Calibration of polarization effects for the focusing lens pair in a micro-spot Mueller matrix ellipsometer

Ellipsometric measurement of transparent samples suffers from substrate backside reflection challenges, including incoherent and partial superposition issues. The recently developed angle-resolved ellipsometry (ARE) can naturally eliminate the backside reflections of substrates with a micro-spot equivalent thickness or thicker; however, for thinner substrates, ARE working with general incoherent backside reflection models shows significant inaccuracy or measurement failure. In this paper, an incoherent partial superposition (IPS) model is proposed to characterize the optical superposition effect between the frontside and uncertain backside reflections from an unknown substrate. IPS introduces a cosine-like correction of the backside reflection, corresponding to the overlapping-area change of backside and frontside reflections along with incident angles. Benefiting from ARE’s wide-angle spectral imaging capability, IPS achieves single-shot measurement of thin film thicknesses on transparent substrates of unknown thickness. An ARE system was built and calibrated regarding the linear relationship between the cosine-corrected angular frequencies and substrate thicknesses. Then, commercial ITO films on glasses of different thicknesses ranging from 200 to 1000 µm were measured. Experimental results show that IPS-ARE results in a root-mean-square accuracy error of ∼1 nm in film thickness measurement and provides a ∼77% error reduction from general incoherent backside reflection models.

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Thin film characterization by learning-assisted multi-angle polarized microscopy

Cao,

Chen,

Xian

et al. 2024

Opt. Lett.

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Thin film characterization is a necessary step in the semiconductor industry and nanodevice fabrication. In this work, we report a learning-assisted method to conduct the measurement based on a multi-angle polarized microscopy. By illuminating the film with a tightly focused vectorial beam with space-polarization nonseparability, the angle-dependent reflection coefficients are encoded into the reflected intensity distribution. The measurement is then transformed into an optimization problem aiming at minimizing the discrepancy between measured and simulated image features. The proposed approach is validated by numerical simulation and experimental measurements. As the method can be easily implemented with a conventional microscope, it provides a low cost solution to measure film parameters with a high spatial resolution and time efficiency.

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Calibration of polarization effects for the focusing lens pair in a micro-spot Mueller matrix ellipsometer

Cited by 4 publications

References 34 publications

Longitudinal magneto-optical Kerr effect in subwavelength thick ferromagnetic films investigated by Mueller matrix ellipsometry

Longitudinal magneto-optical Kerr effect in subwavelength thick ferromagnetic films investigated by Mueller matrix ellipsometry

Incoherent partial superposition modeling for single-shot angle-resolved ellipsometry measurement of thin films on transparent substrates

Thin film characterization by learning-assisted multi-angle polarized microscopy

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