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 |
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.
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