Film thickness measurement by fitting extreme points of the normal spectral reflectance

Jiao Bai; Huaming Chen; Junguang Chen; Haowei Yang

doi:10.1117/12.3034873

20 November 2024 Film thickness measurement by fitting extreme points of the normal spectral reflectance

Jiao Bai, Huaming Chen, Junguang Chen, Haowei Yang

Proceedings Volume 13241, Optical Metrology and Inspection for Industrial Applications XI; 132411D (2024) https://doi.org/10.1117/12.3034873
Event: SPIE/COS Photonics Asia, 2024, Nantong, Jiangsu, China

Conference Poster

Abstract

Films are widely used in electronic shielding, surface protection, etc. Since the spectral reflectance of the thick film layer has enough peaks and troughs, there are various ways to extract its thickness, such as the extreme value method, the envelope method, the Fourier transform and so on. However, because the theoretical model of the extreme value method ignores the extinction coefficient, the envelope method has a large extraction error, and the Fourier method ignores the dispersion characteristics of the refractive index, the measurement accuracy is limited for some precise scenario. In this paper, a new film thickness extracting strategy is proposed with genetic algorithm. At first, the measured spectral reflectance of the film is used to extract the extreme value points, and an extreme value sequence is obtained by dividing their corresponding wavelengths, and then the slope of the extreme value sequence is fitted with the slope of the extreme value sequence of the preset film thickness. When the two slops are consistent, the preset film thickness is the thickness to be measured. Theoretical analysis and measuring experiments are carried out to show a stability of about 0.05nm for a 8630.11nmfilm sample, verifying the feasibility and stability of the proposed strategy.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Jiao Bai, Huaming Chen, Junguang Chen, and Haowei Yang "Film thickness measurement by fitting extreme points of the normal spectral reflectance", Proc. SPIE 13241, Optical Metrology and Inspection for Industrial Applications XI, 132411D (20 November 2024); https://doi.org/10.1117/12.3034873

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