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

Claim 8:
9. A non-transitory computer readable medium having instructions stored thereon, that, when executed on a computing device, cause the computing device to perform operations for determining an overlay error between a first grating on a surface of a substrate and a second grating superimposed on the first grating, the second grating having substantially identical pitch as the first grating, and the second and first gratings forming a composite grating, the operations comprising:
obtaining a first measured signal associated with an intensity of a plus first order diffracted beam produced from a first illumination beam propagating along a direction that has a component along a first horizontal direction along the surface of the substrate and illuminating the composite grating;
obtaining a second measured signal associated with an intensity of a minus first order diffracted beam produced from the second illumination beam propagating along a direction that has a component opposite to the first horizontal direction along the surface of the substrate and illuminating the composite grating; and
determining the overlay error based on the first measured signal and the second measured signal.