US 12,305,979 B2
Interferometer system and lithographic apparatus
Maarten Jozef Jansen, Hoogeloon (NL)
Assigned to ASML NETHERLANDS B.V., Veldhoven (NL)
Appl. No. 18/027,851
Filed by ASML NETHERLANDS B.V., Veldhoven (NL)
PCT Filed Aug. 20, 2021, PCT No. PCT/EP2021/073179
§ 371(c)(1), (2) Date Mar. 22, 2023,
PCT Pub. No. WO2022/078657, PCT Pub. Date Apr. 21, 2022.
Claims priority of application No. 20201359 (EP), filed on Oct. 12, 2020.
Prior Publication US 2023/0332880 A1, Oct. 19, 2023
Int. Cl. G01B 9/02015 (2022.01); G01B 9/02091 (2022.01)
CPC G01B 9/02028 (2013.01) [G01B 9/02091 (2013.01); G01B 2290/45 (2013.01)] 20 Claims
OG exemplary drawing
 
1. An interferometer system for determining a position of a target surface, wherein the interferometer system comprises:
a first detector configured to receive a first reference beam that is adapted to travel a first reference beam path including a reference beam path, and receive a first measurement beam that is adapted to travel a first measurement beam path including a measurement beam path and a reference axis path determined by a reference surface;
a second detector configured to receive a second reference beam that is adapted to travel a second reference beam path including the reference beam path, and receive a second measurement beam that is adapted to travel a second measurement beam path including the measurement beam path and a measurement axis path determined by the target surface; and
a delay path controller configured to adapt a delay length of: a reference variable delay path which is part of the reference beam path, or a measurement variable delay path which is part of the measurement beam path, or both the reference variable delay path and measurement variable delay path,
wherein during operational use:
a reference spectral coherence pulse of the first reference beam and the first measurement beam occurs at the first detector for the delay length that corresponds to a reference coherence arrangement, and
a measurement spectral coherence pulse of the second reference beam and the second measurement beam occurs at the second detector for the delay length that corresponds to a measurement coherence arrangement; and
a control unit configured to:
receive a reference coherence signal from the first detector, and a measurement coherence signal from the second detector; and
determine a zero-position of the target surface based:
on the reference coherence signal and the measurement coherence signal; and
on the reference coherence arrangement and the measurement coherence arrangement, or a delay path difference between the reference coherence arrangement and the measurement coherence arrangement, or the reference coherence arrangement, the measurement coherence arrangement and the delay path difference.