Spatial mapping of optical constants and thickness variations in ITO films and SiO2 buffer layers

Abstract

In this work, we present detailed spectroscopic ellipsometry (SE) measurements across thirty indium tin oxide In₂O₃–SnO₂ (ITO) substrates, providing insights into variations in the complex refractive index $\tilde{N}$ for the same commercial ITO material. This study includes an analysis of the distribution of ITO surface roughness, ITO thickness, SiO₂ buffer layer thickness, and the complex refractive index of ITO including electrical resistivity and its gradient. The SE mapping, conducted over a (1.5 × 1.5) cm scan area on multiple substrates of (2.5 × 2.5) cm size, reveals uniformity in above parameters within single ITO substrate. However, substantial thickness variations in the SiO₂ buffer layer along with fluctuations in the $\tilde{N}$ of ITO are observed across the set of substrates. Our findings underscore the importance of individually assessing each ITO substrate's optical properties prior to additional layer deposition, as this precision is essential for reliable investigations of other materials, such as organic compounds in OLEDs, in both ex-situ and in-situ studies. Additionally, this article provides comprehensive optical property data for ITO substrates consisting of soda lime float glass coated with a thin SiO₂ buffer layer.