Method of reducing effects of reticle heating and/or cooling in a lithographic process
A method of reducing effects of reticle heating and/or cooling in a lithographic process, the method including calibrating a linear time invariant reticle heating model using a system identification method; predicting distortions of the reticle using the reticle heating model and inputs in the lithographic process; and calculating and applying a correction in the lithographic process on the basis of the predicted distortions of the reticle.
1. A method of reducing effects of heating and/or cooling of a reticle in a lithographic process, the method comprising:
calibrating a linear time invariant reticle heating model;
predicting distortions of the reticle in a lithographic apparatus using the reticle heating model and inputs in the lithographic process; and
calculating and applying a correction in the lithographic process on the basis of the predicted distortions of the reticle,
wherein the distortion is expressed in one or more overlay parameters and/or one or more mode shapes.
2. The method of claim 1 , wherein calibrating the reticle heating model comprises using data on inputs in the lithographic process and distortions of the reticle.
3. The method of claim 1 , wherein the inputs in the lithographic process comprise a dose of radiation supplied by a radiation source and/or a transmission of an object used in the lithographic process.
4. The method of claim 1 , wherein the inputs in the lithographic process comprise a cooling dose supplied by an adaptive reticle cooling system.
5. The method of claim 1 , wherein the reticle heating model is a state space model.
6. The method of claim 5 , wherein the calibrating uses measurement data, process data, or data obtained from another reticle heating model.
7. The method of claim 1 , wherein the reticle heating model is calibrated for a single reticle and/or for a specific type or group of reticles having a substantially corresponding behavior.
8. The method of claim 1 , wherein the reticle heating model is used to calculate an observer.
9. The method of claim 1 , wherein the correction is applied between subsequent projections with the same reticle.
10. The method of claim 1 , wherein the correction is a correction of an alignment of a substrate with respect to the reticle to improve imaging performance in the lithographic process.
11. The method of claim 1 , wherein the reticle heating model comprises one or more mode shapes describing a relationship between inputs and distortions resulting from the inputs.
12. A non-transitory computer readable medium comprising computer readable instructions configured to cause a processor system to at least:
calibrate a linear time invariant reticle heating model;
predict distortions of a reticle in a lithographic apparatus using the reticle heating model and inputs in a lithographic process; and
calculate and apply a correction in the lithographic process on the basis of the predicted distortions of the reticle,
wherein the distortion is expressed in one or more overlay parameters and/or one or more mode shapes.
13. The computer readable medium of claim 12 , wherein the reticle heating model comprises one or more mode shapes describing a relationship between inputs and distortions resulting from the inputs.
14. A lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a support constructed to support a reticle, the reticle being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a projection system configured to project the patterned radiation beam onto a target portion of a substrate; and
a control system arranged to reduce effects of heating and/or cooling of a reticle in a lithographic process, the control system configured to at least:
calibrate a linear time invariant reticle heating model;
predict distortions of the reticle using the reticle heating model and inputs in the lithographic process; and
calculate and apply a correction in the lithographic process on the basis of the predicted distortions of the reticle,
wherein the distortion is expressed in one or more overlay parameters and/or one or more mode shapes.
15. The apparatus of claim 14 , wherein the reticle heating model is a state space model.
16. The apparatus of claim 14 , wherein the reticle heating model is used to calculate an observer.
17. The apparatus of claim 14 , wherein the reticle heating model comprises one or more mode shapes describing a relationship between inputs and distortions resulting from the inputs.
18. A device manufacturing method using a lithographic process, the device manufacturing method comprising:
patterning a projection beam with a pattern in its cross-section using a reticle;
projecting the patterned beam of radiation onto a target portion of a substrate using a projection system; calibrating a linear time invariant reticle heating model;
predicting distortions of the reticle using the reticle heating model and inputs in the device manufacturing method; and
calculating and applying a correction in the device manufacturing method on the basis of the predicted distortions of the reticle,
wherein the distortion is expressed in one or more overlay parameters and/or one or more mode shapes.
19. The method of claim 18 , wherein the reticle heating model is a state space model.
20. The method of claim 18 , wherein the reticle heating model is used to calculate an observer.