CPC G03F 7/70633 (2013.01) [G03F 9/7019 (2013.01); G03F 9/7049 (2013.01); G03F 9/7076 (2013.01); G03F 9/7084 (2013.01); G03F 9/7088 (2013.01); G03F 7/70216 (2013.01)] | 40 Claims |
1. An overlay target comprising:
a first pair of alignment targets and a second pair of alignment targets, wherein each of the first and second pairs of alignment targets include:
a first periodic feature on a first layer of a sample, the first periodic feature having a first pitch along a measurement direction;
a second periodic feature on the first layer, the second periodic feature having a second pitch along the measurement direction;
a third periodic feature on a second layer of the sample, the third periodic feature having the second pitch along the measurement direction, wherein the third periodic feature overlaps the first periodic feature to form a first interference pattern; and
a fourth periodic feature on the second layer of the sample, the fourth periodic feature having the first pitch along the measurement direction, wherein the fourth periodic feature overlaps the second periodic feature with a bias offset along the measurement direction to form a second interference pattern;
wherein the bias offset of the first pair of alignment targets has a positive value along the measurement direction, wherein the bias offset of the second pair of alignment targets has a negative value along the measurement direction; and
wherein an overlay error along the measurement direction between the first and second layers of the sample is determinable based on the first and second interference patterns.
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