Abstract:
An apparatus is provided for treating pollutants in a gaseous stream. The apparatus comprises tubular inlets for mixing a gas stream with other oxidative and inert gases for mixture and flame production within a reaction chamber. The reaction chamber is heated by heating elements and has an interior wall with orifices through which heated air enters into the central reaction chamber. The oxidized gases are treated also for particles removal by flowing through a packed bed. The packed bed is cooled and its upper portion with air inlets to enhance condensation and particle growth in the bed. The treated gas stream is also scrubbed in a continuous regenerative scrubber comprising at least two vertically separated beds in which one bed can be regenerated while the other is operative so that the flow may be continuously passed through the bed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a continuation-in-part of U.S. Ser. No. 09/005,856, filed Jan. 12, 1998.  
         [0002]    The present invention relates to an apparatus and method for the treatment of gas streams containing organic and inorganic pollutants, suitable for applications such as treatment of streams resulting from fabrication of semiconductor materials and devices, microelectric products, manufacturing of compact discs and other memory devices. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    The gaseous effluents from the manufacturing of semiconductor materials, devices, products and memory articles involves a wide variety of chemical compounds used and produced in the process facility. These compounds include inorganic and organic compounds, breakdown products of photo-resist and other reagents, and a wide variety of other gases which must be removed from the waste gas streams before being vented from the process facility into the atmosphere. In such systems, process gas, which may be a single component or multi-component composition, is mixed with an oxidant, such as high purity oxygen, air or nitrous oxide, then the resulting gas mixture is oxidized in a reaction chamber.  
           [0004]    In semiconductor manufacturing processes, various processing operations can produce combustible gas streams. Hydrogen and a variety of hydride gases such as silane, germane, phosphine, arsine, etc. may be present and, if combined with air, oxygen or other oxidant species such as nitrous oxide, chlorine, fluorine and the like, form combustible mixtures.  
           [0005]    However, the composition of the waste gas generated at a work station may vary widely over time as the successive process steps are carried out.  
           [0006]    Faced with this variation of the composition of waste gas streams and the need to adequately treat the waste gas on a continuous basis during the operation of the facility, a common approach is to provide a single large scale waste treatment system for an entire process facility, which is over designed in terms of its treatment capacity, which can continuously treat the waste gas. Large scale oxidation units, which often use catalytic chemistry, however, are typically expensive, particularly since they are over designed in terms of treatment capacity, must be heated to an appropriate elevated temperature and often generate a substantial amount of heat. It is difficult to make such gas treatment processes economically viable without recovering a substantial portion of the heat generated.  
           [0007]    Accordingly, oxidation beds in large scale, typically single unit catalytic oxidation systems, are greatly oversized relative for the size and scale of oxidation beds which would be otherwise minimally required for treatment of the effluent stream under an average operating conditions, average concentration levels, and average composition of pollutants.  
           [0008]    The present invention provides discrete units which may be employed at the point of use, that is, applied to a single tool, individual processing operation, and the like, within a plant facility to effectively and efficiently remove the pollutants without being over designed with respect to volume capacity, heat generation and power consumption.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides an apparatus for removing pollutants from gaseous streams which comprises a thermal reactor, a particle removal chamber and a regenerable acid scrubber. The thermal reactor is provided with at least one inlet comprising a conduit terminating with a portion of the conduit within the reactor which projects into the reactor into a tube defining an area in which there is flame formation. The thermal reactor comprises a central chamber accommodating heating elements, a side inlet communicating with an exterior air space between the exterior wall and the heating elements, and an interior air space communicating with the exterior air space. The interior air space is defined by the interior wall and the heating elements, and an orifice in the interior wall is provided for introducing air from the interior space into the central chamber. The gases exiting the thermal reactor are passed through a liquid vortex which cools gases from the reaction chamber.  
           [0010]    The gases from the combustion chamber are then passed through a counter-current/co-current flow packed bed for trapping and condensing particles by upwardly flowing the gas stream through the packed bed against a down flowing liquid. Air inlets are provided for flowing air to the upper portion of the bed to cool the upper portion of the bed for further condensation and particle growth within the bed.  
           [0011]    A scrubber is also provided for removing chemical pollutants. The scrubber comprises at least two vertically separated beds containing coated packing and a monitoring means for automatically controlling selective introduction of a regenerative coating into the beds. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 a  is a partial cut-away view of an intake nozzle according to the invention for introducing the effluent gases from the processing facility into the thermal reactor.  
         [0013]    [0013]FIG. 1 b  shows a modification of the nozzle of FIG. 1 a  having concentric tubes for introducing gases into the thermal reactor.  
         [0014]    [0014]FIG. 2 is a partial cross-section of another embodiment of an inlet nozzle.  
         [0015]    [0015]FIG. 3 a  is a cut-away view of the elevation of a thermal reactor according to the present invention.  
         [0016]    [0016]FIG. 3 b  shows a modification of the reactor of FIG. 3 a  having a centrally located heating element.  
         [0017]    [0017]FIG. 4 is a partial cut-away view of an elevation of a particle removal chamber according to the present invention.  
         [0018]    [0018]FIG. 5 is a partial cut-away view of an elevation of the regenerable acid scrubber according to the invention.  
         [0019]    [0019]FIG. 6 is a diagram of an apparatus comprising the thermal reactor, particle removal chamber and regenerable acid scrubber. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    With reference to FIG. 1 a , there is shown an inlet  10  into which is introduced the process gas  11 . An inlet pressure monitoring port  12  is shown. In this embodiment, there is an independent gas inlet  13  for the introduction of hydrogen, downstream of nitrogen inlet  15 . A bend  16  in the inlet provides optimum mixing of the gases. However, the inlet need not have such a curvature and thus may have a straight configuration. The inlet tube continues pass the reactor wall  17 , terminating with an extension  18  of the inlet tube. The mixed gases exit the extension  18 , however not directly into the reactor volume, but instead into a concentric tube  19 . The temperature of the mixture of gases and gas flow are selected such that the flame is produce entirely within the tube  19 . This provides for use of multiple inlets, each with slightly different gas mixtures, combustion temperatures and flame size as shown in FIG. 1 a . A second inlet  21  adjacent to inlets  10  and  20  is shown for introducing air or nitrogen between the inlet tubes at the reactor chamber. Preferably, nitrogen or other inert gas is introduced through inlet  21  to minimize particle build-up on the walls of the reaction chamber  40  shown in FIG. 3 a . In such a case, if additional air is needed in the reactor, a air inlet (not shown) located away from the reaction wall may be provided. The separate inlets  10  and  20  permit controlled oxidation, reduce the probability of incompatible gas stream mixing and permit active inlet pressure control independent of these parameters being utilized at adjacent inlets. The inside surfaces of extension  18  and/or tube  19  may be coated with an appropriate catalyst to effect desirable reactions of the input gases prior to passage into the thermal reactor.  
         [0021]    Referring to FIG. 1 b , tubes  13   a ,  18   a  and  19  are concentric for delivery of inert gas (or hydrogen, if required), process gas, and oxygen, respectively, into the reactor. The delivery of the process gas is also through a straight tube  18   a.    
         [0022]    Referring to FIG. 2, there is shown a second embodiment of an inlet  30 , also having a bend  31  downstream from the nitrogen inlet  32  which facilitates mixture of the process gases. However, inlet  30  need not have such a curvature and thus may have a straight configuration. An inlet pressure control port  33  is provided. A vertical nitrogen stream inlet  34  is provided downstream of the bend  31  to force gases into the extension  35  which passes through the reactor wall  36 . The extension  35  is surrounded by a concentric tube  37  to isolate the process gas from adjacent inlets. The inside surfaces of extension  35  and/or tube  37  may be coated with an appropriate catalyst to effect desirable reactions of the input gases prior to passage into the thermal reactor.  
         [0023]    Referring to FIG. 3 a , there is shown a thermal reactor according to the present invention. Process gas enters through inlets (not shown) at the top of the reactor into the central chamber  40 . Heating elements  41  are electrically heated to provide high temperature hot surfaces on the interior wall  42 . Heating elements  41  are shown as annularly located surrounding the chamber  40 . Heating elements may also be located within chamber  40 . Heated air is introduced into the upper portion of the reactor chamber  40  as indicated by arrows  43  through orifices  44  in the interior wall  42 .  
         [0024]    In FIG. 3 b , wall  41   a  are not the heating elements but the heating element  41   b  is centrally located within the chamber  40 , suspended by brackets  42   a.    
         [0025]    Air is provided through the air inlet  45  into an exterior heating space formed between the exterior wall  46  and the heating elements  41 . The air downwardly flows along the surface of the heating elements then upwardly flows along the interior heating space defined by the heating elements  41  and interior wall  42 . The heated air exits into the upper portion of the reactor chamber  40  through the orifices  44 . The interior and exterior heated spaces along the annular heaters are isolated from each other by a seal  47 .  
         [0026]    The reacted gases exit the reactor at the bottom of chamber  40  into a vortex of cooling water (not shown). Typically the gases are cooled to a temperature of less than 100° C. by the water vortex.  
         [0027]    Referring to FIG. 4, there is shown a particle removal chamber  50 . The gases from the thermal reactor are introduced through conduit  51  and passed through a water spray and into a packed bed containing packing  53  (shown in partial cut-away view) through which the gases are flowed in both a co-current and counter-current manner through the packing with and against the flow of water provided by intermittent sprayer  54  and continuous sprayer  55 . Particle-containing liquid flows to the bottom to a sump tank  56 . Air is injected through port  57  to provide direct gas cooling and promote water vapor condensation. Water vapor condensing on small particles increases their size. These particles of a size greater than about 1 micron are removed by being flowed through the packed bed at low velocities.  
         [0028]    Referring to FIG. 5, there is shown a regenerative chemical scrubber according to the present invention. The purpose of the scrubber is to treat the effluent gases to lower certain components below the threshold limit value (TLV). The gases to be treated in the scrubber enter through the plenum  60 . The gases flow upwardly through the scrubber  61  comprising two separate dry packed beds  62 . The sprayers  63  introduce a reagent to the top of the packed beds  62 . The reagent coats the packing material and entraps or reacts with the reactant target gases. The reagent is introduced to both beds  62  alternately. Some of the reagent is retained and coats the packing material and the excess drains into a recirculation tank (not shown) past plenum  60 . This periodic recycling of the reagent re-coats the packing and maximizes the lifetime of the reagent. The scrubber is intended to remove the reactant gases from the gas stream by both flow of gas counter to the reagent flow and co-current flow of reagent and entrapped pollutants. The treated effluent gas exits through flue  64  and the liquid containing the removed chemicals drains out the bottom of the scrubber past plenum  60 . It is a feature of the scrubber to have at least two separate packed beds  62  so that when the chemical coating on the packing material becomes depleted in one bed, the coating may be replenished while the other bed is still operable. In this manner, the scrubber may be continuously operated.  
         [0029]    Referring now to FIG. 6, there is shown in diagram form a processing facility using all of the above described features. The process gas from one or more stations enters the inlets  70 , and is mixed, if required, with hydrogen through inlets  71 , oxygen through inlets  72  and with an inert purge gas, such as nitrogen through inlets  73 . The capacity of the facility will depend upon the size of hardware components, types of process gases and reagents, etc. Typical gas flow rates through the facility are less than about 600 slm. The gases are then treated in the thermal reactor  74 , to which air is introduced through lines  75 . The gases exiting the bottom of thermal reactor  74  pass through a vortex of water flowing through line  76  then through a water spray  77  into the particle removal chamber  78 . Air is introduced into the particle removed chamber through line  79  and water is sprayed onto the packed bed through lines  80  and  81 . The liquid effluent from the packed bed  78  is collected in sump  82  and discarded through line  83  or recirculated through line  84  using respective pumps  85  and  86 . Reagents may also be added to sump  82  through line  87 . The recirculated fluids from sump  82  are cooled at heat exchanger  89  before being recirculated to the top of the particle removal chamber  78 . The treated gases are then flowed through conduit  88  through a spray  90  of reagent from sump  82  then into plenum  91  to the regenerative chemical scrubber  92 . After treatment in the scrubber the completely treated gases exit through stack  93 . Reagent from the chemical scrubber  92  is collected in tank  94  and can be recirculated via line  95  and pump  96  to the chemical scrubber  92 . A fresh reagent for the chemical scrubber may be held in tank  97  and added as needed through line  98  to tank  94 . A detector  99  is located in the stack  93  to monitor components intended to be removed in the scrubber. When the detector registers the TLV of a component in the gas, the reagent in tank  94  may be removed by automatic control via line  95  and fresh reagent added from tank  97  via line  98 . This replacement of reagent may also be automatically controlled by a timer  100  to control replacement of reagent in tank  94  after predetermined periods of use.  
       EXAMPLE 1  
       [0030]    In an apparatus as shown in FIG. 3 with inlets as shown in FIG. 1, each of three typical perfluorinated compounds (PFC) present in semiconductor process gases were tested. The abatement achieved (measured as % DRE, decomposition removal efficiency) and NOx formation, based on 10% utilization of the PFC of the wafer process tool, were measured. The optimum gas flow rate (in standard liters/min, slm) and hydrogen gas addition at the reactor inlet are given to achieve the indicated DRE.  
                                                                                                         NOx                   Pump Purge   H2 Addition   Formation           Gas   % DRE   (slm)   (slm)   (kg/year)                                        NF 3     &gt;99.999    10-100   2-20   &lt;0.0064 1             C2F 6     &gt;99.9   10-70   2-12   &lt;0.0064 1             CF 4     &gt;90   10-45   10-45 2     0.22                                              
 
       EXAMPLE 2  
       [0031]    A regenerative acid scrubber as shown in FIG. 5 is tested using potassium hydroxide (50% w/w) as the scrubbing reagent. The scrubber is tested for process gases from four theoretical tools, used 20 hours/day, having the following flow rates/tool: BCl 3  125 sccm; Cl 2  50 sccm; CHF 3  60 sccm; CF 4  60 sccm. The KOH consumption is 1 kg/day and estimated storage lifetime of the KOH solution is about 50 days. The lifetime of storage for solid KOH is about 35 days. Typically, during use of the scrubber, the concentration of KOH in the scrubbing reagent will be in the range of 50% to 10%. The reagent is replaced when the KOH concentration falls below 10%.  
         [0032]    The invention having been fully described, further modifications of the invention will become apparent to those of ordinary skill in the art. Such modifications are within the scope of the invention, which is defined by the claims set forth below.