We report exceptionally good repeatability in non-contact Frequency Space Moire (FSM) Fiber Optic Wafer Thickness Metrology. The FSM method, which is a frequency domain interferometry technique, takes advantage of the low frequency beat-like pattern observed by grating spectrograph in the recorded spectra of the light reflected from the thick samples, and subsequently filtered through the well characterized etalon. In this paper we focus on semiconductor application of the FSM method. The FSM experimentally achieved static repeatability of 0.35 nm for the measurement of thickness of the nominally 508 um thick blanket silicon wafer, which is about 1 part per million, for the acquisition time of 10 ms.

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Wei Chun Hung, Raphael Morency, and Wojtek J. Walecki, "One part-per-million wafer thickness measurement repeatability using fast frequency space Moire effect tool," Proc. SPIE 10749, Interferometry XIX, 1074907 (Presented at SPIE Optical Engineering + Applications: August 21, 2018; Published: 18 August 2018); https://doi.org/10.1117/12.2321654.