JP6941424B2 - Method for purifying monomethylhydrazine gas - Google Patents

Description

The present invention relates to a method for purifying monomethylhydrazine gas, and more particularly to a method for purifying monomethylhydrazine gas by adsorbing and removing impurities contained in monomethylhydrazine to obtain high-purity monomethylhydrazine gas.

Monomethylhydrazine is a liquid at room temperature and has long been used as a fuel in rocket engine propellants. In recent years, it has begun to be used as a nitriding agent for light emitting elements and insulating films of semiconductor devices such as gallium nitride (GaN), silicon nitride (SiN), and titanium nitride (TiN) by utilizing the strength of its reducing property. In order to use it for these purposes, in addition to heating liquid monomethylhydrazine to an appropriate temperature to vaporize it, a method of vaporizing and supplying it by bubbling with a carrier gas such as hydrogen or nitrogen is adopted.

Generally, the purity of monomethylhydrazine commercially available as a reagent is 98% by weight or more, and water and monomethylamine are contained in less than 1% by weight, respectively. Therefore, in order to use it for manufacturing semiconductor devices, it is necessary to remove impurities, particularly water, which is an oxygen source, as much as possible. Therefore, a purification method for removing water in the substituted hydrazine gas by contacting a substituted hydrazine gas such as monomethylhydrazine with a synthetic zeolite-based adsorbent having a pore diameter equivalent to 3 Å, for example, molecular sieve 3A, is known. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 7-77146

When manufacturing a semiconductor device with a semiconductor manufacturing device, high-purity monomethylhydrazine that does not contain not only the water content in monomethylhydrazine but also impurities such as ammonia and methane, which are decomposition products of monomethylhydrazine, in addition to monomethylamine, is used. Required. On the other hand, according to the experiments of the present inventors, it was confirmed that when the water content in monomethylhydrazine is removed by using a synthetic zeolite having a pore size equivalent to 3 Å, a very large amount of monomethylhydrazine is adsorbed on the synthetic zeolite. rice field. At this time, it was found that the heat of adsorption causes the synthetic zeolite to generate heat, and the temperature of monomethylhydrazine rises to promote the self-decomposition of monomethylhydrazine, resulting in the generation of degradable organisms such as ammonia, monomethylamine, and methane.

Furthermore, monomethylhydrazine gas was aerated in a container filled with synthetic zeolite having a pore size equivalent to 3 Å, and monomethylhydrazine was sufficiently adsorbed until the heat generated by the synthetic zeolite subsided, and then the container was sealed and allowed to stand. , It was confirmed that the pressure inside the container increased. Furthermore, when the gas in the container where the pressure increased was analyzed, it was confirmed that the monomethylhydrazine contained ammonia, monomethylamine, and methane.

That is, it has been shown that a synthetic zeolite having a pore size equivalent to 3 Å promotes self-decomposition of monomethylhydrazine, and when monomethylhydrazine gas is purified using a synthetic zeolite having a pore diameter equivalent to 3 Å, water is removed. However, it has been found that the self-decomposition product reduces the purity of monomethylhydrazine gas, which not only makes it unusable as a raw material gas for manufacturing semiconductor devices, but also raises the safety problem of increasing the pressure in the container.

Therefore, the present invention can remove water contained in commercially available monomethylhydrazine having a purity of 98% by weight or more, suppress the generation of ammonia and the like due to self-decomposition, and contain almost no impurities in monomethylhydrazine gas. It is an object of the present invention to provide a method for purifying monomethylhydrazine gas.

In order to achieve the above object, in the method for purifying monomethylhydrazine gas of the present invention, impurities contained in the monomethylhydrazine gas are subjected to a purification treatment in which the monomethylhydrazine gas is brought into contact with an adsorbent containing alumina as a main component. In particular, in the method for purifying monomethylhydrazine gas from which water and / or monomethylamine is removed , the impurities contained in the monomethylhydrazine gas, which is the gas to be purified, are less than 100% by volume ppm before the purification treatment is performed by contacting the monomethylhydrazine gas with the adsorbent. It is characterized by performing a pretreatment in which the high-purity monomethylhydrazine gas of No. 1 is brought into contact with the adsorbent.

Further, the method for purifying monomethylhydrazine gas of the present invention is characterized in that the adsorbent does not contain synthetic zeolite, and the temperature at which the monomethylhydrazine gas is brought into contact with the adsorbent is set to the liquefaction of the monomethylhydrazine gas. It is characterized in that it is set in the range of 120 ° C. or lower above the temperature .

According to the method for purifying monomethylhydrazine gas of the present invention, since an adsorbent containing alumina as a main component is used, water and monomethylamine, which are impurities in monomethylhydrazine gas, are suppressed while suppressing self-decomposition of monomethylhydrazine. It is possible to obtain high-purity monomethylhydrazine by adsorbing and removing these impurities to 10 volume ppm or less, and further to 1 volume ppm or less.

It is a figure which shows the time-dependent change of pressure in Example 1 of this invention. It is a figure which shows the time-dependent change of pressure in the comparative example 1 of this invention.

The gas to be purified in the method for purifying monomethylhydrazine gas of the present invention is monomethylhydrazine gas, and this monomethylhydrazine gas may be monomethylhydrazine alone or hydrogen used as a carrier gas in a semiconductor manufacturing apparatus. It may be a mixed gas with nitrogen, helium, argon or the like.

The method of gasifying liquid monomethylhydrazine at normal temperature and pressure is arbitrary. For example, a method of heating a container filled with liquid monomethylhydrazine with a constant temperature bath, a hot plate heater, a tape heater, etc., a coiled stainless steel pipe It is possible to adopt a method of circulating liquid monomethylhydrazine while heating, or a method of bubbling nitrogen, argon, helium, etc. in a container filled with liquid monomethylhydrazine to vaporize the liquid monomethylhydrazine to make a mixed gas. can. Usually, the concentration of water and monomethylamine contained as impurities in commercially available liquid monomethylhydrazine is less than 1% by weight, respectively.

In the purification treatment of monomethylhydrazine gas, the monomethylhydrazine gas is brought into contact with an adsorbent containing alumina as a main component, so that water and monomethylamine contained as impurities in the monomethylhydrazine gas are adsorbed on the adsorbent and removed. It is a process to do. The adsorbent containing alumina as a main component is obtained by heating and dehydrating alumina trihydrate, and generally has a particle size of 1 mm to 10 mm, a pore size of 700 Å or more, and a pore volume of 700 Å or more. It is 0.1 to 0.8 ml / g. The shape of the adsorbent is not particularly limited, and may be crushed, spherical, honeycomb-shaped, or the like. Commercially available products may be used as the adsorbent containing these aluminas as a main component, and for example, D2017 × 12 (Union Showa Co., Ltd.), NKHD-24HD (Sumitomo Chemical Co., Ltd.), etc. may be used. can.

The purification treatment of monomethylhydrazine gas is usually carried out by passing monomethylhydrazine gas, which is a gas to be purified, through a purification cylinder filled with the adsorbent. Thereby, water and monomethylamine, which are impurities in the monomethylhydrazine gas, can be removed by adsorbing the adsorbent containing alumina as a main component.

Practically, the filling height of the adsorbent to be filled in the purification cylinder is usually 50 to 2000 mm. If the filling height is smaller than 50 mm, the filling height may be shorter than the breakthrough zone length, and the impurity removal rate of the adsorbent may be significantly reduced. On the other hand, if the filling height is larger than 2000 mm, the pressure loss may increase.

The superficial velocity (LV) of monomethylhydrazine gas during the purification process varies depending on the operating conditions such as impurity concentration, pressure, and temperature in the supplied monomethylhydrazine gas, and although it cannot be unequivocally specified, monomethylhydrazine gas alone is supplied. In this case, it is usually 50 cm / sec or less, preferably 15 cm / sec or less.

The contact temperature between monomethylhydrazine and the adsorbent must be set above the saturated vapor pressure temperature at which the monomethylhydrazine gas does not liquefy. On the other hand, monomethylhydrazine has an autolytic property and decomposes at about 240 ° C. in a nitrogen atmosphere, so that it is preferably set to 150 ° C. or lower, usually 120 ° C. or lower. Further, the adsorbent is particularly preferably set at 80 ° C. or lower because the lower the temperature, the higher the adsorption / removal ability. The contact pressure between the monomethylhydrazine gas and the adsorbent may be equal to or lower than the saturated vapor pressure at which the monomethylhydrazine gas does not liquefy, and is usually preferably performed under a pressure of 50 kPaG from vacuum.

The adsorbent containing alumina as a main component is usually activated by heating it to a temperature of about 300 to 350 ° C. while aerating an inert gas before use. The activated adsorbent is cooled to a contact temperature with the monomethylhydrazine gas, and then the monomethylhydrazine gas is circulated in a purification cylinder to purify the monomethylhydrazine gas. When monomethylhydrazine is supplied alone, the inside of the purification cylinder should be evacuated with a dry vacuum pump to remove the inert gas in the purification cylinder before the purification treatment is started, and then the purification treatment of monomethylhydrazine gas should be performed. Is preferable.

Further, if an impurity component is adsorbed in the pores of the adsorbent before starting the purification treatment of the monomethylhydrazine gas, the impurity component is generated when the temperature of the adsorbent rises due to the heat of adsorption during the purification treatment. May desorb and reduce the purity of monomethylhydrazine gas. Therefore, before starting the purification treatment of the monomethylhydrazine gas, the monomethylhydrazine gas for the pretreatment is pre-circulated in the purification cylinder and brought into contact with the adsorbent to desorb the impurity component from the adsorbent, and is sufficient. It is preferable to perform a pretreatment (conditioning operation) in which an amount of monomethylhydrazine is adsorbed on the adsorbent to remove impurity components from the purification cylinder.

As the monomethylhydrazine gas used in the pretreatment, a part of the monomethylhydrazine gas to be purified can be used, but the concentration of water and monomethylamine is set to less than 100% by volume ppm, preferably less than 10% by volume ppm in advance. By using the monomethylhydrazine gas purified as described above, it is possible to effectively remove the impurity component from the adsorbent. The temperature during the pretreatment may be 240 ° C. or lower, which is the decomposition temperature of monomethylhydrazine, but is usually set to 150 ° C. or lower, preferably 120 ° C. or lower, and more preferably 70 ° C. or lower. At this time, the temperature rise due to the heat of adsorption during the pretreatment should be fully considered. The pressure in the purification cylinder during the pretreatment may be less than or equal to the saturated vapor pressure at which the monomethylhydrazine gas does not liquefy, but it is preferably set to 10 kPaA or less so that the adsorption to the adsorbent is not biased.

In this way, by purifying the monomethylhydrazine gas to be purified by contacting it with an adsorbent containing alumina as a main component, high-purity purified monomethylhydrazine containing no impurities such as water, ammonia, monomethylamine, and methane can be obtained. be able to. Further, the component of the adsorbent may be any as long as it contains alumina as a main component and may contain other components, but synthetic zeolite, particularly synthetic zeolite having a pore diameter of 3 Å is included. If so, monomethylhydrazine is adsorbed on the synthetic zeolite and self-decomposes, which may generate impurities such as ammonia. Therefore, the adsorbent should be selected so as not to contain the synthetic zeolite.

As the adsorbent, commercially available activated alumina D-201 (spheroidal product having a diameter of 1.4 to 2.8 mm manufactured by Union Showa Co., Ltd.) was used. 5 g of this adsorbent was filled in a purification cylinder made of SUS316L having an inner diameter of 10.7 mm and a length of 100 mm at a filling density of 0.77 g / ml. Nitrogen gas was flowed through this purification cylinder at a temperature of 300 ° C., a flow rate of 200 Nml / min (N ml / min is 0 ° C., a flow rate converted to 1 atm), and an atmospheric pressure for 5 hours for activation treatment.

Next, after vacuum exhausting the nitrogen gas in the purification cylinder, monomethylhydrazine gas containing 0.6% by volume of water and 0.4% by volume of monomethylamine as impurities is added to the purification cylinder at 70 ° C., 22 kPaA, 200 Nml / min. Then, it was allowed to flow until the temperature of the purification cylinder became stable. After that, the valves provided at both ends of the purification cylinder were closed, and 10 hours later, the impurity components contained in the gas in the purification cylinder were removed using a 3.5 m cell with a Fourier transform infrared spectrophotometer (FTIR) manufactured by Myduck. analyzed. The results are shown in Table 1.

The pressure change in the refining cylinder when the refining cylinder with the valve closed was held at each temperature of 30 ° C., 70 ° C., 120 ° C., and 150 ° C. was measured. The pressure inside the cylinder at the purification cylinder temperature of 30 ° C. was 5 kPaA, which is the pressure at which monomethylhydrazine gas does not liquefy. The time course of pressure is shown in FIG.
[Comparative Example 1]

On the other hand, as an adsorbent, a commercially available synthetic zeolite; Molecular Sieve 3A (manufactured by Union Showa Co., Ltd., pellet-shaped with a diameter of 1.6 mm, pore diameter of about 3 Å) is used, and the packing density of this synthetic zeolite is 0.66 g / The same operation as in Example 1 was performed except that the amount was ml, and the impurity components contained in the gas in the purification cylinder were analyzed in the same manner, and the temperature was maintained at 30 ° C., 70 ° C., and 120 ° C. The pressure change in the purification cylinder was measured. The analysis results are shown in Table 2, and the changes over time in pressure are shown in FIG.

From these results, activated alumina containing alumina as the main component has no change in the encapsulation pressure and no change in the impurity concentration when the purification cylinder temperature is 120 ° C. or lower, whereas it is a synthetic zeolite having a pore diameter of 3 Å or less. At 3A, it can be seen that the encapsulation pressure continuously increased even at the purification cylinder temperature of 30 ° C., and most of the encapsulated monomethylhydrazine was decomposed into ammonia, monomethylamine, and methane.

200 g of activated alumina, which is the same as in Example 1, is filled in an adsorption cylinder made of SUS316L having an inner diameter of 37.1 mm and a length of 300 mm, and nitrogen gas is passed through the adsorption cylinder at a temperature of 300 ° C., a flow rate of 2.0 L / min, and an atmospheric pressure for 5 hours. The activation treatment was carried out. After vacuum exhausting the nitrogen gas in the purification cylinder while maintaining the temperature at 70 ° C., 70% of monomethylhydrazine gas containing 0.6% by volume of water and 0.4% by volume of monomethylamine as impurities is added to the purification cylinder. When the flow was carried out at ° C., 22 kPaA and 500 Nml / min, the temperature of the adsorbent in the purification cylinder increased by a maximum of 12 ° C. Analysis of the impurity concentration of monomethylhydrazine gas obtained from the outlet of the purification cylinder revealed that the maximum water content was 100 ppm by volume, and ammonia, monomethylamine, and methane were below the lower limit of detection (ammonia, methane: <1 volume ppm, monomethylamine: <. 10 volume ppm). When the flow of the monomethylhydrazine gas was continued and the impurity concentration was analyzed again after the adsorbent temperature was stabilized at 70 ° C., all the impurity concentrations were below the lower limit of detection (moisture: <10 volume ppm).

The new purification cylinder prepared in the same manner as in Example 2 was activated under the same conditions as in Example 2, and then the nitrogen gas in the purification cylinder was evacuated. Then, as a pretreatment, purified monomethylhydrazine gas whose impurity concentration was confirmed to be below the lower limit of detection in Example 2 was flowed at 70 ° C., 22 kPaA, 500 Nml / min until the temperature of the purification cylinder became stable. Then, when monomethylhydrazine gas containing 0.6% by volume of water and 0.4% by volume of monomethylamine was flowed at 70 ° C., 22 kPaA, 500 Nml / min as impurities, the impurity concentration of the monomethylhydrazine gas obtained from the outlet of the purification cylinder was obtained. Was below the lower limit of detection (ammonia, methane: <1 volume ppm, water, monomethylamine: <10 volume ppm). After that, when the FTIR was changed to a 10 m cell and remeasured, both water content and monomethylamine were below the lower limit of detection (<1 volume ppm).

Claims (4)

In the method for purifying monomethylhydrazine gas by contacting monomethylhydrazine gas with an adsorbent containing alumina as a main component to remove impurities contained in the monomethylhydrazine gas, the monomethylhydrazine gas which is the gas to be purified Purification of monomethylhydrazine gas, which comprises contacting the adsorbent with a high-purity monomethylhydrazine gas containing less than 100% by volume of ppm of impurities before performing the purification treatment by contacting the adsorbent. Method. The method for purifying monomethylhydrazine gas according to claim 1, wherein the adsorbent does not contain synthetic zeolite. The monomethylhydrazine gas according to claim 1 or 2, wherein the temperature at which the monomethylhydrazine gas is brought into contact with the adsorbent is set in a range of 120 ° C. or lower, which is equal to or higher than the liquefaction temperature of the monomethylhydrazine gas. Purification method. The method for purifying monomethylhydrazine gas according to any one of claims 1 to 3, wherein the impurity is water and / or monomethylamine.

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