Gas abatement using plasma

Abstract

An apparatus and method for treating an exhaust stream from a semiconductor processing tool are disclosed. The plasma abatement apparatus for treating an exhaust stream from a semiconductor processing tool includes a plasma device configured to generate a plasma stream from a plasma gas; an exhaust stream opening configured to convey the exhaust stream into the plasma stream for processing by the plasma stream; a first opening positioned to deliver a reducing reactant to a first region of the plasma stream; and a second opening positioned to deliver an oxidizing reactant to a second region of the plasma stream, the second region being located at a lower temperature in the plasma stream than the first region. In this manner, the reducing reactant is introduced into a higher temperature region of the plasma stream, and the oxidizing reactant is introduced into a lower temperature region of the plasma stream. This allows the reduction reaction to occur more effectively because the reducing reactant is present in the higher temperature region and the oxidizing reactant is absent from the higher temperature region, thereby reducing the presence of undesirable thermally generated oxides. Similarly, the introduction of the oxidizing reactant helps remove by-products generated by the reduction reaction, and the amount of undesirable thermally generated oxides is reduced because the oxidizing reactant is introduced into the lower temperature region of the plasma stream.

Description

[Technical field]

[0001] FIELD OF THEINVENTION The field of the invention relates to plasma abatement.Embodiments relate to an apparatus and method for treating exhaust streams from semiconductor processing tools. [Background technology]

[0002] Plasma abatement devices are generally known and have been used, among other things, to treat exhaust gas streams from manufacturing process tools used in, for example, the semiconductor or flat panel display manufacturing industries. During such manufacturing, residual fluorinated or perfluorinated compounds (PFCs) and other compounds are present in the exhaust gas streams exiting the process tools. These compounds are difficult to remove from the exhaust gas streams and, furthermore, are known to have a relatively high greenhouse effect, making them undesirable to be released into the environment.

[0003] One approach to removing PFCs and other compounds from exhaust gas streams is to use radiant burners, such as those described in European Publication No. 1 773 474. However, it is also known to use plasma abatement devices when the fuel gases typically used for combustion abatement are undesirable or not readily available. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Publication No. 1773474 Summary of the Invention [Problem to be solved by the invention]

[0005] While these devices exist for treating exhaust gas streams, each has its own drawbacks, therefore, it would be desirable to provide improved techniques for treating effluent gas streams. [Means for solving the problem]

[0006] According to a first aspect, a plasma abatement apparatus for treating an exhaust flow from a semiconductor processing tool is provided, the plasma abatement apparatus comprising: a plasma device configured to generate a plasma flow from a plasma gas; an exhaust flow opening configured to convey the exhaust flow into the plasma flow for treatment by the plasma flow; a first opening positioned to deliver a reducing reactant to a first region of the plasma flow; and a second opening positioned to deliver an oxidizing reactant to a second region of the plasma flow, the second region being disposed at a location of the plasma flow that is cooler than the first region.

[0007] The first aspect recognizes that a problem with the configuration of existing plasma abatement devices is that the abatement effect may be less than desired and undesirable by-products may be generated in undesirable amounts. Accordingly, an apparatus is provided. The apparatus may be a plasma abatement apparatus. The apparatus may treat or ablate an effluent stream from a semiconductor processing tool. The apparatus may include a plasma device or generator that generates a plasma stream from a plasma gas. The apparatus may include an exhaust stream opening or aperture that conveys the exhaust stream into the plasma stream. The exhaust stream may then be treated by the plasma stream. The apparatus may include a first aperture or aperture that delivers a reducing reactant to a first location, region or zone of the plasma stream. The first aperture may be the same aperture that delivers the plasma gas to the plasma device from which the plasma is generated. The apparatus may include a second aperture or aperture positioned to deliver an oxidizing reactant to a second location, region or zone of the plasma stream. The second aperture may be positioned to deliver the oxidizing reactant to a location of the plasma stream that is cooler than the location where the reducing reactant is provided. In this manner, the reducing reactant is introduced into the hotter or more active regions of the plasma stream, and the oxidizing reactant is introduced into the cooler or less active regions of the plasma stream. This allows the reducing reaction to occur more effectively since the reducing reactant is present in the hotter regions and the oxidizing reactant is not present in the hotter regions, thus reducing the presence of undesirable thermally generated oxides. Similarly, the introduction of the oxidizing reactant helps remove by-products generated by the reducing reaction, and since the oxidizing reactant is introduced into the cooler regions of the plasma stream, the amount of undesirable thermally generated oxides is reduced.

[0008] The first region may be disposed at a location within the plasma stream that is hotter than the second region.

[0009] The first region may be located at a location within the plasma stream that achieves a temperature of 1000° C. or greater.

[0010] The second region may be located at a location within the plasma stream that achieves a temperature of less than 1000°C.

[0011] The second region may be located at a location within the plasma stream that achieves a temperature of 500° C. or greater.

[0012] The second region can be located downstream of the first region.

[0013] The first region can be located upstream of the second region.

[0014] The reducing reactant may be premixed with the plasma gas before the combined reactant and plasma gas are delivered to the plasma device.

[0015] The first region may be located adjacent or near the plasma device.

[0016] The second region can be located distal or separate from the plasma device.

[0017] The apparatus can include a reaction chamber positioned to receive the plasma effluent, and the second region can be disposed within the reaction chamber.

[0018] The reduction reactant can include H2.

[0019] The apparatus can include a hydrogen generator configured to generate H2 in situ by electrolysis.

[0020] The apparatus may include a power generator used to generate the plasma stream, or a secondary power source configured to power the hydrogen generator.

[0021] The reduction reactant can include NH3.

[0022] The first opening can be configured to deliver an ammonia salt, such as ammonium carbonate (NH4)2CO3, to produce NH3 by thermal decomposition in the first region.

[0023] The apparatus can include a heater configured to generate NH3 by thermal decomposition of an ammonia salt, such as ammonium carbonate (NH4)2CO3.

[0024] The reduction reactants can include hydrocarbons (CxHy), such as propane, methane, etc.

[0025] The reduction reactants can include alkaline earth metals such as beryllium, magnesium, calcium, strontium, and / or barium.

[0026] The reduction reactant can include an alkaline earth metal salt.

[0027] The reduction reactant can include an alkali metal, such as lithium, sodium, potassium, rubidium, etc.

[0028] The reduction reactant can include an alkali salt.

[0029] The oxidation reactant can include O2.

[0030] The oxidation reactant can include O3.

[0031] According to a second aspect, there is provided a method of treating an exhaust flow from a semiconductor processing tool, the method comprising generating a plasma flow from a plasma gas; conveying the exhaust flow into the plasma flow for treatment by the plasma flow; delivering a reducing reactant to a first region of the plasma flow; and delivering an oxidizing reactant to a second region of the plasma flow, the second region being disposed at a location of the plasma flow that is cooler than the first region.

[0032] The method can include positioning a first region at a location in the plasma stream that is hotter than a second region.

[0033] The method can include positioning the first region at a plasma flow that achieves a temperature of at least 1000°C.

[0034] The method can include positioning the second region at a location of the plasma flow that achieves a temperature of less than 1000°C.

[0035] The method can include positioning the second region at a location of a plasma flow that achieves a temperature of at least 500°C.

[0036] The method can include disposing a second region downstream of the first region.

[0037] The method can include disposing a first region upstream of a second region.

[0038] The method may include premixing the reducing reactant with the plasma gas prior to delivery to the plasma device.

[0039] The method can include placing the first region proximate to a plasma device.

[0040] The method can include disposing the second region distal to the plasma device.

[0041] The method can include receiving the plasma effluent into a reaction chamber and disposing a second region within the reaction chamber.

[0042] The reduction reactant can include H2.

[0043] The method can include generating H2 in situ by electrolysis.

[0044] The method may include generating H2 using a hydrogen generator powered by the power generator used to generate the plasma flow or by a secondary power source.

[0045] The reduction reactant can include NH3.

[0046] The method can include generating NH3 by thermal decomposition of an ammonia salt, such as ammonium carbonate (NH4)2CO3.

[0047] The reduction reactants can include hydrocarbons (CxHy), such as propane, methane, etc.

[0048] The reduction reactants can include alkaline earth metals such as beryllium, magnesium, calcium, strontium, and / or barium.

[0049] The reduction reactant can include an alkaline earth metal salt.

[0050] The reduction reactant can include an alkali metal, such as lithium, sodium, potassium, rubidium, etc.

[0051] The reduction reactant can include an alkali salt.

[0052] The oxidation reactant can include O2.

[0053] The oxidation reactant can include O3.

[0054] According to a third aspect, there is provided a plasma abatement apparatus for treating an effluent stream from a semiconductor processing tool, the plasma abatement apparatus comprising: a first opening positioned to deliver a reducing reactant premixed with a plasma gas to a plasma device configured to generate a plasma stream having a reducing agent in a first region of the plasma stream; an exhaust stream opening configured to convey the exhaust stream into the plasma stream for treatment by the plasma stream; and a second opening positioned to deliver an oxidizing reactant to a second region of the plasma stream, the second region being located at a location of the plasma stream that is cooler than the first region.

[0055] The apparatus of the third aspect may have the optional features of the first aspect described above.

[0056] According to a fourth aspect, there is provided a method of treating an effluent stream from a semiconductor processing tool, the method comprising: delivering a reducing reactant premixed with a plasma gas to a plasma device; generating a plasma stream having the reducing reactant in a first region of the plasma stream; conveying the effluent stream to the plasma stream for treatment by the plasma stream; and delivering an oxidizing reactant to a second region of the plasma stream, the second region being located at a location of the plasma stream that is cooler than the first region.

[0057] The method of the fourth aspect may have the optional features of the second aspect described above.

[0058] 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 where appropriate and in combinations other than those explicitly set out in the claims.

[0059] It should be understood that where a device feature is described as operable to provide a functionality, this includes a device feature that provides that functionality or is adapted or configured to provide that functionality.

[0060] Embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0061] [Figure 1] 1 illustrates a DC plasma torch according to one embodiment. [Diagram 2] A similar setup to that of FIG. 1 is shown, but utilizing an induction coupled plasma torch. [Diagram 3] Similar to that shown in FIG. 1, but the reduction reactant is introduced within or near the cathode. [Figure 4] 2, but shows a configuration in which the reducing agent is injected into or near the gas discharge in the insulating tube of the plasma torch. [Figure 5A-5B] The abatement performance under different configurations is shown. [Fig. 5C-5D] The abatement performance under different configurations is shown. [Figure 5E] The abatement performance under different configurations is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Before describing the embodiments in detail, an overview is first presented. Some embodiments provide configurations that improve the abatement efficiency of plasma abatement devices. This is achieved by splitting the introduction of reactants into the plasma flow. In particular, a reducing reactant is delivered to the plasma flow at a first location, and an oxidizing reactant is introduced at a second location in the plasma flow. The reducing reactant can be premixed with the plasma gas, so the first location can be the location where the plasma gas is first introduced or downstream from this location but upstream from the second location. This allows the reducing reactant to be introduced at a high temperature or high activity region of the plasma flow, and the oxidizing reactant to be introduced at a low temperature or low activity region of the plasma flow. Introducing the oxidizing reactant in the low temperature region of the plasma flow can reduce the generation of undesired oxides, while ensuring that reduction of some compounds can still occur in the high temperature region. Improved abatement performance can be achieved with lower levels of undesired by-products compared to introducing the reducing and oxidizing reactants together.

[0063] Plasma torch FIG. 1 shows a DC plasma torch 100A according to one embodiment. A nozzled anode 3 is located at the same position as a coaxial cathode 2. A DC constant current power supply 1 is electrically connected to the cathode 2 and the anode 3. A plasma gas carrier conduit 5B is arranged to deliver a plasma gas carrier 5A to the gap between the cathode 2 and the anode 3. A reaction chamber 8 is located downstream of the anode 3. An exhaust flow conduit 9B is arranged to deliver an exhaust flow 9A to a position between the anode 3 and the reaction chamber 8. A reduction reactant conduit 11B is arranged to deliver a reduction reactant 11A to a position between the anode 3 and the reaction chamber 8. An oxidation reactant conduit 12B is located in a wall of the reaction chamber 8 and delivers an oxidation reactant 12A to the reaction chamber 8. A controller 4 is connected to the power supply 1, a source of the plasma gas carrier 5A, a source of the reduction reactant 11A, and a source of the oxidation reactant 12A.

[0064] In operation, the controller 4 switches the power supply 1 to create a voltage difference between the cathode 2 and the anode 3, initiating a plasma. When the plasma is generated, the controller 4 creates a constant direct current (DC) between the cathode 2 and the anode 3 (the power supply 1 operates as a constant current power supply). The controller 4 causes the delivery of the plasma gas carrier 5A through the plasma gas carrier conduit 5B, which generates a plasma plume 10 by a DC arc discharge between the cathode 2 and the anode 3. The plasma plume 10 spreads into the reaction chamber 8. The discharge is sustained by the injection of the plasma gas carrier 5A.

[0065] Exhaust flow 9A is conveyed by exhaust flow conduit 9B to plasma plume 10. The abatement reaction then takes place inside reaction chamber 8, which is typically cylindrical and provides thermal insulation. Thus, exhaust flow 9A mixes with plasma plume 10 inside reaction chamber 8.

[0066] To aid in the abatement reaction, the controller 4 controls the introduction of the reduction reactant 11A through the reduction reactant conduit 11B. The reduction reactant 11A thus mixes with the exhaust stream 9A in the high temperature zone 6 of the plasma plume 10. Typically, the high temperature zone 6 is at a temperature in excess of 1000° C. Optionally, under the control of the controller 4, a generator 20 produces the reduction reactant 11A (such as H2 by electrolysis or NH3 by pyrolysis).

[0067] The controller 4 controls the introduction of the oxidation reactant 12A through the oxidation reactant conduit 12B into a low temperature zone 7 of the plasma plume 10 downstream from the high temperature zone 6. Typically, the low temperature zone 7 will be at a temperature greater than about 500°C but less than 1000°C.

[0068] performance Figures 5A to 5E show the abatement performance in different configurations. One of the main challenges in thermal plasma torch abatement is to achieve high efficiency of the abatement process so that the torch power can be as small as possible. This leads to low operating costs due to low electrical energy demand. Another challenge in thermal plasma torch abatement is to reduce undesirable NOx emissions. In addition, oxygen can act as an inhibitor of plasma phase reactions due to its electronegative properties (i.e., it can attract bond electrons and inhibit the plasma state).

[0069] A configuration such as that shown in Figure 1 can improve the efficiency of the abatement process because it limits the abatement reactions in the high temperature zone 6 to those involving the breaking of CF, SF, and FF bonds and to those involving the reduction reactants that convert F species to HF. The configuration shown in Figure 1 also helps reduce the likelihood that oxygen-rich reactants will react with N2 radicals at high temperatures. Introducing oxygen-rich reactants into the low temperature zone 7 results in lower amounts of NOx.

[0070] To illustrate this, FIG. 5A shows a thermal equilibrium simulation of a mixture of CF4 and N2 (at concentrations of 1% and 99%, respectively). The injections of the various reactants have stoichiometric amounts that maximize the decomposition and removal efficiency (DRE) of CF4. One method of abatement of CF4 is oxidation to COF2. This is shown in FIG. 5A by injecting only O2 into the hot zone 6 of the plasma flow 6. COF2 is then hydrolyzed to HF in the cold wet section of the abatement device (not shown). As can be seen in FIG. 5B, abatement efficiency can be improved by not injecting O2 into the hot zone 6, but instead injecting only H2O. As shown, this converts CF4 more easily to HF and CO2. However, as can be seen in FIG. 5B, even though the power and temperature required to ablate CF4 is lower, this may be accompanied by an increase in NOx emissions relative to the results shown in FIG. 5A. This is believed to be due to the more favorable NOx generation pathway in which H2O radicals are present along with N2 radicals, as shown by the increase in NO value constant with temperature in FIG. 5B. As can be seen from both Figures 5A and 5B, injecting only O2 or only H2O into the plasma stream 6 results in undesirable levels of NOx as well as undesirable by-products.

[0071] However, as can be seen from Figures 5C and 5D, by splitting the reactant addition using the configuration shown in Figure 1, the abatement performance is significantly improved. As shown in Figures 5C and 5B, respectively, it can be seen that ideal abatement can be achieved with very little by-products such as CO and NOx by reacting CF4 first with H2 in high temperature zone 6 and then with O2 in low temperature zone 7. It is noteworthy that the O2 simulation in Figure 5D refers to the high temperature reaction of O2 with the by-products of the first reaction with hydrogen shown in Figure 5C. This O2 step involves the addition of several C X H Y N Z This is necessary to oxidize the by-products to less harmful compounds.

[0072] FIG. 5E shows that simultaneous injection of H2 and O2 does not produce the same results as the two-stage abatement process shown in FIGS. 5C and 5D, as significant amounts of NOx and other undesirable by-products can still be generated, as shown.

[0073] Other configurations Figure 2 shows a similar configuration to Figure 1, but utilizing an induction coupled plasma torch 100B. In this configuration, the plasma plume 10 is generated by ionizing a plasma gas carrier 5A which is injected into an insulated tube 16 via a plasma gas carrier conduit 15. Electromagnetic energy to sustain the discharge is provided by a radio frequency power supply 13 coupled through a coil 14. A matcher 17 is provided to match the load presented by the gas discharge 18.

[0074] Figure 3 is similar to that shown in Figure 1, but the reducing reactant 11A is introduced in or near the cathode 2 so that it mixes with the plasma gas carrier 5A to maximize its ionization and effectiveness as a reactant. An additional advantage of this configuration is that when N2 is used as the plasma gas, NH3 may be produced, which can reduce the baseline amount of NOx emissions from the plasma torch 100C (e.g., when the exhaust stream 9A does not contain any compounds other than the purge compound).

[0075] FIG. 4 illustrates a configuration similar to that shown in FIG. 2, but in which the reducing reactant 11A is injected within or near the gas discharge 18 of the insulated tube 16 of the plasma torch 100D, providing similar advantages as those described with reference to FIG. 3 above.

[0076] While hydrogen is used as the reducing agent in this example, it should be understood that other reducing agents can be used, such as alkaline earth metals and / or alkaline earth salts, such as beryllium, magnesium, calcium, strontium, barium, etc. Additionally, other reducing agents, such as NH3, and / or hydrocarbons, such as propane, methane, etc., can also be used. As mentioned above, NH3 can be generated by thermal decomposition of ammonia salts, such as ammonium carbonate (NH4)2CO3, in the first region 6 or in situ by the generator 20. Similarly, hydrogen can be generated in situ by electrolysis by the generator 20.

[0077] Similarly, although oxygen is used as the oxidizing reactant in this example, it should be understood that other oxidizing reactants, such as ozone, may be used.

[0078] Also, while the reducing reactant is shown as being introduced between the anode 3 and the reaction chamber 8, it should be understood that this is not necessary, but rather the reducing reactant simply needs to be introduced at a location where the plasma stream is hotter than where the oxidizing reactant is introduced.

[0079] Additionally, although the embodiments are described with reference to DC plasma torches and inductively coupled plasma torches, it should be understood that the same techniques can be used with other plasma devices and sources, such as, for example, microwave plasma discharges.

[0080] Some embodiments address the optimization of thermal plasma abatement with the goal of reducing thermal NOx production and increasing the abatement reaction efficiency. Thermal balance simulations show that the fluorinated species, F, CF x and S.F. yIt has been found that the abatement reaction involving the reduction of H to HF requires a much higher temperature than the oxidation reactions of other abatement by-products such as CO and CxHy. In some embodiments, thermal plasma abatement is carried out in two stages: 1) a hydrogen-rich reactant is injected or premixed with the torch plasma gases into a much hotter reaction zone, and 2) an oxygen-rich reactant is injected further downstream into a less hot zone. This provides for split injection of the two reactants in thermal plasma abatement.

[0081] Although exemplary embodiments of the present invention have been disclosed in detail herein with reference to the accompanying drawings, it is understood that the present invention is not limited to the precise embodiments, and various changes and modifications can be made therein by those skilled in the art without departing from the scope of the present invention, which is defined by the claims and their equivalents. [Explanation of symbols]

[0082] 1, 13 Power supply 2 Anode 3. Cathode 4. Controller 5A Plasma Gas Carrier 5B, 15 Plasma gas carrier conduit 6. Hot Zone 7. Low Temperature Zone 8. Reaction chamber 9A discharge flow 9B Exhaust flow conduit 10 Plasma Plume 11A Reduction Reactants 11B Reduction reactant conduit 12A Oxidation Reactant 12B Oxidation reactant conduit 14 Coil 16 Insulated pipe 17 Matching box 20 Generator 100A, 100B, 100C, 100D Plasma Torch

Claims

1. 1. A plasma abatement apparatus for treating an exhaust stream from a semiconductor processing tool, comprising: a plasma device configured to generate a plasma stream from a plasma gas; an exhaust flow opening configured to convey the exhaust flow into the plasma flow for treatment by the plasma flow; a first opening positioned to deliver a reduction reactant to a first region of the plasma flow, the reduction reactant being premixed with the plasma gas prior to delivery to the plasma device; a second opening positioned to deliver an oxidizing reactant to a second region of the plasma stream downstream from the first region; Equipped with The apparatus, wherein the second region is disposed at a location in the plasma stream that is cooler than the first region.

2. The apparatus of claim 1 , wherein the first region is disposed at a location of the plasma stream that achieves a temperature of at least 1000° C.

3. 3. The apparatus of claim 1 or 2, wherein the second region is located at a location of the plasma stream that achieves a temperature of less than 1000°C.

4. 4. The apparatus of claim 1, wherein the second region is located at a location of the plasma stream that achieves a temperature of at least 500°C.

5. 5. The apparatus of claim 1, further comprising a reaction chamber positioned to receive the plasma effluent, the second region being disposed within the reaction chamber.

6. The reduction reactant is H 2 、 NH 3 、 Hydrocarbons such as propane and methane, Alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; Alkaline earth metal salts, Alkali metals such as lithium, sodium, potassium, and rubidium, Alkaline salts, The apparatus according to claim 1 , further comprising at least one of:

7. The H 2 7. The apparatus of claim 6, comprising a hydrogen generator configured to generate in situ

8. a power generator used to generate the plasma stream; a secondary power source configured to supply power to the hydrogen generator; The apparatus of claim 7 , comprising at least one of:

9. The first opening is formed by thermal decomposition of the NH 3 To produce ammonium carbonate (NH 4 ) 2CO 3 9. The apparatus of claim 6, configured to deliver an ammonia salt such as

10. Ammonium carbonate (NH 4 ) 2CO 3 The NH 3 9. The apparatus of claim 6, further comprising a heater configured to generate

11. The oxidation reactant is O 2 and O 3 11. The apparatus according to claim 1 , further comprising at least one of:

12. 1. A method for treating an exhaust stream from a semiconductor processing tool, comprising: generating a plasma stream from a plasma gas; conveying the exhaust stream into the plasma stream for treatment by the plasma stream; premixing the plasma gas and a reducing reactant prior to delivery to a plasma device and delivering the reducing reactant to a first region of the plasma stream; delivering an oxidizing reactant to a second region of the plasma flow downstream from the first region, the second region being located at a lower temperature than the first region of the plasma flow; The method includes:

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