Methods for measuring overlays

Abstract

A method for measuring overlay includes receiving a first image of a first overlay mark captured using light having a first wavelength. The method includes receiving a second image of a second overlay mark captured using light having a second wavelength different from the first wavelength. The method includes measuring a displacement between a central portion of the first image and a central portion of the second image, wherein the first and second overlay marks are disposed on different levels.

What is claimed is: 
     
         1 . A method for measuring overlay, the method comprising:
 receiving a first image of a first overlay mark captured using light having a first wave length;   receiving a second image of a second overlay mark captured using light having a second wavelength different from the first wavelength; and   measuring a displacement between a central portion of the first image and a central portion of the second image, wherein the first and second overlay marks are disposed on different levels.   
     
     
         2 . The method of  claim 1 , wherein the first overlay mark is disposed on a lower level than the second overlay mark, and
 wherein the first wavelength is longer or shorter than the second wavelength.   
     
     
         3 . The method of  claim 2 , wherein at least one of the first and second wavelengths is included in a range of visible light, a range above the range of visible light, or a range below the range of visible light. 
     
     
         4 . The method of  claim 1 , wherein the first overlay mark is disposed on a first layer of a wafer, and the second overlay mark is disposed on a second layer over the first layer of the wafer. 
     
     
         5 . The method of  claim 4 , wherein the first and second overlay marks are disposed on a scribe lane of the wafer. 
     
     
         6 . A method for measuring overlay, the method comprising:
 receiving a first image corresponding to a first overlay mark captured using light having a first wavelength, the first overlay mark disposed on a first layer of a wafer;   receiving a second image corresponding to a second overlay mark captured using light having a second wavelength different from the first wavelength, the second overlay mark disposed on a second layer over the wafer;   receiving a combined image in which the first and second images are overlapped; and   calculating a displacement between a central portion of the first image and a central portion of the second image in the combined image to measure an overlay between the first overlay mark and the second overlay mark.   
     
     
         7 . The method of  claim 6 , wherein the first wavelength is longer or shorter than the second wavelength. 
     
     
         8 . The method of  claim 6 , further comprising receiving a third image corresponding to a third overlay mark captured using light having a third wavelength,
 wherein the third overlay mark is disposed on a third layer over the second layer, and the third wavelength is different from the first and second wavelengths.   
     
     
         9 . The method of  claim 8 , wherein the first wavelength is longer or shorter than the second wavelength, and the second wavelength is longer or shorter than the third wavelength. 
     
     
         10 . The method of  claim 6 , wherein the first overlay mark is disposed on the first layer that corresponds to a scribe lane of the wafer, and the second overlay mark is disposed on the second layer that corresponds to the scribe lane of the wafer. 
     
     
         11 . The method of  claim 6 , wherein one of the first and second overlay marks is horizontally spaced apart from the other and is not vertically overlapped with the other. 
     
     
         12 . The method of  claim 6 , wherein the second layer is directly on the first layer. 
     
     
         13 . The method of  claim 6 , wherein the first overlay mark comprises a plurality of first parallel lines that are spaced apart, and the second overlay mark comprises a plurality of second parallel lines that are spaced apart. 
     
     
         14 . The method of  claim 13 , wherein capturing the first image comprises:
 selecting the first parallel lines; and   obtaining an image of the first parallel lines using the light having the first wavelength.   
     
     
         15 . The method of  claim 14 , wherein capturing the second image comprises:
 selecting the second parallel lines; and   obtaining an image of the second parallel lines using the light having the second wavelength.   
     
     
         16 . The method of  6 , wherein an additional layer is disposed between the first layer and the second layer. 
     
     
         17 . A method for determining an overlay error, the method comprising:
 receiving a first image of a first overlay mark obtained with light with a first wavelength, wherein the first overlay mark is disposed on a first layer of a wafer and the first overlay mark is an open-centered box;   receiving a second image of a second overlay mark obtained with light with a second wavelength, wherein the second overlay mark is disposed on a second layer of the wafer and the second overlay mark is a closed box; and   determining an overlay error between the first overlay mark and the second overlay mark by overlapping the first image and the second image.   
     
     
         18 . The method of  claim 17 , further comprising determining the overlay error by calculating a displacement between first lines disposed on inner surfaces of the first overlay mark and second lines disposed on outer surfaces of the second overlay mark. 
     
     
         19 . The method of  claim 17 , wherein the light with the first wavelength has a different wavelength than the light with the second wavelength. 
     
     
         20 . The method of  claim 17 , wherein there is an additional layer between the first overlay mark and the second overlay mark.