Characterisation of BaxSr1−xTiO3 films using spectroscopic ellipsometry, Rutherford backscattering spectrometry and X-ray diffraction

Abstract

Optical, compositional, and structural properties of BaxSr1−xTiO3 (BST) films prepared by metal-organic chemical vapor deposition on platinum-coated oxidised silicon wafers were characterised using three non-destructive techniques, spectroscopic ellipsometry (SE), Rutherford backscattering spectrometry (RBS), and X-ray diffraction (XRD). The thicknesses and the refractive indices of the BST layers were determined by SE using the Cauchy dispersion model. The samples were characterised by RBS with a 3.5 MeV 4He+ ion beam to utilize the better heavy mass separation at high ion energies. A good correlation is found between the stoichiometric and structural properties measured by RBS and XRD, and the optical properties obtained by SE. It is shown that the significant changes in composition and texture of the BST layers are reflected by the fast optical measurement performed by SE. The real part of the refractive index of layers containing no BST phase is much lower near the UV range, whereas the BST layers have a significant and rapidly increasing absorption below a wavelength of 500 nm. We show that the structural changes can be sensitively probed by the optical technique, making it usable as an in situ or in line characterisation tool.