Uniform temperature workpiece holder

Abstract

An apparatus and method for maintaining substantially uniform temperature of semiconductor wafers and similar workpieces is provided. The method and apparatus utilize a workpiece holder that is substantially a closed chamber, which includes a wall structure including a workpiece engaging wall in thermal communication with the chamber. The workpiece holder also includes a condenser that communicates with the chamber and a heater that applies heat to the chamber. The heater applies heat to a fluid inside the chamber such that when the fluid vaporizes within the chamber the condenser abstracts the heat from the fluid. This causes continual circulation of vapor through the interior of the chamber, which helps to maintain temperature uniformity. A feedback control system connected to one or more temperature sensors can control the heater, the condenser or both so as to maintain a predetermined set point temperature within the chamber.

1 . A method of holding a workpiece at a substantially uniform temperature comprising: 
 (a) maintaining the workpiece on a holding surface in heat transfer relation with the interior of a chamber;    (b) vaporizing a liquid disposed within the chamber to form vapor by supplying heat to the interior of the chamber; and    (c) condensing the vapor in a condenser in communication with the chamber, said vaporizing and condensing steps being performed so that at least some liquid and some vapor are present in said chamber and so that the vapor continually flows within said chamber and flows to said condenser.    
     
     
         2 . A method as claimed in  claim 1  further comprising the step of returning liquid from said condenser to said chamber.  
     
     
         3 . A method as claimed in  claim 2  wherein said fluid is an aqueous fluid.  
     
     
         4 . A method as claimed in  claim 2  wherein said condenser projects upwardly from said chamber, and wherein said step of returning liquid from said condenser to said chamber includes allowing said liquid to drain from said condenser into said chamber by gravity.  
     
     
         5 . A method as claimed in  claim 1  wherein said workpiece is a semiconductor wafer.  
     
     
         6 . A method as claimed in  claim 5  further comprising the step of performing one or more processes on said semiconductor wafer while said wafer is maintained during the aforesaid steps.  
     
     
         7 . A method as claimed in  claim 6  said one or more processes include baking of a photoresist, the method further comprising exposing the photoresist to patternwise illumination before said baking step.  
     
     
         8 . A method of making a workpiece holder comprising the steps of: 
 (a) forming a wall structure defining a substantially closed chamber, said wall structure including a workpiece-engaging wall;    (b) subjecting said wall structure to a preselected pressure differential between the interior of said chamber and the exterior of said chamber corresponding to a pressure differential expected during use of said wall structure, whereby said workpiece-engaging wall will deform; and    (c) while maintaining said deformed condition of said workpiece-engaging wall, machining said workpiece-engaging wall to a preselected shape, whereby said workpiece-engaging wall will have said preselected shape in service.    
     
     
         9 . A method as claimed in  claim 8  wherein said preselected shape is substantially flat.  
     
     
         10 . A method as claimed in  claim 9  wherein said machining step is performed by grinding said workpiece-engaging wall flat.  
     
     
         11 . A method as claimed in any one of claims  8 ,  9  and  10  wherein said deformed condition of said workpiece is maintained by maintaining said preselected pressure differential during said machining step.