KR20080032089A - Method for plasma treatment of gas effluents - Google Patents

Abstract

The invention concerns a method for plasma treatment of gas effluents substantially at atmospheric pressure, including: injecting the effluent to be treated into a plasma torch; injecting water vapour, upstream or downstream of the plasma.

Description

Plasma treatment of gaseous waste {METHOD FOR PLASMA TREATMENT OF GAS EFFLUENTS}

The present invention provides for the treatment of gaseous waste discharged during semiconductor manufacturing, in particular during thin film-film deposition of materials, or during plasma cleaning of deposition reactors, and during plasma etching of thin films to form geometric patterns of devices. It's about technology.

Methods for etching and cleaning deposition reactors may include perfluorinated gases (C ₂ F ₆ , and / or cC ₄ F ₈ and / or C ₃ F ₈ and / or NF ₃ and / or CF ₄ and / or SF ₆ ) And hydrofluorocarbons (eg, CHF ₃ ) can be used, and if these gases are released into the atmosphere, they will increase the greenhouse effect and have a significant impact on global warming. In general, such gases are not completely consumed in the process.

One preferred way to reduce the air emissions of these gases is to convert these gases into plasma in the presence of certain additive gases to react reactive adsorption or gas scrubbers in a solid alkaline medium (dry-scrubber). It is to convert these gases into chemically reactive species (acidic fluorinated compounds) that can be irreversibly easily removed by conventional methods such as absorption by liquid solutions in a scrubber.

In order to prevent interaction with the operation of the process equipment or the pump, it is desirable to place the plasma downstream of the means for maintaining a rough vacuum. Contaminant concentrations at the outlet of the low vacuum pump and maximum efficiency at total flow conditions are obtained in high-electron-density plasmas such as microwave plasmas.

In this regard, surface wave microwave plasmas and microwave plasma torches are used.

Surface wave plasma solutions are also well applied in the treatment of waste in etching processes, that is, producing gaseous waste which cannot promote the formation of solids in the apparatus.

To treat gaseous waste from reactor deposition and cleaning processes, M. Moisan et al. "Waveguide based single and multiple nozzle plasma torches: the TIAGO concept", Plasma Source Science Tech, 10, 2001, page 387 As described in -394, it is proposed to use a microwave plasma torch burner in the form of a waveguide supported axial injection.

The torch is freely terminated in the chamber that confines the gases to collect the gases in the downstream discharge line. Solid particles are trapped and entrained at slightly spaced distances to prevent solid particles from forming in the plasma plume and flame downstream of the torch nozzle and thus accumulating continuously in the chamber. If not, it will not interfere with the work. To this end, the basic solution is to install a gas scrubber as close as possible to the outlet of the torch chamber.

PFC conversion principles within a microwave plasma include breaking down initial molecules in inelastic collisions caused by high-energy discharge electrons, producing fragments smaller than the initial molecules, atoms, and radicals. These fragments react together, deexcite, recombine, and / or rearrange to produce new compounds that differ from the initial PFCs. More specifically, methods of neutralization in solids or liquids with high reactivity and while being an undeniable immediate threat to lifespan and health, such as F ₂ , HF, COF ₂ , SO ₂ F ₂ , SOF _4, etc. It is aimed to convert most of the incoming PFCs into acidic fluorinated compounds which can be reliably and irreversibly removed by.

In general, in order to carry out the PFC conversion reaction, the addition of additive gas is required. This means that if only PFC molecules diluted in nitrogen were in the plasma, decomposition would be effective, but if the molecules excited the emission region, the fragments would tend to react with each other and rebuild the initial molecule.

The choice of additive gas is an important issue in the optimization of the PFC decomposition process.

First, this choice can affect the conversion efficiency itself.

In fact, the debris produced by the decomposition of the additive gas in the discharge is somewhat easier and quicker to use PFC decomposition debris before the gases have enough time to re-form when the gases are discharged from the discharge zone. To form stable corrosive fluorinated products.

In addition, the corrosive fluorination reaction product will take various forms depending on the type of additive gas. Using this fact, different specific reaction products will preferably be formed, depending on the post-treatment method chosen to reliably and irreversibly remove the corrosive fluorinated product from the gaseous waste stream.

This post-processing approach may be burdensome for cost or other reasons specific to the user in question. Therefore, it is important to be able to apply optimally to various situations of customers. For example, if it is decided to operate with a gas scrubber, it is impossible to use oxygen as the additive gas. This will essentially produce reaction products such as compounds such as COF ₂ (with fluorocarbons) or SO ₂ F ₂ (with SF ₆ ) and SOF ₄ , and in some cases significant amounts of F ₂ , and F ₂ Gases react with water or aqueous caustic soda solutions to produce extremely toxic OF ₂ (50 ppb legal threshold for continuous exposure of the operator), even in the presence of small amounts. do.

To date, oxygen (O ₂ ) has been used as additive gas, which is generally injected in the form of dry air taken from the compressed air supply network of semiconductor plants.

This approach corresponds to a technical choice, including the post-treatment of the corrosive fluorinated product by reactive adsorption on a solid bed, with additive O such as F ₂ , COF ₂ , SO ₂ F ₂ , SOF _4. A unit designed to preferably capture the product of the dry conversion chemistry using ₂ is used.

It is a primary object of the present invention to find novel conversion chemistries for waste from industrial processes, in particular PFCs, in microwave atmosphere plasma.

In addition, in the case of PFC wastes, the problem of promoting HF formation as corrosive fluorinated by-products arises, which is based on soda lime as a means of irreversible capture of reaction by-products prior to discharge of the waste stream into the atmosphere. Allows for the preferred use of solid beds of granules or of gas scrubbers.

A further object of the present invention is to improve the conversion yield by the use of such alternative chemical reactions.

The present invention first relates to a method for plasma treating gaseous waste at substantial atmospheric pressure, which method

Spraying the waste to be treated into a plasma source, and

Spraying water vapor upstream and / or downstream of the plasma and optionally into the plasma itself.

The pressure of the waste is for example 0.8 bar to 1.3 bar.

Water vapor may be injected at a concentration between 100 ppm and 5% in a carrier gas which is generally nitrogen.

The temperature is 20 ° C to 300 ° C, preferably 50 ° C to 200 ° C.

The waste to be treated is a waste from a semiconductor processing process, for example a mixture of perfluorinated gas and / or hydrofluorocarbon gas and oxygen.

Preferably, the plasma source is a surface wave type, in particular a microwave-excited plasma source.

The invention also relates to an apparatus for plasma treating gaseous waste at substantially atmospheric pressure, the apparatus comprising means for generating plasma and means for injecting water vapor into the mixing zone.

The means for injecting water vapor may be located upstream of the plasma forming region, or may be located downstream of the plasma forming region.

According to one embodiment, the means for injecting water vapor comprises a vaporizer having a temperature adjusting means.

The present invention makes it possible to carry out PFC wet conversion chemistry in atmospheric plasma which substantially produces only HF as a fluorinated byproduct. Water vapor is added to the plasma not lower than the vapor pressure at room temperature.

According to another aspect of the invention, at least one chemical compound comprising a molecule comprising at least one hydrogen atom is preferably injected at the plasma outlet, or as soon as possible, in the plasma but adjacent to the outlet of the plasma waste, thereby fluorinating The hydrofluoric acid is essentially produced and then dissolved in water (or in any reducing liquid system) without the need to use a "dry" scrubbing system for the removal of the hydrogen acid (although the user Often prefer to use an additional "dry" system as a preliminary measure).

According to another aspect of the present invention, when a product such as WF ₆ is present in the reactor, the passage of these gases into the plasma with the partial reduction or hydrogenation element results in the deposition of W on the wall of the tube, Therefore, it was confirmed that it causes a break almost immediately.

This problem caused by the use of hydrogenation additives when the first species comprises fluorinated metal derivatives, which can produce metal deposits, in particular WF ₆ , and when the plasma is produced in the dielectric tube In order to solve the problem, it is important to inject at least one hydrogenation element downstream of the plasma, preferably its immediate outlet, so that the hydrogenation element reacts as early as possible with the first species produced in the plasma, and thus the PFC Based on the mixture comprising, it is important to make the second species. (Alternatively, at a position such that the PFC or HFC molecules are already "split" or partially "split" in the so-called plasma post-emission region, such hydrogenated and / or reducing elements are introduced into the plasma itself. Can be sprayed.)

When elements such as WF ₆ are present in the reactor offgas, at the inlet of the plasma, this serves to prevent these products from decomposing in the plasma. In contrast, the first species generated from WF ₆ will react with the reducing species injected downstream at the outlet of the plasma, such that tungsten metal or other solid tungsten compounds such as oxides or oxyfluoride are located at the outlet of the plasma. It will be deposited on the line, which is generally metal, so that no problems arise in the operation of the plasma system.

Alcohols, glycols, hydrocarbons, hydrides, or any other hydrogenated compounds, such as H ₂ O, H ₂ , CH ₄ , NH ₃ , methanol, ethanol, etc., may be used as gaseous sources, especially of hydrogenation and / or source reactants. will be.

Indeed, it has been found that the second species produced (using the hydrogenation additive) contains more hydrofluoric acid HF than when using anhydrous additives, especially oxygen types. In addition, when WF ₆ (or similar product) is randomly present in the waste to be produced from the reactors disposed upstream of the pump, the downstream injection of the hydrogenated product (ie, downstream of the plasma) is located downstream of the plasma. It produces a deposit of W (or a product derived from W) in the lines, the lines are generally made of stainless steel or plastic, and in the case of such lines an apparently very thin deposit is not an absolute disadvantage.

However, it has been found that the solution obtained is not completely satisfactory if the hydrogenated compound is injected only downstream of the plasma without any addition upstream of the gaseous waste. In fact, the decomposition efficiency obtained in this case is lower than that which can be obtained by introducing the same amount of hydrogenated gas, for example water vapor upstream.

The inventors of the present invention believe that a significant proportion of PFCs initially introduced into the plasma will be reconstituted before the decomposition fragments react with the hydrogenated compounds introduced downstream. Thus, the reconstructed PFC cannot be decomposed again before leaving the region where the plasma is present.

In order to simultaneously solve the above two problems, according to a preferred embodiment, the present invention easily reacts with metallic elements such as Al, W, etc. (if present in the plasma) upstream of the plasma or at the very end of the plasma. These hydrogenation is preferably carried out by spraying the hydrogenated compound downstream of the plasma into a mixture of the first gas species produced by chemical conversion in the plasma, while preferably spraying a gaseous oxygenated compound that does not contain hydrogen atoms or other elements that can Causing the compound to react with the first species, wherein the temperature of the first gas species resulting from the plasma is preferably maintained at or above 150 ° C.

Without wishing to be bound by any particular theory, the inventors believe that when anhydrous additives, in particular oxygenated additives, such as oxygen or air, are injected upstream of the plasma, the additives will decompose and / or be excited and the fragments may be PFC or It will react very easily with decomposition fragments of HFC to produce corrosive fluorinated compounds such as F ₂ , COF ₂ , SO ₂ F ₂ , SOF ₄ (first species). Once formed, these compounds are very stable even at high temperatures of the gases in the microwave plasma and are very unlikely to decompose again. In particular, they are not substantially reconverted back to PFC. These anhydrous corrosive fluorinated products such as F ₂ , COF ₂ , SO ₂ F ₂ , SOF ₄ have significantly greater reactivity than PFC. At the plasma outlet, when the hydrogenated compound is injected, the temperature is still high enough to react completely with the hydrogenation additive to some extent, essentially producing HF, and HF is more thermodynamically stable than the anhydrous corrosive fluorinated product. On the other hand, PFCs not converted by the plasma will not substantially react with these hydrogenation additives at the plasma outlet. Thus, the PFC conversion yield is substantially the same as the conversion yield of the contaminant controlled plasma that is used as an additive that is not hydrogenated, especially an oxygenated compound or compounds are injected upstream of the plasma.

1A and 1B are cross-sectional views showing two alternative embodiments of the device according to the invention.

2 is a cross-sectional view showing the structure of a furnace.

3 to 9 are graphs showing the measurement results during the implementation of the method according to the invention under various conditions.

10 is a schematic diagram illustrating an exemplary embodiment for preventing the dielectric tube from breaking.

In the following, exemplary embodiments of the present invention are described with reference to FIGS. 1A and 1B.

Such devices are used to transport gaseous waste to outlets of equipment for the treatment of semiconductor materials or deposition of thin film layers, for example substantially between atmospheric pressure, between 0.7 bar or 0.8 bar and within 1.3 bar or 1.5 bar nitrogen. It can be installed substantially at the rear of the pump. These wastes include perfluorinated compounds such as C ₂ F ₆ , and / or cC ₄ F ₈ , and / or NF ₃ and / or CF ₄ and / or SF ₆ .

A plasma source of surface wave type is used, which is M. M. Moisan and Jet. Microwave Excited Plasma by Z. Zakrzewski, Editors M. Moison and Jay. J. Pelletier, 5, and Elsevier, Amsterdam, 1992.

Reference 2 shows a plasma tube 4 comprising an AlN inner tube 6 and a quartz outer tube 8.

The plasma is initiated by a high voltage initiator 10.

The gas mixture to be treated, for example a mixture of PFC and nitrogen, is transferred to the mixing zone 12.

Gaseous water is sprayed using the vaporizer means 14. Such means 14 comprise, for example, a metering pump 16, which supplies liquid water to an electrothermal vaporization furnace 18.

Water vapor is injected at a flow rate that provides a water vapor concentration between 100 ppm and 5% in the gaseous waste. Thus, there is no need to maintain the condition below the steam condensation limit (2.3%) at room temperature.

In order to convert the controlled amount of water into the gaseous state, deionized water may be obtained from the reservoir 26 in a controlled amount by the metering pump 16.

An exemplary embodiment of the furnace is shown in FIG. This furnace has a FIREWARD 600W type cartridge heater 40, a rockwool jacket 32, a coil 34, and a liquid water inlet channel 30.

Water flows in the coil 22 to completely vaporize it (see FIG. 1A), and the coil consists of a stainless steel body 24 surrounding the cartridge heater.

The cartridge heater may be connected to the temperature control 24. The temperature controller allows the preparation of the mixture by adjusting the temperature of the water discharged into the system using the thermocouple 28 to about 200 ° C to 300 ° C.

The final furnace 18 injects water vapor 20, which is mainly used as a carrier gas for the waste, for example, contained in nitrogen, at which temperature the recondensation takes place before the gas reaches the emission limit, taking into account the concentration. It is determined not to happen.

In addition, the high temperature of the carrier gas prevents the deposition of solids (eg, silica or tungsten oxides) that may be caused by hydrolysis of thin film-film etch products, such as SiF ₄ or WF ₆ , in the process chamber. can do.

Such deposition can result in blockage of the plasma inlet.

The amount of hydrogen provided by this method ensures good conversion efficiency, and preferably the efficiency at least corresponds to the reaction stoichiometry (ie sufficient hydrogen element to form only HF with all incoming fluorine). Indeed, depending on the chemical reactivity of the system, the amount of water needed to obtain the maximum PFC conversion ratio may be higher. This may also vary depending on the type of PFC involved.

If the concentration of water vapor is below 2% after being injected into the mixture comprising gaseous waste, in no case recondensation occurs because the conditions are maintained below the water vapor condensation limit (2.3%) at room temperature.

However, the amount of PFC released can be approximately tens of sccm in the case of an etch reactor, depending on the technical specifications of the low vacuum pump, in a nitrogen dilution stream of 20 to 100 slm, for the CVD reactor during cleaning. It could be hundreds of sccm. For example, in the case of 50 sccm CF ₄ , at least 100 sccm H ₂ O is provided for the formation of HF only. Kinetics should also be considered, resulting in at least 200 sccm of H ₂ O. In the case of 500 sccm C ₂ F ₆ , at least 1500 sccm H ₂ O is required. As such, this provides up to one percent, for example up to one percent, for example up to 3% or 5% water vapor, up to one thousand or several thousand ppmv, for example 2000 ppmv, into nitrogen or into a mixture of waste.

It should be recognized that due to the saturated vapor pressure under these conditions it will be impossible to obtain atmospheric pressure and room temperature. Water that is prone to recondensation in the system in the form of macro drops or liquid films will not make a significant contribution to the conversion reaction. In addition, the presence of liquid water at this level will be incompatible with the satisfactory operation of the release, especially since the water will absorb microwaves.

On the contrary, the present invention helps to eliminate this disadvantage. Spraying water vapor at temperatures between 20 ° C. and 300 ° C., preferably between 50 ° C. and 200 ° C., serves to create satisfactory conditions for carrying out an effective conversion of the PFC. Temperatures above 100 ° C. will further prevent hydrolysis of certain products that can produce solid deposits as described above.

The mixing zone is between an initial mixture (or an initial waste, eg N ₂ + PFC) having a flow rate of about 20 to 100 l / min and an average flow rate of 50 l / min and steam having a flow rate of about 1 l / min, for example. Corresponds to the contact.

In addition, gaseous water is incorporated by nitrogen into the mixing zone where the temperature is about 2500K to 7000K and located adjacent to the plasma, which not only eliminates the risk of recondensation but may also occur between by-products of the etching process. It also prevents undesirable premature reactions.

Before reaching this mixing zone, the water initially provided to the unit in liquid form is subjected to a vaporization process which is carried out using a furnace as described above.

In the case of the actual process waste treatment, water vapor is mixed with the initial waste mixture, preferably at the level as close as possible to the plasma, in order to avoid the early interaction of certain products of the process with water vapor.

According to the first embodiment (see FIG. 1A), the outlet of the vaporizer 14 is located very close to the plasma 4.

As a result, upstream of the plasma, water is sprayed perpendicularly and at an angle to the introduction of the mixture to be treated, here the introduction of PFC-nitrogen.

Another procedure (see FIG. 1B) sprays water vapor downstream of the plasma and as close as possible to the limit.

In FIG. 1B, only furnace 18 is shown, but the furnace will include virtually all of the members 16, 19, 24, 26, 28 described above in connection with the configuration shown in FIG. 1A.

At the outlet of the actual emitting area, by definition, there are no charged particles, ions and electrons. However, this does not mean that the neutral species are all in finally stable form, nor does it mean that they are in the ground energy state. Atmospheric microwave plasmas are not quite far from thermodynamic equilibrium, where the temperature of the heavy particles is typically 2500 to 7000K at the central axis (as opposed to electrons).

In general, due to the high velocity of the gas (small characteristic diameter of the plasma due to radial contraction), the gas will remain at very high temperatures along the characteristic distance before reformulation of the PFC molecules from the decomposed fragments can occur. .

In addition, a metastable high energy state will be present for a particular species, and the gradual downward transition of that high energy state will also play an important role in the reaction rate adjacent to post-discharge.

As shown in Figure 1B, spraying water vapor adjacent to this post-release also helps to convert the PFC to HF with good efficiency.

In the case of a surface wave tube, water vapor is injected from the fluid fitting downstream, and thus after the downstream end of the ceramic discharge tube 6, eventually several cm from the downstream limit of the discharge.

Thus, downstream of the plasma, the injection is made in the horizontal direction and at right angles to the gas exiting the plasma.

In order to show the improved PFC conversion yield and HF formation by the practice of the method according to the invention, the following PFCs: SF ₆ and CF ₄ were each tested. As is known, these in particular, CF ₄ is the most difficult to collapse PFC series.

First, an experimental test was conducted on O ₂ and to destroy PFC, the following mixture was used: PFC + N + O ₂ , where N is the carrier gas and O ₂ was the formation of stable corrosive fluorinated byproducts. As a permissible addition gas, corrosive fluorination by-products are subsequently treated by reactive adsorption in a solid bed (e.g., a commercial system provided by CS Clean Systems).

The PFC concentration may vary within a range from 1000 ppm to 1%, for example, at a total flow rate of about 50 L / min.

The amount of oxygen is typically 1.5 times the concentration of PFC to give the optimum rate of breakdown, the nitrogen is present in sufficient quantities, and the actual gaseous waste is systematically removed from the large stream of nitrogen for safety reasons prior to exiting the low vacuum pump. Dilution, so nitrogen will be most of the components in the actual gaseous waste.

These three gases are mixed using a gas distribution panel with a loop to ensure a uniform and stable mixture. The mixture reaches the plasma surfaguide source 4 via an insulated aluminum fitting, which is one of the members of the fluid connection of the discharge tube.

In an alternative chemical processes according to the invention, such a mixture may be modified by the addition of gaseous H ₂ O (with or O ₂₎ is in place of O _2.

The gas does not enter the same mixing process: as can be seen in connection with FIGS. 1A and 1B, PFC, nitrogen and oxygen, rather in some cases PFC + nitrogen, in other parts water vapor are independent at different locations. Is introduced.

In the two configurations described above, upstream and downstream of the plasma, the formation of by-products and HF produced by the destruction of the PFC, and also the conversion yield, can be observed and compared.

exam

To demonstrate improved conversion yield and HF formation by the practice of the method according to the invention, fracture tests were carried out using SF ₆ (1000 ppm and 5000 ppm) and CF ₄ (5000 ppm).

The experimental conditions are as follows:

Microwave generator: power of 4 to 6 kW at a frequency of 2.45 GHz.

Aluminum nitride tube: length l = 350 mm, inner diameter I _d = 8 mm, outer diameter I _D = 12 mm.

Total yield: Q _total = 50 l / min.

P = 4000 W for SF ₆ and 4500 W for CF ₄ .

To identify by-products generated by PFC destruction by microwave plasma, after treatment with plasma, FTIR analysis was performed using a Fourier transform infrared spectrometer (FTIR) under the following conditions:

Cell length l = 10 cm.

ZnSe window.

Sampling conditions: atmospheric pressure and room temperature.

Flow sampled for analysis = 3 l / min.

At all defined experimental conditions, test results in the gas injection state upstream of the plasma were presented, the first showing the destruction of SF ₆ and the next showing the destruction of CF ₄ .

For each molecule, the spectra of by-products generated by plasma destruction were obtained and the PFC conversion yields were measured:

With O ₂ and without H ₂ O,

-With H ₂ O and without O ₂ ,

-H ₂ O and O ₂ present.

This method makes it possible to clearly observe the role and effect of each of these molecules in the PFC destruction process.

SF ₆  In case of destruction

In the case of spraying O ₂ upstream of the plasma, the following conditions were used:

SF ₆ : concentration 1000 ppm,

Nitrogen flow rate: = 49.5 l / min,

SF ₆ flow rate: = 0.05 I / min,

Oxygen flow rate: = 0.075 l / min.

As shown in FIG. 3 (IR analysis results), by-products generated by the destruction of SF ₆ with O ₂ are as follows: HF, SO ₂ F ₂ , SOF ₄ .

Subsequently, water is added under the following conditions:

SF ₆ : Concentration 1000 ppm,

Nitrogen flow rate: = 49.9 L / min,

SF ₆ flow rate: = 0.05 I / min,

Oxygen flow rate: = 0.075 l / min,

Water flow rate: = 0.4 l / min.

IR analysis results are shown in FIG. 4.

Including H ₂ O with or without O ₂ produces the same by-products: HF, SO ₂ . However, the amount of HF was higher with the addition of H ₂ O, and corrosive compounds such as SO ₂ F ₂ , SOF ₄ disappeared and replaced by SO ₂ .

Post-treatment of these products does not cause problems with scrubbers or soda lime cartridges.

In addition, precautions can be taken in selecting the line material in order to avoid the formation of sulfuric acid, especially in the wet atmosphere when large amounts of excess water are introduced and in the upstream circuit.

Although F ₂ is not quantified, inferring from a similar case, SO ₂ F ₂ , SOF ₄ Can be expected to disappear substantially. Thus, there is no risk of OF ₂ occurring during post-treatment in the scrubber.

In conclusion, in the case of the H ₂ O addition test upstream of the plasma, significant advantages can be identified, namely:

-In a "wet scrubber" or soda lime, corrosive fluorinated by-products incompatible with neutralization post-treatment are effectively removed and essentially replaced by HF.

In addition, from the conversion yield point of view, the breakdown rate is significantly improved.

5 and 6 show the effects of O ₂ and H ₂ O on the destruction of SF ₆ as a function of the added gas flow rate (water vapor), respectively.

Figure 5 shows the SF ₆ destruction at 1000 ppm and 4 kW as a function of the added gas flow rate.

Curve 5-I shows the addition of O ₂ without water vapor, curve 5-II shows the addition of H ₂ O without O ₂ , and curve 5-III adds H ₂ O with O ₂ One case is shown, with the latter being added at a flow rate of 0.075 l / min.

These curves show that the breakdown rate (DRE,%) is higher for curve 5-II, where only H ₂ O is added without O ₂ . The breakdown rate increased from 70% in the current state (O ₂ ) to 88% in the case of using H ₂ O.

At 1000 ppm, only H ₂ O was found to improve the breakdown rate by 18%. In contrast, the introduction or no introduction of O ₂ has little effect on the rate of destruction.

Figure 6 shows the SF ₆ destruction at 5000 ppm and 4 kW as a function of the added gas flow rate.

Curve 6-I shows the case of adding only O ₂ without water, curve 6-II shows the case of adding H ₂ O without O ₂ , and curve 6-III adds H ₂ O with O _2. One case is shown, with the latter being added at a flow rate of 0.25 l / min.

At 5000 ppm, water was found to have less effect on the destruction of SF ₆ . That is, the destruction rate rose from 70% to 80%. In contrast, the effect of water vapor depends on the concentration of SF _{6 in} the mixture, which is different from the conversion chemical reaction used.

CF ₄  In case of destruction

In the case of CF ₄ , O ₂ is first injected upstream of the plasma, and the following experimental conditions were used:

CF ₄ : concentration 5000 ppm,

Power: 4000 W,

Total production: = 50 l / min,

Oxygen flow rate: = 0.375 l / min.

As shown in FIG. 7 (IR analysis results), the by-products produced by the destruction of CF ₄ with O ₂ (without H ₂ O) are: HF, COF ₂ , CO ₂ , FNO, FNO ₂ .

Subsequently, water is added under the following conditions:

CF ₄ : concentration 5000 ppm,

Total production: = 50 l / min,

H ₂ O flow rate: = 0.6 l / min,

Power: = 4000 W.

IR analysis results are shown in FIG. 8.

Including H ₂ O with or without O ₂ produces the same byproducts: HF, CO and NO. However, the amount of HF was higher with the addition of H ₂ O, and corrosive compounds such as COF ₂ , CO ₂ , FNO, FNO ₂ disappeared and were replaced by CO and NO.

9 shows the CF ₄ destruction rate at 5000 ppm and 4.5 kW as a function of the added gas flow rate.

Curve 9-I shows the addition of O ₂ without water, curve 9-II shows the addition of H ₂ O without O ₂ , and curve 9-III adds H ₂ O with O _2. One case is shown, with the latter being added at a flow rate of 0.2 l / min.

At 5000 ppm, the addition of H ₂ O into the CF ₄ + N ₂ mixture had less effect than with SF ₆ and the breakdown rate rose from 56% to 64%. However, in the case of CF ₄ , the effects of H ₂ O were the same at 1000 ppmv and 5000 ppmv.

Plasma  Water jet downstream

During the test, it was found that the rate of destruction was lower than in the previous case if oxygen was not added in advance upstream.

When the SF ₆ or CF ₄ decomposition wavefronts leave the plasma column, they have sufficient time to react substantially with each other to reform the initial PFC molecules before they come into contact with and react with water vapor to form stable corrosive fluorinated byproducts. Is explained by the facts. The conversion rate is not zero because the gas is still very hot at this level, and the temperature is about 700 to 1700 K (and therefore there is a downstream heat exchanger). However, this temperature is lower than the temperature at the plasma column (which is significantly higher than 2000K), and the populations of more excited states beyond the equilibrium, which also plays a large role in decomposition efficiency, are substantially reduced.

Regardless of the embodiment, the present invention allows the use of a solid bed of granules based on gas scrubber or soda lime as a means to irreversibly capture the byproducts of the plasma reaction prior to the release of the waste stream into the atmosphere. do.

A semiconductor manufacturing reactor (not shown in FIG. 10) operating under vacuum is connected to the pumps, and in FIG. 10 (described below) only a low vacuum pump 1 is shown which delivers atmospheric pressure at the outlet 2. .

Multiple pumps 1 connected to several reactors are connected in parallel to simultaneously process waste generated from the reactors performing the various steps of the process (deposition, etching, reactor cleaning, etc.).

Before these gases are introduced through the member 5 into the plasma system 6 (which may be a plasma system for waste destruction, in particular the system disclosed in US Pat. No. 5,965,786), a first particle filter ( 4) is provided.

At the outlet of the plasma system 6, a heat exchange means 9 is arranged to cool the treated gas, the lower part of which means 9 in liquid or means 9 condensed in the means 9. Or means for recovering the solid formed upstream thereof.

If necessary, after passing the valve 10 for isolating the plasma downstream of the (emission line), cold gases are passed through the line 11 to the additional trap 13 to selectively condense or absent the waste product. The solid removed in (15) is captured (optionally, depending on the method), and residual gaseous waste is flowed through line 12 into the so-called dry or wet capture means 14 of gaseous products known to those skilled in the art. .

According to the invention, elements other than the oxidizing element are injected upstream of the plasma 6 (A) 7 and / or downstream of the plasma 6 (B) while, as described above, at least one oxidation An element is optionally (but not required) injected into the plasma means 6.

If the gaseous compounds of the metal, eg WF ₆ , which may generate metal deposits on the walls of the chamber where the plasma is generated by passing through the plasma, do not contain waste in line 5, the plasma generating means 6 Hydrogen and / or reducing gas products can be injected upstream of the plasma, without the risk of metal depositing in the product, the product comprising both oxygen and hydrogen. Spraying exclusively hydrogenation and / or reduction reactants generated from the plasma can be maintained, reduced or eliminated.

Conversely, if the waste comprises one or more gaseous compounds of at least one metal (eg WF ₆ ), at least one anhydrous oxygenating element (oxygen, air, nitrogen) is exclusively into the treatment waste upstream of the plasma. While at least one hydrogenation and / or reduction addition product is preferably injected into the mixture of the first species produced downstream of the plasma (or at the foremost part of the plasma or into the post-emission zone). (In case of uncertainty associated with this injection, it is preferable to use this second solution).

In this case, at least one reducing additive, such as alcohols, glycols, hydrocarbons, hydrides, and / or hydride elements, such as H ₂ O, H ₂ , CH ₄ , NH ₃ , methanol and ethanol, may be injected downstream of the plasma. Can be.

At point B (8) downstream of the plasma, an oxidizing additive may optionally be added, if necessary, prior to cooling.

Claims (18)

Is a method of plasma treating gaseous waste at substantially atmospheric pressure, Spraying the waste to be treated into a plasma source, and Spraying water vapor upstream and / or downstream of the plasma. The method of claim 1, wherein the pressure of the waste is 0.8 bar to 1.3 bar. The method of claim 1 or 2, wherein water vapor is injected at a concentration between 100 ppm and 5%. The method of any one of claims 1 to 3, wherein the water vapor is injected at a temperature of 20 to 300 ° C. The plasma processing method of the gaseous waste of any one of Claims 1-4 whose waste to-be-processed is waste from a semiconductor processing process. The plasma treatment method according to any one of claims 1 to 5, wherein the waste to be treated is a mixture of perfluorinated gas and / or hydrofluorocarbon gas and nitrogen. The method of any one of claims 1 to 6, wherein the plasma source is a surface wave type. Is a device for substantially treating gaseous waste at atmospheric pressure, Plasma torch means (4, 6, 8, 10) and means (14, 16, 18, 24, 26) for injecting water vapor into the mixing zone (12, 21). 9. The apparatus of claim 8, wherein the means for injecting water vapor is located upstream of the plasma forming region. 9. The apparatus of claim 8, wherein the means for injecting water vapor is located downstream of the plasma forming region. The apparatus for treating gaseous waste according to any one of claims 7 to 10, wherein the plasma generating means comprises a surface wave source. The apparatus for treating gaseous waste according to any one of claims 7 to 11, wherein the means for injecting water vapor includes a vaporizer having temperature adjusting means (24, 28). 13. The gas according to any one of claims 7 to 12, further comprising means for irreversibly trapping the plasma reaction product, for example a solid bed or gas scrubber of granules based on soda lime. Plasma treatment unit for waste. The waste generated from the reactor is destroyed and the waste passes through at least one pump between these fluorine and other elements of the PFC or HFC type molecules. Transported to a plasma means capable of breaking at least some of the bonds in the molecules of to produce a first species which is then converted into a second gas, liquid or solid species, these second species being dry or wet stripping. Prior to interacting with the means, at least one hydrogenation and / or reduction reagent is injected downstream of the plasma but upstream of the stripping means to react with the resulting first species and form a second species, at least of these second species Some may be removed by wet stripping means, such as a water scrubber, and may be water upstream and / or forward and / or downstream of the plasma. The plasma processing method of the waste gas exchanger spraying step is to be selectively removed. 15. The method of claim 14, wherein the injection of the at least one hydrogenation and / or reduction reagent is at the forefront of the plasma or in the post-emission zone of the plasma. The process of claim 14 or 15, wherein the hydrogenation and / or reduction reagent is selected from H ₂ O, NH ₃ , CH ₄ and / or alcohols. 17. The method of any one of claims 14 to 16, wherein at least one oxygenated compound is injected upstream of the plasma. The method of claim 17, wherein the waste does not contain elements capable of generating metal deposits on the walls of the chamber where the plasma is generated by passing the plasma, and the oxygenated compound injected upstream may also include hydrogen atoms, A method for plasma treatment of gaseous wastes, characterized in that the injection of hydrogenation and / or reduction reactants can be maintained, reduced or even eliminated.

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