Fluid pressure compensation for immersion litography lens

Abstract

An immersion lithography system compensates for displacement of the final optical element of the optical assembly caused by the immersion fluid. The system includes an optical assembly to project an image defined by a reticle onto a wafer. The optical assembly includes a final optical element spaced from the wafer by a gap. An immersion element supplies an immersion fluid into the gap and recovers any immersion fluid that escapes the gap. A fluid compensation system applies a force to the final optical element of the optical assembly to compensate for pressure variations of the immersion fluid.

1 . A method used in a liquid immersion lithography apparatus, the method comprising:
 measuring a pressure in a gap between a wafer and an optical member of the liquid immersion lithography apparatus in which the wafer is exposed through a liquid filled in the gap during immersion lithography; and   adjusting a distance between the wafer and an immersion device of the liquid immersion lithography apparatus, wherein the immersion device supplies the liquid.   
   
   
       2 . The method of  claim 1 , wherein the distance is adjusted based on the measured pressure. 
   
   
       3 . The method of  claim 2 , wherein the distance is adjusted so as to maintain the distance constant. 
   
   
       4 . The method of  claim 2 , wherein the distance is varied based on the measured pressure. 
   
   
       5 . The method of  claim 2 , wherein the distance is adjusted by adjusting a flow of gas emitted toward the wafer by the immersion device. 
   
   
       6 . The method of  claim 5 , wherein the gas forms a gas seal that confines the liquid within the gap. 
   
   
       7 . The method of  claim 5 , wherein the emitted gas forms a gas bearing that supports the immersion device above the wafer. 
   
   
       8 . The method of  claim 1 , wherein the distance is adjusted so as to maintain the distance constant. 
   
   
       9 . The method of  claim 1 , wherein the distance is varied based on the measured pressure. 
   
   
       10 . The method of  claim 1 , wherein the distance is adjusted by adjusting a flow of gas emitted toward the wafer by the immersion device. 
   
   
       11 . The method of  claim 10 , wherein the gas forms a gas seal that confines the liquid within the gap. 
   
   
       12 . The method of  claim 10 , wherein the emitted gas forms a gas bearing that supports the immersion device above the wafer. 
   
   
       13 . The method of  claim 1 , wherein the liquid is water. 
   
   
       14 . The method of  claim 1 , wherein the liquid is oil. 
   
   
       15 . The method of  claim 1 , wherein the immersion device recovers the liquid that has been supplied to the gap. 
   
   
       16 . A liquid immersion lithography apparatus comprising:
 a wafer table that supports a wafer;   an optical assembly that projects an image of a pattern onto the wafer held by the wafer table, the optical assembly including a final optical element spaced from the wafer by a gap;   an immersion nozzle that supplies an immersion liquid to the gap between the final optical element and the wafer;   a pressure sensor that measures a pressure in the gap between the final optical element and the wafer; and   a control system that adjusts a distance between the immersion nozzle and the wafer based on the pressure measured by the pressure sensor.   
   
   
       17 . The apparatus of  claim 16 , wherein the control system adjusts the distance to maintain the distance constant. 
   
   
       18 . The apparatus of  claim 16 , wherein the control system varies the distance based on the measured pressure. 
   
   
       19 . The apparatus of  claim 16 , wherein the immersion nozzle includes one or more gas nozzles that emit a gas toward the wafer, and the distance is adjusted by controlling a flow of the gas. 
   
   
       20 . The apparatus of  claim 19 , wherein the gas forms a gas seal that confines the immersion liquid within the gap. 
   
   
       21 . The apparatus of  claim 19 , wherein the emitted gas forms a gas bearing that supports the immersion nozzle above the wafer. 
   
   
       22 . The apparatus of  claim 16 , wherein the immersion liquid is water. 
   
   
       23 . The apparatus of  claim 16 , wherein the immersion liquid is oil. 
   
   
       24 . The apparatus of  claim 16 , wherein the immersion nozzle recovers the immersion liquid that has been supplied to the gap. 
   
   
       25 . The apparatus of  claim 16 , wherein the pressure sensor measures the pressure of the immersion liquid in the gap. 
   
   
       26 . A device manufacturing method comprising:
 exposing a wafer with an image of a pattern through the optical assembly and the immersion liquid of the apparatus of  claim 16 ; and   developing the exposed wafer.