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 alignment scope;
an interferometry system which during operation directs a measurement beam along a first path between the stage and a portion of the base to produce an interferometric signal indicative of a position of the stage along the first 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 a 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, to reduce the cyclic error contribution in the determined position,wherein during operation the electronic controller determines whether an alignment mark on a wafer carried by the stage is within view of the alignment scope based on the determined 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
20 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 alignment scope; an interferometry system which during operation directs a measurement beam along a first path between the stage and a portion of the base to produce an interferometric signal indicative of a position of the stage along the first 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 a 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, to reduce the cyclic error contribution in the determined position, wherein during operation the electronic controller determines whether an alignment mark on a wafer carried by the stage is within view of the alignment scope based on the determined position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. 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 a first path between the stage and a portion of the base to produce a first interferometric signal indicative of a position of the stage along the first path, directs a second measurement beam along a second path between the stage and the portion of the base to produce a second interferometric signal indicative of a position of the stage along the second path, wherein a defect in the interferometry system produces a cyclic error contribution to at least the first interferometric signal; and an electronic controller coupled to the interferometry system and the positioning system, wherein during operation the electronic controller determines a position for the stage along each of the first and second paths based on the interferometric signals 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, to reduce the cyclic error contribution to the determined position for at least the first path, and wherein the electronic controller further determines an angular orientation for the stage based on the determined positions of the stage along the first and second paths. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification