Sinusoidal wavelength-scanning interferometer for measurement of thickness and surface profile of thin films

Hisashi Akiyama; Osami Sasaki; Takamasa Suzuki

doi:10.1117/12.666811

9 December 2005 Sinusoidal wavelength-scanning interferometer for measurement of thickness and surface profile of thin films

Hisashi Akiyama, Osami Sasaki, Takamasa Suzuki

Author Affiliations +

Proceedings Volume 6024, ICO20: Optical Devices and Instruments; 602409 (2005) https://doi.org/10.1117/12.666811
Event: ICO20:Optical Devices and Instruments, 2005, Changchun, China

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 Z_b of a time-varying phase and a constant phase α. Two measured values of OPD, which are denoted by L_z and L_α,are obtained from Z_b and α. By combining L_z and L_α, 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 Z_b1, Z_b2, 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 Z_b1, Z_b2, 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.

Citation Download Citation

Hisashi Akiyama, Osami Sasaki, and Takamasa Suzuki "Sinusoidal wavelength-scanning interferometer for measurement of thickness and surface profile of thin films", Proc. SPIE 6024, ICO20: Optical Devices and Instruments, 602409 (9 December 2005); https://doi.org/10.1117/12.666811

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