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Updated: Jun 13, 2026
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Agarose-based Tissue Mimicking Optical Phantoms for Diffuse Reflectance Spectroscopy
Published on: August 22, 2018
Effective medium approximations for modeling optical reflectance from gratings with rough edges.
Brent C Bergner1, Thomas A Germer, Thomas J Suleski
1National Institute of Standards and Technology, Gaithersburg, Maryland 20899,USA.
Summary
Line edge roughness (LER) can affect optical scatterometry measurements. An anisotropic effective medium approximation (EMA) accurately models LER effects on scatterometry signals when correlation lengths are small relative to wavelength.
Area of Science:
- Metrology and Measurement Science
- Nanoscale Engineering
- Optical Physics
Background:
- Line edge roughness (LER) introduces uncertainty in optical scatterometry.
- Accurate characterization of LER's impact is crucial for metrology.
- Computational expense limits rigorous LER modeling in scatterometry.
Purpose of the Study:
- To compare LER effects on scatterometry signals using EMA and direct simulation.
- To evaluate the accuracy of effective medium approximation for LER modeling.
- To determine conditions under which EMA is a suitable approximation for LER in scatterometry.
Main Methods:
- Simulated scatterometry signals with and without LER.
- Employed effective medium approximation (EMA) for modeling LER.
- Compared EMA results with direct simulations of rough interfaces.
Main Results:
- Anisotropic EMA closely approximates scatterometry signals for LER.
- The approximation is valid for correlation lengths smaller than the wavelength.
- EMA is effective when correlation lengths exceed RMS roughness.
Conclusions:
- Anisotropic EMA offers a computationally efficient method for scatterometry LER analysis.
- EMA is a satisfactory approximation for specific LER regimes in optical scatterometry.
- This work validates EMA for assessing scatterometry uncertainty due to LER.
