Plasma foreline

Abstract

An apparatus for conveying an effluent stream from a semiconductor processing tool for plasma treatment comprises a foreline conduit defining an inlet for receiving the effluent stream, and a mixing l

Description

FIELD OF THE INVENTION The present invention relates to an apparatus for conveying an effluent stream 5 from a processing tool for plasma treatment. 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 10 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 15 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 20 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 25 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 30 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 5 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 an apparatus for conveying an 10 effluent stream from a semiconductor processing tool for plasma treatment, comprising: a foreline conduit defining an inlet configured to receive the effluent stream; and a mixing lance positioned within the foreline conduit, the mixing lance defining a mixing conduit coupled with a first plasma reagent conduit configured to supply a first plasma reagent to the mixing lance and with a second 15 plasma reagent conduit configured to supply a second plasma reagent to the mixing lance, the mixing conduit being configured to support mixing of the first plasma reagent and the second plasma reagent and defining a mixing lance outlet configured to deliver mixed first and second plasma reagent into the foreline conduit for mixing with the effluent stream. 20 The first aspect recognizes that a problem with plasma abatement is that it can be difficult to recover noble or other gases from the effluent stream from semiconductor processing tools. Foreline plasma abatement typically uses water vapour as a reagent on an inline chamber, abatement and pump configuration. 25 However, when performing gas recovery from the effluent stream, it is beneficial to minimize the additional gas load caused by the use of water vapour to enable the gases to be recovered efficiently. Accordingly, an apparatus is provided. The apparatus may convey an effluent 30 stream received from a semiconductor processing tool for subsequent plasma treatment. The apparatus may comprise a foreline conduit, duct or tube. The foreline conduit may define an inlet. The inlet may be configured to receive the effluent stream. The apparatus may comprise a mixing lance. The mixing lance may be positioned within the foreline conduit. The mixing lance may define a mixing conduit, duct or tube which may couple with a first plasma reagent conduit, duct or tube which supplies a first plasma reagent to the mixing lance. 5 The mixing conduit may be coupled with a second plasma reagent conduit, duct or tube which supplies a second plasma reagent to the mixing lance. The mixing conduit may be configured to mix the first plasma reagent and the second plasma reagent to provide a mixed first and second plasma reagent. The mixing conduit may define a mixing lance outlet which may deliver the mixed first and second 10 plasma reagent into the foreline conduit to mix with the effluent stream. In this way, controlled amounts of individual reagents can be provided, appropriately mixed and delivered into the effluent stream which enables more precisely controlled quantities of reagent to be introduced into the effluent stream, resulting in reduced excess reagent being present following abatement and reducing the 15 gas load which makes recovery of gases from the abated effluent stream easier. The mixing lance may be positioned centrally within the foreline conduit. This helps to support uniform flow of the effluent stream and provide uniform mixing of the mixed first and second plasma reagents with the effluent stream. 20 The mixing lance may extend along a longitudinal axis of the foreline conduit. Hence, the mixing lance may reuse space already occupied by the foreline conduit. 25 The mixing lance may be elongate, having a length configured to provide a residence time within the mixing conduit to support homogenous mixing of the first plasma reagent and the second plasma reagent. Accordingly, the dimensions of the mixing lance may be selected to provide a dwell time which is sufficient to enable the plasma reagents to mix sufficiently. The mixing lance may have a sloping end facing a major direction of flow of the effluent stream. Hence, the mixing lance may have a sloping end facing towards the inlet of the foreline conduit. Providing a sloping end helps to direct the flow of the effluent stream whilst reducing introduction of turbulent flow and reducing the likelihood of particulate build-up on the mixing lance. 5 The mixing lance outlet may be configured or orientated to convey the mixed first and second plasma reagent around the mixing lance. Accordingly, the mixing lance outlet may distribute the mixed first and second plasma reagents into the effluent stream. This helps to provide for a uniform distribution of the mixed first and second plasma reagents into the effluent stream. 10 The mixing lance may comprise a plurality of apertures, conduits or openings positioned circumferentially around the mixing lance. Again, this helps to provide for uniform delivery of the mixed first and second plasma reagents into the effluent stream. 15 The mixing lance may be configured to convey the mixed first and second plasma reagent into the foreline conduit in a direction having a radial component. In other words, the mixed first and second plasma reagent may be directed from the mixing lance into the effluent stream. The mixed first and second plasma reagent 20 may typically be delivered orthogonally to the major direction of flow of the effluent stream, but may also be delivered with upstream or downstream directional components. The mixing lance outlet may be positioned towards an upstream end of the 25 mixing lance. This helps to reuse space within the foreline conduit, both for mixing of the first and second plasma reagents within the mixing lance and for mixing of the mixed first and second plasma reagent with the effluent stream. The first plasma reagent conduit may couple with a first plasma inlet defined by 30 the mixing lance and the second plasma reagent conduit may couple with a second plasma inlet defined by the mixing lance. Hence, the plasma reagent conduits themselves may help to mechanically support the mixing lance within the foreline conduit. The first plasma inlet and the second plasma inlet may be positioned towards a 5 downstream end of the mixing lance. The first plasma reagent conduit and the second plasma reagent conduit may be configured to supply the first plasma reagent and the second plasma reagent at no greater than a flammable pressure. By supplying the reagents separately, the 10 risk of any combustion is reduced. Ensuring that the pressure within the mixing lance is maintained generally at or below a flammable pressure in at least a portion of the mixing lance helps to reduce the risk of any combustion propagating. 15 The mixing lance, the first plasma reagent conduit and the second plasma reagent conduit may couple using a Y-connector or a T-connector. The first plasma reagent conduit and the second plasma reagent conduit may extend through the foreline conduit to support the mixing lance within the foreline 20 conduit. The first plasma reagent may comprise a fuel and the second plasma reagent may comprise an oxidant. 25 The fuel may comprise hydrogen and the oxidant may comprise oxygen. According to a second aspect, there is provided a method, comprising: receiving an effluent stream at an inlet of a foreline conduit; supplying a first plasma reagent to a first plasma reagent conduit of a mixing lance positioned within the 30 foreline conduit; supplying a second plasma reagent to a second plasma reagent conduit of the mixing lance; mixing the first plasma reagent and the second plasma reagent in a mixing conduit of the mixing lance coupled with the first plasma reagent conduit and the second plasma reagent conduit; and delivering mixed first and second plasma reagent from a mixing lance outlet of the mixing lance into the foreline conduit for mixing with the effluent stream. 5 The method may comprise positioning the mixing lance centrally within the foreline conduit. The mixing lance may extend along a longitudinal axis of the foreline conduit. 10 The mixing lance may be elongate and the method may comprise selecting a length of the mixing lance to provide a residence time within the mixing conduit to support homogenous mixing of the first plasma reagent and the second plasma reagent. 15 The method may comprise positioning a sloping end of the mixing lance to face a major direction of flow of the effluent stream. The method may comprise conveying the mixed first and second plasma reagent around the mixing lance from the mixing lance outlet. 20 The method may comprise positioning a plurality of apertures of the mixing lance outlet circumferentially around the mixing lance. The method may comprise conveying the mixed first and second plasma reagent 25 from the mixing lance outlet into the foreline conduit in a direction having a radial component. The method may comprise positioning the mixing lance outlet towards an upstream end of the mixing lance. The method may comprise coupling the first plasma reagent conduit with a first plasma inlet defined by the mixing lance and coupling the second plasma reagent conduit with a second plasma inlet defined by the mixing lance. 5 The method may comprise positioning the first plasma inlet and the second plasma inlet downstream end of the mixing lance. The method may comprise supplying the first plasma reagent and the second plasma reagent at no greater than a flammable pressure. 10 The method may comprise coupling the mixing lance, the first plasma reagent conduit and the second plasma reagent conduit using one of a Y-connector and a T-connector. 15 The method may comprise extending the first plasma reagent conduit and the second plasma reagent conduit through the foreline conduit to support the mixing lance within the foreline conduit. The first plasma reagent may comprise a fuel and the second plasma reagent 20 may comprise an oxidant. The fuel may comprise hydrogen and the oxidant may comprise oxygen. Further particular and preferred aspects are set out in the accompanying 25 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, 30 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: FIG. 1 is a semi-transparent perspective view of an apparatus according to one 5 embodiment; FIG. 2 is a sectional schematic view through a portion of the apparatus; and FIGS. 3A and 3B are sections through the mixing lance outlet. DESCRIPTION OF THE EMBODIMENTS io Before discussing the embodiments in any more detail, first an overview will be provided. Some embodiments provide an arrangement for providing potentially combustible reagents into an effluent stream for subsequent abatement in a safe and controlled manner. The reagents are introduced to a mixing lance separately to avoid risk of combustion. The amount of reagents introduced are controlled to 15 provide for at least a portion of the mixing lance being below a flammable pressure of the mixed reagents to reduce the risk of propagating combustion. Typically, the conduits used for the reagents can help support the mixing lance. The mixing lance is typically configured to deliver the mixed reagents uniformly into the effluent stream. The amounts of reagents introduced in this way can be 20 carefully controlled to reduce the amount of reagent present in the effluent stream to that necessary to support abatement and reduce excess reagent present following abatement to reduce the gas load when performing gas recovery. FIG. 1 is a semi-transparent perspective view of an apparatus 10 for conveying 25 an effluent stream 130 from a semiconductor processing tool (not shown) to a plasma treatment apparatus (not shown). The apparatus 10 comprises a foreline conduit 20. The foreline conduit 20 defines an inlet 30 and an outlet 40. The inlet 30 couples with an upstream foreline (not shown) from the semiconductor processing tool and the outlet 40 couples with a downstream manifold 55 which 30 couples with the plasma treatment apparatus. Positioned within the foreline conduit 20 is a mixing lance 50. In this arrangement, the mixing lance 50 is positioned centrally within the foreline conduit 20. In this arrangement, the foreline conduit 20 is cylindrical and the mixing lance 50 is coaxially positioned within the foreline conduit 20. However, it 5 will be appreciated that this need not be the case and other shapes of foreline conduit 20, mixing lance 50 and positioning of the mixing lance 50 are possible. A first plasma reagent conduit 60 is provided which extends through the foreline conduit 20 and couples with a T-connector 70 located at a downstream end of the io mixing lance 50. A second plasma reagent conduit 80 also extends through the foreline conduit 20 and couples with the T-connector 70. FIG. 2 is a sectional schematic view through a portion of the apparatus 10. The mixing lance 50 is elongate and extends along a central axis of the foreline 15 conduit 20. The mixing lance 50 defines a mixing conduit 75 which couples with the T-connector 70 and with a mixing lance outlet 90. FIGS. 3A and 3B are sections through the mixing lance outlet 90. As can be seen, the mixing lance 50 is configured as a blind bore with a plurality of radially 20 extending apertures 100 located circumferentially around the mixing lance outlet 90. The mixing lance outlet 90 has a sloped end 110 which is chamfered (or even domed). The size, geometry and length of the apertures 100 is selected to a provide suitable ratio between the velocity of the mixed first and second plasma reagents and the velocity of the effluent stream 130. The latter being the slower 25 effluent stream 130 coming down the foreline, whilst the former mixed first and second plasma reagents velocity was increased by a factor of around ten to optimise gas mixing whilst minimising any “plume” of lighter reagent gases (whilst also ensuring that any flammable reagent gases were kept to suitable velocities well below supersonic speeds). 30 Although the first plasma reagent conduit 60 and the second plasma reagent conduit 80 may be sufficient to support the mixing lance 50, in this arrangement a plurality of supporting struts 120 are provided which extend radially from the upstream end of the mixing lance 50 to the foreline conduit 20 to help retain the mixing lance 50 in place. 5 In operation, a first plasma reagent such as a fuel (for example, hydrogen) is provided through the first plasma reagent conduit 60. A second plasma reagent such as an oxidant (for example, oxygen) is provided through the second plasma reagent conduit 80. The two plasma reagents remain separate until they begin mixing in the T-connector 70. The two plasma reagents continue to mix as they io flow within the mixing conduit 75, along the longitudinal length of the mixing lance 50. The dimensions of the first plasma reagent conduit 60, the second plasma reagent conduit 80, the T-connector 70 and the mixing lance 50, together with the flow rate and pressure of the first and second plasma reagents, are selected to ensure that the plasma reagents remain generally below their flammable 15 pressure for at least a portion of the mixing lance 50 to avoid combustion propagation. The volume and length of the mixing conduit 75 is selected to ensure a sufficient residence time such that the first and second plasma reagents mix substantially homogenously before being delivered into the foreline conduit 20 via the apertures 100. 20 The effluent stream 130 flows from the inlet 30 towards the outlet 40. The sloped end 110 of the mixing lance outlet 90 helps prevent accumulation of any particulates within the effluent stream 130. The effluent stream 130 typically flows through the inlet 30 with a laminar flow. The mixed first and second plasma 25 reagents flow into the effluent stream 130. The mixed plasma reagents mix with the effluent stream 130 as it flows through the foreline conduit 20 and the combined plasma reagent and effluent stream exits the outlet 40 for distribution and supply to the plasma treatment apparatus. 30 Hence, it can be seen that introducing a potentially flammable mixture of reagents such as hydrogen and oxygen into the inlet of an ignition source may be achieved safely by introducing the gases individually under vacuum (vacuum <65mbarg), and at nominal pressure (1bar) through a mixing lance or delivery pipe that increases residence time of the gas to encourage mixing and then passes the gases into an outlet or reagent distribution head that emits streams of mixed reagent gas towards the walls of the foreline conduit or duct. The foreline 5 then has a sufficient vertical straight length that allows the lighter reagent gas mixture to rise up into the oncoming, heavier effluent stream or process gas and mix thoroughly before the process gas and reagent mixture enters the foreline plasma. 10 The hydrogen and oxygen (or other) reagent gases are introduced separately into the foreline (upstream of the foreline plasma) and under vacuum. This is to reduce any concern over ignition or flame propagation. Oxygen flows through one arm or conduit, and through the other arm or conduit a mixture of argon and hydrogen. Computational fluid dynamics simulations show a location near the T 15 coupling where the hydrogen mole fraction lies between the lower and upper flammability limits (4% and 75% respectively) and the oxygen concentration is above the minimum of 5%. In addition, the pressure at this point is above 25mbarg. The minimum pressure that can sustain a flame is a function of the strength of the ignition source. Experiments have shown that the ignition energy 20 rises from 0.0012mJ (in pure oxygen) at atmospheric pressure to 7.5J at 25mbar (in air) - that is a seven orders of magnitude change. For comparison, the minimum ignition energy for a methane-air mixture at atmospheric pressure is reported to be -0.21 mJ. With an extremely strong ignition source it would be possible to get a flame to propagate. However, the pressure falls rapidly as the 25 gas travels up the inlet pipe or mixing lance towards the reagent distribution head or mixing lance outlet and this is likely to extinguish any possible propagation. Regarding detonation, more recent studies put the limiting pressure at >70 mbar. Introducing the reagent in this method: introduces and mixes two flammable gases into a vacuum foreline without causing an ignition, and mixes the reagents 30 with the process gas from a semiconductor etch process, in order to abate the process gas in a foreline plasma, upstream of the vacuum pump. 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 5 from the scope of the invention as defined by the appended claims and their equivalents. REFERENCE SIGNS Apparatus 10 Foreline conduit 20 5 Inlet 30 Outlet 40 Mixing lance 50 Manifold 55 First plasma reagent conduit 60 io T-connector 70 Mixing conduit 75 Second plasma reagent conduit 80 Mixing lance outlet 90 Apertures 100 15 Sloped end 110 Struts 120 Effluent stream 130

Claims

1. An apparatus for conveying an effluent stream from a semiconductor processing tool for plasma treatment, comprising:5 a foreline conduit defining an inlet configured to receive said effluentstream; anda mixing lance positioned within said foreline conduit, said mixing lance defining a mixing conduit coupled with a first plasma reagent conduit configured to supply a first plasma reagent to said mixing lance and with a second plasmaio reagent conduit configured to supply a second plasma reagent to said mixing lance, said mixing conduit being configured to support mixing of said first plasma reagent and said second plasma reagent and defining a mixing lance outlet configured to deliver mixed first and second plasma reagent into said foreline conduit for mixing with said effluent stream.

152. The apparatus of claim 1, wherein said mixing lance is positioned centrally within said foreline conduit.

3. The apparatus of claim 1 or 2, wherein said mixing lance extends along a 20 longitudinal axis of said foreline conduit.

4. The apparatus of any preceding claim, wherein said mixing lance is elongate, having a length configured to provide a residence time within said mixing conduit to support homogenous mixing of said first plasma reagent and25 said second plasma reagent.

5. The apparatus of any preceding claim, wherein said mixing lance has a sloping end facing a major direction of flow of said effluent stream.30 6. The apparatus of any preceding claim, wherein said mixing lance outlet isconfigured to convey said mixed first and second plasma reagent around said mixing lance.

7. The apparatus of any preceding claim, wherein said mixing lance outlet comprises a plurality of apertures positioned circumferentially around said mixing lance.

58. The apparatus of any preceding claim, wherein said mixing lance outlet is configured to convey said mixed first and second plasma reagent into said foreline conduit in a direction having a radial component.io 9. The apparatus of any preceding claim, wherein said mixing lance outlet is positioned towards an upstream end of said mixing lance.

10. The apparatus of any preceding claim, wherein said first plasma reagent conduit couples with a first plasma inlet defined by said mixing lance and said 15 second plasma reagent conduit couples with a second plasma inlet defined by said mixing lance.

11. The apparatus of claim 10, wherein said first plasma inlet and said second plasma inlet are positioned towards a downstream end of said mixing lance.2012. The apparatus of any preceding claim, wherein said first plasma reagent conduit and said second plasma reagent conduit are configured to supply said first plasma reagent and said second plasma reagent at no greater than a flammable pressure.2513. The apparatus of any preceding claim, wherein said mixing lance, said first plasma reagent conduit and said second plasma reagent conduit couple using one of a Y-connector and a T-connector.30 14. The apparatus of any preceding claim, wherein said first plasma reagentconduit and said second plasma reagent conduit extend through said foreline conduit to support said mixing lance within said foreline conduit.

15. The apparatus of any preceding claim, wherein said first plasma reagent comprises a fuel and said second plasma reagent comprises an oxidant.5 16 The apparatus of claim 15, wherein said fuel comprises hydrogen and saidoxidant comprises oxygen.

17. A method, comprising:receiving an effluent stream at an inlet of a foreline conduit;io supplying a first plasma reagent to a first plasma reagent conduit of amixing lance positioned within said foreline conduit;supplying a second plasma reagent to a second plasma reagent conduit of said mixing lance;mixing said first plasma reagent and said second plasma reagent in a15 mixing conduit of said mixing lance coupled with said first plasma reagent conduit and said second plasma reagent conduit; anddelivering mixed first and second plasma reagent from a mixing lance outlet of said mixing lance into said foreline conduit for mixing with said effluent stream.20

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