Method and apparatus for clamping a substrate in a high pressure processing system

Abstract

Pressure biased wafer holding of a semiconductor wafer is provided for use in high pressure processing. The use of vacuum chucking for holding a semiconductor wafer during processing is applied to high pressure systems. Adverse effects of high pressure biases are prevented by a valve arrangement that reduces or limits the holding load on a wafer. Check valves and on-off valves connected to input and output lines to the chamber bias fluid applied to a wafer supporting platen to vary the backside pressure so that the excess of frontside pressure versus backside pressure on the wafer is kept within an effective clamping range without excessive force being applied to the wafer. Use of fluid-mechanical techniques is maximized in certain described embodiments to avoid disadvantages of electronic control systems.

1 . A processing system for treating a substrate comprising: 
 a processing chamber configured to treat said substrate therein with a high pressure fluid;    a platen coupled to said processing chamber and configured to support said substrate;    a fluid supply system;    a fluid flow system coupled to said fluid supply system and said chamber and configured to flow said fluid through said processing chamber over said substrate;    a chuck coupled to said platen and configured to hold said substrate against said platen by a pressure gradient between said high pressure fluid and said platen; and    said chuck including means responsive to the pressure of said fluid in said chamber for limiting the magnitude of said pressure gradient.    
   
   
       2 . The processing system of  claim 1 , wherein said means for limiting includes means for limiting said pressure gradient to less than the pressure difference between the pressure of said fluid in said chamber and atmosphere.  
   
   
       3 . The processing system of  claim 1 , wherein said means for limiting includes means for increasing the pressure of fluid between the substrate and the platen in accordance with increases of the pressure of fluid in the chamber.  
   
   
       4 . The processing system of  claim 1 , wherein said means for limiting includes one or more pressure regulated check valves connected between ports to the backside of the platen to processing fluid inlet or outlet ports of the chamber.  
   
   
       5 . The processing system of  claim 4 , wherein said one or more check valves have bias pressure settings corresponding to the magnitude of said pressure gradient.  
   
   
       6 . The processing system of  claim 4 , further comprising controller operated on-off valves having open and closed positions and coupled to said check valves and said chamber.  
   
   
       7 . The processing system of  claim 1 , wherein a temperature of said high pressure fluid ranges from approximately 31 degrees C. to 350 degrees C.  
   
   
       8 . The processing system of  claim 1 , wherein a pressure of said high pressure fluid ranges from approximately 1,070 psi to approximately 10,000 psi.  
   
   
       9 . The processing system of  claim 1 , wherein said supercritical fluid includes supercritical carbon dioxide (CO2).  
   
   
       10 . The processing system of  claim 1 , wherein said means includes a valve connected to the inlet of the chamber to regulate the pressure to a limited gradient below the chamber pressure during fill and filled conditions.  
   
   
       11 . A vacuum chuck assembly for a high pressure fluid processing system for processing a substrate in a chamber, the assembly comprising: 
 a platen having a wafer supporting surface and configured to support said substrate on said surface for high pressure fluid processing;    one or more fluid channels in said platen coupled to said wafer supporting surface;    a clamping fluid control system including a clamping fluid line, a first pressure-limiting valve, a second pressure-limiting valve and a third pressure-limiting valve;    said clamping fluid line being: 
 coupled to said channels,  
 coupled to the outlet of a first pressure-limiting valve that is operable to maintain the pressure in said clamping fluid line to not less than a first maximum pressure gradient less than the pressure in said chamber, and  
 coupled to the inlet of a second pressure-limiting valve that is operable to maintain the pressure in said clamping fluid line to not more than a second maximum pressure gradient more than the pressure to an exhaust line that is coupled to said chamber; and  
   said third pressure-limiting valve: 
 having an inlet coupled to said chamber,  
 having an outlet coupled to said exhaust line, and  
 being operable to maintain the pressure in said exhaust line at a pressure that is not less than a third maximum pressure gradient less than the pressure in said chamber, said third maximum pressure gradient being greater than said second maximum pressure gradient.  
   
   
   
       12 . The vacuum chuck assembly of  claim 11  wherein: 
 said first maximum pressure gradient is greater than the difference between said third maximum pressure gradient and said second maximum pressure gradient.    
   
   
       13 . The vacuum chuck assembly of  claim 11  wherein: 
 said first maximum pressure gradient is not more than a maximum clamping pressure by which said chuck holds said substrate against said platen.    
   
   
       14 . The vacuum chuck assembly of  claim 11  wherein: 
 said third maximum pressure gradient is less than said second maximum pressure gradient by at least a minimum clamping pressure by which said chuck holds said substrate against said platen.    
   
   
       15 . The vacuum chuck assembly of  claim 11  further comprising: 
 a vacuum pump connected to said clamping fluid line to maintain a minimum clamping pressure by which said chuck holds said substrate against said platen.    
   
   
       16 . The vacuum chuck assembly of  claim 11  wherein: 
 said first maximum pressure gradient is greater than the difference between said third maximum pressure gradient and said second maximum pressure gradient;    said first maximum pressure gradient is not more than a maximum clamping pressure by which said chuck holds said substrate against said platen;    said third maximum pressure gradient is less than said second maximum pressure gradient by at least a minimum clamping pressure by which said chuck holds said substrate against said platen; and    said assembly further comprises a vacuum pump connected to said clamping fluid line to maintain said minimum clamping pressure.    
   
   
       17 . A method of controlling fluid clamping pressure to the backside of a substrate on a platen of a pressure biased wafer holder in a high pressure processing chamber, the method comprising: 
 filling the processing chamber with processing fluid to a high processing pressure;    applying a clamping fluid to the backside of a substrate on a platen in said processing chamber at a backside pressure that is responsive to frontside pressure exerted by said fluid on said substrate, such that said backside pressure is less than the frontside pressure by not more than a maximum clamping pressure gradient.    
   
   
       18 . The method of  claim 17  further comprising: 
 maintaining said backside pressure at not less than a minimum clamping pressure gradient below said frontside pressure.    
   
   
       19 . The method of  claim 18  wherein: 
 said filling includes applying said clamping fluid to said platen from fluid being supplied to said processing chamber through a biased check valve that is set to establish said maximum clamping pressure gradient; and    said maintaining includes removing said fluid from said chamber and said clamping fluid from said platen through one or more biased check valves that are set to establish said minimum clamping pressure gradient.    
   
   
       20 . The method of  claim 17  wherein: 
 said filling includes applying said clamping fluid to said platen from fluid being supplied to said processing chamber through a biased check valve that is set to establish said maximum clamping pressure gradient.