Frequency-picked methodology for diffraction-based overlay measurement

An overlay error measurement structure, comprising:

• a first pattern disposed over a substrate;
• and
• a second pattern disposed over the first pattern and at least partially overlapping with the first pattern, wherein:
• the first pattern comprises a plurality of first sub-patterns extending in a first length along a first direction and being arranged with a first pitch in a second direction crossing the first direction and a plurality of second sub-patterns extending in a second length along the first direction and being arranged with a second pitch in the second direction crossing the first direction, wherein the second sub-patterns are disposed among the first sub-patterns, and wherein the second pitch is smaller than the first pitch to separate a first reflected light from the first pitch from a second reflected light from the second pitch;
• and
• the second pattern comprises a plurality of third sub-patterns extending in the first direction and being arranged with the first pitch in the second direction.

A method comprising:

• forming a first pattern having a plurality of first sub-patterns extending in a first interval along a first direction and being arranged with a first pitch in a second direction crossing the first direction;
• and
• forming a second pattern having a plurality of second sub-patterns extending in a second interval along the first direction and being arranged with a second pitch, smaller than the first pitch, in the second direction crossing the first direction, wherein the second sub-patterns are disposed among the first sub-patterns;
• and
• blocking a reflected first light associated with the second pitch from the second pattern;
• forming a third pattern over the first pattern, the third pattern having the first pitch and at least partially overlapping with the first pattern;
• and
• determining an overlay error between the first pattern and the third pattern based on diffracted light from the third pattern and diffracted light associated with the first pitch from the first pattern.