Optical characterization of polycrystalline silicon thin films

William A. McGahan; Blaine R. Spady; Blaine D. Johs; Olivier Laparra

doi:10.1117/12.240144

21 May 1996 Optical characterization of polycrystalline silicon thin films

William A. McGahan, Blaine R. Spady, Blaine D. Johs, Olivier Laparra

Proceedings Volume 2725, Metrology, Inspection, and Process Control for Microlithography X; (1996) https://doi.org/10.1117/12.240144
Event: SPIE's 1996 International Symposium on Microlithography, 1996, Santa Clara, CA, United States

Abstract

Polycrystalline silicon (poly-Si) thin films are of major importance in the semiconductor industry. As a result precise and rapid determination of the thickness, optical constants, and crystallinity of the poly-Si films is an important metrology issue. Many previous optical efforts were based on the analysis of spectroscopic ellipsometric or reflectance data using effective medium approximation (EMA) models to predict the poly-Si optical constants as a function of the amorphous to crystalline silicon ratio in the film. Such models are effective if the film is nearly crystalline or nearly amorphous, but suffer from systematic inaccuracies due to the failure of the EMA approximations to accurately predict the poly-Si optical constants. Other methods such as transmission electron microscopy (TEM) can provide accurate film thickness information but suffer from being destructive, slow, and relatively expensive. In this work we present an optical model for poly-Si thin films which can accurately reproduce the optical constants of poly-Si films ranging from amorphous to fully crystallized. This model contains a single adjustable parameter which is proportional to the amorphous to crystalline ratio in the film. The model is based on interpolation between previously determined optical constant spectra from films ranging from amorphous to fully crystallized. We demonstrate the use of the model by fitting reflectance and ellipsometric data for poly-Si films deposited on thermal oxide on silicon substrates. When coupled with an accurate reflectometer or ellipsometer this model provides a nondestructive and non-contact means for accurately obtaining the thickness, optical constants, relative crystallinity, and surface roughness of poly-Si thin films.

Citation Download Citation

William A. McGahan, Blaine R. Spady, Blaine D. Johs, and Olivier Laparra "Optical characterization of polycrystalline silicon thin films", Proc. SPIE 2725, Metrology, Inspection, and Process Control for Microlithography X, (21 May 1996); https://doi.org/10.1117/12.240144

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