Abstract

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

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References

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  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).
    [Crossref]
  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).
    [Crossref]
  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).
    [Crossref]
  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).
    [Crossref]
  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).
    [Crossref]
  9. R.M. Sliver, J. Jun, S. Fox, and E. Kornegay, “Overlay Metrology: Recent Advances and Future Solutions,” Future Fab Intl.,  11, 2001.
  10. Miguel Bravo-Zanoguera, 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).
    [Crossref]
  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).
    [Crossref]

2005 (2)

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).
[Crossref]

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).
[Crossref]

2004 (1)

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).
[Crossref]

2003 (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).
[Crossref]

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).

2001 (1)

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

1999 (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).
[Crossref]

1998 (2)

Miguel Bravo-Zanoguera, et al., “High-performance autofocus circuit for biological microscopy,” Rev. Sci. Instrum. 69, 3966–3977(1998).
[Crossref]

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).
[Crossref]

1996 (1)

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

1995 (1)

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).
[Crossref]

1994 (1)

Murali Subbarao, Tae Choi, and Arman Nikzad, “Focusing Techniques,” Proc. SPIE Optical Engineering, 32, 2824–2836 (1994).

1987 (1)

Krotkov Eric , “Focusing?” International J. Computer Vision 1, 223–237 (1987).

Attota, R.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Bishop, M.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Bravo-Zanoguera, Miguel

Miguel Bravo-Zanoguera, et al., “High-performance autofocus circuit for biological microscopy,” Rev. Sci. Instrum. 69, 3966–3977(1998).
[Crossref]

Choi, Tae

Murali Subbarao, Tae Choi, and Arman Nikzad, “Focusing Techniques,” Proc. SPIE Optical Engineering, 32, 2824–2836 (1994).

Dagenais, M.

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).
[Crossref]

Davidson, M.

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).
[Crossref]

Davison, M.

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).
[Crossref]

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).
[Crossref]

Eltoukhy, Helmy A.

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).

Eric, Krotkov

Krotkov Eric , “Focusing?” International J. Computer Vision 1, 223–237 (1987).

Fabrizio, Berizzi

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

Fox, S.

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

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).
[Crossref]

Germer, T. A.

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).
[Crossref]

Giovanni, Corsini

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

Jun, J.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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

Kavusi, Sam

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).

Kornegay, E.

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

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).
[Crossref]

Larrabee, R.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Lee, Je-Ho

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).
[Crossref]

Marx, E.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Nayar, Shree K.

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).

Nikzad, Arman

Murali Subbarao, Tae Choi, and Arman Nikzad, “Focusing Techniques,” Proc. SPIE Optical Engineering, 32, 2824–2836 (1994).

Noguchi, Minori

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).

Silver, R. M.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Sliver, R.M.

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

Stocker, M.

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Subbarao, Murali

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).
[Crossref]

Murali Subbarao, Tae Choi, and Arman Nikzad, “Focusing Techniques,” Proc. SPIE Optical Engineering, 32, 2824–2836 (1994).

Tyan, Jenn-Kwei

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).
[Crossref]

Future Fab Intl. (1)

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

IEEE Trans. Aerosp. Electron. Syst, (1)

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 and Machine Intelligence, (1)

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).
[Crossref]

IEEE Transactions on Consumer Electronics (1)

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).
[Crossref]

International J. Computer Vision (1)

Krotkov Eric , “Focusing?” International J. Computer Vision 1, 223–237 (1987).

Proc. SPIE (5)

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

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).
[Crossref]

Proc. SPIE Int. Soc. Opt. Eng. (1)

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).

Proc. SPIE Optical Engineering, (1)

Murali Subbarao, Tae Choi, and Arman Nikzad, “Focusing Techniques,” Proc. SPIE Optical Engineering, 32, 2824–2836 (1994).

Rev. Sci. Instrum. (1)

Miguel Bravo-Zanoguera, et al., “High-performance autofocus circuit for biological microscopy,” Rev. Sci. Instrum. 69, 3966–3977(1998).
[Crossref]

Other (1)

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).

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Figures (8)

Fig. 1.
Fig. 1.

Bright-field microscope measurement system layout.

Fig. 2.
Fig. 2.

(a) The focused image of the grating with 0.5μm line-width and 0.5μm spacing. The defocused image with (b) 2μm (c) 5μm (d) 10μm focus offset

Fig. 3.
Fig. 3.

Top: The focus measures of the etched silicon grating target (0.5μm linewidth/0.5μm spacing); bottom left: focused image with selected measurement window; bottom right: grating intensity profile.

Fig. 4.
Fig. 4.

Top: The focus measures of the etched SiO2 grating target (0.5μm linewidth/0.5μm spacing); bottom left: focused image with selected measurement window; bottom right: grating intensity profile.

Fig. 5.
Fig. 5.

The minima in the focus plot against order for the (a) 0.5μm/0.5μm (b) 0.5μm/1.0μm (c) 1.0μm/1.0μm (d) 1.0μm/1.5μm (e) 1.0μm/2.0μm (linewidth/spacing) grating target pattern.

Fig. 6.
Fig. 6.

The plot of partial derivative of focus position with respect to minimum intensity order versus pitch. The slope of the fitting curve is approximately 1.42.

Fig. 7.
Fig. 7.

Through focus intensity of grating targets as a function of linewidth at pitch 800nm (linewidth/spacing combinations at 200nm/600nm, 400nm/400nm and 600nm/200nm).

Fig. 8.
Fig. 8.

Through focus intensity of grating targets as a function of linewidth at pitch 1200nm for five linewidth/spacing combinations (200nm/1000nm, 300nm/900nm, 400nm/800nm, 900nm/300nm and 1000nm/200nm).

Tables (2)

Tables Icon

Table 1. Sample wafer for pitch measurement.

Tables Icon

Table 2. Sample wafer for CD measurement

Equations (5)

Equations on this page are rendered with MathJax. Learn more.

Q = x y xy 2
s = I xy I ¯ 2 n 1
Sum = I xy
L = x y 2 xy 2
C = ( I max I min ) ( I max + I min )

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