Overlay measuring pattern, photomask, and overlay measuring method and apparatus

Abstract

An overlay measuring pattern has a rectangular portion and band-shaped portions separated from opposite sides of the rectangular portion by an equal distance and parallel to the sides. Even when a photoresist shrinks upon heating after the overlay measuring pattern is transferred to the photoresist, the taper amounts of the sides of the rectangular portion transferred to the photoresist equal each other in their sections between opposite sides. Hence, the overlay shift can be accurately obtained.

What is claimed is:  
     
         1 . An overlay measuring pattern comprising: 
 a rectangular portion; and    band-shaped portions separated from opposite sides of said rectangular portion by an equal distance and parallel to the sides.    
     
     
         2 . A pattern as claimed in  claim 1 , wherein a ratio of a length of said band-shaped portion opposing the side to a length of the side is not less than 50%.  
     
     
         3 . A photomask comprising an overlay measuring pattern having a rectangular portion and band-shaped portions separated from opposite sides of said rectangular portion by an equal distance and parallel to the sides.  
     
     
         4 . A photomask as claimed in  claim 3 , wherein a ratio of a length of said band-shaped portion opposing the side to a length of the side is not less than 50%.  
     
     
         5 . An overlay measuring method comprising the steps of: 
 transferring a first pattern having a first rectangular portion and band-shaped portions separated from opposite sides of said first rectangular portion by an equal distance and parallel to the sides to a target transfer film as a lower layer;    transferring a second pattern having a second rectangular portion and band-shaped portions separated from opposite sides of said second rectangular portion by an equal distance, parallel to the sides and having a size with which one of said first and second rectangular portions includes the other to a target transfer film as an upper layer while overlaying said second rectangular portion on said first rectangular portion;    measuring distances between sides of said first rectangular portion transferred to the target transfer film as the lower layer and sides of said second rectangular portion, which oppose the sides of said first rectangular portion, transferred to the target transfer film as the upper layer; and    obtaining an overlay shift between said first and second patterns on the basis of the distances in the same direction.    
     
     
         6 . A method as claimed in  claim 5 , wherein a ratio of a length of said band-shaped portion opposing the side to a length of the side is not less than 50%.  
     
     
         7 . An overlay measuring apparatus comprising: 
 an arithmetic section for obtaining a distance between opposite sides of first and second patterns using, of edge signals obtained from edges of said patterns upon scanning said first and second patterns overlaid each other, only edge signals corresponding to the sides, each of said first and second patterns having a rectangular portion and band-shaped portions separated from opposite sides of said rectangular portion by an equal distance and parallel to the sides, and said rectangular portions having sizes with which one of said rectangular portions includes the other.