Condensible gas cooling system

Abstract

A workpiece cooling system and method are disclosed. Transferring heat away from a workpiece, such as a semiconductor wafer during ion implantation, is essential. Typically this heat is transferred to the workpiece support, or platen. In one embodiment, the desired operating temperature is determined. Based on this, a gas having a vapor pressure within a desired range, such as 10-50 torr, is selected. This range is required to be sufficiently low so as to be less than the clamping force. This condensible gas is used to fill the volume between the workpiece and the workpiece support. Heat transfer occurs based on adsorption and desorption, thereby offering improved transfer properties than traditionally employed gases, such as helium, hydrogen, nitrogen, argon and air.

1 . A method for transferring heat from workpiece while said workpiece is being processed, said workpiece mounted on a workpiece support, comprising:
 a. Determining an operating temperature range for said processing;   b. Selecting a gas, said gas having a vapor pressure within a desired range at said operating temperature range;   c. Delivering said gas in the volume between the back side of said workpiece and the top surface of said workpiece support; and   d. Processing said workpiece.   
     
     
         2 . The method of  claim 1 , further comprising the step of waiting for said gas to reach equilibrium in said volume before said workpiece is processed. 
     
     
         3 . The method of  claim 2 , wherein a film of liquid is produced on said back side of said workpiece and said top surface of said workpiece support. 
     
     
         4 . The method of  claim 1 , wherein a force is applied to hold said workpiece on said workpiece support, and said desired range of said vapor pressure produces an opposing force that is less than said force holding said workpiece. 
     
     
         5 . The method of  claim 1 , wherein said gas is delivered at a pressure equal to said vapor pressure. 
     
     
         6 . The method of  claim 1 , further comprising the step of cooling said support before said processed workpiece is removed. 
     
     
         7 . The method of  claim 1 , wherein said operating temperature range is between 0 and 50° C., and said selected gas comprises water vapor. 
     
     
         8 . The method of  claim 7 , wherein said vapor pressure is between 10 and 50 torr. 
     
     
         9 . The method of  claim 1 , wherein said operating temperature range is less than −50° C., and said selected gas comprises ammonia. 
     
     
         10 . The method of  claim 1 , wherein said operating temperature range is greater than 100° C., and said selected gas comprises glycerin. 
     
     
         11 . The method of  claim 1 , wherein said process comprises ion implantation. 
     
     
         12 . A system for transferring heat away from a workpiece, while said workpiece is being processed at a predetermined operating temperature range, comprising:
 a. a workpiece support upon which said workpiece is placed, such that the top surface of said support contacts the back side of said workpiece;   b. means for holding said workpiece on said workpiece support, said means exerting a force on said workpiece;   c. a conduit for providing gas to the volume defined by the back side of said workpiece and said top surface of said workpiece support;   d. and a reservoir for holding said gas, wherein said gas has a vapor pressure at said operating temperature range, wherein said vapor pressure which produces an opposing force on the workpiece that is lower than said force exerted by said means to hold said workpiece.   
     
     
         13 . The system of  claim 12 , wherein said operating temperature range is between 0 and 50° C., and said gas comprises water vapor. 
     
     
         14 . The system of  claim 12 , wherein said operating temperature range is less than −50° C., and said gas comprises ammonia. 
     
     
         15 . The system of  claim 12 , wherein said operating temperature range is greater than 100° C., and said gas comprises glycerin. 
     
     
         16 . The system of  claim 12 , wherein said conduit is located within said workpiece support, and said gas passes through said workpiece support to reach said volume. 
     
     
         17 . The system of  claim 12 , further comprising a mass flow controller or pressure regulator located between said reservoir and said volume. 
     
     
         18 . The system of  claim 17 , wherein said mass flow controller delivers said gas at a pressure equal to said vapor pressure.