Reduction of thermal non-cyclic error effects in interferometers
First Claim
1. An interferometer assembly for use in a lithography tool used for fabricating integrated circuits on a wafer, wherein the lithography tool includes a support structure and a stage for positioning the wafer relative to the support structure, the interferometer assembly comprising:
- an interferometer configured to direct a measurement beam between the stage and the support structure and combine the measurement beam with another beam to form an output beam which comprises a phase related to a position of the stage relative to the support structure,wherein the interferometer is mechanically secured to the lithography tool through an interferometer surface selected to cause a distance between the stage and the support structure along the measurement beam path to be insensitive to thermal expansion of the interferometer over a range of temperatures so that the phase of the output beam is insensitive to thermal changes of the interferometer over the range of temperatures.
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Abstract
In general, in one aspect, the invention features an interferometer assembly for use in a lithography tool used for fabricating integrated circuits on a wafer, wherein the lithography tool includes a support structure and a stage for positioning the wafer relative to the support structure, the interferometer assembly including an interferometer configured to direct a measurement beam between the stage and the support structure and combine the measurement beam with another beam to form an output beam which includes a phase related to a position of the stage relative to the support structure, wherein the interferometer is mechanically secured to the lithography tool through an interferometer surface selected to cause the phase of the output beam to be insensitive to thermal changes of the interferometer over a range of temperatures.
46 Citations
38 Claims
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1. An interferometer assembly for use in a lithography tool used for fabricating integrated circuits on a wafer, wherein the lithography tool includes a support structure and a stage for positioning the wafer relative to the support structure, the interferometer assembly comprising:
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an interferometer configured to direct a measurement beam between the stage and the support structure and combine the measurement beam with another beam to form an output beam which comprises a phase related to a position of the stage relative to the support structure, wherein the interferometer is mechanically secured to the lithography tool through an interferometer surface selected to cause a distance between the stage and the support structure along the measurement beam path to be insensitive to thermal expansion of the interferometer over a range of temperatures so that the phase of the output beam is insensitive to thermal changes of the interferometer over the range of temperatures. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An apparatus, comprising:
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an interferometer, which during operation produces an output beam comprising a phase related to an optical path difference between a path of a first beam, which exits the interferometer at an exit surface and contacts a measurement object, and a path of a second beam; and a mechanical fixture for mechanically securing the interferometer to an object, wherein the interferometer is secured to the mechanical fixture at a location of the interferometer that causes a path length between the exit surface and the measurement object to be insensitive to thermal expansion of the interferometer over a range of temperatures so that the phase of the output beam is insensitive to thermal changes of the interferometer over the range of temperatures. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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38. An apparatus, comprising:
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an interferometer, which during operation produces an output beam comprising a phase related to an optical path difference between a path of a first beam, which exits the interferometer at an exit surface and contacts a measurement object, and a path of a second beam, the interferometer being configured so that a thermal variation of an optical path length of the first beam path within the interferometer is unequal to a thermal variation of an optical path length of the second beam path within the interferometer; and a mechanical fixture for mechanically securing the interferometer to an object, wherein the interferometer is secured to the mechanical fixture at a location of the interferometer displaced from the exit surface by an amount that causes a thermal variation in the optical path difference of the first and second beam paths within the interferometer to be offset by a thermal variation in the optical path length of the first beam path out of the interferometer so that the phase of the output beam is insensitive to thermal changes of the interferometer over a range of temperatures.
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Specification