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Proceedings Paper

Vibration insensitive interferometer using sinusoidal phase-modulation and feedback control
Author(s): Osami Sasaki; Hidetaka Iwai; Takamasa Suzuki
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Paper Abstract

It is easy to extract a signal proportional to a phase fluctuation from a sinusoidally phase-modulated interference signal. This fluctuation is caused by mechanical vibration or air turbulence. In a sinusoidal phase-modulating interferometer using a laser diode (LD) the phase fluctuation is reduced by changing the injection current of the LD with a feedback control system. This control is very useful to a Fizeau type interferometer for surface profile measurement of a large size object. IC wafers of 100 mm diameter are measured with an interferometer insensitive to mechanical vibration and air turbulence. The phase fluctuation with nearly constant amplitude which corresponds to 30nm in surface height is reduced by about 10%. However the reduction in the phase fluctuation is not performed well for an instantaneous and large phase fluctuation. In order to be insensitive to all kinds of phase fluctuations the feedback signal is always observed, so that the interference signal is captured when the amplitude of the feedback signal is less than a specified level during the capturing time of 0.53 s. Thus surface profiles of the IC wafers can be measured with a high repeatability of a few nm even when any kind of vibration exists.

Paper Details

Date Published: 9 December 2005
PDF: 6 pages
Proc. SPIE 6024, ICO20: Optical Devices and Instruments, 60240N (9 December 2005); doi: 10.1117/12.666829
Show Author Affiliations
Osami Sasaki, Niigata Univ. (Japan)
Hidetaka Iwai, 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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