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Applied Optics

Applied Optics


  • Vol. 38, Iss. 23 — Aug. 10, 1999
  • pp: 4980–4984

Interferometric characterization of subwavelength lamellar gratings

Philippe Lalanne, P. Pichon, P. Chavel, E. Cambril, and H. Launois  »View Author Affiliations

Applied Optics, Vol. 38, Issue 23, pp. 4980-4984 (1999)

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We propose a new, to our knowledge, method for determining the two main critical parameters of periodic one-dimensional lamellar structures, namely, linewidths and etched depths. The method is simple and requires only two measurements for the phase of the zero-transmitted order under two orthogonal polarizations. It is inspired by the analogy between subwavelength gratings and anisotropic homogeneous thin films. The method is tested with experimental data obtained with a Mach–Zehnder interferometer. Etched depths and linewidths derived from the interferograms and electromagnetic theory are compared with scanning-electron-microscope observations.

© 1999 Optical Society of America

OCIS Codes
(050.1380) Diffraction and gratings : Binary optics
(050.1950) Diffraction and gratings : Diffraction gratings
(050.1970) Diffraction and gratings : Diffractive optics
(290.3200) Scattering : Inverse scattering

Original Manuscript: January 27, 1999
Revised Manuscript: April 23, 1999
Published: August 10, 1999

Philippe Lalanne, P. Pichon, P. Chavel, E. Cambril, and H. Launois, "Interferometric characterization of subwavelength lamellar gratings," Appl. Opt. 38, 4980-4984 (1999)

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  12. Strictly speaking, the Airy formula for thin films has to be used.
  13. Ph. Lalanne, S. Astilean, P. Chavel, E. Cambril, H. Launois, “Blazed-binary subwavelength gratings with efficiencies larger than those of conventional échelette gratings,” Opt. Lett. 23, 1081–1083 (1998). [CrossRef]
  14. For the sake of illustration, see Fig. 1 in Ref. 13, where it is shown that, for periods larger than the structural cutoff, the phase of the zero order is not a monotonous function of the fill factor and exhibits a rather chaotic behavior.
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  17. Strictly speaking, the phase shifts obtained from the interferograms are known modulo 2π. The indetermination is removed in practice by consideration of the small finite set of possible 2π phase jumps and retention of only physical solutions. If one knows approximately the etched depth (as is the case for most characterization problems) or if in situ monitoring is considered, there is no ambiguity. In the latter case the absolute phase shift is observed in real time.
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  20. For the SEM linewidth measurements the Au film deposited on the sample is a source of error. The additional thickness is difficult to estimate. However, because the gold coating of the vertical walls appears brigther and scummy in the SEM photographs, the additional thickness can be partially removed during estimation of the linewidth.
  21. F. C. Chen, W. C. Chew, “Experimental verification of super resolution in nonlinear inverse scattering,” Appl. Phys. Lett. 72, 3080–3082 (1998). [CrossRef]

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