Abstract

Experimental one-dimensional intensity and phase images of thick (>200 nm) oxide lines on silicon are presented together with profiles predicted from the waveguide model. Experimental results were obtained with a purpose-built Linnik interference microscope that makes use of phase-shifting interferometry for interferogram analysis. Profiles have been obtained for both TE and TM polarizations for a wide range of focal positions and in both bright-field [type 1(a)] scanning and confocal modes of microscope operation. The results show extremely good agreement despite several simplifying assumptions incorporated into the theoretical model to reduce computing times.

© 1996 Optical Society of America

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References

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  1. W. M. Bullis, D. Nyyssonen, “Optical linewidth measurements on photomasks and wafers,” in VLSI Electronics: Microstructure Science, G. Einspruch, ed. (Academic, New York, 1982), Vol. 3, pp. 301–346.
  2. D. Nyyssonen, “Calibration of optical systems for linewidth measurements on wafers,” Opt. Eng. 21, 882–887 (1982).
  3. M. J. Downs, N. P. Turner, “Application of optical microscopy to dimensional measurements in microelectronics,” in Microscopy: Techniques and Capabilities, L. R. Baker, ed., Proc. Soc. Photo-Opt. Instrum. Eng.368, 82–87 (1982).
  4. D. Nyyssonen, “Theory of optical edge detection and imaging of thick layers,” J. Opt. Soc. Am. 72, 1425–1436 (1982).
    [CrossRef]
  5. D. Nyyssonen, C. P. Kirk, “Optical microscope imaging of lines patterned in thick layers with variable edge geometry: theory,” J. Opt. Soc. Am. A 5, 1270–1280 (1988).
    [CrossRef]
  6. C. M. Yuan, A. J. Strojwas, “Modeling optical microscope images of integrated-circuit structures,” J. Opt. Soc. Am. A 8, 778–790 (1991).
    [CrossRef]
  7. T. Wilson, C. Shepard, Theory and Practice of Scanning Optical Microscopy (Academic, London, 1984), Chaps. 1 and 3.
  8. Objective lenses were NPL achromats purchased as matched pairs from E. Leitz Ltd., London.
  9. D. M. Gale, M. I. Pether, F. C. Reavell, “Interference microscopy of surface relief structures,” in Optical Microlitho-graphic Technology for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. Soc. Photo-Opt. Instrum. Eng.811, 40–47 (1987).
  10. P. Hariharan, “Quasi heterodyne hologram interferometry,” Opt. Eng. 24, 632–638 (1985).
  11. P. Carré, “Installation et utilisation du comparateur photoélec-trique et interférentiel du Bureau International des Poids et Mesures,” Metrologia 2, 13 (1966).
    [CrossRef]
  12. K. Creath, “Calibration of numerical aperture effects in interferometric microscope objectives,” Appl. Opt. 28, 3333–3338 (1989).
    [CrossRef] [PubMed]
  13. H. Stahl, J. Tome, “Phase-measuring interferometry: performance characterization and calibration,” in Optical Testing and Metrology II, C. Grover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.954, 78–87 (1988).
  14. M. I. Pether, “Numerical modelling of image formation in the optical microscope,” presented at the First Institute of Physics Conference on Applied Optics and Opto-Electronics, Nottingham, England, 17–20 September 1990;in Applied Optics Digest, J. C. Dainty, ed. (IOP Publishing, Bristol, U.K., 1990), pp. 191–192. Further work to be published.

1991

C. M. Yuan, A. J. Strojwas, “Modeling optical microscope images of integrated-circuit structures,” J. Opt. Soc. Am. A 8, 778–790 (1991).
[CrossRef]

1989

K. Creath, “Calibration of numerical aperture effects in interferometric microscope objectives,” Appl. Opt. 28, 3333–3338 (1989).
[CrossRef] [PubMed]

1988

1985

P. Hariharan, “Quasi heterodyne hologram interferometry,” Opt. Eng. 24, 632–638 (1985).

1982

D. Nyyssonen, “Calibration of optical systems for linewidth measurements on wafers,” Opt. Eng. 21, 882–887 (1982).

D. Nyyssonen, “Theory of optical edge detection and imaging of thick layers,” J. Opt. Soc. Am. 72, 1425–1436 (1982).
[CrossRef]

1966

P. Carré, “Installation et utilisation du comparateur photoélec-trique et interférentiel du Bureau International des Poids et Mesures,” Metrologia 2, 13 (1966).
[CrossRef]

Bullis, W. M.

W. M. Bullis, D. Nyyssonen, “Optical linewidth measurements on photomasks and wafers,” in VLSI Electronics: Microstructure Science, G. Einspruch, ed. (Academic, New York, 1982), Vol. 3, pp. 301–346.

Carré, P.

P. Carré, “Installation et utilisation du comparateur photoélec-trique et interférentiel du Bureau International des Poids et Mesures,” Metrologia 2, 13 (1966).
[CrossRef]

Creath, K.

K. Creath, “Calibration of numerical aperture effects in interferometric microscope objectives,” Appl. Opt. 28, 3333–3338 (1989).
[CrossRef] [PubMed]

Downs, M. J.

M. J. Downs, N. P. Turner, “Application of optical microscopy to dimensional measurements in microelectronics,” in Microscopy: Techniques and Capabilities, L. R. Baker, ed., Proc. Soc. Photo-Opt. Instrum. Eng.368, 82–87 (1982).

Gale, D. M.

D. M. Gale, M. I. Pether, F. C. Reavell, “Interference microscopy of surface relief structures,” in Optical Microlitho-graphic Technology for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. Soc. Photo-Opt. Instrum. Eng.811, 40–47 (1987).

Hariharan, P.

P. Hariharan, “Quasi heterodyne hologram interferometry,” Opt. Eng. 24, 632–638 (1985).

Kirk, C. P.

Nyyssonen, D.

D. Nyyssonen, C. P. Kirk, “Optical microscope imaging of lines patterned in thick layers with variable edge geometry: theory,” J. Opt. Soc. Am. A 5, 1270–1280 (1988).
[CrossRef]

D. Nyyssonen, “Calibration of optical systems for linewidth measurements on wafers,” Opt. Eng. 21, 882–887 (1982).

D. Nyyssonen, “Theory of optical edge detection and imaging of thick layers,” J. Opt. Soc. Am. 72, 1425–1436 (1982).
[CrossRef]

W. M. Bullis, D. Nyyssonen, “Optical linewidth measurements on photomasks and wafers,” in VLSI Electronics: Microstructure Science, G. Einspruch, ed. (Academic, New York, 1982), Vol. 3, pp. 301–346.

Pether, M. I.

M. I. Pether, “Numerical modelling of image formation in the optical microscope,” presented at the First Institute of Physics Conference on Applied Optics and Opto-Electronics, Nottingham, England, 17–20 September 1990;in Applied Optics Digest, J. C. Dainty, ed. (IOP Publishing, Bristol, U.K., 1990), pp. 191–192. Further work to be published.

D. M. Gale, M. I. Pether, F. C. Reavell, “Interference microscopy of surface relief structures,” in Optical Microlitho-graphic Technology for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. Soc. Photo-Opt. Instrum. Eng.811, 40–47 (1987).

Reavell, F. C.

D. M. Gale, M. I. Pether, F. C. Reavell, “Interference microscopy of surface relief structures,” in Optical Microlitho-graphic Technology for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. Soc. Photo-Opt. Instrum. Eng.811, 40–47 (1987).

Shepard, C.

T. Wilson, C. Shepard, Theory and Practice of Scanning Optical Microscopy (Academic, London, 1984), Chaps. 1 and 3.

Stahl, H.

H. Stahl, J. Tome, “Phase-measuring interferometry: performance characterization and calibration,” in Optical Testing and Metrology II, C. Grover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.954, 78–87 (1988).

Strojwas, A. J.

C. M. Yuan, A. J. Strojwas, “Modeling optical microscope images of integrated-circuit structures,” J. Opt. Soc. Am. A 8, 778–790 (1991).
[CrossRef]

Tome, J.

H. Stahl, J. Tome, “Phase-measuring interferometry: performance characterization and calibration,” in Optical Testing and Metrology II, C. Grover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.954, 78–87 (1988).

Turner, N. P.

M. J. Downs, N. P. Turner, “Application of optical microscopy to dimensional measurements in microelectronics,” in Microscopy: Techniques and Capabilities, L. R. Baker, ed., Proc. Soc. Photo-Opt. Instrum. Eng.368, 82–87 (1982).

Wilson, T.

T. Wilson, C. Shepard, Theory and Practice of Scanning Optical Microscopy (Academic, London, 1984), Chaps. 1 and 3.

Yuan, C. M.

C. M. Yuan, A. J. Strojwas, “Modeling optical microscope images of integrated-circuit structures,” J. Opt. Soc. Am. A 8, 778–790 (1991).
[CrossRef]

Appl. Opt.

K. Creath, “Calibration of numerical aperture effects in interferometric microscope objectives,” Appl. Opt. 28, 3333–3338 (1989).
[CrossRef] [PubMed]

J. Opt. Soc. Am. A

C. M. Yuan, A. J. Strojwas, “Modeling optical microscope images of integrated-circuit structures,” J. Opt. Soc. Am. A 8, 778–790 (1991).
[CrossRef]

J. Opt. Soc. Am.

J. Opt. Soc. Am. A

Metrologia

P. Carré, “Installation et utilisation du comparateur photoélec-trique et interférentiel du Bureau International des Poids et Mesures,” Metrologia 2, 13 (1966).
[CrossRef]

Opt. Eng.

P. Hariharan, “Quasi heterodyne hologram interferometry,” Opt. Eng. 24, 632–638 (1985).

D. Nyyssonen, “Calibration of optical systems for linewidth measurements on wafers,” Opt. Eng. 21, 882–887 (1982).

Other

M. J. Downs, N. P. Turner, “Application of optical microscopy to dimensional measurements in microelectronics,” in Microscopy: Techniques and Capabilities, L. R. Baker, ed., Proc. Soc. Photo-Opt. Instrum. Eng.368, 82–87 (1982).

T. Wilson, C. Shepard, Theory and Practice of Scanning Optical Microscopy (Academic, London, 1984), Chaps. 1 and 3.

Objective lenses were NPL achromats purchased as matched pairs from E. Leitz Ltd., London.

D. M. Gale, M. I. Pether, F. C. Reavell, “Interference microscopy of surface relief structures,” in Optical Microlitho-graphic Technology for Integrated Circuit Fabrication and Inspection, H. L. Stover, S. Wittekoek, eds., Proc. Soc. Photo-Opt. Instrum. Eng.811, 40–47 (1987).

W. M. Bullis, D. Nyyssonen, “Optical linewidth measurements on photomasks and wafers,” in VLSI Electronics: Microstructure Science, G. Einspruch, ed. (Academic, New York, 1982), Vol. 3, pp. 301–346.

H. Stahl, J. Tome, “Phase-measuring interferometry: performance characterization and calibration,” in Optical Testing and Metrology II, C. Grover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.954, 78–87 (1988).

M. I. Pether, “Numerical modelling of image formation in the optical microscope,” presented at the First Institute of Physics Conference on Applied Optics and Opto-Electronics, Nottingham, England, 17–20 September 1990;in Applied Optics Digest, J. C. Dainty, ed. (IOP Publishing, Bristol, U.K., 1990), pp. 191–192. Further work to be published.

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Figures (15)

Fig. 1
Fig. 1

Object representation in the waveguide imaging model.

Fig. 2
Fig. 2

Optical schematic of the automated Linnik interference microscope.

Fig. 3
Fig. 3

Physical layout of the microscope (see Fig. 2 for key).

Fig. 4
Fig. 4

Microscope sample stage.

Fig. 5
Fig. 5

Microscope control and processing system: PMT, photomultiplier tube; A/D, analog–digital; PZT, piezoelectric transducer.

Fig. 6
Fig. 6

Experimental line responses for different scanning modes in the microscope. Profiles of a chrome line on glass.

Fig. 7
Fig. 7

Test site on a wafer sample. Numbers indicate the nominal width in micrometers of etched grooves.

Fig. 8
Fig. 8

Raw phase and intensity profiles from the Linnik microscope; silicon oxide bar on silicon, nominal bar height 666 nm.

Fig. 9
Fig. 9

Physical parameters and refractive indices available for modeling the wafer sample.

Fig. 10
Fig. 10

Bright-field intensity and phase profiles of a centered 1-D bar object (silicon oxide on silicon) with vertical edges. Nominal bar height: (a), (b) 151 nm; (c), (d) 640 nm. Comparison of scalar and waveguide images: ——scalar, ------waveguide TE, ––––waveguide TM. All profiles are focused at the top of the bar.

Fig. 11
Fig. 11

(a). Bright-field intensity and phase profiles of a centered 1-D bar object (silicon oxide on silicon): Measured bar height 640 nm, ——experimental profile, ------theoretical profile. Profiles are at four focal positions (a)–(d) measured from the top of the bar; TE polarization throughout. This sequence is continued in Fig. 11(c).

Fig. 12
Fig. 12

(a), (b) Bright-field TE; (c), (d) TM intensity and phase profiles produced by the 2-D waveguide imaging theory. Centered 1-D bar object (silicon oxide on silicon), height 640 nm. ——vertical edges, ------edges sloping at 70°. All profiles are focused at the top of the bar.

Fig. 13
Fig. 13

Bright-field TE intensity and phase profiles produced by the waveguide imaging theory. Centered 1-D bar object 1silicon oxide on silicon2 with vertical edges. Nominal bar height: (a), (b) 151 nm; (c), (d) 640 nm; ——2-D model, ------3-D model. All profiles are focused at the top of the bar.

Fig. 14
Fig. 14

Bright-field intensity and phase profiles produced by the 2-D waveguide imaging theory. Centered 1-D bar object (silicon oxide on silicon) with vertical edges, height 640 nm. Each graph shows an overlay of profiles for focal positions 0.6–1.0 μm below the top of the bar, in 0.1-μm intervals. (a), (b) TE polarization; (c), (d) TM polarization.

Fig. 15
Fig. 15

Bright-field intensity and phase profiles from the Linnik microscope. Centered 1-D bar object (silicon oxide on silicon); measured height 640 nm. Each graph shows an overlay of profiles for focal positions 0.6–1.0 μm below the top of the bar, in 0.1 ± 0.01-μm intervals. (a), (b) TE polarization; (c), (d) TM polarization.

Tables (1)

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Table 1 Microscope Characteristics a

Equations (2)

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S = N . A . effective N . A . imaging ,
ϕ = 2 π λ 2 t .

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