JPH0817911B2 - Exhaust gas treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to nitrogen trifluoride and fluorine in the fluoride as silicon fluoride by reacting a harmful gas containing nitrogen trifluoride and / or activated fluoride with silicon nitride. After fixing and removing the silicon fluoride by washing with an aqueous alkali solution, nitrogen trifluoride and / or
Alternatively, the present invention relates to a method for detoxifying harmful gas containing activated fluoride.

[0002]

2. Description of the Related Art In recent years, LSIs have been miniaturized and the gases used for dry etching have been correspondingly changed to Freon gas (CF ₄ , C ₂ F ₆ , C ₃ F ₈ , CClF ₃ , CHF ₃ , CH ₂ F _2). , CH
₃ F, CF ₃ Br C ₂ ClF _5, etc.) and other various fluorine-based gases have come to be used. Recently, nitrogen trifluoride (NF ₃ ) has attracted attention as a dry etching gas for VLSI. Unlike CFC-based etching gas, NF ₃ does not contain carbon in its molecule, so there is no carbon contamination on the semiconductor substrate, and since it is possible to create a plasma state with relatively low energy, there is little damage on the semiconductor substrate. It is said to be suitable for fine etching.

Further, NF ₃ has been attracting attention as a cleaning gas for plasma and CVD equipment. For example, polycrystalline silicon or silicon oxide deposited on the inner wall of a quartz reaction tube of a CVD equipment can be removed by plasma etching, so that there is a future demand. It is a useful gas that is expected to grow. However,
NF ₃ is a toxic gas with an allowable concentration of 10 ppm (TWA-TLV), and its mutagenicity was confirmed in the AMES test.

Moreover, since it is a gas that is physically and chemically stable at room temperature and hardly decomposes, a method for effectively detoxifying residual NF ₃ contained in exhaust gas when it is used in the above-mentioned useful applications is a method. It has become an extremely important environmental issue.

Further, in the exhaust gas of dry etching, more harmful active fluorides such as N ₂ F ₂ , N ₂ F ₄ , NF ₂ , N ₂ F ₆ and N are contained.
_{OF, OF 2, COF 2,} ClF, ClF 3, SF 4, F these active fluorides not limited to NF ₃ since it may _{the 2} or the like is also included simple and safe can detoxifying, including economical manner It is the current situation that is eager for. Conventionally, these harmful activated fluorides have been burned by a burner flame, or diluted with a large excess of inert gas or the like to an allowable concentration or less, and washed with an alkaline aqueous solution or the like. However, these methods were not the best in terms of operation management and pollution control.

Regarding removal of NF ₃ , a method of reacting with a metal halide (Japanese Patent Laid-Open No. 61-35830) has been reported. However, in this method, chlorine gas and the like are by-produced by a halogen exchange reaction, and the method continues. These treatments are required, many of the metal halides used (eg, aluminum chloride) are easily decomposed, and they are inconvenient to handle, and the metal fluorides produced have a high boiling point, and the products are in the reactor. There is a problem in accumulating in. In order to solve this, a method of reacting NF ₃ with metallic silicon has been reported (Japanese Patent Laid-Open No. 63-12322). This method mixes NF ₃ as an etching gas with a gas containing oxygen and nitrous oxide. When used, the metal silicon surface was oxidized by oxygen and nitrous oxide, such as exhaust of residual air in the etching chamber, and the reaction temperature for decomposing NF ₃ was extremely raised, resulting in NOx generation. .

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides a simple, safe and economical method for detoxifying nitrogen trifluoride and / or activated fluoride.

[0008]

As a result of repeated studies to achieve the above object, the present inventors have found that by reacting a harmful gas containing nitrogen trifluoride and / or active fluoride with silicon nitride, By fixing fluorine in nitrogen trifluoride and / or active fluoride as silicon fluoride and washing the silicon fluoride with an alkaline aqueous solution, a harmful gas containing nitrogen trifluoride and / or active fluoride can be very efficiently prepared. The present invention has been completed with the finding that it can be rendered harmless to the extent that there is no environmental problem.

That is, the gist of the present invention is to use a harmful gas containing nitrogen trifluoride and / or activated fluoride as silicon nitride and 2
Nitrogen trifluoride and / or fluorine in the active fluoride is fixed as silicon fluoride by contact and reaction at a temperature of 00 to 500 ° C., and harmful silicon fluoride is used as an alkali aqueous solution, preferably an ammonium salt aqueous solution as an alkali source. Washing,
A method for detoxifying nitrogen trifluoride and / or activated fluoride is characterized in that it is removed.

Various silicon fluorides are known, but the one produced by the method of the present invention is mainly silicon tetrafluoride (sublimation temperature -96 ° C.). Since the silicon tetrafluoride generated by the reaction is immediately vaporized, a new surface is always exposed without forming a fluoride layer on the surface of the silicon nitride during the reaction, so the reaction efficiency is very good and the silicon nitride can be effectively used. Can be used. A reaction example in the method of the present invention is described below. 4NF ₃ + Si ₃ N ₄ → 3SiF ₄ + 4N ₂ (I) When the treated fluoride is the above-mentioned active fluoride, a reaction similar to that of the formula (I) proceeds and fluorine in the active fluoride is converted into silicon fluoride. Can be fixed.

The silicon nitride used in the present invention may be an ordinary commercial product (purity of 97 to 98%), and the shape is not particularly limited as long as it has good operability such as spherical shape and granular shape, and special treatment or processing is required. Not. When the contact surface area is increased during the contact reaction, the reaction efficiency is further improved. The reaction method is not particularly limited, but a normal flow system is simple in equipment and easy in operation. The reaction temperature between nitrogen trifluoride and / or activated fluoride and silicon nitride is 200 to 50.
0 degreeC, especially 350-450 degreeC are preferable. At a temperature of 200 ° C. or lower, the reaction rate is slow and it is not economical in terms of reaction efficiency. Also, at high temperatures of 500 ° C or higher, the material surface of the reactor,
It is not economical in terms of energy.

Gaseous silicon fluoride produced by the reaction of nitrogen trifluoride and / or activated fluoride with silicon nitride can be removed by washing with an aqueous alkali solution or the like.
Usually, in semiconductor factories and the like, alkali metals and alkaline earths are repelled, and therefore it is preferable to use an ammonium salt aqueous solution such as ammonium carbonate or ammonium bicarbonate as the alkali source.

For example, when an ammonium carbonate aqueous solution is used, its pH is adjusted to 8-10. Concentration is 0.1
Adjusted to 2 mol / l. These ranges are not strict, and the most suitable conditions may be selected depending on the situation, and the kind of alkaline aqueous solution is not limited to the exemplified ones. The cleaning method is a normal method without any problem,
There is no problem if the cleaning temperature is room temperature or higher.

The concentration of nitrogen trifluoride and / or active fluoride in the gas composition to be treated is not particularly limited, and the method of the present invention allows nitrogen trifluoride and / or activated trifluoride to be easily reduced to below the permissible concentration. The gas composition can be rendered harmless by reducing the concentration of active fluoride. As the gas component coexisting in the gas composition containing nitrogen trifluoride and / or activated fluoride, an inert gas such as nitrogen, helium, argon, xenon, or a CFC or HF used in ordinary dry etching is used. Even if one or more of these gases coexist, the gas composition can be rendered harmless without any problem.

[0015]

EXAMPLES The present invention will be specifically described with reference to the following examples. Example 1 A nickel reaction tube having an inner diameter of 140 mm was filled with about 1000 g of granular silicon nitride (purity 98%) having a particle size of 2 to 5 mm, and the reaction tube was kept at 450 ° C. by a heater from the outside. Nitrogen trifluoride gas (purity 99.9% or more) 20 vol%, nitrogen 80
A mixed gas having a vol% composition was introduced at a flow rate of 420 l / hr and continuous treatment was performed for 10 hours. Product gas is vertical 1
The solution was introduced into a washing tower of 60 mm, 160 mm in width, and 1500 mm in height, and an ammonium carbonate aqueous solution (pH 9) was supplied at 5 l / M from the top of the tower for washing by countercurrent flow. As a result of analyzing the exhaust gas over time, the main component of the exhaust gas during the continuous treatment time was nitrogen, and nitrogen trifluoride was not detected.

Example 2 The same nickel reaction tube and alkali washing tower as in Example 1 were used, and the amount of filled silicon nitride and the alkali washing solution were also kept at 400 ° C. under the same conditions. A mixed gas having a composition of 1 vol% of nitrogen trifluoride, 1 vol% of freon 23 (CHF ₃ ) and 98 vol% of nitrogen was introduced at a flow rate of 420 l / hr, and continuous treatment was performed for 8 hours. It was analyzed over time.
During the treatment time, the exhaust gas components were nitrogen and freon gas, and nitrogen trifluoride was not detected.

Example 3 Using the same gas treating apparatus as in Example 1, the reaction temperature was 350 ° C.
Held. Nitrogen trifluoride 1 vol%, Dinitrogen difluoride 1 vol%
%, 420 l of mixed gas having a composition of 98 vol% nitrogen
It was introduced at a flow rate of / hr and continuously treated for 5 hours, and the exhaust gas from the cleaning tower was analyzed over time. During the treatment time, the main component of the exhaust gas was nitrogen, and nitrogen trifluoride and dinitrogen difluoride were not detected.

Example 4 The same gas treating apparatus as in Example 1 was used and the reaction temperature was 300 ° C.
Held. A mixed gas having a composition of 3 vol% fluorine and 97 vol% nitrogen was introduced at a flow rate of 420 l / hr and continuously treated for 2 hours. As a result of analyzing the exhaust gas from the cleaning tower over time, the main component of the exhaust gas was nitrogen during the treatment time, and fluorine was not detected.

[0019]

As described above, according to the present invention, nitrogen trifluoride and / or fluorine in activated fluoride is reacted with silicon nitride to fix it as silicon fluoride, and this is removed by washing with an alkaline aqueous solution. The present invention provides a method for detoxifying nitrogen trifluoride and / or activated fluoride extremely efficiently, conveniently, safely and economically.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B01D 53/34 ZAB (72) Inventor Minoru Konishi 5-1 Ogimachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko Kawasaki Plant Co., Ltd. (56) Reference JP-A-2-245223 (JP, A) JP-A-61-204025 (JP, A)

Claims (1)

[Claims] 1. A gas containing nitrogen trifluoride and / or activated fluoride is brought into contact with silicon nitride at a temperature of 200 ° C. or higher to convert the fluorine in the nitrogen trifluoride and / or activated fluoride into silicon fluoride. The method for treating exhaust gas is characterized in that the silicon fluoride is fixed as a fluoride, and the silicon fluoride is washed and removed with an alkaline aqueous solution.