Abstract
In this paper we use spectrophotometric measurements and a Clustering Global Optimization procedure to determine the complex refractive index of SiO2 layer from 250 nm to 1250 nm. A special commercial optical module allows the reflection and transmission measurements to be made under exactly the same illumination and measurement conditions. We compare the index determination results obtained from two different single layer SiO2 samples, with high and low index glass substrates, respectively. We then determine the refractive index of SiO2 for a bi-layer design in which the first deposited layer is Ta2O5. The corresponding solutions are discussed and we show that the real part of the complex refractive index obtained for a bi-layer is slightly different to that found for a single layer investigation. When SiO2 is included inside a thin film stack, we propose the use of an index determination method in which a bi-layer is used for the real part of the complex refractive index, and single layer determination is used for the imaginary part of the refractive index in the UV range.
Highlights
IntroductionThe determination of the complex refractive index (refractive index n and extinction coefficient k) of thin films is of great importance for the design and production of any optical interference filters
The determination of the complex refractive index of thin films is of great importance for the design and production of any optical interference filters
The corresponding solutions are discussed and we show that the real part of the complex refractive index obtained for a bi-layer is slightly different to that found for a single layer investigation
Summary
The determination of the complex refractive index (refractive index n and extinction coefficient k) of thin films is of great importance for the design and production of any optical interference filters Successful manufacturing of such filters is often directly related to the accuracy of the complex refractive index and thickness (d) measurements, since even a small difference in refractive index can lead to drastic changes in the filters spectral response (reflectance R and transmittance T). The determination of the complex refractive index and thickness, which can be considered to be a reverse engineering process, is clearly necessary. The determination of these optical parameters and thicknesses is generally carried out by means of ellipsometric and spectrophotometric analysis. Due to the complicated nature and high cost of the ellipsometer, more readily available and affordable spectrophometer has attracted considerable attention
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