Method of determining the contribution of a processing apparatus to a substrate parameter

1. A method for determining a contribution of a processing apparatus to a fingerprint of a parameter across a substrate, the method comprising:

obtaining a delta image which relates to a difference between a first pupil image associated with inspection of a first feature on the substrate and a second pupil image associated with inspection of a second feature on the substrate, wherein the first and second features have different dose sensitivities;

determining a rate of change of the difference in response to a variation of a dose used to form the first and second features;

selecting a plurality of pixels comprised within the delta image having a rate of change above a predetermined threshold; and

determining the contribution using the determined rate of change of the difference and the delta image restricted to the plurality of pixels.

2. The method as claimed in claim 1 , wherein the contribution is expressed as one or more values of an effective dose.

3. The method as claimed in claim 2 , wherein the one or more values of effective dose are determined by dividing a summed intensity of the delta image, or part thereof, by the rate of change of the difference.

4. The method as claimed in claim 2 , further comprising determining critical dimensions or critical dimension uniformity of features on a substrate using the one or more values of the effective dose.

5. The method as claimed in claim 1 , wherein the first pupil image and second pupil image form a pair of pupil images, and further comprising obtaining differences for a plurality of pairs of pupil images, wherein a dose used for forming features associated with a first pair of pupil images is different to a dose used for forming features associated with a second pair of pupil images.

6. The method as claimed in claim 5 , further comprising using the difference between the first pair of pupil images and difference between the second pair of pupil images to determine an image intensity vs dose curve and using the image intensity vs dose curve to determine the rate of change of the difference.

7. The method as claimed in claim 6 , wherein the rate of change of the difference is the derivative of the image intensity vs dose curve.

8. The method as claimed in claim 1 , further comprising determining an effective dose map using one or more values of the contribution.

9. The method as claimed in claim 8 , further comprising subtracting the one or more values of the contribution from the delta pupil image to provide a pure process image data which is representative of one or more non-exposure processing steps.

10. The method as claimed in claim 9 , further comprising obtaining pure process image data for a plurality of locations across the substrate to provide a pure process map.

11. The method as claimed in claim 10 , further comprising:

obtaining a difference between a plurality of pupil image pairs for a further substrate to provide a plurality of further substrate delta images; and

using the obtained difference to generate a metrology map for the further substrate.

12. The method as claimed in claim 11 , wherein the further substrate is different from the substrate.

13. The method as claimed in claim 1 , wherein the first feature is an inversion of the second feature.

14. A computer program product comprising a non-transitory computer-readable medium having instructions therein, which instructions, when executed by at least one processor, are configured to cause the at least one processor to at least:

obtain a delta image which relates to a difference between a first pupil image associated with inspection of a first feature on a substrate and a second pupil image associated with inspection of a second feature on the substrate, wherein the first and second features have different dose sensitivities;

determining a rate of change of the difference in response to a variation of a dose used to form the first and second features;

selecting a plurality of pixels comprised within the delta image having a rate of change above a predetermined threshold; and

determining a contribution of a processing apparatus to a fingerprint of a parameter across the substrate using the determined rate of change of the difference and the delta image restricted to the plurality of pixels.

15. The computer program product as claimed in claim 14 , wherein the contribution is expressed as one or more values of an effective dose.

16. The computer program product as claimed in claim 14 , wherein the first pupil image and second pupil image form a pair of pupil images, and the instructions are further configured to cause the at least one processor to obtain differences for a plurality of pairs of pupil images, wherein a dose used for forming features associated with a first pair of pupil images is different to a dose used for forming features associated with a second pair of pupil images.

17. The computer program product as claimed in claim 16 , wherein the instructions are further configured to cause the at least one processor to use the difference between the first pair of pupil images and difference between the second pair of pupil images to determine an image intensity vs dose curve and use the image intensity vs dose curve to determine the rate of change of the difference.

18. The computer program product as claimed in claim 14 , wherein the instructions are further configured to cause the at least one processor to determine an effective dose map using one or more values of the contribution.

19. The computer program product as claimed in claim 18 , wherein the instructions are further configured to cause the at least one processor to subtract the one or more values of the contribution from the delta pupil image to provide a pure process image data which is representative of one or more non-exposure processing steps.

20. The computer program product as claimed in claim 14 , wherein the first feature is an inversion of the second feature.