Method for optimizing the image properties of at least two optical elements as well as methods for optimizing the image properties of at least three optical elements

Abstract

In order to optimize the image properties of several optical elements of which at least one is moved relative to at least one stationary optical element, the overall image defect resulting from the interaction of all optical elements is first of all measured. This is represented as a linear combination of the base functions of an orthogonal function set. The movable element is then moved to a new measurement position and the overall image defect is measured once again. After the linear combination representation of the new overall image defect, the image defects of the movable element and of the stationary element are calculated from the data thereby obtained. With only one movable optical element a target position in which the overall image defect is minimized can be directly calculated and adjusted there from. If several movable optical elements are available, methods are given for the efficient determination of the respective target position.

1 . A measurement system for determining an image defect of at least one of at least two optical elements of an optical system, the measurement system comprising: 
 a) measuring means for measuring 
 a first image defect of the optical system in a first relative position of the at least two optical elements, and  
 a second image defect of the optical system in a second relative position of the at least two optical elements, said second relative position being distinct from the first relative position; and,  
   b) computing means that 
 represent the first image defect as a first combination of base functions of a function set,  
 represent the second image defect as a second combination of the base functions of the function set, and  
 calculate the image defect of at least one of the at least two optical elements using the first combination and the second combination.  
   
   
   
       2 . The measurement system of  claim 1 , further comprising driving means for changing the relative position of the at least two optical elements.  
   
   
       3 . The measurement system of  claim 2 , wherein the driving means are configured to rotate at least one of the at least two optical elements about an optical axis of the optical system.  
   
   
       4 . The measurement system of  claim 1 , wherein the measuring means uses air image data for measuring the first and the second image defect.  
   
   
       5 . The measurement system of  claim 1 , wherein the function set is an orthogonal function set.  
   
   
       6 . The measurement system of  claim 5 , wherein Zernike functions are chosen as the orthogonal function set.  
   
   
       7 . The measurement system of  claim 1 , wherein the first combination and the second combination are linear combinations.  
   
   
       8 . The measurement system of  claim 1 , wherein one of the at least two optical elements is stationary.  
   
   
       9 . A projection exposure apparatus, comprising the measurement system of  claim 1 , wherein the optical system is an objective lens system.  
   
   
       10 . The apparatus of  claim 9 , wherein the measuring means measures wave front data of an imaging light bundle at the image side of the projection objective lens system.  
   
   
       11 . A correction system for reducing an image defect of an optical system, wherein the optical system comprises at least two optical elements, the correction system comprising: 
 a) measuring means for measuring 
 a first image defect of the optical system in a first relative position of the at least two optical elements, and  
 a second image defect of the optical system in a second relative position of the at least two optical elements, said second relative relating being distinct from the first relative position; and,  
   b) computing means that 
 represent the first image defect as a first combination of base functions of a function set,  
 represent the second measured image defect as a second combination of the base functions of the function set, and  
 calculate a target position for the at least two optical elements based on the first combination and the second combination so as to reduce the image defect.  
   
   
   
       12 . The correction system of  claim 11 , further comprising driving means for changing the relative position of the at least two optical elements.  
   
   
       13 . The correction system of  claim 12 , wherein the driving means is configured to rotate at least one of the at least two optical elements about an optical axis of the optical system.  
   
   
       14 . The correction system of  claim 11 , wherein the measuring means uses air image data for measuring the first and the second image defect.  
   
   
       15 . The correction system of  claim 11 , wherein one of the at least two optical elements is stationary.  
   
   
       16 . The correction system of  claim 11 , wherein the function set is an orthogonal function set.  
   
   
       17 . The correction system of  claim 16 , wherein Zernike functions are chosen as the orthogonal function set.  
   
   
       18 . The correction system of  claim 11 , wherein the first combination and the second combination are linear combinations.  
   
   
       19 . The correction system of  claim 11 , wherein the calculating means calculates the target position  
   
   
       20 . A projection exposure apparatus, comprising the measurement system of  claim 12 , wherein the optical system is an objective lens system.  
   
   
       21 . The apparatus of  claim 20 , wherein the measuring means measures wave front data of an imaging light bundle at the image side of the projection objective lens system.