Electronic Structure and Optical Quality of Nanocrystalline Y₂O₃ Film Surfaces and Interfaces on Silicon

Abstract

Nanocrystalline yttrium oxide (Y2O3) thin films were made by sputter deposition onto silicon (100) substrates keeping the deposition temperature fixed at 300 °C. The surface/interface chemistry, Y–O bonding, and optical constants of the Y2O3 film surface and Y2O3–Si interface were evaluated by the combined use of X-ray photoelectron spectroscopy (XPS), depth-profiling, and spectroscopic ellipsometry (SE). XPS analyses indicate the binding energies (BEs) of the Y 3d doublet; i.e., the Y 3p5/2 and Y 3d3/2 peaks are located at 117.0 and 119.1 eV, respectively, characterizing yttrium in its highest chemical oxidation state (Y3+) in the grown films. The optical model is constructed based on the XPS depth profiles, which indicate that the Y2O3//Si heterostructure can be represented with Y2O3 film—YxSiyOz interfacial compound—Si substrate. Such a model accounts for the experimentally determined ellipsometry functions and accurately produces the dispersive index of refraction (n(λ)) of Y2O3 and YxSiyOz. The n(λ) of Y2O3 and YxSiyOz follows Cauchy’s dispersion relation, while the YxSiyOz formation accounts for degradation of optical quality.