JP7360045B2 - Method for producing molybdenum hexafluoride and method for removing oxide film on the surface of molybdenum - Google Patents

Description

The present disclosure relates to a method for producing molybdenum hexafluoride. Molybdenum hexafluoride is used as a gas for semiconductor manufacturing, such as in the formation of metal wiring (circuits) on semiconductor substrates.

Molybdenum is a metal with a high melting point and low electrical resistance, and is widely used as a raw material for various electronic materials in the form of a single metal or its silicide. In the field of electronic materials, particularly in the field of semiconductors, circuits using molybdenum are produced using molybdenum hexafluoride (hereinafter sometimes referred to as MoF ₆ ) as a raw material gas using chemical vapor deposition (hereinafter referred to as CVD method). It is formed by vapor-depositing molybdenum on the circuit. MoF ₆ is usually produced by a reaction between metal molybdenum alone (hereinafter sometimes simply referred to as molybdenum) and fluorine gas (hereinafter sometimes referred to as F ₂ gas).

For example, Patent Document 1 describes a method for producing molybdenum hexafluoride by reacting metal molybdenum with fluorine gas, in which the reaction is carried out for 2 to 4 hours at 200°C to 350°C. is listed.

Further, Patent Document 2 describes a method for producing molybdenum hexafluoride by reacting molybdenum metal with fluorine gas, which is characterized in that a fixed bed on which molybdenum metal is placed inside the reactor is inclined. A method for producing molybdenum is described.

In the following reaction (1) when producing MoF ₆ from molybdenum and F ₂ gas, the standard heat of formation ΔH is -1558 kJ/MoF ₆ mol (298 K, ₁ atm); The standard heat of formation ΔH of the following reaction formula (2) that produces ₆ is -1294 kJ/MoF ₆ mol (298 K, 1 atm).

Mo(s)+F ₂ (g) → MoF ₆ (g) Reaction (1)
Mo(s)+2NF ₃ (g)→MoF ₆ (g)+N ₂ (g) Reaction (2)
s=solid g=gas

Since the reaction rates of the reactions (1) and (2) are extremely fast and the amount of heat generated for MoF ₆ is large, the temperature of the reaction system rises rapidly in the process of producing MoF ₆ . It is known that when the temperature of the reaction system becomes high, the inner wall of the metal reactor (hereinafter sometimes simply referred to as the reactor wall) is attacked (corroded) by the fluorine-containing gas.

Originally, molybdenum is a silvery-white metal with a metallic luster, but its surface becomes oxidized (corroded) by oxygen or moisture in the atmosphere, and an oxide film consisting of molybdenum oxides forms on the surface, gradually becoming shiny. Known to lose. However, it is also known that this oxidation is very thin and does not progress to the inside. In a humid environment, the surface of molybdenum tends to form a natural oxide film (hereinafter sometimes simply referred to as an oxide film) consisting of a very thin molybdenum oxide, and tends to lose its luster. Such molybdenum oxides include molybdenum dioxide (MoO ₂ ) and molybdenum trioxide (MoO ₃ ).

Further, Patent Document 3 describes that the natural oxide film formed on the surface of molybdenum can be chemically removed by contact with hydrogen water from which dissolved oxygen and dissolved hydrogen peroxide have been removed.

China Patent Application Publication No. 103449525 International Publication No. 2019/189715 Patent No. 6415100

In the prior art (Patent Document 1), when starting a reaction for producing MoF ₆ by contacting molybdenum with F ₂ gas, it is recommended to employ a reaction temperature of over 200° C. However, as described above, the reaction rate when reacting molybdenum and F ₂ gas to obtain MoF ₆ is extremely fast and the amount of heat generated is large, so there is concern about thermal runaway of the reaction. In order to suppress such abnormal reactions and corrosion of the metal reactor wall by fluorine-containing gas, a cooling mechanism such as circulating a refrigerant through the reactor jacket is installed to prevent the reactor wall from being eroded during the reaction. It was necessary to suppress the temperature of the reactor to 400° C. or less, and it was also necessary to use an expensive material such as nickel or nickel alloy, which has high corrosion resistance against fluorine, as the material for the reactor.

Therefore, in the production of MoF ₆ , heating is required at the start of the reaction, and cooling is required during the reaction to remove the reaction heat. Therefore, both a heater and a cooler are often attached to the reactor. When both a heater and a cooler are installed, if the timing of switching between heating and cooling is incorrect under high-temperature conditions around 400°C, the temperature of the reactor wall will rise too much, causing damage to nickel, nickel alloys, etc. There was also a risk that the reactor would be damaged even when the material was used.

The present disclosure solves these problems and provides a method for producing MoF ₆ that can start the reaction to obtain MoF ₆ at a low temperature with less damage to the reactor even if molybdenum with an oxide film is used as a raw material. With the goal.

Furthermore, an object of the present disclosure is to provide a method for removing an oxide film on the surface of molybdenum, which can remove the oxide film at a low temperature with less damage to the reactor.

In order to solve the above problem, the present inventors conducted extensive studies and found that by performing a pretreatment in which fluorine gas containing hydrogen fluoride or an inert gas is brought into contact with the molybdenum raw material having an oxide film, an unexpected result can be achieved. In particular, it was found that after the oxide film on the surface of molybdenum is removed, the molybdenum from which the oxide film has been removed reacts quickly with _F2 gas to generate _MoF6 even at a low temperature of 100°C or less. It was completed (see [Table 1] in Examples).

In the pretreatment before synthesizing MoF ₆ , the F ₂ gas contains HF even at a low concentration, so HF removes the oxide film on the outermost surface of molybdenum without corroding the reactor wall. By removing the oxide film on the surface of molybdenum, the surface of molybdenum is activated to quickly react with _F2 gas, making it possible to quickly generate _MoF6 at a lower temperature. Guessed.

The present disclosure includes the following inventions 1 to 10.
[Invention 1]
Molybdenum having an oxide film is brought into contact with at least one gas selected from the group consisting of fluorine gas and an inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride in a reactor to form an oxide film. a first step of obtaining molybdenum from which is removed;
a second step of contacting molybdenum from which the oxide film has been removed in the first step with a fluorine-containing gas in a reactor to obtain molybdenum hexafluoride;
including,
A method for producing molybdenum hexafluoride.

[Invention 2]
In the first step, molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride are heated at 25°C. The method for producing molybdenum hexafluoride according to Invention 1, wherein the contact is carried out at a temperature of 180° C. or lower.

[Invention 3]
In the first step, molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride are heated at 25°C. The method for producing molybdenum hexafluoride according to Invention 2, wherein the contact is carried out at a temperature of at least 100°C.

[Invention 4]
The hexafluoride according to any one of Inventions 1 to 3, wherein the fluorine-containing gas used in the second step is at least one gas selected from the group consisting of fluorine gas and nitrogen trifluoride gas. Method for producing molybdenum.

[Invention 5]
In the second step, the production of molybdenum hexafluoride according to any one of Inventions 1 to 4, wherein the molybdenum from which the oxide film has been removed is brought into contact with a fluorine-containing gas at a temperature of 25°C or higher and 180°C or lower. Method.

[Invention 6]
The method for producing molybdenum hexafluoride according to invention 5, wherein in the second step, the molybdenum from which the oxide film has been removed is brought into contact with a fluorine-containing gas at a temperature of 25° C. or higher and 100° C. or lower.

[Invention 7]
The method for producing molybdenum hexafluoride according to any one of Inventions 1 to 6, wherein in the first step, gas at the outlet of the reactor is circulated into the reactor.

[Invention 8]
The method for producing molybdenum hexafluoride according to any one of Inventions 1 to 7, wherein the first step and the second step are performed continuously using the same reactor.

[Invention 9]
An oxide film on the surface of molybdenum that is brought into contact with molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing hydrogen fluoride gas in an amount of 50 volume ppm or more and 50 volume % or less. How to remove.

[Invention 10]
Molybdenum having an oxide film is brought into contact with at least one gas selected from the group consisting of fluorine gas and inert gas containing hydrogen fluoride gas in an amount of 50 volume ppm or more and 50 volume % or less at a temperature of 25°C or more and 180°C or less. The method for removing an oxide film on the surface of molybdenum according to invention 9.

If the method for producing MoF ₆ of the present disclosure is used, even if molybdenum with an oxide film is used as a raw material, molybdenum and a fluorine-containing gas are brought into contact and the reaction to obtain MoF ₆ can be started even at low temperatures with less damage to the reactor. can do

Further, by using the method for removing an oxide film on the surface of molybdenum of the present disclosure, it becomes possible to remove the oxide film on the surface of molybdenum even at low temperatures with less damage to the reactor.

FIG. 1 is a schematic diagram of a MoF ₆ synthesizer 100 according to the present disclosure. FIG. 2 is a schematic diagram of a MoF ₆ synthesizer 200 according to the present disclosure.

Embodiments of the MoF ₆ manufacturing method of the present disclosure will be described in detail. However, the present disclosure is not limited to the embodiments described below.

The method for producing MoF ₆ according to the first embodiment of the present disclosure includes molybdenum having an oxide film, and at least one gas selected from the group consisting of a fluorine gas and an inert gas containing 50 volume ppm or more and 50 volume % or less of HF. A first step of contacting a seed gas in a reactor to obtain molybdenum from which an oxide film has been removed, and contacting molybdenum from which an oxide film has been removed in the first step with a fluorine-containing gas, a second step of obtaining MoF ₆ .

1. Raw material molybdenum Molybdenum (hereinafter sometimes referred to as raw material molybdenum), which is a raw material for the production method of molybdenum hexafluoride, is commercially available, and can be purchased in ingot or powder form. The outermost surface of molybdenum is very thinly oxidized in the air, and commercially available molybdenum loses its luster and takes on a brown color due to the formation of this natural oxide film.
In this specification, "raw material molybdenum" means "molybdenum having an oxide film".

The first step in the method for producing molybdenum hexafluoride is to combine raw material molybdenum with at least one gas selected from the group consisting of fluorine gas and inert gas containing 50 volume ppm or more and 50 volume % or less of HF. This is a step of bringing the material into contact with the other materials and removing the oxide film. Next, in the second step, molybdenum from which the oxide film was removed in the first step is brought into contact with F ₂ gas to obtain MoF ₆ .

In the method for producing molybdenum hexafluoride of the present disclosure, raw molybdenum can be in various shapes such as powder, lumps, and ingots. The raw molybdenum used in the method for producing molybdenum hexafluoride of the present disclosure can be selected from various shapes such as powder with a particle size of 100 nm or less and ingots with a particle size of 10 cm or more. It is preferable to use powder or lumps with a particle size of 1 μm or more and 10 cm or less, from the viewpoint of ease of filling and gas flow through the raw material molybdenum powder and lumps. In addition, powdery and granular molybdenum raw materials having various particle sizes in the range of 0.5 μm to 1500 μm are commercially available, and any one of these commercially available products can be used. In the present disclosure, the particle size of the raw material molybdenum powder is the average particle size determined by the Fisher Sub-Sieve Sizer method.

The above raw material molybdenum can also be used in the method for removing an oxide film on the surface of molybdenum.

2. First step (hereinafter sometimes referred to as pre-treatment step)
The first step of the method for producing MoF ₆ of this embodiment is selected from the group consisting of molybdenum having an oxide film (raw material molybdenum) and a fluorine gas and an inert gas containing 50 volume ppm or more and 50 volume % or less of HF. This is a step in which molybdenum from which an oxide film has been removed is obtained by contacting at least one type of gas (hereinafter also referred to as "HF-containing gas") in a reactor. The inert gas may include nitrogen ( _N2 ), helium (He), or argon (Ar), with _N2 being preferred due to its easy availability and low cost.

As mentioned above, it is known that the surface of molybdenum corrodes and forms an oxide film in the atmosphere even at room temperature and humidity, and the outermost surface is covered with an oxide film.

Since molybdenum whose outermost surface is covered with an oxide film has poor reactivity with F ₂ , as described in Patent Document 1, a reaction is caused by contacting F ₂ gas at a high temperature exceeding 200°C to convert MoF ₆ . It will have to be manufactured.

However, after intensive study by the present inventor, surprisingly, by adding a pre-treatment step (first step) in which the HF-containing gas is brought into contact with the raw material molybdenum in advance, the method described in Patent Document 3 was discovered. It was found that the oxide film on the surface of the raw molybdenum was removed and activated without hydrogen water treatment, and molybdenum reacted quickly with _F2 gas even at low temperatures below 100°C, and _MoF6 was quickly generated. (See Examples 1 to 5 in [Table 1]).

In the method for producing molybdenum hexafluoride of the present embodiment, MoOF ₄ or MoF ₆ is detected in the reaction system after the first step in which the raw material molybdenum and the HF-containing gas are in contact with each other. From this, the following reaction can be inferred as the mechanism by which the oxide film is removed from the raw material molybdenum when the raw material molybdenum comes into contact with the HF-containing gas.

For example, it is assumed that molybdenum trioxide (MoO ₃ ) and HF react as shown in reactions (3) to (6) below, and MoOF ₄ is produced from MoO ₃ .

HF + MoO ₃ → MoO ₂ F(OH) reaction (3)
HF + MoO ₂ F(OH) → MoOF ₂ (OH) ₂ reaction (4)
HF + MoOF ₂ (OH) ₂ → MoF ₃ (OH) ₃ reaction (5)
HF + MoF ₃ (OH) ₃ → MoOF ₄ + 2H ₂ O reaction (6)

When using an inert gas containing HF in the first step, the MoOF ₄ obtained from reaction (6) is vaporized, and the oxide film on the molybdenum surface becomes a gas, which is removed from the molybdenum surface. It is assumed that.

When using _F2 gas containing HF in the first step, _MoF3 (OH) ₃ generated in reaction (5) and _F2 gas react as shown in equation (7) below, resulting in It is assumed that MoF ₆ is generated from MoO ₃ as follows. It is presumed that the oxide film on the molybdenum surface becomes a gas and is removed from the molybdenum surface by vaporizing MoOF ₄ obtained from reaction (6) and MoF ₆ obtained from reaction (7).

MoF ₃ (OH) ₃ + F ₂ → MoF ₆ + 3HF +3/2O ₂ reaction (7)

The concentration of HF in the _F2 gas or inert gas in the first step of the _MoF6 production method of this embodiment is determined by the combined volume of _F2 gas and HF, or the combined volume of inert gas and HF. Expressed as parts per million or percentage, it is 50 volume ppm or more and 50 volume % or less. When the concentration of HF is less than 50 volume ppm, the effect of removing the oxide film on the surface of the raw molybdenum is small, and as the concentration exceeds 50 volume ppm, the reaction rate improves, but when it exceeds 1 volume %, it does not improve much. If it exceeds the volume %, there is a concern that the reactor wall will corrode due to HF. Preferably, it is 100 volume ppm or more and 1 volume % (10,000 volume ppm) or less.

[Contact temperature]
The contact temperature between the raw material molybdenum and the HF-containing gas in the first step of the method for producing MoF ₆ of the present disclosure is preferably 25° C. or higher and 180° C. or lower.

Even if the temperature during the above-mentioned contact is room temperature (25° C.), the oxide film on the surface of the raw molybdenum is removed and the surface is sufficiently activated. Preferably it is 40°C or higher.

The temperature at which the raw material molybdenum and the HF-containing gas are brought into contact is preferably 150°C or lower, and more preferably 100°C or lower.

[Contact time]
The contact time when the raw material molybdenum and the HF-containing gas are brought into contact in the first step of the method for producing MoF ₆ of this embodiment is determined, for example, by the degree of progress of oxidation on the surface of the raw material molybdenum, and after the second step. It can be arbitrarily determined depending on the yield of MoF ₆ and the like.

[Contact pressure]
The pressure inside the reactor in the first step and the second step of the method for producing MoF ₆ of this embodiment is preferably 0.01 kPa or more and 300 kPa or less in absolute pressure, and 0.01 kPa or more and 100 kPa or less in absolute pressure. It is more preferable that If the absolute pressure value is less than 0.01 kPa, the load on the equipment for maintaining the pressure becomes large, which is not preferable. A pressure of 300 kPa or more is not preferable because there is a possibility that MoF ₆ will liquefy and there is also a risk that MoF ₆ will leak from the device.

3. Second step (hereinafter sometimes referred to as reaction step)
The second step in the method for producing MoF ₆ of this embodiment is a step in which molybdenum from which the oxide film has been removed in the first step is brought into contact with a fluorine-containing gas to obtain MoF ₆ .
[Fluorine-containing gas]
The fluorine-containing gas used in the second step can be exemplified by _F2 gas, _NF3 gas, or a mixed gas thereof, and is diluted with an inert gas selected from the group consisting of _N2 , He, and Ar. You can leave it there. Preferably it is _F2 gas.

[reaction]
In the second step, when the fluorine-containing gas is _F2 gas, the molybdenum (from which the oxide film has been removed) after the first step reacts with the _F2 gas, as shown in reaction formula (1). When MoF ₆ is generated and the fluorine-containing gas is NF ₃ gas, as shown in reaction formula (2), the molybdenum (from which the oxide film has been removed) after the first step and the NF ₃ gas MoF ₆ is produced by the reaction.

[Contact temperature]
In the second step, the temperature at which the molybdenum from which the oxide film has been removed in the first step is brought into contact with the fluorine-containing gas is preferably 25° C. or higher and 180° C. or lower.

Even if the temperature during the above-mentioned contact is room temperature (25° C.), the molybdenum from which the oxide film has been removed reacts with the fluorine-containing gas. Preferably it is 40°C or higher.

The contact temperature between the molybdenum from which the oxide film has been removed and the fluorine-containing gas is preferably 150°C or lower, particularly preferably 100°C or lower.

[Contact time]
In the second step of the method for producing MoF ₆ of the present disclosure, the contact time when the molybdenum from which the oxide film has been removed is brought into contact with the fluorine-containing gas can be arbitrarily determined based on, for example, the yield of MoF ₆ . can.

[Contact pressure]
The preferred pressure range within the reactor in the second step of the method for producing WF ₆ of this embodiment is the same as the pressure range within the reactor in the first step.

4. Production of MoF ₆ [reactor]
The reactor used in the method for producing MoF ₆ of this embodiment only needs to be able to be filled with raw material molybdenum and molybdenum from which an oxide film has been removed, and may be a batch type reactor or a continuous type reactor. The reactor material can be selected from those resistant to F ₂ , MoF ₆ and HF, and may include nickel, nickel alloys and stainless steel. Examples of nickel alloys include Monel (registered trademark), which is mainly composed of nickel and copper, and also contains iron, manganese, or sulfur, and examples of stainless steels include austenitic stainless steels such as SUS304 and SUS316. I can give an example.

In the method for producing MoF ₆ of this embodiment, in the first step, the oxide film on the surface of the raw material molybdenum is removed, and in the second step, the molybdenum is activated so that it can quickly react with the fluorine-containing F ₂ gas. Since the reactor temperature in the first step and the second step can be operated at 100° C. or lower, stable operation is possible under conditions where the load on the reactor is low. Furthermore, it will also be possible to change the reactor material from expensive materials such as nickel and nickel alloys to general-purpose stainless steel.

In the method for producing MoF ₆ of the present embodiment, in order to improve the contact efficiency between the HF-containing gas and the raw material molybdenum in the first step and the fluorine-containing gas and molybdenum in the second step, the raw material molybdenum and the oxide film must be removed. A circulation mechanism may be provided to circulate gas through the molybdenum. For example, as shown in FIG. 2, a gas circulation line 19 may be provided downstream of the reaction vessel 16, and the gas exiting from the reaction vessel 16 may be returned to the reaction vessel 16. However, in the first step, it is possible to remove the oxide film on the surface of molybdenum without providing a circulation mechanism.

[Transition from the first process to the second process]
The transition from the first step (pretreatment step) to the second step (reaction step) in the MoF ₆ manufacturing method of this embodiment will be described.

Although the first step and the second step may be performed in separate reactors, it is easier and more economical to perform them continuously in the same reactor. In the transition from the first step to the second step, if the concentration of HF in the gas after the first step is high, it is preferable to remove the gas after the first step from the reactor. If the concentration of HF in the gas after the first step is low or the HF is completely consumed in the first step and is not present, the fluorine-containing gas may be added to the reactor without removing the gas after the first step. may be supplied to start the second step.

The first step is preferably carried out by filling the reactor with the raw material molybdenum and the HF-containing gas and then sealing the reactor, which is easier. In order to remove the oxide film on the surface of the raw material molybdenum and activate it, it is preferable to circulate and flow the gas inside the reactor.

In the second step, while supplying a fluorine-containing gas, it is convenient to flow it through the molybdenum from which the oxide film has been removed, which is filled in the reactor, to contact the molybdenum, and to collect the gas after contact. It is.

By analyzing the sampled gas with a Fourier transform infrared spectrophotometer, the concentration of MoF ₆ produced in the gas after contact can be measured.

[MoF ₆ synthesis device]
FIG. 1 illustrates an example of a MoF ₆ synthesis apparatus used in the MoF ₆ manufacturing method of this embodiment. The MoF ₆ synthesis apparatus used in the MoF ₆ manufacturing method of this embodiment is not limited to the apparatus shown in FIG.

As shown in FIG. 1, the MoF ₆ synthesis apparatus 100 includes a reaction vessel (reactor) 16 filled with raw material molybdenum 18, a hydrogen fluoride gas (HF) supply device 13, a fluorine-containing gas supply device 14, and a gas supply device (not shown). Consists of an inert gas (N ₂ ) supply device.

The reaction vessel 16 is equipped with a jacket or an electric heater (not shown), and the temperature inside the reaction vessel 16 can be adjusted by circulating temperature-controlled water within the jacket. An electric heater can heat the interior of the reaction vessel 16.

The HF gas supply device 13 and the fluorine-containing gas supply device 14 are equipped with a mass flow controller (not shown). The HF gas supplier 13 and the fluorine-containing gas supplier 14 can be supplied into the reaction vessel 16 while the flow rates of these gases are adjusted by a mass flow controller. The gas after the reaction can be taken out from a product outlet 17 installed at the latter stage of the reaction vessel 16.

Further, the reaction vessel 16 may be provided with a circulation mechanism that circulates the HF-containing gas or the fluorine-containing gas so as to circulate it through the raw material molybdenum 18 .

5. Method for removing an oxide film on the surface of molybdenum A method for removing an oxide film on the surface of molybdenum according to the second embodiment of the present disclosure is a method for removing an oxide film on the surface of molybdenum according to the second embodiment of the present disclosure. This is a method of contacting at least one type of gas selected from the group consisting of gas and inert gas.

As mentioned above, it is known that the surface of molybdenum is oxidized (corroded) and forms an oxide film in the atmosphere even at room temperature and humidity, and the outermost surface is covered with the oxide film.

However, after extensive study by the present inventor, the molybdenum surface can be improved by adding a pretreatment step (first step) in which HF-containing gas is brought into contact with molybdenum, which has an oxide film, at a low temperature of 150°C or lower. It was found that the oxide film was removed and molybdenum became active against fluorine-containing gases, and even at low temperatures below 150°C, molybdenum from which the oxide film was removed reacts quickly with fluorine-containing gases, quickly producing MoF ₆ . (See Examples 1 to 4 in [Table 1]). That is, the oxide film formed on the outermost surface of molybdenum could be removed under mild conditions with a contact temperature of 150° C. or lower.

The concentration of HF in the HF-containing gas in the method for removing an oxide film on the surface of molybdenum of this embodiment is based on the combined volume of HF and at least one gas selected from the group consisting of fluorine gas and inert gas. Expressed in parts per million or percentage, it is 50 volume ppm or more and 50 volume % or less. When the concentration of HF is less than 50 volume ppm, the effect of removing the oxide film on the molybdenum surface is small, and when it is more than 50 volume %, there is a fear that the reactor may be corroded due to the strong oxidizing power of HF. Preferably, it is 100 volume ppm or more and 1 volume % or less.

The contact temperature, contact time, pressure, reactor, etc. in the method for removing an oxide film on the surface of molybdenum of this embodiment are the same as those in the first step of the method for producing MoF ₆ of this embodiment. I can do it.

The method for manufacturing MoF ₆ of this embodiment will be explained using a specific example. However, the method for producing MoF ₆ of the present disclosure is not limited to the following examples. In this example, the raw material molybdenum was not subjected to any hydrogen water treatment or the like to remove the oxide film.

[MoF ₆ synthesis device]
A MoF ₆ synthesis apparatus 100 for synthesizing MoF ₆ from molybdenum from which an oxide film has been removed and F ₂ gas used in the following examples will be described with reference to FIG. 1.

As shown in FIG. 1, the MoF ₆ synthesis apparatus 100 includes a reaction vessel (reactor) 16 filled with raw material molybdenum 18, an HF gas supply device 13, a fluorine-containing gas supply device 14, and an N ₂ gas supply device (not shown). configured.

The reaction vessel 16 is a batch type reaction vessel 16 made of Ni and having an inner diameter of 55 mm, an outer diameter of 60 mm, and a length of 300 mm, and is equipped with a jacket or an electric heater (not shown). The temperature of the inner wall of the reaction vessel 16 can be adjusted by flowing temperature-controlled water into the jacket at a flow rate of 0.5 L/min. An electric heater can heat the interior of the reaction vessel 16.

The HF gas supply device 13 and the fluorine-containing gas supply device 14 are equipped with a mass flow controller (not shown). The HF gas supplier 13 and the fluorine-containing gas supplier 14 can be supplied into the reaction vessel 16 while the flow rates of these gases are adjusted by a mass flow controller.

The gas after the reaction can be taken out from a product outlet 17 installed at the latter stage of the reaction vessel 16.

[Measurement of MoF ₆ concentration]
The concentration of MoF ₆ in the gas taken out from the product outlet 17 was measured using a Fourier transform infrared spectrophotometer (manufactured by Shimadzu Corporation, Model IRPrestage 21).

Example 1
[First step] (Pre-treatment step)
The reaction vessel 16 is filled with commercially available raw material molybdenum 18 (approximately 600 g, particle size 3 μm), which has been confirmed to have an oxide film on its surface by XPS (X-ray Photoelectron Spectroscopy) analysis. The inside of reaction vessel 16 was degassed, and then hot water was passed through a jacket (not shown) to heat the inner wall of reaction vessel 16 to 70°C. With the inner wall of the reaction container 16 maintained at 70° C., the concentration of HF gas was 100 volume ppm (0.01 volume %) with respect to F ₂ gas, and the internal pressure of the reaction container 16 was 80 kPa. , HF gas and _F2 gas were supplied from the HF gas supply device 13 and the fluorine-containing gas supply device 14. After the supply, 24 hours passed while the gas in the reactor 16 was circulated using a circulation mechanism so as to pass through the raw material molybdenum 18 while keeping the inner wall of the reactor 16 at 140°C. After the gas in the reaction vessel 16 was extracted and replaced with an inert gas (N ₂ ), a portion of the reacted molybdenum in the reaction vessel 16 was extracted and subjected to XPS analysis. For the raw material molybdenum which has a peak (232 eV) derived from Mo-O bond, the peak indicating Mo-O bond disappears in the molybdenum after the first step, and only the peak (230 eV) derived from Mo metal remains. It was confirmed that the oxide film was removed.

[Second step] (reaction step)
Next, with the inner wall of the reaction vessel 16 maintained at 140°C, _F2 gas was supplied into the reaction vessel 16 from the fluorine-containing gas supply device 14 at a flow rate of 0.5 slm (0°C) using a mass flow controller (not shown). , a flow rate expressed in liters per minute at 1 atm), and at an internal pressure of 80 kPa in the reaction vessel 16, only F ₂ gas is passed through the molybdenum 18 from which the oxide film has been removed, which is filled in the reaction vessel 16. The mixture was circulated through the reaction vessel 16 in the same manner. After 20 minutes had passed from the start of the flow, a portion of the reaction gas was taken out from the product outlet 17 and measured using the Fourier transform infrared spectrophotometer, and as a result it was found to contain MoF ₆ gas at a concentration of 99% or more.

Example 2
In the first step, the raw material molybdenum 18 was used in the same manner as in Example 1, except that the concentration of HF in the F ₂ gas filled in the reaction vessel 16 was changed to 1,000 volume ppm (0.1 volume %). The first step and then the second step were carried out using the same conditions and procedures. In the second step, after 20 minutes had passed after the start of the flow, a part of the reaction gas was taken out from the product outlet 17 and measured with the Fourier transform infrared spectrophotometer, and it was found that the concentration of MoF ₆ gas was 99% or more. It was included.

Example 3
In the first step, the concentration of HF in the _F2 gas filled in the reaction vessel 16 is set to 10,00
The first step and then the second step were performed using the same raw material Molybdenum 18 as in Example 1 under the same conditions and procedures, except that it was changed to 0 volume ppm (1 volume %). In the second step, after 20 minutes had passed after the start of the flow, a part of the reaction gas was taken out from the product outlet 17 and measured with the Fourier transform infrared spectrophotometer, and it was found that the concentration of MoF ₆ gas was 99% or more. It was included.

Example 4
[First step] (Pre-treatment step)
The reaction container 16 is filled with the same raw material molybdenum 18 used in Example 1, the inside of the reaction container 16 is degassed, and then hot water is passed through a jacket (not shown) to make the inner wall of the reaction container 16 80% Warmed to ℃. With the inner wall of the reaction vessel 16 maintained at 80°C, the concentration of HF relative to the _F2 gas is 100 volume ppm (0.01 volume %) expressed as a volume percentage, and the internal pressure of the reaction vessel 16 is 80 kPa. HF gas and _F2 gas were supplied from the HF gas supply device 13 and the fluorine-containing gas supply device 14. After the supply, the gas in the reaction container 16 was circulated so as to pass through the raw material molybdenum 18, and the inner wall of the reaction container 16 was maintained at 80° C. for 24 hours.

[Second step] (reaction step)
Subsequently, with the inner wall of the reaction vessel 16 maintained at 80° C., F ₂ gas was supplied into the reaction vessel 16 from the fluorine-containing gas supply device 14 at a flow rate of 0.5 slm using a mass flow controller (not shown). At the same time, at an internal pressure of 80 kPa in the reaction container 16, only F ₂ gas was allowed to flow into the reaction container 16 so as to pass through the molybdenum 18 from which the oxide film had been removed and which had been filled in the reaction container 16. After 20 minutes had passed from the start of the flow, a portion of the reaction gas was taken out from the product outlet 17 and measured using the Fourier transform infrared spectrophotometer, and as a result it was found to contain MoF ₆ gas at a concentration of 99% or more.

Example 5
[First step] (Pre-treatment step)
The reaction container 16 is filled with the same raw material molybdenum 18 used in Example 1, the inside of the reaction container 16 is degassed, and then hot water is passed through a jacket (not shown) to make the inner wall of the reaction container 16 80% Warmed to ℃. With the inner wall of the reaction container 16 maintained at 80° C., the concentration of HF relative to N ₂ gas is 100 volume ppm (0.01 volume %) expressed as a volume percentage, and the internal pressure of the reaction container 16 is 80 kPa. HF gas and N ₂ gas were supplied from the HF gas supply device 13 and the N ₂ gas supply device (not shown). After the supply, the gas in the reaction container 16 was circulated so as to pass through the raw material molybdenum 18, and the inner wall of the reaction container 16 was maintained at 80° C. for 24 hours.

[Second step] (reaction step)
Subsequently, with the inner wall of the reaction vessel 16 maintained at 80° C., F ₂ gas was supplied into the reaction vessel 16 from the fluorine-containing gas supply device 14 at a flow rate of 0.5 slm using a mass flow controller (not shown). At the same time, at an internal pressure of 80 kPa in the reaction container 16, only F ₂ gas was allowed to flow into the reaction container 16 so as to pass through the molybdenum 18 from which the oxide film had been removed and which had been filled in the reaction container 16. After 20 minutes had passed from the start of the flow, a portion of the reaction gas was taken out from the product outlet 17 and measured using the Fourier transform infrared spectrophotometer, and as a result it was found to contain MoF ₆ gas at a concentration of 99% or more.

Comparative example 1
In the first step, the same raw material molybdenum 18 as in Example 1 was used, except that the concentration of HF in the F ₂ gas filled in the reaction vessel 16 was changed to 10 volume ppm (0.001 volume %), The first step and then the second step were performed under the same conditions and procedures as in Example 1. A portion of the gas was taken out from the product outlet 17 and measured using the Fourier transform infrared spectrophotometer, and the concentration of MoF ₆ was found to be 18%.

Comparative example 2
The second step was performed in the same manner as in Example 1 using the same raw material Molybdenum 18 as in Example 1 without performing the first step.

After sealing the raw material molybdenum 18 in the reaction vessel 16 and degassing it, water at 140°C is passed through the jacket to maintain the inner wall of the reaction vessel 16 at 140°C, and _F2 gas is introduced into the reaction vessel 16. The reaction vessel 16 was filled with only F 2 gas at a flow rate of 0.5 slm from the fluorine-containing gas supplier 14 using a mass flow controller (not shown), and the reaction vessel 16 was filled with F ₂ gas. It was made to flow into the reaction vessel 16 so as to pass through 18. After 20 minutes had passed after the start of the flow, a part of the generated gas was taken out from the product outlet 17 and measured using the Fourier transform infrared spectrophotometer, and the concentration of MoF ₆ gas was 14%.

Reference example 1
MoF ₆ was produced using the same raw material molybdenum 18 as in Example 1 without performing the first step.

With the inner wall of the reaction vessel 16 heated to 250°C using an electric heater, F ₂ gas was supplied into the reaction vessel 16 from the fluorine-containing gas supply device 14 at a flow rate of 0.5 slm using a mass flow controller (not shown). Only F ₂ gas was allowed to flow into the reaction vessel 16 at an internal pressure of 80 kPa while being supplied at a flow rate expressed in liters per minute at 0° C. and 1 atm. After 20 minutes had passed after the start of the distribution, a part of the produced gas was taken out from the product outlet 17 and measured with the Fourier transform infrared spectrophotometer, and it was found that MoF ₆ gas was contained at a concentration of 99% or more. .

Table 1 shows, for Examples 1 to 4 and Comparative Examples 1 to 2, the contact temperature between raw material molybdenum 18 and F ₂ gas containing HF in the first step, the HF concentration in F ₂ , and the temperature in the second step. , the contact temperature between molybdenum from which the oxide film has been removed and F ₂ gas, and the concentration of MoF ₆ in the product gas at the product outlet 17.

In Examples 1 to 4 belonging to the method for producing MoF ₆ of the present disclosure, the reaction could be started in the second step even though the contact temperature was 80° C. or 140° C., which was lower than the conventional one, and finally MoF ₆ was obtained at a high concentration of over 99%.

In Comparative Example 1, in which the HF concentration in the F ₂ gas was low and was not within the scope of the MoF ₆ production method of the present disclosure, the MoF ₆ concentration was 18%, which was a low concentration.

In Comparative Example 2, in which the first step in the MoF ₆ manufacturing method of the present disclosure was not performed, the final MoF ₆ concentration was 14%, which was a low concentration.

In Reference Example 1 using the conventional method, MoF ₆ was finally obtained at a high concentration of 99% or more. However, the contact temperature between the raw material molybdenum and the _F2 gas is 250°C.

100 MoF ₆ synthesis device 13 Hydrogen fluoride gas supply device (HF gas supply device)
14 Fluorine-containing gas supply device 16 Reaction vessel (reactor)
17 Product outlet 18 Raw material molybdenum 19 Gas circulation line 20 Gas circulation pump

Claims (10)

Molybdenum having an oxide film is brought into contact with at least one gas selected from the group consisting of fluorine gas and an inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride in a reactor to form an oxide film. a first step of obtaining molybdenum from which is removed;
a second step of contacting molybdenum from which the oxide film has been removed in the first step with a fluorine-containing gas in a reactor to obtain molybdenum hexafluoride;
including,
A method for producing molybdenum hexafluoride. In the first step, molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride are heated at 25°C. The method for producing molybdenum hexafluoride according to claim 1, wherein the contact is carried out at a temperature of at least 180°C. In the first step, molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing 50 volume ppm or more and 50 volume % or less of hydrogen fluoride are heated at 25°C. The method for producing molybdenum hexafluoride according to claim 2, wherein the contact is carried out at a temperature of at least 100°C. The fluorine-containing gas according to any one of claims 1 to 3, wherein the fluorine-containing gas used in the second step is at least one gas selected from the group consisting of fluorine gas and nitrogen trifluoride gas. Method for producing molybdenum fluoride. The molybdenum hexafluoride according to any one of claims 1 to 4, wherein in the second step, the molybdenum from which the oxide film has been removed is brought into contact with a fluorine-containing gas at a temperature of 25°C or higher and 180°C or lower. manufacturing method. The method for producing molybdenum hexafluoride according to claim 5, wherein in the second step, the molybdenum from which the oxide film has been removed is brought into contact with a fluorine-containing gas at a temperature of 25°C or higher and 100°C or lower. The method for producing molybdenum hexafluoride according to any one of claims 1 to 6, wherein in the first step, gas at the outlet of the reactor is circulated into the reactor. The method for producing molybdenum hexafluoride according to any one of claims 1 to 7, wherein the first step and the second step are performed continuously using the same reactor. An oxide film on the surface of molybdenum that is brought into contact with molybdenum having an oxide film and at least one gas selected from the group consisting of fluorine gas and inert gas containing hydrogen fluoride gas in an amount of 50 volume ppm or more and 50 volume % or less. How to remove. Molybdenum having an oxide film is brought into contact with at least one gas selected from the group consisting of fluorine gas and inert gas containing hydrogen fluoride gas in an amount of 50 volume ppm or more and 50 volume % or less at a temperature of 25°C or more and 180°C or less. The method for removing an oxide film on the surface of molybdenum according to claim 9.

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