WO2017025709A1

WO2017025709A1 - Plasma generator

Info

Publication number: WO2017025709A1
Application number: PCT/GB2016/052283
Authority: WO
Inventors: Daniel Masse; Ali Shajii; Andrew James Seeley; Michael Colin GRAHAM
Original assignee: Edwards Limited
Priority date: 2015-08-12
Filing date: 2016-07-26
Publication date: 2017-02-16
Also published as: TW201711530A; GB2541214A; GB201514287D0

Abstract

A plasma generator and method are disclosed. The plasma generator is for generating a plasma stream from a gas stream and comprises: a housing configured to receive the gas stream; and a coil located within the housing and operable to generate the plasma stream from the gas stream. Locating the coil within the housing both improves the generation of the plasma stream (which improves the operation of the plasma generator in the treatment of any effluent stream since both capacitively-induced and inductively-induced plasmas are generated) and increases the range of materials from which the housing may be made since the coil is no longer placed outside of the housing, such as materials which are less damaged by reactive gas etching, which results in increased operating life for the chamber.

Description

PLASMA GENERATOR

FIELD OF THE INVENTION

The present invention relates to a plasma generator and method.

Embodiments relate to a plasma generator or plasma abatement apparatus for treating an effluent stream from a processing tool.

BACKGROUND

Plasma abatement apparatus 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.

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 abatement apparatus.

Plasmas for abatement apparatus can be formed in a variety of ways.

Microwave plasma abatement devices can be connected to the exhaust of several process chambers. Each device requires its own microwave generator, which can add considerable cost to a system. Plasma torch abatement devices are advantageous over microwave plasma abatement devices in terms of scalability and in dealing with powder (present in the effluent stream or generated by the abatement reactions). In fact, with regard to microwave plasmas, if powder is present it can modify the dielectric characteristic of the reaction tube and render ineffective the microwave injection that sustains the discharge. The plasma generated by the plasma abatement device is used to destroy or abate unwanted compounds within the effluent gas stream. Although these apparatus exist for processing the effluent gas stream, they each have their own shortcomings. Accordingly, it is desired to provide an improved technique for processing and effluent gas stream.

SUMMARY

According to a first aspect, there is provided a plasma generator for generating a plasma stream from a gas stream, comprising: a housing configured to receive the gas stream; and a coil located within the housing and operable to generate the plasma stream from the gas stream. The first aspect recognizes that in a typical arrangement of a plasma generator, a radio frequency (RF) coil is wound around the outside of a chamber which contains the plasma. The chamber is formed of a dielectric material which is exposed to the generated plasma. Although this helps to protect the RF coil and contains the plasma within the chamber, the dielectric material is easily damaged by reactive gas etching which results in a short operating life for the chamber.

Accordingly, a plasma-generating device or apparatus may be provided. The plasma generator may generate a plasma stream from a gas stream. The plasma generator may comprise a housing or conduit which may receive the gas stream. The plasma generator may also comprise a coil which is located, positioned or arranged within the housing. The coil may operate, function or be activated to generate the plasma stream from the gas stream. Locating the coil within the housing both improves the generation of the plasma stream (which improves the operation of the plasma generator in the treatment of any effluent stream since both capacitively-induced and inductively-induced plasmas are generated) and increases the range of materials from which the housing may be made since the coil is no longer placed outside of the housing, such as materials which are less damaged by reactive gas etching, which results in increased operating life for the chamber. In one embodiment, the housing defines a chamber and the coil is located within the chamber. Accordingly, the coil may be enclosed by or retained within the chamber.

In one embodiment, the housing at least partially surrounds the coil.

In one embodiment, the housing comprises a corrosion-resistant material. Utilizing a corrosion-resistant material increases the life of the plasma generator. In one embodiment, the housing comprises one of a metal and a dielectric. Accordingly, the housing may comprise either a metal or a dielectric, or a combination of both.

In one embodiment, the housing is porous for conveying the gas stream through the housing to the chamber. Accordingly, the housing itself may be porous or foraminous and the gas stream may pass through the housing and into the chamber.

In one embodiment, the housing comprises an inlet configured to convey the gas stream to the chamber. Accordingly, an inlet may be provided in the housing through which the gas stream passes into the chamber.

In one embodiment, the plasma generator comprises a containment shroud extending between the inlet and an upstream opening of the coil. Hence, the containment shroud may provide a conduit within the housing which conveys the gas stream from the inlet to the coil. In one embodiment, the containment shroud has a diameter matching that of the coil. Accordingly, the coil and the containment shroud may have similar diameters (for example, similar internal diameters). Hence, the containment shroud may only extend to the upstream opening of the coil, but may not extend either inside or outside the coil.

In one embodiment, the plasma generator comprises an outer containment shroud located at least partially around the coil, between the coil and the housing. Placing a containment shroud around the coil helps to retain the plasma stream within the coil and away from the housing.

In one embodiment, the plasma generator comprises an inner containment shroud located at least partially within the coil. Providing a containment shroud within the coil acts as a flow guide which helps to contain the plasma stream also within the coil and helps any effluent gas stream to be treated from bypassing the plasma.

In one embodiment, the inner containment shroud extends at least between the inlet and an upstream opening of the coil. Accordingly, the containment shroud may be located between the inlet and a receiving opening of the coil in order to convey the gas stream from the inlet to the coil. Again, this helps to prevent the gas stream from bypassing the plasma generated by the coil.

In one embodiment, the inner containment shroud at least partially extends along an axial length of the coil. Accordingly, the containment shroud may extend along all or a part of the axial length of the coil.

In one embodiment, the inner containment shroud comprises a plurality of shroud sections, adjacent shroud sections being electrically isolated from each other. Accordingly, the shroud may be assembled from a number of sections, with neighbouring or bordering sections being insulated from each other. Typically, a shroud section will be provided within a single-turn of the coil, with adjacent shroud sections being located within corresponding turns of the coil.

In one embodiment, adjacent shroud sections are spaced away from each other to define a void therebetween. Accordingly, the void may provide the electrical isolation between adjacent sections.

In one embodiment, a shroud section extending between the inlet and the upstream opening of the coil comprises a dielectric material. Utilizing a dielectric material provides for electrical insulation between the coil and the inlet.

In one embodiment, a shroud section extending along the axial length of the coil comprises a metal. Within the coil it is possible to utilize a metal shroud section.

In one embodiment, each shroud section extends circumferentially within the coil and the shroud section comprises slotted tube to define a void between opposing edges of the slotted tube. Providing a void, slot or gap along the axial length of the shroud section prevents the shroud section from short- circuiting the coil.

In one embodiment, the coil comprises a pair of feed lines configured to provide an electrical current to the coil and the void is located between pair of feed lines. Aligning the void between the feed lines again ensures that the shroud section does not provide a short-circuit path between the feed lines and ensures that the current passes through the coil.

In one embodiment, the pair of feed lines are configured to prevent current flow other than through the coil. Hence, the feed lines are arranged or positioned so that current flows through the coil. In one embodiment, the pair of feed lines extend from the coil and are parallel. Providing a parallel arrangement of the feed lines helps to cancel out the magnetic field generated by those feed lines, particularly when the feed lines are both parallel and co-located and/or adjacent.

In one embodiment, the coil has a plurality of turns. Increasing the number of turns or loops of the coil increases the inductance and reduces the magnitude of the current flow required to create the plasma. In one embodiment, the coil has two turns.

In one embodiment, each turn is arranged in series. Accordingly, each turn may be arranged sequentially. In one embodiment, adjacent turns are isolated. Accordingly, each turn may be electrically isolated in order to prevent short-circuiting between turns.

In one embodiment, adjacent turns are configured to define a void

therebetween. Accordingly, the void may isolate adjacent turns. In

embodiments, each turn is electrically insulated from adjacent turns.

In one embodiment, each turn comprises an input feed and an output feed configured to prevent current flow other than through that turn. Accordingly, the input and output feeds may be arranged to ensure that the current only flows through the corresponding turn.

In one embodiment, the plasma generator comprises a coupling which couples an output feed from one turn with an input feed of an adjacent turn. Accordingly, the output from one turn may feed the input of an adjacent turn, in order that the current flows from one turn to the next. In one embodiment, the coupling comprises a conductor located to provide additional area for current flow between adjacent turns. Providing the conductor helps to provide an increased conduction path between turns to reduce heating.

In one embodiment, the conductor extends at least between adjacent turns.

In one embodiment, the conductor is grounded to the housing. In one embodiment, each turn comprises an elongate annular section.

Accordingly, each turn may be elongate in the axial direction in order to increase the volume within which the plasma is generated.

In one embodiment, each turn comprises a plurality of co-located tubular sections. Hence, a number of smaller sections may together form a single turn.

In one embodiment, the gas stream comprises at least one of a plasma source gas and an effluent gas stream. Hence, the gas stream may comprise an effluent gas stream and/or the effluent gas stream mixed with a gas from which the plasma is generated.

In one embodiment, the gas stream comprises a plasma source gas and the plasma generator comprises a plasma gas conduit located to convey the plasma source gas to within the coil and an effluent stream inlet located to covey an effluent gas stream around the coil. Accordingly, a plasma source or reagent gas may be fed to the upstream opening of the coil, the effluent or main gas stream to be treated flows around the outside of the coil, and the plasma stream flows out of the downstream end of the coil into the middle of the gas stream to be treated, to promote mixing of the plasma products with the gas stream. According to a second aspect, there is provided a method of generating plasma from a gas stream, comprising: receiving the gas stream within a housing; and generating the plasma stream from the gas stream with a coil located within the housing.

In one embodiment, the housing defines a chamber and the method comprises locating the coil within the chamber.

In one embodiment, the method comprises at least partially surrounding the coil with the housing.

In one embodiment, the housing comprises a corrosion-resistant material.

In one embodiment, the housing comprises one of a metal and a dielectric.

In one embodiment, the housing is porous and the receiving comprises conveying the gas stream through the housing to the chamber.

In one embodiment, the housing comprises an inlet configured and the receiving comprises conveying the gas stream through the inlet to the chamber.

In one embodiment, the method comprises locating a containment shroud extending between the inlet and an upstream opening of the coil.

In one embodiment, the method comprises matching a diameter of the containment shroud with that of the coil.

In one embodiment, the method comprises locating an outer containment shroud at least partially around the coil, between the coil and the housing. In one embodiment, the method comprises locating an inner containment shroud at least partially within the coil.

In one embodiment, the inner containment shroud extends at least between the inlet and an upstream opening of the coil.

In one embodiment, the inner containment shroud at least partially extends along an axial length of the coil. In one embodiment, the inner containment shroud comprises a plurality of shroud sections, adjacent shroud sections being electrically isolated from each other.

In one embodiment, the method comprises spacing adjacent shroud sections away from each other to define a void therebetween.

In one embodiment, a shroud section extending between the inlet and the upstream opening of the coil comprises a dielectric material. In one embodiment, a shroud section extending along the axial length of the coil comprises a metal.

In one embodiment, each shroud section extends circumferentially within the coil and the shroud section comprises slotted tube to define a void between opposing edges of the slotted tube.

In one embodiment, the coil comprises a pair of feed lines configured to provide an electrical current to the coil and comprising locating the void between pair of feed lines.

In one embodiment, the method comprises configuring the pair of feed lines to prevent current flow other than through the coil. ln one embodiment, the pair of feed lines extend from the coil and are parallel. In one embodiment, the coil has a plurality of turns.

In one embodiment, the coil has two turns.

In one embodiment, the method comprises arranging each turn in series. In one embodiment, the method comprises isolating adjacent turns.

In one embodiment, the method comprises configuring adjacent turns to define a void therebetween. In one embodiment, each turn comprises an input feed and comprising configuring an output feed to prevent current flow other than through that turn.

In one embodiment, the method comprises coupling an output feed from one turn with an input feed of an adjacent turn with a coupling.

In one embodiment, the method comprises locating a conductor as the coupling to provide additional area for current flow between adjacent turns.

In one embodiment, the method comprises extending the conductor at least between adjacent turns.

In one embodiment, the conductor is grounded to the housing.

In one embodiment, each turn comprises an elongate annular section.

In one embodiment, each turn comprises a plurality of co-located tubular sections. In one embodiment, the gas stream comprises at least one of a plasma source gas and an effluent gas stream. In one embodiment, the gas stream comprises a plasma source gas and the method comprises locating a plasma gas conduit to convey the plasma source gas to within the coil and locating an effluent stream inlet to covey an effluent gas stream around the coil. 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. Where 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:

Figure 1 is a schematic representation of a plasma generator according to one embodiment;

Figures 2 to 4 illustrate a plasma generator according to one embodiment;

Figure 5 illustrates a single-turn coil according to one embodiment;

Figure 6 illustrates a single-turn coil according to one embodiment;

Figures 7A and 7B illustrate a two-turn coil according to embodiments;

Figure 8 illustrates a plasma generator according to one embodiment;

Figures 9 to 12 illustrate a two-turn plasma generator according to one embodiment. DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments and more detail, first an overview will be provided. Embodiments provide an apparatus which generates a plasma which may be used, for example, in the abatement, treatment or processing of an effluent gas stream in order destroy or break down harmful compounds. A coil is provided which has one or more turns, which is connected to an RF power supply and through which a current passes in order to generate a plasma from a gas present in the vicinity of the coil. The plasma may be generated from the effluent stream itself and/or from a separate plasma or reagent gas stream (such as steam, oxygen or other suitable compounds). A housing is provided which surrounds the coil, retaining the plasma therein and into which the effluent stream to be treated by the plasma is introduced. The arrangement of the coil within the housing enables a wide range of materials to be used for the housing, which provides for a more robust and longer-life apparatus. Embodiments provide for a coil with one or more turns, and each turn of the coil may be axially elongate in order to increase the volume defined by each turn. Embodiments also provide for containment shrouds located around, within and/or extending from the coil in order to direct the flow of the gas stream, any reagent gas stream and/or contain the plasma and promote mixing. For example, a reagent gas stream may be conveyed to within the coil to generate a plasma, with the effluent stream conveyed to surround the coil, the plasma and effluent stream mixing at the downstream opening of the coil. The reagents such as steam, oxygen or other suitable compounds may be added to promote the treatment of the effluent stream.

Plasma Generator - Schematic Representation

Figure 1 is a schematic representation of a plasma generator, generally 10, according to one embodiment. A coil 20 is provided which is multi-turn and which is coupled via couplings 30, 40 to an RF power supply (not shown). The coil 20 is enclosed within a housing 50. An inlet aperture 60 is provided in the housing 50, upstream of the coil 20 and an outlet aperture 70 is provided downstream of the coil 20. In operation, a gas stream, which may comprise an effluent gas stream to be treated (either alone or in combination with another gas source from which a plasma may be generated) is introduced through the inlet aperture 60 into the chamber defined by the housing 50. Power is supplied to the coil 20 and a plasma is generated. Typically, the coil 20 is hollow which enables a fluid to be passed within the coil (such as water), in order that the coil 20 is cooled and therefore temperature-controlled. An inductive plasma is generated within a main region 80 of the chamber and capacitive plasmas are generated in secondary regions 90. As the effluent gas stream passes through the chamber 50, it passes through the regions 80, 90 and is treated by the plasma. A treated effluent gas stream then exits via the outlet aperture 70.

Hence, it can be seen that in this arrangement, the coil 20 is inside the plasma chamber. Because the coil 20 is within the housing 50, the housing can therefore be made of corrosion-resistant material and so no dielectric may be needed. The provision of the secondary capacitive plasmas which form between coil windings or turns and between the coil 20 and the housing 50 provides for further areas of treatment of the effluent gas stream and the flow ratio through the main region 80 and the secondary regions 90 can be tuned, as can the ratio of capacitive to inductive power.

As will be apparent from the discussion below, conduits and/or containment shrouds may be added to this arrangement to direct gas streams, particularly different gas streams such that they are conveyed to within or outside the coil 20.

Plasma Generator - First Arrangement

Figures 2 to 4 illustrate a plasma generator, generally 10A, according to one embodiment. A coil 20A is provided, having couplings 30A and 40A. The couplings 30A, 40A couple with a respective coupling assembly 35A, 45A, which provides power and cooling to the coil 20A. In particular, an electrical connection is provided between the coupling 40A and an electrical connector 47A and between the coupling 30A and an electrical connector 37A. In addition, a fluid coupling is provided between the connection 40A and a cooling connector 43A and between the connector 30A and a cooling connector 33A.

The coil 20A is housed within a housing 50A. In this embodiment, the housing 50A comprises a cylinder onto which are attached an endplate 53A which defines an inlet aperture 60A and a further endplate (not shown) which defines an outlet aperture (also not shown). The coil 20A is electrically insulated from the housing 50A by insulators 41 A, 31 A. A viewing window 55A is provided through which the generated plasma may be viewed and monitored. A flow guide 65A is located in the inlet aperture 60A, extends from the inlet aperture 60A and fits within the inner circumference of the coil 20A. In this embodiment, the flow guide 65A extends for just the first two or three turns of the coil 20A. However, it will be appreciated that the flow guide 65A may extend further along the axial length of the coil 20A and may even protrude from the coil 20A towards the outlet aperture. In this example, the flow guide 65A is retained by a circlip which engages with a recess formed by the endplate 53A. However, it will be appreciated that other fixing mechanisms may be used. The flow guide 65A is a dielectric material (such as alumina, AI2O3. ) and so also insulates the coil 20A from the endplate 53A.

In operation, power is supplied to the coil 20A via the electrical connectors 37A, 47A. A cooling fluid is also passed through the coil (which is hollow) via the cooling connectors 33A, 43A. A gas stream (which may include an effluent gas stream to be treated) is introduced through the inlet aperture 60A. The gas stream is conveyed by the flow guide 65A to within the coil 20A. A plasma is generated within the coil 20A and also in regions outside the coil and between coil turns, as was shown schematically in Figure 1 . As the gas stream is introduced within the coil 20A, the plasma generated treats the effluent gas stream. Any effluent gas stream which exits between the turns of the coil 20A is also treated by the capacitive plasma between the turns of the coil 20A and between the coil 20A and the housing 50A. The flow of the gas stream from the inlet aperture 60A towards the outlet aperture biases the generated plasma regions away from the inlet aperture 60A and towards the outlet aperture. Hence, the plasma is concentrated at the downstream end of the coil 20A and away from the flow guide 65A. The treated gas stream then exits the housing 50A via the outlet aperture (not shown). An air plasma may be established readily by operating the plasma generator 10A at 300W and 1 Torr.

In a slightly modified form, a reagent gas stream is introduced through the inlet aperture 60A. The reagent gas stream is conveyed by the flow guide 65A to within the coil 20A. A plasma is generated within the coil 20A. A further inlet (not shown) is provided in the housing 50A which provides the effluent gas stream to the region outside the coil 20A. A plasma is also generated in regions outside the coil 20A and between coil turns, as was shown schematically in Figure 1 . Any effluent gas stream entering the coil 20A is treated by the plasma. Any plasma which exits between the turns of the coil 20A also treats the effluent gas stream. The flow of the gas stream from the inlet aperture 60A towards the outlet aperture biases the generated plasma regions away from the inlet aperture 60A and towards the outlet aperture. Hence, the plasma is concentrated at the downstream end of the coil 20A and away from the flow guide 65A where it mixes with and treats the surrounding effluent gas stream. The treated gas stream then exits the housing 50A via the outlet aperture (not shown).

The arrangement shown in Figure 3 provides a linear current path through the housing 50A and has high lead inductance. This induces current in the housing 50A which creates higher voltages in the vacuum and decreases match efficiency. Single-Turn Coil

Figure 5 illustrates a single-turn coil 20B for use within a plasma generator such as those illustrated herein, according to one embodiment. As can be seen, the single-turn coil 20B is formed from a plurality (in this example, 10) of co-located tubes 21 B, each placed adjacent each other. This forms a parallel arrangement of tubes 21 B, each coupled with manifolds 23B, 25B. This forms an axially elongate single-turn structure. Electrical connection and cooling fluid occurs via the couplings 30B, 40B. The electrical current and the cooling fluid flow in parallel through each of the tubes 21 B forming the single-turn coil 20B. In this example, the axial length of the coil 20B is 65 mm, made up of ten 6.35 mm tubes arranged in parallel.

This arrangement provides for many advantages due to reduced voltage requirements, but the required current to generate the plasma is high, as 5 kW is required to create plasma from air, argon, nitrogen and water vapour. The low inductance and high current causes increased losses with this arrangement. A nitrogen plasma may be formed by providing 3.5 slm of N2 at 2.5 Torr.

Figure 6 illustrates a single-turn coil, generally 20C, for use within a plasma generator such as those illustrated herein, according to one embodiment. This arrangement is similar to that shown in Figure 5, with manifolds 23C, 25C from which the tubes 21 C extend. This enables the couplings 30C, 40C to be co-located, adjacent each other, such that the electrical connectors 37C, 47C run parallel which helps to cancel out the magnetic fields generated by the electrical connectors 37C, 47C, results in lower lead inductance and provides for no resultant current flow through the housing, unlike the arrangements shown in Figures 1 to 4. Two-Turn Coil

Figure 7A illustrates a two-turn coil, generally 20D, for use within a plasma generator such as those illustrated herein, according to one embodiment. In this arrangement, each tube 21 D forms a double turn. In this example, five tubes 21 D are provided, positioned adjacent each other. As can be seen, the tubes define a gap 27D between adjacent turns in order to ensure that the current flows around each turn. Each tube 21 D is coupled at each end with a respective manifold 23D, 25D. Figure 7B illustrates a two-turn coil, generally 20E, for use within a plasma generator such as those illustrated herein, according to one embodiment. The arrangement of the tubes 21 E forming the coil turns is identical to that shown in Figure 7A, but the electrical connectors 37E, 47E coupled with the manifolds 23E, 25E are such that they are co-located and are parallel in order to cancel out the magnetic fields, in a similar manner to that described in Figure 6 above.

The provision of two turns instead of one turn reduces the required current and match losses while keeping the coil voltage relatively low during plasma generation. Also, the arrangement shown in Figures 6 and 7A results in lower lead inductance and no net current through the housing.

Cylindrical Annular-Coil Plasma Generator

Figure 8 illustrates a plasma generator, generally 10F, according to one embodiment. This embodiment uses a two-turn coil 20F. The coil 20F is cylindrical in overall profile and comprises two turns. This avoids the need for the multiple tubes illustrated in Figures 5 to 7 above, while still retaining an elongated axial length compared to a traditional coil. The coil 20F is retained within a housing 50F and the gas stream flows from an inlet aperture (not shown) adjacent a flow guide 65F, through the coil 20F to an outlet aperture 70F. The couplings 30F, 40F are coupled to provide both electrical power and allow a cooling fluid to flow through the coil 20F. The couplings 30F, 40F protrude through a plate (not shown) provided in one face of the housing 50F.

Two-Turn Plasma Generator

Figures 9 to 12 illustrate a two-turn plasma generator, generally 10G, according to one embodiment. A two-turn coil, generally 20G, is provided. In this example, the internal diameter of the coil 20G is 57mm and its length 120mm, although it will be appreciated that other dimensions are possible. Each turn 27G, 29G comprises a plurality of adjacent and parallel tubes 21 G. In this example, each turn 27G, 29G comprises nine tubes 21 G. A first manifold 23G is coupled with one end of the tubes 21 G of the turn 27G.

Another manifold 25G is coupled with one end of the tubes 21 G of the turn 29G. Ends of the tubes 21 G of both turns 27G, 29G couple with a central manifold 22G. The manifolds engage with a plate 51 G (formed from AI2O3) in the housing 50G (made from Al and having external dimensions of around 160mm high, 200mm long and 140mm wide - although it will be appreciated that other dimensions are possible). In embodiments, the central manifold 22G is grounded to further reduce in-vacuum peak voltage. Located within the turn 27G is a sleeve 67G. Located within the turn 29G is a sleeve 69G. The sleeves 67G, 69G are adjacent but spaced away to be electrically-isolated in order to prevent shorting between the two turns 27G, 29G. The sleeves 67G, 69G are cylindrical and have a longitudinal slot 63G extending along their axial length in order to define a void between opposing edges of the sleeves 67G, 69G. This void or gap is aligned with the ends of the tubes 21 G in order that the sleeves 67G, 69G do not provide a current path which offers a short-circuit to avoid current travelling all the way through the tubes 21 G. The manifolds 23G, 25G provide both a conductive path for current flow through the coil 20G and a conduit through which a cooling fluid may be passed through the coil 20G. In particular, the cooling fluid is introduced through the coupling 30G, which passes into the manifold 23G and in parallel into each of the nine tubes 21 G forming the first turn 27G. The fluid passes (anticlockwise in Figure 9) into the central manifold 22G. The fluid then passes to each of the tubes 21 G in parallel forming the turn 29G and again travels (in this example, anticlockwise) to the manifold 25G where it exits through the coupling 40G. In this example, water is introduced at 8 l/m at 40°C (h «7250 W/m²K) and heat flux is 25W/cm².

Likewise, power is supplied to the connector 31 G and the current travels (in this example, anticlockwise) from the manifold 23G to the central manifold 22G and (in this case, anticlockwise) from the central manifold 22G to a connector (not shown) on the manifold 25G.

Accordingly, when a gas stream (which may include an effluent gas stream) is introduced through the inlet aperture 60G formed in a KF50 plate, it is conveyed by the flow guide 65G (made from AI2O3) into the coil 20G where a plasma is generated which treats the effluent gas stream as it passes towards the outlet aperture 70G (made from NW100). The presence of the sleeves 67G, 69G helps to retain the effluent gas stream within the coil 20G.

Figure 12 illustrates the coil 20G in more detail (which may be made from copper, brass, stainless steel or other corrosion-resistant, conductive material). As can be seen, a gap 27G is provided between the two turns 27G, 29G of the coil 20G to provide electrical isolation between those two turns 27G, 29G. Also, a tab 24G is provided on the central manifold 22G. This tab 24G is provided between the turns 27G, 29G and reduces inductance by giving more area for current flow between the turns 27G, 29G.

Accordingly, it can be seen that embodiments provide a plasma source. The construction of this plasma source allows for long life and improved plasma performance. Long service life is achieved by drastically limiting the exposure of ceramic materials to the active plasma region. The active plasma region is contained within corrosion-resistant metal housing or housings. Plasma power is supplied both inductively and capacitively. The plasma coil / containment unit may be constructed as a one, two, or many-turn coil.

Features allow for voltage reduction, plasma containment, plasma device cooling, plasma coil robustness, plasma coil corrosion resistance, gas condensation prevention and/or reduction, sputtering resistance, creepage (tracking) resistance, arcing prevention and/or reduction, and ignition. Plasma power is coupled into the plasma source using RF energy (typically 2 - 13.56 MHz). Inductively-coupled plasma sources in the past have usually been designed as dielectric containment vessels (such as tubes) surrounded by a current-carrying coil which is in atmosphere. This has a few advantages and a few drawbacks. The advantages are that the high voltage coil is in atmosphere allowing much easier control of arcing and corona, and that the dielectric tube is easily sealed on both ends allowing easy plasma

containment. The biggest drawback is that the dielectric tube (constructed of quartz, ceramic, sapphire, or similar) is easily etched away by the reactive plasma species. In contrast, embodiments provide advantages due to the coil-containment nature of the device. Adverse effects of having the power coupling coil inside vacuum have been mitigated and advantages can be realized, such as corrosion resistance. This has been done primarily by plasma containment and reduction of in-vacuum voltages.

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. REFERENCE SIGNS

Plasma generator 10, 10A, 10F, 10G

Coil 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G

Tubes 21 B, 21 C, 21 D, 21 E, 21 G

Manifolds 23B, 25B, 23C, 25C, 23D, 25D, 23E, 25E, 22G, 23G, 25G Tab 24G

Gap 27D, 27G

Turn 27G, 29G

Couplings 30, 40, 30A, 40A, 30B, 40B, 30F, 40F, 30G, 40G

Connector 31 G

Cooling connector 33A, 43A

Coupling assembly 35A, 45A

Electrical connector 37A, 47A, 37C, 47C, 37E, 47E

Insulator 41A, 31 A

Housing 50, 50A, 50F

Plate 51 G

Endplate 53A

Viewing window 55A

Inlet aperture 60, 60A, 60G

Flow guide 65A, 65F, 65G

Sleeve 67G, 69G

Outlet aperture 70, 70F, 70G

Main region 80

Secondary regions 90

Claims

1 . A plasma generator for generating a plasma stream from a gas stream, comprising: a housing configured to receive said gas stream; and

a coil located within said housing and operable to generate said plasma stream from said gas stream.

2. The plasma generator of claim 1 , wherein said housing defines a

chamber and said coil is located within said chamber.

3. The plasma generator of claim 1 or 2, wherein said housing is porous for conveying said gas stream through said housing to said chamber.

4. The plasma generator of any preceding claim, wherein said housing comprises an inlet configured to convey said gas stream to said chamber.

5. The plasma generator of any preceding claim, comprising a

containment shroud extending between said inlet and an upstream opening of said coil.

6. The plasma generator of any preceding claim, comprising an outer containment shroud located at least partially around said coil, between said coil and said housing.

7. The plasma generator of any preceding claim, comprising an inner containment shroud located at least partially within said coil.

8. The plasma generator of claim 7, wherein said inner containment shroud extends at least between said inlet and an upstream opening of said coil.

The plasma generator of claim 6 or 7, wherein said inner containment shroud comprises a plurality of shroud sections, each shroud section extends circumferentially within said coil and said shroud section comprises slotted tube to define a void between opposing edges of said slotted tube.

10. The plasma generator of any preceding claim, wherein a pair of feed lines extend from the coil and are parallel.

The plasma generator of any preceding claim, wherein said coil has a plurality of turns.

The plasma generator of claim 1 1 , comprising a coupling which couples an output feed from one turn with an input feed of an adjacent turn.

13. The plasma generator of claim 12, wherein said coupling comprises a conductor located to provide additional area for current flow between adjacent turns.

14. The plasma generator of claim 13, wherein said conductor extends at least between adjacent turns.

5. The plasma generator of claim 1 3 or 14, wherein said conductor is grounded to said housing.

6. The plasma generator of any one of claims 1 1 to 1 5, wherein each turn comprises one of an elongate annular section and a plurality of co- located tubular sections.

7. A method of generating plasma from a gas stream, comprising: receiving said gas stream within a housing; and

generating said plasma stream from said gas stream with a coil located within said housing.

8. A plasma generator as hereinbefore described with reference to the accompanying drawings.

9. A method of generating a plasma as hereinbefore described with

reference to the accompanying drawings.