Selection of wavelengths for integrated circuit optical metrology

• US 20070198211A1
• Filed: 04/20/2007
• Published: 08/23/2007
• Est. Priority Date: 06/03/2002
• Status: Active Grant

• Current Assignee: Tokyo Electron America Incorporated (Tokyo Electron Limited)
• Original Assignee: Timbre Technologies Incorporated (Tokyo Electron Limited)
• Inventors: Laughery, Michael, Vuong, Vi, Bao, Junwei, Drege, Emmanuel, Jakatdar, Nickhil, Doddi, Srinivas, Lane, Lawrence, Barry, Kelly
• Granted Patent: US 7,474,993 B2
• Time in Patent Office: Days
• US Class Current: 702/159
• CPC Class Codes: G01B 11/00 Measuring arrangements characterised by the use of optical techniques

Abstract

Specific wavelengths to use in optical metrology of an integrated circuit can be selected using one or more selection criteria and termination criteria. Wavelengths are selected using the selection criteria, and the selection of wavelengths is iterated until the termination criteria are met.

Claims

1. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

determining one or more selection criteria;

creating a correlation matrix for a set of diffraction spectra measured at optical metrology measurement points, the measurement points corresponding to specified wavelengths, the correlation matrix having as matrix members correlation coefficients corresponding to the measurement points;

selecting wavelengths using the set of diffraction spectra for the integrated circuit structure, the selection criteria, and a wavelength selection algorithm; and

performing the selecting step until the termination criteria are met.

2. The method of claim 1 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum, wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

3. The method of claim 1 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to one of the set of diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

4. The method of claim 1 wherein:

the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

5. The method of claim 1 wherein:

the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to one of the set of diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

6. The method of claim 1 wherein the performing the selecting step until the termination criteria are met includes:

creating a symmetric binary matrix derived from the correlation matrix, the symmetric binary matrix having members with values of one or zero,

wherein the correlation matrix member is set to one if the correlation coefficient is equal to or greater than a correlation threshold, and

wherein the correlation matrix member is set to zero if the correlation coefficient is less than the correlation threshold; and

performing at least one iteration of selecting a wavelength corresponding to a row with the most number of one'"'"'s in the symmetric binary matrix and setting the row and a corresponding column of the symmetric binary matrix to zeros, the row and column corresponding to the wavelength selected, the iterations of selecting a wavelength continuing until the symmetric binary matrix members are all zeros.

7. The method of claim 1 further comprising:

saving the selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes termination criteria for the selection of wavelengths and wavelength selection criteria.