Method and apparatus for inspection and metrology
A method including obtaining a plurality of radiation distributions of measurement radiation redirected by the target, each of the plurality of radiation distributions obtained at a different gap distance between the target and an optical element of a measurement apparatus, the optical element being the nearest optical element to the target used to provide the measurement radiation to the target, and determining a parameter related to the target using data of the plurality of radiation distributions in conjunction with a mathematical model describing the measurement target.
1. A method comprising:
obtaining a plurality of radiation distributions of measurement radiation redirected by a same measurement target, each of the plurality of radiation distributions obtained at a different gap distance between the target and an optical element of a measurement apparatus, the optical element being the nearest optical element to the target used to provide the measurement radiation to the target; and
determining a parameter related to the target using a combination of data of the plurality of radiation distributions in conjunction with a mathematical model describing the target.
2. The method of claim 1 , wherein at least two of the radiation distributions are obtained with a different respective measurement beam wavelength.
3. The method of claim 1 , wherein at least two of the radiation distributions are obtained with a different respective measurement beam polarization.
4. The method of claim 1 , wherein the plurality of radiation distributions is obtained at least in part during a relative motion between the target and the optical element.
5. The method of claim 1 , wherein the optical element comprises a solid immersion lens.
6. The method of claim 1 , wherein the radiation distributions are angular resolved detected radiation distributions.
7. The method of claim 1 , wherein the parameter comprises at least one selected from: a critical dimension of a feature of the target, a radiation focus used to print the target, a radiation dose used to print the target, overlay, and/or alignment.
8. The method of claim 1 , wherein obtaining the plurality of radiation distributions comprises:
illuminating, using the optical element, the target with radiation; and
measuring radiation redirected by the target using a detector.
9. The method of claim 1 , wherein the target comprises a fiducial and the parameter comprises a parameter of an effective medium approximation in the model for roughness of a surface of the optical element.
10. The method of claim 1 , wherein determining the parameter comprises a target reconstruction.
11. The method of claim 1 , wherein determining the parameter comprises minimizing a difference between data of the radiation distributions and data corresponding to the radiation distributions at the respective different gap distances determined using the model.
12. The method of claim 1 , wherein the mathematical model comprises a unit cell model representing a period of a periodic structure of the target.
13. The method of claim 12 , comprising a separate unit cell model for each radiation distribution, each unit cell having an identical set of floating parameters of the target and a floating gap distance parameter that is different for each of the unit cells.
14. The method of claim 1 , wherein the measurement apparatus has numerical aperture of greater than 1.
15. The method of claim 1 , wherein the optical element is a transparent optical element positioned between the target and an objective having a numerical aperture of less than or equal to 1.
16. The method of claim 15 , where the optical element comprises a partially transparent and partially reflective coating.
17. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including inspecting at least a target formed as part of or beside the device pattern on at least one of the substrates, using the method of claim 1 , and controlling the lithographic process for later substrates in accordance with the parameter of the method.
18. A non-transitory computer program product comprising machine-readable instructions that when execute cause a processor to at least:
obtain a plurality of radiation distributions of measurement radiation redirected by a same measurement target, each of the plurality of radiation distributions obtained at a different gap distance between the target and an optical element of a measurement apparatus, the optical element being the nearest optical element to the target used to provide the measurement radiation to the target; and
determine a parameter related to the target using a combination of data of the plurality of radiation distributions in conjunction with a mathematical model describing the target.
19. A system comprising:
an inspection apparatus configured to provide a beam on a measurement target on a substrate and to detect radiation redirected by the target to determine a parameter of a lithographic process; and
the non-transitory computer program product of claim 18 .
20. The system of claim 19 , further comprising a lithographic apparatus, the lithographic apparatus comprising a support structure configured to hold a patterning device to modulate a radiation beam and a projection optical system arranged to project the modulated onto a radiation-sensitive substrate.