Abstract

The measurement of flat optical components often presents difficulties because the presence of parallel surfaces generates multiple reflections that confuse conventional laser-based interferometers. These same parts have increasingly demanding surface finish tolerances as technologies improve over time, further complicating the metrology task. Here we describe an interferometric optical system for high-accuracy noncontact evaluation of the form and texture of precision flat surfaces based on an equal-optical-path geometry that uses extended, broadband illumination to reduce the influence of speckle noise, multiple reflections, and coherent artifacts by a factor of 10 when compared to laser-based systems. Combined with a low-distortion, fixed-focus imaging system and 4-Mpixel camera, the 100 mm aperture instrument offers surface height resolutions of 0.1 nm over lateral spatial frequencies extending from 0.01 to 10 cycles/mm. The instrument is vibration resistant for production-line testing of flat optics such as glass hard disks for the data-storage industry and flat-panel-display substrates.

© 2014 Optical Society of America

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References

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  1. J. Greivenkamp and J. Bruning, “Phase shifting interferometry,” in Optical Shop Testing, D. Malacara, ed., 2nd ed. (Wiley, 1992), Chap. 14.
  2. P. de Groot, “Diffractive grazing incidence interferometer,” Appl. Opt. 39, 1527–1530 (2000).
    [CrossRef]
  3. B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
    [CrossRef]
  4. M. Küchel, “Interferometer for measuring optical phase differences,” U.S. Patent4,872,755 (10October1989).
  5. K. Freischlad, “Interferometer for optical waviness and figure testing,” Proc. SPIE 3098, 53–61 (1997).
    [CrossRef]
  6. S. Lin, L.-C. Chen, S.-L. Yeh, H.-X. Trinh, and H.-P. Chen, “Polarization phase-shifting Newton interferometer for plane optical surface measurements,” Opt. Lett. 37, 467–469 (2012).
    [CrossRef]
  7. The principles and methods of the FGT are incorporated into the AccuFlat large-aperture surface-topography measuring instrument manufactured by Zygo Corporation.
  8. L. Deck, P. de Groot, and J. A. Soobitsky, “High precision interferometric testing of transparent, thin plane-parallel parts,” in Technical Digest of SPIE, Optifab TD07-23, Rochester, New York, 2011.
  9. P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).
  10. K. Freischlad, “Large flat panel profiler,” Proc. SPIE 2862, 163–171 (1996).
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    [CrossRef]
  12. L. Deck, “Suppressing phase errors from vibration in phase-shifting interferometry,” Appl. Opt. 48, 3948–3960 (2009).
    [CrossRef]
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    [CrossRef]
  14. C. Evans, “Uncertainty evaluation for measurements of peak-to-valley surface form errors,” CIRP Ann. 57, 509–512 (2008).
    [CrossRef]
  15. P. de Groot and X. Colonna de Lega, “Interpreting interferometric height measurements using the instrument transfer function,” in Proceedings of FRINGE 2005, W. Osten, ed. (Springer-Verlag, 2006), pp. 30–37.
  16. P. Z. Takacs and E. L. Church, “A step-height standard for surface profiler calibration,” Proc. SPIE 1995, 235 (1993).
    [CrossRef]
  17. K. Freischlad, “Sub-angstrom surface metrology with a virtual reference interferometer,” Proc. SPIE 8493, 84930B (2012).
    [CrossRef]
  18. Zygo Corporation, “ZeMapper HS High-Speed Low-Noise 3D Optical Profiler,” Specification sheet (2013).

2012

2009

2008

C. Evans, “Uncertainty evaluation for measurements of peak-to-valley surface form errors,” CIRP Ann. 57, 509–512 (2008).
[CrossRef]

2006

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

2000

1997

K. Freischlad, “Interferometer for optical waviness and figure testing,” Proc. SPIE 3098, 53–61 (1997).
[CrossRef]

1996

K. Freischlad, “Large flat panel profiler,” Proc. SPIE 2862, 163–171 (1996).

1995

P. de Groot, “Vibration in phase-shifting interferometry,” J. Opt. Soc. Am. 12, 354–365 (1995).
[CrossRef]

1993

P. Z. Takacs and E. L. Church, “A step-height standard for surface profiler calibration,” Proc. SPIE 1995, 235 (1993).
[CrossRef]

1983

Biegen, J. F.

P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).

Bruning, J.

J. Greivenkamp and J. Bruning, “Phase shifting interferometry,” in Optical Shop Testing, D. Malacara, ed., 2nd ed. (Wiley, 1992), Chap. 14.

Burow, R.

Chen, H.-P.

Chen, L.-C.

Church, E. L.

P. Z. Takacs and E. L. Church, “A step-height standard for surface profiler calibration,” Proc. SPIE 1995, 235 (1993).
[CrossRef]

Colonna de Lega, X.

P. de Groot and X. Colonna de Lega, “Interpreting interferometric height measurements using the instrument transfer function,” in Proceedings of FRINGE 2005, W. Osten, ed. (Springer-Verlag, 2006), pp. 30–37.

de Groot, P.

P. de Groot, “Diffractive grazing incidence interferometer,” Appl. Opt. 39, 1527–1530 (2000).
[CrossRef]

P. de Groot, “Vibration in phase-shifting interferometry,” J. Opt. Soc. Am. 12, 354–365 (1995).
[CrossRef]

P. de Groot and X. Colonna de Lega, “Interpreting interferometric height measurements using the instrument transfer function,” in Proceedings of FRINGE 2005, W. Osten, ed. (Springer-Verlag, 2006), pp. 30–37.

P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).

L. Deck, P. de Groot, and J. A. Soobitsky, “High precision interferometric testing of transparent, thin plane-parallel parts,” in Technical Digest of SPIE, Optifab TD07-23, Rochester, New York, 2011.

Deck, L.

L. Deck, “Suppressing phase errors from vibration in phase-shifting interferometry,” Appl. Opt. 48, 3948–3960 (2009).
[CrossRef]

P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).

L. Deck, P. de Groot, and J. A. Soobitsky, “High precision interferometric testing of transparent, thin plane-parallel parts,” in Technical Digest of SPIE, Optifab TD07-23, Rochester, New York, 2011.

Elssner, K.-E.

Evans, C.

C. Evans, “Uncertainty evaluation for measurements of peak-to-valley surface form errors,” CIRP Ann. 57, 509–512 (2008).
[CrossRef]

Freischlad, K.

K. Freischlad, “Sub-angstrom surface metrology with a virtual reference interferometer,” Proc. SPIE 8493, 84930B (2012).
[CrossRef]

K. Freischlad, “Interferometer for optical waviness and figure testing,” Proc. SPIE 3098, 53–61 (1997).
[CrossRef]

K. Freischlad, “Large flat panel profiler,” Proc. SPIE 2862, 163–171 (1996).

Greivenkamp, J.

J. Greivenkamp and J. Bruning, “Phase shifting interferometry,” in Optical Shop Testing, D. Malacara, ed., 2nd ed. (Wiley, 1992), Chap. 14.

Grzanna, J.

Hayes, J.

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

Kimbrough, B.

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

Koliopoulos, C.

P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).

Küchel, M.

M. Küchel, “Interferometer for measuring optical phase differences,” U.S. Patent4,872,755 (10October1989).

Lin, S.

Merkel, K.

Millerd, J.

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

Schwider, J.

Soobitsky, J. A.

L. Deck, P. de Groot, and J. A. Soobitsky, “High precision interferometric testing of transparent, thin plane-parallel parts,” in Technical Digest of SPIE, Optifab TD07-23, Rochester, New York, 2011.

Spolaczuk, R.

Takacs, P. Z.

P. Z. Takacs and E. L. Church, “A step-height standard for surface profiler calibration,” Proc. SPIE 1995, 235 (1993).
[CrossRef]

Trinh, H.-X.

Wyant, J.

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

Yeh, S.-L.

Appl. Opt.

CIRP Ann.

C. Evans, “Uncertainty evaluation for measurements of peak-to-valley surface form errors,” CIRP Ann. 57, 509–512 (2008).
[CrossRef]

J. Opt. Soc. Am.

P. de Groot, “Vibration in phase-shifting interferometry,” J. Opt. Soc. Am. 12, 354–365 (1995).
[CrossRef]

Opt. Lett.

Proc. SPIE

B. Kimbrough, J. Millerd, J. Wyant, and J. Hayes, “Low coherence vibration insensitive Fizeau interferometer,” Proc. SPIE 6292, 62920F (2006).
[CrossRef]

K. Freischlad, “Interferometer for optical waviness and figure testing,” Proc. SPIE 3098, 53–61 (1997).
[CrossRef]

K. Freischlad, “Large flat panel profiler,” Proc. SPIE 2862, 163–171 (1996).

P. Z. Takacs and E. L. Church, “A step-height standard for surface profiler calibration,” Proc. SPIE 1995, 235 (1993).
[CrossRef]

K. Freischlad, “Sub-angstrom surface metrology with a virtual reference interferometer,” Proc. SPIE 8493, 84930B (2012).
[CrossRef]

Other

Zygo Corporation, “ZeMapper HS High-Speed Low-Noise 3D Optical Profiler,” Specification sheet (2013).

P. de Groot and X. Colonna de Lega, “Interpreting interferometric height measurements using the instrument transfer function,” in Proceedings of FRINGE 2005, W. Osten, ed. (Springer-Verlag, 2006), pp. 30–37.

J. Greivenkamp and J. Bruning, “Phase shifting interferometry,” in Optical Shop Testing, D. Malacara, ed., 2nd ed. (Wiley, 1992), Chap. 14.

M. Küchel, “Interferometer for measuring optical phase differences,” U.S. Patent4,872,755 (10October1989).

The principles and methods of the FGT are incorporated into the AccuFlat large-aperture surface-topography measuring instrument manufactured by Zygo Corporation.

L. Deck, P. de Groot, and J. A. Soobitsky, “High precision interferometric testing of transparent, thin plane-parallel parts,” in Technical Digest of SPIE, Optifab TD07-23, Rochester, New York, 2011.

P. de Groot, L. Deck, J. F. Biegen, and C. Koliopoulos, “Equal-path interferometer,” U.S. Patent8,045,175 (25October2011).

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Figures (12)

Fig. 1.
Fig. 1.

Interferometer cavity geometry compatible with low-coherence illumination. The tilt angles reject unwanted reflections, resulting in high-contrast interference fringes.

Fig. 2.
Fig. 2.

A broadband extended source illuminates an interferometer cavity consisting of the first surfaces of the reference and beam-splitter elements and the object. Aided by the angle and focus sensor, the object surface is placed at the equal-path location (camera focus). Moving the boxed elements as a whole accomplishes the phase shift.

Fig. 3.
Fig. 3.

Maximum allowed vibration amplitude spectrum to achieve <1nm RMS ripple error compared to a conventional PSI instrument using a five-bucket phase analysis. A 10× improvement over conventional methods is realized over most of the frequency range relevant to production metrology.

Fig. 4.
Fig. 4.

The left figure is the uncertainty matrix (the map of the standard deviations for each pixel) calculated from an ensemble of 50 measurements. The right figure shows the histogram of the standard deviations.

Fig. 5.
Fig. 5.

Distortion of the optical system as predicted by ZEMAX and verified with a distortion artifact.

Fig. 6.
Fig. 6.

RMS residuals as a function of part tilt compared to a standard laser Fizeau after high-pass filtering to minimize turbulence affects. Between 3× and 5× lower noise is achieved with the FGT.

Fig. 7.
Fig. 7.

Measured Zernike astigmatism and coma magnitude coefficients as a function of test surface tilt, showing low retrace error as a function of surface slope.

Fig. 8.
Fig. 8.

Measured system ITF (large black dots on left figure) as determined with a step artifact by averaging the ITF from nine field locations indicated on right, compared to the theoretically expected shape (small dotted blue line) assuming perfectly incoherent illumination.

Fig. 9.
Fig. 9.

Measurements of 65 mm hard-disk blanks made of aluminum (above) and glass (below) illustrate high fringe contrast over a wide range of surface reflectivities.

Fig. 10.
Fig. 10.

Results from a correlation study between the FGT and the ZeMapper of 20 Hoya disks in the spatial frequency range between 0.5 and 5 mm. The plot compares the RMS surface measurements from both instruments in this frequency band for each disk.

Fig. 11.
Fig. 11.

Single acquisition measurement of the front surface of a 25 mm. solid glass retro. Because of the strong and unavoidable retroreflection, the fringe contrast is low, yet the surface measurement shows neither artifacts nor fringe bleed-through.

Fig. 12.
Fig. 12.

Measurement of the substrate (above) and top surface (below) of a mirror coated with a 100-μm-thick fused silica layer.

Equations (3)

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CT(d)=CPeakexp[π(dΔλλ2)2],
CL(s)=somb(sλNA)2,
somb(x)=2J1(πx)πx.

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