Abstract

White-light interferometry has turned into a standard tool in the field of high-accuracy topography measurements. Nevertheless, surfaces with relatively large local surface tilts or height steps often give rise to systematic measuring errors. The reasons are diffraction and dispersion effects, which cause deviations between height values obtained from the envelope maximum of the white-light interference signal and those obtained from the signal's phase. In certain cases this may result in ghost steps appearing in the measured topography. To identify and eliminate these ghost steps we use a second LED emitting light at a different mean wavelength. This now allows the measurement of curved or structured specular surfaces with high resolution, which up to now was restricted by the mentioned effects.

© 2007 Optical Society of America

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References

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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  5. P. de Groot and X. Colonna de Lega, "Signal modeling for low-coherence height-scanning interference microscopy," Appl. Opt. 43, 4821-4830 (2004).
    [CrossRef] [PubMed]
  6. M. Fleischer, R. Windecker, and H. J. Tiziani, "Fast algorithms for data reduction in modern optical three-dimensional profile measurement systems with MMX technology," Appl. Opt. 39, 1290-1297 (2000).
    [CrossRef]
  7. A. Harasaki and J. C. Wyant, "Fringe modulation skewing effect in white-light vertical scanning interferometry," Appl. Opt. 39, 2101-2106 (2000).
    [CrossRef]
  8. A. Harasaki, J. Schmidt, and J. C. Wyant, "Improved vertical-scanning interferometry," Appl. Opt. 39, 2107-2115 (2000).
    [CrossRef]
  9. A. Pförtner and J. Schwider, "Dispersion error in white-light Linnik interferometers and implications for evaluation procedures," Appl. Opt. 40, 6223-6228 (2001).
    [CrossRef]
  10. P. Lehmann, "Systematic effects in coherence peak and phase evaluation of signals obtained with a vertical scanning white-light Mirau interferometer," in Optical Micro- and Nanometrology in Microsystems Technology, C. Gorecki, A. K. Asundi, and W. Osten, eds. Proc. SPIE 6188, 11-1-11-11 (2006).
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    [CrossRef] [PubMed]

2004 (1)

2002 (1)

2001 (1)

2000 (3)

1994 (1)

1992 (1)

1990 (1)

1984 (1)

Appl. Opt. (10)

Y.-Y. Cheng and J. C. Wyant, "Two-wavelength phase shifting interferometry," Appl. Opt. 23, 4539-4543 (1984).
[CrossRef] [PubMed]

B. S. Lee and T. C. Strand, "Profilometry with a coherence scanning microscope," Appl. Opt. 29, 3784-3788 (1990).
[CrossRef] [PubMed]

L. Deck and P. de Groot, "High-speed noncontact profiler based on scanning white-light interferometry," Appl. Opt. 33, 7334-7338 (1994).
[CrossRef] [PubMed]

M. Fleischer, R. Windecker, and H. J. Tiziani, "Fast algorithms for data reduction in modern optical three-dimensional profile measurement systems with MMX technology," Appl. Opt. 39, 1290-1297 (2000).
[CrossRef]

A. Harasaki and J. C. Wyant, "Fringe modulation skewing effect in white-light vertical scanning interferometry," Appl. Opt. 39, 2101-2106 (2000).
[CrossRef]

A. Harasaki, J. Schmidt, and J. C. Wyant, "Improved vertical-scanning interferometry," Appl. Opt. 39, 2107-2115 (2000).
[CrossRef]

T. Dresel, G. Häusler, and H. Venzke, "Three-dimensional sensing of rough surfaces by coherence radar," Appl. Opt. 31, 919-925 (1992).
[CrossRef] [PubMed]

A. Pförtner and J. Schwider, "Dispersion error in white-light Linnik interferometers and implications for evaluation procedures," Appl. Opt. 40, 6223-6228 (2001).
[CrossRef]

P. de Groot, X. Colonna de Lega, J. Kramer, and M. Turzhitsky, "Determination of fringe order in white-light interference microscopy," Appl. Opt. 41, 4571-4578 (2002).
[CrossRef] [PubMed]

P. de Groot and X. Colonna de Lega, "Signal modeling for low-coherence height-scanning interference microscopy," Appl. Opt. 43, 4821-4830 (2004).
[CrossRef] [PubMed]

Other (1)

P. Lehmann, "Systematic effects in coherence peak and phase evaluation of signals obtained with a vertical scanning white-light Mirau interferometer," in Optical Micro- and Nanometrology in Microsystems Technology, C. Gorecki, A. K. Asundi, and W. Osten, eds. Proc. SPIE 6188, 11-1-11-11 (2006).

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Figures (12)

Fig. 1
Fig. 1

Schematic of the Mirau-type white-light interferometer.

Fig. 2
Fig. 2

(a) Photograph of the compact SWLI sensor with steel rod, (b) live image with interference patterns.

Fig. 3
Fig. 3

Sinusoidal profiles obtained from a single line of the CCD sensor with different evaluations.

Fig. 4
Fig. 4

(Color online) Gray graph: difference between envelope evaluation and phase evaluation. Black graph: difference between spatial domain and frequency domain evaluation.

Fig. 5
Fig. 5

Chrome glass grid with batwing effects.

Fig. 6
Fig. 6

Coherence peak evaluation versus unwrapped phase evaluation on a chrome glass grid.

Fig. 7
Fig. 7

Step with height Δh and points h a and h b .

Fig. 8
Fig. 8

Two most common cases of different phase steps.

Fig. 9
Fig. 9

Schematic of the modified Mirau-type white-light interferometer with control electronics and second LED.

Fig. 10
Fig. 10

(a) Section from a chrome glass grid evaluated with the coherence peak evaluation, and (b) captured with alternating LED illumination and corrected with the difference.

Fig. 11
Fig. 11

(a) Section of the profiles taken with the blue and white LED, (b) difference between the profiles taken with different illumination.

Fig. 12
Fig. 12

Different profile types and preferred evaluation for each case with occurring problems and possible solutions.

Equations (15)

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Λ = λ 1 λ 2 λ 1 λ 2 .
h 1 = φ 1 λ 1 4 π + n 1 λ 1 2 ,
h 2 = φ 2 λ 2 4 π + n 2 λ 2 2 ,
h 3 = Δ φ Λ 4 π + n 0 Λ 2 , with Δ φ = φ 2 φ 1 .
h ˜ 1 = ( φ 1 ± δ φ ) λ 1 4 π + n 1 λ 1 2 = h 1 ± δ φ λ 1 4 π ,
h ˜ 2 = ( φ 2 ± δ φ ) λ 2 4 π + n 2 λ 2 2 ,
h ˜ 3 = ( Δ φ ± 2 δ φ ) Λ 4 π + n 0 Λ 2 .
ε ( h ˜ 1 ) = ε ( h ˜ 2 ) = δ φ λ 1 , 2 4 π ,
ε ( h ˜ 3 ) = 2 δ φ Λ 4 π .
ε ( Δ h ˜ 1 , 2 ) = 2 δ φ λ ¯ 4 π = ε ( h ˜ 3 ) λ ¯ Λ .
h b = h a + n 1 λ 1 2 + Δ φ 1 λ 1 4 π = h a + n 2 λ 2 2 + Δ φ 2 λ 2 4 π .
n ˜ 1 λ 1 2 + Δ φ 1 λ 1 4 π n ˜ 2 λ 2 2 + Δ φ 2 λ 2 4 π ,
Δ h 2 Δ h + λ 2 2 ,
Δ h 2 = Δ h + λ 2 2 , Δ h 1 = Δ h + λ 1 2 .
Δ h 2 Δ h 1 = λ 2 2 λ 1 2 .

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