Aberration measuring method for projection optical system with a variable numerical aperture in an exposure apparatus

Abstract

A method disclosed in this specification is an aberration measuring method in which a light flux converged by a condensing optical system is made incident on a optical system to be measured, the light flux that has passed through the optical system to be measured is reflected by a reflecting optical system having a center of curvature at a light convergence point on a light emergence side of the optical system to be measured is made incident on the optical system to be measure again, and wavefront aberration of the optical system to be measured is detected as interference fringes using the light flux that has passed through the optical system to be measured again. Measurement is carried out while changing the numerical aperture of the optical system to be measured to a numerical aperture larger than a numerical aperture in the actual use, thereby realizing highly precise measurement of the wavefront aberration all over the effective numerical aperture of the optical system to be measured.

1 . An exposure apparatus comprising: 
 a projection optical system for projecting a pattern formed on a reticle onto a wafer, a numerical aperture of said projection optical system being variable; and    an aberration measuring system including: 
 a condensing optical system disposed on a light incidence side of said projection optical system;  
 a reflecting optical system disposed on a light emergence side of said projection optical system; and  
 a detection optical system for detecting wavefront aberration of said projection optical system as interference fringes;  
   wherein said aberration measuring system causes a light flux converged by said condensing optical system to enter said projection optical system, causes the light flux having passed through said projection optical system to be reflected by said reflecting optical system having a center of curvature at a light convergence point on a light emergence side of said projection optical system to make the light flux incident on said projection optical system again, and forming the interference fringes using the light flux having passed through said projection optical system again; and    said aberration measuring optical system sets a numerical aperture of said projection optical system to a numerical aperture larger than a maximum numerical aperture in an actual exposure operation, and measures wavefront aberration of said projection optical system at the set numerical aperture.    
   
   
       2 . An exposure apparatus according to  claim 1 , further comprising correction means for correcting the wavefront aberration of said projection optical system based on said wavefront aberration measured by said aberration measuring system.  
   
   
       3 . A device manufacturing method comprising the steps of: 
 applying resist on a wafer;    exposing the wafer on which the resist has been applied using an exposure apparatus according to  claim 1;  and    developing said resist that has been exposed.