Metrology method and apparatus, lithographic system and device manufacturing method
First Claim
1. A method comprising:
- forming three or more targets on a substrate using a lithographic process;
obtaining scatterometry measurements from the three or more targets, each of the scatterometry measurements comprising;
a first value corresponding to an overlay in the three or more targets, anda second value corresponding to an asymmetry of a feature in a corresponding one of the three or more targets; and
calculating an overlay error based on the scatterometry measurements and a non-linear relationship between the overlay and the scatterometry measurements, such that the second value 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
20 Claims
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1. A method comprising:
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forming three or more targets on a substrate using a lithographic process; obtaining scatterometry measurements from the three or more targets, each of the scatterometry measurements comprising; a first value corresponding to an overlay in the three or more targets, and a second value corresponding to an asymmetry of a feature in a corresponding one of the three or more targets; and calculating an overlay error based on the scatterometry measurements and a non-linear relationship between the overlay and the scatterometry measurements, such that the second value 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; an optical system configured to detect radiation scattered from three or more targets of the set of targets to obtain corresponding three or more scatterometry measurements, each of the three or more scatterometry measurements comprising; a first value corresponding to an overlay in the set of targets, and a second value corresponding to an asymmetry of a feature in a corresponding one of the three or more targets of the set of targets; a processor configured to calculate an overlay error based on the three or more scatterometry measurements and a non-linear relationship between the overlay and the three or more scatterometry measurements, such that the second value is excluded from the calculated overlay error. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. 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; and an inspection apparatus comprising; an optical system configured to detect radiation scattered from three or more targets of the set of targets to obtain corresponding three or more scatterometry measurements, each of the three or more scatterometry measurements comprising; a first value corresponding to an overlay in the set of targets, and a second value corresponding to an asymmetry of a feature in a corresponding one of the three or more targets of the set of targets; and a processor configured to calculate an overlay error based on the three or more scatterometry measurements and a non-linear relationship between the overlay and the three or more scatterometry measurements. - View Dependent Claims (20)
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Specification