Method for adjusting a projection objective

Abstract

A projection objective having a number of adjustable optical elements is optimized with respect to a number of aberrations by specifying a set of parameters describing imaging properties of the objective, each parameter in the set having an, absolute value at each of a plurality of field points in an image plane of the projection objective. At least one of the optical elements is adjusted such that for each of the parameters in the set, the field maximum of its absolute value is minimized.

1 . A method for adjusting a projection objective of a projection exposure machine of the type used for microlithography in the fabrication of semiconductor components and having an illumination device for providing an illumination beam and a plurality of optical elements in the path of the illumination beam for projecting an image onto a substrate, at least some of the optical elements being capable of being adjusted for altering aberrations of the projection objective, said method comprising the steps of:
 (a) establishing an initial polarization of the illumination device;   (b) adjusting the projection objective with respect to at least one of the aberrations under initial polarization;   (c) changing the polarization of the illumination device from said initial polarization to a different polarization; and   (d) adjusting the projection objective with respect to said at least one aberration based on said different polarization.   
     
     
         2 . The method of  claim 1  wherein at least one of said adjusting steps comprises the step of satisfying a condition relating to an absolute value of at least one parameter of a set of parameters, each parameter in said set being a parameter representing respective imaging property of the projection objective and having an absolute value at each of a plurality of points in a field of an image plane of the projection objective. 
     
     
         3 . The method of  claim 2  wherein said condition is a condition requiring reduction of the absolute value of each parameter in said set at the one of said plurality of points in said field at which said absolute value is a maximum. 
     
     
         4 . The method of  claim 2  wherein said condition is a condition requiring minimization of the absolute value of each parameter in said set at the one of said plurality of points in said field at which said absolute value is a maximum. 
     
     
         5 . The method of  claim 2  wherein said adjusting step is carried out using a nonlinear numerical method. 
     
     
         6 . The method of  claim 2  wherein one of said absolute values is a maximum of all of said absolute values of all of said parameters and said condition is a condition requiring reduction of said maximum of all of said absolute values of all of said parameters. 
     
     
         7 . The method of  claim 2  wherein one of said absolute values is a maximum of all of said values of all of said parameters and said condition is a condition requiring minimization of said maximum of all of said absolute values of all of said parameters. 
     
     
         8 . The method of  claim 2  wherein said adjusting step is carried out using a nonlinear numerical method. 
     
     
         9 . The method of  claim 2  further comprising the steps of changing an illumination setting of the illumination device after said adjusting step has been carried out, and thereafter repeating said adjusting step. 
     
     
         10 . The method of  claim 9  wherein said illumination setting comprises a setting selected from the group consisting of a coherence setting, a diameter setting, and a polarization setting. 
     
     
         11 . The method of  claim 2  wherein at least one of said parameters comprises individual Zernike coefficients describing wave aberrations of an objective pupil of the projection objective. 
     
     
         12 . The method of  claim 2  wherein at least one of said parameters comprises a linear combination of Zernike coefficients. 
     
     
         13 . The method of  claim 2  wherein at least one of said parameters comprises an average of Zernike coefficients over a plurality of field points lying within a portion of the image plane defined by a scanner slit, said plurality of points lying along a line oriented in a scanning direction. 
     
     
         14 . The method of  claim 2  wherein said average is a weighted average. 
     
     
         15 . The method of  claim 2  wherein said set of parameters is a set which includes at least one parameter selected from the group consisting of distortion and line width. 
     
     
         16 . The method of  claim 2  wherein said set of parameters includes at least one parameter describing a centrable aberration, and said adjusting step comprises the step of tilting a reticle of the projection objective to adjust for said centrable aberration. 
     
     
         17 . The method of  claim 16  wherein said adjusting step comprises at least one of the following steps:
 (i) displacing at least one of the optical elements in a direction perpendicular to an optical axis of the projection objective, and 
 (ii) tilting at least one of the optical elements in a direction perpendicular to said optical axis of the projection objective. 
 
     
     
         18 . The method of  claim 16  wherein said set of parameters further includes at least one parameter describing a tunable aberration, and said adjusting step comprises the step of adjusting at least one of the optical elements to adjust for said tunable aberration and said centrable aberration jointly. 
     
     
         19 . The method of  claim 18  wherein said adjusting step comprises at least one of the following steps:
 (i) displacing at least one of the optical elements in a direction along the optical axis of the projection objective; 
 (ii) changing the wavelength of illumination of the projection objective; 
 (iii) changing a temperature within the projection objective; 
 (iv) changing an air pressure within the projection objective; and 
 (v) changing the composition of a purge gas surrounding the optical elements.