GB2399871A - Device using sound waves to inhibit deposition of particulates on, or remove them from, surfaces - Google Patents

Abstract

The device comprises a sound wave generator and means to direct the waves towards a surface, in the embodiment this being a passage 18, at one end of which is located the sound wave generator 16, and at the other end of which is a diaphragm 22. The passage 18 is filled with a so-called driver gas such as nitrogen, to transmit the sound waves. The intended sue is to inhibit the deposition of particulates on ducting 28 such as the inlet duct of an abatement apparatus in a semi-conductor production process, the duct containing a process gas. The diaphragm 22 is impervious to the driver gas and thus prevents its admixture with the process gas, but transmits the sonic waves into the duct. The diaphragm may be of PTFE. The sound waves may be generated electronically, preferably by a piezo-crystal, or they may be generated pneumatically.

Description

239987 1

INHIBITING OR REMOVING DEPOSITION OF PARTICULATES

The present invention relates to a device and method for inhibiting particulates being deposited on a surface and/or removing particulates deposited on said surface and, particularly but not exclusively, for cleaning a surface in a semiconductor processing system such as the interior surface of an inlet duct of an abatement system for process gases in a semiconductor processing system.

Hazardous process gases may be exhausted from chemical and particularly semiconductor processing systems, and an abatement system is required to treat such hazardous gases. The semiconductor process gases may include flammable, highly toxic, and, in some cases, pyrophoric gases. Examples of hazardous gases that might be encountered include arsine, nitrogen trifluoride, boron trifluoride and boron bichloride. When exhaust gases enter the inlet duct of an abatement system, there is a tendency for them to cause particulates to deposit on the inside of the duct. In a wet scrubber abatement system, the duct is usually moist and cool during operation, and gases passing through the inlet may be caused to condense or to react in the moist environment to cause particulate deposits which decrease flow in the duct within days and in some cases within hours, and reduce efficiency.

The deposits can be removed by stopping the system and manually cleaning the duct but this cleaning method results in unacceptable down times and increased costs. Alternatively, jets of water and nitrogen can be used to prevent particulate build up but the cost of such an alternative may be unattractive, particularly in view 2 M03B1 01/ASB of the relatively high consumption of nitrogen. In the prior art system, nitrogen passes into the abatement system and it is not generally practical to recover the nitrogen. Also, in some circumstances, the presence of nitrogen can affect the efficiency of the abatement system.

It is desirable to provide an improved solution to the above discussed problem.

The present invention provides a device comprising: a sound wave generator for generating sound waves; and means for conveying the waves towards particulate matter to inhibit deposition of particulates on a surface and/or towards the surface in order to remove particulates deposited thereon.

The wave generator may be pneumatically driven, for example using a pneumatic transducer. In such a case the waves may be generated in a driver gas. They may be directed along a passage through a diaphragm towards the surface. The diaphragm may substantially transmit sonic waves and may be substantially impervious to the driver gas and a process gas which carries particulate matter.

This diaphragm may be made of polytetrafluoroethylene.

Alternatively, the wave generator may be electrically driven, perhaps by using a piezo-crystal.

The device may be used in a semiconductor processing system, where the device may be arranged to inhibit the deposition of particulates on a surface of an inlet duct 3 M03B101/ASB of an abatement apparatus. Alternatively, it may be arranged to remove particulates that have been deposited on this surface. The frequency of the sound waves generated, may be selected in accordance with a semiconductor process gas being used in the processing system.

The present invention also provides a method of inhibiting deposition of particulates on a surface and/or removing particulates deposited on the surface, the method comprising: generating sound waves and conveying the sound waves towards the surface to remove particulates deposited thereon and/or towards the particulate matter to inhibit deposition thereof on the surface.

The waves generated may be in the frequency range 1 6Hz to 1 MHz. They may be in the audiosonic range (1 6Hz to 20kHz) or they may be in the ultrasonic range (20kHz to 1 MHz). The waves may be of a variable wave form that sweeps across a range of frequencies in order to target multiple size and composition of particles.

In order that the present invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying figures in which Figure 1 is a schematic view of the first embodiment shown in use; Figure 2 is a schematic view of the second embodiment, shown in use; and Figure 3 is a schematic view of either embodiment used to inhibit transportation of particles with the predominant gas flow.

4 M03B1 01/ASB Figure 1 shows an inlet duct 10 of an abatement apparatus in a semiconductor processing system. In a wet scrubber abatement system, gases may be caused to react or to condense in the moist cool environment and particulate deposits may be formed on the interior surface 12 of the inlet duct. In this embodiment, a device 14, for removing particulates from the surface or preventing depositing, comprises a sound wave generator, here a pneumatic transducer, 16 which, when the device is in use, generates sound waves in a driver gas 17. Typical frequencies of these sound waves are in the audible range (1 6Hz to 20kHz). A passage 18 directs the sound waves 20 onto the surface 12 through a diaphragm 22. The passage 18 may additionally comprise a connection piece 19 which forms part of the inlet duct. The sound generator generates rapid pressure fluctuations in the driver gas and the passage directs these fluctuations towards the area to be cleaned. The generator may include a high grade titanium diaphragm which produces the sound wave.

Suitable sound generators are available from Primasonics_ and are well known in I the art.

The driver gas, which is commonly nitrogen, is supplied along a conduit 24 to the sound wave generator, and is exhausted through a port 26 in passage 18 and port 27 in the generator. Sound waves are caused to pass along passage 18 which usually takes the form of a horn, or bell, section that is designed to select the frequency of the sound waves in accordance with the type of particulates which it is desired to remove from surface 12. Typically, the sound waves generated by the generator are amplified by the horn section to produce a frequency of between 50Hz M03B101 /ASB and 350 Hz in the audiosonic range, although lower frequencies may be adopted in the infrasonic range of 11 Hz to 22Hz. A specific frequency is able to remove specific types of particulate more effectively than other frequencies.

When reactive process gases 28 pass through the inlet duct 10 they are isolated from the driver gas 17 and sound wave generator to prevent the hazardous and/or corrosive process gases from exiting the system through ports 26 and 27.

Accordingly, the diaphragm contains the process gas in the system. The diaphragm substantially transmits sound waves and is substantially impervious to process gases and driver gas. The material from which the diaphragm is made is selected so that the diaphragm is sufficiently flexible to allow the sound waves to pass therethrough but resistant to the passage of gases. Preferably, the diaphragm should also be substantially resistant to erosion by the process gases. Typical process gases which may be used in a semiconductor processing system include, without limitation: arsine, boron bichloride, boron trifluoride, diborane, carbon I tetrafluoride, hexafluoroethane, perfluoropropane, octofluorocyclobutane, methane, trifluoromethane, difluoromethane, fluoromethane, chlorine, chlorine trifluoride, carbon monoxide, fluorine, silane, tetraethylorthosilicate, tetrakisdimethylamido titanium, germane, hydrogen, hydrogen bromide, hydrogen chloride, hydrogen fluoride, nitrogen trifluoride, ammonia, nitrous oxide, oxygen, phosphine, sulphur hexafluoride, dichlorosilane, trichlorosilane, silicon tetrachlororide, hexachlorodisilane, silicon tetrafluoride, titanium tetrachloride, tungsten hexafluoride, bis(tert-butylamino)silane, and the diaphragm should be selected depending on which of these gases are to be used in a specific application. It has been found that 6 M03B101/ASB polytetrafluoroethene is a generally suitable material from which to fabricate the diaphragm because it is chemically inert and flexible. However, any other material which can withstand operating temperatures of about 150 degrees C, is chemically resistant and flexible may be adopted as appropriate. For instance, stainless steel would be suitable for some process gases.

The cleaning device can be operated to remove particulate deposits from surface 12 by causing the deposits to vibrate and lose adhesion to the surface, whereupon they are swept away in the stream of process gases. The frequency of the sound waves provides the correct number of debonding pressure fluctuations and the power provides the correct energy for each fluctuation. The correct frequency and power can be determined by experimentation. Sound waves may be applied to the surface when free of particulates, and the vibration prevents significant depositing from occurring. It has been found in practice that operating the sound generator for about six seconds per minute is suitable for cleaning the surface 12 of deposits. During those six seconds, particulates are inhibited from depositing because it is more difficult for them to adhere to the surface. Although the sound waves are specifically directed at the inlet duct, there is some propagation of the waves upstream and downstream of the duct so that particulates are inhibited from depositing and are removed from surrounding surfaces.

The noise created by the cleaning device may in certain circumstances be considered to be disadvantageous but it should be appreciated that the noise created in semiconductor processing systems is considerable in the first instance 7 M03B1 01/ASB and therefore any further noise is not thought to constitute a problem. Sound proofing can be used though if desired.

The footprint of the cleaning device is relatively small, being in the region of 50 cm in length. Accordingly, such a cleaning system is attractive in semiconductor processing systems in which conservation of space is important. Often a high pressure air line is already supplied to the equipment and since no additional power supply is required, a device according to this embodiment can readily be introduced into the apparatus.

Where space is even more limited but a power supply can be provided and the main controller of the apparatus can be modified, an alternative embodiment may be introduced. In this second embodiment, illustrated in Figure 2, the wave generator is electrically driven and is typically provided by implementing a piezo-crystal in the wave generator 30. Such a device generates a wave form by physically flexing in response to the electrical signal supplied to it. No diaphragm is required as the vibrations are driven through the housing unit of the device and passed directly into the duct 10. The housing of such a wave generator 30 is particularly compact as there is no need for the geometry of the horn to tune the frequency of the wave as in the first embodiment where the pneumatic transducer was implemented. With the piezo-crystal wave generator 30 the wave length generated is dependent on the frequency of the power supplied to the unit.

8 M03B1 01/ASB Using an electrically driven wave generator consequently allows greater flexibility in controlling the frequency of the waveform. It is desirable to be able to modify the frequency of the wave form in order to target particular sizes and types of particles as discussed above. The lower audible frequencies are appropriate for transmitting energy to solid particles such as dust but liquid particles such as droplets of water resonate in response to much higher frequency waveforms. By generating the sound waves electronically, higher frequencies can be achieved into the ultrasonic range (20kHz up to approximately 1 MHz).

Indeed, where particle of different magnitudes and types are present it is useful to generate a variable waveform that sweeps across a range of different frequencies.

Such a variable waveform can readily be generated by varying the characteristics of the power supplied to the wave form generator.

Furthermore, the device could be used as a filter, where it is desirable to only target particular types of particles, particular frequencies can be generated by the device thus allowing others to remain unaffected.

Figure 3 illustrates how sound waves may be directed against a gas flow stream 31, where the frequencies of the waves are intended to interact with particular types of particle, such that directional energy is transmitted to the individual particles such that their transportation with the gas flow can be inhibited. Such a feature may be used where it is desirable to inhibit passage of vapour and particulate matter down an extraction duct. If such matter were to pass down such ducting, the ambient 9 M03B1 01/ASB conditions will change and pooling may occur, such condensation and accumulation of particulate matter can cause damage to the ducting. Preferably, such liquid and particulate matter is redirected, by the application of particular frequency waves, towards a liquid drain where these materials can be disposed of safely.

When compared to prior art methods of cleaning, these embodiments provide a relatively low cost option. The consumption of nitrogen, even in the first embodiment is significantly less than that in the prior art system and it can be re- circulated. There are fewer maintenance requirements, and there are less components in the embodiments meaning that they can be assembled and disassembled more efficiently. In this way, the embodiments enable less down time of the system as a whole. Further, these devices can be retro- fitted into existing systems.

Although this invention has been described with reference to its use in cleaning an interior surface 12 of an inlet duct of an abatement apparatus, it can be used to clean any suitable surface in the system which is prone to particulates being undesirably deposited by a process gas.

In addition to semiconductor processing systems, the device can be used as part of other types of chemical processing systems in which there are surfaces prone to chemical particulates being deposited by a process gas and where isolation of the driver gas and sound wave generator from the process gas is important.

Claims (27)

to M03B1 01/ASB CLAIMS

1. A device comprising: a sound wave generator for generating sound waves; and means for conveying the waves towards particulate matter to inhibit deposition of particulates on a surface and/or towards the surface in order to remove particulates deposited thereon.

2. A device according to claim 1, wherein the wave generator is pneumatically driven.

3. A device according to claim 2, wherein the wave generator is a pneumatic transducer.

4. A device according to claim 2 or claim 3, wherein the waves are generated in a driver gas.

5. A device according to any of claims 2 to 4, wherein the conveying means comprises a passage for directing waves through a diaphragm towards the surface.

6. A device according to claim 5, wherein the diaphragm substantially transmits sound waves towards the surface.

7. A device according to claim 5 or 6, wherein the diaphragm is substantially impervious to the driver gas and a process gas carrying the particulate matter.

1 l M03B101/ASB

8. A device according to claim 5,6 or 7, wherein the diaphragm is made from polytetrafluoroethene.

9. A device according to claim 1, wherein the wave generator is electrically driven.

10. A device according to claim 9, wherein the wave generator comprises a piezo-crystal.

11. A semiconductor processing system comprising a device as claimed in any one of the preceding claims.

12. A system as claimed in claim 11, wherein the device is arranged to inhibit deposition of particulates on a surface of an inlet duct of an abatement apparatus and/or to remove particulates deposited on the surface.

13. A system as claimed in claim 11 or 12, wherein the frequency of the sound waves is selected in accordance with a semiconductor process gas being used.

14. A method of inhibiting deposition of particulates on a surface and/or removing particulates deposited on the surface, the method comprising: generating sound waves and conveying the sound waves towards the surface to remove particulates 12 M03B101/ASB deposited thereon and/or towards the particulate matter to inhibit deposition thereof on the surface.

15. A method according to claim 14, wherein the waves are generated electronically.

16. A method according to claim 15, wherein the waves are generated by a piezo- crystal.

17. A method according to claim 14, wherein the waves are generated pneumatically.

18. A method according to claim 17, wherein the waves are generated in and transmitted via a driver gas.

19. A method according to claim 17 or 18, wherein the waves are conveyed through a passage for directing waves through a diaphragm towards the surface.

20. A method according to claim 19, wherein the diaphragm substantially transmits sound waves.

21. A method according to claim 19 or 20, wherein the diaphragm is substantially impervious to driver gas and a process gas carrying the particulate matter.

13 M03B101/ASB

22. A method any of claims 19 to 21, wherein the diaphragm is made of polytetrafluoroethene.

23. A method as claimed in any of claims 14 to 22, wherein the surface is a surface of a duct in a semiconductor processing system.

24. A method as claimed in any of claims 14 to 23, wherein the waves are in the frequency 16 Hz to 1 MHz.

25. A method as claimed in any of claims 14 to 24, wherein the waves are in the frequency range 16 Hz to 20 kHz.

26. A method as claimed in any of claims 14 to 24, wherein the waves are in the frequency range 20 kHz to 1 MHz.

27. A method as claimed in any of claims 14 to 26, wherein the waves are of a variable waveform that sweeps across a range of frequencies.