Abstract:
A method and an apparatus, the apparatus including appropriate valves and conduits, for increasing throughput in pressurized fluid processing including storing in a storage chamber of the apparatus a quantity of fluid at a pressure higher than a pressure at which an operation is to take place, while a processing chamber is depressurized to allow reception of a new object; sealing the processing chamber; and allowing fluid stored in the storage chamber to pass to the processing chamber to re-pressurize the processing chamber before performing the operation. The fluid may be preheated in the storage chamber to further reduce processing times.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to supercritical/high pressure fluid processing. More particularly, it relates an apparatus and method for processing work pieces in a supercritical fluid or high pressure liquid environment in a time efficient manner. 
     2. Prior Art 
     In the field of microelectronics, semiconductor products such as integrated circuits often undergo processing (for example cleaning) in a supercritical fluid or high pressure liquid, such as, for example carbon dioxide or a mixture of carbon dioxide and a co-solvent. It is necessary for the fluid to be maintained at a controlled pressure and temperature to optimize the process. 
     Processing of work pieces occurs in a high pressure processing chamber, which must be loaded with the work pieces. One of the major inhibitors to incorporating supercritical fluid or high pressure liquid processing into manufacturing is the low throughput due to long cycle times necessary to pressurize and depressurize the chamber in order to load and discharge the work pieces. Currently, in order to process workpieces in a supercritical fluid (SCF)/high pressure liquid tool, the workpieces must be loaded into the process chamber at ambient temperature and pressure, the tool sealed and then the system must be pressurized by purging the atmospheric air with high pressure fluid which will be brought up to critical processing pressures by pumping on the entire system. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method and an apparatus for increasing throughput in high pressure fluid processing operations. 
     The invention is directed to a method for operating a system having a processing chamber for performing an operation at high pressures on an object placed in the chamber. The method comprises storing in a storage chamber a quantity of the fluid at a pressure higher than a pressure at which the operation is to take place, while the processing chamber is depressurized to allow reception of a new object; sealing the processing chamber; and allowing fluid stored in the storage chamber to pass to said processing chamber to re-pressurize the processing chamber before performing the operation. The method may further comprise selecting a pressure to which the storage vessel is pressurized based on relative sizes of the storage vessel and the processing chamber. 
     The method may further comprise purging the process chamber with the fluid before re-pressurizing the processing chamber. It may also further comprise venting the processing chamber after the operation is performed. 
     The invention is also directed to an apparatus for processing an object with fluid from a fluid source at high pressure. The apparatus comprises a storage vessel for storing a quantity of the fluid supplied from the fluid source; a pump for pumping the fluid from the fluid source to the storage vessel, the pump having an input connected to the fluid source and an output connected to the storage vessel; a processing chamber in which objects to be processed are placed for processing and from which the objects are removed after processing; a first valve between the pump and the storage vessel; a second valve between the storage vessel and the processing chamber; and an exhaust valve associated with the processing chamber to permit the processing chamber to be vented. 
     The apparatus may further comprises a bypass for bypassing fluid from the output of the pump to the processing chamber. 
     The first valve may be a two way valve having an input, a first output and a second output, the input being connected to the output of the pump, and a first output connected to the storage vessel, and the second valve may be a two way valve having an output, a first input and a second input, the first input being connected to the storage vessel, and the output connected to the processing chamber; further comprising a bypass connection between the second output of the first valve and the second input of the second valve. In general, the storage vessel has a larger volume than the processing chamber. The storage vessel is pressurized to a higher pressure than the processing chamber. The storage vessel and the processing chamber are relatively sized, and the processing chamber is pressurized, so that when the second valve is opened and pressure equilibrates between the storage vessel and the processing chamber, the processing chamber is at an operating pressure for performing operations on the objects. The fluid source for the apparatus may be a pressured fluid cylinder or a fluid generator. The apparatus may further comprise a heater for heating fluid stored in the storage vessel and a heater for heating fluid in the processing chamber. The pump may be an air driven liquid pump. 
     The fluid may be a supercritical fluid, such as supercritical carbon dioxide and may include a co-solvent. Operations may be performed at a pressure of between approximately 700 and 6000 psi (48 to 408 atmospheres). 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a schematic diagram of a system in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a schematic diagram of a system  10  incorporating features of the present invention. Although the present invention will be described with reference to the single embodiment shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     In accordance with the invention, a processing chamber  12  of a conventional type such as a reactor bomb manufactured by PARR Instruments of Moline, Ill., may be provided. If the processing fluid is carbon dioxide, it will be supercritical at a pressure of at least 1070 psi (72.8 atmospheres) and a temperature of 31 degrees Celsius. Typical processing pressures may be in the range of approximately 1100 psi to 6000 psi (75 to 408 atmospheres), but may be kept at the center of this range, that is preferably at 3000 psi (204 atmospheres). Other applications may dictate liquid phase processing normally in the range of 800 to 100 psi (54 to 68 atm.). 
     A heater  13  may be provided to supply heat to chamber  12  to keep it at a required processing temperature. Alternatively, or in addition, the fluid used in chamber  12  may be preheated externally to chamber  12  before being introduced therein, as more fully described below. 
     System  10  is supplied with fluid from a conventional pressurized fluid source  14 , valved by a conventional valve  15 , such as a pressurized cylinder of a type commercially available and well known in the art. Other sources can be used, depending on the type of fluid. For example, for certain fluids, a fluid generator, which produces the fluid continuously, may be used. 
     In accordance with the invention, a storage chamber or vessel  16  is provided to store a quantity of the fluid that is being used to process the work pieces. It is preferred that vessel  16  have a volume which is greater than that of chamber  12 , and that it be capable of pressurization to a higher pressure. For example if chamber  12  has a volume of 1 liter, then vessel  16  may have a volume of 3 liters. Vessel  16  may also have associated therewith a heater  18  to heat the fluid stored therein. Heater  18  is shown as an electrical coil heater, but it will be understood that other sources of heat can be used, such as, for example, a combustion heater, or a radiative heat source. This has the advantage of contributing to a substantial reduction in cycle times, as explained below. 
     Fluid in fluid source  14  is transferred to storage vessel  16  by way of a pump  20  and a valve  22 . Pump  20  may be any of several well know pumps having an appropriate capacity and pressure output rating, such as an air driven liquid pump manufactured by Haskel International, Inc. of Burbank, Calif. Pump  20  may operate virtually continuously in order to perform the functions as set forth below. 
     Valve  22  is preferably a switching valve having one input and two outputs, with flow directed from the input to one of the two outputs, depending on the position of a control handle thereof (not shown). The input of valve  22  is connected to the output of pump  20 . A first output of valve  22  is connected to a port of storage vessel  16 . A second output of valve  22  is connected to an input of a second valve  24  by way of a bypass conduit  26 . Valve  24  may be of the same construction as valve  22 , but is utilized so that it has two inputs and one output. A first input of valve  24  is connected to a second port of storage vessel  16 . The output of valve  24  is connected to a fluid input port of processing chamber  12 . The second input of valve  24  is connected to bypass conduit  26 , as discussed above. 
     Processing chamber  12  is also connected to a venting valve  28  which may be used to vent processing chamber  12 . 
     Operation of the system will be described below with specific reference to lines in the Operations Table set forth below. It will be understood that operations may be conducted manually by an operator, or automatically by a suitably configured automated system, or by some combination of both. For example, suitable pressure gauges and temperature measuring devices may be employed to assure that certain operation steps do not go forward until the proper conditions exist. 
     At the start of operations, processing chamber  12  is disassembled or otherwise brought to atmospheric pressure and samples to be processed are loaded therein. It is then reassembled in a pressure tight manner. In accordance with step  1  in the Operation Table, valve  28  is opened. Valve  22  is set so that fluid may flow from pump  20  to bypass conduit  26 . Valve  24  is set so that fluid may flow from bypass conduit  26  into processing chamber  12 . Thus, processing chamber  12  is purged of atmospheric gases by the flow of fluid from fluid source  14 . 
     In accordance with line  2  in the Operations Table, after purging, at line  2 , valve  28  is closed. Valve  22  is set so the output of pump  20  is directed into storage vessel  16 . Valve  24  remains in its previous position so that the output thereof is connected to bypass conduit  26 . The combination of these valve settings effectively isolates processing chamber  12 . It also effectively seals the output port of storage vessel  16 . 
     While processing chamber  12  comes up to temperature, as a result of heating by heater  13 , pump  20  builds up pressure of fluid in storage vessel  16  by continuously pumping fluid into vessel  16 . After a predetermined pressure has been reached, by waiting a predetermined period of time, or by monitoring the pressure with a pressure gauge, and processing chamber  12  is at the appropriate temperature for processing to occur, the position of valve  24  is changed (line  3  in the Operations Table), thus allowing the pressures in processing chamber  12  and storage vessel  16  to equilibrate, as fluid flows from storage vessel  16  into processing chamber  12 . As long as the pressure in vessel  16  is high enough, and its volume sufficiently large, processing chamber  12  will be filled by the processing fluid to a pressure at which operations in processing chamber  12  can be conducted on work pieces placed therein. 
     As soon as the pressures in processing chamber  12  and storage vessel  16  have come to equilibrium, the position of valve  24  is shifted, thus isolating processing chamber  12  (line  4  in the Operations Table). However, pump  20  continues to operate, thus increasing the amount and pressure of fluid in storage vessel  16 . The temperature of this fluid is increased appropriately, due to the increasing pressure, and by means of heater  18 , for performing the desired operation on a work piece by means of heater  18 . 
     When the operation performed on the work pieces in processing chamber  12  are complete, valve  28  is opened, thus venting the processing fluid (line  5  in the Operations Table). It will be understood that the vented fluid may be recovered and recycled for further use by suitable means that do not constitute a part of this invention. 
     Processing chamber  12  is then disassembled (line  6  in the Operations Table), and the work pieces removed therefrom. New work pieces are loaded into processing chamber  12 . Processing chamber  12  is then again sealed in a pressure tight manner. The position of valve  22  is changed to connect pump  20  to bypass conduit  26 . Venting valve  28  remains open. Valve  24  is positioned so that bypass conduit  26  is in communication with processing chamber  12 , thus purging processing chamber  12  (line  7  in the Operations Table, which is equivalent to line  1 ). As soon as this is accomplished, valve  28  is closed. The position of valve  22  is changed so that the output of pump  20  is again directed into storage vessel  16 . As soon thereafter as processing chamber  12  is close to its intended operating pressure, the position of valve  24  is changed. In a matter of seconds, the pressure in storage vessel  16  and processing chamber  12  come to equilibrium, and the desired operation can be performed on work pieces in processing chamber  12 . Thus, in sharp contrast to prior systems, it is not necessary for pump  20  to begin the long process of directly pressurizing processing chamber  12 . Instead processing chamber  12  is quickly pressurized by a portion of the fluid previously stored and heated in storage vessel  12 . 
     The process described above, including venting, changing the work piece, and repressurizing, can be repeated any number of times, with time savings occurring during all subsequent cycles. In other words steps  2 - 7  in the Operations table are repeated over and over again until all work pieces have been processed. Thus, the time savings achieved is multiplied by the number of cycles. When all items have been processed and it is time to shut down the system, or when it must be shut down for maintenance or repair, operations are terminated by repeating steps  2 - 5 . 
     
       
         
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 Operations Table 
               
             
          
           
               
                   
                 Valve 22 
                 Valve 24 
                 Valve 28 
               
               
                 Step 
                 Position 
                 Position 
                 Position 
               
               
                   
               
               
                 1) Purge 
                 To Bypass 26 
                 Bypass to Chamber 
                 Open 
               
               
                   
                   
                 12 
               
               
                 2) Initial System 
                 To Storage 
                 Bypass to Chamber 
                 Closed 
               
               
                 Pressurization 
                 Vessel 
                 12 
               
               
                 3) Pressurize 
                 To Storage 
                 Storage Vessel to 
                 Closed 
               
               
                 Processing Chamber 
                 Vessel 
                 Processing Chamber 
               
               
                 4) When equilibrium is 
                 To Storage 
                 Bypass to Chamber 
                 Closed 
               
               
                 achieved (processing) 
                 Vessel 
                 12 
               
               
                 5) Vent 
                 To Storage 
                 Bypass to Chamber 
                 Open 
               
               
                   
                 Vessel 
                 12 
               
               
                 6) Disassemble reload 
                 To Storage 
                 Bypass to Chamber 
                 Open 
               
               
                 and, pressurize storage 
                 Vessel 
                 12 
               
               
                 vessel 
               
               
                 7) Purge 
                 See (1) above 
               
             
          
           
               
                 8) Repeat steps 2-7 as many times as required to process all items in 
               
               
                 processing chamber 12 
               
               
                 9) To terminate Operations Perform Steps 2-5 then Shut Down 
               
               
                   
               
             
          
         
       
     
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.