Methods of determining corrections for a patterning process

1. A method of determining a correction for a process parameter related to a lithographic process, the lithographic process comprising a plurality of runs during each one of which a pattern is applied to one or more substrates, the method comprising:

obtaining pre-exposure parameter data relating to a property of a substrate;

obtaining post-exposure metrology data comprising one or more measurements of the process parameter having been performed by an equivalent lithographic process on one or more previously exposed substrates of the lithographic process;

assigning to the substrate, based on the pre-exposure parameter data, a group membership status from one or more groups, wherein the group membership status is such that a substrate is assigned a degree of membership to one or more of the one or more groups; and

determining the correction for the process parameter based on the group membership status and the post-exposure metrology data, wherein the determining the correction for the process parameter is based on weighing of one or more corrections associated with one or more groups based on degree of membership of that substrate to the one or more groups.

2. The method as claimed in claim 1 , wherein the pre-exposure parameter data comprises pre-exposure metrology data.

3. The method as claimed in claim 2 , wherein the pre-exposure metrology data comprises data describing a shape of the substrate in a direction perpendicular to a substrate plane.

4. The method as claimed in claim 2 , wherein the pre-exposure metrology data comprises leveling data.

5. The method as claimed in claim 1 , wherein the degree of membership to a group is based on a classification score representative of a measure of presence of a fingerprint defining that group in the pre-exposure metrology data.

6. The method as claimed in claim 1 , further comprising an initial training stage wherein the one or more groups are determined from a principal component analysis performed on pre-exposure metrology data, each group being defined by an eigenfingerprint determined from the principal component analysis.

7. The method as claimed in claim 1 , comprising performing the method for each substrate of a run.

8. The method as claimed in claim 1 , further comprising identifying for a particular group, a substrate which is most representative of the group.

9. The method as claimed in claim 8 , further comprising:

obtaining a measurement of the substrate which is most representative of the group; and

updating, based on the measurement, a correction for the process parameter corresponding to the group.

10. The method as claimed in claim 1 , further comprising an initial training stage wherein the one or more groups are determined.

11. The method as claimed in claim 10 , wherein the initial training stage comprises a validation step comprising assigning substrates to the one or more groups based on historical data and simulating the effect on the post-exposure metrology data.

12. The method as claimed in claim 1 , wherein the post-exposure metrology data comprises overlay data.

13. The method as claimed in claim 1 , wherein the pre-exposure parameter data comprises context data relating to a tool used for processing the substrate during a particular processing step.

14. A non-transitory computer program product containing one or more sequences of machine-readable instructions, the instructions, when executed by a processing system, configured to cause the processing system to at least:

obtain pre-exposure parameter data relating to a property of a substrate and post-exposure metrology data comprising one or more measurements of a process parameter related to a lithographic process having been performed on one or more previous substrates;

assign to the substrate, based on the pre-exposure parameter data, a group membership status from one or more groups, wherein the group membership status is such that a substrate is assigned a degree of membership to one or more of the one or more groups; and

determine a correction for a process parameter based on the group membership status and the post-exposure metrology data, wherein the determination of the correction for the process parameter is based on weighing of one or more corrections associated with one or more groups based on degree of membership of that substrate to the one or more groups.

15. The computer program product as claimed in claim 14 , wherein the pre-exposure parameter data comprises pre-exposure metrology data.

16. The computer program product as claimed in claim 15 , wherein the pre-exposure metrology data comprises data describing a shape of the substrate in a direction perpendicular to a substrate plane.

17. The computer program product as claimed in claim 14 , wherein the group membership status is such that each substrate can be assigned a degree of membership to one or more of the one or more groups.

18. A control system for a lithographic apparatus, the control system comprising:

storage for holding the pre-exposure parameter data and the post-exposure metrology data;

the non-transitory computer program product of claim 14 ; and

a processor system configured to execute the instructions.

19. A method for a lithographic process comprising a plurality of runs during each one of which a pattern is applied to one or more substrates, the method comprising:

obtaining pre-exposure parameter data relating to a property of a substrate;

assigning to the substrate, based on the pre-exposure parameter data, a group membership status from one or more groups;

identifying for a particular group of the one or more groups, a substrate which is most representative of the particular group, obtaining a measurement result of the substrate which is most representative of the particular group, and updating or replacing, based on the measurement result, a correction for a process parameter related to the lithographic process and corresponding to the particular group;

obtaining post-exposure metrology data comprising one or more measurements of the process parameter having been performed by an equivalent lithographic process on one or more previously exposed substrates of the lithographic process; and

determining a correction for a process parameter related to the lithographic process based on the group membership status and the post-exposure metrology data.

20. A non-transitory computer program product containing one or more sequences of machine-readable instructions, the instructions, when executed by a processing system, configured to cause the processing system to at least:

obtain pre-exposure parameter data relating to a property of a substrate and post-exposure metrology data comprising one or more measurements of a process parameter related to a lithographic process having been performed on one or more previous substrates;

assign to the substrate, based on the pre-exposure parameter data, a group membership status from one or more groups;

identify for a particular group of the one or more groups, a substrate which is most representative of the particular group, obtain a measurement result of the substrate which is most representative of the particular group, and update or replace, based on the measurement result, a correction for a process parameter corresponding to the particular group; and

determine a correction for a process parameter based on the group membership status and the post-exposure metrology data.