Generic interface for an optical metrology system

1. An optical metrology system, comprising:

a photometric device having:

a source configured to generate and direct light onto a structure,

a detector configured to detect light diffracted from the structure and to convert the detected light into a measured diffraction signal,

a processing module configured to receive the measured diffraction signal from the detector to analyze the structure; and

a generic interface disposed between the photometric device and the processing module configured to provide the measured diffraction signal to the processing module using a standard set of signal parameters comprising:

a reflectance parameter that characterizes the change in intensity of light when reflected on the structure, and

a polarization parameter that characterizes the change in polarization states of light when reflected on the structure.

2. The system of claim 1 , wherein the processing module is configured to:

compare the measured diffraction signal received from the generic interface to a first simulated diffraction signal; and

when the difference of the measured diffraction signal and the first simulated diffraction signal is not within a matching criterion:

generate a second simulated diffraction signal, and

compare the measured diffraction signal to the second simulated diffraction signal.

3. The system of claim 1 , wherein the structure is a thin film structure.

4. The system of claim 1 , wherein the structure is a periodic grating, and wherein the photometric device is configured to use an azimuth angle of 90 degrees.

5. The system of claim 1 , wherein the source generates a focused beam of light.

6. The system of claim 1 , wherein the reflectance parameter is an average of the square of the absolute value of complex reflection coefficients and is an average over depolarization effects, wherein the depolarization effects include numerical aperture and spectrum bandwidth.

7. The system of claim 6 , wherein the polarization parameter comprises:

a first polarization parameter that characterizes half of the difference between the square of the absolute value of the complex reflection coefficients and is an average over the depolarization effects and normalized to the reflectance parameter;

a second polarization parameter that characterizes an imaginary component of an interference of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter; and

a third polarization parameter that characterizes a real component of an interference of the complex reflection coefficients, average over depolarization effects, and normalized to the reflectance parameter.

8. The system of claim 7 , wherein when the incident light is 45 degree linear polarized light and a first input Stokes parameter is one intensity, a second input Stokes parameter is zero, a third Stokes parameter is one intensity, and a fourth input Stokes parameter is zero, then a first output Stokes parameter is the reflectance parameter multiplied by the first input Stokes parameter, a second output Stokes parameter is negative of the first polarization parameter multiplied by the first input Stokes parameter and reflectance parameter, a third output Stokes parameter is the third polarization parameter multiplied by the first input Stokes parameter and reflectance parameter, and a fourth output Stokes parameter is negative of the second polarization parameter multiplied by the first input Stokes parameter and reflectance parameter.

9. The system of claim 1 , wherein the generic interface is configured to operate with a first type of photometric device and a second type of photometric device using the standard set of signal parameters.

10. The system of claim 9 , wherein the first type of photometric device is a reflectometer, and wherein the generic interface provides the measured diffraction signal received from the reflectometer using only the reflectance parameter of the standard set of signal parameters.

11. The system of claim 9 , wherein the second type of photometric device is an ellipsometer, and wherein the generic interface provides the measured diffraction signal received from the ellipsometer using both the reflectance parameter and the polarization parameter of the standard set of signal parameters.

12. The system of claim 1 further comprising:

a library of simulated diffraction signals;

wherein the processing module is configured to compare the measured diffraction signal received from the generic interface to one or more simulated diffraction signals stored in the library to determine a profile of the structure.

13. The system of claim 12 , wherein the library of simulated diffraction signals is indexed by one or more of the standard set of signal parameters.

14. An optical metrology system, comprising:

a processing module configured to receive a measured diffraction signal from a photometric device; and

a generic interface for the processing module configured to provide the measured diffraction signal to the processing module using a standard set of signal parameters comprising:

a reflectance parameter that characterizes the change in intensity of light when reflected on the structure wherein the reflectance parameter is an average of the square of the absolute value of complex reflection coefficients average over depolarization effects, and

a polarization parameter that characterizes the change in polarization states of light when reflected on the structure, wherein the polarization parameter comprises:

a first polarization parameter that characterizes half of the difference between the square of the absolute value of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter,

a second polarization parameter that characterizes an imaginary component of an interference of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter, and

a third polarization parameter that characterizes a real component of an interference of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter.

15. The system of claim 14 , wherein the processing module is configured to:

compare the measured diffraction signal received from the generic interface to a first simulated diffraction signal; and

when the difference of the measured diffraction signal and the first simulated diffraction signal is not within a matching criterion:

generate a second simulated diffraction signal, and

compare the measured diffraction signal to the second simulated diffraction signal.

16. The system of claim 14 further comprising:

a library of simulated diffraction signals;

wherein the processing module is configured to compare the measured diffraction signal received from the generic interface to one or more simulated diffraction signals stored in the library to determine a profile of the structure.

17. The system of claim 16 , wherein the library of simulated diffraction signals is indexed by one or more of the standard set of signal parameters.

18. A method of analyzing a structure using an optical metrology system, comprising:

directing light onto the structure to obtain a measured diffraction signal using a photometric device;

processing the measured diffraction signal using a generic interface to provide the measured diffraction signal to a processing module using a standard set of signal parameters comprising:

a reflectance parameter that characterizes the change in intensity of light when reflected on the structure, and

a polarization parameter that characterizes the change in polarization states of light when reflected on the structure; and

processing the measured diffraction signal using the processing module to analyze the structure.

19. The method of claim 18 , wherein processing the measured diffraction signal comprises:

comparing the measured diffraction signal received from the generic interface to a first simulated diffraction signal; and

when the difference of the measured diffraction signal and the first simulated diffraction signal is not within a matching criterion:

generating a second simulated diffraction signal, and

comparing the measured diffraction signal to the second simulated diffraction signal.

20. The method of claim 18 , wherein the reflectance parameter is an average of the square of the absolute value of complex reflection coefficients average over depolarization effects.

21. The method of claim 20 , wherein the polarization parameter comprises:

a first polarization parameter that characterizes a difference between the square of the absolute value of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter;

a second polarization parameter that characterizes an imaginary component of an interference of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter, and

a third polarization parameter that characterizes a real component of an interference of the complex reflection coefficients average over depolarization effects, and normalized to the reflectance parameter.

22. The method of claim 18 , wherein processing the measured diffraction signal comprises:

comparing the measured diffraction signal received from the generic interface to one or more simulated diffraction signals stored in a library to determine a profile of the structure.

23. The method of claim 22 , wherein the library of simulated diffraction signals is indexed by one or more of the standard set of signal parameters.

24. A computer-readable storage medium containing computer executable instructions for causing a computer to analyze a structure using an optical metrology system, comprising instructions for:

directing light onto the structure to obtain a measured diffraction signal using a photometric device;

processing the measured diffraction signal using a generic interface to provide the measured diffraction signal to a processing module using a standard set of signal parameters comprising:

a reflectance parameter that characterizes the change in intensity of light when reflected on the structure, and

a polarization parameter that characterizes the change in polarization states of light when reflected on the structure; and

processing the measured diffraction signal using the processing module to analyze the structure.

25. The computer-readable medium of claim 24 , wherein processing the measured diffraction signal comprises:

comparing the measured diffraction signal received from the generic interface to a first simulated diffraction signal; and

when the difference of the measured diffraction signal and the first simulated diffraction signal is not within a matching criterion:

generating a second simulated diffraction signal, and

comparing the measured diffraction signal to the second simulated diffraction signal.

26. The computer-readable medium of claim 24 , wherein the reflectance parameter is an average of the square of the absolute value of complex reflection coefficients.

27. The computer-readable medium of claim 26 , wherein the polarization parameter comprises:

a first polarization parameter that characterizes half of the difference between the square of the absolute value of the complex reflection coefficients normalized to the reflectance parameter;

a second polarization parameter that characterizes an imaginary component of an interference of the complex reflection coefficients normalized to the reflectance parameter; and

a third polarization parameter that characterizes a real component of an interference of the complex reflection coefficients normalized to the reflectance parameter.

28. The computer-readable medium of claim 24 , wherein processing the measured diffraction signal comprises:

comparing the measured diffraction signal received from the generic interface to one or more simulated diffraction signals stored in a library to determine a profile of the structure.

29. The computer-readable medium of claim 28 , wherein the library of simulated diffraction signals is indexed by one or more of the standard set of signal parameters.