JPH08962A - Exhaust gas treatment process - Google Patents

Abstract

PURPOSE:To increase the treating amount of NF3 per unit weight of an exhaust gas treatment by bringing a treating agent containing an oxide and/or metal with specified ratio of chrome to iron as effective components with exhaust gas containing nitrogen trifluoride. CONSTITUTION:An exhaust gas treatment agent containing an oxide with the ratio of 1-30wt.% of chrome to iron or/and a metal as effective components is prepared. The exhaust gas treatment agent thus prepared is filled in a column usually, and brought into contact with exhaust gas containing NF3 to carry out an aimed exhaust treatment. At that time, in the case of exhaust gas treatment in which metal is a main body as a chemical type in the treatment agent, the exhaust gas treatment agent is brought into contact with gas at comparatively low temperature, while in the case of exhaust gas treatment in which oxide is a main body in the treatment agent, the agent is brought into contact with exhaust gas at comparatively high temperature. To be concrete, the temperature range is generally 50-600 deg.C. As a result, the problem that the treatable amount of NF3 per unit weight of the treatment agent is far less than the theoritical treatment capability is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detoxifying a gas discharged in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art Nitrogen trifluoride (hereinafter referred to as NF ₃ ) is
It is a strong fluorinating agent at high temperature and plasma, but it is stable at room temperature and easy to store and handle. Further, it is also characterized in that the residual component derived from NF ₃ after fluorinating the substance to be fluorinated is gaseous (mainly nitrogen). Therefore, it is used as a dry etching agent or a cleaning gas for semiconductor manufacturing equipment in the semiconductor manufacturing process, and the demand thereof has been increasing in recent years.

While useful in this way, NF_ThreeIs poison
And its permissible concentration is set to 10 ppm.
ing. Therefore, after being used in the semiconductor manufacturing process
NF _ThreeExhaust gas containing gas is not discharged before it is released into the atmosphere.
It is desirable to carry out a harmful treatment. However, NF_ThreeIs a room
Since it is stable at temperature and hardly absorbed by water, etc.
It doesn't make sense.

Conventionally, several methods have been proposed for treating such exhaust gas. One is a method of treating by contact with a solid chemical agent and the other is a method of treating in a flame using hydrogen as a fuel. It is roughly divided into. Of these, the former,
In the form of a solid fluoride at the operating temperature of the exhaust gas treatment,
The exhaust gas treatment method using a metal (or a metal compound) capable of fixing the fluorine component in NF ₃ plays a role in the exhaust gas treatment method using the above-mentioned solid chemical agent.

The treatment of NF ₃ is to convert the fluorine component (F) into a fluoride form which is easy to decompose or has low toxicity. Since NF ₃ has a high thermodynamic potential among fluorides, the reaction for converting other chemical species into fluoride is thermodynamically spontaneous in most cases. Therefore, as a solid drug, in principle, almost all chemical species can be targeted. When the thermodynamic consideration as described above is also performed on the currently proposed solid drug, all of them are spontaneous reactions even at low temperature.

There are reaction cases of NF ₃ and Sb, alkali metals, alkaline earth metals, Zn, Cd, Al, Fe, Cu, etc. (GMELIN HANDBUCH, Volume)
F: SVol. 1, 1959, p244-245),
These are of course mentioned as solid agents.

[0007]

However, when such an exhaust gas treating agent is used, the treated amount of NF ₃ per unit weight (or unit capacity) of the exhaust gas treating agent (hereinafter,
There is a problem in that the treatment capacity is much smaller than the theoretical treatment capacity (the amount of NF ₃ treated when all the active ingredient metals (or metal compounds) are used for treatment to form fluorides). It was

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the solution of the above-mentioned problems. The above-mentioned problem is that the functional surface of the exhaust gas treating agent (exhaust gas treatment reaction It is estimated that the effective surface involved) is reduced and the throughput is reduced. Therefore, as a result of further investigations aimed at solving this problem, the present inventors have developed an exhaust gas treating agent containing at least iron and chromium as active ingredients, and using this agent suppresses the above-mentioned problems and improves treatment capacity. The inventors have found that they are going up and have completed the present invention. The form of the active ingredient may be a metal, an oxide, or a form in which these coexist, and even if a part of these is changed to the form of a partial fluoride, the effect is not affected.

That is, the present invention provides an oxide or / and a metal containing at least iron and chromium, wherein the ratio of chromium to iron is 1 to 30% by weight, and the oxide or / and the metal is used as an active ingredient. The present invention relates to a method for treating exhaust gas, which comprises bringing the treating agent contained therein into contact with the exhaust gas containing nitrogen trifluoride.

The present invention will be described in more detail below. The components required for the exhaust gas treating agent are iron and chromium, and their chemical forms may be in a metallic state, an oxide state, or a form in which they coexist. Further, it does not matter if it contains components other than iron and chromium. For example, it may contain components that are inactive with respect to the treatment of exhaust gas (eg, alkali metal fluorides, alkaline earth metal fluorides), alumina, and the like. However, regarding the latter, it can be an active ingredient in exhaust gas treatment,
Of course, the effect (influence) of the present invention is not enjoyed.

The ratio of chromium to iron is 1 to 30% by weight.
Is more preferable, 3 to 20% by weight is more preferable, and 5 to 15% by weight is most preferable. The ratio of iron to chromium is important, and the ratio of chromium to iron (10
If the weight ratio of chromium when 0 is less than 1% by weight,
Further, even if it exceeds 30% by weight, the effect of the present invention is significantly reduced.

There are several methods for preparing an exhaust gas treating agent containing iron and chromium. The first is a method in which an iron alloy containing chromium is used as a starting material, which is once pulverized by a milling method and then pelletized into an appropriate size as an exhaust gas treating agent. Smashing is a method of crushing metal and uses a crusher that utilizes mechanical impact from the motion of a crushing rod.

The second is a ball mill method which uses an improved mill in which obstacles are attached to the inner surface of the pot. Similar to the milling method, the iron alloy is crushed by mechanical impact. Forming the obtained powder into an appropriate shape for an exhaust gas treating agent is the same as in the milling method. When an oxide is required as a chemical form of the exhaust gas treating agent, the oxidation treatment may be performed regardless of before or after molding the powder obtained by the above method.

The third method is a method in which a water-soluble iron salt and a chromium salt are made into an aqueous solution, and the aqueous solution is treated with an alkali to coprecipitate an oxide. An exhaust gas treating agent can be easily obtained by filtering the obtained precipitate, drying it, and molding it into an appropriate shape as an exhaust gas treating agent. In this case, when a metal is required as the chemical form of the exhaust gas treating agent, the reduction treatment may be performed with an appropriate reducing agent regardless of whether the obtained precipitate is formed or not.

If necessary, the exhaust gas treating agent may be fluorinated by an appropriate method. Of course,
Strong fluorination is inconvenient because it reduces the exhaust gas treatment capacity, but usually the amount of fluorine added is several% by weight.
If it is below, there is almost no influence on the exhaust gas treatment capacity.

The exhaust gas treating agent thus obtained is
Usually, the target exhaust gas treatment is performed by packing in a column and contacting with an exhaust gas containing NF ₃ . At this time, in the case of an exhaust gas treating agent mainly composed of a metal as a chemical form, at a relatively low temperature, and in the case of an exhaust gas treating agent mainly composed of an oxide, the exhaust gas is treated at a higher temperature than the former. Contact. The specific temperature range is approximately 50 to 600 ° C.
Exhaust gas treatment is possible even when the temperature is lower than a predetermined temperature, but the effect of the present invention is not remarkable. The same applies to the case of high temperature.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. Hereinafter,% means% by weight unless otherwise specified. Example 1 A binder (PVA solution) was added to an alloy fine powder (specific surface area: about 0.3 m ² / g, ratio of chromium to iron: 10%) obtained by a ball mill method, and a disc pelleter was used to measure about 3 mmφ × 3 mm. Into pellets.
This was heat-treated in air at 500 ° C. to obtain an exhaust gas treating agent. Next, 30 g of this exhaust gas treating agent is added to an inner diameter of 16 mm.
The column temperature was raised to 400 ° C., the NF ₃ gas diluted to 1% by volume (balance gas was nitrogen) was 1200 cc / min (superficial velocity about 10 cm).
/ Sec). The column outlet gas was sampled at intervals of 8 minutes, and the presence or absence of NF ₃ was analyzed by gas chromatography. As a result, NF ₃ was detected in about 96 minutes after the start of NF ₃ containing gas flow.

Example 2 Using the exhaust gas treating agent of Example 1, the column temperature was increased to 550.
Example 1 was repeated except that the temperature was changed to ° C. As a result, NF ₃ was detected at about 120 minutes after the start of NF ₃ containing gas flow.

Example 3 The iron alloy of Example 1 was mixed with an iron alloy containing 3% of chromium in iron.
Example 1 was repeated except that gold was used. That conclusion
Fruit, NF_ThreeNF about 80 minutes after the start of gas distribution _ThreeIs inspected
I was informed.

Example 4 The same procedure as in Example 1 was carried out except that the iron alloy of Example 1 was replaced with an iron alloy having a chromium ratio of 18% to iron. As a result, NF ₃ was detected at about 128 minutes after the start of NF ₃ containing gas flow.

Example 5 10% iron (III) nitrate and 10% nitric (III) nitrate
Rom 100 to 3 and 100 to 15 respectively
Two kinds of aqueous solutions were prepared so that Created it
Add sodium hydroxide solution to each solution to make it weakly alkaline.
Until 2 hours, two types of precipitates were obtained. Wash and filter this with water
Then, after drying, tablet-molding is performed and a 3 mmφ × 3 mm tablet
Got The ratio of chromium to iron is 3% and 15%, respectively.
there were. Reduction treatment for each chromium ratio
Exhaust gas treatment for those that are not processed and those that have been reduced
I used it as an agent. Next, 30 g of each exhaust gas treatment agent
Along the way, it is packed in a column with an inner diameter of 16 mm and is not reduced.
The column temperature is 400 ° C, and the reduced one is the column
The temperature was set to 60 ° C and each was diluted to 1% by volume
NF_ThreeGas (balance gas is nitrogen) 1200 cc / m
It was flown at in (superficial velocity of about 10 cm / sec). That conclusion
As a result, in the case of non-reduction treatment, chromium content of 3% is eliminated.
After 152 minutes, the gas treatment agent was exhaust gas containing 15% chromium.
Treatment agent is NF after 168 minutes_ThreeWas detected. Also reduction
For the processed ones, 40 and 48 respectively
NF in minutes _ThreeWas detected.

Example 6 An exhaust gas treating agent was prepared by changing the mixing ratio of iron (III) nitrate and chromium (III) nitrate in Example 5 to produce a chromium ratio of 25% with respect to iron. Set the column temperature to 40
When contacted with NF ₃ gas in the same manner as in Example 5 except that the temperature was 0 ° C., NF ₃ was detected after 176 minutes.

Example 7 A tablet having a chromium ratio of 15% obtained in the same manner as in Example 5 was fluorinated with a diluted NF ₃ gas (concentration: 0.05% by volume) after the reduction treatment (fluorination ratio of about 1). %) Was performed, and this was used as an exhaust gas treating agent. Column temperature is 200 ℃
Other than the above, when contacted with NF ₃ gas in the same manner as in Example 5, NF ₃ was detected after 240 minutes, and there was no particular adverse effect due to the fluorination treatment regarding exhaust gas treatment.

Comparative Example 1 In the same manner as in Example 5, the chromium ratio was 0.5% and 33.
Got a% tablet. Next, those having a chromium ratio of 0.5% were subjected to reduction treatment, and those having a chromium ratio of 33% were used as they were as an exhaust gas treating agent. Then, the column temperature of the reduced treatment was 60 ° C., and the column temperature of the non-reduced treatment was 400 ° C., and the column was brought into contact with NF _{3 in} the same manner as in Example 5. As a result, NF ₃ was already detected after 24 minutes in the chromium content of 0.5%. In addition, NF ₃ was detected after 120 minutes for a chromium content of 33%.

Comparative Example 2 With respect to an exhaust gas treating agent obtained by the same method as in Example 1 using iron containing no chromium as a starting material, NF ₃ gas was obtained in the same manner as in Example 1 except that the column temperature was 400 ° C. Shed.
As a result, NF ₃ was detected after 56 minutes.

[0026]

[Table 1]

[0027]

According to the present invention, N per unit weight (or unit volume) of treating agent, which has not been achieved by the prior art, is obtained.
The problem that the processing amount of F ₃ (hereinafter, referred to as processing capacity) is much smaller is improved. That is, the comparative example in which chromium with respect to iron is out of the range of the present invention has a short breakthrough time and N
Insufficient removal of F ₃ gas. In addition, it is clear that the examples in which chromium with respect to iron is within the range of the present invention are excellent in these performances, and the significance of the present invention is great.

Claims (2)

[Claims] 1. A treatment containing an oxide or / and a metal containing at least iron and chromium, wherein the ratio of chromium to iron is 1 to 30% by weight, and containing the oxide or / and the metal as an active ingredient. A method for treating exhaust gas, which comprises contacting an agent with an exhaust gas containing nitrogen trifluoride. 2. The temperature at which exhaust gas is contacted is 50 to 50.
The method for treating exhaust gas according to claim 1, wherein the temperature is 600 ° C.