Abstract

A simultaneous measurement method for the total interference and self-interference of a sample is proposed. The proposed method is capable of making separate measurements of the thickness and surface profile of micro-patterned thin film. The system is an extension of a full-field wavelength scanning interferometer with a single acousto-optic tunable filter (AOTF) as a spectral imaging device. Separate measurements are realized via the polarization-sensitive diffraction of non-collinear acousto-optic interaction. That is, the diffraction angle of an AOTF is separated into different directions depending on the polarization state of the incident light. In so doing, the polarization states of a reference and a sample light were manipulated differently so that a single AOTF can generate the total interference and the self-interference signal in different directions simultaneously. Thus, a compact and light-efficient system is realized with an AOTF, a beam splitter and two CCDs. Thus, a compact system with light-efficiency of two to four times higher than the previously reported system is realized with an AOTF, a beam splitter and two CCDs. Details of the calibration procedures such as wavelength-frequency relation, image shift and registration between two CCDs are provided for the proposed setup. Experimental results are provided and compared to those using commercial equipment that demonstrate the efficiency of the proposed system for the high-speed measurements of the thickness and the surface profile of micro-patterned thin film.

©2009 Optical Society of America

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References

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  2. H. G. Tompkins and W. A. McGahan, Spectroscopic Ellipsometry and Reflectometry: A User’s Guide, (Wiley, New York, 1999).
  3. S. Ye, S. H. Kim, Y. K. Kwak, H. M. Cho, Y. J. Cho, and W. Chegal, “Angle-resolved annular data acquisition method for microellipsometry,” Opt. Express 15, 18056–18065 (2007).
    [Crossref] [PubMed]
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    [Crossref]
  6. D. Kim, S. Kim, H. J. Kong, and Y. Lee, “Measurement of the thickness profile of a transparent thin-film deposited upon a pattern structure with an acousto-optic tunable filter,” Opt. Lett. 27, 1893–1895 (2002).
    [Crossref]
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    [Crossref] [PubMed]
  8. Y. -S. Ghim and S. -W. Kim, “Fast, precise, tomographic measurements of thin films,” Appl. Phys. Lett. 91, 091903 (2007).
    [Crossref]
  9. J. W. You, S. Kim, and D. Kim, “High speed volumetric thickness profile measurement based on full-field wavelength scanning interferometer,” Opt. Express 16, 21022–21031 (2008).
    [Crossref] [PubMed]
  10. Y. -S. Ghim and S. -W. Kim, “Thin-film thickness profile and its refractive index measurements by dispersive white-light interferometry,” Opt. Express 14, 11885–11891 (2006).
    [Crossref] [PubMed]
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    [Crossref] [PubMed]
  13. S. Y. Ryu, J. W. You, Y. K. Kwak, and S. Kim, “Design of a prism to compensate the image-shifting error of the acousto-optic tunable filter,” Opt. Express 16, (2008).
    [Crossref] [PubMed]

2008 (2)

J. W. You, S. Kim, and D. Kim, “High speed volumetric thickness profile measurement based on full-field wavelength scanning interferometer,” Opt. Express 16, 21022–21031 (2008).
[Crossref] [PubMed]

S. Y. Ryu, J. W. You, Y. K. Kwak, and S. Kim, “Design of a prism to compensate the image-shifting error of the acousto-optic tunable filter,” Opt. Express 16, (2008).
[Crossref] [PubMed]

2007 (2)

2006 (1)

2004 (1)

2002 (1)

1999 (1)

1996 (1)

1994 (1)

1991 (1)

Azzam, R. M. A.

R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, New York, 1979).

Bashara, N. M.

R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, New York, 1979).

Bergstralh, J.

Chegal, W.

Cho, H. M.

Cho, Y. J.

Dandliker, R.

Gass, P. A.

Ghim, Y. -S.

Glenar, D. A.

Gray, S.

Hillman, J. J.

Kim, D.

Kim, G. -H.

Kim, S.

Kim, S. H.

Kim, S. -W.

Kong, H. J.

Kwak, Y. K.

S. Y. Ryu, J. W. You, Y. K. Kwak, and S. Kim, “Design of a prism to compensate the image-shifting error of the acousto-optic tunable filter,” Opt. Express 16, (2008).
[Crossref] [PubMed]

S. Ye, S. H. Kim, Y. K. Kwak, H. M. Cho, Y. J. Cho, and W. Chegal, “Angle-resolved annular data acquisition method for microellipsometry,” Opt. Express 15, 18056–18065 (2007).
[Crossref] [PubMed]

Lee, Y.

McGahan, W. A.

H. G. Tompkins and W. A. McGahan, Spectroscopic Ellipsometry and Reflectometry: A User’s Guide, (Wiley, New York, 1999).

Ryu, S. Y.

S. Y. Ryu, J. W. You, Y. K. Kwak, and S. Kim, “Design of a prism to compensate the image-shifting error of the acousto-optic tunable filter,” Opt. Express 16, (2008).
[Crossref] [PubMed]

Saif, B.

Sambles, J. R.

Schnell, U.

Tompkins, H. G.

H. G. Tompkins and W. A. McGahan, Spectroscopic Ellipsometry and Reflectometry: A User’s Guide, (Wiley, New York, 1999).

Ye, S.

You, J. W.

S. Y. Ryu, J. W. You, Y. K. Kwak, and S. Kim, “Design of a prism to compensate the image-shifting error of the acousto-optic tunable filter,” Opt. Express 16, (2008).
[Crossref] [PubMed]

J. W. You, S. Kim, and D. Kim, “High speed volumetric thickness profile measurement based on full-field wavelength scanning interferometer,” Opt. Express 16, 21022–21031 (2008).
[Crossref] [PubMed]

Appl. Opt. (2)

Appl. Phys. Lett. (1)

Y. -S. Ghim and S. -W. Kim, “Fast, precise, tomographic measurements of thin films,” Appl. Phys. Lett. 91, 091903 (2007).
[Crossref]

Opt. Express (5)

Opt. Lett. (3)

Other (2)

R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, New York, 1979).

H. G. Tompkins and W. A. McGahan, Spectroscopic Ellipsometry and Reflectometry: A User’s Guide, (Wiley, New York, 1999).

Supplementary Material (4)

» Media 1: AVI (2195 KB)     
» Media 2: AVI (2026 KB)     
» Media 3: AVI (1222 KB)     
» Media 4: AVI (1312 KB)     

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Figures (9)

Fig. 1.
Fig. 1. (a). The principle of non-collinear AOTF: The polarization state becomes its opposite after the acousto-optic interaction and becomes separated from the undiffracted light, (b) the wavelength of two diffracted lights as a function of the RF frequency f.
Fig. 2.
Fig. 2. The proposed full-field wavelength scanning interferometer that can simultaneously measure the total interference (CCD1) and the self-interference from a sample (CCD2).
Fig. 3.
Fig. 3. Calibration of f-λ relationship for the ordinary and extraordinary incident light
Fig. 4.
Fig. 4. Image shift after scanning the AOTF for (a) CCD1 and (b) CCD2: This is calibrated by shifting the window to capture the same region of interest.
Fig. 5.
Fig. 5. (Media 1) Movie of calibrated images recorded by (a) CCD1 and (b) (Media 2) CCD2 while scanning the AOTF: Image shift is calibrated and the ROI for each CCD is registered at the same position.
Fig. 6.
Fig. 6. (a). Interference of the light from Cr-coated glass and reference mirror while scanning the wavelength by AOTF: The raw spectrum (dash) is interpolated to an equally sampled wavenumber (k) space (solid) and the Gaussian window is multiplied (dash-dot). (b) FFT of each spectrum in (a). The narrow peak of the k-mapping spectrum shows that the system is well calibrated.
Fig. 7.
Fig. 7. Picture of the patterned thin film of SiO2 over the Si wafer substrate and a cross-sectional view showing the measurement parameters
Fig. 8.
Fig. 8. (a). (Media 3) Movie of total interference of the light reflected from the patterned thin film and the reference mirror recorded by CCD1 when scanning the wavelength by AOTF, (b). (Media 4) self-interference from the thin film recorded by CCD2
Fig. 9.
Fig. 9. (a). 3D thickness profile h(x,y) & d(x,y) and (b) line profile along y-axis at a pixel position of x=27

Tables (2)

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Table 1. SiO2 thin film thickness measured by commercial instruments and the proposed system with self-interference detection scheme. * data is not available

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Table 2. Comparison of measurement results for the thickness profile h(x,y) & d(x,y)

Equations (6)

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R = r 01 + r 12 exp [ j 2 dN ( k ) k ] 1 + r 01 r 12 exp [ j 2 dN ( k ) k ] , ψ k d = tan 1 ( R )
d = π 2 { k 1 N ( k 1 ) k 2 N ( k 2 ) }
I ( x , y , k , h , d ) = E r x y + E s x y h 2
= i 0 k d [ 1 + γ ( k , d ) cos { 2 kh + ψ k N d } ]
ϕ ( k ) = 2 kh + ψ k N d
h = ( ϕ ( k 1 ) ϕ ( k 0 ) ) ( ψ ( k 1 ) ψ ( k 0 ) ) 2 ( k 1 k 0 )

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