Abstract

A wavelength scanning interferometer for measuring the surface and thickness of a transparent film has been studied. A halogen light source combined with an acousto-optic tuneable filter is used to generate a sequence of filtered light in a Linnik interferometer, which leads to a sequence of interferograms captured by a CCD camera. When a transparent thin film is measured, the reflection signals from both the top and bottom surfaces of the film will interfere with the reference signal. At the same time, the multiple reflection signals between the two film surfaces will also interfere with each other. Effective separation of the interference signals from each other is the key to achieving a successful measurement. By performing a frequency-domain analysis, these interference signals can be separated. An optimized Fourier transform method is used in the analysis. Measurements of the top and bottom surface finishes of the film, as well as the film thickness map, have been achieved. The film needs to be more than 3 µm in optical path length, and must transparent with no absorption of light. The film’s refractive index needs to be known as a function of wavelength. In this paper, the theoretical analysis and simulation study of wavelength scanning interferometry for transparent film measurement is discussed. Experiments on thin film layers of Parylene N coated on a glass slide surface are studied and analyzed. Comparison study results with other contact and non-contact methods are also presented.

© 2012 OSA

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References

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    [CrossRef]
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    [CrossRef]
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    [CrossRef] [PubMed]
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2012

2011

H. Mahamedsalih, X. Jiang, and F. Gao, “Comparison of fast Fourier transform and convolution in wavelength scanning interferometry,” Proc. SPIE8082, 899357 (2011).

2010

2008

P. de Groot and X. de Lega, “Transparent film profiling and analysis by interference microscopy,” Proc. SPIE7064, 794936 (2008).
[CrossRef]

D. Mansfield, “Extraction of film interface surfaces from scanning white light interferometry,” Proc. SPIE7101, 797978 (2008).
[CrossRef]

2005

2002

1999

Akiyama, H.

Choi, S.

Davies, A.

de Groot, P.

P. de Groot and X. de Lega, “Transparent film profiling and analysis by interference microscopy,” Proc. SPIE7064, 794936 (2008).
[CrossRef]

de Lega, X.

P. de Groot and X. de Lega, “Transparent film profiling and analysis by interference microscopy,” Proc. SPIE7064, 794936 (2008).
[CrossRef]

Gao, F.

H. Mahamedsalih, X. Jiang, and F. Gao, “Comparison of fast Fourier transform and convolution in wavelength scanning interferometry,” Proc. SPIE8082, 899357 (2011).

X. Jiang, K. Wang, F. Gao, and H. Muhamedsalih, “Fast surface measurement using wavelength scanning interferometry with compensation of environmental noise,” Appl. Opt.49(15), 2903–2909 (2010).
[CrossRef] [PubMed]

Ghim, Y. S.

Hirakubo, S.

Jiang, X.

H. Mahamedsalih, X. Jiang, and F. Gao, “Comparison of fast Fourier transform and convolution in wavelength scanning interferometry,” Proc. SPIE8082, 899357 (2011).

X. Jiang, K. Wang, F. Gao, and H. Muhamedsalih, “Fast surface measurement using wavelength scanning interferometry with compensation of environmental noise,” Appl. Opt.49(15), 2903–2909 (2010).
[CrossRef] [PubMed]

Kim, D.

Kim, G. H.

Kim, S.

Kim, S. W.

Kong, H. J.

Lee, Y.

Mahamedsalih, H.

H. Mahamedsalih, X. Jiang, and F. Gao, “Comparison of fast Fourier transform and convolution in wavelength scanning interferometry,” Proc. SPIE8082, 899357 (2011).

Mansfield, D.

D. Mansfield, “Extraction of film interface surfaces from scanning white light interferometry,” Proc. SPIE7101, 797978 (2008).
[CrossRef]

Muhamedsalih, H.

Sasaki, O.

Suratkar, A.

Suzuki, T.

Wang, K.

Appl. Opt.

Opt. Express

Opt. Lett.

Proc. SPIE

P. de Groot and X. de Lega, “Transparent film profiling and analysis by interference microscopy,” Proc. SPIE7064, 794936 (2008).
[CrossRef]

D. Mansfield, “Extraction of film interface surfaces from scanning white light interferometry,” Proc. SPIE7101, 797978 (2008).
[CrossRef]

H. Mahamedsalih, X. Jiang, and F. Gao, “Comparison of fast Fourier transform and convolution in wavelength scanning interferometry,” Proc. SPIE8082, 899357 (2011).

Other

SCS Parylene properties, http://www.scscoatings.com/parylene_knowledge/specifications.aspx

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Figures (7)

Fig. 1
Fig. 1

Schematic diagram of the WSI system.

Fig. 2
Fig. 2

Multiple beam interference of the two film surfaces and the reference mirror.

Fig. 3
Fig. 3

(a) The three interference signals in the captured signal. (b) FFT analysis result.

Fig. 4
Fig. 4

(a) Measured image of the sample surface. (b) Interferogram on the film surface. (c) Interferogram on glass substrate.

Fig. 5
Fig. 5

Measurement data from one area showing: (a) Top surface of the film and glass substrate. (b) Bottom surface of the film and the glass substrate.

Fig. 6
Fig. 6

(a) Reconstructed top surface of the film. (b) Reconstructed bottom surface of the film

Fig. 7
Fig. 7

(a) Measured image of the film on glass substrate by a commercial white light scanning interferometer. (b) Step height analysis of the measured step height.

Equations (3)

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λ=Δnα ν a f a
Δ φ f = 4πntcos( θ ' ) /λ
I r = I 0 ( F sin 2 ( Δ φ f /2 ) / ( 1+F sin 2 ( Δ φ f /2 ) ) )

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