Vol. 56, Issue 2, pp. 313-325 (2026)

Abstract

Semiconductor oxide thin films are widely applied in the internal cavity mirror protection of lasers and inner wall coatings of semiconductor device due to their excellent optical transparency and thermal stability. Film thickness is critical for functional performance, yet conventional methods cannot obtain in situ spatial distribution of film thickness within confined internal structures. To address this limitation, this study proposes a novel in situ film thickness measurement method integrating fiber optic endoscope with hyperspectral imaging. First, optical defocusing is first employed to mitigate intensity differences caused by the endoscope's honeycomb pattern. Second, the calibration of pseudo-color images is performed based on the reflectance spectra of the thin film. Finally, considering the endoscope's field of view angle, the incident angle is recalculated, and film thickness is inverted using spectrum fitting method. Experimental results demonstrate that the developed method successfully captures the reflectance spectrum at each spatial point on the film surface, and generates an accurate thickness distribution map. The thickness fitting results, after the incidence angle correction, are highly consistent with ellipsometer measurements, with an average relative error of less than 1%. This work provides a promising solution for large-area thickness inspection of the thin films in confined spaces.