Packed tower

Abstract

A packed tower 10a for treating an abated effluent stream 100 comprising a gas mixture and combustion particles. The packed tower comprises: a packed tower housing 20a having an inlet for receiving the abated effluent stream; an outlet for venting the abated effluent stream; a packed substrate housed within the packed tower housing and a sonic transducer. The packed substrate is housed between the inlet and the outlet and is configured to entrain at least some of the combustion particles from the gas mixture as the abated effluent stream flows therethrough. The sonic transducer is configured to generate acoustic waves to cause interaction with the combustion particles to assist in entraining at least some of the combustion particles from the gas mixture. The abated effluent stream 100 may be from an abatement apparatus configured to abate an effluent stream from a semiconductor processing tool.

Description

FIELD OF THE INVENTION The field of the invention relates to packed tower for treating an abated effluent 5 stream comprising a gas mixture and combustion particles from an abatement apparatus, and method. BACKGROUND Abatement treatment apparatus are known. Such apparatus are used for 10 treatment of effluent gases arising from, for example, epitaxial deposition or other semiconductor fabrication processes. Epitaxial deposition processes are increasingly used for high-speed semiconductor devices, both for silicon and compound semiconductor applications. An epitaxial layer is a carefully grown, single crystal silicon film. Epitaxial deposition utilises a silicon source gas, 15 typically silane or one of the chlorosilane compounds, such as trichlorosilane or dichlorosilane, in a hydrogen atmosphere at high temperature, typically around 800 - 1100°C, and under a vacuum condition. Epitaxial deposition processes are often doped with small amounts of boron, phosphorus, arsenic, germanium or carbon, as required, for the device being fabricated. Etching gases supplied to a 20 process chamber may include halocompounds such as HCI, HBr, BCI3, CI2 and Br2, and combinations thereof. Hydrogen chloride (HCI) or another halocompound, such as SFe or NF3, may be used to clean the chamber between process runs. 25 In such processes, only a small proportion of the gas supplied to the process chamber is consumed within the process chamber, and so a high proportion of the gas supplied to the process chamber is exhausted from the process chamber, together with solid and gaseous by-products from the process occurring within the chamber. A process tool typically has a plurality of process chambers, each 30 of which may be at respectively different stages in a deposition, etching or cleaning process. Therefore, during processing a waste effluent stream formed from a combination of the gases exhausted from the chambers may have various different compositions. Before the waste stream is vented into the atmosphere, it is treated to remove 5 selected gases and solid particles therefrom using the abatement apparatus. Acid gases such as HF and HCI are commonly removed from a gas stream using a packed tower scrubber, in which the acid gases are taken into solution by a scrubbing liquid flowing through the scrubber. Silane is pyrophoric, and so before the waste stream is conveyed through the scrubber it is common practice for the 10 waste stream to be conveyed through a thermal incinerator or abatement chamber to react silane or other pyrophoric gas present within the waste stream with air. Any perfluorocompounds such as NF3 may also be converted into HF within the abatement chamber. 15 When silane burns, large amounts of silica (SiO2) particles are generated. Other compounds also produce particles when exposed to heat. Whilst many of these particles may be taken into suspension by the scrubbing liquid within the packed tower scrubber, it has been observed that the capture of relatively smaller particles (for example, having a size less than 1 micron) by the scrubbing liquid is 20 relatively poor. Although such apparatus provides for treatment of the effluent gas stream, they have a number of shortcomings. Accordingly, it is desired to provide an improved abatement apparatus. 25 SUMMARY According to a first aspect, there is provided a packed tower for treating an abated effluent stream comprising a gas mixture and combustion particles from an abatement apparatus configured to abate an effluent stream from a 30 semiconductor processing tool, the packed tower comprising: a packed tower housing having an inlet for receiving the abated effluent stream; an outlet for venting the abated effluent stream; a packed substrate housed within the packed tower housing between the inlet and the outlet, the packed substrate being configured to entrain at least some of the combustion particles from the gas mixture as the abated effluent stream flows therethrough; and a sonic transducer configured to generate acoustic waves to cause interaction with the combustion 5 particles to assist in entraining at least some of the combustion particles from the gas mixture. The first aspect recognizes that a problem with existing techniques to reduce combustion particles in the effluent stream is that they can be inefficient and can require the use of high volumes of gases to assist in the removal of those combustion particles, which can increase the gas load on the packed tower 10 and downstream components. Accordingly, a packed tower is provided. The packed tower may be for treating or processing an abated effluent stream. The abated effluent stream may comprise a gas mixture typically including a number of compounds together with 15 combustion particles or particulates produced by an abatement apparatus which is configured to abate an effluent stream from a semiconductor processing tool. The packed tower may comprise a pack tower housing or chamber. The packed tower housing may have or define an inlet which receives the abated effluent stream. The packed tower housing may have or define an outlet which vents or 20 exhausts the abated effluent stream. The packed tower housing may have a packed substrate housed or located within the packed tower housing. The packed tower substrate may be housed between the inlet and the outlet. The packed substrate may be configured or arranged to entrain or trap some of the combustion particles as they flow through the packed substrate. The packed 25 tower housing may have a sonic transducer. The sonic transducer may be configured or arranged to generate or produce acoustic or pressure waves. The acoustic waves may cause an interaction with the combustion particles. That interaction may assist in entraining or trapping at least some of the combustion particles within the gas mixture. In this way, acoustic or pressure waves may be 30 utilized to help entrain some of the combustion particles within the abated effluent stream to help improve the removal of those combustion particles without substantially increasing the gas load on the packed tower and its downstream components. The sonic transducer may comprise one of an internal and an external ultrasonic 5 transducer configured to generate droplets to entrain at least some of the combustion particles from the gas mixture. Using a sonic transducer to generate or produce droplets helps to entrain or trap some of the combustion particles without resulting in a substantial increase in the gas load that may otherwise occur from using conventional atomizers utilizing a gas to produce the droplets. 10 The internal sonic transducer may comprise at least one ultrasonic transducer positioned in a fluid held in a fluid bath positioned within the packed tower housing and configured to generate the droplets from the fluid. Placing the ultrasonic transducer in a fluid in a bath helps the transducer to generate the 15 droplets. The at least one transducer may be is submerged in the fluid. Submerging or immersing helps to protect the ultrasonic transducer from corrosive or adhesive particles within the abated effluent stream. 20 The internal sonic transducer may comprise a plurality of ultrasonic transducers each positioned in a fluid held in a fluid bath positioned around the packed tower housing. Utilizing multiple transducers positioned around the packed tower housing improves the distribution of the droplets and improves the effectiveness 25 of entraining the combustion particles. The internal sonic transducer may comprise a plurality of ultrasonic transducers each positioned in a fluid held in a fluid bath distributed circumferentially around the packed tower housing. 30 The plurality of ultrasonic transducers may be each distributed circumferentially in a fluid held in an annular fluid bath extending around the packed tower housing. The external sonic transducer may comprise at least one ultrasonic transducer positioned in a fluid held in a fluid bath positioned outside of the packed tower housing and configured to generate the droplets from the fluid, the packed tower 5 housing comprising a droplet inlet configure to convey the droplets from the external sonic transducer to within the packed tower housing. Hence, the droplets may be generated by an external ultrasonic transducer and those droplets conveyed into the packed tower housing. 10 The packed tower housing may comprise a flow diverter configured to divert a flow of at least one of the droplets and the abated effluent stream to mix the droplets and the combustion particles. Hence, the flow diverter may alter the flow direction of the droplets and / or the abated effluent stream to improve mixing and enhance entrainment. 15 The flow diverter may comprise a baffle configured and positioned to mix the droplets and the combustion particles. Hence, a baffle or plate may be shaped and / or positioned to cause the droplets and combustion particles to mix. 20 The flow diverter may comprise a gas flow configured to mix the droplets and the combustion particles. Hence, a flow or stream of gas may be arranged to cause the droplets and the combustion particles to mix to improve entrainment. The gas flow may comprise a gas curtain. 25 The gas flow may comprise an annular gas curtain configured to impart an inward radial flow component to the droplets. This helps to concentrate the droplets towards the centre of the packed tower housing to improve the likelihood of entrainment. 30 The packed tower may comprise a driver configured to drive each ultrasonic transducer to generate the droplets with a selected size. Accordingly, the signals provided by the driver may cause each ultrasonic transducer to generate droplets with an associated selected, configured or chosen size. The driver may be configured to drive each ultrasonic transducer to generate the 5 droplets with a selected distribution of sizes. Accordingly, the signals provided by the driver may cause each ultrasonic transducer to generate the droplets with a particular distribution of sizes. The driver may be configured to drive each ultrasonic transducer to generate the 10 droplets with a varying distribution of sizes. Accordingly, the signals provided to each ultrasonic transducer may generate the droplets with differing or varying distributions of sizes. The driver may be configured to drive each ultrasonic transducer to generate the 15 droplets with the varying distribution of sizes based on at least one of anticipated and measured size of the combustion particles. The anticipated size may be determined from signals provided from upstream equipment such as the semiconductor processing tool or abatement apparatus, based on pre-program sizes and / or on measured sizes provided by a suitable particle size measurement 20 device. The driver may be configured to drive each ultrasonic transducer to generate the droplets with a size distribution which overlaps a particle size distribution of the combustion particles. Accordingly, the size distribution of the droplets may be 25 selected to at least partially overlap with the size distribution of the combustion particles to improve entrainment. The driver may be configured to drive each ultrasonic transducer to generate the droplets with a size distribution which matches a particle size distribution of the 30 combustion particles. Typically, the closer the match between the droplets and the combustion particles, the greater the entrainment efficiency becomes. The driver may be configured to drive each ultrasonic transducer to generate the droplets which have a droplet size which is up to 200 times and preferably up to 20 times the particle size of the combustion particles. 5 The driver may be configured to drive each ultrasonic transducer to generate the droplets with a differing droplet size distribution from each ultrasonic transducer. Accordingly, the ultrasonic transducers may generate different droplet size distributions in order to obtain the required overall droplet size distribution. io The internal ultrasonic transducer and / or the droplet inlet may be located upstream of the packed substrate. The sonic transducer may comprise a sonic transducer array configured to generate an acoustic field to displace at least entrained combustion particles. 15 Accordingly, the sonic transducer array may generate an acoustic field or pressure waves which displace or move entrained combustion particles, the droplets and / or the combustion particles. The acoustic field may be configured to concentrate at least entrained 20 combustion particles into a convergence zone for agglomeration. Accordingly, the entrained combustion particles, the droplets and / or the combustion particles may be moved together or closer into the convergence zone to improve the rate of agglomeration or combination to help increase mass to fall out of the abated effluent stream flow. 25 The acoustic field may be configured to displace at least entrained combustion particles radially into a convergence zone for agglomeration. Hence, the acoustic field may be an annular acoustic field which moves entrained combustion particles, the droplets and / or the combustion particles towards a central axis of 30 the packed tower. The convergence zone may be positioned centrally in the packed tower housing. The sonic transducer array may comprise at least a pair of opposing sonic transducers. 5 The sonic transducer array may comprise at least a plurality of pairs of opposing sonic transducers distributed circumferentially around the packed tower housing. Positioning the pairs of sonic transducers around the packed tower housing helps to improve the distribution and performance of the acoustic field. 10 The packed tower may comprise a driver configured to drive each sonic transducer to generate an acoustic field to displace entrained combustion particles having a selected size. The driver may be configured to drive each sonic transducer to generate the 15 acoustic field to displace entrained combustion particles having a selected distribution of sizes. The driver may be configured to drive each sonic transducer to generate the acoustic field to displace entrained combustion particles having a varying 20 distribution of sizes. The driver may be configured to drive each sonic transducer to generate the acoustic field to displace entrained combustion particles having the varying distribution of sizes based on at least one of anticipated and measured size of the 25 combustion particles. The driver may be configured to drive each ultrasonic transducer to generate the acoustic field to displace entrained combustion particles having a differing size distribution. 30 The sonic transducer may be located downstream of the packed substrate. According to a second aspect, there is provided a method of treating an abated effluent stream comprising a gas mixture and combustion particles from an abatement apparatus configured to abate an effluent stream from a semiconductor processing tool, comprising: receiving the abated effluent stream 5 at an inlet of a packed tower having an outlet for venting the abated effluent stream and a packed substrate housed within the packed tower housing between the inlet and the outlet; entraining at least some of the combustion particles from the gas mixture as the abated effluent stream flows therethrough; and generating acoustic waves with a sonic transducer to cause interaction with the combustion 10 particles to assist in entraining at least some of the combustion particles from the gas mixture. The method may comprise generating droplets to entrain at least some of the combustion particles from the gas mixture with one of an internal and an external 15 ultrasonic transducer. The method may comprise positioning at least one internal sonic transducer in a fluid held in a fluid bath positioned within the packed tower housing to generate the droplets from the fluid. 20 The method may comprise submerging the at least one ultrasonic transducer in the fluid. The internal sonic transducer may comprise a plurality of ultrasonic transducers 25 and the method may comprise positioning the plurality of ultrasonic transducers in a fluid held in a fluid bath positioned around the packed tower housing. The internal sonic transducer may comprise a plurality of ultrasonic transducers and the method may comprise positioning each of the plurality of ultrasonic 30 transducers in a fluid held in a fluid bath distributed circumferentially around the packed tower housing. The method may comprise distributing each of the plurality of ultrasonic transducers circumferentially in a fluid held in an annular fluid bath extending around the packed tower housing. 5 The external sonic transducer may comprise at least one ultrasonic transducer and the packed tower housing may comprise a droplet inlet, the method may comprise positioning the at least one ultrasonic transducer in a fluid held in a fluid bath positioned outside of the packed tower housing to generate the droplets from the fluid and conveying the droplets from the external sonic transducer 10 through the droplet inlet to within the packed tower housing. The method may comprise diverting flow of at least one of the droplets and the abated effluent stream with a flow diverter to mix the droplets and the combustion particles. 15 The flow diverter may comprise a baffle and the method may comprise mixing the droplets and the combustion particles with the baffle. The flow diverter may comprise a gas flow and the method may comprise mixing 20 the droplets and the combustion particles with the gas flow. The gas flow may comprise a gas curtain. The gas flow may comprise an annular gas curtain and the method may comprise 25 imparting an inward radial flow component to the droplets with the annular gas curtain. The method may comprise driving each ultrasonic transducer with a driver to generate the droplets with a selected size. 30 The method may comprise driving each ultrasonic transducer with the driver to generate the droplets with a selected distribution of sizes. The method may comprise driving each ultrasonic transducer with the driver to generate the droplets with a varying distribution of sizes. 5 The method may comprise driving each ultrasonic transducer with the driver generate the droplets with the varying distribution of sizes based on at least one of anticipated and measured size of the combustion particles. The method may comprise driving each ultrasonic transducer with the driver to 10 generate the droplets with a size distribution which overlaps a particle size distribution of the combustion particles. The method may comprise driving each ultrasonic transducer with the driver to generate the droplets with a size distribution which matches a particle size 15 distribution of the combustion particles. The method may comprise driving each ultrasonic transducer with the driver to generate the droplets which have a droplet size which is up to 200 times and preferably up to 20 times the particle size of the combustion particles. 20 The method may comprise driving each ultrasonic transducer with the driver to generate the droplets with a differing droplet size distribution from each ultrasonic transducer. 25 The method may comprise locating at least one of the internal ultrasonic transducer and the droplet inlet upstream of the packed substrate. The sonic transducer may comprise a sonic transducer array and the method may comprise generating an acoustic field with the sonic transducer array to 30 displace entrained combustion particles. The method may comprise configuring the acoustic field to concentrate at least entrained combustion particles into a convergence zone for agglomeration. The method may comprise configuring the acoustic field to displace at least 5 entrained combustion particles radially into a convergence zone for agglomeration. The method may comprise positioning the convergence zone centrally in the packed tower housing. 10 The sonic transducer array may comprise at least a pair of opposing sonic transducers. The sonic transducer array may comprise at least a plurality of pairs of opposing 15 sonic transducers and the method may comprise distributing the at least a plurality of pairs of opposing sonic transducers circumferentially around the packed tower housing. The method may comprise driving each sonic transducer with a driver to 20 generate an acoustic field to displace at least entrained combustion particles having a selected size. The method may comprise driving each sonic transducer with a driver to generate the acoustic field to displace at least entrained combustion particles 25 having a selected distribution of sizes. The method may comprise driving each sonic transducer with a driver to generate the acoustic field to displace at least entrained combustion particles having a varying distribution of sizes. 30 The method may comprise driving each sonic transducer with a driver to generate the acoustic field to displace at least entrained combustion particles having the varying distribution of sizes based on at least one of anticipated and measured size of the combustion particles. The method may comprise driving each sonic transducer with a driver to 5 generate the acoustic field to displace at least entrained combustion particles having a differing size distribution. The method may comprise locating the sonic transducer downstream of the packed substrate. 10 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. 15 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. 20 BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1a illustrates schematically a portion of a packed tower according to one embodiment; 25 Figure 1 b illustrates schematically a portion of a packed tower according to one embodiment; and Figure 2 illustrates schematically a portion of a packed tower according to one embodiment. 30 DESCRIPTION OF THE EMBODIMENTS Before discussing the embodiments in any more detail, first an overview will be provided. Some embodiments provide an arrangement which utilizes acoustic waves to assist in capturing particulates within an effluent or waste stream. Those acoustic or pressure waves may be used to generate fluid particles or droplets which then adhere or combine with the particulates and / or displace the particulates (whether entrained or not) to help capture the particulates from the 5 effluent stream. The droplets when attached with particulate improve the likelihood of the particulate being trapped on walls or media within the packed tower, agglomerating with other droplets (with or with particulates) and / or falling out of suspension within the effluent stream flow. The displacement using the acoustic waves helps to move or concentrate droplets and / or particulates 10 together in order to help improve the likelihood of the particulate being trapped. The use of acoustic waves to generate droplets and the use of acoustic waves for displacement may be performed individually or together. Packed Tower - 1st Arrangement 15 Figure 1 a illustrates schematically a portion of a packed tower 10a according to one embodiment. The packed tower 10a has a packed tower housing 20a shown partially in Figure 1a. In this embodiment, the packed tower housing 20a is cylindrical, but it will be appreciated that other shapes are possible. Arranged circumferentially around an inner surface of the packed tower housing 20a is a 20 fluid bath 30a. In this embodiment, the fluid bath 30a is formed as an annular trough extending circumferentially around the packed tower housing 20a. The fluid bath 30a contains a fluid 40 (typically water) and a number of ultrasonic transducers 50a. In this example, the ultrasonic transducers 50a are uniformly distributed around the fluid bath 30a. However, this need not be the case and 25 fewer or more ultrasonic transducers 50a may be provided, which may be grouped or located irregularly or in other positions within the fluid bath 30a other than that shown. A controller 60 is provided which drives each of the ultrasonic transducers 50a with an electrical signal. Coupled with the fluid bath 30a is a fluid source 70a which provides the fluid 40 to the fluid bath 30a. Positioned 30 above the fluid bath 30a are one or more gas sources 80a which direct a stream, a plurality of streams and / or a curtain of gas 90a into the packed tower housing 20a. Typically, the arrangement shown in Figure 1a is located in a lower part of the packed tower housing 20a, below any media. However, this need not be the case and the arrangement shown in Figure 1a may located in an upper part of the packed tower housing 20a, above any media. 5 In operation, an effluent stream 100 containing gases and combustion particles or particulates is introduced into the packed tower housing 20a. The effluent stream 100 flows through the packed tower housing 20a past the fluid bath 30a. Fluid 40 is provided by the fluid source 70a to substantially fill the fluid bath 30a and typically submerge the ultrasonic transducers 50a. The controller 60 generates io electrical signals to power the ultrasonic transducers 50a which generate droplets 110. The droplets 110 interact with the effluent stream 100. This interaction is assisted by the flow of the gas 90a provided by the gas source 80a. The droplets 110 entrain combustion particles within the effluent stream 100. Some of the droplets with entrained combustion particles will agglomerate until they fall out of 15 the flow of the effluent stream 100 under gravity into a sump 120. Others travel with the effluent stream 100 and may become trapped by packed media (not shown) within the packed tower housing 20a, downstream of the fluid bath 30a. Packed Tower - 2nd Arrangement 20 Figure 1 b illustrates schematically a packed tower 10b according to one embodiment. This arrangement is similar to that described above with reference to Figure 1a, but has an alternative approach for the generation of the droplets. In this embodiment, the fluid bath 30a is omitted and instead droplets are generated externally and provided to the interior of the packed tower housing 25 20b. In particular, droplets 110a are generated typically using an external ultrasonic transducer (not shown) positioned outside the packed tower housing 20b and conveyed via a droplet source 130a into the packed tower housing 20b. A flow diverter 140a is provided which alters the flow of the droplets 110a exiting the droplet source 130a. Likewise, droplets 110b are generated using an 30 ultrasonic transducer (not shown) located outside the packed tower housing 20b and are provided to the droplet source 130b which also has a flow diverter 140b which diverts the flow of the droplets 110b exiting the droplet source 130b. Although two droplet sources 130a, 130b are shown, it will be appreciated that fewer or more droplet sources may be provided, either distributed around or grouped around the housing 20b to provide sources or annular curtains of droplets. Typically, the arrangement shown in Figure 1b is located in a lower part 5 of the packed tower housing 20b, below any media. However, this need not be the case and the arrangement shown in Figure 1 b may located in an upper part of the packed tower housing 20b, above any media. In operation, an effluent stream 100 containing gases and combustion particles or io particulates is introduced into the packed tower housing 20b. The effluent stream 100 flows through the packed tower housing 20b past the droplet sources 130a, 130b. Droplets 110a are generated and conveyed by the droplet source 130a into the interior of the housing 20b. The flow diverter 140a diverts the flow of the droplets 110a exiting the droplet source 130a to flow generally radially inward 15 towards the centre of the housing 20b to interact with the flow of the effluent stream 100. Likewise, droplets 110b are generated and conveyed by the droplet source 130b into the interior of the housing 20b. The flow diverter 140b diverts the flow of the droplets 110b exiting the droplet source 130b to flow generally radially inward towards the centre of the housing 20b to interact with the flow of 20 the effluent stream 100. The droplets 110a, 110b entrain combustion particles within the effluent stream 100. Some of the droplets with entrained combustion particles will agglomerate until they fall out of the flow of the effluent stream 100 under gravity into a sump 120. Others travel with the effluent stream 100 and may become trapped by packed media (not shown) within the packed tower 25 housing 20b, downstream of the droplet sources 130a, 130b. The droplets 110 produced by the transducers 50a and the droplets 110a, 110b conveyed by the droplet sources 130a, 130b are typically sized based on the predicted or measured size and / or distribution of sizes of particulates in the 30 effluent stream 100. Different ultrasonic transducers 50a may produce different sized droplets and / or different distribution of sized droplets to entrain those particulates. Likewise, the size and / or distribution of sizes of droplets supplied to the droplet sources 130a, 130b may be generated based on the predicted or measured sizes and / or distribution of sizes of particulates in the effluent stream 100. Typically, those sizes are selected to match or overlap the sizes and / or distribution of sizes of particulates in the effluent stream 100. 5 Packed Tower - 3rd Arrangement Figure 2 illustrates schematically a portion of a packed tower 10c according to one embodiment. The packed tower 10c has a packed tower housing 20c. Typically located upstream of the packed tower substrate (not shown) are located io a pair or more of sonic transducers 50b. The sonic transducers 50b are typically located on an inner wall of the packed tower housing 20c. Typically, the sonic transducers 50b are orientated to face radially inwards towards a central region of the packed tower housing 20c. Although one pair of sonic transducers 50b are shown, it will be appreciated that further pairs (or single) sonic transducers 50b 15 may be provided. Also, the sonic transducers 50b need not be uniformly distributed, but may be grouped or located to provide an acoustic field or pressure waves to provide the required displacement. In operation, the effluent stream 100 together with any droplets and any 20 particulates entrained by droplets flows past the sonic transducers 50b. The controller 60 generates signals which generate an acoustic field or pressure waves having a frequency selected to displace those materials towards the centre of the packed tower housing 20c. The frequency of the acoustic field or pressure waves is selected based on predicted or measured sizes or sized 25 distribution of those materials. This concentration towards the centre of the packed tower housing helps to increase the probability of particles agglomerating or combining. As the mass of those agglomerated particles increases, they fall out of the flow of the effluent stream back down through the packed tower. 30 Hence, some embodiments provide a combined method of atomising water into vapour for use of entraining particulate in the vapour stream and then using acoustic wave generation to re-combine manipulate and direct the vapour / particulate mix into larger droplets, which fall due to gravity (and their increased combined mass) into a water stream for wet scrubbing. This approach replaces high air / N? requirements of standard mechanical 5 atomising devices and to increase the entrained particulate using more reliable vapour size generation methods and to allow more of this particulate to enter the water stream for wet scrubbing. Some embodiments use acoustic waves acting upon vapour and particulate, to 10 allow for recombination and agglomeration of vapour and particulates, for easier filtering and scrubbing in further water processes. This provides for smaller atomised vapour size than mechanical nozzle atomisers, which should increase entrainment of particulate from gasses; massively reduced nitrogen / CDA flow (from 200 slm to 20); smaller particulate entrainment size; aerosol size tuning for 15 specific particulate sizes (i.e. different processes); greater particulate transfer into the water stream for wet scrubbing; lower cost and higher reliability, due to consistent atomisation; and / or reduced moisture carry-over, due to forced vapour coalescence (gravity drop) in the second stage. Some embodiments provide for dual or single stage acoustic particulate entrainment and manipulation. During 20 the process of abatement, the gas stream flows from Inlet, through to the burner and out through the packed-tower and exhaust. During the abatement high temperature destruction phase, varying size of particulate is generated in the exhaust gas stream. A typically two-stage atomisation technique is designed to more efficiently and more effectively entrain this particulate and transfer to the 25 water stream. Stage 1: Water vapour generation - Ultrasonic atomisers generate the water vapour. This is achieved using multiple Piezo-electric (or other type of) transducers in a clean-water bath. The high frequency vibrations (in the range of, but not exclusively 1-3 MHz band) of the transducers below the surface, agitates the water causing fine surface vapour / mist. This water vapour is ‘pushed’ into the 30 gas stream using a ‘curtain’ of inert gas (usually nitrogen). The vapour contacts with the particulate in the gas stream and entrains the particulate in the vapour droplet. The combined particulate and water droplet will continue upwards as long as its mass is not sufficient to overcome the upward gas flow. As the water droplets coalesce and agglomerate into the gas stream, their mass becomes high enough to counter the upward gas flow and they fall back down through the gas stream due to gravity and into a tank or bund, this tank would likely be water filled 5 and a mechanism of draining / filtering may be used. Stage 2: Recombination stage - Should the water droplets not coalesce and increase their mass sufficiently to overcome the upward force of the gas stream, a second stage can be used to assist in the coalescence of the water droplets. This second stage consists of targeted sonic or ultrasonic waves, at such a frequency to impart io kinetically energy upon the droplets, such that they are forced together towards the centre of the vessel and into coalescence. Stages 1 &2 could be used interchangeably and independently as required. Multiple stages may be used independently, or together. Differing types of acoustic wave generation is possible. Acoustic levitation is used to recombine vapour, atomised spray and 15 particulate in specific way to manipulate agglomeration or ‘forced’ direction of vapour. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the 20 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 Packed tower 10a; 10b; 10c Housing 20a; 20b; 20c 5 Fluid bath 30a Fluid 40 Ultrasonic transducers 50a; 50b Controller 60 Fluid source 70a io Gas sources 80a Gas 90a Effluent stream 100 Droplets 110; 110a; 110b Sump 120 15 Droplet source 130a; 130b Flow diverter 140a; 140b

Claims

1. A packed tower for treating an abated effluent stream comprising a gas mixture and combustion particles from an abatement apparatus configured to5 abate an effluent stream from a semiconductor processing tool, said packed tower comprising:a packed tower housing havingan inlet for receiving said abated effluent stream;an outlet for venting said abated effluent stream;io a packed substrate housed within said packed tower housingbetween said inlet and said outlet, said packed substrate being configured to entrain at least some of said combustion particles from said gas mixture as said abated effluent stream flows therethrough; anda sonic transducer configured to generate acoustic waves to cause15 interaction with said combustion particles to assist in entraining at leastsome of said combustion particles from said gas mixture.

2. The packed tower of claim 1, wherein said sonic transducer comprises at least one of an internal and an external ultrasonic transducer configured to20 generate droplets to entrain at least some of said combustion particles from said gas mixture.

3. The packed tower of claim 2, wherein said internal sonic transducer comprises at least one ultrasonic transducer positioned in a fluid held in a fluid25 bath positioned within said packed tower housing and configured to generate said droplets from said fluid and preferably wherein said at least one ultrasonic transducer is submerged in said fluid.

4. The packed tower of claim 2 or 3, wherein said internal sonic transducer30 comprises at least one of:a plurality of ultrasonic transducers each positioned in a fluid held in a fluid bath positioned around said packed tower housing; anda plurality of ultrasonic transducers each positioned in a fluid held in a fluid bath distributed circumferentially around said packed tower housing, and preferably wherein said plurality of ultrasonic transducers are each distributed circumferentially in a fluid held in an annular fluid bath extending around said5 packed tower housing.

5. The packed tower of claim 2, wherein said external sonic transducer comprises at least one ultrasonic transducer positioned in a fluid held in a fluid bath positioned outside of said packed tower housing and configured to generate io said droplets from said fluid, said packed tower housing comprising a droplet inlet configure to convey said droplets from said external sonic transducer to within said packed tower housing.

6. The packed tower of any preceding claim, comprising a flow diverter15 configured to divert flow of at least one of said droplets and said abated effluent stream to mix said droplets and said combustion particles.

7. The packed tower of claim 6, wherein said flow diverter comprises at least one of:20 a baffle configured and positioned to mix said droplets and saidcombustion particles; anda gas flow configured to mix said droplets and said combustion particles, and preferably wherein said gas flow comprises at least one of:a gas curtain; and25 an annular gas curtain configured to impart an inward radial flowcomponent to said droplets.

8. The packed tower of any preceding claim, comprising a driver configured to at least one of:30 drive each ultrasonic transducer to generate said droplets with a selectedsize;drive each ultrasonic transducer to generate said droplets with a selected distribution of sizes;drive each ultrasonic transducer to generate said droplets with a varying distribution of sizes;5 drive each ultrasonic transducer to generate said droplets with saidvarying distribution of sizes based on at least one of anticipated and measured size of said combustion particles;drive each ultrasonic transducer to generate said droplets with a size distribution which overlaps a particle size distribution of said combustion10 particles;drive each ultrasonic transducer to generate said droplets with a size distribution which matches a particle size distribution of said combustion particles;drive each ultrasonic transducer to generate said droplets which have a15 droplet size which is up to 200 times and preferably up to 20 times said particle size of said combustion particles; anddrive each ultrasonic transducer to generate said droplets with a differing droplet size distribution from each ultrasonic transducer.20 9. The packed tower of any one of claims 2 to 8, wherein at least one of saidinternal ultrasonic transducer and said droplet inlet is located upstream of said packed substrate.

10. The packed tower of any preceding claim, wherein said sonic transducer25 comprises a sonic transducer array configured to generate an acoustic field to displace at least entrained combustion particles.

11. The packed tower of claim 10, wherein said acoustic field is at least one of:30 configured to concentrate at least entrained combustion particles into aconvergence zone for agglomeration; andconfigured to displace at least entrained combustion particles radially intoa convergence zone for agglomeration.

12. The packed tower of claim 11, wherein said convergence zone is5 positioned centrally in said packed tower housing.

13. The packed tower of claim 10, wherein said sonic transducer array comprises at least one of:at least a pair of opposing sonic transducers; andio at least a plurality of pairs of opposing sonic transducers distributedcircumferentially around said packed tower housing.

14. The packed tower of claim 10, comprising a driver configured to at least one of:15 drive each sonic transducer to generate an acoustic field to displaceentrained combustion particles having a selected size;drive each sonic transducer to generate said acoustic field to displace entrained combustion particles having a selected distribution of sizes;drive each sonic transducer to generate said acoustic field to displace20 entrained combustion particles having a varying distribution of sizes;drive each sonic transducer to generate said acoustic field to displace entrained combustion particles having said varying distribution of sizes based on at least one of anticipated and measured size of said combustion particles; anddrive each ultrasonic transducer to generate said acoustic field to displace 25 entrained combustion particles having a differing size distribution.

15. The packed tower of any preceding claim, wherein said sonic transducer is located downstream of said packed substrate.30 16. A method of treating an abated effluent stream comprising a gas mixtureand combustion particles from an abatement apparatus configured to abate an effluent stream from a semiconductor processing tool, comprising:receiving said abated effluent stream at an inlet of a packed tower having an outlet for venting said abated effluent stream and a packed substrate housed within said packed tower housing between said inlet and said outlet;entraining at least some of said combustion particles from said gas mixture5 as said abated effluent stream flows therethrough; andgenerating acoustic waves with a sonic transducer to cause interaction with said combustion particles to assist in entraining at least some of said combustion particles from said gas mixture.

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