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

Claim 0:
1. A method for measuring 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 method comprising:
illuminating, using a first illumination beam, the composite grating under a first angle of incidence, such that the first illumination beam propagates along a direction that has a component along a first horizontal direction along the surface of the substrate;
measuring a first signal associated with an intensity of a plus first order diffracted beam produced from the first illumination beam illuminating the composite grating;
illuminating, using a second illumination beam, the composite grating under a second angle of incidence, such that the second illumination beam propagates along a direction that has a component along a second horizontal direction along the surface of the substrate, wherein the second horizontal direction is opposite to the first horizontal direction; and
measuring a second signal associated with an intensity of a minus first order diffracted beam produced from the second illumination beam illuminating the composite grating.