Selecting a set of locations associated with a measurement or feature on a substrate

1. A method comprising:

defining a first candidate solution comprising a first set of locations;

defining, by a hardware computer system, a second candidate solution comprising a second set of locations based on modification of a coordinate in a solution domain of the first candidate solution, wherein the modification of the coordinate involves one or more operations selected from duplication, mutation and/or cross-over; and

selecting the first and/or second candidate solution as a set of locations on a substrate associated with positions configured for performing measurements or for placement of features, other than device features, for measurement, according to a constraint associated with one or more selected from available positions for placement of features on the substrate, available measurement time, a minimum amount of measurements or features associated with a region on the substrate, and/or a required degree of uniformity of measurement or feature locations as distributed across the substrate.

2. The method according to claim 1 , wherein the defining the first candidate solution is based on generation of a random or pseudo-random number.

3. The method according to claim 1 , wherein the defining the first candidate solution is based on knowledge of the constraint.

4. The method according to claim 1 , wherein the first and second candidate solutions are individuals in successive populations of candidate solutions and the method is performed according to an evolutionary approach.

5. The method according to claim 1 , wherein the selecting the first and/or second candidate solution is further done according to a value of a cost function associated with a required measurement accuracy or feature layout on the substrate.

6. The method according to claim 5 , wherein the cost function is associated with optimal determination of a focus metric across the substrate.

7. The method according to claim 5 , wherein the cost function is associated with optimal determination of a substrate distortion characteristic.

8. The method according to claim 5 , wherein the cost function is associated with optimal positioning of focus markers, alignment markers, dose markers or overlay markers across the substrate.

9. The method according to claim 5 , wherein the cost function is associated with a quality parameter of a fitting procedure performed on a graph of observables defined at one or more of the locations associated with the measurement and/or feature locations.

10. The method according to claim 1 , wherein the substrate is a patterning device or a wafer.

11. The method according to claim 5 , wherein the cost function is associated with an optimal number of measurements or features taking measurement time into account.

12. The method according to claim 1 , further comprising determination of a Pareto front establishing a relation between a first objective of selecting the optimal solution comprising an optimal set of locations and a second objective of selecting the optimal solution comprising an optimal set of locations.

13. A non-transitory computer-readable medium comprising computer readable instructions which, when run on a suitable computer system, cause the computer system to at least:

define a first candidate solution comprising a first set of locations;

define a second candidate solution comprising a second set of locations based on modification of a coordinate in a solution domain of the first candidate solution, wherein the modification of the coordinate involves one or more operations selected from duplication, mutation and/or cross-over; and

select the first and/or second candidate solution as a set of locations on a substrate associated with positions configured for performing measurements or for placement of features, other than device features, for measurement, according to a constraint associated with one or more selected from: available positions for placement of features on the substrate, available measurement time, a minimum amount of measurements or features associated with a region on the substrate, and/or a required degree of uniformity of measurement or feature locations as distributed across the substrate.

14. A lithographic apparatus comprising:

a transfer system configured to transfer a pattern to a substrate; and

the non-transitory computer-readable medium as claimed in claim 13 .

15. A method comprising:

defining a first candidate solution comprising a first set of locations;

defining a first candidate solution comprising a first set of locations;

defining a second candidate solution comprising a second set of locations based on modification of a coordinate in a solution domain of the first candidate solution; and

selecting, by a hardware computer system, the first and/or second candidate solution as a set of locations on a substrate associated with positions configured for performing measurements or for placement of features, other than device features, for measurement, according to a constraint associated with one or more selected from available positions for placement of features on the substrate, available measurement time, a minimum amount of measurements or features associated with a region on the substrate, and/or a required degree of uniformity of measurement or feature locations as distributed across the substrate,

wherein the first and second candidate solutions are states in a search space comprising the solution domain and at least the selecting is performed according to a simulated annealing approach.

16. A non-transitory computer-readable medium comprising computer readable instructions which, when run on a suitable computer system, cause the computer system to at least:

define a first candidate solution comprising a first set of locations;

define a second candidate solution comprising a second set of locations based on modification of a coordinate in a solution domain of the first candidate solution; and

select the first and/or second candidate solution as a set of locations on a substrate associated with positions configured for performing measurements or for placement of features, other than device features, for measurement, according to a constraint associated with one or more selected from available positions for placement of features on the substrate, available measurement time, a minimum amount of measurements or features associated with a region on the substrate, and/or a required degree of uniformity of measurement or feature locations as distributed across the substrate,

wherein the first and second candidate solutions are states in a search space comprising the solution domain and at least the selecting is performed according to a simulated annealing approach.

17. The computer-readable medium according to claim 13 , wherein the selection of the first and/or second candidate solution is further done according to a value of a cost function associated with a required measurement accuracy or feature layout on the substrate.

18. The computer-readable medium according to claim 13 , wherein the definition of the first candidate solution is based on generation of a random or pseudo-random number.

19. The computer-readable medium according to claim 13 , wherein the definition of the first candidate solution is based on knowledge of the constraint.

20. The computer-readable medium according to claim 13 , wherein the substrate is a patterning device or a wafer.