US 12,247,883 B2
Wavelength tracking system, method to calibrate a wavelength tracking system, lithographic apparatus, method to determine an absolute position of a movable object, and interferometer system
Engelbertus Antonius Fransiscus Van Der Pasch, Oirschot (NL); Suzanne Johanna Antonetta Geertruda Cosijns, Casteren (NL); Koen Govert Olivier Van De Meerakker, Eindhoven (NL); and Ivo Widdershoven, Eindhoven (NL)
Assigned to ASML Netherlands B.V., Veldhoven (NL)
Filed by ASML Netherlands B.V., Veldhoven (NL)
Filed on Oct. 20, 2022, as Appl. No. 18/048,119.
Application 18/048,119 is a division of application No. 16/965,753, granted, now 11,525,737, previously published as PCT/EP2019/050848, filed on Jan. 15, 2019.
Claims priority of application No. 18154460 (EP), filed on Jan. 31, 2018; and application No. 18197177 (EP), filed on Sep. 27, 2018.
Prior Publication US 2023/0056872 A1, Feb. 23, 2023
Int. Cl. G01J 9/02 (2006.01); G01B 9/02001 (2022.01); G01B 9/02002 (2022.01); G01B 9/02015 (2022.01); G01B 11/00 (2006.01); G03F 7/00 (2006.01)
CPC G01J 9/0246 (2013.01) [G01B 9/02002 (2013.01); G01B 9/02007 (2013.01); G01B 9/02028 (2013.01); G01B 11/002 (2013.01); G03F 7/0002 (2013.01); G03F 7/70725 (2013.01)] 14 Claims
OG exemplary drawing
 
1. A wavelength tracking system comprising:
a wavelength tracking unit with reflection surfaces disposed at a constant distance from each other and configured to provide a first reflection path with a first path length and a second reflection path with a second path length, wherein:
the wavelength tracking unit comprises a wavelength tracking cavity comprising a cavity opening,
the cavity comprises a first reflection path reflection surface within the cavity and arranged in the first reflection path and a second reflection path reflection surface arranged outside the cavity in the second reflection path next to the cavity opening, and
the first path length is substantially larger than the second path length based on the second reflection path not traversing the cavity, and
an interferometer system, wherein the interferometer system comprises:
a beam splitter to split a light beam into a first measurement beam and a second measurement beam, at least one optic element to guide the first measurement beam, at least partially, along the first reflection path and the second measurement beam, at least partially, along the second reflection path,
a first light sensor arranged at an end of the first reflection path to receive the first measurement beam and to provide a first sensor signal on the basis of the first measurement beam,
a second light sensor arranged at an end of the second reflection path to receive the second measurement beam and to provide a second sensor signal on the basis of the second measurement beam, and
a processing unit to determine a wavelength or change in wavelength based on the first sensor signal and the second sensor signal.