Reduction of fit error due to non-uniform sample distribution
AssigneeASML Netherlands B.V.
InventorBearrach Moest
Life of this patent
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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.
Claims27
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.
A device for generating an alignment curve in a lithographic apparatus, comprising:
- 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.
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.
A system for controlling overlay in a lithography apparatus, comprising:
- 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.
Dependencies are inferred from the claim text.