Uncertainty improvement of geometrical thickness and refractive index measurement of a silicon wafer using a femtosecond pulse laser

We have proposed a modified method to improve the measurement uncertainty of the geometrical thickness and refractive index of a silicon wafer. Because measurement resolution based on Fourier domain analysis depends on the spectral bandwidth of a light source directly, a femtosecond pulse laser havi...

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Bibliographic Details
Published in:Optics express 2012-05, Vol.20 (11), p.12184-12190
Main Authors: Maeng, Saerom, Park, Jungjae, O, Byungsung, Jin, Jonghan
Format: Article
Language:English
Subjects:
Algorithms
Data Interpretation, Statistical
Interferometry - instrumentation
Lasers
Refractometry - instrumentation
Refractometry - methods
Silicon - chemistry
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Summary:We have proposed a modified method to improve the measurement uncertainty of the geometrical thickness and refractive index of a silicon wafer. Because measurement resolution based on Fourier domain analysis depends on the spectral bandwidth of a light source directly, a femtosecond pulse laser having the broad spectral bandwidth of about 100 nm was adopted as a new light source. A phase detection algorithm in Fourier domain was also modified to minimize the effect related to environmental disturbance. Since the wide spectral bandwidth may cause a dispersion effect in the optical parts of the proposed interferometer, it was considered carefully through numerical simulations. In conclusion, the measurement uncertainty of geometrical thickness was estimated to be 48 nm for a double-polished silicon wafer having the geometrical thickness of 320.7 μm, which was an improvement of about 20 times that obtained by the previous method.
ISSN:1094-4087
1094-4087
DOI:10.1364/oe.20.012184