Method and System for Correction of Intrinsic Birefringence in UV Microlithography

Abstract

Systems and methods for improved correction of intrinsic birefringence are provided. Two pairs of optical elements correct for intrinsic birefringence of optical materials. A combination of design criteria for the set of optical elements, including refractive power type, intrinsic birefringence signs, and crystal axis rotation, is used to correct for intrinsic birefringence.

1 . An optical system corrected for intrinsic birefringence, comprising: 
 a first pair of optical elements having a first intrinsic birefringence sign and disposed along an optical axis, said first pair including:    a first optical element made up of a first material having a first crystal axis; and    a second optical element made up of said first material having a second crystal axis;    a second pair of optical elements having a second intrinsic birefringence sign and disposed along said optical axis, said second pair including:    a third optical element made up of a second material having a third crystal axis; and    a fourth optical element made up of said second material having a fourth crystal axis;    wherein said first intrinsic birefringence sign is different from said second intrinsic birefringence sign;    wherein a type of refractive power of said first pair is the same as a type of refractive power of said second pair;    wherein the type of refractive power and the first and second intrinsic birefringence signs tend to correct for intrinsic birefringence; and    wherein said first and second optical elements are rotated with respect to one another such that the first crystal axis and the second crystal axis form a first angle which tends to correct for intrinsic birefringence and said third and fourth optical elements are rotated with respect to one another such that the third crystal axis and the fourth crystal axis form a second angle which tends to correct for intrinsic birefringence.    
     
     
         2 . A semiconductor fabrication method for exposing a wafer with an image representative of a pattern on a mask comprising: 
 illuminating the mask with an exposure light; and    projecting and reducing the exposure light transmitted from the illuminated mask toward the wafer including passing the light through the optical system corrected for intrinsic birefringence as recited in  claim 1 .    
     
     
         3 . An optical system corrected for intrinsic birefringence, comprising: 
 a first pair of birefringence-compensating optical elements disposed along an optical axis and rotated relative to one another to null intrinsic birefringence; and    a second pair of birefringence-compensating optical elements disposed along said optical axis and rotated relative to one another to null intrinsic birefringence,    wherein said first pair and said second pair have the same type of refractive power; and    wherein an intrinsic birefringence sign of said first pair is different than an intrinsic birefringence sign of said second pair.    
     
     
         4 . An exposure system for microlithography, comprising: 
 an optical reduction system that includes an optical system corrected for intrinsic birefringence as recited in  claim 3 .    
     
     
         5 . An optical system corrected for intrinsic birefringence, comprising: 
 first through fourth optical elements disposed along an optical axis, each of the first through fourth optical elements having a respective refractive power, a respective intrinsic birefringence sign, and a respective crystal axis,    wherein each of said first through fourth optical elements have the same type of refractive power;    wherein any two of said first through fourth optical elements have intrinsic birefringence signs different from the intrinsic birefringence signs of the remaining two of said first though fourth optical elements; and    wherein any two of said first through fourth optical elements have crystal axes aligned with respect to each other, and wherein the remaining two of said first through fourth optical elements have crystal axes aligned with respect to each other and at an angle with respect to the crystal axes of the other two of said first through fourth optical elements which nulls intrinsic birefringence.