Patent number 8647580 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "CF.sub.4, C.sub.2F.sub.6, NF.sub.3 and SF.sub.6 are commonly used in the semiconductor and flat panel display manufacturing industries, for example, in dielectric layer etching and chamber cleaning. Following the manufacturing or cleaning process there is typically a residual PFC content in the effluent gas stream pumped from the process tool. PFCs are difficult to remove from the effluent stream, and their release into the environment is undesirable because they are known to have relatively high greenhouse activity.
"As illustrated in FIG. 1, it is known to provide an abatement device for treating such gases exhaust from process tools. In the illustrated example, the abatement device 200 is located downstream from one or more evacuation systems each for evacuating a respective process chamber 202 of a process tool. In this example, each evacuation system comprises a Roots blower 204 or other secondary pump for drawing the effluent stream from the process chamber 202, the Roots blower 204 being backed by a multi-stage dry pump 206 that exhausts the effluent stream at or around atmospheric pressure to the abatement device 200. A suitable backing pump 206 comprises a combination of Roots and Northey ('claw') type pumping mechanisms.
"The object of the abatement is to convert relatively harmful components of the effluent stream into compounds that are less harmful to the environment and/or into compounds that can be more conveniently disposed of, for example, by a wet scrubber (not shown) located downstream from the abatement device 200. Conventional abatement devices include incineration, plasma abatement and thermal decomposition tools.
"Semiconductor manufacturing processes typically produce as by-products particulates or powders that are drawn from the process chamber 202 by the to evacuation system. As the pumping mechanisms of the backing pump 206 require close tolerances to be maintained between the rotor and stator components of the pumping stages during use, it is normal practice to inject an inert purge gas, such as nitrogen, into the pumping mechanisms. This purge gas serves to reduce the level of by-product contamination of the backing pump 206. However, in view of the relatively high flow rates of purge gas into each backing pump 206 (typically around 40 to 50 slm) in comparison to the flow rate of the effluent stream exhaust from each process tool 202 (typically around 5 slm), the injection of purge gas into one or more of the backing pumps 206 significantly increases the power requirement of the abatement device 200, as abatement of an effluent stream containing 70 to 90% purge gas requires significantly more power than the abatement of an effluent stream containing no purge gas.
"It is an aim of at least the preferred embodiment of the present invention to seek to provide a relatively simple, efficient and low cost technique for treating an effluent gas stream from a process tool."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "In a first aspect, the present invention provides apparatus for treating an effluent gas stream from a process tool, the apparatus comprising an abatement device for converting a component of the effluent stream into a liquid-soluble component at a sub-atmospheric pressure, a pump for at least partially evacuating the abatement device, and means for conveying a liquid to the pump, the pump comprising a pumping mechanism, means for receiving the effluent stream from the abatement device and the liquid from the liquid conveying means, and an outlet for exhausting a solution comprising the liquid and the liquid-soluble component of the gas stream.
"In another embodiment, the pump comprises a screw pumping mechanism, preferably a multi-rotor screw mechanism. Multi-rotor screw-mechanism pumps are capable of pumping mixtures of gas and liquid, and can thus be used as an alternative to a liquid ring pump for the present invention. Multi-rotor screw pumping mechanisms comprise of two or more rotating screws within a stationary stator, in which fluid is transported axially in the cavities formed by the meshing teeth of the screw rotors. The direction of fluid movement through the mechanism is dependent upon the direction of rotation of the screw rotors. Compression is provided, not within the pump itself but by the restriction to the outlet, which is often simply atmospheric pressure.
"In the preferred embodiment, the pump is located downstream of the abatement device such that, during use, the effluent stream passes through the abatement device at a sub-atmospheric pressure. With this configuration, the abatement device can convert a component of the effluent stream into a compound that is less reactive than said component with the liquid of the pump. For example, whilst F2 is soluble within water, it may react with water to form insoluble compounds, such as OF.sub.2. Conversion of F.sub.2 into HF can inhibit the formation of such compounds. Thus, with this configuration the abatement device can convert one or more components of the effluent stream into components that are soluble within the liquid of the pump.
"In an alternative abatement technique, the effluent waste stream is brought into contact with a stream containing a reactant for reacting with the components within the waste stream. For example, where these components are PFCs, a superheated stream of water vapour may be used to convert the PFCs into components, such as HF, which can be taken into solution in the pump. By providing a method in which reactive species are formed from a reactive fluid for subsequent reaction with such components of the effluent stream, it has been found that the energy required to cause the destruction of the component in the effluent stream, and the efficiency of that destruction, can be radically improved. For example, H.sup.+ and OH.sup.- ions formed from the dissociation of water are capable of reacting with, for example, a PFC contained in the effluent stream at ambient temperature, and thus at a much lower temperature than would be required if the water had not been pre-ionised before being introduced into the effluent stream. Further advantages are that a relatively cheap and readily available fluid, such as water vapour or a fuel, for example methane or an alcohol, can be used to generate H.sup.+ and/or OH.sup.- ions, as the reactive species, and that the reaction can take place at sub-atmospheric or atmospheric pressure.
"In the preferred embodiment, a single plasma gun is used to inject the plasma stream into the reaction chamber. However, a plurality of such guns may be provided to inject a plurality of plasma streams into the same chamber, each for abating a common or respective gas stream. Alternatively, a plurality of gas streams may be conveyed to a single chamber, into which a single plasma stream is injected. This can increase further the efficiency of the treatment of the waste stream. These guns may be connected to a common power source or to respective sources.
"In a further aspect, the present invention provides a system for evacuating a process tool, the system comprising a vacuum pump for drawing an effluent fluid stream from the tool and apparatus as aforementioned for receiving and treating the effluent stream exhaust from the vacuum pump. Such a pump may comprise any convenient pump for exhausting the effluent stream at a pressure in the range from 10 to 200 mbar. For example, the vacuum pump may comprise a turbomolecular pump, a molecular drag pump, or a multi-stage dry pump. Such a pump preferably comprises a plurality of Roots-type pumping stages, as such pumping mechanisms have larger tolerances than Northey-type mechanisms and so are less prone to seizure due to the accumulation of solid by-products within the running clearances of the pumping mechanism.
"In a yet further aspect, the present invention provides a method of treating an effluent gas stream from a process tool, the method comprising the steps of conveying the effluent stream to an abatement device for converting a component of the effluent stream into a liquid-soluble component at a sub-atmospheric pressure, conveying the effluent stream from the abatement device to a pump for at least partially evacuating the abatement device, simultaneously conveying to the pump a liquid, and exhausting from the pump the liquid containing the liquid-soluble component of the gas stream."
URL and more information on this patent, see: Smith,
Keywords for this news article include: Electronics, Semiconductor,
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