Application of spectral reflectivity to the measurement of thin-film thickness

The aim of this work is to investigate the application of the spectral reflectance technique to thickness measurement of highly localised semi-transparent coatings on miniature geometries, such as those used in the medical devices industry. The paper will describe the application of the technique to coatings on curved or non-uniform surfaces such as narrow-bore metal tubes and thin wires. The paper will describe the equipment used including a spectrometer with micro-focus attachment, and optical modelling software. This work also involved laser-drilling of the polymer films to allow complementary step-height measurements to be made. Special steps were also required to overcome problems in measurement due to the transparency of the thin films. Complementary techniques including white-light interferometry, which were used to benchmark the method, will also be described.