Patent Application
20250223164
The present invention relates to a method for storing a fluorine-containing nitrogen compound containing nitrosyl fluoride (NOF) and nitroyl fluoride (FNO2).
For example, fluorine-containing nitrogen compounds disclosed in PTLS 1, 2, for example, are sometimes used as an etching gas for dry etching.
However, the nitrosyl fluoride and the nitroyl fluoride react as in the following formula in the presence of a specific type of metal, and therefore has posed a risk of a decrease in purity of the fluorine-containing nitrogen compound during long-term storage.
NOF+2FNO2→F3NO+2NO2
It is an object of the present invention to provide a method for storing a fluorine-containing nitrogen compound that prevents the progress of the reaction of the fluorine-containing nitrogen compound during storage.
To achieve the above-described object, one aspect of the present invention is as described in [1] to [4] below.
According to the present invention, the reaction of the fluorine-containing nitrogen compound hardly progresses during storage.
Hereinafter, one embodiment of the present invention is described. This embodiment describes one example of the present invention, and the present invention is not limited to this embodiment. This embodiment can be variously altered or improved, and such altered or improved aspects can also be included in the present invention.
A method for storing a fluorine-containing nitrogen compound according to this embodiment is a method for storing a fluorine-containing nitrogen compound containing nitrosyl fluoride and nitroyl fluoride, including: storing the fluorine-containing nitrogen compound in a container, in which the fluorine-containing nitrogen compound contains or does not contain at least one type among sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) as metal impurities and, when any of the foregoing is contained, the total concentration of the sodium, the potassium, the magnesium, and the calcium is set to 1000 ppb by mass or less.
When the fluorine-containing nitrogen compound contains at least one type among sodium, potassium, magnesium, and calcium as the metal impurities, a reaction between the nitrosyl fluoride and the nitroyl fluoride is accelerated by the catalysis of the metal impurities. Therefore, when the fluorine-containing nitrogen compound containing nitrosyl fluoride and nitroyl fluoride contains the metal impurities, there is a risk that nitrogen dioxide (NO2), for example, is generated as a reaction product of the nitrosyl fluoride and the nitroyl fluoride during storage, reducing the purity of the fluorine-containing nitrogen compound.
The fluorine-containing nitrogen compound stored according to the method for storing a fluorine-containing nitrogen compound of this embodiment does not contain the metal impurities or, even when the fluorine-containing nitrogen compound contains the metal impurities, the content of the metal impurities is small, and therefore, even in the case of long-term storage, the reaction between the nitrosyl fluoride and the nitroyl fluoride hardly progresses and a decrease in purity hardly occurs. Thus, the fluorine-containing nitrogen compound can be stably stored over a long period of time.
The concentrations of the metal impurities in the fluorine-containing nitrogen compound are not considered in the technologies disclosed in PTLS 1, 2. Therefore, when the fluorine-containing nitrogen compound has been stored according to the technologies disclosed in PTLS 1, 2, the reaction between the nitrosyl fluoride and the nitroyl fluoride has been sometimes accelerated by the metal impurities. As a result, the reaction between the nitrosyl fluoride and the nitroyl fluoride has sometimes progressed during storage, resulting in a decrease in purity.
Hereinafter, the method for storing a fluorine-containing nitrogen compound according to this embodiment is described in more detail.
The fluorine-containing nitrogen compound means a compound having a fluorine atom and a nitrogen atom. However, the fluorine-containing nitrogen compound according to this embodiment contains nitrosyl fluoride and nitroyl fluoride as described above. More specifically, the fluorine-containing nitrogen compound may be a mixture containing two types of substances of nitrosyl fluoride and nitroyl fluoride or may be a mixture of three types of substances obtained by adding trifluoroamine-N-oxide (F3NO) to the two types of substances above. The fluorine-containing nitrogen compound may have compounds other than nitrosyl fluoride, nitroyl fluoride, and trifluoroamine-N-oxide.
When the fluorine-containing nitrogen compound is the mixture of two types of substance or the mixture of three or more types of substances above, the content of the main component, which is a component having the largest content, is preferably 50% by mol or more, more preferably 99% by mol or more, and still more preferably 99.99% by mol or more. The total content of components other than the main component is preferably 50% by mol or less, more preferably 1% by mol or less, and still more preferably 0.001% by mol or less. The ratio of the number of moles of the nitrosyl fluoride or the nitroyl fluoride to the total number of moles of the nitrosyl fluoride and the nitroyl fluoride is preferably 0.5 or more and less than 1 and more preferably 0.99 or more and 0.9999 or less.
When the fluorine-containing nitrogen compound is stored in a container, gas containing only the fluorine-containing nitrogen compound may be stored in the container or mixed gas containing the fluorine-containing nitrogen compound and dilution gas may be stored in the container. The fluorine-containing nitrogen compound may also be partially or entirely liquefied and stored in the container. As the dilution gas, at least one type selected from nitrogen gas (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) is usable. The content of the dilution gas is preferably 90% by volume or less and more preferably 50% by volume or less based on the total amount of the gas stored in the container.
The container in which the fluorine-containing nitrogen compound is stored is not particularly limited in shape, size, material, and the like insofar as it is capable of housing and sealing the fluorine-containing nitrogen compound. However, the container is preferably one having corrosion resistance to the fluorine-containing nitrogen compound. Examples of materials of the container include manganese steel, stainless steel, nickel, Hastelloy (registered trademark), Inconel (registered trademark), Monel (registered trademark), and the like from the viewpoint of the corrosion resistance.
The fluorine-containing nitrogen compound in the method for storing a fluorine-containing nitrogen compound according to this embodiment is stored in a container, in which the fluorine-containing nitrogen compound contains or does not contain at least one type among sodium, potassium, magnesium, and calcium as the metal impurities and, when any of the foregoing is contained, the total concentration of the sodium, the potassium, the magnesium, and the calcium is set to 1000 ppb by mass or less. Therefore, the reaction between the nitrosyl fluoride and the nitroyl fluoride is hardly accelerated and, as a result, the reaction of the fluorine-containing nitrogen compound hardly progresses during storage as described above. Herein, the “does not contain” means that the sodium, the potassium, the magnesium, and the calcium cannot be quantified with an inductively coupled plasma mass spectrometer (ICP-MS).
To prevent the progress of the reaction of the fluorine-containing nitrogen compound during storage, the total concentration of the sodium, the potassium, the magnesium, and the calcium contained in the fluorine-containing nitrogen compound is required to be 1000 ppb by mass or less, and is preferably 500 ppb by mass or less and more preferably 100 ppb by mass or less.
To further suppress the progress of the reaction of the fluorine-containing nitrogen compound during storage, the concentrations of the sodium, the potassium, the magnesium, and the calcium contained in the fluorine-containing nitrogen compound are individually preferably 300 ppb by mass or less and more preferably 100 ppb by mass or less.
The total concentration of the sodium, the potassium, the magnesium, and the calcium may be 1 ppb by mass or more.
The concentrations of the metal impurities, such as the sodium, the potassium, the magnesium, and the calcium, in the fluorine-containing nitrogen compound can be quantified with an inductively coupled plasma mass spectrometer (ICP-MS).
To further suppress the progress of the reaction of the fluorine-containing nitrogen compound during storage, the concentrations of manganese (Mn), cobalt (Co), nickel (Ni), and silicon (Si) are preferably set to be low as well as the concentrations of the sodium, the potassium, the magnesium, and the calcium in the fluorine-containing nitrogen compound. In the present invention, the metals, such as sodium, potassium, magnesium, calcium, manganese, cobalt, nickel, and silicon, include metal atoms and metal ions.
More specifically, the fluorine-containing nitrogen compound is preferably stored as follows. The fluorine-containing nitrogen compound contains or does not contain at least one type among sodium, potassium, magnesium, and calcium as the metal impurities and, when any of the foregoing is contained, the total concentration of the sodium, the potassium, the magnesium, and the calcium is set to 1000 ppb by mass or less. In addition thereto, the fluorine-containing nitrogen compound contains or does not contain at least one type among manganese, cobalt, nickel, and silicon as the metal impurities and, when any of the foregoing is contained, the total concentration of the sodium, the potassium, the magnesium, and the calcium and the manganese, the cobalt, the nickel, and the silicon is set to 2000 ppb by mass or less. The total concentration of the manganese, the cobalt, the nickel, and the silicon is more preferably 1000 ppb by mass or less.
When any of the foregoing is contained, the total concentration of the sodium, the potassium, the magnesium, and the calcium and the manganese, the cobalt, the nickel, and the silicon is preferably set to 1500 ppb by mass or less and more preferably set to 500 ppb by mass or less.
The total concentration of the sodium, the potassium, the magnesium, and the calcium and the manganese, the cobalt, the nickel, and the silicon may be 2 ppb by mass or more.
To further suppress the progress of the reaction of the fluorine-containing nitrogen compound during storage, the concentrations of copper (Cu), zinc (Zn), and aluminum (Al) is preferably set to be low as well as the concentrations of the sodium, the potassium, the magnesium, and the calcium and the manganese, the cobalt, the nickel, and the silicon in the fluorine-containing nitrogen compound.
More specifically, when the fluorine-containing nitrogen compound contains at least one type among sodium, potassium, magnesium, and calcium and at least one type among manganese, cobalt, nickel, and silicon as the metal impurities, and further contains at least one type among copper, zinc, and aluminum as the metal impurities, the fluorine-containing nitrogen compound is preferably stored with the total concentration of all of these contained metal impurities set to 3000 ppb by mass or less. The total concentration of all of these contained metal impurities is more preferably set to 1500 ppb by mass or less and still more preferably set to 1000 ppb by mass or less.
The above-described metal impurities are sometimes contained in the fluorine-containing nitrogen compound in the forms of a metal simple substance, a metal compound, a metal halide, and a metal complex. The forms of the metal impurities in the fluorine-containing nitrogen compound include fine particles, liquid droplets, gas, and the like. The sodium, the potassium, the magnesium, and the calcium are considered to be mixed into the fluorine-containing nitrogen compound originating from raw materials, reaction catalysts, reactors, refining devices, and the like used in the synthesis of the fluorine-containing nitrogen compound.
A method for producing a fluorine-containing nitrogen compound having a low concentration of metal impurities is not particularly limited, and includes a method for removing metal impurities from a fluorine-containing nitrogen compound having a high concentration of metal impurities, for example. A method for removing metal impurities from the fluorine-containing nitrogen compound is not particularly limited, and known methods can be adopted. Examples include a method using a filter, a method using an adsorbent, and distillation.
A material of a filter, through which a fluorine-containing nitrogen compound gas is selectively passed, is preferably resin to avoid the mixing of metal components into the fluorine-containing nitrogen compound and is particularly preferably polytetrafluoroethylene. The average pore size of the filter is preferably 0.01 μm or more and 30 μm or less and more preferably 0.1 μm or more and 10 μm or less. When the average pore size is in the ranges above, the metal impurities can be sufficiently removed, and a sufficient flow rate of the fluorine-containing nitrogen compound gas can be ensured and high productivity can be achieved.
The flow rate at which the fluorine-containing nitrogen compound gas is passed through a filter is preferably set to 3 mL/min or more and 300 mL/min or less and more preferably set to 10 mL/min or more and 50 mL/min or less per cm2 of the filter area. When the flow rate of the fluorine-containing nitrogen compound gas is in the ranges above, the pressure of the fluorine-containing nitrogen compound gas is prevented from becoming high, so that a risk of leakage of the fluorine-containing nitrogen compound gas is lowered and high productivity can be achieved.
A pressure condition in storage in the method for storing a fluorine-containing nitrogen compound according to this embodiment is not particularly limited insofar as the fluorine-containing nitrogen compound can be sealed and stored in a container, and is preferably set to 0.05 MPa or more and 5 MPa or less and more preferably set to 0.1 MPa or more and 3 MPa or less. The pressure condition in the ranges above makes it possible to make the fluorine-containing nitrogen compound flow without being humidified when the container is connected to a dry etching device.
A temperature condition in storage in the method for storing a fluorine-containing nitrogen compound according to this embodiment is not particularly limited, and is preferably set to −20° C. or more and 50° C. or less and more preferably set to 0° C. or more and 40° C. or less. When the temperature in storage is −20° C. or more, the container is hardly deformed, and therefore a possibility that the airtightness of the container is lost, allowing the mixing of oxygen, water, and the like into the container, is low. The mixing of oxygen, water, and the like poses a risk that the reaction of the fluorine-containing nitrogen compound is accelerated. When the temperature in storage is 50° C. or less, the reaction of the fluorine-containing nitrogen compound is suppressed.
The fluorine-containing nitrogen compound stored according to the method for storing a fluorine-containing nitrogen compound of this embodiment is usable as an etching gas. An etching gas containing the fluorine-containing nitrogen compound stored according to the method for storing a fluorine-containing nitrogen compound of this embodiment is usable for both plasma etching using plasma and plasma-less etching without using plasma.
Examples of the plasma etching include reactive ion etching (RIE), inductively coupled plasma (ICP) etching, capacitively coupled plasma (CCP) etching, electron cyclotron resonance (ECR) plasma etching, and microwave plasma etching.
In the plasma etching, plasma may be generated in a chamber where a material to be etched is placed or a plasma generating chamber and the chamber where a material to be etched is placed may be separated from each other (i.e., remote plasma may be used).
Hereinafter, the present invention is more specifically described with reference to Examples and Comparative Examples. Fluorine-containing nitrogen compounds containing various concentrations of metal impurities were prepared. Preparation Examples of the fluorine-containing nitrogen compounds are described below.
One 10 L volume manganese steel cylinder and four 1 L volume sealable manganese steel cylinders were prepared. The cylinders are referred to as a cylinder A, a cylinder B, a cylinder C, and a cylinder D in order. A cylinder was filled with 2000 g (40.8 mol) of nitrosyl fluoride (boiling point under normal pressure: −59.9° C.) and 2000 g (30.8 mol) of nitroyl fluoride (boiling point under normal pressure: −72° C.). The nitrosyl fluoride and the nitroyl fluoride were liquefied by being cooled to −78° C., forming a liquid phase part and a gas phase part at almost 100 kPa. The cylinders A, B, C, D were cooled to −78° C. after the inside was depressurized to 1 kPa or less with a vacuum pump.
500 g of a mixture of the nitrosyl fluoride and the nitroyl fluoride (hereinafter referred to as “fluorine-containing nitrogen compound mixture” was extracted at −50° C. from an upper outlet, where the gas phase part is present, of the cylinder, passed through a filter, and then liquefied at −78° C. and collected in the cylinder A in the depressurized state. The filter is a PTFE filter manufactured by FLON INDUSTRY and has an outer diameter of 50 mm, a thickness of 80 μm, and an average pore size of 0.3 μm. The flow rate of gas when passed through the filter was controlled to 500 mL/min with a mass flow controller. The amount of the fluorine-containing nitrogen compound mixture collected in the cylinder A was 498 g.
The molar ratio of the fluorine-containing nitrogen compound mixture collected in the cylinder A can be estimated to be Nitrosyl fluoride:Nitroyl fluoride=0.36:0.64 based on the vapor pressure value of each component at −50° C. The vapor pressure at −50° C. is about 0.162 MPa for the nitrosyl fluoride and 0.287 MPa for the nitroyl fluoride.
The fluorine-containing nitrogen compound mixture collected in the cylinder A is set as Sample 1-1. The fluorine-containing nitrogen compound mixture collected in the cylinder A has a gas phase part and a liquid phase part. The gas phase part was extracted from an upper outlet and the concentrations of various metal impurities were measured with an inductively coupled plasma mass spectrometer. The results are shown in Table 1. The details of a method for measuring the concentrations of various metal impurities using an inductively coupled plasma mass spectrometer are as follows.
While the fluorine-containing nitrogen compound mixture in the liquid phase in the cylinder A was being vaporized at −50° C., the fluorine-containing nitrogen compound mixture was extracted from the gas phase part, and made to flow at a flow rate of 100 mL/min into 100 g of an aqueous nitric acid solution having a concentration of 1 mol/L for bubbling. This bubbling brought the fluorine-containing nitrogen compound mixture and the aqueous nitric acid solution into contact with each other, making the aqueous nitric acid solution absorb the metal impurities. The mass of the aqueous nitric acid solution after the bubbling was 94 g (M1). As a mass difference in the cylinder A before and after the bubbling, the mass decreased by 13 g (M2).
10 g (M3) of the aqueous nitric acid solution after the bubbling was collected and diluted to 100 mL (V) with ultrapure water using a female flask. The concentrations of various metal atoms in the diluted aqueous nitric acid solution were measured with an inductively coupled plasma mass spectrometer, and the concentrations (C, unit: g/g) of various metal atoms in the fluorine-containing nitrogen compound mixture were calculated using the measured values (c1, unit: g/mL) and the following equation.
Next, the cylinder A was controlled to about −50° C., forming a liquid phase part and a gas phase part. 100 g of the fluorine-containing nitrogen compound mixture (0.61 mol of nitrosyl fluoride and 1.08 mol of nitroyl fluoride) was extracted from an upper outlet, where the gas phase part is present, of the cylinder A, and transferred to the cylinder B in the depressurized state. Further, 10 g of the fluorine-containing nitrogen compound mixture (0.06 mol of nitrosyl fluoride and 0.11 mol of nitroyl fluoride) was extracted at −50° C. from the cylinder and transferred to the cylinder B in the depressurized state. Then, the temperature of the cylinder B was raised to room temperature, and the cylinder B was allowed to stand still for 24 hours. The fluorine-containing nitrogen compound mixture after standing still is set as Sample 1-2. The fluorine-containing nitrogen compound mixture was extracted from an upper outlet, where the gas phase part is present, of the cylinder B after standing still, and the concentrations of various metal impurities were measured in the same manner as above using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.
Similarly, 100 g of the fluorine-containing nitrogen compound mixture was extracted from the upper outlet, where the gas phase part is present, of the cylinder A, and transferred to the cylinder C in the depressurized state. Further, 100 g of the fluorine-containing nitrogen compound mixture was extracted from the cylinder and transferred to the cylinder C in the depressurized state. Then, the temperature of the cylinder C was raised to room temperature, and the cylinder C was allowed to stand still for 24 hours. The fluorine-containing nitrogen compound mixture after standing still is set as Sample 1-3. The fluorine-containing nitrogen compound mixture was extracted from an upper outlet, where the gas phase part is present, of the cylinder C after standing still, and the concentrations of various metal impurities were measured in the same manner as above using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.
Similarly, 100 g of the fluorine-containing nitrogen compound mixture was extracted from the upper outlet, where the gas phase part is present, of the cylinder A, and transferred to the cylinder D in the depressurized state. Further, 200 g of the fluorine-containing nitrogen compound mixture was extracted from the cylinder and transferred to the cylinder D in the depressurized state. Then, the temperature of the cylinder D was raised to room temperature, and the cylinder D was allowed to stand still for 24 hours. The fluorine-containing nitrogen compound mixture after standing still is set as Sample 1-4. The fluorine-containing nitrogen compound mixture was extracted from an upper outlet, where the gas phase part is present, of the cylinder D after standing still, and the concentrations of various metal impurities were measured in the same manner as above using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.
The cylinder A was allowed to stand still at 20° C. for 30 days, and then the fluorine-containing nitrogen compound mixture was extracted from the gas phase part of the cylinder A and analyzed with an infrared spectrophotometer to determine the concentration of nitrogen dioxide present in Sample 1-1. The nitrogen dioxide is a reaction product of the nitrosyl fluoride and the nitroyl fluoride. As a result, the concentration of the nitrogen dioxide was 20 ppm by mass. The measurement wavelength (wave number) of the nitrogen dioxide used in the analysis with the infrared spectrophotometer is 1630 cm−1.
The analysis targets and the analysis results in Examples 2, 3, and Comparative Example 1 are shown in Table 2, in comparison with Example 1. More specifically, the analysis was performed by the same operation as that in Example 1, except for the items shown in Table 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-062963 | Apr 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2023/013518 | 3/31/2023 | WO |
