JPH07289850A - Method for purifying waste gas - Google Patents

Abstract

PURPOSE:To provide a method for purifying waste gas by which SiF4 and HF generated at the time of subjecting Si and an Si compd. to a treatment with fluorine-contg. gas such as etching or cleaning are selectively separated from base gas and this base gas and unutilized fluorine-contg. gas are recovered. CONSTITUTION:Waste gas contg. SiO4 as a formed impurity is brought. into contact with an alkali metal fluoride in the temp. range of 200-500 deg.C. Especially in the case of waste gas contg. HF, an alkali metal fluoride packed column is placed in the former or latter stage of a system and the waste gas is brought into contact with the fluoride at <=100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to SiF ₄ gas or SiF ₄ gas and H generated when an amorphous Si / single crystal or polycrystal Si or solid Si compound is subjected to a treatment such as etching with fluorine gas, cleaning or the like.
The present invention relates to an exhaust gas refining method for selectively separating F gas from a base gas and recovering the base gas and an unused fluorine-based gas.

[0002]

2. Description of the Related Art Thin film forming processes have spread widely in the semiconductor industry, and many CVD, vacuum deposition, and sputtering devices are operating. In thin film forming equipment, a large amount of deposits are formed on the inner wall of the equipment and the surface of jigs other than the purpose for which a thin film is to be formed, and if left unattended, particles will be generated and the target thin film will be contaminated by this and the quality will deteriorate. Therefore, cleaning work is regularly performed to remove deposits. The method of cleaning is shifting from a wet method of disassembling the apparatus and immersing it in a cleaning tank to a dry method (so-called gas cleaning method) in which gas is simply passed without disassembling the apparatus.

Many thin films are composed of Si or Si compounds.
However, for deposits composed of these components,
CF as burning gas_Four, SF₆, NF₃, F₂, C
IF ₃Fluorine-based gas such as is effective. Gas cleaning
Si component is SiF_FourIt becomes gas and can be easily removed
Be shipped. CF among the cleaning gases listed here
_Four, SF₆, NF₃Is inert at room temperature, so plasma
Auxiliary measures such as activating by taking etc. are taken. On the other hand
F₂, ClF₃Is very active even at room temperature
No auxiliary means required and no plasma generation mechanism
Applicable as cleaning gas to equipment
It In addition, it is also applicable to equipment equipped with a plasma generation mechanism.
Even the parts that are difficult to clean due to the shadow of the Zuma irradiation are
Excellent because it can be easily cleaned by the diffusion of
It has features.

However, such a cleaning gas or etching gas (hereinafter collectively referred to as a cleaning gas) having excellent cleaning properties and etching properties, such as F ₂ and ClF ₃ , will be improved in its utilization efficiency due to its chemical activity. When this happens, we face difficulties in recovering the unused portion. Only unnecessary SiF ₄ in the cleaning exhaust gas and etching exhaust gas is selectively removed to remove unused cleaning gas components such as F ₂ and ClF ₃ and N ₂ ,
A technique for reusing a base gas such as Ar, He, Ne has not been proposed yet, and it is extracted to the outside of the system while containing a useful component and released to the atmosphere after being removed.

[0005]

In the above prior art, the gas cost is high because the cleaning exhaust gas and the etching exhaust gas are disposable, and unreacted F ₂ and ClF _{3 which} can be used because it goes against the trend of resource saving. The development of technology for recovering and reusing useful components such as cleaning gas and base gas has been awaited.

[0006]

[Means for Solving the Problems] Si, SiO ₂ , various silicates, Si compounds such as SiC and SiNx are added to SF ₆ , C
SiF is obtained by performing treatments such as cleaning and etching with a fluoride gas such as F ₄ , F ₂ , ClF ₃ and NF _{3.
Although four} gases are generated, it is necessary to discharge this unnecessary component SiF ₄ out of the system in order to recover the useful components in the used gas and recycle them. Since SiF ₄ reacts quickly with an alkaline agent, the following reaction occurs when it is brought into contact with a solid alkaline agent such as CaO, soda lime, Ca (OH) _{2 in} the case of a dry method and an alkaline solution such as an aqueous solution of NaOH or KOH in the case of a wet method. Can be easily removed according to.

For example, Is.

The H ₂ O (steam) produced as a by-product can be removed by using a dehydrating agent such as zeolite. This method is effective in recovering the base gas and the unused cleaning gas by removing SiF ₄ from the used gas of the cleaning gas which does not substantially react with the alkaline agent such as SF ₆ , CF ₄ , NF _{3 at} room temperature. , F ₂ , Cl
When applied to a cleaning gas system such as F ₃ that reacts with an alkaline agent at room temperature, unused cleaning gas is removed together with SiF ₄ , and O _{2 that} is not easy to remove outside the system is generated (the following formula), Not suitable for that reason.

For example, Is.

In a cleaning gas system which reacts with an alkaline agent even at room temperature, as a result of extensive studies on a method for selectively removing SiF ₄ in exhaust gas from the cleaning gas and the base gas, the heated alkali metal fluoride was found. The inventors have found that the method of contacting the oxide with the exhaust gas is effective, and have reached the present invention. The method of the present invention comprises a system using a cleaning gas such as F ₂ and ClF ₃ that reacts with an alkaline agent even at room temperature and a cleaning gas that does not substantially react with an alkaline agent such as SF ₆ , CF ₄ and NF ₃ at room temperature. It can be applied to any of the systems.

As alkali metal fluorides, LiF, N
Both aF and KF are effective, and the temperature is 200 to 50.
A range of 0 ° C is suitable. Substantially no reaction occurs below 200 ° C, and the higher the temperature, the higher the reaction rate.
The re-release (decomposition) of SiF ₄ once captured starts at around 0 ° C, and the limit is around 500 ° C, and at 600 ° C or higher, SiF ₄ is not substantially captured. A more desirable temperature range is 300 ° C ± 50 ° C. SiF ₄ is fixed by NaF
Taking the case of as an example, the following reaction occurs.

[0012] Although the equilibrium is largely biased to the right up to around 300 ° C, the reverse reaction cannot be ignored above 400 ° C as described above.

Under these conditions, F ₂ and ClF ₃ are LiF and N
Since it does not react with aF and KF, when the exhaust gas is brought into contact with the heated alkali metal fluoride, it passes through with the base gas (N ₂ , Ar, He, Ne, etc.) which does not react with it, so that it can be recycled and reused. Naturally, the concentration of the cleaning gas is reduced by the amount consumed after being converted to SiF ₄ , so it must be replenished in the middle of the circulation line, but the amount of replenishment is sufficient for the amount consumed, so the use of cleaning gas Efficiency is theoretically 100%.
Similarly, the base gas (He) has no theoretical loss.

That is, the present invention is (F ₂ , ClF ₃ )-
It provides a principle method of selectively removing only SiF ₄ from a mixed gas such as (SiF ₄ )-(N ₂ , Ar, He, Ne) system out of the system.

The specific method of contacting the cleaning exhaust gas with the heated alkali metal fluoride is not particularly limited, but an airtight metal container equipped with a heater in the periphery is filled with granular alkali metal fluoride, Introducing etching exhaust gas and cleaning exhaust gas from one side of the container,
It is recommended because of the simplicity of a conventional fixed bed gas-solid reactor in which the purified SiF ₄ gas is discharged from the other end.

The present invention uses (F ₂ , ClF ₃ )-(Si
SiF ₄ from the F ₄ )-(N ₂ , Ar, He, Ne) system
The selective removal of H was carried out mainly, but by appropriately combining the temperature conditions, H
It also has the effect that F can be removed.

In cleaning and etching of a Si-based material with a fluorine-based cleaning gas, in addition to SiF ₄ , H contained in the material and water remaining adsorbed on the inner wall of the chamber act on F to generate HF. Therefore, it is desirable to remove such HF when the cleaning gas / base gas is circulated and reused. It is generally known that HF is absorbed by an alkali metal fluoride to form a solid acid fluoride, but the alkali metal fluoride is also the SiF ₄ adsorbent of the present invention and the adsorption conditions of SiF ₄ and HF.
Since the adsorption conditions are simply different in temperature, it is possible to remove SiF ₄ and HF at the same time by selecting the temperature condition of the alkali metal fluoride.

The principle of HF removal is that HF acts on an alkali metal fluoride to form an acid salt thereof, for example, NaF in NaF.
-It is based on the chemical reaction of being fixed in the form of HF. It is appropriate to absorb HF in a temperature range of 100 ° C. or lower, that is, the HF absorption equilibrium vapor pressure is 1.5 mmHg or less, and the absorption parallel vapor pressure near room temperature (20 ° C.) is 4 × 10 ⁻³ mmHg. Since it is sufficiently low, there is no need to particularly cool it. When the temperature rise of the absorbent is inevitable, it is usually 1
Up to 00 ° C (absorption parallel vapor pressure is 1.5 mmHg) is a practical range. HF is absorbed even at temperatures above 100 ° C, but 150 ° C (14 mmHg) and 180 ° C (50 mm
Hg) rapidly increases the absorption equilibrium vapor pressure.

When removing both SiF ₄ and HF,
The order of removing F ₄ and HF does not matter. That is, the components to be removed later do not interfere with the absorption compared to the components to be removed first.

Another feature of the method for treating SiF ₄ and HF according to the present invention is that the used treating agent can be easily regenerated and can be used repeatedly. Therefore, the running cost of the treatment chemical is low, and it can be said that this is also an industrially advantageous method.

Regeneration of the used treatment chemicals can be carried out by a simple method in which the fixed SiF ₄ and HF are heat-treated and decomposed and released. At this time, it is not necessary to take out the medicine from the container, and it is sufficient to simply switch the valves of the processing line and the regeneration line and change the temperature of the heater.
In order to obtain a practical dissociation pressure, it is appropriate to regenerate the alkali metal fluoride having SiF ₄ fixed at 600 ° C. or higher, and to regenerate the alkali metal fluoride having HF fixed to 20 ° C.
A temperature of 0 ° C or higher is suitable. Regeneration while heating a small amount of N ₂
It is efficient to carry out under reduced pressure while flowing a purge gas such as.

The separated and discharged SiF ₄ and HF may be removed by a wet scrubber process which is a cheaper method than the present method. In some cases, it may be more cost effective to dispose of the used alkali metal fluoride, such as when there is no wet scrubber for cleaning separated SiF ₄ or HF or when the amount of gas treatment is small. It goes without saying that the most advantageous method may be appropriately selected depending on the situation.

As an embodiment of the present invention, as shown in the following examples, the SiF ₄ removal column and the HF removal column may be independent, but this is for the purpose of showing the function of the present invention in an easily understandable form. It is also a device to reduce the number of columns by adding a temperature distribution to one column to supplement SiF ₄ in the high temperature part and HF in the low temperature part to save the installation area of the device. Included in the embodiments of the present invention.

[0024]

The present invention will be described in more detail below with reference to examples. All gas concentrations are expressed on a volume basis.

Examples 1 to 23 A heater is provided on the outer periphery, and granular NaF, KF having a diameter of 3 mm,
Inner diameter 7.6 mm and height 240 mm filled with 12 g of LiF
The above two stainless steel columns were connected in series in the vertical direction to form an exhaust gas treatment device. The inner diameter of the front column (upper side) and the rear column (lower side) is 4.3 so that they do not affect each other thermally.
mm Stainless steel pipes with a length of 300 mm were connected at a distance. Under the conditions shown in Table 1, Table 2 and Table 3, the mixed gas of each component was introduced to the preceding (upper) column at a rate of 1 liter / min, and the gas after the treatment which passed through the two columns sequentially was subjected to UV absorption. It was analyzed by a photometric method and an infrared absorption spectrophotometric method. The results are shown in Tables 1, 2 and 3.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

Example 24 A heater was provided on the outer circumference, and 12 g of granular NaF having a diameter of 3 mm was used.
Two filled stainless steel columns having an inner diameter of 7.6 mm and a height of 240 mm were connected in series vertically with a stainless pipe having an inner diameter of 4.3 mm and a length of 300 mm to form an exhaust gas treatment device.

Keep the front column at 300 ° C with a heater,
The latter column was left at room temperature of 20 ° C. SiF ₄ = 1
0000 ppm, HF = 10000 ppm / He (ba
(Lance) mixed gas was introduced at a rate of 1 liter / min in the order of the front (upper) column and the rear (lower) column, and the gas after the treatment that passed through the two columns was analyzed.

Immediately after the start of the treatment, SiF was added to the outlet of the latter column.
₄ , HF was not detected, but 170 minutes after the start, S
HF started to be detected in iF ₄ after 200 minutes (lower limit of detection: 1 pm for SiF _{4 and} 10 ppm for HF). 26
After 0 min, the SiF ₄ concentration at the outlet of the latter column became the same as the concentration of HF at the outlet of the latter column after 500 min, and became the same as the concentration of the supplied mixed gas.

At this time, the supply of the mixed gas is stopped, and then the outlet side is drawn with an exhaust pump while the N ₂ is flowing at 0.2 liter / min, the pressure inside the system is reduced to 200 torr, and the preceding column is heated to 600 ° C. 2H for 2nd column at room temperature
hold for about r and then raise the temperature of the latter column to 200 ° C,
The drug was regenerated by keeping it for about 2 hours. After the regeneration, the mixed gas of SiF ₄ and HF / He was treated again under the same conditions, and the time until the SiF ₄ concentration and the HF concentration at the outlet of the latter column became the same as the concentration of the supplied mixed gas were respectively 270 min and 500 min. It was confirmed that the drug was completely regenerated.

Comparative Example 1 10% F ₂ (H) was applied to a plasma CVD apparatus in which amorphous Si made of SiH ₄ as a raw material adhered to the reactor wall other than the substrate.
(e-dilution) was introduced at a rate of 1 liter / min to remove deposits by gasification, that is, dry cleaning was performed.
When the cleaning exhaust gas is monitored, F ₂ = 4%, SiF ₄ = 2.4%, HF = 2.6% in the initial stage of cleaning, and then the F ₂ concentration gradually increases, while SiF ₄ , HF
The density of the
iF ₄ and HF were not detected, and 10% F ₂ was discharged as it was. As a result of elemental analysis, it was found that the H source of HF was contained in the amorphous Si of the deposit.
It took 16 hours to complete the cleaning, and the cleaning exhaust gas was drawn by an exhaust pump and discarded without being collected. The amount of F ₂ consumed was 960 liters (100% conversion).

Example 25 Inner diameter 100 filled with 3.5 kg of granular NaF having a diameter of 3 mm
Two columns equipped with a heater having a height of 500 mm and a heater of 500 mm were connected in series in the upper and lower sides to form an exhaust gas treatment device. The apparatus is arranged in series after the exhaust pump of Comparative Example 1, the front column (upper side) is heated to 300 ° C., and the rear column (lower side).
Was set to room temperature of 20 ° C. With the amorphous Si adhered to the same extent as in Comparative Example 1, 10% F ₂ (He diluted) was introduced at 1 liter / min to clean the CVD reactor, and the gas discharged from the subsequent column had a F ₂ concentration of Always 10
It was circulated to the cleaning gas inlet by replenishing the consumed amount so as to become%. SiF is contained in the gas coming out of the latter column.
₄ and HF were not detected. It takes 16 hours to complete the cleaning as in Comparative Example 1, and F ₂ at this time is required.
290 liters (100% conversion) was enough.

[0035]

According to the refining method of the present invention, the exhaust gas for cleaning and etching Si-based solids and deposits is removed by 20 times.
When contacted with a solid alkali metal fluoride at 0 to 500 ° C and 100 ° C or less, SiF ₄ or SiF ₄ and H
By removing F, the gas can be recovered and reused.

Claims (5)

[Claims] 1. A gas containing SiF ₄ is heated at 200 to 500 ° C.
A method for purifying exhaust gas, which comprises bringing into contact with a solid alkali metal fluoride heated to a low temperature. 2. Exhaust gas purification, characterized in that a gas containing SiF ₄ and HF is brought into contact with a first stage solid alkali metal fluoride at 100 ° C. or lower and a second stage solid alkali metal fluoride heated to 200 to 500 ° C. in sequence. Law. 3. Exhaust gas purification, characterized in that a gas containing SiF ₄ and HF is brought into contact with a solid alkali metal fluoride heated to 200 to 500 ° C. in the first stage and a solid alkali metal fluoride at 100 ° C. or lower in the second stage in sequence. Law. 4. The solid alkali metal fluoride is LiF, N
4. The exhaust gas purification method according to claim 1, wherein the exhaust gas purification method is at least one or more selected from aF and KF. 5. The solid alkali metal fluoride treated with SiF ₄ is regenerated at a temperature of 600 ° C. or higher, and the solid alkali metal fluoride treated with HF is regenerated at a temperature of 200 ° C. or higher. The exhaust gas purification method according to claim 1.