Determination of the refractive index and the thickness of double side coated thin films

The well-known Swanepoel's method to calculate the refractive index and the thickness of thin films based on their optical transmission, is only applicable to single facet coated substrates (SFCS), and does not return the correct values when applied to double facet coated substrates (DFCS). In this work, we present a novel model and an analytical method to characterize the thin film coated on both sides of a substrate. In order to confirm the validity of our novel method, we have fabricated two samples; a DFCS and a SFCS with identical thin films. The thin film on SFCS is analyzed using Swanepoel's method, and the thin films on DFCS are analyzed using our novel method. The refractive index and the thickness value calculated with these two different methods on two different substrates are in agreement with each other and also with the SEM measurements.