Method of adjusting projection optical apparatus

Abstract

This invention relates to an adjusting method for correcting the random component of distortion of a projection optical apparatus without performing complicated assembly and adjustment. This adjusting method has the first step of measuring the residual distortion component of a projection optical system having a predetermined target member in its optical path, the second step of calculating, based on the measurement result of the first step, the surface shape of the target member to cancel the residual distortion component, the third step of removing the target member from the projection optical system and machining the target member so as to have the surface shape calculated in the second step, and the fourth step of inserting the target member machined in the third step into the optical path of the projection optical system.

What is claimed is:  
     
         1 . A method of adjusting a projection optical apparatus that projects an image of a first object on a second object, comprising: 
 the first step of measuring a distortion component of said projection optical apparatus having a projection optical system and a correction optical member which is arranged at a predetermined position with respect to said projection optical system;    the second step of calculating, based on a measurement result of the first step, a surface shape that said correction optical member should have, the distortion component of said projection optical apparatus being canceled to zero when said correction optical member has the surface shape that said correction optical member should have;    the third step of removing said correction optical member from said projection optical apparatus and machining said correction optical member so that the surface shape of said correction optical member coincides with the surface shape calculated in the second step; and    the fourth step of re-arranging said correction optical member machined in the third step at a position where said correction optical member has been arranged in the first step.    
     
     
         2 . A method according to  claim 1 , further comprising the step, executed prior to the first step, of correcting components of various aberrations of said projection optical apparatus that are symmetric with respect to an optical axis of said projection optical system.  
     
     
         3 . A method according to  claim 1 , wherein 
 said projection optical system sequentially has a front group, an aperture stop, and a rear group in an order named from a side of said first object, and    a distance between one of said front and rear groups through which a beam having a smaller numerical aperture passes and said correction optical member is smaller than a distance between the other of said front and rear groups through which a beam having a larger numerical aperture passes and said correction optical member.    
     
     
         4 . A method according to  claim 1 , wherein 
 said projection optical system sequentially has a front group, an aperture stop, and a rear group in the order named from the side of said first object, and    said correction optical member is arranged at a position close to said front or rear group and farthest from said aperture stop.    
     
     
         5 . A method according to  claim 4 , wherein an inequality 
         d/f< 0.07 
       is satisfied where f is the focal length of one of said front and rear groups which is closer to said correction optical member, and d is a distance between, of optical members belonging to said group closer to said correction optical member, one closest to said correction optical member and said correction optical member.  
     
     
         6 . A method according to  claim 1 , wherein an inequality 
       −0.005<Φ<0.005 
       is satisfied where Φ is the refracting power of said correction optical member.  
     
     
         7 . A method according to  claim 6 , wherein the refracting power Φ of said correction optical member is substantially zero.  
     
     
         8 . A method according to  claim 7 , wherein said correction optical member is a plane-parallel plate.  
     
     
         9 . A method according to  claim 1 , wherein said correction optical member arranged in the first step is a dummy and is different from said correction optical member machined in the third step.  
     
     
         10 . A method according to  claim 1 , wherein the second step comprises: 
 the step of calculating a normal vector at a first point of a surface shape that said correction optical member should have;    the step of calculating a tangential vector at the first point that concerns a predetermined direction perpendicular to a direction of an optical axis of said projection optical system;    the step of setting a point remote from the first point in the predetermined direction by a predetermined distance as a second point, and calculating a product of an angle defined by the predetermined direction and the tangential vector and the predetermined distance; and    the step of adding the product to a height at the first point in the direction of the optical axis of the surface shape that said correction optical member should have, thereby obtaining a height in the direction of the optical axis of the surface shape at the second point.    
     
     
         11 . A method according to  claim 10 , wherein a height is set at a predetermined value at the beginning at a point through which the optical axis of said projection optical system passes, in the direction of the optical axis of the surface shape that said correction optical member should have.  
     
     
         12 . A method according to  claim 10 , wherein a height in the direction of the optical axis of the surface shape that said correction optical member should have is obtained by a plurality of manners by changing the predetermined direction, and a plurality of obtained values are averaged.  
     
     
         13 . An exposure apparatus for transferring an image on an original plate onto a photosensitive substrate, comprising: 
 an illumination optical system for supplying light to said original plate;    a first stage for supporting said original plate;    a second stage for supporting said photosensitive substrate; and    a projection optical apparatus, having a projection optical system and a correction optical member arranged at a predetermined position with respect to said projection optical system, for causing a position of said original plate supported by said first stage and a position of said photosensitive substrate supported by said second stage to be conjugated,    wherein said projection optical apparatus is adjusted by a method comprising:    the first step of measuring a distortion component of said projection optical apparatus;    the second step of calculating, based on a measurement result of the first step, a surface shape that said correction optical member should have, the distortion component of said projection optical apparatus being canceled to zero when said correction optical member has the surface shape that said correction optical member should have;    the third step of removing said correction optical member from said projection optical apparatus and thereafter machining said correction optical member so that the surface shape of said correction optical member coincides with the surface shape calculated in the second step; and    the fourth step of re-arranging said correction optical member machined in the third step at a position where said correction optical member has been arranged in the first step.    
     
     
         14 . An exposure apparatus according to  claim 13 , wherein 
 said projection optical system sequentially has a front group, an aperture stop, and a rear group in the order named from a side of said original plate, and    a distance between one of said front and rear groups through which a beam having a smaller numerical aperture passes and said correction optical member is smaller than a distance between the other of said front and rear groups through which a beam having a larger numerical aperture passes and said correction optical member.    
     
     
         15 . An exposure apparatus according to  claim 13 , wherein 
 said projection optical system sequentially has a front group, an aperture stop, and a rear group in the order named from the side of said original plate, and    said correction optical member is arranged at a position close to said front or rear group and farthest from said aperture stop.    
     
     
         16 . An exposure apparatus according to  claim 15 , wherein an inequality 
         d/f< 0.07 
       is satisfied where f is the focal length of one of said front and rear groups which is closer to said correction optical member, and d is a distance between, of optical members belonging to said group closer to said correction optical member, one closest to said correction optical member and said correction optical member.  
     
     
         17 . An exposure apparatus according to  claim 13 , wherein an inequality 
       −0.005<Φ<0.005 
       is satisfied where Φ is the refracting power of said correction optical member.  
     
     
         18 . An exposure apparatus according to  claim 17 , wherein the refracting power Φ of said correction optical member is substantially zero.  
     
     
         19 . An exposure apparatus according to  claim 18 , wherein said correction optical member is a plane-parallel plate.