Structure identification using scattering signatures

• US 6,728,663 B2
• Filed: 09/12/2001
• Issued: 04/27/2004
• Est. Priority Date: 09/13/2000
• Status: Active Grant

• Current Assignee: Onto Innovation Inc.
• Original Assignee: Accent Optical Technologies, Inc. (Onto Innovation Inc.)
• Inventors: Krukar, Richard H., Wilson, Scott R., Raymond, Christopher J., Farrer, Steve W.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): SUAREZ, FELIX E
• Application Number:
  US09/952,546
• Publication Number:
  US 20020046008A1
• Time in Patent Office: 958 Days
• Field of Search: 702/22, 702/27, 702/28-32, 702/179, 702/188, 702/189, 356/700, 89/111, 244/62, 376/319, 382/100
• US Class Current: 702/189
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 2201/1293 resolving multicomponent spectra

Abstract

A method of pruning a reference library of signatures and corresponding known structure parameter vectors, each signature composed of a reference signal vector, including, for a given reference signal vector, interpolating a parameter vector and deleting the given reference signal vector and the corresponding parameter vector for a sufficiently small interpolation error. Also a method of accessing an indexed reference library of signatures and corresponding known structure parameter vectors, each signature comprising a reference signal vector, including acquiring an unknown signal, calculating an index vector for the unknown signal; determining error between the index vector for the unknown signal and a calculated reference signal index vector of the library; and thereby identifying as a match candidate for the unknown signal a reference signal vector.

Claims

1. A method of pruning a reference library of signatures and corresponding known structure parameter vectors, each signature comprising a reference signal vector, the method comprising the steps of:

generating a library of metrology reference signal vectors;

for at least one given reference signal vector, interpolating a parameter vector assuming that the given reference signal vector and its corresponding parameter vector were deleted from the reference library; and

deleting the given reference signal vector and the corresponding parameter vector if an interpolation error between the corresponding parameter vector and the interpolated parameter vector is less than a threshold value.

2. The method of claim 1 additionally comprising the step of repeating the interpolating and deleting steps a predetermined plurality of times for a plurality of given reference signal vectors.

3. The method of claim 1 wherein performance of the steps is submitted to a remote computer on a computer network.

4. The method of claim 3 wherein results of the steps are retrieved from or returned by the remote computer.

5. The method of claim 3 wherein the steps are performed utilizing a dedicated CD-ROM on the remote computer.

6. The method of claim 3 wherein the steps are performed utilizing a dedicated ramdisk on the remote computer.

7. The method of claim 3 wherein performance of the steps is submitted and results retrieved automatically.

8. The method of claim 3 wherein performance of the steps is submitted and results retrieved manually.

9. A method of accessing an indexed reference library of signatures and corresponding known structure parameter vectors, each signature comprising a reference signal vector, the method comprising the steps of:

acquiring an unknown metrology signal;

calculating an index vector for the unknown metrology signal;

calculating a plurality of reference signal index vectors from the reference signal vectors of the library;

determining error between the index vector for the unknown metrology signal and the reference signal index vector; and

identifying as a match candidate for the unknown metrology signal a reference signal vector corresponding to the reference signal index vector if the error is below a predetermined threshold.

10. The method of claim 9 additionally comprising the step of establishing a plurality of computer systems for performing the calculating, determining, and identifying steps, wherein each of the computer systems performs the steps on a discrete portion of the reference library.

11. The method of claim 9 additionally comprising the step of performing the calculating, determining, and identifying steps for a plurality of reference signal index vectors.

12. The method of claim 9 wherein performance of the steps is submitted to a remote computer on a computer network.

13. The method of claim 12 wherein results of the steps are retrieved from or returned by the remote computer.

14. The method of claim 12 wherein the steps are performed utilizing a dedicated CD-ROM on the remote computer.

15. The method of claim 12 wherein the steps are performed utilizing a dedicated ramdisk on the remote computer.

16. The method of claim 12 wherein performance of the steps is submitted and results retrieved automatically.

17. The method of claim 12 wherein performance of the steps is submitted and results retrieved manually.

18. A method of accessing an indexed reference library of signatures and corresponding known structure parameter vectors, each signature comprising a reference signal vector, the method comprising the steps of:

acquiring an unknown metrology signal;

calculating an index vector for the unknown metrology signal;

calculating a plurality of reference signal index vectors from the reference signal vectors of the library;

determining an absolute difference vector from the index vector for the unknown metrology signal and the reference signal index vector; and

identifying as a match candidate for the unknown metrology signal a reference signal vector corresponding to the reference signal index vector if all values in the absolute difference vector are below corresponding values in a predetermined threshold vector.

19. The method of claim 18 additionally comprising the step of establishing a plurality of computer systems for performing the calculating, determining, and identifying steps, wherein each of the computer systems performs the steps on a discrete portion of the reference library.

20. The method of claim 18 additionally comprising the step of performing the calculating, determining, and identifying steps for a plurality of reference signal index vectors.

21. The method of claim 18 wherein performance of the steps is submitted to a remote computer on a computer network.

22. The method of claim 21 wherein results of the steps are retrieved from or returned by the remote computer.

23. The method of claim 21 wherein the steps are performed utilizing a dedicated CD-ROM on the remote computer.

24. The method of claim 21 wherein the steps are performed utilizing a dedicated ramdisk on the remote computer.

25. The method of claim 21 wherein performance of the steps is submitted and results retrieved automatically.

26. The method of claim 21 wherein performance of the steps is submitted and results retrieved manually.