Cyclic error compensation in interferometric encoder systems
AssigneeZygo Corporation
InventorFrank C. Demarest
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Abstract
Methods and apparatuses for performing the same, where the methods include obtaining, from an interferometer, a time-varying interference signal S(t) based on a combination of a first beam and a second beam, the first beam being diffracted from an encoder scale, in which at least one of the encoder scale and the interferometer is moveable with respect to the other, obtaining one or more error correction signals based on one or more errors that modify the time-varying interference signal S(t), and outputting information about a change in a position of the encoder scale relative to the interferometer based on the time-varying interference signal S(t) and the one or more error correction signals.
Claims59
A method comprising:
- obtaining, from an interferometer, a time-varying interference signal S(t) based on a combination of a first beam and a second beam, subsequent to the first beam being diffracted from an encoder scale, wherein at least one of the encoder scale and the interferometer is moveable with respect to the other;
- obtaining one or more error correction signals based on one or more errors that modify the time-varying interference signal S(t), wherein the one or more error correction signals comprises an error correction signal representative of a baseband Doppler error;
- and
- outputting information about a change in a position of the encoder scale relative to the interferometer based on the time-varying interference signal S(t) and the one or more error correction signals.
An apparatus comprising:
- an interferometry system configured to, during operation of the apparatus, combine a first beam diffracted from an encoder scale and a second beam to produce an output beam corresponding to a time-varying interference signal S(t),
- wherein at least one of the encoder scale and the interferometry system is moveable with respect to the other, and imperfections in the interferometry system produce one or more errors that modify the time-varying interference signal S(t);
- and
- an electronic processor configured to, during operation of the apparatus, perform operations comprising:
- obtaining one or more error correction signals based on the one or more errors, wherein the one or more error correction signals comprises an error correction signal representative of a baseband Doppler error;
- and
- outputting information about a change in a position of the encoder scale relative to the interferometry system based on the time-varying interference signal S(t) and the one or more error correction signals.
A computer program product, encoded on a non-transitory computer-readable medium, operable to cause a data processing apparatus to perform operations comprising:
- obtaining, from an interferometer, a time-varying interference signal S(t) based on a combination of a first beam and a second beam, the first beam being diffracted from an encoder scale, wherein at least one of the encoder scale and the interferometer is moveable with respect to the other;
- obtaining one or more error correction signals based on one or more errors that modify the time-varying interference signal S(t), wherein the one or more error correction signals comprises an error correction signal representative of a baseband Doppler error;
- and
- outputting information about a change in a position of the encoder scale relative to the interferometer based on the time-varying interference signal S(t) and the one or more error correction signals.
A lithography system comprising:
- a moveable stage for supporting a wafer, wherein the moveable stage comprises an encoder scale that moves with the moveable stage;
- an illumination system configured to image radiation onto the wafer during operation of the lithography system;
- a positioning system configured to adjust a position of the moveable stage during operation of the lithography system;
- an interferometry system configured to, during operation of the lithography system:
- direct a primary beam toward the encoder scale;
- and
- combine a first beam diffracted from the encoder scale and a second beam to produce an output beam corresponding to a time-varying interference signal S(t),
- wherein imperfections in the interferometry system produce one or more errors that modify the time-varying interference signal S(t);
- and
- an electronic processor configured to, during operation of the lithography system, perform operations comprising:
- obtaining one or more error correction signals based on the one or more errors, wherein the one or more error correction signals comprises an error correction signal representative of a baseband Doppler error;
- and
- outputting information about a change in a position of the encoder scale relative to the interferometry system based on the time-varying interference signal S(t) and the one or more error correction signals.
Dependencies are inferred from the claim text.