Patent Application
20100074821
The present invention relates to apparatus for, and a method of, treating a gas stream.
Various different gases may be supplied to a process chamber during the formation of a semiconductor or flat panel display device within the chamber. In a chemical vapour deposition process, gases are supplied to a process chamber housing the substrate and react to form a thin film over the surface of the substrate. Chemical vapour deposition (CVD) is used to deposit thin films or layers on the surface of a substrate or wafer located in a deposition chamber. This process operates by supplying one or more reactive gases to the chamber, often using a carrier gas, to the substrate's surface under conditions that encourage chemical reactions to take place at the surface. For example, TEOS and one of oxygen and ozone may be supplied to the deposition chamber for the formation of a silicon oxide layer on the substrate, and silane and ammonia may be supplied for the formation of a silicon nitride layer. Polycrystalline silicon, or polysilicon, is deposited on the substrate by the decomposition of silane or a chlorosilane by heat.
Gases are also supplied to an etch chamber to perform selective etching of areas of the deposited layers, for example during the formation of electrodes and the source and drain regions of a semiconductor device. Etching gases can include the perfluorinated (PFC) gases such as CF4, C2F6, C3F8, and C4F8, although other etchants including hydrofluorocarbon gases, such as CHF3, C2HF5 and CH2F2, fluorine, NF3 and SF6. Such gases are commonly used to form an opening in a region of a nitride or oxide layer formed over a polysilicon layer and which is exposed by a photoresist layer. Argon is generally also conveyed to the chamber with the etching gas to provide a facilitating gas for the process being conducted in the etch chamber.
During such an etch process, the exhaust gas drawn from the etch chamber by a vacuum pump usually contains a residual amount of the gas supplied to the etch chamber, together with by-products from the etching process. The perfluorinated gases mentioned above are greenhouse gases, and so are particularly undesirable.
Historically, PFC gases such as CF4 are destructed by use of high temperature, and thus energy intensive, processes. For example a thermal processing unit (TPU), or a microwave plasma abatement unit can be used. Gas burners such as TPUs are expensive and not cost effective for low flows of CF4 whilst microwave plasma abatement units have a relatively low destruction efficiency for CF4 unless large, high-powered systems are used.
Both of these abatement units typically generate HF and COF2 from the reaction between the fluorocarbon gas and one of O2 and H2O. The HF and COF2 is subsequently removed from the gas stream using a water-based scrubber, wherein the HF is taken into aqueous solution. The aqueous HF is then conveyed from the scrubber to an acid drain, or more commonly to a fluoride treatment facility, where a compound such as calcium hydroxide is typically used to neutralise the aqueous HF and precipitate from the aqueous HF a “cake” or “sludge” containing CaF2. Such fluoride treatment facilities tend to be expensive, and are often capacity limited. Furthermore, disposal of the CaF2 cake also tends to be expensive.
It is an aim of at least the preferred embodiment of the invention to provide a relatively inexpensive and solid state apparatus for treating a gas stream containing PFC species.
In a first aspect, the present invention provides apparatus for treating a gas stream, the apparatus comprising:
The apparatus can thus provide an apparatus for treating a gas stream to remove a halogen-containing component, for example a fluorine-containing component such as a perfluorocompound (PFC), a hydrofluorocarbon compound (HFC), or a chlorofluorocarbon compound (CFC), which does not require a water-based abatement device for removing from the gas stream any acidic gases and by-products from the removal of this halogen-containing component of the gas stream. The use of a nonthermal plasma reactor to remove this component from the gas stream enables the apparatus to be operated at low power, and thus at a relatively low cost.
The silicon-containing solid may comprise silicon oxide, for example in the form of silica glass beads or a silica member, a mixture of silicon and silica beads, or a mixture of silicon beads with another dielectric material, for example alumina.
The plasma reactor may contain a catalyst material for promoting the reaction between the silicon-containing solid and the halogen-containing component of the gas stream. This catalyst preferably comprises a metal, which may be supported on an acidic metal oxide. Examples of a suitable metal include vanadium, molybdenum, palladium, iron, manganese, chromium, nickel, cobalt and tungsten, whilst examples of a suitable metal oxide include gamma-alumina, a zeolite, silica, zirconium oxide, titanium oxide, and TiO2—ZrO2.
The plasma reactor may comprise a dielectric barrier discharge (DBD) plasma reactor, a tandem packed bed plasma reactor, a combined plasma catalysis reactor or a glow discharge plasma reactor.
In the preferred embodiments, the plasma reactor comprises first and second electrodes, with the silicon-containing solid being located between the electrodes. The silicon-containing solid may be provided by a dielectric member located between the electrodes. For example, if the second electrode is in the form of a cylinder or mesh, or otherwise surrounds the first electrode, the dielectric member preferably comprising a tube located between the electrodes. The dielectric member is preferably formed from silicon oxide. An air gap may be provided between the outer surface of the dielectric member and the inner surface of the second electrode. This air gap may be optionally packed with beads or pellets, at least some of which may be formed from silicon-containing material, such as silicon or silicon oxide. As an alternative to providing a dielectric tube or other such member between the electrodes, the gap between the electrodes may be packed with beads or pellets, of which at least some are formed from silicon-containing material.
Depending on the nature of the halogen-containing component of the gas stream, a plurality of plasma reactors may be provided in series to increase the destruction and removal efficiency (DRE) of the apparatus. The apparatus preferably treats the gas stream substantially at atmospheric pressure, although the gas stream may be treated at a sub-atmospheric pressure.
The third reactor preferably comprises a sorbent bed of material selected to chemically react with the silicon halide. Examples of material that may be used include one of a hydroxide, a perborate, a bicarbonate, a percarbonate and a carbonate of one of sodium, calcium and magnesium. In the preferred embodiment, the bed of material comprises one of soda lime, washing soda (sodium carbonate), sodium bicarbonate, sodium percarbonate and sodium perborate. This can enable the third reactor to be operated at ambient temperature, and can enable an exhausted bed to be disposed of in an environmentally safe manner. Furthermore, in the event that the gas stream exhausted from the plasma reactor also contains HF and/or COF2, these species will also react with the aforementioned materials and so will be removed from the gas stream.
The first reactor may comprise a sorbent bed of material similar to that of the third reactor provided downstream from the plasma reactor. The use of washing soda as the solid material for the first reactor is preferred as it may react with acid gases within the gas stream to form species such as H2O and/or CO2, which may enhance the conversion efficiency of the plasma reactor.
In a second aspect, the present invention provides a method of treating a gas stream, the method comprising the steps of:
Features described above relating to apparatus aspects of the invention are equally applicable to method aspects, and vice versa.
Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which
With reference first to
The plasma etch reactor may be any suitable reactor for generating a plasma for etching the surface of a substrate located therein to a desired geometry. Examples include an inductively coupled plasma etch reactor, an electron cyclotron resonance (ECR) plasma etch reactor, or other high-density plasma reactor. In this example, the plasma etch reactor is a reactor in which a semiconductor manufacturing process takes place, and so the surface of the substrate may comprise a polysilicon or a dielectric film. Alternatively, the manufacture of flat panel displays may take place within the plasma etch reactor.
A gas stream is drawn from the outlet 16 of the chamber 10 by a vacuum pumping arrangement comprising one or more vacuum pumps, indicated generally at 18. The vacuum pumping arrangement may be in the form of a turbomolecular pump and/or a dry pump having intermeshing rotors. A turbomolecular pump can generate a vacuum of at least 10−3 mbar in the chamber 10. The flow rate of the gas stream from the chamber 10 is generally around 0.5 to 5 slm.
During the etching process, only a portion of the reactants will be consumed, and so the gas stream exhausted from the outlet 16 of the chamber 10 will contain a mixture of the reactants, any unreactive noble gases supplied to the chamber, and by-products from the etch process. For example, the gas stream may contain a mixture of CxFyHz, Ar, Xe, He, SiF4, and COF2. The etching process may include a number of different process steps, and so the composition of the gas stream exhausted from the chamber 10, and/or the relative proportions of the components of the gas stream, may vary with time.
As illustrated in the drawing, a stream of inert purge gas, such as helium or, as in this example, nitrogen, may be supplied from a source 20 thereof to the vacuum pumping arrangement, for example for increasing the longevity and effectiveness of dynamic shaft seals of the pump(s) 18, and/or for diluting the gas stream to reduce corrosion and degradation resulting from the pumping of aggressive gas molecules. However, in order to minimise the gas flow rate downstream from the vacuum pumping arrangement, the flow rate of purge gas is preferably minimised, and ideally the apparatus will operate without any purge gas supply to the vacuum pumps.
In this embodiment, the gas stream is exhausted from the vacuum pumping arrangement substantially at atmospheric pressure, and now contains nitrogen in addition to the gas exhausted from the chamber 10. In order to remove some of the more undesirable components from the gas stream, for example any PFCs, SiF4, and any other acid gas components from the gas stream, the gas stream exhausted from the vacuum pumping arrangement is conveyed through a plurality of reactors, or abatement devices, connected in series.
In this embodiment, one of these abatement devices comprises a nonthermal plasma reactor 30 for converting any PFCs or other halogen-containing species within the gas stream into a gaseous silicon halide. With reference to
The inner diameter of the second electrode 34 is greater than the outer diameter of the first electrode 32 to establish an annular space between the electrodes 32, 34. In this example, a dielectric tube 40, which is formed from silicon oxide or other silicon-containing material, is located within the space between the electrodes 32, 34. As illustrated in
A second example of a nonthermal plasma reactor 30 suitable for use in the apparatus of
Alternatively, or additionally, a catalyst material may be provided within this packing material 48 for promoting the reaction between the silicon-containing solid and the halogen-containing component of the gas stream. This catalyst preferably comprises a metal, which may be supported on an acidic metal oxide. Examples of a suitable metal include vanadium, molybdenum, palladium, iron, manganese, chromium, nickel, cobalt and tungsten, whilst examples of a suitable metal oxide include gamma-alumina, a zeolite, silica, zirconium oxide, titanium oxide, and TiO2—ZrO2.
An another alternative, the dielectric tube 40 of the nonthermal plasma reactor 30 of
Returning to
The gas stream exhausted from the first reactor 50 will thus comprise, in this example, N2, CxFyHz, Ar, Xe, He, CO2, and H2O. The gas stream enters the nonthermal plasma reactor 30 through gas inlet 44 and passes through the nonthermal plasma reactor 30 between the two electrodes 32, 34. Within the plasma generated between the electrodes 32, 34 the CxFyHz species are activated and react with the silicon-containing material of the dielectric tube 40 and/or of the packed material 48 to form predominantly SiF4 and CO and CO2.
The gas exhausted from the gas outlet 46 of the nonthermal plasma reactor 30 is then conveyed to a third reactor 60 comprising a sorbent bed of material for chemically reacting with any SiF4 and CO2 contained in the gas stream exhausted from the nonthermal plasma reactor 30. Similar to the first reactor 50, this bed of material preferably comprises material that reacts with SiF4 to form inorganic fluoride and silicate species, and so may also comprise a hydroxide, a percarbonate, a perborate, a bicarbonare or a carbonate of one of sodium, calcium and magnesium. In this example, the material comprises soda lime, comprising predominantly calcium hydroxide, for reacting with the SiF4 and CO2 to form inorganic silicates and carbonates. Alternatives include sodium carbonate, sodium bicarbonate, sodium percarbonate and sodium perborate.
The gas stream exhausted from the third reactor 60 will thus comprise N2, Ar, Xe, and He, and so may be exhausted into the atmosphere. Alternatively, the gas stream may be conveyed to a xenon recovery and recycling system for recovering the xenon from the gas stream and returning the recovered xenon to the chamber 10.
Whist the first and third reactors 50, 60 do not require heating, either or both of the reactors may be heated to a moderate temperature, for example less than 200° C., to promote the reactions occurring therein, and so may be formed from plastics or other relatively low cost materials. As the reactions occurring within the reactors 50, 60 are exothermic, thermocouples or other temperature measuring devices may be located within the reactors 50, 60 to detect the reactions occurring within the reactors 50, 60. Exhaustion of the reactors 50, 60 can be predicted by monitoring the duration of these elevated temperatures, and this can enable a reactor 50, 60 to be replaced at a convenient time prior to complete exhaustion, for instance, when the process chamber 10 is “off-line”. The materials in the replaced reactor can be replaced and recycled as required.
Whilst a single first reactor 50 and a single third reactor 60 may be provided, two or more similar reactors 50, 60 may be provided in parallel. For example, where two first reactors 50 are provided, one or more valves may be disposed between the vacuum pumping arrangement and the first reactors to enable the gas stream exhausted from the vacuum pumping arrangement to be directed to one of the first reactors 50 while the other first reactor 50 is off-line, for example for replacement of the bed of material. This enables the gas stream to be continuously treated. In this case, an arrangement of one or more valves is also provided downstream from the first reactors to connect the outputs from the first reactors to the inlet of the nonthermal plasma reactor 30. A by-pass conduit may also be provided to allow the gas stream exhausted from the vacuum pumping arrangement to be diverted directly to the nonthermal plasma reactor 30 without passing through a first reactor 50, for example, when the gas stream contains no components that would be removed by a first reactor 50.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0615271.4 | Aug 2006 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2007/050429 | 7/20/2007 | WO | 00 | 11/3/2009 |
