PROCESS VARIATION-BASED MODEL OPTIMIZATION FOR METROLOGY

1 . A method of optimizing parametric models for structural analysis using metrology of repeating structures on a semiconductor substrate or wafer, the method comprising:

determining a first model of a structure, the first model based on a first set of parameters;

determining a set of process variations data for the structure;

modifying, based on the set of process variations data, the first model of the structure to provide a second model of the structure, the second model of the structure based on a second set of parameters different from the first set of parameters; and

providing a simulated spectrum derived from the second model of the structure.

2 . The method of claim 1 , the method further comprising:

comparing the simulated spectrum to a sample spectrum derived from the structure.

3 . The method of claim 1 , wherein modifying the first model of the structure to provide the second model of the structure comprises reducing the degrees of freedom (DoF) of the first set of parameters to provide the second set of parameters.

4 . The method of claim 3 , wherein reducing the DoF of the first set of parameters comprises:

analyzing design of experiment (DoE) data;

selecting an appropriate parameterization; and

fixing parameters having a smallest variation or error.

5 . The method of claim 1 , wherein modifying the first model of the structure to provide the second model of the structure comprises reparameterizing geometric parameters or material parameters, or both, to provide the second set of parameters.

6 . The method of claim 5 , wherein reparameterizing geometric parameters comprises using bottom critical dimension (CD) and top CD of the structure in the first set of parameters and using, in their place, middle CD and sidewall angle of the structure in the second set of parameters.

7 . The method of claim 1 , wherein modifying the first model of the structure to provide the second model of the structure comprises reparameterizing non-geometric and non-material parameters to provide the second set of parameters, the non-geometric and non-material parameters selected from the group consisting of function+delta parameters, principal component analysis (PCA) parameters, and non-linear principal component analysis (NLPCA).

8 . The method of claim 7 , wherein the reparameterizing comprises using function+delta parameters in linear or non-linear parameter correlations.

9 . The method of claim 8 , wherein the reparameterizing comprises reducing a library size of the second set of parameters relative to the first set of parameters.

10 . The method of claim 1 , wherein modifying based on the set of process variations data comprises sampling a space defined by set of process variations data.

11 . The method of claim 10 , wherein providing the second model of the structure comprises performing a regression only in the space defined by set of process variations data.

12 . The method of claim 10 , wherein providing the second model of the structure comprises performing analysis of one or more of auto wavelength selection, auto truncation order (TO), or auto truncation order pattern selection (TOPS) only in the space defined by set of process variations data.

13 . The method of claim 1 , wherein determining the set of process variations data for the structure comprises obtaining actual process data or synthetic process data based on a process analysis, or both.

14 . The method of claim 1 , wherein modifying the first model of the structure based on the set of process variations data comprises estimating a geometric parameter error of fixing a parameter in the second set of parameters.

15 . A machine-accessible storage medium having instructions stored thereon which cause a data processing system to perform a method of optimizing parametric models for structural analysis using metrology of repeating structures on a semiconductor substrate or wafer, the method comprising:

determining a first model of a structure, the first model based on a first set of parameters;

determining a set of process variations data for the structure;

modifying, based on the set of process variations data, the first model of the structure to provide a second model of the structure, the second model of the structure based on a second set of parameters different from the first set of parameters; and

providing a simulated spectrum derived from the second model of the structure.

16 . The storage medium as in claim 15 , the method further comprising:

comparing the simulated spectrum to a sample spectrum derived from the structure.

17 . The storage medium as in claim 15 , wherein modifying the first model of the structure to provide the second model of the structure comprises reducing the degrees of freedom (DoF) of the first set of parameters to provide the second set of parameters.

18 . The storage medium as in claim 17 , wherein reducing the DoF of the first set of parameters comprises:

analyzing design of experiment (DoE) data;

selecting an appropriate parameterization; and

fixing parameters having a smallest variation or error.

19 . The storage medium as in claim 15 , wherein modifying the first model of the structure to provide the second model of the structure comprises reparameterizing geometric parameters or material parameters, or both, to provide the second set of parameters.

20 . The storage medium as in claim 19 , wherein reparameterizing geometric parameters comprises using bottom critical dimension (CD) and top CD of the structure in the first set of parameters and using, in their place, middle CD and sidewall angle of the structure in the second set of parameters.

21 . The storage medium as in claim 15 , wherein modifying the first model of the structure to provide the second model of the structure comprises reparameterizing non-geometric and non-material parameters to provide the second set of parameters, the non-geometric and non-material parameters selected from the group consisting of function+delta parameters, principal component analysis (PCA) parameters, and non-linear principal component analysis (NLPCA).

22 . The storage medium as in claim 21 , wherein the reparameterizing comprises using function+delta parameters in linear or non-linear parameter correlations.

23 . The storage medium as in claim 22 , wherein the reparameterizing comprises reducing a library size of the second set of parameters relative to the first set of parameters.

24 . The storage medium as in claim 15 , wherein modifying based on the set of process variations data comprises sampling a space defined by set of process variations data.

25 . The storage medium as in claim 24 , wherein providing the second model of the structure comprises performing a regression only in the space defined by set of process variations data.

26 . The storage medium as in claim 24 , wherein providing the second model of the structure comprises performing analysis of one or more of auto wavelength selection, auto truncation order (TO), or auto truncation order pattern selection (TOPS) only in the space defined by set of process variations data.

27 . The storage medium as in claim 15 , wherein determining the set of process variations data for the structure comprises obtaining actual process data or synthetic process data based on a process analysis, or both.

28 . The storage medium as in claim 15 , wherein modifying the first model of the structure based on the set of process variations data comprises estimating a geometric parameter error of fixing a parameter in the second set of parameters.

29 . A system to generate a simulated diffraction signal to determine process parameters of a wafer application to fabricate a structure on a wafer using optical metrology, the system comprising:

a fabrication cluster configured to perform a wafer application to fabricate a structure on a wafer, wherein one or more process parameters characterize behavior of structure shape or layer thickness when the structure undergoes processing operations in the wafer application performed using the fabrication cluster; and

an optical metrology system configured to determine the one or more process parameters of the wafer application, the optical metrology system comprising:

a beam source and detector configured to measure a diffraction signal of the structure; and

a processor configured to determine a first model of a structure, the first model based on a first set of parameters, configured to determine a set of process variations data for the structure, configured to modify the first model of the structure to provide a second model of the structure based on the set of process variations data, the second model of the structure based on a second set of parameters different from the first set of parameters, and configured to provide a simulated spectrum derived from the second model of the structure.

30 . The system of claim 29 , further comprising:

a library of simulated diffraction signals and values of one or more process parameters associated with the simulated diffraction signals, wherein the simulated diffraction signals were generated using values of one or more shape or film thickness parameters, and wherein the values of the one or more shape or film thickness parameters used to generate the simulated diffraction signals were derived from the values of the one or more process parameters associated with the simulated diffraction signals.