JPH0230731B2 - SANFUTSUKACHITSUSOGASUNOSHORIHOHOOYOBISONOSOCHI - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method and apparatus for treating exhaust gas and the like containing nitrogen trifluoride gas (NF ₃ ). [Prior Art] Recently, LSI devices have become more highly integrated year by year, manufacturing processes have become more precise and new technologies have been introduced, and the importance of using new semiconductor gases has been emphasized. One particular gas that shows promise as a dry etching or cleaning gas for semiconductors is NF ₃
It is. For example, when silicon is etched by ionized reactive gas in NF ₃ discharge, the reaction products become volatile substances, so compared to etching in conventional fluorocarbon plasma, reaction residues on the wafer surface due to C or S are reduced. No pollution. Furthermore, since there are no reaction residues, the etching rate becomes faster. Generally, the above-mentioned advantages are the reasons why NF ₃ is viewed as a promising dry etching gas or cleaning gas. [Problems to be solved by the invention] The above-mentioned NF ₃ is a very stable and nonflammable gas at room temperature, but it is a toxic gas with a permissible concentration of 10 ppm, so countermeasures against this toxic gas have been urgently needed. . However, since NF ₃ does not react with water, alkali, or acid aqueous solutions, it cannot be treated with these aqueous solutions, and the reality is that it is diluted with large amounts of nitrogen and air and then discharged. On the other hand, it has been proven that diluted and discharged NF ₃ is not decomposed in nature, and there are concerns that it may have negative effects on living organisms. The present invention was made to solve the problems of the dilution treatment method for NF ₃ exhaust gas, and converts toxic NF ₃ into a harmless one.
It is processed by converting it into CF ₄ and N ₂ gas. [Means for Solving the Problems] In order to solve the above problems, the present invention provides the following processing method and processing apparatus. That is, the method for treating nitrogen trifluoride gas (NF ₃ ) according to the present invention involves reacting exhaust gas containing nitrogen trifluoride gas NF ₃ with a carbon mass such as activated carbon or charcoal at a reaction temperature of 300 to 600°C; It is characterized by converting into non-toxic CF ₄ gas and N ₂ gas. Further, the processing apparatus according to the invention includes a reaction tube filled with carbon lumps, a flow pipe for introducing nitrogen trifluoride gas into the reaction tube, and a bypass provided in parallel with the reaction tube, Control that opens and closes the valve so that when the temperature of the cylinder exceeds a set value or the pressure of the reaction cylinder exceeds a set value, the nitrogen trifluoride gas supplied to the reaction cylinder is released through the bypass. It is characterized by the fact that it is equipped with a device. [Example] Hereinafter, an example will be explained in more detail. In the present invention, when NF ₃ is reacted with carbon mass,
The following reaction converts _NF3 into _CF4 and _N2 gas. 4NF ₃ +3C→3CF ₄ +2N _2The reaction temperature at this time is preferably 300 to 600°C. If this temperature is too low, NF ₃ will be adsorbed by the carbon mass and will not be desorbed as carbon tetrafluoride CF ₄ . On the other hand, if this temperature is too high, corrosion will rapidly progress even if a corrosion-resistant reaction tube is used. moreover,
Since the reaction proceeds rapidly at high temperatures, it becomes difficult to control the reaction heat. The concentration of NF ₃ can be treated from a low concentration to 100% concentration, but since the above reaction is an exothermic reaction, it is difficult to control the reaction temperature when treating a high concentration of NF ₃ . Become. Therefore, from the viewpoint of controlling the reaction temperature, the concentration of _NF3 to be treated should be 10~
It is desirable to set it to 30%. Next, regarding the carbon mass which is a filler for the reaction column, it is preferable that the particle size of this carbon mass is 4 to 8 mesh. From the viewpoint of reaction, the smaller the particle size, the larger the surface area, which is advantageous, but the smaller the particle size, the greater the pressure loss, so it is not practical. Furthermore, if the particle size is larger than 4 meshes, the surface area becomes small and the desired effect cannot be obtained. For example, activated carbon or charcoal is used as the carbon mass, but this type of carbon mass usually contains 15 to 20% water, and in this way, the water-containing carbon mass and NF ₃ are combined. When reacted, HF is generated and causes corrosion of equipment materials. Therefore, when the carbon mass is first filled into the reaction column, it is preferable to heat the moisture in the carbon mass to be removed in advance. As an example of heat treatment for removing moisture, the treatment shown in FIG. 1 is practically preferable. First, inert gas (N ₂ , Ar, or He) is introduced into the reaction tube.
Flow at a flow rate of 2 l/min and set the temperature of the reaction tube temperature controller to 200°C. After increasing the temperature to 200%, this temperature is maintained for about 30 minutes, during which time most of the moisture is removed. Next, the temperature of the reaction column was raised to 400°C and maintained at this temperature for about 60 minutes. This retention allows the moisture contained in the carbon mass to be completely desorbed, resulting in NF ₃
This can prevent HF generation during the reaction between carbon and carbon blocks. Once dried, the dry state can be maintained by constantly flowing a dry inert gas such as N ₂ gas (usually with a dew point of -69° C.) even when the NF ₃ treatment is not performed. In this case, the temperature of the reaction column may remain elevated or may be maintained at room temperature. In addition, to illustrate the above drying processing conditions, the amount of drying inert gas flowed during the heating time in Fig. 1 is as follows:
For example, it is preferable to set it to 360 or more per 1.3 kg of carbon mass, and the dew point of the inert gas is −60°C or less,
The O ₂ concentration is preferably 100 ppm or less. Also,
It is preferable that the drying pressure is atmospheric pressure and the temperature is 400°C. Next, a processing apparatus used for the above-mentioned NF ₃ gas processing will be explained. FIG. 2 shows the configuration of this apparatus. This processing apparatus 1 includes an apparatus main body 2 and a control box 3. As shown in FIG. The apparatus body 2 is equipped with a pair of reaction tubes 4 and 5 that are used selectively, and each reaction tube has a
100V heat transfer heaters 6 and 7 are provided. Taking as an example the case where one reaction tube 4 is used, the NF ₃ to be treated flows from the inlet 10 to the valve 11, the oil separator 12, and the three-way switching valve 13.
It is supplied to the reaction tube 4 on the left side via the reaction tube, reacts with the carbon mass filled in the reaction tube to become CF ₄ and N ₂ , and is discharged through the cooling coil 14 and valves 15 and 16. On the other hand, _N2 gas for dilution is supplied from the flow meter 19, and dilutes the _NF3 so that the _NF3 concentration becomes a preferable concentration, that is, 10 to 30%. During this steady operation, the air-operated bypass valve 20 is closed. Next, a case where the temperature rises abnormally will be explained. When the reaction cylinder temperature exceeds the set value during processing, the air-operated valve 22 at the inlet of the reaction cylinder automatically closes, the bypass air-operated valve 23 automatically opens, and the NF ₃ -containing gas flows into the bypass circuit 24. is discharged through. Further, the emergency inert gas supply valve 26 is automatically opened, and the temperature inside the cylinder is lowered while purging the reaction cylinder 4. Similarly, to explain the operation when the pressure abnormally increases, when the pressure inside the device exceeds the set value, the pressure switch 30 is activated, the reaction cylinder inlet air-operated valve 22 is automatically closed, and the main bypass air-operated valve is activated. Valve 20 automatically opens to reduce the pressure within the device below the set point. Next, to explain the operation during a power outage, if a power outage occurs during processing, the air-operated valve 22 at the inlet of the reaction cylinder will automatically close, and at the same time, the bypass air-operated valves 22 and 23 will open, and the reaction caused by the power outage will be automatically closed. This is designed to prevent adsorption of NF ₃ due to temperature drop in the cylinder 4. Adsorption of NF ₃ generates a large amount of heat at the start of the reaction, making temperature control difficult, but since adsorption is prevented during a power outage, such accidents due to adsorption do not occur. In addition, in the figure, 32 is a pressure gauge, 33 is a regulator, 34 is a stop valve, 35 is a sample plug,
36 represents a solenoid valve, and 37 represents a valve head and a drain plug. The reaction cylinders, valves, instruments, and piping necessary for operation are functionally housed within the processing box. This processing box is provided with an exhaust fan, an air suction port, and an exhaust port, and the exhaust port is connected to an exhaust duct at the installation location. If NF ₃ gas leaks from piping joints, etc., use an exhaust fan to suck in outside air from the air intake port provided at the bottom of the treatment box.
By discharging from the exhaust port, leakage to the outside of the processing box is prevented. In addition, the exhaust fan works to efficiently cool the reaction tubes 4 and 5, making it easy to control the temperature of the reaction tubes. The reaction tube is made of a material such as monel or nickel that has good corrosion resistance against fluorine gases. This reaction tube has a cylindrical body, an NF ₃ inlet, an outlet, a filler (carbon lump) replenishment port, a filler outlet, a heater,
It is equipped with thermocouples, heat insulators, heat insulating cases, etc., and the filler outlet and outlet are each equipped with a filter and drain to prevent leakage of fine carbon particles.
The NF ₃ outlet is connected to the cooling coil 14 . Next, a specific example in which NF ₃ gas treatment was performed according to the present invention will be described. Specific Example 1 NF ₃ at a concentration of 100% was reacted at a reaction temperature of 400°C and a reaction pressure of 1
Table 1 shows the results of processing at atmospheric pressure and flow rate SV15 to 170l/Hr. Here, SV=flow rate (l/Hr)/filling volume (). As can be seen from the table, NF ₃ is processed to 5 ppm or less (gas chromatography detection limit). Specific Example 2 Table 2 shows the results of reaction treatment after diluting NF ₃ with N ₂ gas to a concentration of 3%. 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 ₃ is 4%, and 1% chlorine gas (Cl ₂ )
Table 3 shows the results of treatment with 1% hydrochloric acid (HCl). 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. [Effects of the Invention] As is clear from the above explanation, according to the present invention, it has become possible to convert NF ₃ , which is very stable and highly toxic at room temperature, into a non-toxic gas. The processing method of the present invention has a very low running cost compared to other methods and is suitable for industrial-scale processing, and its apparatus is structurally simple and highly practical.

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【table】 [Brief explanation of drawings]

Figure 1 is a graph showing the drying process of carbon lumps.
FIG. 2 is a configuration explanatory diagram showing one example of a processing device. 1... Processing device, 2... Device main body, 3... Control box, 4, 5... Reaction tube.

Claims (1)

[Claims] 1. Reacting exhaust gas containing nitrogen trifluoride gas NF ₃ with a carbon mass such as activated carbon or charcoal at a reaction temperature of 300 to 600°C to convert it into non-toxic CF ₄ gas and N ₂ gas. A method for processing nitrogen trifluoride gas, characterized by: 2. The method for treating nitrogen trifluoride gas according to claim 1, wherein the carbon mass is a granular material with a particle size of 4 to 8 mesh. 3. The method for treating nitrogen trifluoride gas according to claim 1 or 2, wherein the carbon mass is dried in advance by flowing an inert gas such as N ₂ , Ar, or He gas. 4 A reaction tube filled with carbon lumps, a flow pipe for introducing nitrogen trifluoride gas into the reaction tube, and a bypass provided in parallel with the reaction tube, so that the temperature of the reaction tube is equal to or higher than a set value. A control device is installed that opens and closes the valve so that the nitrogen trifluoride gas supplied to the reaction tube is released through the bypass when the temperature rises or the pressure in the reaction tube exceeds a set value. Characteristic nitrogen trifluoride gas treatment equipment.