US 6,982,793 B1
Method and apparatus for using an alignment target with designed in offset
Weidong Yang, Milpitas, Calif. (US); Roger R. Lowe-Webb, Sunnyvale, Calif. (US); John D. Heaton, Fremont, Calif. (US); and Guoguang Li, Fremont, Calif. (US)
Assigned to Nanometrics Incorporated, Milpitas, Calif. (US)
Filed on Apr. 04, 2002, as Appl. No. 10/116,863.
Int. Cl. G01B 11/27 (2006.01)
U.S. Cl. 356—401 49 Claims
OG exemplary drawing
 
1. A method of determining the alignment of a first element with respect to a second element, said method comprising:
providing an alignment target on said first element and said second element, the alignment target having a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude;
illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target;
detecting the radiation that is diffracted from said first overlay pattern, said second overlay pattern, and said third overlay pattern; and
calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference;
calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference, and
determining the approximate alignment error based on said first measured difference and said second measured difference.