Method of obtaining measurements, apparatus for performing a process step, and metrology apparatus
Measurements are obtained from locations across a substrate before or after performing a lithographic process step. Examples of such measurements include alignment measurements made prior to applying a pattern to the substrate, and measurements of a performance parameter such as overlay, after a pattern has been applied. A set of measurement locations is selected from among all possible measurement locations. At least a subset of the selected measurement locations are selected dynamically, in response to measurements obtained using a preliminary selection of measurement locations. Preliminary measurements of height can be used to select measurement locations for alignment. In another aspect, outlier measurements are detected based on supplementary data such as height measurements or historic data.
1. A method of determining a weighting factor for a measurement made at a measurement location on a substrate, the method comprising:
applying a quality test to the measurement, the quality test based at least partly on supplementary data associated with the measurement location; and
determining the weighting factor based on a result of the quality test.
2. The method according to claim 1 , wherein the supplementary data comprises statistical data based on previously processed substrates.
3. The method according to claim 2 , wherein the statistical data represents a variation of measurements across the previously processed substrates, and the quality test is based on a comparison of the measurement with the variation seen at corresponding locations on the previously processed substrates.
4. The method according to claim 3 , wherein the variation is determined using residual values relative to a fitted model.
5. The method according to claim 2 , wherein the statistical data represents a set of component vectors describing spatial distributions of measurements of the previously processed substrates.
6. The method according to claim 5 , wherein the quality test compares the measurement with a value predicted by one or more of the component vectors.
7. The method according to claim 2 , wherein an outlier measurement identified using the quality test is replaced with a value based at least partly on the statistical data.
8. The method according to claim 1 , wherein the quality test is based at least partly on height data measured on the substrate.
9. The method according to claim 1 , wherein a zero weighting is applied to an outlier measurement identified using the quality test.
10. The method according to claim 1 , wherein an outlier measurement identified using the quality test is replaced with a measurement at a neighboring position.
11. A method of manufacturing devices including a lithographic process step, wherein, before or after performing the lithographic process step, measurements are obtained at a selected set of locations across a substrate, wherein weighing factors for the measurements are obtained by the method according to claim 1 , and wherein the obtained measurements modified in accordance with the weighting factors are used to adjust one or more parameters of the lithographic process step for the processing of the substrate and/or further substrates.
12. A computer program product comprising a non-transitory computer-readable medium comprising machine-readable instructions therein, the instructions, upon execution by a processing system, configured to cause the processing system to at least:
receive measurements made at measurement locations across a substrate;
apply a quality test to a measurement of the measurements, the quality test based at least partly on supplementary data associated with the measurement location associated with the measurement; and
determine a weighting factor for the measurement based on a result of the quality test.
13. The computer program product of claim 12 , wherein the supplementary data comprises statistical data based on previously processed substrates.
14. The computer program product of claim 13 , wherein the statistical data represents a variation of measurements across the previously processed substrates, and the quality test is based on a comparison of the measurement with the variation seen at corresponding locations on the previously processed substrates.
15. The computer program product of claim 14 , wherein the variation is determined using residual values relative to a fitted model.
16. The computer program product of claim 13 , wherein the statistical data represents a set of component vectors describing spatial distributions of measurements of the previously processed substrates.
17. The computer program product of claim 16 , wherein the quality test compares the measurement with a value predicted by one or more of the component vectors.
18. The computer program product of claim 13 , wherein an outlier measurement identified using the quality test is replaced with a value based at least partly on the statistical data.
19. The computer program product of claim 12 , wherein the quality test is based at least partly on height data measured on the substrate.
20. A metrology apparatus arranged to obtain measurements of one or more properties of structures at a selected set of locations across a substrate, the metrology apparatus comprising the computer program product of claim 12 and configured to apply the weighting factor to one or more measurements made using the metrology apparatus.