We report results of experimental investigations into a through-focus method relevant to sub-wavelength feature dimension measurement. The method linearizes the partial derivative values of a focus indicator with respect to minimum intensity order, and hence permits determination of pitch using a classical linear method. By evaluating the variations in focus indicator of the different captured images obtained at various focal positions, the through-focus curves show a response to sub-resolution changes in the grating structure. The results suggest that sub-wavelength feature dimensions can be evaluated using regular optical microscopes by implementing the through focus method.

© 2005 Optical Society of America

1. S. Fox, R. M. Silver, E. Kornegay and M. Dagenais., �??Focus and Edge Detection Algorithm and their Relevance to the Development of an Optical Overlay Calibration Standard,�?? Proc. SPIE 3677, 95-106 (1999).
2. R. Attota, R. M. Silver, M. Stocker, E. Marx, J. Jun, M. Davidson and R. Larrabee., �??A New Method to Enhance Overlay Tool Performance,�?? Proc. SPIE 5038, 428-436 (2003).
3. R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davison and R. Larrabee, �??High-resolution Optical Overlay Metrology,�?? Proc. SPIE 5375, 78-95 (2004).
4. Murali Subbarao, Tae Choi, and Arman Nikzad, �??Focusing Techniques,�?? Proc. SPIE Optical Engineering, 32, 2824-2836 (1994).
5. Je-Ho Lee, et al., �??Implementation of a Passive Automatic Focusing Algorithm for Digital Still Camera,�?? IEEE Transactions on Consumer Electronics, 41, 449-454 (1995).
6. Minori Noguchi and Shree K. Nayar, �??Microscopic Shape from Focus Using Active Illumination,�?? in Proceedings of the International Conference on Pattern Recognition, 147-152 (1994).
7. Helmy A. Eltoukhy and Sam Kavusi, �??A Computationally Efficient Algorithm for Multi-Focus Image Reconstruction,�?? Proc. SPIE Int. Soc. Opt. Eng. 5017, 332-341 (2003).
8. Murali Subbarao and Jenn-Kwei Tyan, �??Selecting the Optimal Focus Measure for Autofocusing and Depth-From-Focus�?? IEEE Transaction on Pattern Analysis and Machine Intelligence, 20, 864-869 (1998).
9. R.M. Sliver, J. Jun, S. Fox, E. Kornegay, �??Overlay Metrology: Recent Advances and Future Solutions,�?? Future Fab Intl., 11, 2001.
10. Bravo-Zanoguera, Miguel, et al., �??High-performance autofocus circuit for biological microscopy,�?? Rev. Sci. Instrum. 69, 3966-3977(1998). [CrossRef]
11. Berizzi, Fabrizio, and Corsini, Giovanni, �??Autofocusing of Inverse Synthetic Aperture Radar Images Using Contrast Optimization�?? IEEE Trans. Aerosp. Electron. Syst, 32, 118-1191 (1996).
12. Krotkov, Eric, �??Focusing?�?? International J. Computer Vision 1, 223-237 (1987).
13. R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davison and R. Larrabee, �??High-resolution Optical Metrology,�?? Proc. SPIE 5752, 67-79 (2005).
14. R. Attota, R. M. Silver, T. A. Germer and M. Bishop, �??Application of Through-focus Focus-metric Analysis in High Resolution Optical Metrology,�?? Proc. SPIE 5752, 1441-1449(2005).

Future Fab Intl.

• R.M. Sliver, J. Jun, S. Fox, E. Kornegay, �??Overlay Metrology: Recent Advances and Future Solutions,�?? Future Fab Intl., 11, 2001.

IEEE Trans. Aerosp. Electron. Syst

• Berizzi, Fabrizio, and Corsini, Giovanni, �??Autofocusing of Inverse Synthetic Aperture Radar Images Using Contrast Optimization�?? IEEE Trans. Aerosp. Electron. Syst, 32, 118-1191 (1996).

IEEE Transaction on Pattern Analysis

• Murali Subbarao and Jenn-Kwei Tyan, �??Selecting the Optimal Focus Measure for Autofocusing and Depth-From-Focus�?? IEEE Transaction on Pattern Analysis and Machine Intelligence, 20, 864-869 (1998).

IEEE Transactions on Consumer Electronic

• Je-Ho Lee, et al., �??Implementation of a Passive Automatic Focusing Algorithm for Digital Still Camera,�?? IEEE Transactions on Consumer Electronics, 41, 449-454 (1995).

International J. Computer Vision

• Krotkov, Eric, �??Focusing?�?? International J. Computer Vision 1, 223-237 (1987).

Proc. SPIE

• R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davison and R. Larrabee, �??High-resolution Optical Metrology,�?? Proc. SPIE 5752, 67-79 (2005).
• R. Attota, R. M. Silver, T. A. Germer and M. Bishop, �??Application of Through-focus Focus-metric Analysis in High Resolution Optical Metrology,�?? Proc. SPIE 5752, 1441-1449(2005).
• Helmy A. Eltoukhy and Sam Kavusi, �??A Computationally Efficient Algorithm for Multi-Focus Image Reconstruction,�?? Proc. SPIE Int. Soc. Opt. Eng. 5017, 332-341 (2003).
• S. Fox, R. M. Silver, E. Kornegay and M. Dagenais., �??Focus and Edge Detection Algorithm and their Relevance to the Development of an Optical Overlay Calibration Standard,�?? Proc. SPIE 3677, 95-106 (1999).
• R. Attota, R. M. Silver, M. Stocker, E. Marx, J. Jun, M. Davidson and R. Larrabee., �??A New Method to Enhance Overlay Tool Performance,�?? Proc. SPIE 5038, 428-436 (2003).
• R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davison and R. Larrabee, �??High-resolution Optical Overlay Metrology,�?? Proc. SPIE 5375, 78-95 (2004).

Proc. SPIE Optical Engineering

• Murali Subbarao, Tae Choi, and Arman Nikzad, �??Focusing Techniques,�?? Proc. SPIE Optical Engineering, 32, 2824-2836 (1994).

Proceedings of the International

• Minori Noguchi and Shree K. Nayar, �??Microscopic Shape from Focus Using Active Illumination,�?? in Proceedings of the International Conference on Pattern Recognition, 147-152 (1994).

Rev. Sci. Instrum.

• Bravo-Zanoguera, Miguel, et al., �??High-performance autofocus circuit for biological microscopy,�?? Rev. Sci. Instrum. 69, 3966-3977(1998). [CrossRef]

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