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Infrared Absorption by Free Carriers in Si and Influence on Oxygen Determination by Ftir-Spectroscopy

Published online by Cambridge University Press:  03 September 2012

L. Koster  and
F. Bittersberger
L. Koster
Affiliation:
Wacker-Chemitronic GmbH, 8263 Burghausen, Germany
F. Bittersberger
Affiliation:
Wacker-Chemitronic GmbH, 8263 Burghausen, Germany
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Abstract

Using FTIR-spectroscopy for the determination of the oxygen content in CZ Si, an additional absorption of IR light occurs for doping densities above 1015/cm3, which is caused by the free carriers. It increases nearly linearly with the carrier density and reduces multiple reflections within the sample. Excessively low oxygen values are obtained if this effect is neglected. The deviation from the true values can amount up to 15 % and depends on carrier density, type of doping, oxygen content and sample thickness. Measurements of the absorption coefficient induced by the free carriers were performed for p-and n-type FZ material in dependence of the IR wavelength and of the doping concentration. The obtained values at the wavelength of the oxygen absorption band (1107 cm−1) were used to calculate correction factors for the oxygen content in the doping range from 1 * 1017 to 1 * 1015/cm3. An example shows that the correction reaches 5 % for carrier densities of 1 * 1017/cm3, n-type and 2 * 1016/cm3, p-type, respectively, for an assumed sample thickness of 0.7 mm.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 262: Symposium E – Defect Engineering in Semiconductor Growth, Processing and Device Technology , 1992 , 271
Copyright
Copyright © Materials Research Society 1992

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References

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