Metrology method and apparatus, lithographic system and device manufacturing method
First Claim
1. A method comprising:
- forming a set of targets on a substrate using a lithographic process, each target of the set of targets comprising an overlay bias, the overlay bias of each target of the set of targets being different from each other target of the set of targets;
obtaining three or more asymmetry measurements from corresponding three or more targets of the set of targets, each of the three or more asymmetry measurements comprising;
a first asymmetry value corresponding to an overlay error in the lithographic process, anda second asymmetry value corresponding to feature asymmetry in the set of targets; and
calculating the overlay error based on the three or more asymmetry measurements and an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error.
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Abstract
A lithographic process is used to form a plurality of target structures (T) on a substrate (W). Each target structure comprises overlaid gratings each having a specific overlay bias. Asymmetry (A) of each grating, measured by scatterometry, includes contributions due to (i) the overlay bias, (ii) an overlay error (OV) in the lithographic process and (iii) bottom grating asymmetry within the overlaid gratings. Asymmetry measurements are obtained for three or more target structures having three or more different values of overlay bias (e.g., −d, 0, +d). Knowing the three different overlay bias values and a theoretical curve relationship between overlay error and asymmetry, overlay error (OV) can be calculated while correcting the effect of bottom grating asymmetry. Bias schemes with three and four different biases are disclosed as examples. Gratings with different directions and biases can be interleaved in a composite target structure.
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Citations
17 Claims
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1. A method comprising:
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forming a set of targets on a substrate using a lithographic process, each target of the set of targets comprising an overlay bias, the overlay bias of each target of the set of targets being different from each other target of the set of targets; obtaining three or more asymmetry measurements from corresponding three or more targets of the set of targets, each of the three or more asymmetry measurements comprising; a first asymmetry value corresponding to an overlay error in the lithographic process, and a second asymmetry value corresponding to feature asymmetry in the set of targets; and calculating the overlay error based on the three or more asymmetry measurements and an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An inspection apparatus comprising:
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a support configured to hold a substrate having a set of targets, each of the targets comprising an overlay bias, the overlay bias of each of the targets being different from each other of the targets; an optical system configured to detect radiation scattered by three or more targets of the set of targets to obtain corresponding three or more asymmetry measurements, each of the three or more asymmetry measurements comprising; a first asymmetry value corresponding to an overlay error in the lithographic process, and a second asymmetry value corresponding to feature asymmetry in the set of targets; and a processor configured to calculate the overlay error based on the three or more asymmetry measurements and an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A non-transitory computer readable medium having stored thereon computer-executable instructions that, in response to execution by a computing device, cause the computing device to perform operations comprising:
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forming a set of targets on a substrate using a lithographic process, each target of the set of targets comprising an overlay bias, the overlay bias of each target of the set of targets being different from each other target of the set of targets; obtaining three or more asymmetry measurements from corresponding three or more targets of the set of targets formed on the substrate, each of the three or more asymmetry measurements comprising; a first asymmetry value corresponding to an overlay error in the lithographic process, and a second asymmetry value corresponding to feature asymmetry in the set of targets; and calculating the overlay error based on the three or more asymmetry measurements and an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error.
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16. A lithographic system comprising:
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a lithographic apparatus comprising; an illumination system configured to illuminate a pattern, a projection system configured to project an image of the pattern onto a substrate, and a support configured to hold a substrate having a set of targets, each of the targets comprising an overlay bias, the overlay bias of each of the targets being different from each other of the targets; and an inspection apparatus comprising; an optical system configured to detect radiation scattered by three or more targets of the set of targets to obtain corresponding three or more asymmetry measurements, each of the three or more asymmetry measurements comprising; a first asymmetry value corresponding to an overlay error in the lithographic process, and a second asymmetry value corresponding to feature asymmetry in the set of targets; and a processor configured to calculate the overlay error based on the three or more asymmetry measurements an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error, wherein the lithographic apparatus is configured to use the calculated overlay error from the inspection apparatus in applying the pattern to further substrates.
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17. A method comprising:
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forming a set of targets on a substrate using a lithographic process, each target of the set of targets comprising an overlay bias, the overlay bias of each target of the set of targets being different from each other target of the set of targets; obtaining three or more asymmetry measurements from corresponding three or more targets of the set of targets formed on the substrate, each of the three or more asymmetry measurements comprising; a first asymmetry value corresponding to an overlay error in the lithographic process, and a second asymmetry value corresponding to feature asymmetry in the set of targets; and calculating the overlay error based on the three or more asymmetry measurements and an assumed non-linear relationship between the overlay error and the three or more asymmetry measurements, such that the second asymmetry value corresponding to feature asymmetry is excluded from the calculated overlay error; and controlling the lithographic process for later substrates based on the calculated overlay error.
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Specification