Methods and systems for parameter-sensitive and orthogonal gauge design for lithography calibration
Methods provide computationally efficient techniques for designing gauge patterns for calibrating a model for use in a simulation process. More specifically, the present invention relates to methods of designing gauge patterns that achieve complete coverage of parameter variations with minimum number of gauges and corresponding measurements in the calibration of a lithographic process utilized to image a target design having a plurality of features. According to some aspects, a method according to the invention includes transforming the space of model parametric space (based on CD sensitivity or Delta TCCs), then iteratively identifying the direction that is most orthogonal to existing gauges' CD sensitivities in this new space, and determining most sensitive line width/pitch combination with optimal assist feature placement which leads to most sensitive CD changes along that direction in model parametric space.
1. A method for designing test gauges, the method comprising:
identifying a parameter of a lithographic process; and
designing, by a hardware computer system, a test gauge for the parameter, the test gauge including one or more main features maximizing radiation intensity sensitivity to changes with respect to the parameter.
2. The method according to claim 1 , further comprising computing one or more assisting features for arrangement in the test gauge that further maximizes the sensitivity.
3. The method according to claim 2 , wherein computing the one or more assisting features includes applying one or more manufacturability constraints to a size and spacing of the one or more assisting features.
4. The method according to claim 1 , wherein the designing includes:
determining a perturbed value of the identified parameter;
using the perturbed value to compute a delta operator; and
using the delta operator to compute an aerial image.
5. The method according to claim 4 , wherein the delta operator comprises transmission cross coefficients.
6. The method according to claim 1 , wherein the sensitivity is characterized in connection with predicted and actual critical dimensions of the one or more main features printed using the lithographic process.
7. The method of claim 1 , wherein the test gauge includes at least two main features having a difference in a metric between the main features that maximizes the sensitivity.
8. The method according to claim 7 , wherein the at least two main features are lines and wherein designing includes computing optimal first and second respective line widths for the at least two main features.
9. The method according to claim 7 , wherein the at least two main features are lines and wherein designing includes computing an optimal center-to-center distance between the at least two main features.
10. The method according to claim 7 , wherein the metric represents critical dimension.
11. A non-transitory computer program product having therein, the instructions which, when executed by a computer system, configured to cause the computer system to at least:
identify a parameter of a lithographic process; and
design a test gauge for the parameter, the test gauge including one or more main features maximizing radiation intensity sensitivity to changes with respect to the parameter.
12. The computer program product according to claim 11 , wherein the instructions are further configured to cause the computer system to compute one or more assisting features for arrangement in the test gauge that further maximizes the sensitivity.
13. The computer program product according to claim 12 , wherein computation of the one or more assisting features includes application of one or more manufacturability constraints to a size and spacing of the one or more assisting features.
14. The computer program product according to claim 11 , wherein the design of the test gauge includes:
determination of a perturbed value of the identified parameter;
use of the perturbed value to compute a delta operator; and
use of the delta operator to compute an aerial image.
15. The computer program product according to claim 14 , wherein the delta operator comprises transmission cross coefficients.
16. The computer program product according to claim 11 , wherein the sensitivity is characterized in connection with predicted and actual critical dimensions of the one or more main features printed using the lithographic process.
17. The computer program product according to claim 11 , wherein the instructions are configured to design the test gauge to include at least two main features having a difference in a metric between the main features that maximizes the sensitivity.
18. The computer program product according to claim 17 , wherein the at least two main features are lines and wherein the design of the test gauge includes computation of optimal first and second respective line widths for the at least two main features.
19. The computer program product according to claim 17 , wherein the at least two main features are lines and wherein design of the test gauge includes computation of an optimal center-to-center distance between the at least two main features.
20. The computer program product according to claim 17 , wherein the metric represents critical dimension.