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Optical Engineering

Measurement of discontinuous surfaces using multiple-wavelength interferometry
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Paper Abstract

Interferometric surface profilers using a single wavelength offer excellent vertical resolution, but have an ambiguity-free range of less than half a wavelength. Multiple-wavelength or white light interference techniques are used to overcome the problem. We discuss a three-wavelength interferometric technique used with a phase-shifting phase evaluation procedure. The phase evaluation at the three wavelengths gives wrapped phase at any pixel corresponding to these wavelengths. We use the fact that the variation of phase with wavenumber for a given profile height is linear to determine the absolute value of the profile height. The height is then used to ascertain the fringe order. The fringe order, along with the wrapped phase, gives the profile height with a resolution given by the phase-shifting technique. Experimental results for large step height measurement on etched silicon samples are presented.

Paper Details

Date Published: 1 July 2009
PDF: 8 pages
Opt. Eng. 48(7) 073603 doi: 10.1117/1.3159867
Published in: Optical Engineering Volume 48, Issue 7
Show Author Affiliations
Paul Kumar Upputuri, Indian Institute of Technology Madras (India)
Nandigana Krishna Mohan, Indian Institute of Technology Madras (India)
Mahendra Prasad Kothiyal, Indian Institute of Technology Madras (India)

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