second gas-phase regions at substantially equal set values.

In a sixth aspect of the present invention, the fluorine gas generator according to any of the first through fifth aspects is characteristically also provided with a temperature regulator that regulates the temperature of the first cartridge. In addition, the embodiments of this invention explore a variety of executions of this invention, and various embodiments of this invention can be derived by suitable combination of the plural number of disclosed constituent elements. For example, when an embodiment of the invention has been derived in which some constituent elements have been omitted from the overall set of constituent elements presented for the embodiments, these omitted elements can be suitably fulfilled by conventional well-known technologies in the actual working of the derived inventive embodiment.

During the course of the development of the present invention, the inventors studied the safety and reliability problems of the prior-art fluorine gas generators and obtained the knowledge described below as a result.

Safety and reliability considerations make control of the liquid level of the electrolytic bath in the electrolytic cell an extremely important issue in the case of fluorine gas generators that employ an electrolytic cell. In the apparatus in Patent Reference 2, the level of the electrolytic bath in the electrolytic cell is controlled by placing level probes on both the anode side and cathode side of the electrolytic cell and using the detection results from these probes to operate solenoid valves placed in the product gas feed conduit and the by-product gas exhaust conduit. On the other hand, the placement of a control valve between the gas generator and refrigerated column is required in the case of Patent Reference 1 in order to control the level of the electrolytic bath in the electrolytic cell, although absolutely no details on this point are taught therein. These apparatus structures, however, are not capable of swiftly responding to changes in the liquid level, particularly unexpected changes.

The present inventors have already discovered that the pressure at both electrodes in the electrolytic cell can be subjected to a very discriminating and highly responsive control by continuously monitoring the pressures at the anode and cathode and subjecting the pressures to fine control independently of the flow rate (using, for example, a flow rate controller that also incorporates a piezo valve) (Japanese Patent Application 2002-202734). Since this type of flow rate control valve has an extremely small gas flow path diameter that poses a risk of blockage by contaminants (for example, microparticles and dust) entrained by the gas, the flow rate control valves are protected by the installation of upstream filters on both the anode and cathode sides.

In continuing experiments with this apparatus developed by the present inventors, control of the electrolytic bath was excellent during the initial period of electrolysis, but a new problem was created in that continuing operation was made impossible due to the rapid development of blockage in regions within the conduits on both the anode and cathode sides where pressure differences were created (for example, the filters). The cause of this was found to be a mist of molten salt entrained in the respective gases produced by the electrolytic cell: this mist deposited on the filter surfaces and plugged the filter.

A fine molten salt mist entrained by the gas enters the piping and the various elements present between the electrolytic cell and compressor. Since this mist has a melting point around 80⁰C, it is present in the piping in the form of a solid. As the amount of this mist grows, problems appear such as pipe blockage and valve seat damage at ON/OFF valves.

When pipe blockage occurs, operation of the electrolytic cell must be immediately halted and the salt blocking the pipe must be removed. Since reactive fluorine gas is also present in the pipe, the operation to remove the material within the pipe is hazardous and requires utmost caution. In the case of valve seat damage, the occurrence of valve leakage again requires that operation of the electrolytic cell be halted. In addition, ON/OFF valve life is shortened since these valves are subject to frequent operation. In experiments carried out in connection with these circumstances, the results of electron microscopic measurements showed that the molten salt mist captured on filters has a size distribution of 0.4-0.6 μm. Corrosion of the filter media by the molten salt mist was also confirmed in the case of filter media fabricated in particular of stainless steel (for example, SS316L). Although a filter has heretofore been provided only in the piping on the anode side of the electrolytic cell, i.e., the side on which product gas (main component = fluorine gas) is generated, it was found that the molten salt mist is also present (and pipe blockage therefore occurs) in the by¬ product gas (main component = hydrogen) that is generated from the cathode.

As also indicated in Patent Reference 2, sodium fluoride (NaF) has heretofore been used by electrolytic cell-based fluorine gas generators to remove the hydrogen fluoride (HF) present in the product gas. In order to improve fluorine gas generators, the present inventors also conducted various experiments with regard to the fluorine gas adsorption capacity of NaF and during these experiments obtaining additional findings with regard to the functionality of NaF as described below. The fluorine gas adsorption capacity of NaF was investigated in some experiments by placing a cartridge filled with NaF pellets in the product gas feed conduit of a fluorine gas generator. It was found as a result that, in addition to the hydrogen fluoride that is the original target for removal, the NaF cartridge could also remove the molten salt-derived potassium fluoride (KF) component (main component of the molten salt mist) down to the sub-ppb level. In addition, it was confirmed that other components entrained in the molten salt mist were also almost completely absent downstream from the NaF cartridge. Metal analysis was carried out in these experiments by bubbling the product gas directly into a PFA container filled with ultrapure water in order to collect the metal impurities and analyzing the resulting aqueous hydrogen fluoride with an inductively coupled plasma-mass spectrometric (ICP-MS) instrument.

Based on these results, additional investigations were carried out into whether or not NaF cartridges could be used for removal of the molten salt mist.

When a one-quarter inch guard filter (0.04 μm) was used in both the anode side conduit and cathode side conduit of a fluorine gas generator, the life until filter blockage by mist was 4-15 hours on the cathode side and approximately 120 hours on the anode side. In view of these results and considering the time advantage, the experimental apparatus shown in Figure 3 was placed on the cathode side (side that produces by-product gas whose main component is hydrogen) of a fluorine gas generator and experiments were conducted that confirmed the ability of NaF cartridges to remove the molten salt mist.

As shown in Figure 3, a pressure gauge 116 and a piezo valve 118 were connected to the cathode of a fluorine gas generator through parallel and switchable first and second conduits 112, 114. The piezo valve 118 was set up to be aperture controllable based on the pressure at the cathode of the fluorine gas generator. A guard filter 124 and NaF pellet-filled cartridge 122 were placed in the first conduit 112, while only a guard filter 126 was placed in the second conduit 114.

The first and second conduits 112, 114 were used in alternation and the time required until the occurrence of blockage by mist was measured for each guard filter 124, 126. Blockage was considered to have occurred when the following condition persisted for at least 1 minute: pressure at the pressure gauge 116 < -30 kPa while the aperture of the piezo valve 118 was at least 100%. The piezo valve 118 was set so as to maintain a valve aperture of about 60% under normal conditions. The aperture of the piezo valve 118 increased when the pressure at the cathode rose due to blockage upstream from the valve: the valve aperture was made larger in an attempt to provide a larger by-product gas flow.

The specific experimental procedure was as follows. (1) In order to measure the blockage time for the guard filter 126, the valves Via,

V1b were closed and the valves V2a, V2b were opened. (2) The integrated quantity of electrolysis (Ah) prior to starting was recorded.

(3) Electrolysis at 100 A was carried out continuously (fluorine generation rate = approximately 688 cc/min).

(4) Fluorine electrolysis was halted when the blockage occurrence condition provided above was satisfied and the integrated quantity of electrolysis for fluorine generation was recorded at that point.

(5) Then, in order to measure the blockage time for the guard filter 124, the NaF cartridge 122 was heated to 200⁰C, the valves Via, V1b were opened, and the valves V2a, V2b were closed. (6) The integrated quantity of electrolysis (Ah) prior to starting was recorded.

(7) Electrolysis at 100 A was carried out continuously (fluorine generation rate = approximately 688 cc/min).

(8) Fluorine electrolysis was halted when the blockage occurrence condition provided above was satisfied and the integrated quantity of electrolysis for fluorine generation was recorded at that point.

The results of the preceding experiments are reported in Table 1, in which F124 refers to the guard filter 124 (presence of the NaF cartridge 122), F126 refers to the guard filter 126 (absence of the NaF cartridge 122), IEs refers to the starting value for the integrated quantity of electrolysis, IEe refers to the end value for the integrated quantity of electrolysis, and IEc refers to the amount of electrolysis (Ah) until blockage.

Table 1.

IEs (Ah) IEe (Ah) IEc (Ah) Life

F124 23010 30567 7557 75 h : 34 m

F126 21469 23010 1541 15 h : 24 m

As these experimental results show, the mist blockage time of the guard filters was extended by the use of the NaF cartridge 122 by as much as 5-times. Since the conduit diameter of the NaF cartridge 122 is larger than that of ordinary piping, the accompanying reduction in flow rate may have contributed to the improved life.

However, since the capture sections containing the guard filters 124, 126 both had the same one-quarter inch conduit diameter, one can still conclude based on a simple comparison that the NaF cartridge 122 is effective for spray capture.

Embodiments of the present invention, which was framed based on the aforementioned knowledge, are described hereinbelow with reference to the drawings. In the description that follows, constituent elements that have about the same structure and function have been assigned the same reference symbol and will not be described more than once unless necessary.

Figure 1 contains a schematic drawing that illustrates a semiconductor processing system that incorporates a fluorine gas generator according to an embodiment of the present invention. This semiconductor processing system contains a semiconductor processing apparatus 10 that implements a process, such as film formation, etching, or diffusion, on a substrate such as a semiconductor wafer or LCD substrate.

The semiconductor processing apparatus 10 is provided with a processing compartment 12 for holding the substrate and for implementing semiconductor processing. A mounting platform 14 (support member) that also functions as a lower electrode is disposed in the processing compartment 12 in order to mount the substrate. An upper electrode 16 is disposed within the processing compartment 12 facing the mounting platform 14. A high-frequency (RF) field for converting the process gas into a plasma is formed in the processing compartment 12 by the application between the two electrodes 14, 16 of RF power from an RF power source 15. The lower region of the processing compartment 12 is connected to an exhaust system 18 for exhausting the interior thereof and establishing a vacuum therein. A gas feed system 20 is also connected at the top of the processing compartment 12 in order to supply process gas.

Figure 2 contains a schematic diagram that shows a modified semiconductor processing apparatus 1Ox that can be used in combination with the gas feed system 20 illustrated in Figure 1. The semiconductor processing apparatus 1Ox is provided with a processing compartment 12 for holding the substrate and for implementing semiconductor processing. A mounting platform 14 (support member) is disposed in the processing compartment 12 in order to mount the substrate. The lower region of the processing compartment 12 is connected to an exhaust system 18 for exhausting the interior thereof and establishing a vacuum therein. The top of the processing compartment 12 is connected to a remote plasma compartment 13 that can generate a plasma. A coil antenna 17 is wrapped about the circumference of the remote plasma compartment 13. An induction field for converting the process gas into plasma is formed within the remote plasma compartment 13 by the application of RF power from a high-frequency (RF) power source 15 to the coil antenna 17. A gas feed system 20 is also connected at the top of the remote plasma compartment 13 in order to supply process gas.

The fluorine gas generator according to this embodiment of the present invention can also be used with semiconductor processing tools that do not employ a plasma, for example, it can be used to feed cleaning gas to a thermal CVD tool.

Returning to Figure 1 , a flow management section 22 is disposed in the gas feed system 20; this flow management section 22 is provided in order to selectively switch between or among gases, for example, a process gas for semiconductor processing and a process gas for cleaning the interior of the processing compartment 12, and in order to feed gas at a specified flow rate. The flow management section 22 is connected to a gas storage section 24 that has a plurality of gas sources that store various active and inert gases. The flow management section 22 is also connected to a gas generation section 26 that generates fluorine gas-type process gases by reaction processes.

A fluorine gas generator 30 according to this embodiment of the present invention is detachably connected to the flow management section 22 and the gas generation section 26. That is, the generator 30 either directly feeds fluorine gas to the flow management section 22 or is used to feed precursor fluorine gas to the gas generation section 26 (switching valve not shown).

The generator 30 has a gastight electrolytic cell 32 that holds an electrolytic bath comprising molten salt that contains hydrogen fluoride. The molten salt comprises a mixture of potassium fluoride (KF) and hydrogen fluoride (HF) (KF/2HF) or Fremy's salt (KF/2HF + additive). The electrolytic cell 32 is partitioned into an anode compartment 34 and a cathode compartment 36 by a partition plate 35 that extends into the molten salt from the top. A carbon electrode (anode) 42 and a nickel electrode (cathode) 44 are immersed in the molten salt, respectively, in an anode compartment 34 and a cathode compartment 36. There are attached to the electrolytic cell 32 a power source 38 to feed current across the anode 42 and cathode 44 and a current integrator 40 that integrates the current input.

During the course of electrolysis the electrolytic cell 32 is heated and maintained at 80-90⁰C by an attached heater 33. Electrolysis of the hydrogen fluoride in the electrolytic bath generates product gas (main component = fluorine gas (F2)) in

the gas-phase region of the anode compartment 34 and generates by-product gas (main component = hydrogen) in the gas-phase region of the cathode compartment 36. Hydrogen fluoride gas is admixed (for example, at 5%) in both the product gas and by-product gas in correspondence to the vapor pressure of the hydrogen fluoride gas in the molten salt starting material.

A first conduit 52 is connected to the anode compartment 34 in order to withdraw the product gas and transport it to the flow management section 22 and gas generation section 26 of the gas feed system 20. The following, inter alia, are disposed in the first conduit 52 in the given sequence considered from the upstream side: an adsorption cartridge 54, a first flow rate control valve 56, a mini-buffer tank 58, a compressor (suction means) 62, and a main buffer tank 64. The product gas generated in the anode compartment 34 is forcibly suctioned from the anode compartment 34 due to suction of the first conduit 52 by the compressor 62 and is stored in the main buffer tank 64. Reference symbol 66 in Figure 1 refers to a line filter.

The pressure within the main buffer tank 64 is continuously measured by a pressure gauge 65 disposed on the tank 64. The result of this measurement is transmitted to a control element 39 that is attached to the power source 38. This control element 39 controls the current feed to the electrolytic cell 32 by switching the power source 38 on and off based on the transmitted measurement result. Specifically, when the pressure in the tank 64 has fallen to some specified pressure, the power source 38 is switched on and fluorine gas generation is begun; when the pressure has risen to some specified pressure, the power source 38 is switched off and fluorine gas generation is halted. This enables electrolysis to be stopped without causing a difference in the molten salt level between the anode compartment 34 and cathode compartment 36 in the electrolytic cell 32. The pressure in the tank 64 is set at, for example, atmospheric pressure to atmospheric pressure + 0.18 MPa.

A second conduit 72 is connected to the cathode compartment 36 in order to withdraw the by-product gas. The second conduit 72 is detachably connected to, for example, a conduit in the exhaust system (suction means) 79 of the semiconductor fabrication plant. The following, inter alia, are disposed in the second conduit 72 in the given sequence considered from the upstream side: an adsorption cartridge 74, a second flow rate control valve 76, and a detoxification section 78. The by-product gas generated at the cathode compartment 36 is forcibly suctioned from the cathode compartment 36 due to the suctioning of the second conduit 72 by the exhaust system 79 and is sent into the exhaust system 79 after passage through the detoxification section 78.

The pressure balance between the anode compartment 34 and the cathode compartment 36 is prone to disturbance during electrolysis by a variety of factors as described above, leading to fluctuations in the liquid level within the electrolytic cell 32. In addition, fluctuations in the liquid level within the electrolytic cell 32 are also prone to occur even when electrolysis is not in progress, mainly directly after a gas switching step such as, for example, a nitrogen purge of the interior of the electrolytic cell 32 or a nitrogen purge after completion of feed of the starting hydrogen fluoride gas. These cause a deterioration in the safety and reliability of the fluorine gas generator.

In response to this, the pressures in the gas-phase region of both the anode compartment 34 and the cathode compartment 36 are continuously measured, respectively, by the first and second pressure gauges 46, 48 in the fluorine gas generator shown in Figure 1. These measurement results are transmitted, respectively, to first and second control members 57, 77 attached to the first and second flow rate control valves 56, 76. The first and second control members 57, 77 adjust the apertures of the first and second flow rate control valves 56, 76 based on the transmitted measurement results so as to maintain the pressures in the gas- phase regions of the anode compartment 34 and the cathode compartment 36 at first and second set values that are substantially equal to one another. That is, the first and second flow rate control valves 56, 76 are subjected to continuous aperture adjustment under control by the respectively attached first and second control members 57, 77.

A uniform state is maintained for the molten salt levels in the anode compartment 34 and cathode compartment 36 due to this independent and continuous measurement and control of the pressures in the anode compartment 34 and cathode compartment 36. In other words, this configuration protects the electrolytic cell 32 from undesirable influences arising from fluctuations in the status of fluorine generation, the status of the first conduit 52, the status of the second conduit 72, the operating status of the compressor 62, the operating status of the exhaust system 79 in the semiconductor fabrication plant, and other elements of the operating environment. This enables damage to the expensive electrodes, etc., for example, the anode effect, to be avoided before anything happens and enables processing to proceed safely and without unexpected stoppages in electrolysis.

The first and second set values for the gas-phase regions of the anode compartment 34 and the cathode compartment 36 are desirably atmospheric pressure to 820 torr and more desirably atmospheric pressure to 770 torr. In order to stabilize the pressures in the anode compartment 34 and the cathode compartment 36, the apertures of the first and second flow rate control valves 56, 76 must be capable of a very response and continuous adjustment. With this in mind, piezo valves are desirably used as the first and second flow rate control valves 56, 76.

As mentioned above, hydrogen fluoride is admixed at a few percent (for example, 5%) in the product gas and by-product gas. Molten salt mist (main component = KF) from the electrolytic cell is also entrained in the product gas and by¬ product gas. This hydrogen fluoride and molten salt mist are removed when the product gas and by-product gas pass through, respectively, the adsorption cartridge 54 and the adsorption cartridge 74. This eliminates blockage of the first and second conduits 52, 72 by solidification of the molten salt at their inlets and eliminates the requirement for frequent maintenance.

A large number of sodium fluoride (NaF) pellets are held within the cartridges 54, 74 as the adsorbent that adsorptively captures the hydrogen fluoride and molten salt mist. Considering such factors as handling characteristics and pressure losses, the NaF pellets are produced with a shape and in dimensions suitable for the elaboration of pellet-to-pellet gaps that form gas flow paths. In addition, since the capacity of sodium fluoride to adsorb hydrogen fluoride varies with temperature, temperature adjustment jackets (heaters) 55, 75 are respectively disposed on the circumferences of the cartridges 54, 74 for purposes of temperature adjustment. Based on the criterion of optimal hydrogen fluoride adsorption, the cartridges 54, 74 are maintained at room temperature to 300⁰C and desirably at 80-120⁰C.

Since the by-product gas will be discarded, the hydrogen fluoride need not necessarily be removed from the by-product gas. In other words, the cartridge 74 disposed in the second conduit 72 carrying the by-product gas need only be capable of removing the molten salt mist in order to prevent blockage of the conduit system. In view of this, the adsorbent filled in the adsorption cartridge 74 for the by-product gas can be an inorganic fluorine compound such as calcium fluoride or potassium fluoride rather than sodium fluoride.

In the embodiment described hereinabove, the aperture of the first and second flow rate control valves 56, 76 is adjusted using the pressures within the anode compartment 34 and the cathode compartment 36 as the information that directly or indirectly indicates the state within the electrolytic cell 32. However, this invention is similarly applicable to an apparatus that adjusts the aperture of the flow rate control valves based on other information that directly or indirectly indicates the state within the electrolytic cell 32, for example, based on the liquid level within the electrolytic cell 32.

In addition, the fluorine gas generator 30 is detachably incorporated in the semiconductor processing system, but it may be permanently installed in the semiconductor processing system. Moreover, elements situated in the semiconductor fabrication plant may also be used for some of the elements in the fluorine gas generator 30, for example, the compressor 62, main buffer tank 64, detoxification section 78, etc. While the fluorine gas is fed either to the flow management section 22 or the gas generation section 26, this gas may be fed directly to the processing compartment 12 separately from other process gases. The gas generation section 26 can also be set up to generate other fluorine-type process gases that are not interhalogen fluorine compound gases.

While various modifications and alterations within the technical sphere of the concept of this invention can be devised by the individual skilled in the art, it should be understood that these modifications and alterations also fall within the scope of this invention.

As described hereinabove, the present invention provides a fluorine gas generator that is capable of very stable and highly reliable operation even during long-term use.

Brief Description of the Drawings

Figure 1 contains a schematic drawing that illustrates a semiconductor processing system that incorporates a fluorine gas generator according to an embodiment of the present invention. Figure 2 contains a schematic drawing that illustrates a modified semiconductor processing apparatus that is used in combination with the gas feed system illustrated in Figure 1. Figure 3 contains a schematic drawing that illustrates an experimental apparatus for confirming the capacity of NaF cartridges to remove molten salt mist.

Claims

1. Fluorine gas generator that is characteristically provided with an electrolytic cell that effects electrolysis of hydrogen fluoride in an electrolytic bath comprising molten salt that contains potassium fluoride and hydrogen fluoride, thereby producing product gas whose main component is fluorine gas in a first gas- phase region on the anode side and producing by-product gas whose main component is hydrogen gas in a second gas-phase region on the cathode side, a first conduit that withdraws the product gas from the first gas-phase region, a second conduit that withdraws the by-product gas from the second gas-phase region, a first valve that is disposed in the first conduit and that controls the flow rate of the gas passing through the first conduit, a first control member that adjusts the aperture of the first valve based on information that directly or indirectly indicates the state within the electrolytic cell, and a first cartridge that is disposed in the first conduit upstream from the first valve and that holds sodium fluoride pellets that adsorb the hydrogen fluoride and mist of the aforementioned molten salt that are admixed in the product gas.

2. The fluorine gas generator described in Claim 1 , that is characteristically also provided with a second cartridge that is disposed in the second conduit and that holds adsorbent that adsorbs mist of the aforementioned molten salt.

3. The fluorine gas generator described in Claim 2, characterized in that the adsorbent is provided with sodium fluoride pellets.

4. Fluorine gas generator as described in Claim 2 or 3, that is characteristically also provided with a second valve that is disposed in the second conduit and that controls the flow rate of the gas passing through the second conduit and a second control member that adjusts the aperture of the second valve based on information that directly or indirectly indicates the state within the electrolytic cell, wherein the second cartridge is disposed upstream from the second valve.

5. The fluorine gas generator described in Claim 4, that is characteristically also provided with a first pressure gauge that measures the pressure in the first gas-phase region and a second pressure gauge that measures the pressure in the second gas-phase region, wherein the aforesaid first and second control members adjust, respectively, the apertures of the first and second valves based on the measurement results from the first and second pressure gauges so as to maintain the pressures in the first and second gas-phase regions at substantially equal set values.

6. Fluorine gas generator according to any of Claims 1-5, that is characteristically also provided with a temperature regulator that regulates the temperature of the first cartridge