Snapshot Fourier ellipsometry: Pushing to sub-nanometer accuracy for high-throughput thin film metrology

Fourier ellipsometry (FE) has emerged as a promising candidate for high-throughput thin-film metrology in semiconductors, addressing critical demands for inline integration with a compact design, micro-spot resolution, and high-speed capability. However, its adoption has been hindered by skepticism about its accuracy, which is often perceived as significantly lower than that of commercial spectroscopic ellipsometry (SE). To overcome this limitation, this work presents a high-accuracy, snapshot FE based on a polarizer-compensator-compensator-analyzer configuration. Assisted by a corrected Mueller algebra model algorithm, the FE leverages the self-rotational polarization modulation effect inherent in high-numerical aperture optics for ellipsometric angle-resolved spectra (EARS) acquisition in a single snapshot. A stepwise in-situ calibration strategy employing dual-rotating compensators is developed to address critical error factors, including polarization errors, polarization aberration, and system depolarization effects. The FE finally achieved 95% accuracy improvement, reducing the root-mean-square error of thickness measurement from >3 nm to ∼0.2 nm when referenced to a commercial SE. It attains a precision of ∼0.002 in N/C/S -EARS acquisition, which translates to 3–10 pm in thickness measurement, with a repeatability of <50 pm subject to sample re-adjustment. The snapshot characteristic with ∼1 ms exposure enables a dense 60,000-point scan of a 4-inch wafer within 600 s, over 100 times faster than commercial SE. This work demonstrates that FE can simultaneously deliver sub-nanometer-level accuracy and high-throughput mapping, establishing it as a next-generation metrology tool for atomic-level manufacturing.