Modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) CD extraction

1. A method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during photolithography process model calibration, the method comprising:

receiving a measured CD value which was obtained using a CD-SEM extraction process, wherein the CD-SEM extraction process determines the measured CD value for a feature by measuring multiple CD values of the feature along multiple electron beam scans;

determining a simulated CD value for the feature, wherein the simulated CD value is determined based at least on a set of CD extraction cut-lines which are substantially parallel to each other and are used to compute a single CD value for the feature; and

during photolithography process model calibration, fitting, by computer, a parameter that models an aspect of a photolithography process based at least on both the measured CD value and the simulated CD value.

2. The method of claim 1 , wherein determining the simulated CD value involves:

placing a measurement window to enclose a target feature;

placing the set of CD extraction cut-lines within the measurement window based at least on a placement spacing parameter, wherein the placement spacing parameter models a spacing between the multiple electron beam scans in the CD-SEM extraction process;

extracting a set of single-cut-line CD values for the set of CD extraction cut-lines; and

determining the simulated CD value using the set of single-cut-line CD values.

3. The method of claim 2 , wherein the fitting parameter includes the placement spacing parameter.

4. The method of claim 2 , wherein prior to placing the measurement window, the method further comprises obtaining the simulated pattern by convolving the feature with a photolithography process model.

5. The method of claim 1 , wherein determining the simulated CD value using the set of single-cut-line CD values involves computing an average of the set of single-cut-line CD values.

6. The method of claim 1 , wherein fitting the parameter involves, iteratively:

updating the simulated CD value based at least on an updated photolithography process model; and

updating the parameter's value based at least on a difference between the updated simulated CD value and the measured CD value.

7. The method of claim 1 , wherein fitting the parameter involves minimizing a difference between the simulated CD value and the measured CD value.

8. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during photolithography process model calibration, the method comprising:

receiving a measured CD value which was obtained using a CD-SEM extraction process, wherein the CD-SEM extraction process determines the measured CD value for a feature by measuring multiple CD values of the feature along multiple electron beam scans;

determining a simulated CD value for the feature, wherein the simulated CD value is determined based at least on a set of CD extraction cut-lines which are substantially parallel to each other and are used to compute a single CD value for the feature; and

during photolithography process model calibration, fitting a parameter that models an aspect of a photolithography process based at least on both the measured CD value and the simulated CD value.

9. The non-transitory computer-readable storage medium of claim 8 , wherein determining the simulated CD value involves:

placing a measurement window to enclose a target feature;

placing the set of CD extraction cut-lines within the measurement window based at least on a placement spacing parameter, wherein the placement spacing parameter models a spacing between the multiple cut-lines in the CD-SEM extraction process;

extracting a set of single-cut-line CD values for the set of CD extraction cut-lines; and

determining the simulated CD value using the set of single-cut-line CD values.

10. The non-transitory computer-readable storage medium of claim 9 , wherein the fitting parameter includes the placement spacing parameter.

11. The non-transitory computer-readable storage medium of claim 9 , wherein prior to placing the measurement window, the method further comprises obtaining the simulated pattern by convolving the feature with a photolithography process model.

12. The non-transitory computer-readable storage medium of claim 8 , wherein determining the simulated CD value using the set of single-cut-line CD values involves computing an average of the set of single-cut-line CD values.

13. The non-transitory computer-readable storage medium of claim 8 , wherein fitting the parameter involves, iteratively:

updating the simulated CD values based at least on an updated photolithography process model; and

updating the parameter's value based at least on a difference between the updated simulated CD value and the measured CD value.

14. The non-transitory computer-readable storage medium of claim 8 , wherein fitting the parameter involves minimizing a difference between the simulated CD value and the measured CD value.

15. A method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during photolithography process model calibration, the method comprising:

receiving a simulated CD value for a feature, wherein the simulated CD value is extracted from a simulated pattern associated with the feature using a single cut-line placed on the simulated pattern;

receiving raw CD-SEM measurement data for the feature, wherein the raw CD-SEM measurement data comprises multiple measured CD values extracted for the feature using multiple electron beam scans;

using the multiple measured CD values to determine a predicted CD value which predicts the simulated CD value, wherein determining the predicted CD value involves performing a curve fitting on the multiple measured CD values to determine a local minimum or maximum CD value; and

calibrating, by computer, a photolithography process model based at least on both the predicted CD value and the simulated CD value.

16. The method of claim 15 , wherein determining the predicted CD value involves determining a CD value along a cut-line on the feature, wherein a location of the cut-line matches a location of the single cut-line used to extract the simulated CD value.

17. A method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during post-optical-proximity-correction (post-OPC) verification of a design layout, the method comprising:

receiving a measured CD value which was obtained using a CD-SEM extraction process, wherein the CD-SEM extraction process determines the measured CD value for a feature by measuring multiple CD values of the feature along multiple electron beam scans;

determining a simulated CD value for the feature, wherein the simulated CD value is determined based at least on a set of CD extraction cut-lines which are substantially parallel to each other and are used to compute a single CD value for the feature; and

during post-OPC verification, verifying, by computer, a quality of design layout corrected by OPC by comparing the measured CD value with the simulated CD value.

18. The method of claim 17 , wherein determining the simulated CD value involves:

placing a measurement window to enclose a target feature;

placing the set of CD extraction cut-lines within the measurement window based at least on a placement spacing parameter, wherein the placement spacing parameter models a spacing between the multiple electron beam scans in the CD-SEM extraction process;

extracting a set of single-cut-line CD values for the set of CD extraction cut-lines; and

determining the simulated CD value using the set of single-cut-line CD values.

19. The method of claim 18 , wherein prior to placing the measurement window, the method further comprises obtaining the simulated pattern by convolving the feature with the photolithography process model.

20. The method of claim 17 , wherein determining the simulated CD value using the set of single-cut-line CD values involves computing an average of the set of single-cut-line CD values.

21. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during post-optical-proximity-correction (post-OPC) verification of a photolithography process model, the method comprising:

receiving a measured CD value which were obtained using a CD-SEM extraction process, wherein the CD-SEM extraction process determines the measured CD value for a feature by measuring multiple CD values of the feature along multiple electron beam scans;

determining a simulated CD value for the feature, wherein the simulated CD value is determined based at least on a set of CD extraction cut-lines which are substantially parallel to each other and are used to compute a single CD value for the feature; and

during post-OPC verification, verifying a quality of design layout corrected by OPC by comparing the measured CD value with the simulated CD value.

22. The non-transitory computer-readable storage medium of claim 21 , wherein determining the simulated CD value involves:

placing a measurement window to enclose a target feature;

placing the set of CD extraction cut-lines within the measurement window based at least on a placement spacing parameter, wherein the placement spacing parameter models a spacing between the multiple electron beam scans in the CD-SEM extraction process;

extracting a set of single-cut-line CD values for the set of CD extraction cut-lines; and

determining the simulated CD value using the set of single-cut-line CD values.

23. The non-transitory computer-readable storage medium of claim 22 , wherein prior to placing the measurement window, the method further comprises obtaining the simulated pattern by convolving the feature with the photolithography process model.

24. The non-transitory computer-readable storage medium of claim 21 , wherein determining the simulated CD value using the set of single-cut-line CD values involves computing an average of the set of single-cut-line CD values.

25. A method for modeling critical-dimension (CD) scanning-electron-microscopy (CD-SEM) extraction during post-optical-proximity-correction (post-OPC) verification of a photolithography process model, the method comprising:

receiving a simulated CD value for a feature, wherein the simulated CD value is extracted from a simulated pattern associated with the feature using a single cut-line placed on the simulated pattern;

receiving raw CD-SEM measurement data for the feature, wherein the raw CD-SEM measurement data comprises multiple measured CD values extracted for the feature using multiple electron beam scans;

using the multiple measured CD values to determine a predicted CD value which predicts the simulated CD value, wherein determining the predicted CD value involves performing a curve fitting on the multiple measured CD values to determine a local minimum or maximum CD value; and

during post-OPC verification, verifying, by computer, a quality of design layout corrected by OPC by comparing the predicted CD value with the simulated CD value.

26. The method of claim 25 , wherein determining the predicted CD value involves determining a CD value along a cut-line on the feature, wherein a location of the cut-line matches a location of the single cut-line used to extract the simulated CD value.