Patent ID: 11953450
Assignee: ASML NETHERLANDS B.V.
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 6:
7. The method of claim 6, further comprising:
obtaining a third measured signal associated with an intensity of a plus first order diffracted beam produced from the first illumination beam by illuminating a second composite grating formed by a third grating and a fourth grating on top of the third grating, wherein the third grating and the fourth grating have a substantially identical pitch as the first and the second gratings, and the third grating is shifted with respect to the fourth grating along the grating direction;
obtaining a fourth measured signal associated with an intensity of a minus first order diffracted beam produced from the second illumination beam by illuminating the second composite grating; and
wherein the determining the overlay error is further based on the third measured signal and the fourth measured signal.