A laser reflectometry technique for on-device coating thickness measurements

Stephen J. Morris

doi:10.1117/12.840897

23 February 2010 A laser reflectometry technique for on-device coating thickness measurements

Stephen J. Morris

Proceedings Volume 7556, Design and Quality for Biomedical Technologies III; 75560M (2010) https://doi.org/10.1117/12.840897
Event: SPIE BiOS, 2010, San Francisco, California, United States

Abstract

We demonstrate the use of Beam Profile Reflectometry (BPR) to measure coating thicknesses on small, highly curved devices such as cardiac stents. BPR has long been used in the semiconductor industry as a powerful technique for measuring the thickness and refractive index of transparent films. The method uses a diffraction-limited focused laser beam to provide light at multiple angles-of-incidence simultaneously within a sub-micron measurement area. By analyzing the reflected light as a function of angle-of-incidence and polarization, robust and deterministic measurements of film-thickness and refractive index can be obtained taking proper account of birefringence. For the current work, the technique has been implemented in a compact desktop configuration suitable, for example, for the in-line monitoring of coating thickness and composition as part of a stent manufacturing process. Provision is made for the alignment and manipulation of the small and fragile samples, and for the location of the measurement spot at the appropriate site on the stent's surface. Validation measurements on stent-like reference samples, comparing results from the technique with destructive measurements on the same samples, show correlation of better than 99% over a range of coating thicknesses and sample morphologies down to curvature radii of ~50μm.

Citation Download Citation

Stephen J. Morris "A laser reflectometry technique for on-device coating thickness measurements", Proc. SPIE 7556, Design and Quality for Biomedical Technologies III, 75560M (23 February 2010); https://doi.org/10.1117/12.840897

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