Projection system for EUV lithography

Abstract

An EUV optical projection system includes at least six mirrors (M 1 , M 2 , M 3 , M 4 , M 5 , M 6 ) for imaging an object (OB) to an image (IM). At least one mirror pair is preferably configured as an at least phase compensating mirror pair. The system is preferably configured to form an intermediate image (IMI) along an optical path from the object (OB) to the image (IM) between a second mirror (M 2 ) and a third mirror (M 3 ), such that a first mirror (M 1 ) and the second mirror (M 2 ) form a first optical group (G 1 ) and the third mirror (M 3 ), a fourth mirror (M 4 ), a fifth mirror (M 5 ) and a sixth mirror (M 6 ) form a second optical group (G 1 ). The system also preferably includes an aperture stop (APE) located along the optical path from the object (OB) to the image (IM) between the first mirror (M 1 ) and the second mirror (M 2 ). The second mirror (M 2 ) is preferably convex, and the third mirror (M 3 ) is preferably concave. The system preferably forms an image (IM) with a numerical aperture greater than 0.18.

1 - 24 . (canceled)  
   
   
       25 . An EUV optical projection system, comprising: 
 a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror and a sixth mirror for imaging an object to an image; and    an aperture stop located along an optical path from said object to said image between said first mirror and second mirror,    wherein, along said optical path, said second mirror is convex, said fifth mirror is convex, and said sixth mirror is concave, and    wherein said system forms an intermediate image along said optical path.    
   
   
       26 . The EUV optical projection system of  claim 25 , wherein along said optical path said first mirror is concave.  
   
   
       27 . The EUV optical projection system of  claim 25 , wherein, along said optical path, said fourth mirror is concave.  
   
   
       28 . The EUV optical projection system of  claim 25 , wherein said aperture stop is not located on said first mirror and not located on said second mirror.  
   
   
       29 . The EUV optical projection system of  claim 25 , wherein said intermediate image is formed between said second mirror and said third mirror.  
   
   
       30 . The EUV optical projection system of  claim 25 , 
 wherein said first mirror and said second mirror form a first optical group, and    wherein said third mirror, said fourth mirror, said fifth mirror and said sixth mirror form a second optical group.    
   
   
       31 . The EUV optical projection system of  claim 30 , 
 wherein said first optical group has a magnification ratio between about −0.8 and about −1.2, and    wherein said second optical group has a magnification ratio between about −0.15 and about −0.35.    
   
   
       32 . The EUV optical projection system of  claim 25 , 
 wherein at least a mirror pair is configured as an at least partially phase compensating mirror pair,    wherein said at least partially phase compensating mirror pair has a first mirror with a first incidence angle variation and a second mirror with a second incidence angle variation, and    wherein said first and said second incidence angle variation have a difference of less than 5° for a field point of a field at said object.    
   
   
       33 . The EUV optical projection system of  claim 32 , wherein said at least partially phase compensating mirror pair comprises a second mirror and a fifth mirror along said optical path.  
   
   
       34 . The EUV optical projection system of  claim 25 , wherein each of said six mirrors is disposed between said object and said image and wherein a physical distance between said object and said image is about 1500 mm or less.  
   
   
       35 . The EUV optical projection system of  claim 25 , wherein said system forms an image with a numerical aperture greater than 0.18.  
   
   
       36 . The EUV optical projection system of  claim 25 , wherein each of the six mirrors receives a chief ray from a central field point at an incidence angle of less than about 16°.  
   
   
       37 . The EUV optical projection system of  claim 25 , wherein five of the six mirrors receive a chief ray from a central field point at an incidence angle of less than about 13°.  
   
   
       38 . The EUV optical projection system of  claim 25 , wherein a maximum aspheric departure of said sixth mirror along said optical path, from a best fitting sphere, is less or equal to 36 μm.  
   
   
       39 . The EUV optical projection system of  claim 25 , wherein said system has an RMS wavefront error of 0.017λ or less.  
   
   
       40 . An EUV optical projection system, comprising: 
 a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror and a sixth mirror for imaging an object to an image; and    an aperture stop located along an optical path from said object to said image, between said first mirror and second mirror,    wherein, along said optical path, said fifth mirror is convex and said sixth mirror is concave,    wherein said system forms an intermediate image along said optical path, and    wherein said system forms an image with a numerical aperture greater than 0.18.    
   
   
       41 . The EUV optical projection system of  claim 40 , wherein said system has an RMS wavefront error of 0.017λ or less.  
   
   
       42 . The EUV optical projection system of  claim 40 , wherein each of the six mirrors receives a chief ray from a central field point at an incidence angle of less than about 16°.  
   
   
       43 . The EUV optical projection system of  claim 40 , wherein five of the six mirrors receive a chief ray from a central field point at an incidence angle of less than about 13°.  
   
   
       44 . An EUV optical projection system, comprising: 
 a first mirror, a second mirror, a third mirror, a fourth mirror, a fifth mirror and a sixth mirror for imaging an object to an image,    wherein, along an optical path from said object to said image, said second mirror is convex, said fifth mirror is convex and said sixth mirror is concave, and    wherein said system forms an intermediate image along said optical path from said object to said image before said third mirror.    
   
   
       45 . The EUV optical projection system of  claim 44 , wherein said system has an RMS wavefront error of 0.017λ or less.  
   
   
       46 . The EUV optical projection system of  claim 44 , wherein each of the six mirrors receives a chief ray from a central field point at an incidence angle of less than about 16°.  
   
   
       47 . The EUV optical projection system of  claim 44 , wherein five of the six mirrors receive a chief ray from a central field point at an incidence angle of less than about 13°.