Reduction of fit error due to non-uniform sample distribution
First Claim
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1. An alignment method for a lithography apparatus, comprising:
- determining a plurality of data points associated with an object that moves with a wafer table, the data points including a position and radiation intensity associated with the position; and
performing an interpolation of the plurality of data points to produce a best fit curve, wherein the performing the interpolation comprises adjusting a weighting assigned to the plurality of data points during the interpolation to provide less weight to the densely spaced data points and more weight to the sparsely spaced data points.
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Abstract
A weighted fit based on a sample density of a plurality of samples is used to determine an alignment curve. A scan that produces the samples may include portions having greater and lesser sample density. While performing an interpolation to produce a best fit curve, a plurality of neighboring samples are chosen for each sample point, for sample points associated with a value above a threshold. A weighting function may be performed based on a distance between a given sample and the chosen nearest neighbors, wherein measurements that are taken in a region with denser samples are given less weight than measurements that are taken in a region with sparser samples.
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Citations
27 Claims
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1. An alignment method for a lithography apparatus, comprising:
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determining a plurality of data points associated with an object that moves with a wafer table, the data points including a position and radiation intensity associated with the position; and performing an interpolation of the plurality of data points to produce a best fit curve, wherein the performing the interpolation comprises adjusting a weighting assigned to the plurality of data points during the interpolation to provide less weight to the densely spaced data points and more weight to the sparsely spaced data points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A device for generating an alignment curve in a lithographic apparatus, comprising:
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a mask table constructed and arranged to support a mask; a wafer table constructed and arranged to support a wafer; a projection system; and a control system configured (i) to generate a plurality of data points from radiation intensity measurements generated during a water scan, (ii) to perform an interpolation of the plurality of the data points to produce a best fit curve, and (iii) to adjust a weighting assigned to the plurality of data points during the interpolation to provide less weight to the densely spaced data points and more weight to the sparse data points. - View Dependent Claims (14, 15, 16, 17)
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18. A method for controlling overlay in a lithography system, comprising:
- performing a one dimensional (1-D) scan using an image sensor within a plane of best focus;
generating a set of data points based the 1-D scan, each data point representing a measured intensity and position; generating a best fit curve based on a density-weighted fit applied to the set of data points; and determining a position of maximum intensity corresponding to optimum alignment based on a peak position of the best fit curve. - View Dependent Claims (19, 20, 21)
- performing a one dimensional (1-D) scan using an image sensor within a plane of best focus;
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22. A system for controlling overlay in a lithography apparatus, comprising:
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a mask table constructed and arranged to support a mask; a wafer table constructed and arranged to support a wafer; an image sensor that moves in concert with the wafer table and is configured to determine an alignment position based on a peak in detected light intensity; a projection system; and
a control system configured (i) to generate a plurality of data points generated during a wafer scan using the image sensor, (ii) to perform an interpolation of the plurality of data points to produce a best fit curve, and (iii) to adjust a weight assigned to the plurality of data points during the interpolation to provide less weight to the dense data points and more weight to the sparse data points. - View Dependent Claims (23, 24, 25, 26, 27)
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Specification