JPH0471619A - Method and device for treating gaseous nf3 - Google Patents

Abstract

PURPOSE:To prevent the consumption of a carbon material as a catalyst and a rapid increase in the differential pressure in replacement by forming the carbon material into a honeycomb structure pierced with many through-holes, passing a waste gas through the through-hole and bringing the waste gas into contact with the carbon material. CONSTITUTION:A waste gas enters a three-way valve 12. In this case, a reaction cylinder 1 is used between the cylinders 1 and 2, and the cylinder 2 is reserved. The waste gas is introduced into the cylinder 1 and catalyzed by the carbon material in the through-hole of a honeycomb structure to form harmless gaseous CF4 and N2. The honeycomb structure is consumed in the treatment of the waste gas. When the differential pressure of a differential pressure gage is decreased below a definite value, the cylinders 1 and 2 are opened, and the honeycomb structure is replaced by a fresh one. Since the honeycomb structure is provided with many through-holes from the beginning and the through-hole is not clogged with powdery carbon, the differential pressure is not rapidly increased by the replacement of the honeycomb structure.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to 2. A method for processing NF3 gas that converts exhaust gas containing NF3 gas into non-toxic CF, gas and N2 gas, and an apparatus used therefor. It is.

[Prior Art] NF3 gas is generally used as a dry etching gas or cleaning gas for semiconductors. In other words, NF! When silicon is etched with ionized reactive gas during discharge, the reaction products become volatile substances, so compared to conventional etching in fluorocarbon plasma, reaction residues on the wafer surface due to carbon (C) or sulfur (S) are reduced. There is no contamination and there is no reaction residue contamination, which has the advantage of increasing the etching rate. From this point of view, NF.

Although gases are increasingly being used, NF3 gas is extremely stable at room temperature (therefore, even if released into the atmosphere, it will not decompose and there is concern that it may have negative effects on living organisms) and is a nonflammable gas. However, since NF is a toxic gas with an allowable concentration of 10 ppm, the treatment of exhaust gas containing NF poses a major problem.

[Problems to be Solved by the Invention] The applicant of the present application has developed a method of reacting exhaust gas containing the above NF3 gas with carbon lumps such as charcoal at high temperatures to produce non-toxic CF, gas and N.
We have proposed a method of changing to two gases and have already filed an application (Japanese Patent Application No. 61-78863).

In this method, granular carbon is used as a carbon mass, and the NF3-containing exhaust gas is passed between the granular carbon particles, which is packed in a reaction tube, and in the process, NF3 is released.

The idea is to change the gas into non-toxic CF, gas and N2 gas. This method converts NF's into non-toxic CFs.

and N2, as well as NF, zero in the exhaust gas.
It is excellent in that even if □ is mixed in, it can be converted into CO2 gas. That is, as another method for treating NF and exhaust gas, there is a method using Si as a catalyst, but this method has the drawback that an extra step is required to reprocess 5iFa, which is highly toxic to NF x. And recently, NF,
In order to increase the cleaning effect of 0□, it has become common to use 0□ in combination. However, in the above method using a Si catalyst, 0□ reacts with Si to form solid SiO□, which helps prevent clogging of pipes. It is the cause. According to the above method of the present applicant using a carbon block as a catalyst, NF is directly converted into non-toxic CF and N2 gas, and even if 0□ is contained in NF or exhaust gas, 0. Because it reacts with C and becomes CO□ gas, piping will not be clogged. However, when the apparatus according to this proposed method was actually assembled and operated, the following problems arose. That is, the granular carbon is consumed by the reaction with NF, and the particle size gradually decreases, so the intervals between each particle become narrower, and the flow resistance of NF3 exhaust gas gradually increases.
The pressure difference between the inlet and outlet sides of the reaction column increases. Therefore, in semiconductor manufacturing equipment connected to NF and exhaust gas treatment equipment via pipes, the back pressure (outlet side pressure)
becomes higher. This increases the pressure within the semiconductor manufacturing equipment, and this pressure fluctuation impairs stable operation. In addition, in the above processing equipment, the degree of consumption of granular carbon is measured by applying a liquid level gauge using a laser beam.
The top surface of the granular carbon layer packed in the reaction tube is determined by detecting the position, and when the top surface position falls below the reference position, granular carbon is replenished into the reaction tube. ing. In this case, the above replenishment increases the layer thickness of the granular carbon and also narrows the gaps between the granular carbon (powdered carbon mixed with the granular carbon gets mixed in between the granular carbon)
Therefore, the flow resistance of the NFI exhaust gas increases rapidly, and the back pressure of the semiconductor manufacturing equipment increases rapidly, impairing stable operation.

The present invention was made in view of the above circumstances, and an object thereof is to provide a method for processing NF and gas that does not cause a sudden increase in differential pressure when consuming or replacing a carbon material serving as a catalyst, and an apparatus used therein. do.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for converting exhaust gas containing NF3 gas into non-toxic CF, gas and N2 gas by contacting the exhaust gas containing NF3 gas with a carbon material at high temperature. .

In a gas treatment method, a carbon material is formed into a honeycomb structure in which a large number of through holes are accumulated, and exhaust gas containing NF3 gas is passed through the through holes in the honeycomb structure, and in the process of passing, the through holes are The first gist is a method of treating NF and gas by bringing them into contact with the carbon material on the pore wall, and as an apparatus for realizing the above method, a reaction column is formed so as to be openable and closable.
The second gist is an NF and gas processing apparatus in which a carbon material is formed into a honeycomb structure and is replaceably filled in the reaction column.

[Effect]

The present invention involves forming a carbon material into a honeycomb structure, allowing exhaust gas containing NF and gas to pass through the through holes of the honeycomb structure, and in the process of passing through, contacting with the carbon material on the hole wall of the through hole to cause a reaction. NF3 gas is converted into CF gas and N2 gas by

In this case, when the carbon material is consumed by the reaction with NF3, the diameter of the through-holes in the honeycomb structure is increased. Therefore, in the present invention, the consumption of carbon material conversely reduces the differential pressure. Further, in the present invention, when the differential pressure becomes smaller than a predetermined value, the honeycomb structure is replaced, but the honeycomb structure has a large number of through holes formed from the beginning, and Since the honeycomb structure is not clogged with powdered carbon, the pressure difference does not suddenly increase due to replacement of the honeycomb structure.

Next, the present invention will be explained in detail.

The present invention converts exhaust gas containing NF3 gas into non-toxic CF, gas and N2 gas by bringing it into contact with a carbon material formed in a honeycomb structure at high temperature to cause a reaction.

In this case, the reaction between the NF3 gas and the carbon material is expressed by the following reaction formula.

4NF, +3C→3CF4 +2Nz The reaction temperature at this time is preferably set at 300 to 600°C. That is, if the temperature is too low than the above temperature range, NF is adsorbed to the carbon material and carbon tetrafluoride (C
On the other hand, if the temperature is too high, corrosion of the reaction tube itself will rapidly progress and at the same time it will become difficult to control the reaction heat. From this result, in the present invention, when the exhaust gas containing NF and gas is brought into contact with the carbon material at high temperature, the high temperature is 300 to 600°.
This means a temperature range of C.

The concentration of NF in the exhaust gas treated in the present invention is low (
For example, ppm order) to high concentration (for example, 10.Ov
o 1%). In this case, since the above reaction is exothermic, high concentrations (e.g. 40v
of % or more), the temperature of the reaction column becomes too high when treating exhaust gas containing NF3. Therefore, when processing such a high concentration of NF, an inert gas such as N2 gas is usually blown in at the same time as a carrier gas (substantially the NF3 concentration falls to about 3Qvo%), The flow of the carrier gas can prevent the temperature of the reaction tube from rising. Note that even for NF and exhaust gas having a concentration lower than the above concentration, there is no problem even if an inert gas is used as a carrier gas.

Generally, the honeycomb structure has through holes with a diameter of 0.
．． 1 to 15mo, and the length of the through hole is 10cm to
It is set within a range of 5 m, preferably 1 to 2 m. Usually, a honeycomb structure with long through holes is used for high concentration NF and exhaust gas, and a honeycomb structure with short through holes is used for low concentration NF3 exhaust gas.

The above honeycomb structured carbon material can be formed by sintering fine water-free pure carbon particles. The reactor is accommodated in the reaction cylinder so that the through holes of the honeycomb structure are aligned in the axial direction of the reactor. The diameter of the above-mentioned through-hole is normally set to be the same from the inlet side (left side in Figure 1) to the outlet side (right side in the figure), but as shown in Figure 2, the diameter is larger on the inlet side and extends toward the outlet side. It is also possible to form the diameter gradually to become smaller. Further, as shown in FIG. 3, the through hole may be formed so as to become narrower in two steps from the middle. Furthermore, formation in multiple stages such as three or four stages is also performed. By doing this, the exhaust gas will swirl inside the through hole, and the N
Contact between the F3 gas and the carbon material on the hole wall of the through hole becomes more effective. Furthermore, the through-hole is not limited to having a hexagonal opening as described above, but may be round, triangular, square, or the like.

Furthermore, when treating high-concentration NF with the honeycomb structure, the concentration of NF3 gas is detected in advance and the mixing ratio of exhaust gas and inert gas is determined as described above. When high concentrations of NF and gas react, reaction heat is generated and the temperature inside the reaction cylinder increases.The temperature inside the reaction cylinder is detected and the mixing ratio of inert gas is automatically adjusted according to that temperature. Alternatively, the amount of inert gas mixed may be increased as the temperature increases, and vice versa as the temperature decreases.

Furthermore, when the honeycomb structure is made to be very long as described above, short honeycomb structures are stacked in multiple stages. In this way, a long honeycomb structure can be obtained at low cost.

Next, examples will be described.

[Example] FIG. 4 shows an example of an apparatus for treating NF3-containing exhaust gas according to the present invention. This device consists of a pair of left and right reaction tubes 1,
2, and a honeycomb structure shown in FIG. 1 is inserted into the reaction tubes 1 and 2 with its through holes aligned with the longitudinal direction (vertical direction in the drawing) of the reaction tubes 1 and 2. The bottom surface of the honeycomb structure is supported by a ring-shaped top (not shown) provided on the inner peripheral surface of the reaction tube, and it can be attached to and removed from the reaction tube 1.2. It is performed by opening the torso to the left and right. That is, as shown in FIG. 5, the reaction tubes 1 and 2 have a body section 3 that is divided into two halves along the longitudinal direction to the left and right, and can be opened and closed left and right around a hinge section 4. It is now possible to do so. Reference numeral 5 denotes a stopper for holding the two halves in a closed state. 20 is the reaction tube 1,
This is a differential pressure gauge that measures the differential pressure between the inlet and outlet sides of 2. As shown in FIG. 4, these reaction tubes 1 and 2 are provided with an electric heater 6, and are connected to a pipe 8 extending from an inlet 7 for exhaust gas containing NF3. This pipe 8 is provided with a gas mixer 9 on the inlet hole 7 side, and an inert gas pipe 11 extending from an inert gas inlet 10 is attached to this gas mixer 9. A three-way valve 12 is provided at a portion of the pipe 8 on the downstream side of the gas mixer 9, from which the pipe 8 branches left and right and is connected to a reaction tube 12. The reaction tubes 1 and 2 are provided with a control section 13 including a temperature sensor, and when the temperature inside the reaction tubes 1 and 2 becomes high, the control valve 14 provided in the inert gas pipe 11 is opened or The opening degree is increased to increase the amount of inert gas introduced, thereby lowering the concentration of NF. When the temperature becomes low, the valve 14 is controlled to reduce or cut off the introduction of inert gas. In addition, 15 is a control full box, and the introduction hole 7
NF3 concentration sensor 1 installed in the pipe 8 part of the example
The control valve 14 of the inert gas pipe 11 is controlled based on the concentration signal of NF 6, to appropriately adjust the concentration of NF supplied to each reaction column 1.2. in this way,
This device uses NF3 based on the temperature inside the reaction tubes 1 and 2.
In addition to the control system for controlling the concentration of , there is also a control system centered on the control box 15 . Usually, a control unit 1 with a temperature sensor installed in the reaction tubes 1 and 2
3, the pulp 14 is controlled, and the control system of the control box 15 is used in the event of a failure of that system.

In the device having such a structure, the exhaust gas containing N F 3 passes through the pipe 8 from the introduction lower part to the gas mixer 9.
It enters the three-way valve 12 via. In this case, either one of reaction columns 1 or 2 is used, and the other 2 is kept as a reserve. Therefore, the exhaust gas is introduced into the reaction tube 1, contacts and reacts with the carbon material in the through holes of the honeycomb structure, and becomes non-toxic CF, gas and N2. This non-toxic gas passes through the process gas discharge pipe 17 and is discharged to the outside from the exhaust hole 18. When the honeycomb structure is consumed by the treatment of NF and exhaust gas and the differential pressure of the differential pressure gauge 20 falls below a certain value, the reaction tube 1.2 shown in FIG. 5 is opened and replaced with a new honeycomb structure. will be held. In Figure 4,
19 is a cooling coil, and the dashed line is a processing box that accommodates each of the above parts.

Next, a specific example in which exhaust gas containing NF3 was actually treated will be described.

[Specific Example 1] NF at a concentration of 100% was prepared using the apparatus shown in Fig. 4 (incorporating a honeycomb structure with through holes shown in Fig. 2) at a reaction temperature of 400°C, a reaction pressure of 1 atm, and a flow rate of SV3 ( ]
-2501/Hr. The results are shown in Table 1. Here, S■=flow rate (f/Hr)/filling volume (ri).As can be seen from the table, NF is treated to 5 ppm or less (gas chromatography detection limit).

[Specific Example 2] NF3 was diluted to a concentration of 3% with N2 gas, and treated using the apparatus shown in FIG. 4 (incorporating a honeycomb structure with the same inlet and outlet diameters). The results are shown in Table 2. It can be seen that according to the present invention, even such low concentrations can be completely treated.

[Specific Example 3] The concentration of NF was set to 4%, and 1% chlorine gas (C12) and 1% hydrochloric acid (HCj2) were added to the apparatus shown in Figure 4 (with the through hole shown in Figure 3). (Incorporates honeycomb structure)
Processed with. The results are shown in Table 3. From the same table, it can be seen that even if chlorine-based gas is mixed in, the reaction is not inhibited and the treatment is carried out.

(The following is a blank space) [Effects of the Invention] As described above, the present invention uses a honeycomb structure having a large number of through holes as a carbon material to be reacted with NF3. When consumed, it appears as an increase in the diameter of the through holes in the honeycomb structured carbon material. Therefore, unlike the conventional example, the differential pressure does not increase due to consumption of the carbon material, and on the contrary, the differential pressure decreases. Therefore, stable operation can be realized without causing internal pressure fluctuations due to increases in back pressure of the semiconductor manufacturing equipment connected to the NF3 exhaust gas treatment equipment. Further, in the present invention, when the differential pressure becomes smaller than a predetermined value, the honeycomb structure is replaced, but the honeycomb structure has a large number of through holes formed from the beginning, and Since the honeycomb structure is not clogged with powdered carbon, the pressure difference does not suddenly increase due to replacement of the honeycomb structure.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of a honeycomb structure used in the present invention, FIGS. 2 and 3 are explanatory diagrams showing modified examples of the shape of the through holes, and FIG. 4 is an NF3 gas processing apparatus of the present invention. FIG. 5 is an enlarged explanatory view of the reaction tube. 1.2...Reaction tube 7...Exhaust gas introduction hole 8...
Pipe 9... Gas mixer 10... Inert gas introduction hole 11... Pipe 13... Control section 14...
Control valve 17...Discharge pipe

Claims (3)

[Claims] (1) In the NF_4 gas treatment method, the exhaust gas containing NF_3 gas is brought into contact with a carbon material at high temperature to turn it into non-toxic CF_4 gas and N_2 gas, in which the carbon material is formed into a honeycomb structure with a large number of through holes. A method for treating NF_3 gas, characterized in that the exhaust gas containing NF_3 gas is passed through the through-holes of the honeycomb structure, and in the process of passing, the exhaust gas is brought into contact with the carbon material on the wall of the through-holes. (2) The method for processing NF_3 gas according to claim (1), wherein the diameter of the through hole is set to 0.1 to 15 mm. (3) An inlet pipe for exhaust gas containing NF_3 gas, a reaction tube connected to the end of this inlet tube, a carbon material filled in this reaction tube, and a treated gas discharge tube extending from the reaction tube. The carbon material is formed in the honeycomb structure, and the reaction tube is formed to be openable and closable, and the honeycomb structure is inserted into the reaction tube with the through holes of the honeycomb aligned in the flow direction of the exhaust gas. An NF_3 gas processing device characterized by being filled in a replaceable manner.