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

Claim 14:
15. The system of claim 13, wherein: a) the illumination source is further configured to illuminate a second composite grating on the substrate by said first and second illumination beams, wherein the second composite grating is 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 a grating direction, and b) the image detector is further configured to obtain a third measured signal associated with an intensity of a plus first order diffracted beam produced from the first illumination beam by illuminating the second composite grating, and 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.