GB2308991A

GB2308991A - Purification of waste gas

Info

Publication number: GB2308991A
Application number: GB9626931A
Authority: GB
Inventors: Horst Reichardt; Lothar Ritter; Gunter Firkert; Konrad Gehmlich; Gerold Hofmann; Michael Hentrich; Wido Wiesenberg
Original assignee: Das Duennschicht Anlagen Systeme GmbH
Current assignee: Das Duennschicht Anlagen Systeme GmbH
Priority date: 1996-01-12
Filing date: 1996-12-24
Publication date: 1997-07-16
Also published as: GB9626931D0; DE19600873A1; FR2743617B3; FR2743617A1

Abstract

Waste gas, eg. from CVD or plasma processes, are purified by pyrolysis followed by scrubbing. As shown in the Figure, the waste gas is introduced into burner 30 via pump 34; also introduced is a combustible gas which generates flame 32. The combustion chamber is surrounded by chamber 29, which may contain ceramic wool, and is water-cooled. The fumes pass around a body made of two facing convex elements 6, 7 and are exposed to liquid issuing firstly from scrubber 17 and then from scrubber 18, the latter passing through packed bed 25. Used liquid collects in trough 13.

Description

METHOD AND APPARATUS FOR THE PURIFICATION OF TOXIC WASTE GASES BY COMBUSTION AND CHEMICAL CONVERSION BY THE AID OF A FLAME IN A COMBUSTION CHAMBER The invention relates to an apparatus for the purification of waste gases containing various, preferably fluorine-containing toxic agents that originate from systems for the etching by plasma processes, and containing preferably silicon-, phosphorus- and boron-containing toxic agents originating from systems for the coating by chemical vapor deposition. Processes of this type play an important part in the production of semiconductor circuits.

The waste gases contain toxic agents of varying cheminal composition. Important groups of these toxic agents are hydrides, for instance silanes. Frequently, fluorohydrocarbons and other fluorine compounds are occasioned.

The toxic agents or their reaction products are toxic, meaning a danger to man and environment and, because of their toxic action, contributing to ozone annihilation and the greenhouse effect in the atmosphere. Some of the toxic agents or their reaction products exercise strong corrosive action on members of the purification apparatus itself.

Quite a few methods and apparatuses are known for waste gas purification.

Very frequently, purification takes place by sorption of the toxic gases from the waste gas by the latter being guided for instance through oxidizing, aequeous solutions (DE 33 42 816 Al). Any occasioned water-soluble compounds can be precipitated in a second process stage, for instance by alkaline solutions. Volatile toxic agents or secondary products are removed from the waste gas in a third process stage, for instance by activated carbon filters.

Another group of purification apparatuses is based on processes of solids reaction with indirectly - electrically or inductively - heated materials.

Non-organic halides or hydrides as well as metal-organic compounds will decompose at heated metal catalysts (European patent 0 384 803 Al). For different chemical reactions to be utilized for the removal of the toxic agents or/and for toxic agents to be eliminated in process sequences, various reactive materials are disposed in an indirectly heated column (WO 89/11905, WO 91/08041). In this way, halogens and hydrides are chemically transformed and converted into solid compounds. The efficiency of such a proceeding is however strongly reduced by progressive sealing of the surfaces by precipitating solid compounds in the course of the process.

As a result, the efficiency of purification decreases. The purification process requires periodic renewal of the reactive substances.

Contamination of the reactive surfaces in the solids reactor (for instance by carbon or carbides) can be reduced by the addition of oxygen to the waste gas (DD 221 088 Al). The limited reaction surfaces of the reactive materials and the thus restricted throughput of toxic-agent-containing waste gases remain problematic.

A plurality of waste gas purification apparatuses are based on methods of thermal decomposition or oxidation of the toxic agents in a combustion chamber. If toxic agents themselves are not combustible or if they are only constituents of waste gases with a high portion of inert gas, they are led into a flame of combustible gas, for instance a natural gas/oxygen or hydrogen/oxygen mixture, for chemical conversion (U.S. patent 5 183 646).

Noxious secondary substances of the conversion are then removed from the waste gas, for instances by sorption or washing processes (US-A 2 889 002).

However, in the conversion of the toxic agents in a flame of combustible gas, the efficiency of purfication varies with different toxic agents. Frequently the efficiency of purification is not sufficient to comply with required standards. Reasonable consumption of combustible gas is accompanied with the purified waste gases still containing critically high portions of toxic agents. Any improvement of the efficiency of purification towards low toxic contents in the purified waste gas can be obtained to some extent by the quantity of combustible gas being increased in relation to the quantitiy of waste gas fed in, however, the increase in the comsumption of combustible gas will lead to critical deterioration of the economy of waste gas purification.

In most of the known waste gas purification apparatuses, several partial processes are carried out, such as the thermal decomposition or oxidation, thermally activated chemical conversion, cooling of the gas, sorption, hydrolysis und neutralisation (EP 0 346 893 B1). To this end, the waste gas is guided through an arrangement having a combustion chamber followed by at least another arrangement working for instance on the washing principle.

Apparatuses for the purification of waste gas have been proposed, in which the waste gas is led through a combustion chamber for combustion of the toxic agents followed by a washing chamber, both being combined constructionally to form a unit (EP 0 346 893 B1). Also, a multi-stage purification process was realized in a single reaction chamber, in which the burnt waste gas is guided through a finely dispersed liquid (sorbent or coolant) or is brought into contact with a film of liquid on the walls of the combustion chamber (DE 43 20 044).

Apparatuses presently used for the removal of toxic agents from waste gases, which comprise a combustion chamber, a vacuum pump and at least another arrangement, for instance a spray washer, have a lot of technical drawbacks. Major drawbacks will lead to restricted efficiency of purification and to high consumption of combustible gas. But there may also be critical drawbacks that result in malfunction of members of the purification apparatus.

For instance, the compression of the waste gases from the coating or etching systems by means of the vacuum pump may result in the condensation of toxic agents in the conduits between the vacuum pump and the purification apparatus and - under the action of moisture entering the conduits this may lead to solid reaction products.

If water is supplied to the combustion chamber or parts of the latter for reaction products - for example silicon dioxide as a reaction product of silane combustion - to be washed off the latters inner wall, this may result in a very harmful increase of corrosion acting of parts of the combustion chamber - in particular if, in addition, fluorine-containing waste gases are chemically converted in the flame - hydrofluoric acid is one of the most corrosive substances that may form. If water with the addition of lyes or carbonates is used as a sorbent, harmful encrustations by precipation of salts, for instance potassium fluoride, will form in the combustion chamber on functionally important members, such as the burner, the ignition device, the temperature sensor und the flame sensor.

During the conversion in particular of fluorine-containing and chlorinecontaining toxic agents in the flame of combustible gas, the fact that moisture forms in apparatuses with water-cooled combustion chambers is inherent in the process, but consequently, also the forming of corrosively acting acids is inherent in the process and evidently, their acting on functional members of the combustion is inevitable.

It is the object of the invention, in the elimination of toxic agents from non-combustible waste gases in a combustion chamber by a flame of combustible gas, to increase the efficiency of purification, i.e. the degree of conversion of the toxic agents. In particular, it is to be ensured that a high purification effect is attained when the waste gas contains various toxic constituents. The economy of waste gas purification is to be improved by reduction of the comsumption of combustible gas and by reduction of investments required in semiconductor producing works.

Prolongations of the continuous running time of the purfication apparatus are necessary, on the one hand by extension of the effective running time between cleaning jobs that may become necessary, and on the other hand by the increased service life of the members of the combustion chamber due to reduced corrosion by aggressive constituents of toxic agents and their reaction products.

According to the invention, the object is attained as follows: The apparatus makes use of a method in which, in a combustion chamber, a combustible gas mixture, preferably hydrogen/oxygen or methane/oxygen, is burnt by the aid of a burner, the toxic waste gas being fed into the flame. Even though containing combustible components, for instance hydrides, the waste gases themselves are not combustible, because as a rule they consist by 90 percent of non-combustible inert gases, for instance N2 or Ar. If the toxic agents are only to be activated for thermal decomposition in the flame, the components of the combustible gas mixture are supplied stoichiometrically.Is conversion of toxic agents intended to take place by chemical reactions in the flame, the hydrogen-containing constituent or the hydrogen is supplied in excess if this takes place by reduction, or, respectively, air or oxygen is supplied in excess if oxidation is to be obtained. Accurate proportioning and/or separate or additional supply of gas components will purposefully affect the efficiency of toxic agent conversion in the flame. An increase in the efficiency of toxic agent conversion in the flame is obtained by special burner designs and devices for the turbulent mixing of the gas streams and for the separate supply of the components of the combustible gas mixture.

The hot stream of gas at the end of the effective portion of the flame then consists of the burnt combustible gas mixture (proportionately mostly CO2 and water vapor), of heated inert gases (proportionately mostly N2 and Ar) and either of the products of thermal decomposition in O2 atmosphere (for example SiO2 and water vapor) or of production of chemical conversion (for instance hydrogen fluoride, silicon fluoride, carbon dioxide and water vapor in the case of combustion of silane and carbon tetrafluoride in an oxyhydrogen flame). Solid reaction products deposit on the inner wall of the combustion chamber and on other members of the combustion chamber (for example SiO2).

At the exit of the combustion chamber, the hot gases are fed to an arrangement for further treatment, for instance a spray washer. As a rule, several partial processes take place in this arrangement, such as cooling, hydrolising, neutralising and scouring.

The waste gas treated in the purification apparatus, i.e. substantially free from toxic agents, is fed to the waste air passage and discharged into the open.

According to the invention, in an apparatus for the elimination of toxic agents in waste gases which comprises at least one combustion chamber with a burner and appropriate supply means of waste gas and of combustible gas mixture, a spray washer, a vacuum pump and a regeneration arrangement for the washing agent, the combustion chamber pipe is dispsed in a jacket that is directly cooled and comprises closed cooling passage. In the simplest of cases, water is used as a washing agent. Even more suitable is the use of a sorbent out of water with alkaline additions, for instance NaOH, KOH or carbonates.

The gap between this jacket and the combustion chamber pipe is filled with a substance of a certain thermal conductivity. This helps ensure that neither sorbent nor cooling water get into the combustion chamber and will not contact the external surface of the jacket either. As opposed to ambient temperature or to the cooling water temperature, the temperature of the combustion chamber pipe can thus be set to a temperature definedly elevated, amounting to at least 1200C, preferably more than 1500C, throughout the pipe.

Between the combustion chamber and the spray washer, a cylindrical member is inserted, comprising a body, the projection of which in the direction of the axis of the combustion chamber pipe exceeds the clear width of the combustion chamber pipe and which is limited in the radial direction such that a gap remains between the inner wall of the cylindrical member and the said body, the surface of this gap preferably being in the range of the size of the surface of the opening of the combustion chamber pipe. The said body is fastened to the cylindrical member or to the combustion chamber pipe by means of retaining elements in such a way that the surface of the passage between the combustion chamber pipe and the body is likewise in the range of the size of the surface of the opening of the combustion chamber pipe.This design of the cylindrical member and of the body ensures that on the one hand the hot stream of waste gas can flow from the combustion chamber into the spray washer without any substantial impairment to the flow and that on the other hand no washing agent or sorbent gets into the combustion chamber.

The body in the cylindrical member comprises two parts, one of which being oriented in a direction towards the opening of the combustion chamber pipe and the other in the direction of the spray washer, both parts being mounted in a manner heat-insulated toward each other. Forming the said body of two parts mounted in a manner heat-insulated toward each othr will ensure that the body part on the side of the combustion chamber pipe assumes approximately the temperature of the gas stream or of the combustion chamber pipe and the body part on the side of the spray washer assumes the temperature of the coolant, the washing agent or the sorbent.

In this way, the gas stream will keep a high temperature as long as directly before entering the gap, filled with sprayed coolant, washing agent or sorbent, between the cylindrical member and the body, after which it is cooled down at the shortest possible distance, i.e. it is chilled de facto. In this way, secondary toxic agents such as nitric oxides, dioxins and farans are prevented from forming, as a result of which the contents of toxic agents, in particular of highly toxic constituents, in the waste gas is reduced drastically.

The lower part of the cylindrical member is designed for an annular trough to form for the washing liquid. Axially, the combustion chamber pipe reaches into the cylindrical member at least by the height of the inner boundary of the annular trough and is mounted to be heat insulated.

The coolant, washing agent or sorbent from the spray washer will collect in the annular trough without entering the combustion chamber pipe or wetting the latter from outside. It is discharged from this trough. The wall of the combustion chamber pipe is neither directly cooled nor exposed to the corrosive effect of the coolant, the washing agent of the sorbent.

The lower end of the combustion chamber pipe is placed by heat insulation on a member in which is disposed the burner. In the direction of the axis, the water-cooled jacket is limited to the range of longitudinal extension of the combustion chamber pipe.

Due to the fact that the combustion chamber pipe is heat insulated twoards the spray washer und towards the mostly water-cooled member in which the burner is disposed, and due to the defined thermal conduction between the combustion chamber pipe and the jacket, an elevated temperature, which is substantially regularly spread over the longitudinal extension of the combustion chamber pipe, will result under the action of the thermal radiation from the flame of combustible gas and the heat convection from the hot gas stream.

This has the following effects: The excessive temperature, uniform over great distances, of the combustion chamber pipe favorably affects the degree of combustion of the toxic agents and the conditions of reaction for the chemical conversion of toxic agents in the combustion chamber pipe (reactor). The elevated temperature of all the inner wall surfaces of the combustion chamber pipe prevents the condensation of water vapor and, consequently, the corrosion of the wall surfaces under the action of acids that form during combustion. The elevated temperature renders the precipitation of solid reaction products such as silicon oxide more difficult. Since virtually no lyes or carbonates from the sorbent can get into the combustion chamber, encrustations on functionally important members are prevented, consisting for instance of potassium fluoride when KOH is utilized for neutralisation.

For defined heat transmission to be obtained between the external surface of the combustion chamber pipe and the water-cooled jacket, the annular gap between these members is filled with a gas, preferably with air or nitrogen. This can be a stationary filling, geometric dimensions and constructional solutions being used for the setting of a required temperature of the combustion chamber pipe under working conditions. For instance, with a given capacity of the burner, the diameter of the combustion chamber pipe can be constructionally adapted to that of the cooling jacket. However, for the adjustment of the temperature of the combustion chamber pipe, it is also possible that a certain volume of gas is blown through the said gap in order to discharge excessive heat output.

For defined heat flow to be obtained between the external surface of the combustion chamber pipe and the water-cooled jacket with a view to the establishment of a required temperature, the annular gap between these member may just as well be filled with a solid of a certain thermal conductivity, for instance a packing of ceramic wool.

Two advantageous embodiments exist for the integration of the cylindrical member with the said body: It can be suitable to incorporate the cylindrical member constructionally into the spray washer. However, the cylindrical member with the said body can also be separate.

For heat insulating fastening to be ensured of the combustion chamber pipe to the cylindrical member, it is suitable to unite these members by the aid of a plug connection by loose fit The necessary heat insulation of the combustion chamber pipe towards the cylindrical member can be obtained by a flanged joint in which is inserted a ceramic spacer ring. Suitably, the required heat insulation can also be sufficiently obtained by thin-walled design of part of the cylindrical member from X steel and by a weld joint.

The degree of combustion of the toxic agents can also be influenced favorably by the way of supply of the toxic gas to the ring burner. It can be suitable to feed the natural gas or a hydrogen/oxygen mixture in a first supply line to the ring burner and the toxic waste gas in a second central supply line. In this case, the toxic gas is fed into the hot core of the flame. However, it can also be advantageous to mix the combustible gas, i.e. natural gas or hydrogen, with the toxic waste gas before or in the burner and to blow in exclusively the oxygen directly in the vicinity of the orifice of the ring burner. This way of proceeding leads to lower flame temperatures, which has a favorable effect on the harmful forming of nitric oxides in the flame.

In the simplest of cases water is utilized as a washing agent in the spray washer. However, the neutralisation of acids of the converted toxic agents or their precipitation as salts can be attained already in the spray washing process, when water with the addition of caustic lye of soda, potash lye, lime milk, sodium carbonates or potassium carbonates is used as a washing agent.

For the purpose of cleaning the combustion chamber pipe and functional parts in the combustion chamber, these parts can be removed after the purification apparatus has been put out of operation and they can be treated correspondingly outside the apparatus.

On the other hand, cleaning of precipitations of solid substances can also take place by mechanical means being disposed within the combustion chamber pipe, adapted to the inside diameter of the pipe, and by a flap being provided in the vicinity of the bottom of the subassembly where the burner is arranged. Removal of the solid combustion or reaction products such as oxides or carbon takes place by the mechanical means, for instance brushes or scrapers, being moved periodically in the non-working time of the waste gas purification apparatus. During the waste gas purification job, these means are suitably shifted into a portion underneath the burner for undisturbed operation of the combustion chamber.

The maintenance requirements of functional subassemblies strongly differ in time intervals and necessary operations. For reasons of accessibility and replaceability it is suitable to make the subassemblies of the waste gas puri fication apparatus, namely the combustion chamber and burner, the cylindrical member, the spray washer, the vacuum pump and the regeneration arrangement, modular and to integrate them together with the arrangements additionally required for media supply, the sensors and the electronic control to form a complete installation on a surface as limited as possible. This provides for advantages involving the space required within the semiconductor production works, which has an ecomonically favorable effect on the demand of investments.

Advantages regarding the method of operating the waste gas purification apparatus result from the fact that, with an extremely short distance in the range of several 100 mm between the flange on the outlet side of the vacuum pump and the combustion chamber, the volume of-the gas line remains small between the said elements. Consequently, the waste gas compressed approximately to atmospheric pressure by the vacuum pump virtually does not cool down on its way between the pump and the combustion chamber. The demand for energy necessary for the toxic gases to be heated to the temperature needed by the reaction in the combustion chamber is reduced considerably, which contributes to savings in the need of combustible gas mix and thus to a reduction of the cost of waste gas purification.

In the case of a temperature of the waste gas in the connecting line elevated by at least 80"C, preferably by more than 1500C, as opposed to room temperature, condensation is prevented of constituents of the toxic gas or of reaction products of the toxic agents which are produced under the action of moisture in the connecting line. Moisture can penetrate through the connecting line or it can originate from back diffusion of moisture in the combustion chamber.However, in the apparatus according to the invention, back diffusion of moisture from the combustion chamber cannot take place or, if so, only to some minor extent, there being no moisture in the combustion chamber during the operating phase of the combustion chamber, and the combustion chamber pipe being kept at an elevated temperature as compared with apparatuses having a directly cooled combustion chamber pipe. In the phases of cleaning of the combustion chamber, moisture cannot get into the combustion chamber (in the case of mechanical cleaning) or is eliminated by drying (in case precipitations are washed off and subsequent drying takes place by a gas being admitted).

For certain applications of the waste gas purification apparatus, it can be necessary not to integrate the vacuum pump for the waste gas or the regeneration arrangement for the washing liquid spatially into the waste gas purification apparatus, but to put them up as separate modules. For instance, the requirements of different semiconductor process systems can demand for the vacuum pumps, which may differ conditioned by process, to be directly placed into the process systems. In this case, connecting lines of a length of several meters are inevitable between the vacuum pump and the combustion chamber.So as to avoid the condensation of toxic agents or reaction products of the toxic agents in the pipelines and to ensure an elevated temperature of the toxic gas during its entry into the combustion chamber, the connecting lines are heat-insulated, whereby the compression energy of the pumps can be utilized, or the waste gas and the connecting lines are heated additionally.

Separate design and positioning of the module for the regeneration of the washing agent and sorbent is appropriate where a single regeneration ar rangement of higher capacity is used for several gas purification apparatuses.

For the operating method to be monitored and controlled in gas purification apparatuses according to the invention, sensors are inserted in the vicinity of the combustion chamber pipe, which measure the temperature of the flame of combustible gas, which control whether the flame burns and which control the temperature and pressure in the waste gas supply line.

Furthermore, it can be suitable to complete the apparatus by sensors for the volume flowrates of combustible gas, oxygen and waste gas. During operation of the apparatus, the measured values of the sensors installed are used for control and monitoring purposes. It is of special advantage if the measured values of the volume flowrates of the process gases from the coating and etching systems and the volume flow of the rinsing gas of the vacuum pump is used for the control of the volumes of combustible gas and oxygen for the burner.

Details of the invention will become apparent from a preferred embodiment of the apparatus, taken in conjunction with Fig. 1. Fig. 1 is a diagrammatic longitudinal section through an embodiment of the apparatus.

The apparatus according to the invention comprises a cylindrical combustion chamber (1) of corrosion-resisting material. It has a diameter of 15 cm and a height of 70 cm. This combustion chamber is mounted in a directly water-cooled jacket (2) comprising closed cooling passages (3).

By the aid of the flanges (4), a cylindrical member (5) is placed on the jacket (2). In the cylindrical member (5), provision is made for a body con sisting of two parts (6) and (7), both of which have convex surfaces and are joined to each other by retaining ribs (8) and (9) of special steel in such a way that the convex outer surfaces of the parts of the body are oriented in opposite directions relative to the axis of the combustion chamber. The part (7) has a diameter of 19 cm. The body consisting of the parts (6) and (7) is placed on the upper edge of the combustion chamber (1) by means of retaining ribs (10) and (11). Because of the length ofthese retaining ribs, the distance of the upper edge of the combustion chamber (1) from the part (6) is defined by 2 cm.In the vicinity of the flange (4), a ring (12) of 4 cm of height is formed on the cylindrical member (5), an annular trough for the coolant, the washing agent and the sorbent (13) thus being produced. This is where an outlet (14) for the washing agent is provided. The inside diameter of the cylindrical member (5) is 23 cm.

With the aid of the flanges (15), the cylindrical member (5) is joined to the spray washer (16). In the spray washer (16), two conical nozzles (17) and (18) comprising the inlet pipes (19) and (20) are disposed one after the other in the direction of the axis. The nozzles spray two washing agent cones (21) and (22). Washing rings (25) are disposed between retaining sieves (23) and (24) in the spray washer in the portion between the conical nozzles (17) and (18). The connector (26) for connection to the waste air system is situated in the upper portion of the spray washer.

The upper end of the combustion chamber pipe (1) lodges in the ring (12) by loose fit.

The lower end of the combustion chamber pipe (1) lodges in a loose fitting (27) in a member (28).

An annular gap of 4 cm of width between the combustion chamber pipe (1) and the water-cooled jacket (2) is filled with ceramic wool (29).

The ring burner (30) is disposed centrally in the member (28), the combustible gas mixture of hydrogen and oxygen being supplied to the burner via a supply line (31). The ring burner (30) has a diameter of 25 mm. The flame (32) of combustible gas forms above the ring burner (30).

With the gas purification apparatus in operation, the waste gas from the process systems of semiconductor-circuit production is supplied via the supply line (33) to the dry-running vacuum pump (34) and compressed to approximately atmospheric pressure. The waste gas comprising toxic agents of differing composition is then led through the inlet (35) into the burner (30). It is fed centrally into the flame (32) of combustible gas. The connecting line (36) between the vacuum pump (34) and the inlet (35) of the burner of the purification apparatus is 450 mm long. The compressed waste gas together with the purge gas of the vacuum pump has a temperature of 1600C when entering the burner. The waste gas supply into the ring burner (30) takes place after the valve (37) has been opened. Thermal and/or chemical conversion of the toxic gases of the waste gas stream takes place after they are fed into the flame (32) within the combustion chamber (38). The hot stream of gas flows in the direction of the arrow (39), first through the combustion chamber, then through the cylindrical member (5), where it is cooled down suddenly by the washing agent to the latter's tem- perature and where the sorption process is started. The cooled stream of waste gas flows in the direction ofthe arrows (40) and (41) through the washing rings (25) of the second washing path in the spray washer (16).

Once the washing of the gas stream in the spray washer (16) is finished, the purified waste gas is transferred in the direction of the yarrow (42) through the connector (26) into the waste air system.

Solid reaction products of toxic agent conversion in the combustion chamber collect on the ground of the member 28, where they can be discharged by means of the flap (43).

Claims

1. Apparatus for the removal of toxic agents from the waste gases of CVD and plasma etching processes, comprising at least one combustion chamber and a burner, with the supply of waste gas compressed by a vacuum pump and the supply of combustible gas and oxygen, and further comprising a spray washer and a regeneration arrangement for the washing agent, char acterized a) in that the combustion chamber pipe is disposed in a directly cooled jacket, preferably with water being used as a coolant in closed cooling passage, the gap between this jacket and the combustion chamber pipe being filled with a substance of a certain thermal conductivity, b) in that, between the combustion chamber and the spray washer, a cylindrical member is inserted, comprising a body, the projection of which in the direction of the axis of the combustion chamber pipe exceeds the clear width of the combustion chamber pipe and which is limited in the radial direction such that a gap remains between the inner wall of the cylindrical member and the said body, the surface of the gap perferably being in the range of the size of the surface of the opening of the combustion chamber pipe, c) in that the said body is fastened by retaining elements on the cylindrical member or on the combustion chamber pipe in such a way that the surface of the passage between the combustion chamber pipe and the body is likewise in the range of the size of the surface of the opening of the combustion chamber pipe, d) in that the body is formed by at least two parts, one of which is oriented in a direction towards the opening of the combustion chamber pipe and the other in the direction towards the spray washer, both parts of the body being mounted in a manner heat-insulated one relative to the other, e) in that the lower portion of the cylindrical member is configured for an annular trough for the washing agent to form, f) in that the combustion chamber pipe reaches into the cylindrical member axially at least by the height of the inner boundary of the annular trough and is mounted to be heat insulated, g) in that the combustion chamber pipe is placed by heat insulation on a member in which is disposed the burner, and h) in that in the direction of the axis, the water-cooled jacket is limited to the range of longitudinal extension of the combustion chamber pipe.

2. Apparatus according to claim 1, characterized in that a gas, preferably air or nitrogen, is used as a substance of a certain thermal conductivity.

3. Apparatus according to claim 1, characterized in that a solid, for instance a packing of ceramic wool, is used as a substance of a certain low thermal conductivity.

4. Apparatus according to claim 1, characterized in that the cylindrical member is integrated constructionally into the spray washer.

5. Apparatus according to claim 1, characterized in that the cylindrical member comprising the said body is embodied as a separate subassembly and inserted between the combustion chamber housing and the washer.

6. Apparatus according to claim 1, characterized in that the heat insulation between the combustion chamber pipe and the cylindrical member is attained by a loose fitting of a plug connection.

7. Apparatus according to claim 1 to 5, characterized in that the heat insulation between the combustion chamber pipe and the cylindrical member is obtained by spacer rings on the screwings.

8. Apparatus according to claim 1 to 5, characterized in that the heat insulation between the combustion chamber pipe and the cylindrical member is obtained by a thin-walled element and a weld.

9. Apparatus according to claim 1 to 8, characterized in that water is used as a washing agent.

10. Apparatus according to claim 1 to 8, characterized in that water with the addition of alkaline substances, for example NaOH, KOH or carbonates, is employed as a washing agent.

11. Apparatus according to claim 1 to 10, characterized in that the ring burner is provided with a waste gas supply and a combustible gas mixture supply.

12. Apparatus according to claim 1 to 10, characterized in that a supply is provided for the combustible gas together with the toxic gas and a separate supply for the oxygen.

13. Apparatus according to claim 1 to 12, characterized in that mechanical means such as brushes or scrapers are arranged within the combustion chamber pipe, adapted to the latter's inside diameter, and in that a flap is provided in the vicinity of the bottom of the subassembly in which the burner is fixed.

14. Apparatus according to claim 1 to 13, characterized in that the subassemblies of the purification apparatus, combustion chamber and burner, cylindrical member, spray washer, vacuum pump and regeneration arrangement, are modular and in that they are integrated with the media supply systems as well as the electronic control to form a compact installation.

15. Apparatus according to claim 14, characterized in that the subassemblies of the purification apparatus, combustion chamber and burner, cylindrical member, spray washer, are modular and in that they are integrated with the media supply systems as well as the electronic control to form a compact installation, and in that the vacuum pump and the regeneration arrangement are embodied as separate modules.

16. Apparatus according to claim 1 to 5, characterized in that in the vicinity of the combustion chamber pipe and on the media supplies, sensors are disposed, in particular for the temperature and pressure of the waste gas supplied, for the volume flowrates of combustible gas, oxygen and waste gas, for the control of the flame and for the pH of the washing agent.

17. Apparatus according to claim 1 to 6, characterized in that the measured values of the volume flowrates of the process gases of the coating and etching systems and the measured values of the volume flowrate of the rinsing gas of the vacuum pump are utilized for the control of the waste gas purification apparatus, in particular for the control of the volumes of combustible gas and oxygen for the burner.

18. Apparatus for the removal of toxic agents from the waste gases of CVD and plasma etching processes, substantially as hereinbefore described and with reference to the accompanying drawings.