Method and structure for producing flat wafer chucks

Abstract

Methods and structures are provided for extremely flat wafer chucks, allowing close thermal contact uniformly across a semiconductor processing substrate. An upper and a lower section are tightly fit to one another with flat inner surfaces in face-to-face contact. The sections also define at least one groove therebetween. The two sections have asymmetrical thickness, but the groove defined therebetween is correspondingly asymmetrical such that the groove is centered in the assembled chuck. A heater element, such as a resistive heater, is placed within the groove with some clearance prior to assembling the upper and lower sections. After assembly and tightening, the chuck is thermally cycled above the normal operating temperature prior to secondary machining, thus assuring flatness that is maintained during high temperature operation.

We claim:  
     
         1 . A substrate chuck for semiconductor processing, comprising: 
 a first part having a groove therein;    a second part configured to tightly fit with the first part and thereby enclose the groove of the first part; and    a heater element enclosed within the groove.    
     
     
         2 . The substrate chuck of    claim 1   , wherein the mating surface of the second part is substantially flat and without grooves and the groove is formed entirely within the first part.  
     
     
         3 . The substrate chuck of    claim 2   , where the first part is thicker than the second part.  
     
     
         4 . The substrate chuck of    claim 3   , wherein the groove is a difference in thickness between the first part and the second part is about equal the depth of the groove.  
     
     
         5 . The substrate chuck of    claim 1   , wherein the groove is formed as mating grooves in a lower surface of the first part and an upper surface of the second part, the parts having a difference in thickness equal to a difference in relative depth of the grooves in the two parts.  
     
     
         6 . The substrate chuck of    claim 1   , wherein the first and second parts have different thicknesses and the heater element is vertically centered within the chuck.  
     
     
         7 . The substrate chuck of    claim 1   , wherein the heater element fits within the enclosed groove with a clearance gap of between about 0.0001 inch and 0.005 inch within the groove.  
     
     
         8 . The substrate chuck of    claim 7   , wherein the clearance gap is between about 0.0005 inch and 0.002 inch.  
     
     
         9 . The substrate chuck of    claim 1   , wherein the first part includes a supporting surface sized for receiving a substrate, the supporting surface having a roughness of no more than about RMS 0.002 inch.  
     
     
         10 . The substrate chuck of    claim 9   , wherein the supporting surface has a roughness of no more than about RMS 0.001 inch.  
     
     
         11 . The substrate chuck of    claim 10   , wherein the supporting surface has roughness of no more than about RMS 0.0005 inch.  
     
     
         12 . The substrate chuck of    claim 1   , configured for gravitationally supporting a substrate without electrostatic force and without vacuum suction.  
     
     
         13 . The substrate chuck of    claim 12   , configured for operating temperatures between 20° C. and 275° C.  
     
     
         14 . A method of producing a chuck for supporting a substrate during thermal processing, comprising: 
 assembling two parts with a heater element therebetween;    thermally treating the assembled chuck; and    machining a supporting surface of the chuck after thermally treating.    
     
     
         15 . The method of    claim 14   , wherein thermally treating comprises operating the heater element within the assembled chuck.  
     
     
         16 . The method of    claim 14   , wherein thermally treating comprises raising a temperature of the chuck to an elevated temperature above a desired operating temperature, maintaining the chuck at the elevated temperature, and ramping the chuck temperature down to less than about 50° C.  
     
     
         17 . The method of    claim 16   , wherein the elevated temperature is higher than a normal operation temperature for the chuck.  
     
     
         18 . The method of    claim 17   , wherein the elevated temperature is about 300° C. and the normal operation temperature for the chuck is between about 20° C. and 275° C.  
     
     
         19 . The method of    claim 17   , wherein maintaining the chuck at the elevated temperature is conducted for more than 1 hour.  
     
     
         20 . The method of    claim 19   , wherein maintaining the chuck at the elevated temperature is conducted for between about 2 hours and 15 hours.  
     
     
         21 . The method of    claim 19   , wherein maintaining the chuck at the elevated temperature is conducted for between about 8 hours and 12 hours.  
     
     
         22 . The method of    claim 19   , wherein ramping the chuck temperature down to less than 50° C. comprises ramping the chuck temperature down to about room temperature.  
     
     
         23 . The method of    claim 19   , wherein thermally treating comprises repeatedly raising, maintaining and ramping down the temperature of the chuck at least 6 times.  
     
     
         24 . The method of    claim 14   , wherein assembling comprises tightly fitting the upper and lower part together to enclose the groove.  
     
     
         25 . The method of    claim 24   , wherein tightly fitting comprises arranging close face-to-face contact between the upper part and the lower part at portions between legs of the groove, and leaving a clearance gap within the groove between the parts and the heater.  
     
     
         26 . The method of    claim 25   , wherein the clearance gap within the groove is between about 0.0001 inch and 0.005 inch within the groove.  
     
     
         27 . The method of    claim 26   , wherein the clearance gap within the groove is between about 0.0005 inch and 0.002 inch.  
     
     
         28 . A method of preparing a flat substrate support for supporting a substrate during high temperature processing at an operating temperature, the method comprising: 
 providing a chuck with a heater element embedded therein;    thermally cycling the chuck at a temperature greater than the operating temperature; and    machining a support surface of the chuck after thermally cycling.