In situ study of interface reactions of ion beam sputter deposited (Ba0.5Sr0.5)TiO3 films on Si, SiO2, and Ir

Abstract

( Ba 0.5 ,Sr 0.5 )TiO 3 (BST) thin films were deposited on MgO, Si, SiO2 and Ir surfaces by ion beam sputter deposition in oxygen at 700 °C. In situ spectroscopic ellipsometry (SE) has been used to investigate the evolution of the BST films on different surfaces during both deposition and postannealing processes. First, the optical constants of the BST films in the photon energy range of 1.5–4.5 eV were determined by SE analysis on crystallized BST films deposited on MgO single crystal substrates. The interfaces in BST/Si and BST/SiO2/Si structure were examined by SE and Auger electron spectroscopy depth profiles. Subcutaneous oxidation in the BST/Ir structure was observed by in situ SE during both ion beam sputter deposition and postdeposition annealing in oxygen at 700 °C. A study of the thermal stability of the Ir/TiN/SiO2/Si structure in oxygen at 700 °C was carried out using in situ SE. The oxidation of Ir was confirmed by x-ray diffraction. The surface composition and morphology evolution after oxidation were investigated by time of flight mass spectroscopy of recoiled ions (TOF-MSRI) and atomic force microscopy. It has been found that Ti from the underlying TiN barrier layer diffused through the Ir layer onto the surface and thereupon became oxidized. It was also shown that the surface roughness increases with increasing oxidation time. The implications of the instability of Ir/TiN/SiO2/Si structure on the performance of capacitor devices based on this substrate are discussed. It has been shown that a combination of in situ SE and TOF-MSRI provides a powerful methodology for in situ monitoring of complex oxide film growth and postannealing processes.