Frequency-comb-referenced Terahertz Fabry-Perot interferometry for monitoring semiconductor wafer thinning process with a nanometer precision

Abstract

High-precision, non-destructive thickness measurement is essential in semiconductor manufacturing. Optical methods often struggle with strong surface scattering and absorption during wafer thinning. We present nano-meter-precision, non-destructive wafer thickness measurement using the absolute frequency positions of Fabry-Perot interference modes in the terahertz frequency regime, referenced to a frequency comb. By leveraging the comb's SI-traceable frequency uncertainty and terahertz radiation's scattering insensitivity, this approach achieves a 58.4-nm precision in 0.2-s and 7.2-nm in 25.6-s averaging. Such unprecedented performance enables effective monitoring of wafer thinning processes (e.g., chemical mechanical polishing), crucial for advanced semiconductor packaging. (c) 2025 CIRP. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.