JPH0739721A - Treatment of nitrogen trifluoride - Google Patents

Abstract

PURPOSE:To eliminate and treat an exhaust gas of NF3 with coexisting oxygen at a low temp. and without decreasing the treating rate by using an Si the surface of which is adhered with Cu with a specified wt. ratio as a treating agent. CONSTITUTION:As a treating agent which is brought into contact with an exhaust gas contg. NF3 as a hazardous ingredient, an Si the surface of which is adhered with Cu with a wt. ratio of 0.01-2.0wt.%. Then, Cu acts as a catalyst and even when oxygen coexists, the surface of the Si is not oxidized and NF3 is decomposed at a sufficiently high rate to form a decomposed product of SiF4. It is extremely effective to adhere the surface of Si with a small amt. of metal Cu as a catalyst as a chemical material which can treat NF3 gas with coexisting oxygen while advantages of Si are well used.

Description

Detailed Description of the Invention

[0001]

[Industrial application] In addition to rocket fuel, NF ₃ has recently attracted attention as a dry etching agent or a fluorinating agent for LSI.
Compared with a perfluorocarbon type etching agent such as F _4, it has an advantage that the contamination of the LSI substrate generated during etching is extremely small. On the other hand, NF ₃ is extremely stable in the atmosphere, dissolves only slightly in water, and TL 3
It is a toxic gas of V10 ppm, and when it is used, its treatment is always necessary when exhausting the residual gas. The present invention relates to a method for treating such a gas containing NF ₃ .

[0002]

2. Description of the Related Art As a method for treating NF ₃ , we have investigated various metals such as Si, and these non-oxide compounds and NF ₃ at 200 ° C. to 800 ° C.
We proposed a method of collecting the obtained fluoride gas by reacting with. (Japanese Examined Patent Publication No. 63-48570) Among these reaction agents, particularly the reaction product (SiF ₄ ) having good reactivity with metal Si and having a low cost has a sufficient vapor pressure at room temperature,
Therefore, SiF ₄ that can be easily discharged from the system has the feature that it can be completely treated with alkali, and it can be said that it is most suitable for NF ₃ treatment.

However, when oxygen coexists with NF ₃ , this treatment method causes the surface of Si to be oxidized by oxygen and NF ₃
Since the processing speed decreases, it is necessary to raise the reaction temperature in order to obtain the required processing speed, which requires extra heat energy for processing, and the material required for the reactor will also be of high quality. There was a problem.

The present invention has been made in view of the above points, and an object of the present invention is to provide a NF ₃ treatment method in which the NF ₃ treatment rate does not decrease even when oxygen coexists.

[0005]

[Means for Solving the Problems] As a result of repeated studies on the above-mentioned problems, the present inventors have found that a small amount on the Si surface as a drug capable of treating NF ₃ gas in the presence of oxygen while taking advantage of Si. The inventors of the present invention have found that the above-mentioned metal Cu attached with Cu as a catalyst is effective, and completed the present invention.

[0006] Metallic Cu itself is NF under heating
₃Can be decomposed, but Cu alone is NF ₃Used as a treatment agent for
There is a problem with being For example, Cu alone is NF₃React with
Solid fluoride (CuF)₂) Is generated
NF because it covers the surface of Cu₃Of the reaction is hindered
The rate goes down. Also CuF₂Powder could block the reactor
There is such a thing. On the other hand, Si is NF₃After processing
Reaction product is gaseous SiF_FourNext, Cu alone
NF₃Where oxygen coexists
In this case, the problems mentioned in the previous section are included. Like this
This is itself a perfect NF by itself₃Cannot be processed
Although Si and Cu, the present inventors have successfully combined these
Succeeded in creating a new function by combining
It was

Although the details of the mechanism of the NF ₃ decomposition reaction of Si with Cu attached to the surface are unknown, at least Cu
Can be said to act as a catalyst from the following two points. That is, when decomposing NF ₃ in said agent hundreds times the chemical equivalent of Cu being impregnated, it thousands times more NF ₃ is processed, also degradation products at that time react a SiF ₄ The main ingredient is that it is Si. In addition, the catalytic effect of Cu is extremely high in that it lasts until the total amount of Si is consumed.
The processing capacity of the chemical agent with respect to the O ₂ coexisting NF ₃ exhaust gas does not depend so much on the Cu impregnation method as described in (a) to (d) described later, and anyway, the metallic Cu comes into contact with the Si surface. If it is in a state of being present, its effect will be exhibited.

Since the treatment capacity of the chemical agent for NF ₃ exhaust gas coexisting with O ₂ depends on the amount of Cu impregnated per unit amount of Si, it should be adjusted within the range of the optimum impregnation amount shown below. That is, the amount of Cu to be attached to the Si surface is at least 0.01 wt% in weight ratio, and if it is less than this, a sufficient effect cannot be expected for the treatment of oxygen coexisting NF ₃ exhaust gas. On the other hand, although it can be said that there is essentially no upper limit of the amount of Cu, when Cu is impregnated by the method shown in the present specification, when it exceeds 2.0 wt%, Cu covers the Si surface and NF ₃ and Si Contact is hindered and the treatment effect is reduced. The amount of Cu impregnated at the maximum treatment rate when treating NF ₃ exhaust gas coexisting with oxygen is 0.05 to 0.4 wt%, and even if a large amount of Cu is added unnecessarily, the corresponding effect cannot be expected and it is uneconomical Therefore, the Cu content should be 2.0% as a practical upper limit. The impregnated amount of Cu expressed by weight ratio is NF
The value gradually increases as Si is consumed by reacting with ₃ (since Cu is not consumed), but it goes without saying that the impregnated amount of Cu here refers to the drug in the initial state. Absent.

Various generally known methods can be applied to deposit Cu on the Si surface. For example,
(a) A method of plating Cu on the Si surface by an electroless method,
(b) A method in which Cu and Si are mixed and heat treated in an inert atmosphere such as N ₂ to form an alloy with Cu on the Si surface, (c)
Cuprous chloride and Si mixed, N ₂ atmosphere 400-500 ° C
There is a method of forming an alloy with Cu that has been reduced and produced on the Si surface by baking at (3), a method of spraying Cu on the (d) Si surface, and any method is effective.

Further, as an embodiment of the present invention, from the viewpoint of effectively utilizing the internal space of the reactor, it is desirable to use a method of depositing as much as necessary and sufficient Cu as a catalyst on the surface of Si as the main component. However, even in the method of simply filling Si and Cu into the reactor at the same time, an active catalyst region as shown in (b) is formed at the contact portion between Si particles and Cu particles, which is effective for treating NF ₃ exhaust gas coexisting with O _2. There is no change.

[0011]

The present invention will be described in more detail with reference to the following examples, but the invention is not limited to the examples.

Comparative Example 1 A 1/2 inch Ni pipe was used as a reactor and horizontally fixed in an annular furnace. The reaction agent used was one in which Si particles were sieved to have a particle size of 3 mm to 5 mm. About 11 g of the reaction agent was filled in a zone having a length of about 100 mm of the reactor and heated by a heater. As simulated exhaust gas (NF ₃ =
2%, N ₂ = 98%) and (NF ₃ = 2%, O ₂ = 2)
%, N ₂ = 96%) was mixed at a rate of 1 liter / min, and 10 minutes after the start of the treatment, the NF ₃ concentration of the outlet gas was analyzed. (Gas concentration is volume ratio.
The same shall apply hereinafter). The results are shown in Table 1. SiF ₄ having a concentration corresponding to decomposed NF ₃ was detected in components other than NF _{3 in the} outlet gas.

When O ₂ = 0%, NF ₃ is easily decomposed by Si, but when O ₂ coexists with NF ₃ , the TLV value is 1
It became very difficult to treat the powder to 0 ppm or less, and in this comparative example, it was not achieved even at a temperature of 800 ° C. If the NF ₃ of the gas after the treatment is intended to be 10 ppm or less, the reactor becomes large in order to secure the reaction time, and the installation space, production cost, and running cost become uneconomical.

Example 1 Table 1 shows the results of an experiment conducted in the same manner as in Comparative Example 1 except that Si in which Cu was impregnated under various conditions was used as a reaction agent. The method of impregnating Cu is as follows according to what has been described above.
It depends on (a)-(d).

Impregnation method (a): A bath of CuSO ₄ .5H ₂ O and Rochelle salt was adjusted to pH = 12.3 with NaOH, and Si was added.
After immersing the grains, HCHO was added and reduced to plate Cu. The Si particles were taken out, washed with water, dried and used.

Impregnation method (b): Si particles and Cu powder were mixed in equal amounts and heat-treated at 900 ° C. for 1 hour in an N ₂ atmosphere to form a Cu alloy layer on the Si surface. Excessive Cu powder was sieved and removed.

Impregnation method (c): Si grains and CuCl were mixed in equal amounts and heat-treated at 450 ° C. for 1 hour in an N ₂ atmosphere to form a reduced Cu layer on the Si surface. Excessive CuCl powder was sieved and removed.

Impregnation method (d): Cu particles plasma-sprayed on Si particles were used.

[0019]

[Table 1]

Comparative Example 2 The composition of the feed gas: (NF ₃ = 2%, N ₂ = 98%), the flow rate of the feed gas: 1 liter / min, and the temperature were measured in the same apparatus as in Comparative Example 1 using Si plain particles as a drug. : NF ₃ of the outlet gas was continuously analyzed until about 80% of the drug was consumed at 700 ° C. The result is shown in FIG.

In this comparative example in which O ₂ = 0%, NF ₃ was easily decomposed as pure Si, and NF ₃ was not detected in the outlet gas at the beginning (3 ppm>). As Si was consumed, a space was created in the upper part of the medicine-filled part of the horizontally arranged reactor, and NF ₃ which short-passed this space was detected in the outlet gas and its concentration gradually increased. . However, the supplied NF ₃ (inlet concentration = 2
0000 ppm), most of the Si is still decomposed even when 80% of the charged amount of Si is consumed 8 hours after the start of the treatment, and NF ₃ is efficiently decomposed by a small amount of Si. Is shown.

COMPARATIVE EXAMPLE 3 Using pure Si particles as a chemical, the same apparatus as in Comparative Example 1 was used to supply gas composition: (NF ₃ = 2%, O ₂ = 2%, N ₂ = 96).
%), Supply gas flow rate: 1 liter / min, temperature: 70
NF ₃ of the outlet gas was continuously analyzed until about 80% of the drug was consumed at 0 ° C. The result is shown in FIG.

[0023] In this comparative example the NF ₃ O ₂ coexist NF ₃ concentration in the outlet gas at the beginning of 200ppm or even there Si Plain is difficult to completely decomposing NF ₃ for coexistence of O ₂ It indicates that there is.

Example 2 The chemical composition used in Example 1 prepared by the Cu impregnation method (a) (plating method) was supplied to the same apparatus as in Comparative Example 1 with the composition of gas supplied: (NF
_{3 = 2%, O 2 =} 2%, N 2 = 96%), the feed gas flow rate: 1 liter / min, temperature: under the condition of 700 ° C. The NF ₃ in the outlet gas to about 80% of the drug is consumed Continued analysis. The result is shown in FIG.

From this example, Cu-impregnated S in the present invention
The effect of i is S at O ₂ = 0% even when O ₂ = 2% coexists.
It can be seen that NF ₃ can be decomposed as efficiently as in the case of i alone (Comparative Example 2). Moreover, the Cu catalytic effect continues until at least 80% (probably the total amount) of Si is consumed.

[0026]

INDUSTRIAL APPLICABILITY According to the present invention, it becomes possible to remove NF ₃ exhaust gas coexisting with oxygen at a low temperature without lowering the processing rate.

[Brief description of drawings]

FIG. 1 shows the treatment results of NF ₃ exhaust gas of Example 2 and Comparative Examples 2 and ₃ .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/34 128

Claims (1)

[Claims] 1. A method for treating exhaust gas, which comprises contacting exhaust gas containing NF ₃ as a harmful component with a treating agent to remove NF ₃ from the exhaust gas, the treating agent being 0.01 to 2. A method for treating NF ₃ , wherein Si containing 0 wt% of Cu is used.