Noise correction for alignment signal
AssigneeASML Holding N.V.
InventorsZahrasadat DASTOURI, Greger Göte ANDERSSON, Krishanu SHOME, Igor Matheus Petronella AARTS
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Abstract
A method of applying a measurement correction includes determining an orthogonal subspace used to characterize the measurement as a plot of data. A first axis of the orthogonal subspace corresponds to constructive interference output from an interferometer of the metrology system plus a first error variable and a second axis of the orthogonal subspace corresponds to destructive interference output from the interferometer of the metrology system plus a second error variable. The method also includes determining a slope of the plot of data and determining a fitted line to the plot of data in the orthogonal subspace based on the slope.
Claims20
A metrology system, comprising:
- a radiation source configured to generate light;
- a reflector configured to direct at least a portion of the light towards a substrate;
- an interferometer configured to receive light diffracted from a pattern on the substrate or reflected from the substrate, and to produce output light from interference generated based on the diffracted or reflected light;
- a detector configured to receive the output light and to produce a measurement;
- and
- a controller configured to determine a correction to the measurement by:
- determining an orthogonal subspace used to characterize the measurement as a plot of data, wherein a first axis of the orthogonal subspace corresponds to constructive interference output from the interferometer plus a first error variable and a second axis of the orthogonal subspace corresponds to destructive interference output from the interferometer plus a second error variable,
- determining a slope of the plot of data, and
- determining a fitted line to the plot of data in the orthogonal subspace based on the slope.
A lithographic apparatus, comprising:
- an illumination system configured to illuminate a pattern of a patterning device;
- a projection system configured to project an image of the pattern onto a target portion of a substrate;
- and
- a metrology system comprising:
- a radiation source configured to generate light;
- a reflector configured to direct at least a portion of the light towards a substrate;
- an interferometer configured to receive light that has been diffracted from a pattern on the substrate, or reflected from the substrate, and to produce output light from interference generated based on the diffracted or reflected light;
- a detector configured to receive the output light and to produce a measurement;
- and
- a controller configured to determine a correction to the measurement by:
- determining an orthogonal subspace used to characterize the measurement as a plot of data, wherein a first axis of the orthogonal subspace corresponds to constructive interference output from the interferometer plus a first error variable and the second axis of the orthogonal subspace corresponds to destructive interference output from the interferometer plus a second error variable,
- determining a slope of the plot of data, and
- determining a fitted line to the plot of data in the orthogonal subspace based on the slope.
A method of applying a correction to a measurement determined by a metrology system in order to account for multiple noise sources, the method comprising:
- determining an orthogonal subspace used to characterize the measurement as a plot of data, wherein a first axis of the orthogonal subspace corresponds to constructive interference output from an interferometer of the metrology system plus a first error variable and the second axis of the orthogonal subspace corresponds to destructive interference output from the interferometer of the metrology system plus a second error variable;
- determining a slope of the plot of data;
- and
- determining a fitted line to the plot of data in the orthogonal subspace based on the slope.
Dependencies are inferred from the claim text.