Method of measuring, device manufacturing method, metrology apparatus, and lithographic system

1. A method of measuring a plurality of structures formed on a substrate, the method comprising:

obtaining data from a first measurement process, the first measurement process comprising individually measuring each of the plurality of structures to measure a first property of the structure; and

using a second measurement process to measure a second property of each of the plurality of structures, the second measurement process comprising illuminating each structure with radiation having a radiation property that is individually selected for that structure using the measured first property for the structure.

2. The method of claim 1 , wherein the individual selection of the radiation property for the second measurement process is performed for each structure based on a previously measured correlation between the first property and a choice of the radiation property for the second measurement process that enables a performance of the second measurement process to be higher than for other choices of the radiation property for the second measurement process.

3. The method of claim 1 , wherein the first property of the structure comprises reflectivity.

4. The method of claim 1 , wherein the first property of the structure comprises an effect of the structure on the polarization of radiation scattered from the structure.

5. The method of claim 1 , wherein the second property of each structure comprises overlay between different layers of the structure.

6. The method of claim 1 , wherein the radiation property for the second measurement process comprises a spectral distribution of intensity.

7. The method of claim 6 , wherein the spectral distribution of intensity comprises central wavelength and/or bandwidth.

8. The method of claim 1 , wherein the radiation property for the second measurement process comprises a polarization of the radiation.

9. The method of claim 1 , wherein:

the first measurement process uses a first radiation source to illuminate each structure with radiation; and

the second measurement process uses a second radiation source to illuminate each structure with radiation, wherein the first radiation source is different from the second radiation source.

10. The method of claim 1 , wherein the first measurement process uses the output from a focus sensor configured to measure a focus of an optical system used for the second measurement process.

11. The method of claim 10 , wherein the first property of the structure comprises reflectivity and the signal strength from the focus sensor is used to determine the reflectivity.

12. The method of claim 1 , wherein the first measurement process uses one or more optical elements that are also used when measuring a focus of an optical system used for the second measurement process, wherein the one or more optical elements are not used when performing the second measurement process.

13. The method of claim 1 , wherein the first measurement process uses a first radiation source to illuminate each structure with broadband radiation and the individual selection of the radiation property for the second measurement process is performed for each structure based on a spectroscopic analysis of the data from the first measurement process.

14. The method of claim 1 , comprising performing the first measurement process.

15. The method of claim 1 , wherein the plurality of structures formed on the substrate are formed by a lithographic process.

16. A metrology apparatus for measuring a plurality of structures on a substrate, the metrology apparatus comprising:

a first measurement system configured to perform a first measurement process, the first measurement process comprising individually measuring each of the plurality of structures to measure a first property of the structure;

a second measurement system configured to perform a second measurement process, the second measurement process comprising measuring a second property of each of the plurality of structures; and

a control system configured to control the second measurement process such that a radiation property of radiation used to illuminate each structure during the second measurement process is individually selected for that structure using the measured first property for the structure.

17. The apparatus of claim 16 , wherein the control system is configured to perform the individual selection of the radiation property for the second measurement process for each structure based on a previously measured correlation between the first property and a choice of the radiation property for the second measurement process that enables a performance of the second measurement process to be higher than for other choices of the radiation property for the second measurement process.

18. The apparatus of claim 16 , wherein the first property of the structure comprises reflectivity or an effect of the structure on the polarization of radiation scattered from the structure.

19. The apparatus of claim 16 , wherein the second property of each structure comprises overlay between different layers of the structure.

20. A non-transitory computer-readable medium comprising instructions, when executed, configured to cause a computer system to at least:

obtain data from a first measurement process, the first measurement process comprising individually measuring each of a plurality of structures formed on a substrate to measure a first property of the structure; and

cause use of a second measurement process to measure a second property of each of the plurality of structures, the second measurement process comprising illuminating each structure with radiation having a radiation property that is individually selected for that structure using the measured first property for the structure.