Abstract

We have constructed a correlation microscope based on the Mirau interferometer configuration using a thin silicon nitride film beam splitter. This microscope provides the amplitude and phase information for the reflected signal from a sample located on the microscope–object plane. The device is remarkably insensitive to vibrations and is self-correcting for spherical and chromatic range aberrations of the objective. An imaging theory for the correlation microscope has been derived, which predicts accurately both the transverse resolution at a sharp edge and the range resolution for a perfect plane reflector. The range resolution is slightly better than that for a scanning optical microscope using a lens with the same aperture.

© 1990 Optical Society of America

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References

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  1. T. Wilson, C. J. R. Sheppard, Theory and Practice of Scanning Optical Microscopy (Academic, New York, 1984).
  2. G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
    [CrossRef]
  3. M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).
  4. S. C. Chim, P. A. Beck, G. S. Kino, “A Novel Thin Film Interferometer,” submitted to Rev. Sci. Instrum.61 (3), March1990.
    [CrossRef]
  5. G. S. Kino, G. Q. Xiao, “Real-Time Scanning Optical Microscopes,” Scanning Optical Microscopes, T. Wilson, Ed. (Pergamon, London, 1990).
  6. P. A. Reinholdsten, B. T. Khuri-Yakub, “Confocal Imaging at Multiple Frequencies for Improved Depth Resolution,” J. Opt. Soc. America A7 in press.
  7. J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968).
  8. P. C. D. Hobbs, G. S. Kino, “Generalizing the Confocal Microscope via Heterodyne Interferometry and Digital Filtering,” J. Microsc. (1990).
    [CrossRef]

1990

P. C. D. Hobbs, G. S. Kino, “Generalizing the Confocal Microscope via Heterodyne Interferometry and Digital Filtering,” J. Microsc. (1990).
[CrossRef]

1988

G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
[CrossRef]

1987

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Beck, P. A.

S. C. Chim, P. A. Beck, G. S. Kino, “A Novel Thin Film Interferometer,” submitted to Rev. Sci. Instrum.61 (3), March1990.
[CrossRef]

Chim, S. C.

S. C. Chim, P. A. Beck, G. S. Kino, “A Novel Thin Film Interferometer,” submitted to Rev. Sci. Instrum.61 (3), March1990.
[CrossRef]

Cohen, F.

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Corle, T. R.

G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
[CrossRef]

Davidson, M.

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Goodman, J. W.

J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968).

Hobbs, P. C. D.

P. C. D. Hobbs, G. S. Kino, “Generalizing the Confocal Microscope via Heterodyne Interferometry and Digital Filtering,” J. Microsc. (1990).
[CrossRef]

Kaufman, K.

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Khuri-Yakub, B. T.

P. A. Reinholdsten, B. T. Khuri-Yakub, “Confocal Imaging at Multiple Frequencies for Improved Depth Resolution,” J. Opt. Soc. America A7 in press.

Kino, G. S.

P. C. D. Hobbs, G. S. Kino, “Generalizing the Confocal Microscope via Heterodyne Interferometry and Digital Filtering,” J. Microsc. (1990).
[CrossRef]

G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
[CrossRef]

G. S. Kino, G. Q. Xiao, “Real-Time Scanning Optical Microscopes,” Scanning Optical Microscopes, T. Wilson, Ed. (Pergamon, London, 1990).

S. C. Chim, P. A. Beck, G. S. Kino, “A Novel Thin Film Interferometer,” submitted to Rev. Sci. Instrum.61 (3), March1990.
[CrossRef]

Mazor, I.

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Reinholdsten, P. A.

P. A. Reinholdsten, B. T. Khuri-Yakub, “Confocal Imaging at Multiple Frequencies for Improved Depth Resolution,” J. Opt. Soc. America A7 in press.

Sheppard, C. J. R.

T. Wilson, C. J. R. Sheppard, Theory and Practice of Scanning Optical Microscopy (Academic, New York, 1984).

Wilson, T.

T. Wilson, C. J. R. Sheppard, Theory and Practice of Scanning Optical Microscopy (Academic, New York, 1984).

Xiao, G. Q.

G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
[CrossRef]

G. S. Kino, G. Q. Xiao, “Real-Time Scanning Optical Microscopes,” Scanning Optical Microscopes, T. Wilson, Ed. (Pergamon, London, 1990).

Appl. Phys. Lett.

G. Q. Xiao, T. R. Corle, G. S. Kino, “Real-Time Confocal Scanning Optical Microscope,” Appl. Phys. Lett. 53, 716–718 (1988).
[CrossRef]

J. Microsc.

P. C. D. Hobbs, G. S. Kino, “Generalizing the Confocal Microscope via Heterodyne Interferometry and Digital Filtering,” J. Microsc. (1990).
[CrossRef]

Proc. Soc. Photo-Opt. Instrum. Eng.

M. Davidson, K. Kaufman, I. Mazor, F. Cohen, “An Application of Interference Microscopy to Integrated Circuit Inspection and Metrology,” Proc. Soc. Photo-Opt. Instrum. Eng. 775 (1987).

Other

S. C. Chim, P. A. Beck, G. S. Kino, “A Novel Thin Film Interferometer,” submitted to Rev. Sci. Instrum.61 (3), March1990.
[CrossRef]

G. S. Kino, G. Q. Xiao, “Real-Time Scanning Optical Microscopes,” Scanning Optical Microscopes, T. Wilson, Ed. (Pergamon, London, 1990).

P. A. Reinholdsten, B. T. Khuri-Yakub, “Confocal Imaging at Multiple Frequencies for Improved Depth Resolution,” J. Opt. Soc. America A7 in press.

J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968).

T. Wilson, C. J. R. Sheppard, Theory and Practice of Scanning Optical Microscopy (Academic, New York, 1984).

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Figures (11)

Fig. 1
Fig. 1

Linnik correlation microscope.

Fig. 2
Fig. 2

Mirau correlation microscope.

Fig. 3
Fig. 3

Filtering process in the Fourier domain: (a) raw data from the detector; (b) magnitude of the individual frequency components in the Fourier domain; (c) filtering in the Fourier domain to eliminate the negative frequencies and centering the positive frequency packet, as shown; (d) transformed data from inverse Fourier transforming the frequency packet in (c).

Fig. 4
Fig. 4

Detected signals in same coordinates (xS,yS,zS).

Fig. 5
Fig. 5

Three-decibel width of the intensity scans plotted as a function of the bandwidth of the illumination spectrum.

Fig. 6
Fig. 6

Spatial frequency response of the correlation microscope compared with the perfect response. The optimized windowed response is shown as a dotted line.

Fig. 7
Fig. 7

Measured and filtered edge responses.

Fig. 8
Fig. 8

Phase line scan across the SAW-321 resonator showing both the raw and filtered data.

Fig. 9
Fig. 9

Intensity and phase line scans across the bottom of the photoresist trenches 1.25 μm thick of different widths: (a) 1.0-μm wide trench; (b) 0.7-μm wide trench; (c) 0.4-μm wide trench.

Fig. 10
Fig. 10

Comparison between the MCM measurements and SEM measurements for the photoresist trenches.

Fig. 11
Fig. 11

(a) Sixteen cross-sectional intensity images of an integrated circuit at different foci. The axial separation of each image is 0.137 μm along the z-axis. (b) Corresponding phase images of the same integrated circuit.

Equations (20)

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I = A 2 + B 2 + 2 A B γ ( z - z 0 ) ,
U ( k x , k y ) = - u ( x , y ) exp [ - j ( k x x - j k y y ) ] d x d y .
U S ( k x , k y ) = B U ( - k x , - k y ) exp [ - j ( 2 k z z + ϕ ) ] ,
U R ( k x , k y ) = A U ( - k x , - k y ) exp ( - 2 j k z z 0 ) ,
i ( z ) = 2 π U R + U S 2 k r d k r = 4 π k 2 U 2 0 θ 0 { A 2 + B 2 + 2 A B cos [ 2 k ( z - z 0 ) + ϕ ] } × sin θ cos θ d θ .
I A B b ( z ) = 4 π A B U 2 bandwidth 0 θ 0 k 2 × { cos [ 2 k ( z - z 0 ) cos θ + ϕ ] sin θ cos θ d θ } F ( k ) d k ,
I A B b p ( z ) = 4 π A B U 2 bandwidth 0 θ 0 k 2 × ( exp { - j [ ϕ + 2 k ( z - z 0 ) cos θ ] } sin θ cos θ d θ ) F ( k ) d k ,
I A B ( z ) = 2 A B W 2 0 θ 0 exp [ - 2 j k 0 ( z - z 0 ) ] sin θ cos θ d θ .
I ( z ) = sin [ k 0 ( z - z 0 ) ( 1 - cos θ 0 ) ] k 0 ( z - z 0 ) ( 1 - cos θ 0 ) × exp [ - j k 0 ( z - z 0 ) ( 1 + cos θ 0 ) ] .
d z = 0.45 λ 1 - cos θ 0 ,
g ( z - z 0 ) = sin [ Δ k 2 ( z - z 0 ) ( 1 + cos θ 0 ) ] Δ k 2 ( z - z 0 ) ( 1 + cos θ 0 ) .
d z = 1.78 π Δ k ( 1 + cos θ 0 ) .
Δ k z = 2 k 1 ( 1 - cos θ 0 ) + 2 Δ k = 2 k 0 ( 1 - cos θ 0 ) + Δ k ( 1 + cos θ 0 ) ,
I ( z S ) = sin { k 0 [ z S - h ( x S , y S ) ] ( 1 - cos θ 0 ) } k 0 [ z S - h ( x S , y S ) ] ( 1 - cos θ 0 ) × exp { - j k 0 [ z S - h ( x S , y S ) ] ( 1 + cos θ 0 ) ] .
φ = k 0 ( 1 + cos θ 0 ) h ( x S , y S ) .
u R ( x i , y i ) = h ( x 0 - x i , y 0 - y i ) u R ( x 0 , y 0 ) d x 0 d y 0 ,
u S ( x i , y i ) = h ( x - x i , y - y i ) u S ( x , y ) d x d y ,
u R ( x i , y i ) u S ( x i , y i ) = h ( x - x i , y - y i ) h ( x 0 - x i , y 0 - y i ) × u R ( x 0 , y 0 ) u S ( x , y ) d x d y d x 0 d y 0 .
I A B ( x i , y i ) = 2 A B h ( x - x i y - y i ) 2 d x d y .
h ( r ) = J 1 ( 2 π r / λ sin θ 0 ) π r / λ sin θ 0 .

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