Cyclic error reduction in average interferometric position measurements
First Claim
1. An interferometric stage system comprising:
- a translatable stage;
a base defining a reference frame;
a positioning system coupled to the stage for adjusting the position of the stage relative to the reference frame;
an interferometry system which during operation directs a measurement beam along path between the stage and a portion of the base to produce an interferometric signal indicative of a position of the stage along the path, wherein a defect in the interferometry system produces a cyclic error contribution to the interferometric signal; and
an electronic controller coupled to the interferometry system and the positioning system, wherein during operation the electronic controller determines an average position for the stage along the first path based on the interferometric signal corresponding to each of multiple positions of the stage, wherein the multiple positions of the stage include an initial position and at least one additional position, and wherein the controller selects each of the additional positions to reduce the cyclic error contribution in the average position.
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Accused Products
Abstract
The invention features a system and method for reducing the contribution of cyclic errors to an interferometric position measurement of a movable stage. An initial interferometric position measurement of the stage is averaged with at least one additional measurement corresponding to a displacement(s) of the stage from its initial position. The displacements are selected to reduce the overall cyclic error contribution to an average position measurement. As a result, the average position of the stage can be measured more accurately than any of its individual positions. The average position can be used to more accurately determine the average position of an alignment mark on a wafer carried by the stage. Furthermore, the averaging described above can be applied to additional interferometric measurement axes. For example, the averaging can be applied to two laterally displacement measurement axes that are substantially parallel to one another to more accurately determine an average angular orientation of the stage. The result can be used to more correctly determine an Abbe offset error in the average position of an off-axis alignment mark (i.e., an alignment mark that is not aligned with one of the interferometric measurement axes).
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Citations
2 Claims
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1. An interferometric stage system comprising:
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a translatable stage;
a base defining a reference frame;
a positioning system coupled to the stage for adjusting the position of the stage relative to the reference frame;
an interferometry system which during operation directs a measurement beam along path between the stage and a portion of the base to produce an interferometric signal indicative of a position of the stage along the path, wherein a defect in the interferometry system produces a cyclic error contribution to the interferometric signal; and
an electronic controller coupled to the interferometry system and the positioning system, wherein during operation the electronic controller determines an average position for the stage along the first path based on the interferometric signal corresponding to each of multiple positions of the stage, wherein the multiple positions of the stage include an initial position and at least one additional position, and wherein the controller selects each of the additional positions to reduce the cyclic error contribution in the average position.
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2-43. -43. (canceled)
Specification