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Proceedings Paper

Sinusoidal wavelength-scanning interferometer for measurement of thickness and surface profile of thin films
Author(s): Hisashi Akiyama; Osami Sasaki; Takamasa Suzuki
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Paper Abstract

We propose a sinusoidal wavelength scanning interferometer for measuring thickness and surfaces profiles with a thin film. An acousto-optic tunable filter (AOTF) is used to produce sinusoidally wavelength-scanned light from a superluminescent laser diode (SLD) with a wide spectral bandwidth of 46nm. The interference signal contains an amplitude Zb of a time-varying phase and a constant phase α. Two measured values of OPD, which are denoted by Lz and Lα, are obtained from Zb and α. By combining Lz and Lα, an OPD longer than a wavelength is measured with an error less than a few nanometers. When the object has two reflective surfaces, the detected interference signal contains two interference signals which are caused by the front and rear surfaces. In this case we must determine the values of Zb1, Zb2, α1, and α2, where suffixes of 1 and 2 are corresponding to the front and rear surfaces, respectively. We define an error function that is the difference between the detected signal and the theoretical signal, and reduce the value of the error function with the multidimensional nonlinear least-squares algorithm to search the values of Zb1, Zb2, α1, and α2. Experimental results show that the thickness and surfaces profiles of a silica glass plate of 20μm-thickness are measured with error less than 1.5nm.

Paper Details

Date Published: 9 December 2005
PDF: 6 pages
Proc. SPIE 6024, ICO20: Optical Devices and Instruments, 602409 (9 December 2005); doi: 10.1117/12.666811
Show Author Affiliations
Hisashi Akiyama, Niigata Univ. (Japan)
Osami Sasaki, Niigata Univ. (Japan)
Takamasa Suzuki, Niigata Univ. (Japan)


Published in SPIE Proceedings Vol. 6024:
ICO20: Optical Devices and Instruments
James C. Wyant; X. J. Zhang, Editor(s)

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