JP5335423B2 - Method for plasma treatment of gas effluent - Google Patents

Description

  The present invention provides a gas effluent that is released during semiconductor manufacturing, particularly during thin film deposition of materials, or during plasma cleaning of deposition reactors, and during plasma etching of thin films to define device geometry. It relates to processing technology.

Method of cleaning etch and deposition reactors, when released into the atmosphere, perfluorinated gases that might significantly contribute to global warming by increasing the greenhouse effect (C 2 _{F 6,} and / or c- C ₄ F ₈ , and / or C ₃ F ₈ , and / or NF ₃ and / or CF ₄ and / or SF ₆ ) and hydrofluorocarbon (eg, CHF ₃ ) gas may be used. In general, they are not completely consumed during the process.

  One advantageous way to reduce the atmospheric emissions of these gases is to convert them to plasma in the presence of certain additive gases and to chemically active species (acid fluorides). They can then be easily and irreversibly removed by conventional methods such as reactive adsorption on solid alkaline media (dry scrubbers) or absorption by solutions in gas scrubbers (wet scrubbers).

  It is advantageous to place the plasma downstream of the means for maintaining a low vacuum and avoid interacting with the operation of the process equipment or pump. Maximum efficiency at conditions of total flow rate and pollutant concentration at low vacuum pump exhaust is obtained with high electron density plasma such as microwave plasma.

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

  The surface wave plasma solution is well suited to the treatment of effluents for the etching process, i.e., produces gas effluents that cannot cause solids to form in the device.

  The use of axial injection assisted by a microwave plasma torch burner with a waveguide has been proposed to treat gas effluents from the reactor deposition and cleaning processes, for example M.M. Moisan et al. ("Waveguide-based singular and multi-nozzle plasma torches: TIAGO concept", Plasma Sources Sci. Tech., 10, 2001, p. 387-394).

  The torch terminates freely in a chamber for trapping gases and collecting them in the downstream exhaust line. Solid particles are formed in the flame and plasma plume downstream of the torch nozzle and therefore do not interfere with their operation if they are trapped and carried to a distance to prevent indefinite accumulation in the chamber. A standard solution for this purpose is a gas scrubber introduced as close as possible to the exit of the torch chamber.

The principle of PFC conversion in microwave plasma is to dissociate the first molecule in inelastic collisions caused by high energy discharge electrons, creating smaller fragments, ie atoms and radicals, than the first molecule. These fragments react with each other, are de-excited, recombine and / or rearrange, yielding new compounds that are different from the original PFC. More precisely, the aim is to convert the majority of the incoming PFC example _{F 2,} HF, acidified fluoride such as _{COF 2, SO 2 F 2,} SOF 4. Although they cannot be denied to be immediately dangerous gases for life and the body, they are highly reactive and can be removed decisively and irreversibly by conventional methods of neutralization with solids or liquids.

  In general, the PFC conversion reaction requires the addition of an additive gas. This is because dissociation is effective if the PFC molecules diluted in nitrogen are isolated in the plasma, but once they exit the discharge zone, the fragments react with each other and simply reshape the first molecule It means that there is a tendency to.

  The choice of additive gas is important for optimizing the PFC decomposition process.

  First, this choice can affect the conversion efficiency itself.

  In fact, the fragments generated by the dissociation of the additive gas during the discharge are more or less easily and quickly the PFC dissociated fragments and the stable corrosive fluoride before the PFC spends time to re-form when the gas leaves the discharge zone. Will have the property of forming

  Further, the corrosive fluorination reaction product varies depending on the type of the additive gas. This fact is utilized to favor the formation of special reaction products rather than others, and is a post-treatment solution chosen to decisively and irreversibly remove the corrosive fluoride from the gas effluent stream. Depends on your strategy.

This post-processing solution may be forced for cost reasons or other reasons specific to a particular user. It is therefore important to be able to optimally adapt to the various situations that occur with customers. For example, if it is decided to operate with a gas scrubber, it is not a problem to use oxygen as the additive gas. This in effect essentially produces, for example, COF ₂ (with respect to fluorocarbons), or SO ₂ F ₂ and SOF ₄ (with respect to SF ₆ ), and in any case a substantial amount of F ₂ OF ₂ may be generated by reaction with an aqueous caustic soda solution. This is a very toxic gas (worker's statutory continuous exposure limit is 50 volume ppb) and generally its users will not tolerate the presence of trace amounts on the premises.

To date, oxygen O ₂ has been used as an additive gas and is injected in the form of dry air taken from the compressed air distribution network of the semiconductor plant.

This solution, together with a solution for post-treatment of corrosive fluorides by reactive adsorption on a solid adsorbent bed, generally results in products of dry conversion chemistry using added O ₂ , such as F ₂ , COF ₂ , SO ₂ F _2. This corresponds to the technical choice of using a unit designed to trap SOF ₄ suitably.

  The primary objective of the present invention is to find a novel conversion chemistry for waste effluents from industrial processes, especially PFCs in microwave atmospheric plasmas.

  This problem also occurs in the case of PFC effluents that promote the formation of HF as corrosive fluorinated by-products because they irreversibly trap these by-products before releasing the effluent stream into the atmosphere. As a means, an advantageous use of a soda-lime based granular solid bed or gas scrubber is possible.

  A further object of the present invention is to improve the conversion yield by carrying out this alternative chemistry.

SUMMARY OF THE INVENTION The present invention first relates to a method of plasma treating a gas effluent at substantially atmospheric pressure,
Injecting the effluent to be treated into a plasma source;
-Injecting water vapor upstream and / or downstream of the plasma and optionally into the plasma itself.

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

  The water vapor will be injected at a concentration of 100 ppm to 5% in a carrier gas, usually nitrogen.

  The temperature will be 20-300 ° C, preferably 50-200 ° C.

The effluent to be treated will be a effluent from a semiconductor processing process, such as a mixture of perfluorinated gas and / or hydrofluoro gas and nitrogen .

  The plasma source is preferably of the surface wave type, more specifically a microwave excited plasma source.

  The present invention also relates to a device for plasma processing a gas effluent at substantially atmospheric pressure, including plasma generating means and means for injecting water vapor into the mixing zone.

  The means for injecting water vapor is installed upstream of the plasma formation zone or downstream of the plasma formation zone.

  According to one embodiment, the means for injecting water vapor includes a vaporizer with temperature control means.

  The present invention provides for the implementation of PFC wet conversion chemistry that generates only HF as a fluorinated byproduct in atmospheric pressure plasma. Water vapor is added to the plasma except under its vapor pressure at room temperature.

  According to another aspect of the invention, at least one compound whose molecule contains at least one hydrogen atom is preferably at the plasma outlet or at the earliest in the plasma but close to the outlet of the plasma effluent. Do not require the use of a “dry” scrubbing system that dissolves in water (or any reducing liquid system) and removes hydrofluoric acid (substantially generating hydrofluoric acid). Despite this, users will prefer to use an additional “dry” system as a precaution).

According to another aspect of the invention, when a product such as WF ₆ is present in the reactor, this gas passing through the plasma with a partial reducing or hydrogenating component is Has been found to cause the deposition of W, thereby almost immediately breaking it.

This problem caused by the use of hydrogenation additives when the first species comprises a fluorinated metal derivative, such as WF ₆ , that can generate metal deposits, and when the plasma is generated in a dielectric tube. In order to solve this, at least one hydrogenation component is preferably injected downstream of the plasma, preferably just at its outlet, so that this hydrogenation component is as quickly as possible a plasma based on a mixture containing PFC. It is important that it reacts with the first species generated in it, thereby generating a second species (or this hydrogenated component and / or reducing component is already split by the PFC or HFC molecule. ”Or partially“ split ”, preferably in a zone called the post discharge zone. It may be injected itself into Zuma).

If a component such as WF ₆ is present in the reactor off gas at the plasma inlet, this helps to prevent this product from decomposing in the plasma. However, the first species generated from WF ₆ then reacts with the reducing species injected downstream at the plasma outlet, line tungsten metal, or other solid tungsten compound such as oxide or oxyfluoride deposits. Within this, metal is generally located at the plasma outlet, thereby causing no problems in the operation of the plasma system.

In particular as a source of gaseous hydrogenating agents and / or reducing agents, H ₂ O, H ₂ , CH ₄ , NH ₃ , alcohols such as methanol, ethanol, glycols, hydrocarbons, hydrides, or any hydride compounds Can be used.

In fact, the second species thus created (using hydrogenation additives) contains much more hydrofluoric acid HF than using anhydrous additives, especially those of the oxygen type. I know. In addition, if WF ₆ (or similar product) is randomly present in the effluent to be processed, generated from a reactor installed upstream of the pump, downstream injection of hydrogenated product (ie, plasma Downstream) produces deposits of W (or products derived from W) in lines located downstream of the plasma, usually lines made of stainless steel or plastic, and such deposits are clearly very thin It doesn't matter at all.

  However, if the hydride compound is injected exclusively downstream of the plasma and does not add anything to the gas effluent upstream, the resulting solution is not completely satisfactory. In fact, the decomposition efficiency obtained in this case is lower than that obtained by introducing the same amount of hydrogenation additive gas, for example water vapor, upstream of the plasma if all else is the same.

  The inventor believes that a significant portion of the PFC that is initially introduced into the plasma is probably reconstituted before those cracked fragments can react with the hydrogenated compounds introduced downstream. The reconstructed PFC can no longer dissociate again before leaving the zone where the plasma is present.

  In order to solve the above two problems at the same time, according to a preferred embodiment, the present invention provides for the upstream or at the latest of the plasma to contain metallic elements such as Al, W, etc. (if they are present in the plasma). A first gas species generated by chemical conversion in the plasma downstream of the plasma by injecting a reactive oxygen atom or other oxygen-free, preferably gaseous, oxygenated compound (The temperature of the first gas species generated from the plasma remains above 150 ° C.) so that these hydride compounds react with the first species.

Without wishing to be bound by any particular theory, the inventor believes that when an anhydrous, especially oxygenated additive, such as oxygen or air, is injected upstream of the plasma, the additive is dissociated and / or excited. And that fragment reacts very easily with the dissociated fragment of PFC and / or HFC, resulting in corrosive fluorides such as F ₂ , COF ₂ , SO ₂ F ₂ , SOF ₄ (first species). ing. These compounds are very stable at the high temperature of the gas in the microwave plasma, and once formed, there is little possibility that they will dissociate again. In particular, they are hardly reconverted to PFC. These anhydrous corrosive fluorides such as F ₂ , COF ₂ , SO ₂ F ₂ , SOF ₄ are much more reactive than PFC. When hydride compounds are injected, at the plasma outlet, the temperature is still high enough that they react more or less completely with the hydrogenation additive and are much more thermally stable than anhydrous corrosive fluorides. HF is substantially produced. On the other hand, PFCs that have not been converted by the plasma will hardly react with these hydrogenation additives at the plasma outlet. Thus, the conversion yield of PFC is substantially the same as that of a pollution control process using one or more non-hydrogenated compounds, especially oxygenates, injected upstream of the plasma as an additive.

Detailed Overview of Specific Embodiments Exemplary embodiments of the present invention are now presented in connection with FIGS. 1A and 1B.

Such a device is generally discharged at the outlet of an apparatus for the deposition of thin films or processing of semiconductor materials, for example at a substantially atmospheric pressure of eg 0.7 or 0.8, or 1.3 or 1.5 bar. Can be introduced behind the pump used to transport the gas effluent. These effluents _include perfluorinated compound, such as C 2 _{F 6,} and / or _c-C 4 _{F 8,} and / or NF ₃ and / or CF ₄ and / or SF _6.

  The plasma source used is Microwave Excited Plasma, eds, M .; Moisan and J.M. Pelletier, chap. 5, Elsevier, Amsterdam, 1992; Moisan and Z.M. It is a surface wave type as described by Zakrzewski.

  Reference numeral 2 indicates a plasma tube 4 including an AlN inner tube 6 and a quartz outer tube 8.

  The plasma will be generated by the high pressure initiator 10.

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

  Gaseous water is injected using the vaporization means 14. These means 14 include a metering pump 16 that supplies, for example, liquid water to the electrothermal vaporizer 18.

  Water vapor is injected at a flow rate that provides a water vapor concentration of 100 ppm to 5% into the gas effluent. Thus, the conditions do not necessarily have to remain below the water vapor aggregation threshold at room temperature (2.3%).

  Deionized water can be withdrawn from the reserve 26 in a controlled amount by the metering pump 16 to convert the controlled amount of water into a gaseous state.

  An exemplary embodiment of a furnace is shown in FIG. This furnace has a FIREWORD (600 W) type cartridge heater 40, a rock wool jacket 32, a coil 34, and a liquid water inlet channel 30.

  The water flows through the coil 22 (FIG. 1A) in the stainless steel body 24 that encloses the cartridge heater and is completely vaporized.

  This cartridge heater may be connected to the temperature controller 24. The latter uses thermocouple 28 to control the temperature of the water leaving the system and prepare the mixture so that it is approximately 200-300 ° C.

  The last furnace 18 contains water vapor 20 carried in, for example, nitrogen, which is often used as a carrier gas for the effluent at a temperature where re-agglomeration does not occur before the gas reaches the discharge limit when concentration is considered. inject.

The hot carrier gas also prevents the deposition of solids (eg silica or tungsten oxide) resulting from hydrolysis of thin film etch products such as SiF ₄ or WF _{6 in} the processing chamber.

  Such deposition may cause damage to the plasma inlet.

  The amount of hydrogen supplied by this method helps to ensure good conversion efficiency. Preferably, it is at least related to the stoichiometric ratio of the reaction (ie, sufficient elemental hydrogen for all introduced fluorine forms only HF). In fact, depending on the chemical reactivity of the system, more water will be required to obtain the maximum PFC conversion rate. It will also depend on the type of PFC involved.

  If the concentration of water vapor after injection into the gas effluent mixture is 2% or less, reagglomeration will not occur in all cases. This is because the condition remains below the water vapor aggregation threshold at room temperature (2.3%).

However, the amount of PFC released is about tens of sccm for the etch reactor in a nitrogen dilution flow of 20 to 100 slm, or about several hundred sccm during CVD reactor cleaning, depending on the technical characteristics of the low vacuum pump To do. For example, for 50 sccm of CF ₄ , at least 100 sccm of H ₂ O is supplied to form HF exclusively. In order to involve at least 200 sccm of H ₂ O, the reaction rate must be taken into account. For 500 sccm C ₂ F ₆ , at least 1500 sccm H ₂ O is required. Thus, this provides from several thousand ppmv or more (eg 2000 ppmv) to several% or more (eg 3% or 5%) of water vapor into the nitrogen or effluent mixture.

  It should be observed that due to the saturated vapor pressure under these conditions, it may not be possible to obtain atmospheric pressure and room temperature. Water that will re-agglomerate in the system in the form of macroscopic drops or liquid films will contribute little to the conversion reaction. Furthermore, the presence of this level of water will not be compatible with satisfactory discharge operation (especially because water will absorb microwaves).

  However, the present invention helps to avoid these drawbacks. The injection of water vapor at a temperature of 20-300 ° C., especially 50-200 ° C., helps to create satisfactory conditions to achieve an efficient conversion of PFC. Temperatures above 100 ° C will further prevent the hydrolysis of certain products that produce solid deposits as previously described.

The mixing zone is between the first mixture (or the first effluent such as N ₂ + PFC) with a flow rate of approximately 20 to 100 l / min and on average 50 l / min and, for example, approximately 1 l / min water vapor. Related to contact.

  Furthermore, gaseous water is carried by nitrogen to the mixing zone, which is located near the plasma and has a temperature of approximately 2500-7000K. This removes unwanted reactions at an early stage with potential by-products of the etching process, as well as any risk of reaggregation.

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

  The water vapor is mixed with the initial effluent mixture, preferably at a level as close as possible to the plasma, and in the case of actual process stream processing, avoid early interaction of certain products with the water vapor. .

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

  As a result, the water is injected upstream of the plasma and perpendicular to the arrival of the mixture to be treated (here PCF-nitrogen).

  Another procedure (FIG. 1B) is here to inject water vapor downstream of the plasma and as close to its limits as possible.

  In FIG. 1B, only the furnace 18 is shown, but it actually involves all the elements 16, 19, 24, 26, 28 described above in connection with the configuration in FIG. 1A.

  Of course, there are no charged particles (ions or electrons) at the exit of the actual discharge zone. However, this does not mean that all neutral species are ultimately in a stable shape, nor are they in their basic energy state. Atmospheric microwave plasma is not far from thermodynamic equilibrium, where the temperature of heavy particles (as opposed to electrons) is typically 2500-7000K on the central axis.

  In general, due to the high velocity of the gas (small characteristic diameter of the plasma due to radial contraction), the gas may be separated for a certain distance before it becomes very prone to re-form PFC molecules from their dissociated fractions. Will remain very hot.

  Furthermore, metastable high energy states may also exist for certain chemical species where continuous deexcitation plays a role in the kinetics of near post discharge.

  This almost post-discharge water vapor injection, as in FIG. 1B, therefore also helps to convert PFC to HF with good efficiency.

  In the case of surface waves, water vapor is injected from the downstream fluid coupling (thus behind the downstream end of the ceramic discharge tube 6 and consequently a few centimeters from the downstream limit of the discharge).

  Downstream of the plasma, the injection is therefore performed horizontally and perpendicular to the gas leaving the plasma.

The following PFCs, SF ₆ and CF ₄ , can each be tested to demonstrate HF formation and improved PFC conversion efficiency by carrying out the method according to the invention. In the known method, in particular these CF ₄ are the most difficult to destroy in the PFC family.

Experimental testing was first done with O ₂ . The following mixture, PFC + N + O _2, was used to destroy the PFC. Where N is a carrier gas and O ₂ is an additive gas that subsequently forms a stable corrosive fluorinated byproduct that is processed by active adsorption on a solid adsorbent bed (eg, a commercial system by CS Clean System). It is.

  For example, the concentration of PFC varies from 1000 ppm to 1% at a total flow rate of approximately 50 l / min.

  The amount of oxygen is generally 1.5 times higher than the concentration of PFC to achieve an optimum destruction rate, and there is a sufficient amount of nitrogen, and for safety reasons, a large amount of nitrogen before they leave the low vacuum pump It is always a major component in the actual gas effluent that is intentionally diluted in the stream.

  These three gases are mixed using a gas distribution panel that includes a loop that ensures a uniform and stable mixture. It reaches the plasma surfguide source 4 via an insulated alumina joint, which is one element of the fluid communication of the discharge tube.

In an alternative chemical processes according to the invention, the mixture is changed by adding in place of O ₂ (or together) of H 2 _O in the gas phase.

  Gas does not enter the same mixing process. PFC, nitrogen and oxygen as part, but rather PFC + nitrogen, and water vapor as another part, are independently introduced at other locations as previously seen in connection with FIGS. 1A and 1B.

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

Testing In order to demonstrate the formation of HF and the improved conversion yield by carrying out the method according to the invention, degradation tests were performed with SF ₆ (1000 ppm and 5000 pm) and CF ₄ (5000 ppm).

  The experimental conditions are as follows.

- The microwave generator: Frequency 2.45GHz in 4~6kW output - aluminum nitride tube: length l = 350 mm, an inner diameter I _d = 8 mm, an outer diameter I _D = 12 mm
_-Total flow rate: Q _total = 50 l / min
For -SF ₆ P = 4000W, for CF ₄ P = 4500W
In order to identify by-products created by the destruction of PFC by microwave plasma, Fourier transform infrared spectroscopy (FTIR) analysis is performed after treatment with plasma using an FTIR spectrometer ("Thermo Nicolet Avatar 360") under the following conditions: Made using.

-Cell length l = 10cm
-ZnSe window -Sampling conditions: atmospheric pressure and room temperature -Flow rate sampled for analysis = 3 l / min
All experimental conditions are defined and the results of injecting gas upstream of the plasma are provided. First, the decomposition of SF ₆ and then the decomposition of CF ₄ .

  For each molecule, a spectrum of by-products created by plasma decomposition was obtained and the PFC conversion yield was determined.

-O ₂ there, and _{H 2} O without -H ₂ O there, and _{O 2} without -H ₂ O there, and _{O 2} there this method clearly observe the effect and role of each of these molecules in the PFC decomposition step To help.

In the case of SF ₆ decomposition For the O ₂ injection upstream of the plasma, the following conditions were used.

-SF _6: concentration 1000ppm
-Nitrogen flow rate: = 49.5 l / min
-SF ₆ flow rate: = 0.05 l / min
-Oxygen flow rate: = 0.075 l / min
As shown in FIG. 3 (IR analysis results), the by-products produced by the decomposition of SF ₆ with O ₂ (without H ₂ O) are as follows: HF, SO ₂ F ₂ , SOF ₄ .

  Next, water was added under the following conditions.

-SF _6: concentration 1000ppm
-Nitrogen flow rate: = 49.9 l / min
-SF ₆ flow rate: = 0.05 l / min
-Oxygen flow rate: = 0.075 l / min
-Water flow rate: 0.4 l / min
The result of IR analysis is shown in FIG.

Incorporation of H ₂ O yields the same by-products (HF, SO ₂ ) with or without O ₂ . However, the amount of HF increases with the addition of H ₂ O, and corrosive compounds such as SO ₂ F ₂ and SOF ₄ disappear and are replaced with SO ₂ .

  The post-treatment of these products does not cause any problems with the scrubber or soda lime cartridge.

  It is also possible to take precautions to avoid the formation of sulfuric acid in the upstream circuit and in the humid atmosphere, especially when line materials are selected and a large excess of water is introduced.

Although F ₂ is not quantified, it is presumed that it has actually disappeared as SO ₂ F ₂ and SOF ₄ by analogy in the same case. Therefore, there is no risk of generating OF ₂ during post-processing with a scrubber.

As a result, significant advantages can be observed in practice for the H ₂ O addition test performed upstream of the plasma. That is,
-Corrosive fluorinated by-products that are not compatible with "wet scrubbers" or post-neutralization treatment with soda lime effectively disappear and are effectively replaced by HF.

  In addition, the decomposition rate is significantly improved from the standpoint of conversion yield.

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

FIG. 5 shows the degradation rate of 1000 ppm SF ₆ at 4 kW as a function of applied gas flow rate.

Curve 5-I shows only O ₂ without water, curve 5-II shows no O ₂ and only H ₂ O, and curve 5-III shows H ₂ O and O ₂ at a flow rate of 0.075 l / min. The case where it added is shown.

These curves show that the decomposition rate (DRE (%)) is large in the case of curve 5-II in which only H ₂ O is added without O ₂ . This rate increases from 70% in the presence of O ₂ to 88% in the presence of H ₂ O.

At 1000 ppm, H ₂ O alone is observed to improve the DRE by 18%. However, whether or not O ₂ is introduced has almost no effect on the decomposition rate.

FIG. 6 shows the decomposition rate (%) of 5000 ppm SF ₆ at 4 kW as a function of applied gas flow rate.

Curve 6-I shows only O ₂ without water, curve 6-II shows no O ₂ and only H ₂ O, and curve 6-III shows H ₂ O and O ₂ at a flow rate of 0.25 l / min. The case where it added is shown.

At 5000 ppm, it can be seen that water does not significantly affect the degradation of SF ₆ (the rate has only increased from 70% to 80%). However, the effect of oxygen (O ₂ ) is the same. Effect of water vapor depends on the SF ₆ concentration in the mixture, not seen in the case of oxygen conversion chemistry.

For the case of decomposition of CF ₄ CF _4, and O ₂ was first injected upstream of the plasma, the following experimental conditions were used.

-CF _4: concentration 5000ppm
-Output: 4000W
-Total flow rate: = 50 l / min
-Oxygen flow rate: = 0.375 l / min
As shown in FIG. 7 (IR analysis results), by-products produced by the decomposition of CF ₄ with O ₂ (without H ₂ O) are as follows: HF, COF ₂ , CO ₂ , FNO, FNO _2.

  Then water was added under the following conditions.

-CF _4: concentration 5000ppm
-Total flow rate: = 50 l / min
-H ₂ O flow rate: = 0.6 l / min
-Output: 4000W
The result of IR analysis is shown in FIG.

Of H ₂ O uptake, _{O 2} with or without _{O 2,} produces the same products (HF, CO and NO). However, the amount of HF increases with the addition of H ₂ O, and products such as COF ₂ , CO ₂ , FNO, FNO ₂ have disappeared and are replaced by CO and NO.

FIG. 9 shows the decomposition rate of 5000 ppm CF ₄ at 4.5 kW as a function of applied gas flow rate.

Curve 9-I shows only O ₂ without water, curve 9-II shows no O ₂ and only H ₂ O, and curve 9-III shows H ₂ O and O ₂ at a flow rate of 0.2 l / min. The case where it added is shown.

At 5000 ppm, adding H ₂ O to the CF ₄ + N ₂ mixture has less impact than with SF ₄ . The degradation rate increases from 56% to 64%. However, in the case of CF ₄ , the influence of H ₂ O is the same at 1000 ppm and 5000 ppm.

In the water injection test downstream of the plasma, it was clear that the destruction efficiency was lower than in the previous case, unless oxygen was added in excess upstream.

This is in fact the fact that SF ₆ or CF ₄ dissociated fragments can come into contact with water vapor as they leave the plasma column and react significantly with each other before reacting to form a stable corrosive fluorinated byproduct. Explained by the fact that there is time to reform the PFC molecules. The conversion rate is not zero. This is because the gas is still very hot at this level and the temperature is around 700-1700K (thus there is a heat exchanger downstream). However, this temperature is lower than the plasma column (much higher than 2000K) and the number of more highly excited states out of equilibrium that play a role in dissociation efficiency is substantially reduced.

  Regardless of its embodiment, as a means of irreversibly trapping by-products of the plasma reaction before releasing the effluent stream to the atmosphere, the present invention uses a soda lime granule based solid adsorbent bed, or gas scrubber. Can do.

  A semiconductor manufacturing reactor (not shown in FIG. 10) operating under vacuum is connected to a pump, but FIG. 10 (described here) shows a low vacuum pump 1 carrying effluent at atmospheric pressure at outlet 2. It only shows.

  A plurality of pumps 1 connected to the various reactors are connected in parallel to simultaneously process the effluents coming from the reactors that will perform different process steps (deposition, etching, reactor cleaning, etc.).

  Before introduction of these gases into the plasma system 6 via 5 (optional plasma system for effluent decomposition, in particular as described in US Pat. No. 5,965,786), the first particles A filter 4 is provided.

  At the outlet of the plasma system 6 there is installed a heat exchanger 9 for cooling the gas to be treated, and at the bottom of these means 9 any liquid condensed in these means 9 or formed upstream or in means 9. A means 16 for collecting any solids is installed.

  After passing through the valve 10 which serves to separate the plasma from downstream (its discharge line), if necessary, the cold gas passes through the line 11 and into an additional trap 13 (optional and method dependent). And optionally coagulate the waste product or trap any solids removed at 15, while the remaining gas effluent is routed via line 12 to dry or wet trap means 14 for the gas product. (Means are known to those skilled in the art).

  According to the present invention, components other than the oxidizing component are injected at the point A (7) upstream of the plasma 6 and / or B downstream of the plasma 6, but at least the oxidizing component is arbitrarily selected as described above. It is injected into the plasma means 6 (not necessarily required).

If the effluent in line 5 does not contain a gaseous gaseous compound of metal, such as WF ₆ , that tends to deposit on the walls of the chamber where the plasma is generated by passing through the plasma, it will contain both oxygen and hydrogen. Any hydrogenated gas product and / or reducing gas product, including product, can be injected upstream of the plasma without the risk of metal deposition in the plasma generating means 6. Injection of hydrogenating agent and / or reducing agent exclusively originating from the plasma will be maintained, reduced or eliminated.

However, if the effluent contains at least one gaseous compound of at least one metal (eg WF ₆ ), the effluent is processed at least one anhydrous oxygenate component (oxygen, air, nitrogen) exclusively upstream of the plasma. While at least one hydrogenation and / or reduction additive product is preferably injected downstream of the plasma (or at least in the plasma or in the post-discharge zone) of the first species created It is injected into the mixture (when this injection is uncertain, it is preferable to use this second solution).

In this case, at least one reducing additive such as, for example, H ₂ O, H ₂ , CH ₄ , NH ₃ , alcohols such as methanol, ethanol, glycols, hydrocarbons, hydrides and / or hydrogenation components is added downstream of the plasma. Can be injected.

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

FIG. 1A shows device options according to the present invention. FIG. 1B shows device options according to the present invention. FIG. 2 shows the structure of the furnace. FIG. 3 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 4 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 5 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 6 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 7 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 8 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 9 shows the measurement results during the performance of the method according to the invention under various conditions. FIG. 10 illustrates an exemplary embodiment that avoids any breakage of the dielectric tube.

Claims (8)

A method of plasma treating a gas effluent from a semiconductor processing process at substantially atmospheric pressure, the gas effluent being a mixture of SiF ₄ or WF ₆ and nitrogen,
Injecting the effluent to be treated into a plasma source;
A method comprising injecting water vapor at a temperature of 100-300 ° C. from both upstream and downstream of the plasma to prevent hydrolysis of certain products to produce solid deposits.   The process according to claim 1, wherein the pressure of the effluent is from 0.8 to 1.3 bar. The method according to claim 1 or 2 , wherein water vapor is injected at a concentration of 100 ppm to 5%. Plasma source is a surface-wave type, the method according to one of claims 1 to 3. A device for plasma processing a gas effluent from a semiconductor processing step at substantially atmospheric pressure, the gas effluent being a mixture of SiF ₄ or WF ₆ and nitrogen, comprising plasma torch means (4, 6, 8, 10) and means (14, 16, 18, 24, 26) for injecting water vapor into the mixing zone (12, 21) at a temperature of 100-300 ° C,
A device in which the means for injecting the water vapor is installed both upstream of the plasma formation zone and downstream of the plasma formation zone. The device of claim 5 , wherein the plasma generating means comprises a surface wave source. 7. Device according to claim 5 or 6 , wherein the means for injecting water vapor comprises a vaporizer with temperature control means (24, 28). The device according to any one of claims 5 to 7 , further comprising means for irreversibly trapping the plasma reaction product.

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