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arXiv · 2608.10146

Practical Evaluation of FFT-Based Thickness Extraction for Thick-Film Reflectometry

Zimu Zhou·Enrique A. Lopez-Guerra·Michael Kwan·Chester Chien
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Abstract

Fast Fourier transform (FFT) is widely used for thick-film reflectometry because of its simplicity and computational efficiency. However, its performance under practical thick-film measurement conditions has received limited experimental evaluation. In this work, FFT, Linearized Reflectance Zero-Crossing (LRZ), and optical model fitting were compared using reflectometry measurements from a nominal 52 {\mu}m dielectric film acquired on a production wafer, with White-Light Interferometry (WLI) serving as an independent reference. Although FFT exhibited excellent repeatability, it showed systematic deviation from WLI (RMSE = 0.62 {\mu}m), whereas LRZ significantly improved accuracy (RMSE = 0.20 {\mu}m). Simulations and theoretical analysis indicate that the observed systematic deviation is consistent with spectral leakage caused by finite measurement windows and non-integer fringe periodicity. These results demonstrate that excellent repeatability does not necessarily imply high accuracy and highlight the advantages of zero-crossing-based approaches for thick-film thickness metrology.

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Zimu Zhou, Enrique A. Lopez-Guerra, Michael Kwan, Chester Chien. 2026-08-10. Practical Evaluation of FFT-Based Thickness Extraction for Thick-Film Reflectometry. https://arxiv.org/abs/2608.10146

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