Overlay key, method of forming the overlay key and method of measuring overlay accuracy using the overlay key

Abstract

In an overlay key used for measuring overlay accuracy between first and second layers on a substrate, a first mark may be formed in the first layer, and a second mark may be formed on the second layer. The first mark may include first patterns having a first pitch and extending in a first direction. The second mark may include second patterns extending in substantially the same direction as the first direction and having a second pitch substantially equal to the first pitch. First and second images may be acquired from the first and second marks. The overlay accuracy may be produced from position information of first and second interference fringes formed by overlaying a test image having a third pitch onto the first and second images.

1 . An overlay key for measuring overlay accuracy between a first layer and a second layer on a substrate, the overlay key comprising:
 a first mark including first patterns with a first pitch formed in the first layer and extending in a first direction; and   a second mark including second patterns formed on the second layer, the second mark disposed adjacent to the first mark, and the second patterns having a second pitch substantially equal to the first pitch and extending in a substantially same direction as the first direction.   
     
     
         2 . The overlay key of  claim 1 , wherein the second mark is disposed adjacent to the first mark in the first direction. 
     
     
         3 . The overlay key of  claim 1 , wherein the second mark is disposed adjacent to the first mark in a second direction substantially perpendicular to the first direction. 
     
     
         4 . The overlay key of  claim 1 , wherein the first and second patterns are arranged such that each of the first and second marks has a rectangular box shape, and the first and second marks are arranged such that a side portion of the first mark is adjacent to a side portion of the second mark. 
     
     
         5 . The overlay key of  claim 1 , further comprising:
 a third mark including third patterns with a third pitch formed in the first layer and extending in a second direction substantially perpendicular to the first direction; and   a fourth mark including fourth patterns formed on the second layer, the fourth mark disposed adjacent to the third mark, and the fourth patterns having a fourth pitch substantially equal to the third pitch and extending in a substantially same direction as the second direction.   
     
     
         6 . The overlay key of  claim 5 , wherein the second mark is disposed adjacent to the first mark in the first direction. 
     
     
         7 . The overlay key of  claim 6 , wherein the fourth mark is disposed adjacent to the third mark in the first direction. 
     
     
         8 . The overlay key of  claim 6 , wherein the fourth mark is disposed adjacent to the second mark in the second direction. 
     
     
         9 . The overlay key of  claim 5 , wherein the third mark is disposed adjacent to the first mark in the second direction. 
     
     
         10 . A method of forming an overlay key comprising:
 forming a first layer on a substrate;   patterning the first layer to form a first mark including first patterns extending in a first direction and having a first pitch;   forming a second layer on the patterned first layer; and   forming a second mark on the second layer adjacent to the first mark, the second mark including second patterns extending in a substantially same direction as the first direction and having a second pitch substantially equal to the first pitch.   
     
     
         11 . The method of  claim 10 , wherein the second mark is formed adjacent to the first mark in the first direction. 
     
     
         12 . The method of  claim 10 , wherein the second mark is formed adjacent to the first mark in a second direction substantially perpendicular to the first direction. 
     
     
         13 . The method of  claim 10 , wherein the first and second patterns are arranged such that each of the first and second marks has a rectangular box shape, and the first and second marks are arranged such that a side portion of the first mark is adjacent to a side portion of the second mark. 
     
     
         14 . The method of  claim 10 , further comprising:
 patterning the first layer to form a third mark, the third mark including third patterns extending in a second direction substantially perpendicular to the first direction and having a third pitch; and   forming a fourth mark adjacent to the third mark on the second layer, the fourth mark comprising fourth patterns extending in a substantially same direction as the second direction and having a fourth pitch substantially equal to the third pitch.   
     
     
         15 . The method of  claim 14 , wherein the second mark is formed adjacent to the first mark in the first direction. 
     
     
         16 . The method of  claim 15 , wherein the fourth mark is formed adjacent to the third mark in the first direction. 
     
     
         17 . The method of  claim 15 , wherein the fourth mark is formed adjacent to the second mark in the second direction. 
     
     
         18 . The method of  claim 14 , wherein the third mark is formed adjacent to the first mark in the second direction.