Advancements in optical metrology for gloss and thin-film characterization

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2025-11-21
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Date

2025

Department

Sähkötekniikan ja automaation laitos
Department of Electrical Engineering and Automation

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Mcode

Degree programme

Language

en

Pages

49 + app. 48

Series

Aalto University publication series Doctoral Theses, 216/2025

Abstract

This doctoral thesis presents advancements in optical measurement methods critical for characterizing surface gloss and thin-film thickness, focusing on gonio-reflectometry and microscope-based reflectometry techniques. This study addresses the challenges associated with conventional gloss measurement methods, particularly limitations and uncertainties related to the receptor aperture’s dimensions and position. Using a gonio-reflectometer configured according to ISO 2813 standards, the research validates this approach by comparing results with commercial glossmeters across high-, medium-, and low-gloss samples. Furthermore, employing an angular scanning technique enables accurate gloss value meausrement using narrower apertures. This approach enables a detailed examination of angular distribution effects, which are particularly significant for surfaces that produce asymmetrical and diffuse reflectance. The scanning method enables precise characterization of angular reflectance distribution in specular directions, providing a robust basis for evaluating uncertainty parameters related to standard aperture dimensions and positions. The thesis then compares spectroscopic gonio-reflectometry and ellipsometry methods for thin-film characterization, emphasizing their accuracy and uncertainty across a range of thicknesses (10 nm to 2000 nm) for silicon dioxide (SiO2) and aluminium oxide (Al2O3) films. Both methods exhibit good agreement within uncertainty limits, with ellipsometry proving particularly precise for thinner films, whereas reflectometry excels at thicker layers. This comparative analysis highlights practical considerations for selecting appropriate thin-film measurement techniques based on specific thickness ranges and provides guidelines for comprehensive uncertainty evaluation. Finally, the research introduces a novel analysis method for characterizing thin-films using microscope-based reflectometers. Key improvements include accurate modeling of angle-of-incidence distributions, bandwidth corrections, and consideration of film thickness variations within the measurement area. Validation against the gonio-reflectometer confirms the reliability and enhanced accuracy of the optimized micro-reflectometry approach. This method significantly improves the accuracy of thin-film measurements and their associated uncertainty analysis, particularly advantageous for applications requiring micro-scale resolution. This thesis contributes to substantial methodological advancements, addressing critical challenges in gloss and thin-film optical metrology. It provides robust, traceable measurement methods and clear guidelines for selecting appropriate techniques, significantly benefiting various industrial and research applications.

Description

Supervising professor

Ikonen, Erkki, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland

Thesis advisor

Manoocheri, Farshid, Dr., Aalto University, Department of Electrical Engineering and Automation, Finland

Keywords

gloss measurement, thin-film characterization, gonio-reflectometry, ellipsometry, micro-reflectometry, uncertainty analysis

Other note

Parts

  • [Publication 1]: M. Rastgou, F. Manoocheri, E. Ikonen, "Surface Gloss Measurement using a Gonio-Spectrophotometric Method," 13 pages, submitted, August 2025
  • [Publication 2]: M. Rastgou, D. Hülagü, A. Danilenko, F. Manoocheri, A. Hertwig, E. Ikonen, "Comparison of Thin-Film Thickness Measurements using Ellipsometry and Reflectometry with Uniform Samples," 16 pages, submitted, June 2025
  • [Publication 3]: M. Rastgou, A. Danilenko, J. Peltoniemi, F. Manoocheri, E. Ikonen, "Optimizing Measurement Accuracy in Microscope-Based Reflectometry for Thin Film Optical Properties," Measurement Science and Technology, 36, 075001, 11 pages, 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202508085824
    DOI: 10.1088/1361-6501/ade329 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-2804-8

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[diss] Sähkötekniikan korkeakoulu / ELEC