GB2554406A

GB2554406A - Plasma abatement

Info

Publication number: GB2554406A
Application number: GB1616286.9A
Authority: GB
Inventors: Magni Simone; Soo Choi Yun; Kyoo Ko Chan; James Attwood Mark
Original assignee: Edwards Korea Ltd
Current assignee: Edwards Korea Ltd
Priority date: 2016-09-26
Filing date: 2016-09-26
Publication date: 2018-04-04
Also published as: GB201616286D0; CN207868157U; KR20180000936U; TWM561683U

Abstract

A plasma torch abatement apparatus 10 for treating an effluent stream 22 with a plasma stream 18 comprises a reaction chamber 26 defined by a reaction chamber wall. The reaction chamber wall is a composite structure comprising a passivation layer (26B, Fig. 4) of passivation material facing the effluent stream 22 and the plasma stream 18 and a substrate layer formed from a substrate material surrounding the passivation layer (26B, Fig. 4), the passivation material being less chemically reactive to the effluent stream 22 and the plasma stream 18 than the substrate material. The substrate layer may be a high alumina cement and may be more resistant to thermal fracture than the passivation layer (26B, Fig. 4). The passivation layer (26B, Fig. 4) may be thinner than the substrate layer and may be painted, chemical vapour deposited, or sprayed onto the substrate layer, or may be a sleeve or tiles fixed to the substrate layer. A method of manufacturing a reaction chamber 26 is also claimed. The chamber may be made by moulding a ceramic mix.

Description

(54) Title of the Invention: Plasma abatement

Abstract Title: Treating waste gas with a plasma stream in a reaction chamber with walls comprising a passivation layer on a substrate (57) A plasma torch abatement apparatus 10 for treating an effluent stream 22 with a plasma stream 18 comprises a reaction chamber 26 defined by a reaction chamber wall. The reaction chamber wall is a composite structure comprising a passivation layer (26B, Fig. 4) of passivation material facing the effluent stream 22 and the plasma stream 18 and a substrate layer formed from a substrate material surrounding the passivation layer (26B, Fig. 4), the passivation material being less chemically reactive to the effluent stream 22 and the plasma stream 18 than the substrate material. The substrate layer may be a high alumina cement and may be more resistant to thermal fracture than the passivation layer (26B, Fig. 4). The passivation layer (26B, Fig. 4) may be thinner than the substrate layer and may be painted, chemical vapour deposited, or sprayed onto the substrate layer, or may be a sleeve or tiles fixed to the substrate layer. A method of manufacturing a reaction chamber 26 is also claimed. The chamber may be made by moulding a ceramic mix.

This print incorporates corrections made under Section 117(1) of the Patents Act 1977.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

12 17

12 17

FIG. 3

12 17

- 1 PLASMA ABATEMENT

FIELD OF THE INVENTION

The present invention relates to plasma abatement.

BACKGROUND

Thermal plasma torches are known and are typically used for treating an effluent gas stream from a manufacturing process tool used in, for example, the semiconductor or flat panel display manufacturing industry. During such manufacturing, residual fluorinated or perfluorinated compounds (PFCs) and other compounds exist in the effluent gas stream pumped from the process tool. These compounds are difficult to remove from the effluent gas stream and their release into the environment is undesirable because they are known to have relatively high greenhouse activity or toxicity.

One approach to remove the PFCs and other compounds from the effluent gas stream is to use a radiant burner as described, for example, in EP1773474. However, when fuel gases normally used for abatement by combustion are undesirable or not readily available, it is also known to use a plasma torch abatement device. The plasma generated by the plasma abatement device is used to destroy or abate unwanted compounds within the effluent gas stream.

Existing plasma abatement devices each have their own shortcomings. Accordingly, it is desired to provide an improved plasma abatement device.

SUMMARY

According to a first aspect, there is provided a plasma torch abatement apparatus for treatment of an effluent stream from a processing tool with a plasma stream, comprising: a reaction chamber defined by a reaction chamber wall for receiving the effluent stream and the plasma stream, the reaction chamber wall comprising a composite structure having a passivation layer facing the effluent stream and the plasma stream, the passivation layer being formed from a passivation

-2material, the composite structure having a substrate layer formed from a substrate material surrounding the passivation layer, the passivation material being less chemically reactive to the effluent stream and the plasma stream than the substrate material.

The first aspect recognises that although reaction chambers have advantages (for example, simpler installation, enhanced safety due to no need of fuel gas), plasma abatement devices face a set of different challenges from burners and currently have own their shortcomings. In particular, existing reaction chambers might suffer from poor life due to the intense chemical environment within the reaction chamber. The high temperatures generated by a thermal plasma torch can induce acute chemical reactions useful to break PFC chemical bonds. However, these high temperatures can also quickly deteriorate the parts downstream such as the reaction chamber. Also thermal energy might be lost ineffectively to the coolant with detriment to the Destruction and Removal Efficiency (DRE). Accordingly, a reaction chamber for a plasma torch abatement apparatus may be provided. The plasma torch abatement apparatus may be for treatment of an effluent stream from a processing tool. The treatment of the effluent stream may be with a plasma stream. The reaction chamber may receive the effluent stream and the plasma stream. The reaction chamber may comprise or be defined by a reaction chamber wall. The reaction chamber wall may have a composite structure. The composite structure may have a passivation layer and a substrate layer. The passivation layer may face or be adjacent or be in contact with the effluent stream and the plasma stream. The passivation layer may be formed from or comprise a passivation material. The substrate layer may be formed from or comprise a substrate material. The substrate layer may surround or be provided adjacent the passivation layer, away from the effluent stream and the plasma stream. The passivation material may be less chemically reactive to the effluent stream and the plasma stream than the substrate material. In this way, a composite or multi-layer reaction chamber is provided which has advantageous properties provided by both the substrate layer and the passivation layer, with the passivation layer being more resistant to the

-3effluent stream and the plasma stream and with the bulk material still being capable of coping with thermo-mechanical stress and transfer some heat to the coolant. These features can improve the life of the reaction chamber, which improves the life of the reaction chamber.

In one embodiment, the passivation material is more chemically resistant to the effluent stream and plasma stream than the substrate material.

In one embodiment, the passivation material is more chemically inert to the effluent stream and plasma stream than the substrate material.

In one embodiment, the passivation material is chemically less reactive to halogen radicals in the effluent stream and plasma stream than the substrate material.

In one embodiment, the substrate layer is more resistant to thermal fracture than the passivation layer. Providing a substrate layer that is more resistant to thermal fracture improves the bulk properties of the reaction chamber during rapid thermal cycling.

In one embodiment, the passivation layer is thinner than the substrate layer.

In one embodiment, the passivation material has a higher purity than the substrate material.

In one embodiment, the passivation material comprises at least one of: Alumina, Alumina Mullite, Zirconia, Yttria-Stabilized Zirconia, Zirconia Toughened Alumina, Fused Quartz, Yttria, Hafnia, Aluminosilicate and Lanthanum Hexaboride.

In one embodiment, the passivation layer is at least one of painted, physical deposited, chemical vapour deposited and sprayed onto the substrate layer.

-4ln one embodiment, the passivation layer comprises at least one of a sleeve and tiles fixed onto the substrate layer.

In one embodiment, the substrate material comprises one of a ceramic and a solid.

In one embodiment, the substrate material comprises a cement.

In one embodiment, the substrate material comprises a high alumina castable cement.

In one embodiment, the substrate material comprises AI2O3.

In one embodiment, the substrate material comprises AI2O3 having a purity of at least 90%.

According to a second aspect, there is provided a method of manufacturing a reaction chamber of a plasma torch abatement apparatus for treatment of an effluent stream from a processing tool with a plasma stream, comprising: forming a reaction chamber wall from a composite structure having a passivation layer formed from a passivation material and a substrate layer formed from a substrate material, the passivation layer facing the effluent stream and plasma stream and the passivation material being less chemically reactive to the effluent stream and plasma stream than the substrate material.

-5ln one embodiment, the passivation material is chemically less reactive to halogen radicals in the effluent stream and plasma stream than the substrate material.

In one embodiment, the substrate layer is more resistant to thermal fracture than the passivation layer.

In one embodiment, the passivation layer is thinner than the substrate layer.

In one embodiment, the passivation material comprises at least one of: Alumina, Alumina Mullite, Zirconia, Yttria-Stabilized Zirconia, Zirconia Toughened Alumina, Fused Quartz, Yttria, Hafnia and Aluminosilicate and Lanthanum Hexaboride.

In one embodiment, the passivation layer comprises at least one of a sleeve and tiles fixed onto the substrate layer.

In one embodiment, the substrate material comprises a cement.

In one embodiment, the substrate material comprises AI2O3.

-6ln one embodiment, the substrate material comprises AI2O3 having a purity of at least 90%.

In one embodiment, the substrate layer comprises a ceramic mix and the method comprises performing at least one annealing step on the ceramic mix.

In one embodiment, the substrate layer comprises a ceramic mix and the method comprises performing a plurality of annealing steps on the ceramic mix.

In one embodiment, the annealing steps elevate a temperature of the ceramic mix to an upper temperature.

In one embodiment, the annealing steps elevate the temperature of the ceramic mix from ambient to the upper temperature.

In one embodiment, the annealing steps elevate the temperature of the ceramic mix from ambient to the upper temperature one of continuously and discontinuously.

In one embodiment, each annealing step elevates the temperature of the ceramic mix to an elevated temperature for a first period and maintains the elevated temperature for a second period.

In one embodiment, the second period is longer than the first period.

In one embodiment, the method comprises controlling cooling of the ceramic mix following the plurality of annealing steps.

In one embodiment, the controlling cooling of the ceramic mix comprises reversing the annealing steps.

-7ln one embodiment, the controlling cooling cools the ceramic mix more slowly than the plurality of annealing steps heat the ceramic mix.

In one embodiment, a time taken to cool the ceramic mix is longer than a time taken to heat the ceramic mix.

In one embodiment, the method comprises mixing a ceramic with a fluid to form the ceramic mix.

In one embodiment, the fluid comprises water.

In one embodiment, the method comprises moulding the ceramic mix in a mould to form the reaction chamber.

In one embodiment, the method comprises agitating the ceramic mix within the mould to homogenise the ceramic mix.

In one embodiment, the method comprises agitating the ceramic mix within the mould to displace bubbles within the ceramic mix.

In one embodiment, the agitating comprises one of vibrating and rotating.

In one embodiment, the method comprises setting the ceramic mix within the mould.

In one embodiment, the method comprises removing the ceramic mix from the mould prior to performing the plurality of annealing steps.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

-8Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figures 1 and 2 illustrate components of a plasma torch abatement apparatus in cross-section according to one embodiment;

Figure 3 illustrates components of a plasma torch abatement apparatus of Figures 1 and 2 in perspective with the anode and cathode omitted to improve clarity; and

Figure 4 illustrates a cross-section through a reaction chamber according to one embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide a multi-material reaction chamber. The reaction chamber is typically a tubular structure. An inner volume of the tubular structure defines a void within which plasma abatement occurs. A substrate is provided which forms the bulk of the reaction chamber wall. A layer of passivation material is provided on the inner surface of the reaction chamber, on top of the substrate material. The passivation material provides greater chemical resistance to reactants within the reaction chamber. Providing a comparatively thinner passivation layer compared to the substrate layer provides both a more cost effective reaction chamber and a reaction chamber with improved thermal properties compared to one formed solely from the passivation material, which tends to be more susceptible to damage during thermal cycling. A variety of different techniques may be employed to create the multi-material structure, such as physical or chemical deposition techniques, thermal baking, curing or annealing steps of both the passivation and the substrate material, providing a

-9separate passivation layer and fitting that together with the substrate layer. This arrangement helps to improve the life of the reaction chamber.

Plasma Torch Abatement Apparatus

Figures 1 and 2 illustrate components of a plasma torch abatement apparatus, generally 10, in cross-section according to one embodiment. Figure 3 illustrates components of the plasma torch abatement 10 in perspective. The plasma torch abatement apparatus 10 comprises a cathode 12 upstream of an opening of a generally tubular anode 14. A space is provided between the cathode 12 and the anode 14 through which a plasma source gas 16 (a neutral, inert gas such as, but not limited to argon or nitrogen) can flow. The cathode 12 and the anode 14 is electrically connected to a power supply (not shown) which is configured to apply a direct current between the cathode 12 and the anode 14 or an alternating current to either or both of the cathode 12 and the anode 14. The magnitude and frequency of the current required is generally determined and selected by reference to other process parameters, such as effluent stream or plasma source gas species and flow rate, the cathode-anode spacing, gas temperature, etc.

The voltage magnitude of the plasma discharge is directly influenced by these parameters. In any event, an appropriate, initial high-voltage regime is one that causes the plasma source gas 16 to ionise and thereby form a plasma (in a process known as breakdown).

The cathode 12 is typically manufactured from a high-conductivity metal, such as copper. A downstream-facing end of the cathode 12 may provide a preferential electrical discharge site which is accomplished by selecting a different material for this portion than the main body of the cathode 12, i.e. the main body of the cathode 12 is typically formed of a conducting material with a higher thermal conductivity than that of the thermionic material of the downstream-facing portion. For example, it would be typical to use a copper cathode body and a hafnium or thoriated tungsten downstream-facing portion. The anode 14 can then be formed of a similar material to the main body of the cathode 12; for example, copper.

The plasma stream 18 is thus nucleated in the small region immediately below

- 10the cathode 12, guided by a frusto-conical portion of the anode 14 and exits as a jet from the anode 14.

In order to generate the plasma, the plasma source gas 16 (typically a moderately inert ionisable gas such as nitrogen or argon) is conveyed to the region between the cathode 12 and the anode 14. To initiate or start the plasma, a breakdown must first be generated between the cathode 12 and the anode 14. This is typically achieved by a high frequency, high voltage signal which may be provided by a generator associated with the power supply (not shown). The difference in thermal conductivity between the main body of the cathode 12 and the downstream-facing portion means that the cathode temperature will be higher and the electrons are preferably emitted from the downstream-facing portion. Therefore, when the signal is provided between the cathode 12 and the anode 14, an arc discharge is induced in the plasma source gas 16. The arc forms a current path between the anode 14 and the cathode 12, the plasma is then maintained by a controlled direct current between the anode 14 and the cathode

12. The plasma source gas 16 produces a high momentum plasma stream 18 of ionised plasma source gas 16.

Venturi Cone

Downstream of the anode 14 is a Venturi cone 20. The Venturi cone 20 comprises an inwardly-tapering, frusto-conical portion leading to a substantially parallel-sided throat portion. An annular space is provided between the anode 14 and the Venturi cone 20 through which an effluent gas stream 22 to be processed and a secondary gas stream 24 is provided. The secondary gas stream 24 may be compressed dry air or other gases and is typically used as a reagent to assist in the downstream reaction. The effect of the geometry of the Venturi cone 20 is to accelerate and compress the incoming gases to create a region of relatively high speed, relatively compressed gas in a region downstream of the anode 14 to assist with drawing in the effluent gas stream 22 and the secondary gas 24 and facilitate mixing with the plasma stream 18. The high speed of gas exiting from

- 11 the Venturi cone 20 can promote turbulence to enhance the mixing of the plasma stream 18, effluent gas stream 22 and secondary gas stream 24.

Reaction Chamber

Downstream of the Venturi cone 20 is provided a reaction chamber 26. The reaction chamber receives the plasma stream 18 mixed with the effluent gas stream 22 and secondary gas stream 24. The reaction chamber 26 is a cylindrical tube coaxially aligned with the cathode 12, anode 14 and the Venturi cone 20.

The reaction chamber 26 has an inner surface 26A which defines a cylindrical space within which the plasma stream 18, effluent gas stream 22 and secondary gas stream 24 are received. As will be appreciated, an intense heat is generated by the plasma stream 18 and this heat, together with reagents within the secondary gas stream 24, help to break down compounds within the effluent gas stream 22. An axial length of the reaction chamber 26 helps to increase the residence time of the effluent gas stream 22 within the reaction chamber 26 and improve its Destruction and Removal Efficiency (DRE). Most of the energy is confined inside the internal volume of the reaction chamber 26.

A water jacket 28 concentrically surrounds the reaction chamber 26. An air gap 30 separates an inner wall 28A of the water jacket 28 from the reaction chamber

26. An outer wall 28B concentrically surrounds the inner wall 28A and defines a tubular void 28C which receives a coolant, such as water. The reaction chamber 26 is indirectly cooled by the coolant through radiative heat transfer across the air gap 30 and directly by thermal contact at either end of the reaction chamber 26. Most of the energy generated by the plasma stream 18 is confined inside the internal volume of the reaction chamber.

Typically, the reaction chamber 26 is formed from a cement such as a High Alumina Castable (HAC) cement. Such cements need to be able to withstand the high temperatures generated by the plasma stream 18, withstand the thermal

- 12shock caused by switching the plasma stream 18 on and off, and deal with the effects of the different gas streams.

Reaction Tube Casting

Embodiments provide a long-life reaction chamber 26 which is less prone to failure. Table 1 shows the main steps to manufacture the reaction chamber 26.

Step	Process	Description
S1	Preparation Cement	HACT180S (93% AI2O3)
Preparation water	Water 320 gram
Preparation outer mould	Stainless steel 316L
Preparation inner mould	Stainless steel
Mould support	Steel
Ceramic powder into the bowl	HACT-180S 2100 gram
Mix ceramic powder	1 minute, manual
Water into the bowl	Water 320 gram
Mix ceramic powder and water	5 minutes, manual
S2	Mixed ceramic power with water into mould	Remove bubbles with shaker
S3	Protect top of reaction tube with mould	Steel
Fix inner mould with bolt
S4	Dry the complete tube+ cast assembly	24 hours
S5	Remove the inner mould	Press
S6	Baking the reaction tube in oven	see table 2/3
S7	Cooling down reaction tube	1 day min.

Table 1

- 13At step S1, a ceramic powder cement is mixed in a bowl with a mixing fluid such as water for a period of time by mechanical mixing.

At step S2, the mixed cement and fluid is poured in to a void created by an inner and outer mould for forming the reaction chamber 26. The mould is agitated in order to reduce the presence of any bubbles or voids within the cement and fluid mix. The mould may also be agitated in order to increase the homogeneity of the cement and fluid mix.

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At step S3, the mould is closed and the inner mould is fixed with a bolt.

At step S4, the cement and fluid mix is allowed to set within the mould.

At step S5, a press is used to remove the inner mould and the outer mould is removed.

At step S6, the reaction tube 26 removed from the mould and is baked in an oven which follows a temperature profile to perform a sequence of one or more annealing steps. The temperature profile increases the temperature of the reaction chamber 26 in ramped steps and maintains that temperature for a period in order to perform iterative annealing. The most elevated annealing temperature is set to exceed the operating temperature of the reaction chamber 26. One embodiment follows the temperature profile shown in Table 2.

Step	Temp range	duration
1	ambient -180 °C	ramp 60 minutes
2	180-360 °C	ramp 60 minutes
3	360-540 °C	ramp 60 minutes
4	540-720 °C	ramp 60 minutes
5	720-900 °C	ramp 60 minutes
6	900 °C	steady plateau 60 mins
Total time:	6 hours

Table 2

Another embodiment follows the temperature profile shown in Table 3.

Step	Temp range	duration
1	Room Temp - 500°C	60 minutes (increase gradually)
2	500°C	10 minutes of maintenance
3	500 - 900 °C	60 minutes (increase gradually)
4	900 °C	180 minutes of maintenance

Table 3 io At step S7, the reaction tube undergoes controlled cooling. Typically, this involves allowing the reaction chamber to cool to ambient inside the oven. In one embodiment, the reaction chamber is cooled by following the temperature profile of the annealing steps but in reverse order.

- 15Passivation Layer

In one embodiment, the reaction chamber 26 has a passivation layer, as shown in Figure 4. The passivation layer improves the chemical inertness of the inner surface 26A of the reaction chamber 26 when in contact with halogen radicals generated during the plasma phase of the abatement. The passivation layer is formed by one or more materials which are halogen resistant (for example, fluorine) at high temperatures. Suitable materials include: AL=ALumina, AM=Alumina Mullite (corundum), ZR= ZiRconia, YSZ=Yttria-Stabilized Zirconia (fully stabilized), ZTA = Zirconia Toughened Alumina, FQ = Fused Quartz (Silica), io YR=Yttria, HF=Hafnia, AS= aluminosilicate (sillimanite) and/or LaB6 =

Lanthanum Hexaboride.

The passivation layer 26B is typically provided as a layer deposited on at least the inner surface 26A of the reaction chamber 26. The passivation layer may also be deposited to extend on to one or more of the annular ends of the reaction chamber 26.

Providing a comparatively thin passivation layer 26B compared to the thickness of the reaction chamber 26 reduces the thermal shock experienced by the passivation layer 26B when the plasma stream 18 is started and stopped, while still providing chemical protection to the underlying structure of the reaction chamber 26.

A variety of different techniques may be employed to deposit the passivation layer 26B on the reaction chamber 26. These techniques are shown in Table 4:

Main Techniques

Available materials

Additional processes

AL

AM

ZR

YSZ

SC

ZTA

FQ

YR

HF

AS

LaB6

Refractory paint

X

Curing the paint with an additional baking step

Sputter coating

X

Heating of substrate, annealing of coating

Sleeve/tiles insert

X

Insert tiles or sleeve on fresh cement (after step S2 of Table 1)

It will be appreciated that additional techniques, such as physical vapour deposition and chemical vapour deposition may also be utilised.

Accordingly, embodiments increase the ceramic reaction tube lifetime employed in plasma abatement systems. Embodiments create a passivation layer in order to improve the chemical inertness of its internal wall when in contact with halogen radicals generated during the plasma phase of the abatement.

Embodiments utilise a hollow cylinder named “ceramic reaction tube” in the socalled reaction section of a plasma system. The internal volume encompassed by the tube is the area where the main reaction takes place. Here converge the thermal plasma generated by the DC-arc torch, the process gas and the reagent respectively after being mixed by crossing a coned orifice called “Venturi cone”.

- 17Compressed dried air (CDA) is typically used as a reagent returning a dry reaction possible free from corrosion from acid such as HF, HCI.

The reaction tube is indirectly cooled by cooling water (PCW) through radiative heat transfer across the air gap and directly by the thermal contact at the bottom of the reaction section. Most of the torch energy has to be confined inside the internal volume of the tube (hence the choice of the cooling design and the insulating ceramic material for the tube). The tube can be elongate in order to increase the residence time of the effluent gas to be treated. All of these features improve the Destruction and Removal Efficiency (DRE) of the system.

In embodiments, the tube is formed by employing “High Alumina Castable” (HAC) cement between an internal mould and an external shell (a stainless steel tube of appropriate dimension. The recipe to prepare the tube is described above. Tube life time is a function of the erosion rate of the HAC cement. The hightemperature can change the chemical state of AI2O3 enabling the halogens to attack it. Experiments have shown that HAC cement with >90% of AI2O3 content and a baking/annealing temperature of up to 900°C are required for an acceptable part lifetime.

Other key factors to improve the tube lifetime are the increases of both the Venturi cone aperture and of the tube bore itself. Both result in an increase the space between the tube and plasma plume but they have an impact on DRE.

The tube preparation described above deals with techniques to prepare the tube cement free from defect (inhomogeneous density, trapped bubbles etc.). The temperature profiles mentioned illustrate in detail the steps to anneal the HAC cement to allow a partial sintering of its particles. This makes the tube less permeable to erosion.

The HAC reaction tube is fit for the purpose due its excellent thermo-mechanical (T-M) properties. Experimental data shows HAC tubes sitting under the “hot”

- 18plasma plume for some weeks without loss of material, while tests with a similar tube made of pure alumina cracks in minutes due the T-M stress.

Embodiments passivate the tube internal wall with a purer material with improved 5 chemical resistance. This layer is made thin so that the T-M properties of the bulk material (HAC cement) are retained. This allows also to use a small amount of exotic materials in this layer while minimizing the part cost. This layer can be made a high purity Alumina (AL), Alumina Mullite (corundum - AM), Zirconia (ZR), Yttria-Stabilized Zirconia (fully stabilized - YSZ), Zirconia Toughened

Alumina (ZTA), Fused Quartz (Silica - ZTA FQ),Yttria (YR), Hafnia (HF), aluminosilicate (sillimanite - AS). With regard to the techniques to build this passivation layer one can use the following:

a) Some materials are available as refractory paint allowing the layer to be applied with a brush and then cured in oven in a further thermal step;.

b) Thermal plasma spray coating; this technique allows a layer with excellent quality to be deposited onto the tube wall.

c) Tile or sleeve insert; a sleeve or some tiles are typically applied to the internal wall while the HAC cement is still wet; these tiles (or the sleeve) can stay attached to the tube internal wall due to the cement cohesion forces.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

- 19REFERENCE SIGNS

plasma torch abatement apparatus	10
cathode	12
anode	14
plasma source gas	16
plasma stream	18
venturi cone	20
effluent gas stream	22
secondary gas stream	24
reaction chamber	26
inner surface	26a
passivation layer	26b
water jacket	28
inner wall	28a
outer wall	28b
tubular void	28c
air gap	30

Claims

1. A plasma torch abatement apparatus for treatment of an effluent stream from a processing tool with a plasma stream, comprising:

5 a reaction chamber defined by a reaction chamber wall for receiving said effluent stream and said plasma stream, said reaction chamber wall comprising a composite structure having a passivation layer facing said effluent stream and said plasma stream, said passivation layer being formed from a passivation material, said composite structure having a io substrate layer formed from a substrate material surrounding said passivation layer, said passivation material being less chemically reactive to said effluent stream and said plasma stream than said substrate material.

15

2. The plasma torch abatement apparatus of claim 1, wherein said substrate layer is more resistant to thermal fracture than said passivation layer.

3. The plasma torch abatement apparatus of claim 1 or 2, wherein said passivation layer is thinner than said substrate layer.

4. The plasma torch abatement apparatus of any preceding claim, wherein said passivation material comprises at least one of: Alumina, Alumina Mullite, Zirconia, Yttria-Stabilized Zirconia, Zirconia Toughened Alumina, Fused Quartz, Yttria, Hafnia and Aluminosilicate and Lanthanum

25 Hexaboride.

5. The plasma torch abatement apparatus of any preceding claim, wherein said passivation layer is at least one of painted, phyiscal deposited, chemical vapour deposited and sprayed onto said substrate layer.

-21

6. The plasma torch abatement apparatus of any preceding claim, wherein said passivation layer comprises at least one of a sleeve and tiles fixed onto said substrate layer.

7. The plasma torch abatement apparatus of any preceding claim, wherein said substrate material comprises a high alumina castable cement.

8. A method of manufacturing a reaction chamber of a plasma torch io abatement apparatus for treatment of an effluent stream from a processing tool with a plasma stream, comprising:

forming a reaction chamber wall from a composite structure having a passivation layer formed from a passivation material and a substrate layer formed from a substrate material, said passivation layer facing said

15 effluent stream and plasma stream and said passivation material being less chemically reactive to said effluent stream and plasma stream than said substrate material.

9. The method of manufacturing of claim 8, wherein said substrate layer is

20 more resistant to thermal fracture than said passivation layer.

10. The method of manufacturing of claim 8 or 9, wherein said substrate layer comprises a ceramic mix and said method comprises performing at least one annealing step on said ceramic mix.

11. The method of manufacturing of any one of claims 8 to 10, wherein said annealing steps elevate a temperature of said ceramic mix to an upper temperature.

-2212. The method of manufacturing of claims 10 or 11, comprising controlling cooling of said ceramic mix following said annealing steps.

13. The method of manufacturing of any one of claims 10 to 12, comprising

5 mixing a ceramic with a fluid to form said ceramic mix.

14. The method of manufacturing of any one of claims 8 to 10, wherein said forming comprises moulding said ceramic mix in a mould to form said reaction chamber.

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15. The method of manufacturing of claim 14, comprising agitating said ceramic mix within said mould to homogenise said ceramic mix.

16. The method of manufacturing of claim 14 or 15, comprising agitating said

15 ceramic mix within said mould to displace bubbles within said ceramic mix.

17. A plasma torch abatement apparatus or method of manufacturing as hereinbefore described with reference to the accompanying drawings.

Intellectual

Property

Office

-23Application No: GB1616286.9 Examiner: Dr Rhys Williams