Non-destructive thickness measurement of Si wafers via optical third-harmonic generation with femtosecond laser pulses

•High-precision, non-destructive thickness measurement method using surface-sensitive optical third-harmonic generation•Sub-10 nm measurement precision•Sub-100 nm measurement uncertainty for the certified thickness reference sample•A high depth-selectivity enabling stacked wafers’ defect detection•A universality for various transparent wafers, such as MgO or sapphire wafers Si wafers are vital substrate materials in semiconductor manufacturing and require precise non-destructive thickness measurements. However, the conventional electrical and optical measurement techniques are limited by depth selectivity and system complexity. Here, we propose a simple, high-precision, non-destructive thickness measurement method based on surface-sensitive optical third-harmonic generation at both sides of Si wafers. We irradiated a highly stabilized near-infrared femtosecond pulse laser with a broad spectrum and central wavelength of 1550 nm on the Si wafers, which are non-transparent in the visible to ultraviolet wavelength range. Using the proposed system, the thickness of the certified reference wafer was measured, yielding results that fall within the certified uncertainty.