Abstract

We present a detailed experimental study of a new through-focus technique to measure critical dimension linewidth with nanometer sensitivity using a bright field optical microscope. This method relies on analyzing intensity gradients in optical images at different focus positions, here defined as the focus metric (FM) signature. The contrast of an optical image of a structured target, where a particular structure is repeated several times, varies greatly as it is moved through-focus if the spacing between the structures is such that the scattered field from the features interferes. Complex, distinguishable through-focus optical response occurs under this condition giving rise to the formation of several cyclic high and low contrast images. As a result it exhibits several FM signature peaks as opposed to a single FM peak for structures nearly isolated. This complex optical behavior is very sensitive to the dimensions of the target geometry. By appropriately analyzing the through-focus optical image, information can be obtained regarding the target. An array of lines is used as a structured target. Linewidth measurements were made by using experimental through-focus optical data obtained using a bright field microscope and simulated optical data. The optical results are compared with reference metrology tools such as a critical dimension atomic force microscope and critical dimension scanning electron microscope.

© 2008 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |

  1. C. J. Raymond, S. S. H. Naqvi, and J. R. McNeil, "Scatterometry for CD measurements of etched structures," Proc. SPIE 2725, 720-728 (1996).
  2. R. Attota, R. M. Silver, M. Bishop, E. Marx, J. Jun, M. Stocker, M. Davidson, and R. Larrabee, "Evaluation of new in-chip and arrayed line overlay target designs," Proc. SPIE 5375, 395-402 (2004).
  3. Y.-S. Ku, A.-S. Liu, and N. Smith, "Through-focus technique for nano-scale grating pitch and linewidth analysis," Opt. Express 13, 6699-6708 (2005).
    [PubMed]
  4. A.-S. Liu, Y.-S. Ku, and N. Smith, "Through-focus algorithm to improve overlay tool performance," Proc. SPIE 5908, 383-391 (2005).
  5. Y.-S. Ku, A.-S. Liu, and N. Smith, "Through-focus technique for grating linewidth analysis with nanometer sensitivity," Opt. Eng. 45, 123602 (2006).
  6. E. Krotkov, "Focusing," Int. J. Comput. Vis. 1, 223-237 (1987).
  7. S. Fox, R. M. Silver, E. Kornegay, and M. Dagenais, "Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard," Proc. SPIE 3677, 95-106 (1999).
  8. R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davidson, and R. Larrabee, "High resolution optical overlay metrology," Proc. SPIE 5375, 78-95 (2004).
  9. R. Attota, R. M. Silver, and J. Potzick, "Optical illumination and critical dimension analysis using the through-focus focus metric," Proc. SPIE 6289, 62890Q (2006).
  10. H. F. Talbot, "Facts relating to optical science, No. IV," Philos. Mag. 9, 401-407 (1836).
  11. P. Latimer and R. F. Crouse, "Talbot effect reinterpreted," Appl. Opt. 31, 80-89 (1992).
    [PubMed]
  12. P. Latimer, "Talbot plane patterns: grating images or interference effects?," Appl. Opt. 32, 1078-1083 (1993).
    [PubMed]
  13. M. Davidson, "Analytic waveguide solutions and the coherence probe microscope," Microelectron. Eng. 13, 523-526 (1991).
  14. E. Marx, "Images of strips on and trenches in substrates," Appl. Opt. 46, 5571-5587 (2007).
    [PubMed]
  15. T. A. Germer and E. Marx, "Simulations of optical microscope images," Proc. SPIE 6152, 61520I (2006).
  16. T. V. Pistor, "Electromagnetic simulation and modeling with applications in lithography," Ph.D. dissertation (University of California at Berkeley, 2001).
  17. R. Attota, R. M. Silver, T. A. Germer, M. Bishop, R. Larrabee, M. T. Stocker, and L. Howard, "Application of through-focus focus-metric analysis in high resolution optical metrology," Proc. SPIE 5752, 1441-1449 (2005).
  18. R. M. Silver, B. M. Barnes, R. Attota, J. Jun, J. Filliben, J. Soto, M. Stocker, P. Lipscomb, E. Marx, H. J. Patrick, R. Dixson, and R. Larrabee, "The limits of image-based optical metrology," Proc. SPIE 6152, 61520Z (2006).
  19. R. G. Dixson, R. A. Allen, W. F. Guthrie, and M. W. Cresswell, "Traceable calibration of critical-dimension atomic force microscope linewidth measurements with nanometer uncertainty," J. Vac. Sci. Technol. B 23, 3028-3032 (2005).
  20. N. Orji, A. Martinez, R. Dixson, and J. Allgair, "Progress on implementation of a CD-AFM based reference measurement system," Proc. SPIE 6152, 61520O (2006).
  21. N. G. Orji and R. G. Dixson, "Higher order tip effects in traceable CD-AFM based linewidth measurements," Meas. Sci. and Technol. 18, 448-455 (2007).

2007 (2)

E. Marx, "Images of strips on and trenches in substrates," Appl. Opt. 46, 5571-5587 (2007).
[PubMed]

N. G. Orji and R. G. Dixson, "Higher order tip effects in traceable CD-AFM based linewidth measurements," Meas. Sci. and Technol. 18, 448-455 (2007).

2006 (5)

N. Orji, A. Martinez, R. Dixson, and J. Allgair, "Progress on implementation of a CD-AFM based reference measurement system," Proc. SPIE 6152, 61520O (2006).

T. A. Germer and E. Marx, "Simulations of optical microscope images," Proc. SPIE 6152, 61520I (2006).

R. M. Silver, B. M. Barnes, R. Attota, J. Jun, J. Filliben, J. Soto, M. Stocker, P. Lipscomb, E. Marx, H. J. Patrick, R. Dixson, and R. Larrabee, "The limits of image-based optical metrology," Proc. SPIE 6152, 61520Z (2006).

R. Attota, R. M. Silver, and J. Potzick, "Optical illumination and critical dimension analysis using the through-focus focus metric," Proc. SPIE 6289, 62890Q (2006).

Y.-S. Ku, A.-S. Liu, and N. Smith, "Through-focus technique for grating linewidth analysis with nanometer sensitivity," Opt. Eng. 45, 123602 (2006).

2005 (4)

Y.-S. Ku, A.-S. Liu, and N. Smith, "Through-focus technique for nano-scale grating pitch and linewidth analysis," Opt. Express 13, 6699-6708 (2005).
[PubMed]

A.-S. Liu, Y.-S. Ku, and N. Smith, "Through-focus algorithm to improve overlay tool performance," Proc. SPIE 5908, 383-391 (2005).

R. G. Dixson, R. A. Allen, W. F. Guthrie, and M. W. Cresswell, "Traceable calibration of critical-dimension atomic force microscope linewidth measurements with nanometer uncertainty," J. Vac. Sci. Technol. B 23, 3028-3032 (2005).

R. Attota, R. M. Silver, T. A. Germer, M. Bishop, R. Larrabee, M. T. Stocker, and L. Howard, "Application of through-focus focus-metric analysis in high resolution optical metrology," Proc. SPIE 5752, 1441-1449 (2005).

2004 (2)

R. Attota, R. M. Silver, M. Bishop, E. Marx, J. Jun, M. Stocker, M. Davidson, and R. Larrabee, "Evaluation of new in-chip and arrayed line overlay target designs," Proc. SPIE 5375, 395-402 (2004).

R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davidson, and R. Larrabee, "High resolution optical overlay metrology," Proc. SPIE 5375, 78-95 (2004).

1999 (1)

S. Fox, R. M. Silver, E. Kornegay, and M. Dagenais, "Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard," Proc. SPIE 3677, 95-106 (1999).

1996 (1)

C. J. Raymond, S. S. H. Naqvi, and J. R. McNeil, "Scatterometry for CD measurements of etched structures," Proc. SPIE 2725, 720-728 (1996).

1993 (1)

1992 (1)

1991 (1)

M. Davidson, "Analytic waveguide solutions and the coherence probe microscope," Microelectron. Eng. 13, 523-526 (1991).

1987 (1)

E. Krotkov, "Focusing," Int. J. Comput. Vis. 1, 223-237 (1987).

1836 (1)

H. F. Talbot, "Facts relating to optical science, No. IV," Philos. Mag. 9, 401-407 (1836).

Appl. Opt. (3)

Int. J. Comput. Vis. (1)

E. Krotkov, "Focusing," Int. J. Comput. Vis. 1, 223-237 (1987).

J. Vac. Sci. Technol. B (1)

R. G. Dixson, R. A. Allen, W. F. Guthrie, and M. W. Cresswell, "Traceable calibration of critical-dimension atomic force microscope linewidth measurements with nanometer uncertainty," J. Vac. Sci. Technol. B 23, 3028-3032 (2005).

Meas. Sci. and Technol. (1)

N. G. Orji and R. G. Dixson, "Higher order tip effects in traceable CD-AFM based linewidth measurements," Meas. Sci. and Technol. 18, 448-455 (2007).

Microelectron. Eng. (1)

M. Davidson, "Analytic waveguide solutions and the coherence probe microscope," Microelectron. Eng. 13, 523-526 (1991).

Opt. Eng. (1)

Y.-S. Ku, A.-S. Liu, and N. Smith, "Through-focus technique for grating linewidth analysis with nanometer sensitivity," Opt. Eng. 45, 123602 (2006).

Opt. Express (1)

Philos. Mag. (1)

H. F. Talbot, "Facts relating to optical science, No. IV," Philos. Mag. 9, 401-407 (1836).

Proc. SPIE (10)

T. A. Germer and E. Marx, "Simulations of optical microscope images," Proc. SPIE 6152, 61520I (2006).

R. Attota, R. M. Silver, T. A. Germer, M. Bishop, R. Larrabee, M. T. Stocker, and L. Howard, "Application of through-focus focus-metric analysis in high resolution optical metrology," Proc. SPIE 5752, 1441-1449 (2005).

R. M. Silver, B. M. Barnes, R. Attota, J. Jun, J. Filliben, J. Soto, M. Stocker, P. Lipscomb, E. Marx, H. J. Patrick, R. Dixson, and R. Larrabee, "The limits of image-based optical metrology," Proc. SPIE 6152, 61520Z (2006).

A.-S. Liu, Y.-S. Ku, and N. Smith, "Through-focus algorithm to improve overlay tool performance," Proc. SPIE 5908, 383-391 (2005).

C. J. Raymond, S. S. H. Naqvi, and J. R. McNeil, "Scatterometry for CD measurements of etched structures," Proc. SPIE 2725, 720-728 (1996).

R. Attota, R. M. Silver, M. Bishop, E. Marx, J. Jun, M. Stocker, M. Davidson, and R. Larrabee, "Evaluation of new in-chip and arrayed line overlay target designs," Proc. SPIE 5375, 395-402 (2004).

S. Fox, R. M. Silver, E. Kornegay, and M. Dagenais, "Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard," Proc. SPIE 3677, 95-106 (1999).

R. M. Silver, R. Attota, M. Stocker, M. Bishop, J. Jun, E. Marx, M. Davidson, and R. Larrabee, "High resolution optical overlay metrology," Proc. SPIE 5375, 78-95 (2004).

R. Attota, R. M. Silver, and J. Potzick, "Optical illumination and critical dimension analysis using the through-focus focus metric," Proc. SPIE 6289, 62890Q (2006).

N. Orji, A. Martinez, R. Dixson, and J. Allgair, "Progress on implementation of a CD-AFM based reference measurement system," Proc. SPIE 6152, 61520O (2006).

Other (1)

T. V. Pistor, "Electromagnetic simulation and modeling with applications in lithography," Ph.D. dissertation (University of California at Berkeley, 2001).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (16)

Fig. 1
Fig. 1

Schematic showing the process of obtaining an FM value from an optical image.

Fig. 2
Fig. 2

FM plot obtained using a simulated profile of an array of lines, where lines are NOT optically interacting. Insets are intensity profiles at indicated focus positions. Parameters for simulation: Si line on Si substrate; linewidth = 0.5 μ m , pitch = 10 μ m , line height = 0.5 μ m ; NA = 0.8 ; INA = 0.4 ; wavelength = 546   nm . Zero position represents substrate.

Fig. 3
Fig. 3

(a) FM signature for the line array features exhibiting proximity effects. Insets are intensity profiles at the indicated focus positions. Parameters for simulation: linewidth = 140   nm ; line height = 200   nm ; pitch = 600   nm ; INA = 0.4 ; NA = 0.8 ; wavelength = 546   nm . Zero position represents substrate. (b) Intensity profiles at the two FM signature peaks shown in Fig. 3(a).

Fig. 4
Fig. 4

FM signature obtained from the simulated profiles as a function of the linewidth in nanometers: (a) 5   nm change in the linewidth, and (b) 1   nm change in the linewidth. Pitch is 600   nm ; line height is 230   nm ; NA is 0.8; INA is 0.5. Zero position represents top of the line feature.

Fig. 5
Fig. 5

FM signature obtained from the simulated profiles as a function of the line height in nanometers: (a) 5   nm change in the line height for 150   nm wide line, and (b) 1   nm change in the line height for 157   nm wide line. Pitch is 600   nm ; linewidth is 150   nm ; NA is 0.8; INA is 0.5. Zero position represents top of the line feature.

Fig. 6
Fig. 6

FM signature obtained from simulated profiles as a function of the line pitch in nanometers. Linewidth is 157   nm ; line height is 230   nm ; NA is 0.8; INA is 0.5. Zero position represents top of the line feature.

Fig. 7
Fig. 7

FM signature as a function of the INA obtained from the simulated profiles: (a) 0.1 change in INA and (b) 0.01 change in INA. Linewidth = 140   nm ; line height = 200   nm ; pitch = 600   nm ; NA = 0.8 ; wavelength = 546   nm . Zero position represents substrate.

Fig. 8
Fig. 8

FM signature as a function of the collection NA obtained from the simulated profiles: (a) 0.1 change in NA and (b) 0.01 change in NA. Linewidth = 140   nm ; line height = 200   nm ; pitch = 600   nm ; INA = 0.4 ; wavelength = 546   nm . Zero position represents substrate.

Fig. 9
Fig. 9

FM signature as a function of the illumination wavelength obtained from the simulated profiles: (a) 10   nm change in the wavelength and (b) 1   nm change in the wavelength. Linewidth = 140   nm ; line height = 200   nm ; pitch = 600   nm ; INA = 0.4 ; NA = 0.8 . Zero position represents substrate.

Fig. 10
Fig. 10

(Color online) FM signature as a function of the optical properties obtained from the simulated profiles: (a) 0.1   nm change in the refractive index (n) and (b) 0.1   nm change in the absorption coefficient (k). Linewidth = 140   nm ; line height = 200   nm ; pitch = 600   nm ; NA = 0.4 ; NA = 0.8 . Zero position represents substrate.

Fig. 11
Fig. 11

Measured bottom linewidth values in nanometers, using CD-SEM and CD-AFM.

Fig. 12
Fig. 12

Mean experimental FM signatures for the six target locations selected normalized to the bigger FM peak. The SEM measured linewidths and their standard deviations are indicated in the figure in nanometers.

Fig. 13
Fig. 13

Simulated FM signatures for 125, 135, 145, 155, 165, and 175   nm bottom linewidths at 0.37 INA. Other input parameters are: line height = 230   nm , pitch = 601   nm , collection NA = 0.8 , illumination wavelength = 546   nm , and Si lines on Si substrate.

Fig. 14
Fig. 14

Simulated FM signatures for 146 to 156   nm bottom linewidths at 0.36 INA. Other input parameters are: line height = 230   nm , pitch = 601   nm , collection NA = 0.8 , wavelength = 546   nm , and Si lines on Si substrate.

Fig. 15
Fig. 15

Plot of the normalized left peak intensity versus the linewidth for the simulations and the experiments.

Fig. 16
Fig. 16

Measured linewidths using the SEM and the FM signature optical microscope method.

Equations (1)

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

FM = 1 N 1 i = 2 N ( S i S i 1 ) 2 ,

Metrics