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1. WO2020108846 - METHOD FOR OF MEASURING A FOCUS PARAMETER RELATING TO A STRUCTURE FORMED USING A LITHOGRAPHIC PROCESS

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[ EN ]

CLAIMS:

1. A method of measuring a focus parameter relating to formation of a structure using a lithographic process, wherein said method comprises:

obtaining measurement data relating to a cross-polarized measurement of said structure; and determining a value for said focus parameter based on the measurement data.

2. A method as claimed in claim 1, wherein said measurement data comprises one or more of HV polarization state measurement data, VH polarization state measurement data, HH polarization state measurement data and VV polarization state measurement data.

3. A method as claimed in any preceding claim, wherein said structure comprises a line-space grating.

4. A method as claimed in any preceding claim, wherein said line-space grating is designed to be substantially symmetrical.

5. A method as claimed in any preceding claim, comprising performing said cross-polarized measurement of said structure on a production substrate.

6. A method as claimed in any preceding claim, wherein said determining step is performed using a focus model.

7. A method as claimed in claim 6, wherein the focus model is created in a calibration stage using calibration measurement data, relating to a cross-polarized calibration measurement of an exposure matrix, said exposure matrix comprising at least a calibration structure exposed in multiple exposures with a plurality of different focus offsets.

8. A method as claimed in claim 7, wherein the exposure matrix comprises multiple exposures having a plurality of different dose offsets, and said step of creating a focus model comprises creating a focus dose model which is further operable to enable determination of a dose parameter based on said measurement data.

9. A method as claimed in claim 7 or 8, wherein each of said multiple exposures comprises a plurality of calibration structures, each calibration structure comprising a line-space grating, wherein the pitch and/or critical dimension is varied between calibration structures.

10. A method as claimed in any of claims 7 to 9, wherein the calibration measurement data comprises one or more of HV polarization state calibration measurement data relating to a HV polarization state calibration measurement, VH polarization state calibration measurement data relating to a VH polarization state calibration measurement, HH polarization state calibration measurement data relating to a HH polarization state calibration measurement and VV polarization state calibration measurement data relating to a VV polarization state calibration measurement.

11. A method as claimed in any of claims 6 to 10, comprising the step of processing said calibration measurement data to obtain processed calibration measurement data, said processed calibration measurement data having a monotonic relationship with the focus parameter in at least a focus range around best focus sufficient for monitoring of focus in a lithographic process and

wherein, optionally, said processed calibration measurement data comprises one or more principal or independent components, and/or scores thereof, of calibration measurement data following a principal or independent component analysis.

12. A computer program comprising program instructions operable to perform the method of any of claims 1 to 11, when run on a suitable apparatus.

13. A non-transient computer program carrier comprising the computer program of claim 12.

14. A processing system comprising a processor and the computer program of claim 12.

15. A metrology system comprising:

a substrate holder for a substrate;

an illumination source for illuminating a structure on the substrate with radiation with an illumination polarization state selectable between a first polarization state and a second polarization state;

a sensor for sensing scattered illumination from the structure with a sensing illumination state selectable between said first polarization state and said second polarization state; and

the processing system of claim 14.