Supercritical fluid processes with megasonics

Abstract

An apparatus and process for cleaning residual matter, photoresist and other foreign materials off wafers, substrates and semiconductor work pieces including photomasks, compact discs, flat panel displays using megasonic acoustic wave action techniques in conjunction with supercritical fluid cleaning processes, and in particular, for coupling megasonics techniques with supercritical carbon dioxide processing with co-solvents and surfactants, using cycles of soak, rapid decompression and flushing, to improve cleaning capability and to remove submicron particles from the surfaces of wafers.

We claim:  
     
         1 . A process for cleaning semiconductor wafers comprising the steps of: 
 soaking a wafer in a supercritical phase cleaning fluid mixture at an elevated pressure,    applying a megasonic acoustical wave action to the cleaning fluid mixture,    rapidly reducing the elevated pressure to a substantially lower pressure, and    flowing a supercritical flushing fluid across the wafer.    
     
     
         2 . The process of  claim 1 , said cleaning fluid mixture remaining in supercritical phase at the lower pressure.  
     
     
         3 . The process of  claim 1 , said step of applying megasonic acoustical wave action being conducted concurrently with said step of soaking.  
     
     
         4 . The process of  claim 1 , said step of applying megasonic acoustical wave action being conducted concurrently with said step of rapidly reducing pressure.  
     
     
         5 . The process of  claim 1 , said step of applying megasonic acoustical wave action being conducted concurrently with said step of flushing.  
     
     
         6 . The process of  claim 1 , said cleaning fluid mixture comprising carbon dioxide and a co-solvent.  
     
     
         7 . The process of  claim 1 , said flushing fluid comprising carbon dioxide and a surfactant.  
     
     
         8 . The process of  claim 1 , said wafer having a preferred side to which said cleaning is directed, said process further comprising the initial step: 
 suspending said wafer in a substantially horizontal plane with the preferred side down.    
     
     
         9 . The process of  claim 1 , comprising the preliminary steps: 
 using a process chamber connected to a source of supercritical phase carbon dioxide,    placing a wafer within and closing the process chamber,    filling the process chamber with said supercritical phase carbon dioxide,    pressurizing the process chamber to an elevated supercritical pressure,    adding co-solvents and surfactants to said supercritical phase carbon dioxide thus forming a supercritical phase cleaning fluid mixture,    said soaking a wafer comprising soaking said wafer in said process chamber in said fluid mixture at the elevated pressure.    
     
     
         10 . The process of  claim 9 , further comprising the step: 
 repeating said steps of pressurizing, adding, soaking, applying, rapidly reducing, and flushing.    
     
     
         11 . The process of  claim 1 , said elevated pressure being at least 5000 psi.  
     
     
         12 . The process of  claim 11 , said substantially lower pressure being about 1500 psi.  
     
     
         13 . The process of  claim 1 , said step of soaking comprising a period of not more than about two minutes.  
     
     
         14 . The process of  claim 9 , the temperature within said process chamber maintained at about 80 degrees Centigrade.  
     
     
         15 . The process of  claim 1 , said megasonic acoustical wave action being applied to the surface of said wafer with a transducer array having power input in the range of 5-10 watts/cm 2 .  
     
     
         16 . An apparatus for cleaning semiconductor wafers comprising 
 a closable cleaning vessel connected to a source of cleaning fluid and having a fluid outlet, said vessel being capable of sustaining the cleaning fluid at supercritical phase temperature and pressure,    said vessel configured with at least one megasonic transducer.    
     
     
         17 . The apparatus of  claim 16 , said cleaning fluid components comprising carbon dioxide.  
     
     
         18 . The apparatus of  claim 16 , said cleaning fluids components comprising, supercritical phase carbon dioxide, co-solvent, and surfactant.  
     
     
         19 . The apparatus of  claim 16 , said vessel comprising an inverted cleaning chamber, a vertically movable underside lid, said lid configured with a vertically movable wafer support system.  
     
     
         20 . The apparatus of  claim 19 , said wafer support system configured for supporting a wafer upside down.  
     
     
         21 . The apparatus of  claim 16 , said vessel comprising an upright cleaning chamber and an inverted wafer support system.  
     
     
         22 . The apparatus of  claim 16 , said vessel comprising an inverted cleaning chamber, a vertically movable underside lid, said lid configured with a rotable wafer holding mechanism.  
     
     
         23 . The apparatus of  claim 16 , said transducer comprising at least one ceiling mounted, downward directed transducer.  
     
     
         24 . The apparatus of  claim 16 , said transducer comprising a multi-segment transducer array.  
     
     
         25 . The apparatus of  claim 17 , said multi-segment transducer array configured for inter-segmentally variability in operational parameters.  
     
     
         26 . The apparatus of  claim 16 , said transducer comprising at least one side mounted, horizontally directed transducer.  
     
     
         27 . An apparatus for cleaning semiconductor wafers comprising 
 a closable cleaning vessel connected to a source of cleaning fluid components and having at least one exhaust port, said vessel being capable of sustaining the cleaning fluid at supercritical phase temperature and pressure,    said vessel configured with at least one megasonic transducer on the lower platen,    an inverted wafer holder pedestal    apparatus for wafer rotation.    
     
     
         28 . The apparatus of  claim 27 , said transducer comprising at least one side mounted, horizontally directed transducer.  
     
     
         29 . The apparatus of  claim 27 , said transducer comprising a multi-segment transducer array.  
     
     
         30 . The apparatus of  claim 16 , further comprising a wafer edge support system for supporting, said transducer comprising first and second wafer side transducer arrays.  
     
     
         31 . An apparatus for cleaning both sides of a semiconductor wafer comprising 
 a closable cleaning vessel consisting of a base, a lid, and a wafer holder for holding a wafer therein between when said vessel is closed, said vessel having at least one exhaust outlet, said vessel being capable of sustaining the cleaning fluid at supercritical phase temperature and pressure,    each of said base and said lid configured with at least one large surface area megasonic transducer and at least one fluid inlet,    apparatus for wafer rotation.    
     
     
         32 . The apparatus of  claim 31 , said transducers comprising multi-segment transducer arrays.